Development of Bi-axial Tensile Testing for Porous Polymer Membranes and Its Deformation Characteristics

Abstract Porous polymer membranes are generally polymeric materials having numerous pores and complicate network structure. Due to their features, these materials sometimes exhibit anisotropic deformation in their elasto-plastic deformation. It is thus important to investigate the deformation behavior of materials, including anisotropic deformation under multi-axial loading. Here we developed a new testing machine for bi-axial tension for porous polymer membranes, in order to evaluate the deformation behavior under bi-axial tension and elucidate the deformation mechanism based on their microstructure. First, uni-axial tensile tests were conducted in each direction to investigate the change in Young’s modulus and yield strength depending on the tensile direction. It was found that there was deformation anisotropy. Next, we newly developed a bi-axial tensile testing for the present membranes. Since the present membrane has lower deformation rigidity and the thickness is very thin, gripping of specimen and applying uniform deformation are difficult. Thus, this study developed the gripping part to enable uniform tensile deformation during the test. Stress-strain curves of each loading axis were obtained by changing the applying strain ratio. Based on the results, a yield surface was created to investigate the deformation behavior under bi-axial tensile loading. We also investigated the deformation mechanism of the microstructure (porous structure) by using SEM observation.