The aggregate modulus of a similar specimen is determined from a unidirectional deformational testing configuration, i.e., the only non-zero strain component is E 11. 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 e 1 direction. In this test, the only non-zero component of the stress tensor is T 11.