PREDICTION OF BUCKLING AND FAILURE OF UNIDIRECTIONAL CARBON-FIBER EPOXY STRUTS

The buckling response of 2 mm thick struts of length 20, 30 and 50 mm with approximately built-in end conditions was determined experimentally. Good correlation was obtained with the results of large displacement finite element analysis taking into account non-linear material behaviour. The 50 mm struts buckled stably and then failed due to interlaminar shear. The 20 and 30 mm struts failed due to a catastrophic instability after the onset of buckling. The instability results from an interaction between geometrical and material non-linearity which does not appear to have been previously recognised. For all three lengths, ultimate failure was not controlled by the material compressive strength. For the longest struts the buckling stress can be predicted reasonably well assuming linear-elastic material properties. However, for the shorter struts which fail at relatively high stresses, it is essential to take account of the non-linear material behaviour in the fibre direction, and also in shear.