Modeling the crack propagation of ductile fibril reinforced polymer membrane with the consideration of drawing fibrils

Abstract

Microfibril reinforced polymer composites (MFCs) are polymer-polymer composites with ductile fibrils embedded, usually increasing the tenacity of the polymer matrix. One of the successful applications is the expanded polytetrafluoroethylene (ePTFE) reinforced perfluorinated sulfonic acid (PFSA) membrane, in which the embedded ePTFE fibrils evolve into drawing fibril connecting crack surfaces, significantly increasing the fracture toughness of the membrane. Among the fracture modeling techniques, the virtual crack closure technique (VCCT) provides a thermodynamics-consistent explanation of crack propagation of the material, while the effect of drawing fibrils in the case is hard to be considered. The cohesive zone model (CZM) considers the gradual damage progress of the material at the crack tip through the traction-separation law, which is suitable for describing the evolution of drawing fibrils but the applicability of the empirical traction-separation laws to drawing fibrils remains uncertain. This paper establishes the constitutive and fracture models of the ePTFE reinforced PFSA membrane, and numerically realizes the fracture propagation of the microfibril reinforced material through the user subroutine of ABAQUS. For the constitutive modeling, an extended eight-chain model with the consideration of the fibril orientation is established to describe the deformation resistance of the fibril reinforcement. For the fracture modeling, a fracture criterion with the consideration of the negative work of the drawing fibrils at the crack tip is established, and numerically implemented through the extended VCCT. Uniaxial tensile tests and fracture tests of pure and various composite membranes are conducted, which verified the accuracy of the present model in describing the higher mechanical property and fracture tenacity of the composite materials. The model reveals the enhancement mechanism of the ductile fibril network and providing a new perspective of fracture modeling for ductile fibril reinforced polymer membranes.