STUDY ON NONLINEAR CONSTITUTIVE RELATIONSHIP AND FRACTURE BEHAVIOR OF STITCHED C/SiC COMPOSITES

C/SiC composites have a series of advantages such as high specific strength, high specific modulus, excellent thermal stability, etc, being widely used in the aerospace field. Brittle fracture caused by crack propagation is one of its main failure forms. Therefore, the fracture performance analysis of the material has important guiding significance for the structural design and application of the material. Simple mechanical experiments and fracture experiments of stitched C/SiC composites are carried out, the mechanical response and fracture characteristics of the materials under different loads being studied in the paper. Based on simple mechanical experiments of stitched C/SiC composites, the macroscopic nonlinear damage constitutive equation is established, and the fracture behavior of stitched C/SiC composites with unilateral notched beam and double cantilever beam are simulated. The constitutive equation uses simple equations to describe the nonlinear stress-strain curve of the material under complex stress conditions, and considers the crack closure on the reverse loading process. Based on the commercial finite element software ABAQUS, the non-linear damage constitutive equations are realized by writing a UMAT subroutine. The validity of the established constitutive equation is verified by a single element. On this basis, the linear elastic damage constitutive model and the nonlinear damage constitutive model are used to simulate the fracture behavior of the stitched C/SiC composites with a single-side notched beam and a double cantilever beam, respectively. The force-displacement curves simulated by the nonlinear damage constitutive equation are more consistent with the test results, and the failure load predicted by the nonlinear damage constitutive are closer to the test failure load, which verifies the accuracy of the nonlinear damage constitutive equation established in this paper. The paper provides a reference for the study of the fracture behavior of C/SiC composites and provides a theoretical basis for the design and application of stitched C/SiC composites structures.