CONSTITUTIVE-EQUATIONS FOR MULTIAXIAL STRAINING OF LEATHER UNDER UNIAXIAL-STRESS

Uni-axial tensile tests on chrome-tanned calfskin leather have been carried out for the butt, the belly, and the shoulder regions of the animal skin. The non-linear mechanical properties of the leather are described and presented. A strain energy density function has been proposed to describe the non-linear orthotropic constitutive behaviour of shoe upper leather undergoing large deformation. The constants in the constitutive equations have been determined using an unconstrained optimization technique. It is shown how the developed constitutive equations may be used to predict lateral and the thickness strains, and how close agreement has been obtained with the results of experiments. A linear mapping technique has been developed, and shown to be capable of mapping the material model over the entire animal skin to describe the behaviour of the leather at any point in terms of the properties of the butt, the belly, and the shoulder regions.