Study Of Crack Propagation In Graded Composites

Graded composite is a new kind of composite material, comparing to traditional composites, its composition and property vary continuously in space, hence possessing an enhanced thermodynamic performance and a high degree of designability, which contribute to its broaden use in military and civil areas like aeronautics and astronautics, energy and mechanical engineering. With the role that graded composites play become more and more important, studies on its fracture behavior become more and more of the essence. Cracks emerge and grow inevitably during the manufacture and service of materials, therefore a deep study into the propagating mechanism of the cracks and minimize its damage to material property by an altered way of manufacture according to the behavior of materials, indicate substantial practical significance to the optimization of graded composite materials.Based on extended finite element method(XFEM), crack propagation and cracking load among the fracture behavior of graded composites were studied, followed by the discussion of the influence rule and controlling mechanism of cracking path and crack initiation load. In this content, the research background and significance of graded composites as well as its manufacture and property evaluation method were first introduced, and then conclusion about the study on stress intensify factors(SIFs), crack propagation criterion and subsequent continuous growth was made. Afterwards, theoretical basis of extended element method and integral integration were elaborated, along with selectable auxiliary fields that could be used combining integral integration during the computation of stress intensify factors. At last, simulation method of material equivalent parameters and various propagation criterions that could be used for the continuous extension of cracks were provided. By means of programming UEL subroutines, crack propagation path and crack initiation loads in graded materials were both predicted. Influences of gradient parameters like components’ Young’s modulus ratio and gradient parameter on cracking paths and loads were discussed. Differences in crack propagation path and crack initiation load between graded composites and traditional homogeneous materials were incorporated through a series of case studies, hence validating the possibility of enhancing fracture performance of graded composites via control of the distribution of components’ property gradient.