DEVELOPMENT OF A BIAXIAL TENSILE TESTING MACHINE AND A NONDISTURBING DISPLACEMENT MEASUREMENT METHOD

A biaxial tensile machine is presented which describes the mechanical behavior of anisotropic sheet materials. Two servohydraulic actuators, controlling each other independently, impose a tensile stress on a cr uciform flat specimen in two perpendicular directions. The sample desi gn has been optimized to reach the highest possible isotropic biaxial strain field. The heterogeneous and anisotropic nature of fibrous mate rials, the ratifying of behavior laws, and the inadequacy of the usual techniques have led us to develop an optical method to measure in-pla ne displacements. This technique is based on real-time location of a g rid of points by an image processing system composed of two CCD camera s and two video digitizers. Data are numerically stored to calculate t he in-plane strain field of the tested material.