composite material

The earliest composite materials were made from straw and mud combined to form bricks for building construction. Ancient brick-making was documented by Egyptian tomb paintings.{{cite book |first=Andreas |last=Haka |title=Engineered Stability.The History of Composite Materials |location=Cham |publisher=Springer 2023 Chap. 1 on "Early composites".}}

Wattle and daub might be the oldest composite materials, at over 6000 years old.{{cite journal |last=Shaffer |first=Gary D. |title=An Archaeomagnetic Study of a Wattle and Daub Building Collapse |journal=Journal of Field Archaeology |volume=20 |number=1 |date=Spring 1993 |pages=59–75 |doi=10.2307/530354 |jstor=530354}}

• Woody plants, both true wood from trees and such plants as palms and bamboo, yield natural composites that were used prehistorically by humankind and are still used widely in construction and scaffolding.
• Plywood, 3400 BC,{{cite web |url=https://www.mar-bal.com/applications/history-of-composites/ |title=History of Composite Materials |publisher=Mar-Bal Incorporated |access-date=2018-01-03 |url-status=live |archive-url=https://web.archive.org/web/20180104193808/http://www.mar-bal.com/language/en/applications/history-of-composites/ |archive-date=2018-01-04 |date=2013-08-19}} by the Ancient Mesopotamians; gluing wood at different angles gives better properties than natural wood.
• Cartonnage, layers of linen or papyrus soaked in plaster dates to the First Intermediate Period of Egypt c. 2181–2055 BC and was used for death masks.
• Cob mud bricks, or mud walls, (using mud (clay) with straw or gravel as a binder) have been used for thousands of years.{{cite web |url=https://expandusceramics.com/qa/is-cob-a-composite.html |title=Is Cob A Composite? |access-date=2020-12-19 |website=expandusceramics.com |date=27 August 2019 |archive-date=2021-05-23 |archive-url=https://web.archive.org/web/20210523201857/https://expandusceramics.com/qa/is-cob-a-composite.html |url-status=live}}
• Concrete was described by Vitruvius, writing around 25 BC in his Ten Books on Architecture, distinguished types of aggregate appropriate for the preparation of lime mortars. For structural mortars, he recommended pozzolana, which were volcanic sands from the sandlike beds of Pozzuoli brownish-yellow-gray in colour near Naples and reddish-brown at Rome. Vitruvius specifies a ratio of 1 part lime to 3 parts pozzolana for cements used in buildings and a 1:2 ratio of lime to pulvis Puteolanus for underwater work, essentially the same ratio mixed today for concrete used at sea.{{cite book |last1=Lechtmann |first1=Heather |last2=Hobbs |first2=Linn |chapter=Roman Concrete and the Roman Architectural Revolution |pages=81–128 |editor1-last=Kingery |editor1-first=W. D. |editor2-last=Lense |editor2-first=Esther |title=High-technology Ceramics: Past, Present, and Future : The Nature of Innovation and Change in Ceramic Technology |date=1986 |publisher=American Caeramic Society |isbn=978-0-608-00723-6 }} Natural cement-stones, after burning, produced cements used in concretes from post-Roman times into the 20th century, with some properties superior to manufactured Portland cement.
• Papier-mâché, a composite of paper and glue, has been used for hundreds of years.{{cite web |title=Papier Mache - Articles - Papier Mache And Paper Clay |url=http://www.papiermache.co.uk/articles/papier-mache-and-paper-clay/ |access-date=2020-12-19 |website=www.papiermache.co.uk |archive-date=2011-04-29 |archive-url=https://web.archive.org/web/20110429211934/http://www.papiermache.co.uk/articles/papier-mache-and-paper-clay/ |url-status=live}}
• The first artificial fibre reinforced plastic was a combination of fiber glass and bakelite, performed in 1935 by Al Simison and Arthur D Little in Owens Corning CompanyOwens corning milestones 2017{{vs|date=January 2025}}
• One of the most common and familiar composite is fibreglass, in which small glass fibre are embedded within a polymeric material (normally an epoxy or polyester). The glass fibre is relatively strong and stiff (but also brittle), whereas the polymer is ductile (but also weak and flexible). Thus the resulting fibreglass is relatively stiff, strong, flexible, and ductile.{{cite web |title=What is Fibreglass or Fiberglass? |url=https://www.fibreglassdirect.co.uk/blog/post/what-is-fibreglass-or-fiberglass |access-date=2020-12-19 |website=www.fibreglassdirect.co.uk |language=en |archive-date=2020-09-30 |archive-url=https://web.archive.org/web/20200930060753/https://www.fibreglassdirect.co.uk/blog/post/what-is-fibreglass-or-fiberglass |url-status=live}}
• Composite bow
• Leather cannon, wooden cannon

File:Concrete aggregate grinding.JPG

Concrete is the most common artificial composite material of all. {{as of|2009}}, about 7.5 billion cubic metres of concrete are made each year.{{cite web |title=Minerals commodity summary – cement – 2009

|publisher=US United States Geological Survey |date=1 June 2007 |url=http://minerals.usgs.gov/minerals/pubs/commodity/cement/index.html |access-date=16 January 2008 |url-status=live |archive-url=https://web.archive.org/web/20071213052530/http://minerals.usgs.gov/minerals/pubs/commodity/cement/index.html |archive-date=13 December 2007}}

Concrete typically consists of loose stones (construction aggregate) held with a matrix of cement. Concrete is an inexpensive material resisting large compressive forces,{{cite web |url=http://www.constructionknowledge.net/concrete/concrete_basics.php |title=Slabs On Grade |publisher=Construction Knowldegs.net |access-date=January 3, 2018 |url-status=live |archive-url=https://web.archive.org/web/20171002174044/http://www.constructionknowledge.net/concrete/concrete_basics.php |archive-date=October 2, 2017}} however, susceptible to tensile loading.{{cite web |url=https://theconstructor.org/practical-guide/concrete-under-tension/6805/ |title=Behaviour of Concrete Under Tension |publisher=The Constructor |access-date=January 3, 2018 |url-status=live |archive-url=https://web.archive.org/web/20180104192350/https://theconstructor.org/practical-guide/concrete-under-tension/6805/ |archive-date=January 4, 2018 |date=2012-12-06}} To give concrete the ability to resist being stretched, steel bars, which can resist high stretching (tensile) forces, are often added to concrete to form reinforced concrete.{{cite web |title=Reinforced concrete |url=https://www.designingbuildings.co.uk/wiki/Reinforced_concrete |access-date=2020-12-17 |website=www.designingbuildings.co.uk |language=en-gb |archive-date=2016-07-11 |archive-url=https://web.archive.org/web/20160711094546/https://www.designingbuildings.co.uk/wiki/Reinforced_concrete |url-status=live}}

File:Cfaser_haarrp.jpg (used as a reinforcement component) compared to a human hair]]

Fibre-reinforced polymers include carbon-fiber-reinforced polymers and glass-reinforced plastic. If classified by matrix then there are thermoplastic composites, short fibre thermoplastics, long fibre thermoplastics or long-fiber-reinforced thermoplastics. There are numerous thermoset composites, including paper composite panels. Many advanced thermoset polymer matrix systems usually incorporate aramid fibre and carbon fibre in an epoxy resin matrix.{{cite web |last=Reeve |first=Scott |title=3 Reasons to use Fiber-Reinforced Polymer (FRP) |url=https://www.compositeadvantage.com/blog/3-reasons-use-fiber-reinforced-polymer-frp |access-date=2020-12-17 |website=www.compositeadvantage.com |language=en-us |archive-date=2020-10-24 |archive-url=https://web.archive.org/web/20201024143918/https://www.compositeadvantage.com/blog/3-reasons-use-fiber-reinforced-polymer-frp |url-status=live}}{{cite web |date=2014-08-05 |title=A Beginner's Guide to Fiber Reinforced Plastics (FRP's) - Craftech Industries - High-Performance Plastics - (518) 828-5001 |url=https://www.craftechind.com/beginners-guide-fiber-reinforced-plastics-frps/ |access-date=2020-12-17 |website=Craftech Industries |language=en-US |archive-date=2017-05-14 |archive-url=https://web.archive.org/web/20170514110108/https://www.craftechind.com/beginners-guide-fiber-reinforced-plastics-frps/ |url-status=dead}}

Shape-memory polymer composites are high-performance composites, formulated using fibre or fabric reinforcements and shape-memory polymer resin as the matrix. Since a shape-memory polymer resin is used as the matrix, these composites have the ability to be easily manipulated into various configurations when they are heated above their activation temperatures and will exhibit high strength and stiffness at lower temperatures. They can also be reheated and reshaped repeatedly without losing their material properties. These composites are ideal for applications such as lightweight, rigid, deployable structures; rapid manufacturing; and dynamic reinforcement.{{cite web |title=Shape Memory Polymers - A Complete Guide |url=https://www.bpf.co.uk/plastipedia/applications/shape-memory-polymer.aspx |access-date=2020-12-17 |website=www.bpf.co.uk |archive-date=2021-05-23 |archive-url=https://web.archive.org/web/20210523194900/https://www.bpf.co.uk/plastipedia/applications/shape-memory-polymer.aspx |url-status=live}}{{cite web |title=Shape Memory Polymers {{!}} Sheffield Hallam University|url=https://www.shu.ac.uk/research/specialisms/materials-and-engineering-research-institute/what-we-do/expertise/shape-memory-polymers|access-date=2020-12-17|website=www.shu.ac.uk|archive-date=2021-05-23|archive-url=https://web.archive.org/web/20210523194851/https://www.shu.ac.uk/research/specialisms/materials-and-engineering-research-institute/what-we-do/expertise/shape-memory-polymers|url-status=live}}

High strain composites are another type of high-performance composites that are designed to perform in a high deformation setting and are often used in deployable systems where structural flexing is advantageous.{{citation needed|date =August 2017}} Although high strain composites exhibit many similarities to shape-memory polymers, their performance is generally dependent on the fibre layout as opposed to the resin content of the matrix.{{cite web |title=Tensile Fiber Failure on High Strain Composites |url=https://www.colorado.edu/faculty/lopezjimenez/sites/default/files/attached-files/tensile_fiber_failure_on_high_strain_composites.pdf |access-date=Dec 17, 2020 |website=University of Colorado, Boulder |archive-date=May 23, 2021 |archive-url=https://web.archive.org/web/20210523194900/https://www.colorado.edu/faculty/lopezjimenez/sites/default/files/attached-files/tensile_fiber_failure_on_high_strain_composites.pdf |url-status=live}}

Composites can also use metal fibres reinforcing other metals, as in metal matrix composites (MMC){{cite web |title=7: Metal Matrix Composites {{!}} School of Materials Science and Engineering|url=http://www.materials.unsw.edu.au/tutorials/online-tutorials/7-metal-matrix-composites|access-date=2020-12-17|website=www.materials.unsw.edu.au|archive-date=2021-01-25|archive-url=https://web.archive.org/web/20210125180839/http://www.materials.unsw.edu.au/tutorials/online-tutorials/7-metal-matrix-composites|url-status=live}} or ceramic matrix composites (CMC),{{cite web |title=What are Ceramic Matrix Composites? |url=https://llfurnace.com/blog/what-are-ceramic-matrix-composites/ |work=L&L Special Furnace |date=30 August 2018 }} which includes bone (hydroxyapatite reinforced with collagen fibres), cermet (ceramic and metal), and concrete. Ceramic matrix composites are built primarily for fracture toughness, not for strength. Another class of composite materials involve woven fabric composite consisting of longitudinal and transverse laced yarns. Woven fabric composites are flexible as they are in form of fabric.

Organic matrix/ceramic aggregate composites include asphalt concrete, polymer concrete, mastic asphalt, mastic roller hybrid, dental composite, syntactic foam, and mother of pearl.{{cite web |title=Composite Material |url=https://www.hi-techindia.in/composite-material |access-date=2020-12-21 |website=hi-techindia |language=en |archive-date=2021-03-03 |archive-url=https://web.archive.org/web/20210303031856/https://www.hi-techindia.in/composite-material |url-status=live}} Chobham armour is a special type of composite armour used in military applications.{{citation needed|date=October 2023}}

Additionally, thermoplastic composite materials can be formulated with specific metal powders resulting in materials with a density range from 2 g/cm³ to 11 g/cm³ (same density as lead). The most common name for this type of material is "high gravity compound" (HGC), although "lead replacement" is also used. These materials can be used in place of traditional materials such as aluminium, stainless steel, brass, bronze, copper, lead, and even tungsten in weighting, balancing (for example, modifying the centre of gravity of a tennis racquet), vibration damping, and radiation shielding applications. High density composites are an economically viable option when certain materials are deemed hazardous and are banned (such as lead) or when secondary operations costs (such as machining, finishing, or coating) are a factor.{{cite web |date=2001-02-15 |title=Thermoplastic Composites - An Introduction |url=https://www.azom.com/article.aspx?ArticleID=85 |access-date=2020-12-17 |website=AZoM.com |language=en |archive-date=2012-04-05 |archive-url=https://web.archive.org/web/20120405141717/https://www.azom.com/article.aspx?ArticleID=85 |url-status=live}}

There have been several studies indicating that interleaving stiff and brittle epoxy-based carbon-fiber-reinforced polymer laminates with flexible thermoplastic laminates can help to make highly toughened composites that show improved impact resistance.{{cite journal |last1=Quan |first1=Dong |last2=Bologna |first2=Francesca |last3=Scarselli |first3=Gennaro |last4=Ivankovic |first4=Alojz |last5=Murphy |first5=Neal |title=Interlaminar fracture toughness of aerospace-grade carbon fibre reinforced plastics interleaved with thermoplastic veils |journal=Composites Part A: Applied Science and Manufacturing |date=January 2020 |volume=128 |pages=105642 |doi=10.1016/j.compositesa.2019.105642 }} Another interesting aspect of such interleaved composites is that they are able to have shape memory behaviour without needing any shape-memory polymers or shape-memory alloys e.g. balsa plies interleaved with hot glue,{{cite book |doi=10.2514/6.2007-1717 |chapter=Morphing Structures by way of Stiffness Variations |title=48th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference |date=2007 |last1=Gordon |first1=Benjamin |last2=Clark |first2=William |isbn=978-1-62410-013-0 }} aluminium plies interleaved with acrylic polymers or PVC{{cite journal |last1=Gandhi |first1=Farhan |last2=Kang |first2=Sang-Guk |title=Beams with controllable flexural stiffness |journal=Smart Materials and Structures |date=1 August 2007 |volume=16 |issue=4 |pages=1179–1184 |doi=10.1088/0964-1726/16/4/028 |bibcode=2007SMaS...16.1179G |hdl=10203/25282 |hdl-access=free }} and carbon-fiber-reinforced polymer laminates interleaved with polystyrene.{{cite journal |last1=Robinson |first1=Paul |last2=Bismarck |first2=Alexander |last3=Zhang |first3=Bohao |last4=Maples |first4=Henry A. |title=Deployable, shape memory carbon fibre composites without shape memory constituents |journal=Composites Science and Technology |date=June 2017 |volume=145 |pages=96–104 |doi=10.1016/j.compscitech.2017.02.024 |hdl=10044/1/49550 |hdl-access=free }}

File:Glare honeycomb.jpg

A sandwich-structured composite is a special class of composite material that is fabricated by attaching two thin but stiff skins to a lightweight but thick core. The core material is normally low strength material, but its higher thickness provides the sandwich composite with high bending stiffness with overall low density.{{cite web |title=What is a sandwich structure? |url=https://www.twi-global.com/technical-knowledge/faqs/faq-what-is-a-sandwich-structure.aspx |access-date=2020-12-17 |website=www.twi-global.com |language=en-GB |archive-date=2021-05-23 |archive-url=https://web.archive.org/web/20210523200354/https://www.twi-global.com/technical-knowledge/faqs/faq-what-is-a-sandwich-structure.aspx |url-status=live}}{{cite web |title=Basics of sandwich technology |url=https://www.diabgroup.com/en-GB/Knowledge/Sandwich-technology/Basics-of-sandwich-technology |access-date=2020-12-17 |website=www.diabgroup.com |archive-date=2018-02-26 |archive-url=https://web.archive.org/web/20180226141624/https://www.diabgroup.com/en-GB/Knowledge/Sandwich-technology/Basics-of-sandwich-technology |url-status=dead}}

File:Spruce plywood.JPG

Wood is a naturally occurring composite comprising cellulose fibres in a lignin and hemicellulose matrix.{{cite web |date=2019-07-09 |title=Is Wood A Composite Material or A Pure Substance? |url=https://woodwoodland.com/is-wood-composite-material/ |access-date=2020-12-17 |website=WoodWoodLand |language=en-US |archive-date=2020-08-12 |archive-url=https://web.archive.org/web/20200812055100/https://woodwoodland.com/is-wood-composite-material/ |url-status=live}} Engineered wood includes a wide variety of different products such as wood fibre board, plywood, oriented strand board, wood plastic composite (recycled wood fibre in polyethylene matrix), Pykrete (sawdust in ice matrix), plastic-impregnated or laminated paper or textiles, Arborite, Formica (plastic), and Micarta. Other engineered laminate composites, such as Mallite, use a central core of end grain balsa wood, bonded to surface skins of light alloy or GRP. These generate low-weight, high rigidity materials.{{cite web |title=Composite wood; what is it? Origin and advantages |url=https://uk.silvadec.com/silvadec/history-of-composite-wood/ |access-date=2020-12-17 |website=Silvadec |language=en-US |archive-date=2017-12-01 |archive-url=https://web.archive.org/web/20171201054125/https://uk.silvadec.com/silvadec/history-of-composite-wood/ |url-status=dead}}

Particulate composites have particle as filler material dispersed in matrix, which may be nonmetal, such as glass, epoxy. Automobile tire is an example of particulate composite.{{cite book |doi=10.1016/B978-075067124-8/50001-1 |quote=A particulate composite is characterized as being composed of particles suspended in a matrix. Particles can have virtually any shape, size or configuration. Examples of well-known particulate composites are concrete and particle board. There are two subclasses of particulates: flake and filled/skeletal |chapter=Introduction to Composite Materials |title=Laminar Composites |date=1999 |last1=Staab |first1=George H. |pages=1–16 |isbn=978-0-7506-7124-8 }}

Advanced diamond-like carbon (DLC) coated polymer composites have been reported{{cite journal |last1=Zia |first1=Abdul Wasy |last2=Shah |first2=Atta Ur Rehman |last3=Lee |first3=Seunghun |last4=Song |first4=Jung Il |title=Development of diamond-like-carbon coated abaca-reinforced polyester composites for hydrophobic and outdoor structural applications |journal=Polymer Bulletin |volume=72 |issue=11 |year=2015 |pages=2797–2808 |doi=10.1007/s00289-015-1436-y }} where the coating increases the surface hydrophobicity, hardness and wear resistance.

Ferromagnetic composites, including those with a polymer matrix consisting, for example, of nanocrystalline filler of Fe-based powders and polymers matrix. Amorphous and nanocrystalline powders obtained, for example, from metallic glasses can be used. Their use makes it possible to obtain ferromagnetic nanocomposites with controlled magnetic properties.{{cite journal |last1=Nowosielski |first1=Ryszard |last2=Gramatyka |first2=Paweł |last3=Sakiewicz |first3=Piotr |last4=Babilas |first4=Rafał |title=Ferromagnetic composites with polymer matrix consisted of nanocrystalline Fe-based filler |journal=Journal of Magnetism and Magnetic Materials |date=August 2015 |volume=387 |pages=179–185 |doi=10.1016/j.jmmm.2015.04.004 |bibcode=2015JMMM..387..179N }}

Fibre-reinforced composite materials have gained popularity (despite their generally high cost) in high-performance products that need to be lightweight, yet strong enough to take harsh loading conditions such as aerospace components (tails, wings, fuselages, propellers), boat and scull hulls, bicycle frames, and racing car bodies. Other uses include fishing rods, storage tanks, swimming pool panels, and baseball bats. The Boeing 787 and Airbus A350 structures including the wings and fuselage are composed largely of composites.{{cite web |title=Airbus takes on Boeing with composite A350 XWB |url=https://www.materialstoday.com/composite-applications/features/airbus-takes-on-boeing-with-composite-a350-xwb/ |access-date=2020-12-17 |website=Materials Today |archive-date=2015-10-23 |archive-url=https://web.archive.org/web/20151023204900/https://www.materialstoday.com/composite-applications/features/airbus-takes-on-boeing-with-composite-a350-xwb/ |url-status=dead}} Composite materials are also becoming more common in the realm of orthopedic surgery,{{cite book |doi=10.1007/978-1-59259-197-8_12 |chapter=Orthopedic Applications of Carbon Fiber Composites |title=Biomaterials Engineering and Devices: Human Applications |date=2000 |last1=Longo |first1=Joseph A. |last2=Koeneman |first2=James B. |pages=203–214 |isbn=978-1-61737-227-8 }} and it is the most common hockey stick material.

Carbon composite is a key material in today's launch vehicles and heat shields for the re-entry phase of spacecraft. It is widely used in solar panel substrates, antenna reflectors and yokes of spacecraft. It is also used in payload adapters, inter-stage structures and heat shields of launch vehicles. Furthermore, disk brake systems of airplanes and racing cars are using carbon/carbon material, and the composite material with carbon fibres and silicon carbide matrix has been introduced in luxury vehicles and sports cars.

In 2006, a fibre-reinforced composite pool panel was introduced for in-ground swimming pools, residential as well as commercial, as a non-corrosive alternative to galvanized steel.

In 2007, an all-composite military Humvee was introduced by TPI Composites Inc and Armor Holdings Inc, the first all-composite military vehicle. By using composites the vehicle is lighter, allowing higher payloads.{{cite web |date=2007-07-20 |title=TPI Composites and Armor Holdings Unveil Army's First All-Composite Military Vehicle |url=https://www.businesswire.com/news/home/20070720005465/en/TPI-Composites-and-Armor-Holdings-Unveil-Armys-First-All-Composite-Military-Vehicle |access-date=2020-12-21 |website=www.businesswire.com |language=en |archive-date=2021-05-23 |archive-url=https://web.archive.org/web/20210523194850/https://www.businesswire.com/news/home/20070720005465/en/TPI-Composites-and-Armor-Holdings-Unveil-Armys-First-All-Composite-Military-Vehicle |url-status=live}} In 2008, carbon fibre and DuPont Kevlar (five times stronger than steel) were combined with enhanced thermoset resins to make military transit cases by ECS Composites creating 30-percent lighter cases with high strength.

Pipes and fittings for various purpose like transportation of potable water, fire-fighting, irrigation, seawater, desalinated water, chemical and industrial waste, and sewage are now manufactured in glass reinforced plastics.

Composite materials used in tensile structures for facade application provides the advantage of being translucent. The woven base cloth combined with the appropriate coating allows better light transmission. This provides a very comfortable level of illumination compared to the full brightness of outside.{{cite web |url=http://www.spandesign.com/technical/article_pros_and_cons_of_fabric_structures.aspx |title=The pros and cons of fabric structures | Span Design |access-date=2018-09-24 |archive-date=2009-07-27 |archive-url=https://web.archive.org/web/20090727013044/http://www.spandesign.com/technical/article_pros_and_cons_of_fabric_structures.aspx |url-status=live}}

The wings of wind turbines, in growing sizes in the order of 50 m length are fabricated in composites since several years.{{cite web |title=Wind Power Blades Energize Composites Manufacturing |url=https://www.ptonline.com/articles/wind-power-blades-energize-composites-manufacturing |access-date=2020-12-21 |website=www.ptonline.com |date=October 2008 |language=en |archive-date=2011-02-16 |archive-url=https://web.archive.org/web/20110216083220/https://www.ptonline.com/articles/wind-power-blades-energize-composites-manufacturing |url-status=live}}

Two-lower-leg-amputees run on carbon-composite spring-like artificial feet as quick as non-amputee athletes.{{cite web |title=Carbon fibre prostheses and running in amputees: A review |url=https://www.clinicalkey.com/#!/content/playContent/1-s2.0-S1268773108000672?returnurl=https://linkinghub.elsevier.com/retrieve/pii/S1268773108000672?showall=true&referrer=https://www.researchgate.net/ |access-date=2020-12-21 |website=www.clinicalkey.com |archive-date=2013-04-25 |archive-url=https://web.archive.org/web/20130425174959/https://www.clinicalkey.com/#!/content/playContent/1-s2.0-S1268773108000672?returnurl=https://linkinghub.elsevier.com/retrieve/pii/S1268773108000672?showall=true&referrer=https://www.researchgate.net/ |url-status=live}}

High-pressure gas cylinders typically about 7–9 litre volume x 300 bar pressure for firemen are nowadays constructed from carbon composite. Type-4-cylinders include metal only as boss that carries the thread to screw in the valve.

On 5 September 2019, HMD Global unveiled the Nokia 6.2 and Nokia 7.2 which are claimed to be using polymer composite for the frames.{{cite web |date=2019-09-05 |title=HMD Global debuts two killer mid-range Nokia phones |url=https://www.androidauthority.com/nokia-7-2-6-2-1022274/ |access-date=2020-12-17 |website=Android Authority |language=en-US |archive-date=2019-09-13 |archive-url=https://web.archive.org/web/20190913015951/https://www.androidauthority.com/nokia-7-2-6-2-1022274/ |url-status=live}}

File:Cfk heli slw.jpg

Composite materials are created from individual materials. These individual materials are known as constituent materials, and there are two main categories of it. One is the matrix (binder) and the other reinforcement.{{cite web |title=Composite materials - Using materials - AQA - GCSE Chemistry (Single Science) Revision - AQA |url=https://www.bbc.co.uk/bitesize/guides/ztrwng8/revision/6 |access-date=2020-12-18 |website=BBC Bitesize |language=en-GB |archive-date=2021-05-23 |archive-url=https://web.archive.org/web/20210523194850/https://www.bbc.co.uk/bitesize/guides/ztrwng8/revision/6 |url-status=live}} A portion of each kind is needed at least. The reinforcement receives support from the matrix as the matrix surrounds the reinforcement and maintains its relative positions. The properties of the matrix are improved as the reinforcements impart their exceptional physical and mechanical properties. The mechanical properties become unavailable from the individual constituent materials by synergism. At the same time, the designer of the product or structure receives options to choose an optimum combination from the variety of matrix and strengthening materials.

To shape the engineered composites, it must be formed. The reinforcement is placed onto the mould surface or into the mould cavity. Before or after this, the matrix can be introduced to the reinforcement. The matrix undergoes a melding event which sets the part shape necessarily. This melding event can happen in several ways, depending upon the matrix nature, such as solidification from the melted state for a thermoplastic polymer matrix composite or chemical polymerization for a thermoset polymer matrix.

According to the requirements of end-item design, various methods of moulding can be used. The natures of the chosen matrix and reinforcement are the key factors influencing the methodology. The gross quantity of material to be made is another main factor. To support high capital investments for rapid and automated manufacturing technology, vast quantities can be used. Cheaper capital investments but higher labour and tooling expenses at a correspondingly slower rate assists the small production quantities.

Many commercially produced composites use a polymer matrix material often called a resin solution. There are many different polymers available depending upon the starting raw ingredients. There are several broad categories, each with numerous variations. The most common are known as polyester, vinyl ester, epoxy, phenolic, polyimide, polyamide, polypropylene, PEEK, and others. The reinforcement materials are often fibres but also commonly ground minerals. The various methods described below have been developed to reduce the resin content of the final product, or the fibre content is increased. As a rule of thumb, lay up results in a product containing 60% resin and 40% fibre, whereas vacuum infusion gives a final product with 40% resin and 60% fibre content. The strength of the product is greatly dependent on this ratio.

Martin Hubbe and Lucian A Lucia consider wood to be a natural composite of cellulose fibres in a matrix of lignin.{{cite journal |last1=Hubbe |first1=Martin A. |last2=Lucia |first2=Lucian A. |title=The 'love-hate' relationship present in lignocellulosic materials |journal=BioResources |date=2007 |volume=2 |issue=4 |pages=534–535 |doi=10.15376/BIORES.2.4.534-535 |doi-access=free }}{{cite book |doi=10.1201/9781482269741 |oclc=50869397 |page=5 ff |title=Wood and Cellulosic Chemistry, Revised, and Expanded |date=2000 |last1=Hon |first1=David N.S. |last2=Shiraishi |first2=Nobuo |isbn=978-0-429-17533-6 }}

Several layup designs of composite also involve a co-curing or post-curing of the prepreg with many other media, such as foam or honeycomb. Generally, this is known as a sandwich structure. This is a more general layup for the production of cowlings, doors, radomes or non-structural parts.

Open- and closed-cell-structured foams like polyvinyl chloride, polyurethane, polyethylene, or polystyrene foams, balsa wood, syntactic foams, and honeycombs are generally utilized core materials. Open- and closed-cell metal foam can also be utilized as core materials. Recently, 3D graphene structures ( also called graphene foam) have also been employed as core structures. A recent review by Khurram and Xu et al., have provided the summary of the state-of-the-art techniques for fabrication of the 3D structure of graphene, and the examples of the use of these foam like structures as a core for their respective polymer composites.{{cite journal |last1=Shehzad |first1=Khurram |last2=Xu |first2=Yang |last3=Gao |first3=Chao |last4=Duan |first4=Xiangfeng |title=Three-dimensional macro-structures of two-dimensional nanomaterials |journal=Chemical Society Reviews |date=2016 |volume=45 |issue=20 |pages=5541–5588 |doi=10.1039/c6cs00218h |pmid=27459895}}

Although the two phases are chemically equivalent, semi-crystalline polymers can be described both quantitatively and qualitatively as composite materials. The crystalline portion has a higher elastic modulus and provides reinforcement for the less stiff, amorphous phase. Polymeric materials can range from 0% to 100%{{cite journal |last1=Agbolaghi |first1=Samira |last2=Abbaspoor |first2=Saleheh |last3=Abbasi |first3=Farhang |title=A comprehensive review on polymer single crystals—From fundamental concepts to applications |journal=Progress in Polymer Science |date=June 2018 |volume=81 |pages=22–79 |doi=10.1016/j.progpolymsci.2017.11.006 }} crystallinity aka volume fraction depending on molecular structure and thermal history. Different processing techniques can be employed to vary the percent crystallinity in these materials and thus the mechanical properties of these materials as described in the physical properties section. This effect is seen in a variety of places from industrial plastics like polyethylene shopping bags to spiders which can produce silks with different mechanical properties.{{cite journal |last1=Termonia |first1=Yves |title=Molecular Modeling of Spider Silk Elasticity |journal=Macromolecules |date=December 1994 |volume=27 |issue=25 |pages=7378–7381 |doi=10.1021/ma00103a018 |bibcode=1994MaMol..27.7378T }} In many cases these materials act like particle composites with randomly dispersed crystals known as spherulites. However they can also be engineered to be anisotropic and act more like fiber reinforced composites.{{cite journal |last1=Quan |first1=Hui |last2=Li |first2=Zhong-Ming |last3=Yang |first3=Ming-Bo |last4=Huang |first4=Rui |title=On transcrystallinity in semi-crystalline polymer composites |journal=Composites Science and Technology |date=June 2005 |volume=65 |issue=7–8 |pages=999–1021 |doi=10.1016/j.compscitech.2004.11.015 }} In the case of spider silk, the properties of the material can even be dependent on the size of the crystals, independent of the volume fraction.{{cite journal |last1=Keten |first1=Sinan |last2=Xu |first2=Zhiping |last3=Ihle |first3=Britni |last4=Buehler |first4=Markus J. |title=Nanoconfinement controls stiffness, strength and mechanical toughness of β-sheet crystals in silk |journal=Nature Materials |date=14 March 2010 |volume=9 |issue=4 |pages=359–367 |doi=10.1038/nmat2704 |pmid=20228820 |bibcode=2010NatMa...9..359K }} Ironically, single component polymeric materials are some of the most easily tunable composite materials known.

Normally, the fabrication of composite includes wetting, mixing or saturating the reinforcement with the matrix. The matrix is then induced to bind together (with heat or a chemical reaction) into a rigid structure. Usually, the operation is done in an open or closed forming mould. However, the order and ways of introducing the constituents alters considerably. Composites fabrication is achieved by a wide variety of methods, including advanced fibre placement (automated fibre placement),{{cite web |last=drawpub |title=Automated Fiber Placement |url=http://www.automateddynamics.com/article/thermoplastic-composite-basics/processing-methods/automated-fiber-placement |access-date=2020-12-17 |website=Automated Dynamics - Composite Structures, Automation Equipment, and Engineering Services |language=en-US |archive-date=2014-04-12 |archive-url=https://web.archive.org/web/20140412144432/http://www.automateddynamics.com/article/thermoplastic-composite-basics/processing-methods/automated-fiber-placement |url-status=live}} fibreglass spray lay-up process,{{cite web |title=Lay-up methods for fibreglass composites {{!}} Resin Library|url=https://www.resinlibrary.com/articles/lay-up-methods-for-fibreglass-grp-composites/|access-date=2020-12-17|language=en-GB|archive-date=2023-01-22|archive-url=https://web.archive.org/web/20230122175624/https://www.resinlibrary.com/knowledge/guide/lay-up-methods-for-fibreglass-grp-composites/|url-status=live}} filament winding,{{cite web |title=Filament Winding - Open Molding |url=http://compositeslab.com/composites-manufacturing-processes/open-molding/filament-winding/ |access-date=2020-12-17 |website=CompositesLab |language=en-US |archive-date=2015-09-27 |archive-url=https://web.archive.org/web/20150927011402/http://compositeslab.com/composites-manufacturing-processes/open-molding/filament-winding/ |url-status=live}} lanxide process,{{cite journal |last=Yamaguchi |first=Y. |date=1994-08-01 |title=Unique methods of making MMC and CMC by Lanxide process; Lanxide hoshiki ni yoru CMC oyobi MMC no seiho |url=https://www.osti.gov/etdeweb/biblio/27381 |journal=Seramikkusu (Ceramics Japan) |language=ja |volume=29 |access-date=2020-12-17 |archive-date=2021-05-23 |archive-url=https://web.archive.org/web/20210523194851/https://www.osti.gov/etdeweb/biblio/27381 |url-status=live}} tailored fibre placement,{{cite web |date=2020-03-12 |title=Tailored Fibre Placement - complex composite designs delivered at speed with reduced waste |url=https://knowledge.ulprospector.com/10345/pe-tailored-fibre-placement/ |access-date=2020-12-17 |website=Prospector Knowledge Center |language=en |archive-date=2021-05-23 |archive-url=https://web.archive.org/web/20210523194851/https://knowledge.ulprospector.com/10345/pe-tailored-fibre-placement/ |url-status=live |last1=Pye |first1=Andy }} tufting,{{cite journal |last1=Dell’Anno |first1=G. |last2=Treiber |first2=J.W.G. |last3=Partridge |first3=I.K. |title=Manufacturing of composite parts reinforced through-thickness by tufting |journal=Robotics and Computer-Integrated Manufacturing |date=February 2016 |volume=37 |pages=262–272 |doi=10.1016/j.rcim.2015.04.004 |hdl=1983/a2f04bfb-1b46-4029-9318-aa47f9c29f2f |hdl-access=free }} and z-pinning.{{cite web |title=Z pinning - CSIR - NAL |url=https://www.nal.res.in/en/techniques/z-pinning |access-date=2020-12-17 |website=www.nal.res.in |archive-date=2020-11-10 |archive-url=https://web.archive.org/web/20201110130309/https://www.nal.res.in/en/techniques/z-pinning |url-status=live}}

The reinforcing and matrix materials are merged, compacted, and cured (processed) within a mould to undergo a melding event. The part shape is fundamentally set after the melding event. However, under particular process conditions, it can deform. The melding event for a thermoset polymer matrix material is a curing reaction that is caused by the possibility of extra heat or chemical reactivity such as an organic peroxide. The melding event for a thermoplastic polymeric matrix material is a solidification from the melted state. The melding event for a metal matrix material such as titanium foil is a fusing at high pressure and a temperature near the melting point.

It is suitable for many moulding methods to refer to one mould piece as a "lower" mould and another mould piece as an "upper" mould. Lower and upper does not refer to the mould's configuration in space, but the different faces of the moulded panel. There is always a lower mould, and sometimes an upper mould in this convention. Part construction commences by applying materials to the lower mould. Lower mould and upper mould are more generalized descriptors than more common and specific terms such as male side, female side, a-side, b-side, tool side, bowl, hat, mandrel, etc. Continuous manufacturing utilizes a different nomenclature.

Usually, the moulded product is referred to as a panel. It can be referred to as casting for certain geometries and material combinations. It can be referred to as a profile for certain continuous processes. Some of the processes are autoclave moulding,{{cite web |title=Autoclave molding - CSIR - NAL |url=https://www.nal.res.in/en/techniques/autoclave-molding |access-date=2020-12-18 |website=www.nal.res.in |archive-date=2020-08-05 |archive-url=https://web.archive.org/web/20200805185436/https://www.nal.res.in/en/techniques/autoclave-molding |url-status=live}} vacuum bag moulding,{{cite web |title=Vacuum bag moulding - CSIR - NAL |url=https://www.nal.res.in/en/techniques/vacuum-bag-moulding |access-date=2020-12-18 |website=www.nal.res.in |archive-date=2020-08-06 |archive-url=https://web.archive.org/web/20200806182059/https://www.nal.res.in/en/techniques/vacuum-bag-moulding |url-status=live}} pressure bag moulding,{{cite web |title=Pressure Bag Moulding |url=https://netcomposites.com/glossary/pressure-bag-moulding/ |access-date=2020-12-18 |website=NetComposites |language=en-US |archive-date=2020-11-10 |archive-url=https://web.archive.org/web/20201110153732/https://netcomposites.com/glossary/pressure-bag-moulding/ |url-status=usurped}} resin transfer moulding,{{cite web |title=Resin Transfer Moulding Processes - CSIR - NAL |url=https://www.nal.res.in/en/techniques/resin-transfer-moulding-processes |access-date=2020-12-18 |website=www.nal.res.in |archive-date=2020-08-06 |archive-url=https://web.archive.org/web/20200806182447/https://www.nal.res.in/en/techniques/resin-transfer-moulding-processes |url-status=live}} and light resin transfer moulding.{{cite web |title=Light Resin Transfer Molding : CompositesWorld |url=https://www.compositesworld.com/knowledgecenter/closed-molding/closed-mold-process/resin-transfer-molding#:~:text=Light%20Resin%20Transfer%20Molding,%20or,side%20mold%20using%20vacuum%20pressure. |access-date=2020-12-18 |website=www.compositesworld.com |archive-date=2014-07-22 |archive-url=https://web.archive.org/web/20140722234324/https://www.compositesworld.com/knowledgecenter/closed-molding/closed-mold-process/resin-transfer-molding#:~:text=Light%20Resin%20Transfer%20Molding,%20or,side%20mold%20using%20vacuum%20pressure. |url-status=live}}

Other types of fabrication include casting,{{cite web |title=Composite Casting Processes |url=http://www.sicomin.com/processes/casting |access-date=2020-12-20 |website=www.sicomin.com |archive-date=2020-05-14 |archive-url=https://web.archive.org/web/20200514185622/http://www.sicomin.com/processes/casting |url-status=live}} centrifugal casting,{{cite web |title=Centrifugal Casting - Closed Molding |url=http://compositeslab.com/composites-manufacturing-processes/closed-molding/centrifugal-casting/ |access-date=2020-12-20 |website=CompositesLab |language=en-US |archive-date=2015-09-26 |archive-url=https://web.archive.org/web/20150926120921/http://compositeslab.com/composites-manufacturing-processes/closed-molding/centrifugal-casting/ |url-status=live}} braiding (onto a former), continuous casting,{{cite journal |last1=Kwaśniewski |first1=Paweł |last2=Kiesiewicz |first2=Grzegorz |title=Studies on Obtaining Cu-CNT Composites by Continuous Casting Method |journal=Metallurgy and Foundry Engineering |date=2014 |volume=40 |issue=2 |pages=83 |doi=10.7494/mafe.2014.40.2.83 }} filament winding,{{cite web |title=Filament Winding |url=https://netcomposites.com/guide/manufacturing/filament-winding/ |access-date=2020-12-20 |website=NetComposites |language=en-US |archive-date=2021-05-23 |archive-url=https://web.archive.org/web/20210523194853/https://netcomposites.com/guide/manufacturing/filament-winding/ |url-status=usurped}} press moulding,{{cite web |title=PRESS MOULDING OF AUTOMOTIVE COMPOSITES – Shape Group |url=http://www.shape-group.com/press-moulding-of-automotive-composites |access-date=2020-12-20 |language=en-US |archive-date=2020-09-20 |archive-url=https://web.archive.org/web/20200920183451/http://www.shape-group.com/press-moulding-of-automotive-composites |url-status=live}} transfer moulding, pultrusion moulding,{{cite book |doi=10.1016/B978-0-323-39500-7.00005-8 |quote=The term 'pultrusion' combines the word 'pull' and 'extrusion.' It is a continuous manufacturing process to produce products with constant cross sections such as profiles and sheets. Fig. 5.25 is a schematic illustration of general pultrusion setup. As shown in the figure, continuous fiber reinforcements are saturated (wet out) with desired resin matrix either in a resin bath or in resin injection chamber. The coated fibers then pass through heating and forming dies where curing of the resin and forming of the shape occur. After the die the composite is allowed to postcure while being pulled to the saw which cuts it into stock length. Different resin–fiber combinations are used to achieve the final desired properties |chapter=Plastics Processing |title=Introduction to Plastics Engineering |date=2018 |last1=Shrivastava |first1=Anshuman |pages=143–177 |isbn=978-0-323-39500-7 }} and slip forming.{{cite patent |title=System and method for slip forming monolithic reinforced composite concrete structures having multiple functionally discrete components |gdate=2015-05-24 |url=https://patents.google.com/patent/US9435085B1/en}} {{Webarchive|url=https://web.archive.org/web/20210608191250/https://patents.google.com/patent/US9435085B1/en |date=2021-06-08}} There are also forming capabilities including CNC filament winding, vacuum infusion, wet lay-up, compression moulding, and thermoplastic moulding, to name a few. The practice of curing ovens and paint booths is also required for some projects.

The composite parts finishing is also crucial in the final design. Many of these finishes will involve rain-erosion coatings or polyurethane coatings.

The mould and mould inserts are referred to as "tooling". The mould/tooling can be built from different materials. Tooling materials include aluminium, carbon fibre, invar, nickel, reinforced silicone rubber and steel. The tooling material selection is normally based on, but not limited to, the coefficient of thermal expansion, expected number of cycles, end item tolerance, desired or expected surface condition, cure method, glass transition temperature of the material being moulded, moulding method, matrix, cost, and other various considerations.

{{main|Rule of mixtures}}

File:Composite elastic modulus.svg

Usually, the composite's physical properties are dependent on the direction of consideration, and so are anisotropic. This applies to many properties including elastic modulus,{{cite book|last=Alger|first=Mark. S. M.|title=Polymer Science Dictionary|edition=2nd|year=1997|publisher=Springer Publishing|isbn=0412608707}} ultimate tensile strength, thermal conductivity, and electrical conductivity.{{cite book|last1=Askeland|first1=Donald R.|last2=Fulay|first2=Pradeep P.|last3=Wright|first3=Wendelin J.|title=The Science and Engineering of Materials|edition=6th|date=2010-06-21|publisher=Cengage Learning|isbn=9780495296027}} The rule of mixtures and inverse rule of mixtures give upper and lower bounds for these properties. The real value will lie somewhere between these values and can depend on many factors including:

• the orientation of interest
• the length of the fibres
• the accuracy of the fibre alignment
• the properties of the matrix and fibres
• delamination of the fibres and matrix
• the inclusion of any impurities

File:Isostress and isostrain conditions for composite materials.gif

For some material property $E$, the rule of mixtures states that the overall property in the direction parallel to the fibers could be as high as

:$E\_\backslash parallel\; =\; fE\_f\; +\; \backslash left(1-f\backslash right)E\_m$

The inverse rule of mixtures states that in the direction perpendicular to the fibers, the elastic modulus of a composite could be as low as

:$E\_\backslash perp\; =\; \backslash left(\backslash frac\{f\}\{E\_f\}\; +\; \backslash frac\{1-f\}\{E\_m\}\backslash right)^\{-1\}.$

where

• $f\; =\; \backslash frac\{V\_f\}\{V\_f\; +\; V\_m\}$ is the volume fraction of the fibers
• $E\_\backslash parallel$ is the material property of the composite parallel to the fibers
• $E\_\backslash perp$ is the material property of the composite perpendicular to the fibers
• $E\_f$ is the material property of the fibers
• $E\_m$ is the material property of the matrix

The majority of commercial composites are formed with random dispersion and orientation of the strengthening fibres, in which case the composite Young's modulus will fall between the isostrain and isostress bounds. However, in applications where the strength-to-weight ratio is engineered to be as high as possible (such as in the aerospace industry), fibre alignment may be tightly controlled.

In contrast to composites, isotropic materials (for example, aluminium or steel), in standard wrought forms, possess the same stiffness typically despite the directional orientation of the applied forces and/or moments. The relationship between forces/moments and strains/curvatures for an isotropic material can be described with the following material properties: Young's Modulus, the shear modulus, and the Poisson's ratio, in relatively simple mathematical relationships. For the anisotropic material, it needs the mathematics of a second-order tensor and up to 21 material property constants. For the special case of orthogonal isotropy, there are three distinct material property constants for each of Young's Modulus, Shear Modulus and Poisson's ratio—a total of 9 constants to express the relationship between forces/moments and strains/curvatures.

Techniques that take benefit of the materials' anisotropic properties involve mortise and tenon joints (in natural composites such as wood) and pi joints in synthetic composites.

In general, particle reinforcement is strengthening the composites less than fiber reinforcement. It is used to enhance the stiffness of the composites while increasing the strength and the toughness. Because of their mechanical properties, they are used in applications in which wear resistance is required. For example, hardness of cement can be increased by reinforcing gravel particles, drastically. Particle reinforcement a highly advantageous method of tuning mechanical properties of materials since it is very easy implement while being low cost.{{cite journal |last1=Wu |first1=Xiangguo |last2=Yang |first2=Jing |last3=Mpalla |first3=Issa B. |title=Preliminary design and structural responses of typical hybrid wind tower made of ultra high performance cementitious composites |journal=Structural Engineering and Mechanics |date=25 December 2013 |volume=48 |issue=6 |pages=791–807 |doi=10.12989/sem.2013.48.6.791 }}{{cite journal |last1=Li |first1=Mo |last2=Li |first2=Victor C. |title=Rheology, fiber dispersion, and robust properties of Engineered Cementitious Composites |journal=Materials and Structures |date=March 2013 |volume=46 |issue=3 |pages=405–420 |doi=10.1617/s11527-012-9909-z |hdl=2027.42/94214 |hdl-access=free }}{{cite journal |date=2008 |title=Large-Scale Processing of Engineered Cementitious Composites |journal=ACI Materials Journal |volume=105 |issue=4 |doi=10.14359/19897 }}{{cite journal |last1=Zeidi |first1=Mahdi |last2=Kim |first2=Chun IL |last3=Park |first3=Chul B. |date=2021 |title=The role of interface on the toughening and failure mechanisms of thermoplastic nanocomposites reinforced with nanofibrillated rubbers |journal=Nanoscale |volume=13 |issue=47 |pages=20248–20280 |doi=10.1039/D1NR07363J |pmid=34851346 }}

The elastic modulus of particle-reinforced composites can be expressed as,

:$E\_c\; =\; V\_m\; E\_m\; +\; K\_c\; V\_p\; E\_p$

where E is the elastic modulus, V is the volume fraction. The subscripts c, p and m are indicating composite, particle and matrix, respectively. $K\_c$ is a constant can be found empirically.

Similarly, tensile strength of particle-reinforced composites can be expressed as,

:$(T.S.)\_c\; =\; V\_m\; (T.S.)\_m\; +\; K\_s\; V\_p\; (T.S.)\_p$

where T.S. is the tensile strength, and $K\_s$ is a constant (not equal to $K\_c$) that can be found empirically.

{{ see also | Short_fiber_thermoplastics#Mechanical_properties}}

Short fibers are often cheaper or more convenient to manufacture than longer continuous fibers, but still provide better properties than particle reinforcement. A common example is carbon fiber reinforced 3D printing filaments, which use chopped short carbon fibers mixed into a matrix, typically PLA or PETG.

Shear lag theory uses the shear lag model to predict properties such as the Young's modulus for short fiber composites. The model assumes that load is transferred from the matrix to the fibers solely through the interfacial shear stresses $\backslash tau\_i$ acting on the cylindrical interface. Shear lag theory says then that the rate of change of the axial stress in the fiber as you move along the fiber is proportional to the ratio of the interfacial shear stresses over the radius of the fibre $r\_0$:

:$\backslash frac\{d\backslash sigma\_f\}\{dx\}\; =\; -\backslash frac\{2\backslash tau\_i\}\{r\_0\}$

This leads to the average fiber stress over the full length of the fibre being given by:

:$\backslash sigma\_f\; =\; E\_f\backslash varepsilon\_1\backslash left(1-\backslash frac\{\backslash tanh(ns)\}\{ns\}\backslash right)$

where

• $\backslash varepsilon\_1$ is the macroscopic strain in the composite
• $s$ is the fiber aspect ratio (length over diameter)
• $n\; =\; \backslash left(\; \backslash frac\{2E\_m\}\{E\_f(1+\backslash nu\_m)\backslash ln(1/f)\}\; \backslash right)^\{1/2\}$ is a dimensionless constant{{cite journal | title=On the Use of Shear-Lag Methods for Analysis of Stress Transfer in Unidirectional Composites | author=John A. Nairn | journal=Mechanics of Materials | year = 1997 | volume=26 | issue=2 | pages=63–80 | doi=10.1016/S0167-6636(97)00023-9| bibcode=1997MechM..26...63N }}
• $\backslash nu\_m$ is the Poisson's ratio of the matrix

By assuming a uniform tensile strain, this results in:{{cite journal | author=P.J. WITHERS | title=4.02 - Elastic and Thermoelastic Properties of Brittle Matrix Composites | journal=Comprehensive Composite Materials | year=2000 | pages=25–45 | doi=10.1016/B0-08-042993-9/00087-5| isbn=978-0-08-042993-9 }}

:$E\_1\; =\; \backslash frac\{\backslash sigma\_1\}\{\backslash varepsilon\_1\}\; =\; fE\_f\; \backslash left(\; 1\; -\; \backslash frac\{\backslash tanh(ns)\}\{ns\}\backslash right)\; +\; (1-f)\; E\_m$

As s becomes larger, this tends towards the rule of mixtures, which represents the Young's modulus parallel to continuous fibers.

In general, continuous fiber reinforcement is implemented by incorporating a fiber as the strong phase into a weak phase, matrix. The reason for the popularity of fiber usage is materials with extraordinary strength can be obtained in their fiber form. Non-metallic fibers are usually showing a very high strength to density ratio compared to metal fibers because of the covalent nature of their bonds. The most famous example of this is carbon fibers that have many applications extending from sports gear to protective equipment to space industries.{{cite book |last1=Courtney |first1=Thomas H. |title=Mechanical Behavior of Materials |date=2005 |publisher=Waveland Press |isbn=978-1-4786-0838-7 }}{{pn|date=January 2025}}{{cite book |doi=10.1007/978-981-13-0538-2 |title=Carbon Fibers |series=Springer Series in Materials Science |date=2018 |volume=210 |isbn=978-981-13-0537-5 |first1=Soo-Jin |last1=Park }}{{pn|date=January 2025}}

The stress on the composite can be expressed in terms of the volume fraction of the fiber and the matrix.

:$\backslash sigma\_c\; =\; V\_f\; \backslash sigma\_f\; +\; V\_m\; \backslash sigma\_m$

where $\backslash sigma$ is the stress, V is the volume fraction. The subscripts c, f and m are indicating composite, fiber and matrix, respectively.

Although the stress–strain behavior of fiber composites can only be determined by testing, there is an expected trend, three stages of the stress–strain curve. The first stage is the region of the stress–strain curve where both fiber and the matrix are elastically deformed. This linearly elastic region can be expressed in the following form.

:$\backslash sigma\_c\; -\; E\_c\; \backslash epsilon\_c\; =\; \backslash epsilon\_c\; (V\_f\; E\_f\; +\; V\_m\; E\_m)$

where $\backslash sigma$ is the stress, $\backslash epsilon$ is the strain, E is the elastic modulus, and V is the volume fraction. The subscripts c, f, and m are indicating composite, fiber, and matrix, respectively.

After passing the elastic region for both fiber and the matrix, the second region of the stress–strain curve can be observed. In the second region, the fiber is still elastically deformed while the matrix is plastically deformed since the matrix is the weak phase. The instantaneous modulus can be determined using the slope of the stress–strain curve in the second region. The relationship between stress and strain can be expressed as,

:$\backslash sigma\_c\; =\; V\_f\; E\_f\; \backslash epsilon\_c\; +\; V\_m\; \backslash sigma\_m\; (\backslash epsilon\_c)$

where $\backslash sigma$ is the stress, $\backslash epsilon$ is the strain, E is the elastic modulus, and V is the volume fraction. The subscripts c, f, and m are indicating composite, fiber, and matrix, respectively. To find the modulus in the second region derivative of this equation can be used since the slope of the curve is equal to the modulus.

:$E\_c\text{'}\; =\; \backslash frac\{d\; \backslash sigma\_c\}\{d\; \backslash epsilon\_c\}\; =\; V\_f\; E\_f\; +\; V\_m\; \backslash left(\backslash frac\{d\; \backslash sigma\_c\}\{d\; \backslash epsilon\_c\}\backslash right)$

In most cases it can be assumed $E\_c\text{'}=\; V\_f\; E\_f$ since the second term is much less than the first one.

In reality, the derivative of stress with respect to strain is not always returning the modulus because of the binding interaction between the fiber and matrix. The strength of the interaction between these two phases can result in changes in the mechanical properties of the composite. The compatibility of the fiber and matrix is a measure of internal stress.

The covalently bonded high strength fibers (e.g. carbon fibers) experience mostly elastic deformation before the fracture since the plastic deformation can happen due to dislocation motion. Whereas, metallic fibers have more space to plastically deform, so their composites exhibit a third stage where both fiber and the matrix are plastically deforming. Metallic fibers have many applications to work at cryogenic temperatures that is one of the advantages of composites with metal fibers over nonmetallic. The stress in this region of the stress–strain curve can be expressed as,

:$\backslash sigma\_c\; (\backslash epsilon\_c)\; =\; V\_f\; \backslash sigma\_f\; \backslash epsilon\_c\; +\; V\_m\; \backslash sigma\_m\; (\backslash epsilon\_c)$

where $\backslash sigma$ is the stress, $\backslash epsilon$ is the strain, E is the elastic modulus, and V is the volume fraction. The subscripts c, f, and m are indicating composite, fiber, and matrix, respectively. $\backslash sigma\_f\; (\backslash epsilon\_c)$ and $\backslash sigma\_m\; (\backslash epsilon\_c)$ are for fiber and matrix flow stresses respectively. Just after the third region the composite exhibit necking. The necking strain of composite is happened to be between the necking strain of the fiber and the matrix just like other mechanical properties of the composites. The necking strain of the weak phase is delayed by the strong phase. The amount of the delay depends upon the volume fraction of the strong phase.

Thus, the tensile strength of the composite can be expressed in terms of the volume fraction.

:$(T.S.)\_c=V\_f(T.S.)\_f+V\_m\; \backslash sigma\_m(\backslash epsilon\_m)$

where T.S. is the tensile strength, $\backslash sigma$ is the stress, $\backslash epsilon$ is the strain, E is the elastic modulus, and V is the volume fraction. The subscripts c, f, and m are indicating composite, fiber, and matrix, respectively. The composite tensile strength can be expressed as

:$(T.S.)\_c=V\_m(T.S.)\_m$ for $V\_f$ is less than or equal to $V\_c$ (arbitrary critical value of volume fraction)

:$(T.S.)\_c=\; V\_f(T.S.)\_f\; +\; V\_m(\backslash sigma\_m)$ for $V\_f$ is greater than or equal to $V\_c$

The critical value of volume fraction can be expressed as,

:$V\_c=\; \backslash frac\{[(T.S.)\_m\; -\; \backslash sigma\_m(\backslash epsilon\_f)]\}\{[(T.S.)\_f\; +\; (T.S.)\_m\; -\; \backslash sigma\_m(\backslash epsilon\_f)]\}$

Evidently, the composite tensile strength can be higher than the matrix if $(T.S.)\_c$ is greater than $(T.S.)\_m$

.

Thus, the minimum volume fraction of the fiber can be expressed as,

:$V\_c=\; \backslash frac\{[(T.S.)\_m\; -\; \backslash sigma\_m(\backslash epsilon\_f)]\}\{[(T.S.)\_f\; -\; \backslash sigma\_m(\backslash epsilon\_f)]\}$

Although this minimum value is very low in practice, it is very important to know since the reason for the incorporation of continuous fibers is to improve the mechanical properties of the materials/composites, and this value of volume fraction is the threshold of this improvement.

A change in the angle between the applied stress and fiber orientation will affect the mechanical properties of fiber-reinforced composites, especially the tensile strength. This angle, $\backslash theta$, can be used predict the dominant tensile fracture mechanism.

At small angles, $\backslash theta\; \backslash approx\; 0^\{\backslash circ\}$, the dominant fracture mechanism is the same as with load-fiber alignment, tensile fracture. The resolved force acting upon the length of the fibers is reduced by a factor of $\backslash cos\; \backslash theta$ from rotation. $F\_\{\backslash mbox\{res\}\}=F\backslash cos\backslash theta$. The resolved area on which the fiber experiences the force is increased by a factor of $\backslash cos\; \backslash theta$ from rotation. $A\_\{\backslash mbox\{res\}\}=A\_\{0\}/\backslash cos\backslash theta$. Taking the effective tensile strength to be $(\backslash mbox\{T.S.\})\_\{\backslash mbox\{c\}\}=F\_\{\backslash mbox\{res\}\}/A\_\{\backslash mbox\{res\}\}$ and the aligned tensile strength $\backslash sigma^*\_\backslash parallel=F/A$.

:$(\backslash mbox\{T.S.\})\_\{\backslash mbox\{c\}\}\backslash ;(\backslash mbox\{longitudinal\; fracture\})=\backslash frac\{\backslash sigma^*\_\backslash parallel\}\{\backslash cos^2\backslash theta\}$

At moderate angles, $\backslash theta\; \backslash approx\; 45^\{\backslash circ\}$, the material experiences shear failure. The effective force direction is reduced with respect to the aligned direction. $F\_\{\backslash mbox\{res\}\}=F\backslash cos\backslash theta$. The resolved area on which the force acts is $A\_\{\backslash mbox\{res\}\}=A\_m/\backslash sin\backslash theta$. The resulting tensile strength depends on the shear strength of the matrix, $\backslash tau\_m$.

:$(\backslash mbox\{T.S.\})\_\{\backslash mbox\{c\}\}\backslash ;(\backslash mbox\{shear\; failure\})=\backslash frac\{\backslash tau\_m\}\{\backslash sin\{\backslash theta\}\backslash cos\{\backslash theta\}\}$

At extreme angles, $\backslash theta\; \backslash approx\; 90^\{\backslash circ\}$, the dominant mode of failure is tensile fracture in the matrix in the perpendicular direction. As in the isostress case of layered composite materials, the strength in this direction is lower than in the aligned direction. The effective areas and forces act perpendicular to the aligned direction so they both scale by $\backslash sin\backslash theta$. The resolved tensile strength is proportional to the transverse strength, $\backslash sigma^\{*\}\_\{\backslash perp\}$.

:$(\backslash mbox\{T.S.\})\_\{\backslash mbox\{c\}\}\backslash ;(\backslash mbox\{transverse\; fracture\})=\backslash frac\{\backslash sigma^*\_\{\backslash perp\}\}\{\backslash sin^2\backslash theta\}$

The critical angles from which the dominant fracture mechanism changes can be calculated as,

:$\backslash theta\_\{c\_1\}=\backslash tan^\{-1\}\backslash left(\{\backslash frac\{\backslash tau\_m\}\{\backslash sigma^*\_\backslash parallel\}\}\backslash right)$

:$\backslash theta\_\{c\_2\}=\backslash tan^\{-1\}\backslash left(\{\backslash frac\{\backslash sigma^*\_\backslash perp\}\{\backslash tau\_m\}\}\backslash right)$

where $\backslash theta\_\{c\_1\}$ is the critical angle between longitudinal fracture and shear failure, and $\backslash theta\_\{c\_2\}$ is the critical angle between shear failure and transverse fracture.

By ignoring length effects, this model is most accurate for continuous fibers and does not effectively capture the strength-orientation relationship for short fiber reinforced composites. Furthermore, most realistic systems do not experience the local maxima predicted at the critical angles.{{cite journal |last1=Lasikun |last2=Ariawan |first2=Dody |last3=Surojo |first3=Eko |last4=Triyono |first4=Joko |date=2018 |title=Effect of fiber orientation on tensile and impact properties of Zalacca Midrib fiber-HDPE composites by compression molding |journal=The 3rd International Conference on Industrial |series=AIP Conference Proceedings |volume=1927 |issue=1 |location=Jatinangor, Indonesia |pages=030060 |doi=10.1063/1.5024119 |bibcode=2018AIPC.1931c0060L |doi-access=free}}{{cite journal |last1=Mortazavian |first1=Seyyedvahid |last2=Fatemi |first2=Ali |title=Effects of fiber orientation and anisotropy on tensile strength and elastic modulus of short fiber reinforced polymer composites |journal=Composites Part B: Engineering |date=April 2015 |volume=72 |pages=116–129 |doi=10.1016/j.compositesb.2014.11.041 }}{{cite journal |id={{ProQuest|1030964421}} |last1=Banakar |first1=Prashanth |last2=Shivananda |first2=H K |last3=Niranjan |first3=H B |title=Influence of Fiber Orientation and Thickness on Tensile Properties of Laminated Polymer Composites |journal=International Journal of Pure and Applied Sciences and Technology |volume=9 |issue=1 |date=March 2012 |pages=61–68 }}{{cite journal |last1=Brahim |first1=Sami Ben |last2=Cheikh |first2=Ridha Ben |title=Influence of fibre orientation and volume fraction on the tensile properties of unidirectional Alfa-polyester composite |journal=Composites Science and Technology |date=January 2007 |volume=67 |issue=1 |pages=140–147 |doi=10.1016/j.compscitech.2005.10.006 }} The Tsai-Hill criterion provides a more complete description of fiber composite tensile strength as a function of orientation angle by coupling the contributing yield stresses: $\backslash sigma^\{*\}\_\backslash parallel$, $\backslash sigma^\{*\}\_\backslash perp$, and $\backslash tau\_m$.{{cite journal |last1=Azzi |first1=V. D. |last2=Tsai |first2=S.W. |date=1965 |title=Anisotropic Strength of Composites |journal=Experimental Mechanics |volume=5 |issue=9 |pages=283–288 |doi=10.1007/BF02326292 }}

:$(\backslash mbox\{T.S.\})\_\{\backslash mbox\{c\}\}\backslash ;(\backslash mbox\{Tsai-Hill\})=\backslash bigg[\{\backslash frac\{\backslash cos^4\backslash theta\}\{(\{\backslash sigma^*\_\backslash parallel\})^2\}\}+\backslash cos^2\backslash theta\backslash sin^2\backslash theta\backslash left(\{\backslash frac\{1\}\{(\{\backslash tau\_m\})^2\}\}-\{\backslash frac\{1\}\{(\{\backslash sigma^*\_\backslash parallel\})^2\}\}\backslash right)+\{\backslash frac\{\backslash sin^4\backslash theta\}\{(\{\backslash sigma^*\_\backslash perp\})^2\}\}\backslash bigg]^\{-1/2\}$

Anisotropy in the tensile strength of fiber reinforced composites can be removed by randomly orienting the fiber directions within the material. It sacrifices the ultimate strength in the aligned direction for an overall, isotropically strengthened material.

:$E\_c=KV\_\{f\}E\_\{f\}+V\_\{m\}E\_\{m\}$

Where K is an empirically determined reinforcement factor; similar to the particle reinforcement equation. For fibers with randomly distributed orientations in a plane, $K\; \backslash approx\; 0.38$, and for a random distribution in 3D, $K\; \backslash approx\; 0.20$.

Composite materials are generally anisotropic, and in many cases are orthotropic. Voigt notation can be used to reduce the rank of the stress and strain tensors such that the stiffness $C$ (often also referred to by $Q$) and compliance $S$ can be written as a matrix:{{cite book |last1=Lekhnit͡skiĭ |first1=Sergeĭ Georgievich |title=Theory of Elasticity of an Anisotropic Elastic Body |date=1963 |publisher=Holden-Day |oclc=652279972 }}{{pn|date=January 2025}}

$\backslash begin\{bmatrix\}\; \backslash sigma\_1\; \backslash \backslash \; \backslash sigma\_2\; \backslash \backslash \; \backslash sigma\_3\; \backslash \backslash \; \backslash sigma\_4\; \backslash \backslash \; \backslash sigma\_5\; \backslash \backslash \; \backslash sigma\_6\; \backslash end\{bmatrix\}\; =$

\begin{bmatrix}

C_{11} & C_{12} & C_{13} & C_{14} & C_{15} & C_{16} \\

C_{12} & C_{22} & C_{23} & C_{24} & C_{25} & C_{26} \\

C_{13} & C_{23} & C_{33} & C_{34} & C_{35} & C_{36} \\

C_{14} & C_{24} & C_{34} & C_{44} & C_{45} & C_{46} \\

C_{15} & C_{25} & C_{35} & C_{45} & C_{55} & C_{56} \\

C_{16} & C_{26} & C_{36} & C_{46} & C_{56} & C_{66} \end{bmatrix}

\begin{bmatrix} \varepsilon_1 \\ \varepsilon_2 \\ \varepsilon_3 \\ \varepsilon_4 \\ \varepsilon_5 \\ \varepsilon_6 \end{bmatrix} and $\backslash begin\{bmatrix\}\; \backslash varepsilon\_1\; \backslash \backslash \; \backslash varepsilon\_2\; \backslash \backslash \; \backslash varepsilon\_3\; \backslash \backslash \; \backslash varepsilon\_4\; \backslash \backslash \; \backslash varepsilon\_5\; \backslash \backslash \; \backslash varepsilon\_6\; \backslash end\{bmatrix\}\; =$

\begin{bmatrix}

S_{11} & S_{12} & S_{13} & S_{14} & S_{15} & S_{16} \\

S_{12} & S_{22} & S_{23} & S_{24} & S_{25} & S_{26} \\

S_{13} & S_{23} & S_{33} & S_{34} & S_{35} & S_{36} \\

S_{14} & S_{24} & S_{34} & S_{44} & S_{45} & S_{46} \\

S_{15} & S_{25} & S_{35} & S_{45} & S_{55} & S_{56} \\

S_{16} & S_{26} & S_{36} & S_{46} & S_{56} & S_{66} \end{bmatrix}

\begin{bmatrix} \sigma_1 \\ \sigma_2 \\ \sigma_3 \\ \sigma_4 \\ \sigma_5 \\ \sigma_6 \end{bmatrix}

When considering each ply individually, it is assumed that they can be treated as thi lamina and so out–of–plane stresses and strains are negligible. That is $\backslash sigma\_3\; =\; \backslash sigma\_4\; =\; \backslash sigma\_5\; =\; 0$ and $\backslash varepsilon\_4\; =\; \backslash varepsilon\_5\; =\; 0$.{{cite book |doi=10.1007/978-94-011-4489-6 |title=Mechanics of Composite Materials and Structures |date=1999 |isbn=978-0-7923-5871-8 |editor-last1=Soares |editor-last2=Soares |editor-last3=Freitas |editor-first1=Carlos A. Mota |editor-first2=Cristóvão M. Mota |editor-first3=Manuel J. M. }} This allows the stiffness and compliance matrices to be reduced to 3x3 matrices as follows:

$C\; =$

\begin{bmatrix}

\tfrac{E_{\rm 1}}{1-{\nu_{\rm 12}}{\nu_{\rm 21}}} & \tfrac{E_{\rm 2}{\nu_{\rm 12}}}{1-{\nu_{\rm 12}}{\nu_{\rm 21}}} & 0 \\

\tfrac{E_{\rm 2}{\nu_{\rm 12}}}{1-{\nu_{\rm 12}}{\nu_{\rm 21}}} & \tfrac{E_{\rm 2}}{1-{\nu_{\rm 12}}{\nu_{\rm 21}}} & 0 \\

0 & 0 & G_{\rm 12} \\

\end{bmatrix} \quad and $\backslash quad\; S\; =$

\begin{bmatrix}

\tfrac{1}{E_{\rm 1}} & - \tfrac{\nu_{\rm 21}}{E_{\rm 2}} & 0 \\

-\tfrac{\nu_{\rm 12}}{E_{\rm 1}} & \tfrac{1}{E_{\rm 2}} & 0 \\

0 & 0 & \tfrac{1}{G_{\rm 12}} \\

\end{bmatrix}

File:Transform coordinate system.png

For fiber-reinforced composite, the fiber orientation in material affect anisotropic properties of the structure. From characterizing technique i.e. tensile testing, the material properties were measured based on sample (1-2) coordinate system. The tensors above express stress-strain relationship in (1-2) coordinate system. While the known material properties is in the principal coordinate system (x-y) of material. Transforming the tensor between two coordinate system help identify the material properties of the tested sample. The transformation matrix with $\backslash theta$ degree rotation is

$T(\backslash theta)\_\backslash epsilon\; =$

\begin{bmatrix} \cos^2 \theta & \sin^2 \theta & \cos \theta\sin \theta

\\ sin^2 \theta & \cos^2 \theta & -\cos \theta\sin \theta

\\ -2\cos \theta\sin \theta & 2\cos \theta\sin \theta & \cos^2 \theta - \sin^2 \theta \end{bmatrix} for $\backslash begin\{bmatrix\}\; \backslash acute\{\backslash epsilon\}\; \backslash end\{bmatrix\}\; =\; T(\backslash theta)\_\backslash epsilon\; \backslash begin\{bmatrix\}\; \backslash epsilon\; \backslash end\{bmatrix\}$

$T(\backslash theta)\_\backslash sigma\; =$

\begin{bmatrix} \cos^2 \theta & \sin^2 \theta & 2\cos \theta\sin \theta

\\ sin^2 \theta & \cos^2 \theta & -2\cos \theta\sin \theta

\\ -\cos \theta\sin \theta & \cos \theta\sin \theta & \cos^2 \theta - \sin^2 \theta \end{bmatrix} for $\backslash begin\{bmatrix\}\; \backslash acute\{\backslash sigma\}\; \backslash end\{bmatrix\}\; =\; T(\backslash theta)\_\backslash sigma\; \backslash begin\{bmatrix\}\; \backslash sigma\; \backslash end\{bmatrix\}$

The most common types of fibers used in industry are glass fibers, carbon fibers, and kevlar due to their ease of production and availability. Their mechanical properties are very important to know, therefore the table of their mechanical properties is given below to compare them with S97 steel.{{cite web |title=Carbon Fibre, Tubes, Profiles – Filament Winding and Composite Engineering |url=http://www.performance-composites.com/carbonfibre/carbonfibre.asp |website=www.performance-composites.com |access-date=2020-05-22 |archive-date=2020-05-05 |archive-url=https://web.archive.org/web/20200505133007/http://www.performance-composites.com/carbonfibre/carbonfibre.asp |url-status=live}}{{cite web |title=Composite Manufacturing {{!}} Performance Composites|url=https://www.performancecomposites.com/|website=www.performancecomposites.com|access-date=2020-05-22|archive-date=2020-05-03|archive-url=https://web.archive.org/web/20200503120735/http://www.performancecomposites.com/|url-status=live}}{{cite web |title=Composite Materials • Innovative Composite Engineering |url=http://www.innovativecomposite.com/materials/ |website=Innovative Composite Engineering |language=en-US |access-date=2020-05-22 |archive-date=2020-05-05 |archive-url=https://web.archive.org/web/20200505134923/http://www.innovativecomposite.com/materials/ |url-status=live}}{{cite web |title=Reinforcement Fabrics – In Stock for Same Day Shipping {{!}} Fibre Glast|url=https://www.fibreglast.com/category/Composite-Fabrics|website=www.fibreglast.com|access-date=2020-05-22|archive-date=2020-07-16|archive-url=https://web.archive.org/web/20200716204826/https://www.fibreglast.com/category/Composite-Fabrics|url-status=live}} The angle of fiber orientation is very important because of the anisotropy of fiber composites (please see the section "Physical properties" for a more detailed explanation). The mechanical properties of the composites can be tested using standard mechanical testing methods by positioning the samples at various angles (the standard angles are 0°, 45°, and 90°) with respect to the orientation of fibers within the composites. In general, 0° axial alignment makes composites resistant to longitudinal bending and axial tension/compression, 90° hoop alignment is used to obtain resistance to internal/external pressure, and ± 45° is the ideal choice to obtain resistance against pure torsion.{{cite web |title=Filament Winding, Carbon Fibre Angles in Composite Tubes |url=http://www.performance-composites.com/carbonfibre/fibreangles.asp |website=www.performance-composites.com |access-date=2020-05-22 |archive-date=2020-05-05 |archive-url=https://web.archive.org/web/20200505132959/http://www.performance-composites.com/carbonfibre/fibreangles.asp |url-status=live}}

Although strength and stiffness of steel and aluminum alloys are comparable to fiber composites, specific strength and stiffness of composites (i.e. in relation to their weight) are significantly higher.

Shock, impact of varying speed, or repeated cyclic stresses can provoke the laminate to separate at the interface between two layers, a condition known as delamination.{{cite journal |last1=Ma |first1=Binlin |last2=Cao |first2=Xiaofei |last3=Feng |first3=Yu |last4=Song |first4=Yujian |last5=Yang |first5=Fei |last6=Li |first6=Ying |last7=Zhang |first7=Deyue |last8=Wang |first8=Yipeng |last9=He |first9=Yuting |title=A comparative study on the low velocity impact behavior of UD, woven, and hybrid UD/woven FRP composite laminates |journal=Composites Part B: Engineering |date=February 2024 |volume=271 |pages=111133 |doi=10.1016/j.compositesb.2023.111133 }}{{cite journal |last1=Sanchez-Saez |first1=S. |last2=Barbero |first2=E. |last3=Zaera |first3=R. |last4=Navarro |first4=C. |title=Compression after impact of thin composite laminates |journal=Composites Science and Technology |date=October 2005 |volume=65 |issue=13 |pages=1911–1919 |doi=10.1016/j.compscitech.2005.04.009 |hdl=10016/7498 |hdl-access=free }} Individual fibres can separate from the matrix, for example, fibre pull-out.

Composites can fail on the macroscopic or microscopic scale. Compression failures can happen at both the macro scale or at each individual reinforcing fibre in compression buckling. Tension failures can be net section failures of the part or degradation of the composite at a microscopic scale where one or more of the layers in the composite fail in tension of the matrix or failure of the bond between the matrix and fibres.

Some composites are brittle and possess little reserve strength beyond the initial onset of failure while others may have large deformations and have reserve energy absorbing capacity past the onset of damage. The distinctions in fibres and matrices that are available and the mixtures that can be made with blends leave a very broad range of properties that can be designed into a composite structure. The most famous failure of a brittle ceramic matrix composite occurred when the carbon-carbon composite tile on the leading edge of the wing of the Space Shuttle Columbia fractured when impacted during take-off. It directed to the catastrophic break-up of the vehicle when it re-entered the Earth's atmosphere on 1 February 2003.

Composites have relatively poor bearing strength compared to metals.

File:Composite Strength as a Function of Fiber Misalignment.png

Another failure mode is fiber tensile fracture, which becomes more likely when fibers are aligned with the loading direction, so is the possibility of fiber tensile fracture, assuming the tensile strength exceeds that of the matrix. When a fiber has some angle of misorientation θ, several fracture modes are possible. For small values of θ the stress required to initiate fracture is increased by a factor of (cos θ)⁻² due to the increased cross-sectional area (A cos θ) of the fibre and reduced force (F/cos θ) experienced by the fiber, leading to a composite tensile strength of σ_parallel /cos² θ where σ_parallel is the tensile strength of the composite with fibers aligned parallel with the applied force.

Intermediate angles of misorientation θ lead to matrix shear failure. Again the cross sectional area is modified but since shear stress is now the driving force for failure the area of the matrix parallel to the fibers is of interest, increasing by a factor of 1/sin θ. Similarly, the force parallel to this area again decreases (F/cos θ) leading to a total tensile strength of τ_my /sin θ cos θ where τ_my is the matrix shear strength.

Finally, for large values of θ (near π/2) transverse matrix failure is the most likely to occur, since the fibers no longer carry the majority of the load. Still, the tensile strength will be greater than for the purely perpendicular orientation, since the force perpendicular to the fibers will decrease by a factor of 1/sin θ and the area decreases by a factor of 1/sin θ producing a composite tensile strength of σ_perp /sin²θ where σ_perp is the tensile strength of the composite with fibers align perpendicular to the applied force.

{{cite book |last=Courtney |first=Thomas H. |date=2000 |title=Mechanical Behavior of Materials |edition= 2nd |publisher=Waveland Press, Inc. |location=Long Grove, IL |pages=263–265 |isbn=978-1-57766-425-3}}

Composites are tested before and after construction to assist in predicting and preventing failures. Pre-construction testing may adopt finite element analysis (FEA) for ply-by-ply analysis of curved surfaces and predicting wrinkling, crimping and dimpling of composites.{{cite news |last1=Waterman |first1=Pamela |title=The Life of Composite Materials |url=https://www.digitalengineering247.com/article/the-life-of-composite-materials/ |work=Digital Engineering |date=1 May 2007 }}{{cite journal |last1=Aghdam |first1=M.M. |last2=Morsali |first2=S.R. |title=Damage initiation and collapse behavior of unidirectional metal matrix composites at elevated temperatures |journal=Computational Materials Science |date=November 2013 |volume=79 |pages=402–407 |doi=10.1016/j.commatsci.2013.06.024}}{{cite book |doi=10.1201/9781351228466 |title=Primary and Secondary Manufacturing of Polymer Matrix Composites |date=2017 |isbn=978-1-351-22846-6 |editor-last1=Debnath |editor-last2=Singh |editor-first1=Kishore |editor-first2=Inderdeep }}{{pn|date=January 2025}}[https://coventivecomposites.com/explainers/what-is-finite-element-analysis/ What is Finite Element Analysis?]{{Dead link|date=August 2023 |bot=InternetArchiveBot |fix-attempted=yes }} Materials may be tested during manufacturing and after construction by various non-destructive methods including ultrasonic, thermography, shearography and X-ray radiography,{{cite journal

|last1=Matzkanin |first1=George A.

|last2=Yolken |first2=H. Thomas

|title=Techniques for the Nondestructive Evaluation of Polymer Matrix Composites

|journal=AMMTIAC Quarterly

|volume=2

|issue=4

|url=http://ammtiac.alionscience.com/pdf/AQV2N4.pdf

|url-status=dead

|archive-url=https://web.archive.org/web/20081217033116/http://ammtiac.alionscience.com/pdf/AQV2N4.pdf

|archive-date=2008-12-17

}} and laser bond inspection for NDT of relative bond strength integrity in a localized area.

• 3D composites
• Aluminium composite panel
• American Composites Manufacturers Association
• Chemical vapour infiltration
• Composite laminate
• Discontinuous aligned composite
• Epoxy granite
• Hybrid material
• Lay-up process
• Nanocomposite
• Pykrete
• Rule of mixtures
• Scaled Composites
• Smart material
• Smart Materials and Structures
• Void (composites)

{{Reflist}}

{{Refbegin}}

• {{cite book |doi=10.1201/9781498711067 |title=Mechanics of Composite Materials |date=2018 |last1=Jones |first1=Robert M. |isbn=978-1-315-27298-6 }}
• {{cite book |last1=Aboudi |first1=Jacob |last2=Cederbaum |first2=Gabriel |last3=Elishakoff |first3=Isaac |last4=Librescu |first4=Liviu |title=Random Vibration and Reliability of Composite Structures |date=1992 |publisher=CRC Press |isbn=978-0-87762-865-1 }}
• {{cite book |doi=10.1007/1-4020-4203-5 |title=Thin-Walled Composite Beams |series=Solid Mechanics and Its Applications |date=2006 |volume=131 |isbn=978-1-4020-3457-2 |first1=Liviu |last1=Librescu |first2=Ohseop |last2=Song }}
• {{cite book |doi=10.1007/978-3-642-37179-0 |title=Polymers and Polymeric Composites: A Reference Series |date=2016 |isbn=978-3-642-37179-0 |editor-last1=Palsule |editor-first1=Sanjay }}
• {{cite book |doi=10.1201/9781420058291 |title=Mechanics of Composite Materials |date=2005 |last1=Kaw |first1=Autar K. |isbn=978-0-429-12539-3 }}
• {{cite book |last1=Hollaway |first1=L. C. |title=Handbook of Polymer Composites for Engineers |date=1994 |publisher=Woodhead Publishing |isbn=978-1-85573-129-5 }}
• {{cite book |last1=Madbouly |first1=Samy |last2=Zhang |first2=Chaoqun |last3=Kessler |first3=Michael R. |title=Bio-Based Plant Oil Polymers and Composites |date=2015 |publisher=William Andrew |isbn=978-0-323-37128-5 }}
• {{cite book |last1=Matthews |first1=F. L. |last2=Rawlings |first2=Rees D. |title=Composite Materials: Engineering and Science |date=1999 |publisher=Woodhead Publishing |isbn=978-0-8493-0621-1 }}
• {{cite book |doi=10.1007/978-3-658-41408-5 |title=Engineered Stability |date=2023 |last1=Haka |first1=Andreas T. |isbn=978-3-658-41407-8 }}

{{Refend}}

{{Commons category|Composite materials}}

• [https://community.cdmhub.org/ cdmHUB – the Global Composites Community]
• [https://web.archive.org/web/20070219024138/http://www3.open.ac.uk/courses/bin/p12.dll?C01T838 Distance learning course in polymers and composites]
• [http://www.wmc.eu/optimatblades_optidat.php OptiDAT composite material database] {{Webarchive|url=https://web.archive.org/web/20131104214439/http://www.wmc.eu/optimatblades_optidat.php |date=2013-11-04 }}

{{Composite Material}}

{{Fundamental aspects of materials science}}

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