A study has been performed to quantify the anisotro- pic, viscoelastic characteristics of the human skin. Servo controlled biaxial loading methods were utilized to apply perscribed strain and stress histories on in vitro preparations of the skin removed from human cadaver subjects. Full thickness samples of the dermis, 38 mm. square, were loaded in two directions simultaneously by imposing a monotonically increasing strain on one axis while maintaining specified displacement boundary conditions in the orthogonal direction. These planer, biaxial stress-strain data are presented for a range of displacements comparable to the in situ strains existing in vivo. A constitutive equation is proposed for the human skin based on a two dimensional strain energy formulation. The material stresses were computed as a function of the biaxial strains and a series of constants which were evaluated from the experimental data using a nonlninear least squares curve fitting technique. Similarly, the stress relaxation and strain rate sensitivity features of the skin were elicited using the biaxial loading scheme.

A companion investigation examined a tearing failure mechanism for excised human skin due to the advancement of a cut introduced into a skin specimen. Founded on the mechanics of large material deformations an expression was derived from which an energy of tearing can be calculated for a simple extension or "trousers" test specimen configuration. series of experiments were performed utilizing human cadaver tissue to determine the effects of anatomic location, loading direction, and test specimen geometry on the energy of tearing value for the dermis.