Therefore, they are all suitable to describe the material response and develop constitutive laws, since they are independent of the observer.

Ballistic impact loads are necessary to study material response.

The material response can be significantly different according to the loading condition considered.

Hence, research in acoustic metamaterials has the same goal of broader material response with sound waves.

Anisotropic materials such as wood, paper and also essentially all single crystals exhibit differing material response to stress or strain when tested in different directions.

Second, the material response can be controlled at will.

Hence, metamaterials extend the material response, among other capabilities.

Thus, two criteria must be accounted for when considering failure and two constitutive equations that describe material response.

This implies that the material response has time-dependence.

The material response is linear up until the upper yield point, but the lower yield point is used in structural engineering as a conservative value.