Experimental and numerical study on mode I interlaminar fracture toughness of lightly stitched ceramic-matrix composites

To determine whether the mode I interlaminar fracture toughness of the lightly stitched ceramic-matrix composites (CMCs) can be characterized by a single equivalent energy release rate value, a critical stitch density was obtained through modified double cantilever beam (DCB) tests and two finite element (FE) models with different stitch modeling methods. As results, the values at crack-initiation points from tests and the modeling of the sparsely distributed stitches were recommended. The stitch parameters of the two models were gained and verified by comparison with the test results. The FE model using multiple cohesive laws is more efficient and appropriate for parametric modeling while the other model using solid stitch modeling may need a great deal of work when geometric stitch parameters need to be changed. Then the mechanism of the critical stitch density and complex test results were all analyzed theoretically and numerically. Finally, the effects of the stitch density and parameters were discussed and may provide some references for the design of anti-delamination performance of CMCs.