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. The aggregate modulus can be calculated from Young's modulus (E) and the Poisson ratio (v).
H a = E ( 1 − v ) ( 1 + v ) ( 1 − 2 v ) {\displaystyle 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. 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.
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