Figure 1.

A summary of mechanical properties deforming under stress. (a) A material resistance to elastic deformation to force (F) or stress (σ) is the elastic modulus. E is Young's modulus, a response to tensile or compressive stress, G is the shear modulus, a response to shear stress, and K is the bulk modulus, a response to hydrostatic pressure. (b) A viscoelastic material dissipates energy upon loading and unloading, whereas an elastic material does not. (c) Different modes of testing the response of viscoelastic materials, which is strain- and frequency-dependent. Viscoelastic materials have an initial linear response to the storage modulus (G′) at low strains followed by a nonlinear response with increasing strain.