Aggregate modulus

In relation to biomechanics, the aggregate modulus (Ha) is a measurement of the stiffness of a material at equilibrium when fluid has ceased flowing through it, under the application of a constant load or strain in a confined compression configuration.Mansour, J. M. (2003). Biomechanics of cartilage. Kinesiology: the mechanics and pathomechanics of human movement, 2, 66-79. The aggregate modulus can be calculated from Young's modulus (E) and the Poisson ratio (v).{{Cite journal |last1=Boschetti |first1=Federica |last2=Pennati |first2=Giancarlo |last3=Gervaso |first3=Francesca |last4=Peretti |first4=Giuseppe M. |last5=Dubini |first5=Gabriele |date=2004 |title=Biomechanical properties of human articular cartilage under compressive loads |url=https://pubmed.ncbi.nlm.nih.gov/15299249/ |journal=Biorheology |volume=41 |issue=3–4 |pages=159–166 |doi=10.1177/0006355X2004041003004001 |issn=0006-355X |pmid=15299249}}

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Ha=\frac{E(1-v)}{(1+v)(1-2v)}

The aggregate modulus of a similar specimen is determined from a unidirectional deformational testing configuration, i.e., the only non-zero strain component is E₁₁.{{Citation |last1=Loret |first1=Benjamin |title=Biomechanical topics in soft tissues |date=2017-05-08 |url=http://dx.doi.org/10.1201/9781315110783-1 |work=Biomechanical Aspects of Soft Tissues |pages=1–10 |location=Boca Raton, FL |publisher=CRC Press |isbn=978-1-315-11078-3 |access-date=2022-03-15 |last2=Simões |first2=Fernando M. F.|doi=10.1201/9781315110783-1 |url-access=subscription }} This configuration is opposed to the Young's modulus, which is determined from a unidirectional loading testing configuration, i.e., the only non-zero stress component is, say, in the e₁ direction. In this test, the only non-zero component of the stress tensor is T₁₁.