Development studies on in-situ observation apparatus of microscopic damage for durability evaluation of high-temperature composites under HSCT simulated environment

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In order to evaluate and assure the durability of advanced CFRP laminate structures, it is necessary to formulate the failure process including initiation and growth of transverse cracks, delamination, and fiber failure up to the final fracture. The allowable design strain is still limited due to lack of accurate formulation of the failure process.In the present study, the authors developed an in-situ observation apparatus of microscopic damage for durability evaluation of high-temperature composites under HSCT simulated environment Based on the experimental results, finite element analysis(FEA) code was developed to simulate the failure process up to the final fracture. The following failure stages were identified in the experiments and theoretically formulated : (1)initiation of transverse cracks in 90-degree plies, (2)evolution of multiple transverse cracks, (3)initiation and growth of delamination generated at the transverse crack tips, and (4)fiber failure.In particular, we successfully presented a new FEM code to characterize the initiation of transverse cracks in 90-degree plies in more rigorous way. This code includes the following features : (1)Elasto-plastic behavior of the polymer matrix was realized, (2)Cohesive elements were introduced for physical understanding of transverse crack initiation and growth, and (3)The Weibull-of-Weibull model was introduced to formulate the multiple fiber failures along a fiber length.