ABSTRACT
Most biological materials, except perhaps tooth enamel and cortical bone, are relatively soft and pliable. Thus, most biological materials (or tissue) are nonlinear both in material properties (e.g., stress-strain and stress-strain rate relations) and in geometric response (e.g., strain-displacement relations). These nonlinearities together with inhomogeneity and anisotropy make biological materials signicantly more difcult to model than common structural materials such as steel, aluminum, and glass. Similarly, the properties of biouids (e.g., blood) are more difcult to model than water or oil.
