Finite-element modeling of initial matrix failure in CFRP under static transverse tensile load

The failure of transversely loaded unidirectional CFRP has been investigated by the use of mechanical and thermo-mechanical test methods and finite-element analysis. The case considered here is characterized by a high interfacial strength between fiber and matrix, so that matrix failure governs the fracture process of the composite. On the basis of the experimental results, the parabolic and other failure criteria were applied to the FE calculations. The failure dependence of the resin on the actual stress state could be described. Furthermore, the influence of thermal residual stresses on the initial matrix failure has been investigated, and the actual stiffnesses and thermal expansion changes 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 pure resins and on the composites were incorporated into a finite-element analysis 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 could explain the low strain to failure of transverse laminates under tensile loading.