The influence of thermal residual stresses on the transverse strength of CFRP using FEM

The failure of transversely loaded unidirectional CFRP has been investigated using mechanical and thermo-mechanical test methods as well as finite element analysis (FEA). The FEA analysis consists of two cases: a high interfacial strength between fiber and matrix, so that matrix failure governs the fracture process of the composite, as well as a weak interface, so that fiber matrix debonding is the dominating failure process of the composite. The failure dependence of the resin on the actual stress-state could be described. Furthermore, the influence of the thermal residual stresses on the initial matrix failure has been investigated, and the actual stiffness as well as the thermal expansion change of the epoxy resins and the composites as a function of temperature have been determined experimentally. The results of the mechanical and thermo-mechanical tests performed on the neat resin and on the composites were incorporated into FEA and compared with the transverse tensile properties of the composite laminates. In the FE-analysis, the local fiber volume fraction was varied over a wide range in order to investigate its influence on the thermal residual stresses and transverse composite strength. The results can explain the low strain to failure of transverse laminates under tensile loading. The calculated interfacial shear strength (ISS) and the interfacial normal strength (INS) are in good agreement with values found in the literature.

Subjects

B. Debonding

B. Residual stress

B. Transverse cracking

C. Finite element analysis (FEA)

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The influence of thermal residual stresses on the transverse strength of CFRP using FEM