Central crack tearing test and fracture parameter determination of PTFE coated fabric

Catastrophic failure caused by crack propagation is the most common failure mode of tensile fabric structure, the tearing resistance of the coated fabric is the key issue of structural design. This study concerns the residual strength and fracture resistance of PTFE coated fabric. Central crack tearing (CCT) tests are conducted, experimental results shown that the existence of initial crack significantly reduces the residual strength. Furthermore, fracture parameters which can be treated as material constants are obtained to estimate the tearing resistance. The available theoretical solutions, based on the classical linear elastic fracture mechanics (LEFM) theory, are adopted to calculate the fracture parameters. Results indicated that these theoretical solutions cannot estimate the fracture parameters properly due to the nonlinear stiffness of the coated fabric. Therefore, the numerical method virtual crack closure technique (VCCT) is introduced to the fracture parameters determination of PTFE coated fabric. Combined with the nonlinear material constitutive model, critical energy release rate G _IC obtained from VCCT effectively reducing its dependence on crack length and thus can be treated as material tearing resistance. Finally, the influence of boundary condition and shear modulus are discussed. Results shown that uniform displacement boundary condition should be used in VCCT. When the shear modulus decreases, the G _IC increases gradually and the dependence on the crack length is reduced due to the decrease of stress concentration zone.