Nonlinear and viscoelastic characteristics of skin under compression: experiment and analysis

In physiological loading conditions, the soft tissues in the hands and fingers are predominantly in compression. The goal of the present study was to characterize the nonlinear and time-dependent behavior of skin in compression. The pigskin samples used in the study were collected from five different animals. The compression tests were performed in confined and unconfined loading configurations and at four different loading speeds (0.5, 1.0, 40, and 400 microm/s). A multi-axial material model was proposed to simulate the nonlinear and viscoelastic behavior of the skin in compression. The good agreement between the model predictions and experimental data suggests that the mechanical behavior of the skin in compression can be well characterized using the Ogden strain energy potential combined with a time-integration using a Prony series. Our results show that the stress/strain curve of the skin is much stiffer in confined compression compared to that in unconfined compression, indicating that the compressibility of the skin is small.