MODELING LAMINA LONGITUDINAL COMPRESSION STRENGTH OF CARBON-FIBER COMPOSITE LAMINATES

The determination of the lamina longitudinal compression strength rema ins an unsolved problem. Non-valid failure modes are commonly observed in compression tests of unidirectional specimens. Micromechanical mod elling has also proven to be a difficult task. It is believed that fai lure is initiated by fibre microbuckling, and that non-linear matrix b ehaviour and fibre misalignments play a major role. The main obstacles are thus the non-linear nature of the phenomenon and the scarcity of material data. Here 2D and 3D Finite Element models are presented. The Finite Element Method can easily deal with non-linear problems. The m odels are computationally inexpensive and can be easily implemented on a commercial code. A sensitivity analysis was performed using realist ic input data. The model predictions are well above the unreliable exp erimental values so far available. Further, the most important variabl es were found to be the fibre misalignment angle and the matrix yield stress. The fibre spatial arrangement also affects the predicted resul ts. Reliable strength data are essential to validate the models here p resented. Nevertheless this study shows that accurate predictions shou ld be expected to prove difficult, mainly because of the complex matri x stress-strain behaviour and the statistical nature of fibre misalign ments and spatial distribution. In addition, the important role of the matrix in model results raises the question of the existence of a uni que lamina longitudinal compression strength (LLCS). Lay-up dependent transverse and shear stresses acting on the load aligned laminae shoul d accordingly yield lay-up dependent LLCSs, which is confirmed by expe rimental data.