Mode‐I fracture behavior of carbon/epoxy plain‐weave composites containing double‐edge through‐the‐thickness cracks

Abstract A stress method to evaluate the stress intensity factor at the ends of a discontinuity contained by an orthotropic medium is developed. Unlike the classic stress method, of which determination of the stress intensity factor (SIF) is largely dependent on data collected from singularity‐dominated zone, the proposed stress method is based on a stress expression in the form of multiterm expansion, including two higher‐order terms. By adopting higher‐order terms, far‐field effect can be taken into consideration. Carbon/epoxy plain‐weave textile composites are prepared and tensile‐tested with double‐edge notched (DEN) configuration. Effective crack length ( a / W ) ranges from 0.064 to 0.624. Prediction of the proposed model matches the definition, $\sigma_\infty\sqrt{\pi a}$ , with errors less than 5% for 0.064 < a / W < 0.402, whereas errors are reported up to 45.78% for 0.413 < a / W < 0.624. It is postulated that the errors beyond a / W = 0.4 results from finite geometry and interaction between cracks. A strain‐gage test is carried out to verify the proposed stress method, utilizing two strain gages to realize the three‐parameter strain gage method. The test result exhibits good agreement with the proposed method. POLYM. COMPOS. 27:213–220, 2006. © 2006 Society of Plastics Engineers