Instabilities of a Finitely Deformed Fiber-Reinforced Elastic Material

The instabilities of a finitely deformed Blatz-Ko material reinforced with fibers in a single direction (an anisotropic, nonlinearly elastic material) are examined. The loading is one of plane strain uniaxial stress with the load axis being inclined with respect to the fiber direction. In general one finds a critical applied stress (or stretch) at which surface instabilities of the body occur. This is then followed by a shear band-type instability. For a certain range of fiber orientations these instabilites appear a maximum stress level has been reached. It has also been found that when the fiber direction approaches the loading axis, the material is stabilized in tension but destabilized in compression.