In order to determine the normal cohesive strength of composite laminates, a new test methodology was proposed. The values of cohesive zone parameters (the cohesive strength and the separation energy) for mode I interlamiar fracture of E-glass/epoxy woven fabrication were computed from a series of experimental tests. Cohesive zone model simulation based on interface finite elements was conducted. A modified form of the Park-Paulino-Roesler (PPR) traction-separation law together with a bilinear mixed-mode damage model was used to simulate the damage processes, using Abaqus cohesive elements. The numerical results were compared with experimental tests and confirmed the adequacy of normal cohesive strength. To ensure the sufficient dissipation of energy that successfully predicts delamination onset and propagation, cohesive zone length and minimum number of cohesive elements at cohesive zone length were determined. Interfacial penalty stiffness and the resistance curve of the composite specimen were also computed. The results show that the modified PPR model accurately simulates the fracture process zone ahead of the crack tip as compared to the bilinear model.
The increasing use of composite materials in industry leads to the need for a detailed investigation on fiber-reinforced composite joints. In the present study, fracture behavior of woven fabric-reinforced glass/epoxy composite laminates under mode III crack growth was experimentally investigated and numerically modeled. Two methods were used for the calculation of the strain energy release rate: the experimental compliance calibration method and the virtual crack closure technique. To achieve this aim, edge crack torsion was used to evaluate fracture toughness in mode III loading (out of plane-shear) at different crack lengths. Load–displacement and associated energy release rates were obtained for various cases of interest. To calculate fracture toughness JIII, two criteria were considered in load–displacement curve which included non-linearity and maximum points; it was observed that JIII increased with the increase of crack length. Based on the finite element analysis, the recommended crack length range was given in order to design a configuration which would give 97% mode III contribution to the total energy release rate. Both the experimental compliance method and the virtual crack closure technique proved applicable for the interpretation of the fracture mechanics data of woven glass/epoxy laminates in mode III.
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