Developing a new mixed mode I/II fracture criterion for cracked functionally graded materials considering the fracture process zone effect

This article presents a novel mixed mode I/II fracture criterion specifically developed for functionally graded materials, incorporating the fracture process zone effect based on strain energy release rate theory. The proposed criterion is validated through a combination of experimental and numerical investigations, demonstrating its effectiveness in predicting crack growth behavior in functionally graded material fabricated using a new method based on controlling resin gel time and varying chopped fiber volume fractions, offering several advantages. In this study, cracks are assumed to be located along the material gradation within the brittle side of the material. The critical mixed mode stress intensity factors and pure mode II fracture toughness of the fabricated specimens are determined through three-point and four-point bending tests. The comparison between experimental data and the derived fracture limit curve demonstrates the efficacy of the newly developed criterion in analyzing mixed mode fracture in functionally graded materials. Notably, numerical and experimental findings reveal that increasing fiber volume fraction does not consistently enhance mode I fracture toughness, although it consistently increases elastic modulus.