LARGE DEFORMATION BEHAVIOR OF POROUS POLYMER MATERIALS WITH 3D RANDOM PORE STRUCTURE: EXPERIMENTAL INVESTIGATION AND FEM MODELING

This study investigates the deformation behavior of porous polymer materials with 3D random pore structure. The test sample has sub-micron-sized pores with an open cellular structure, which plays a critical role for water purification. The base polymer is PVDF (polyvinylidene difluoride). First, the surface and cross section of the sample are observed using FESEM to investigate the microstructure (cell size and geometry of the cell ligament, etc). Next, uni-axial tensile loading is carried out for polymeric membrane and it is found that the membranes underwent elasto-plastic deformation. In order to establish a numerical model, finite element metod (FEM) is employed. Using a software of Surface Evolver, 3D random pore structure is created in the representative volume element (RVE). The established computational model can predict both elastic deformation and plastic deformation. Furthermore, viscoplastic deformation behavior (i.e. time-dependent deformation and creep deformation) is investigated, experimentally and numerically. In particular, creep compliance is measured, and we investigate the effect of applied loading on creep deformation behavior. Using the time-temperature-stress superposition principle (TTSSP), we obtain a new master curve, which covers higher stress level, and successfully establish an FEM model of creep deformation of the test sample. The present model enables the prediction of the macroscopic and microscopic deformation behavior of the porous materials, by taking into account of 3D random pore structure.