EXPERIMENTAL STUDY OF DELAMINATION THRESHOLD IN UD CARBON EPOXY COMPOSITE

Carbon fiber-epoxy composite show good strength, but interlaminar defects may always grow under cyclic loading and cause the fatigue of the tructure. However, interlaminar defects may always grow under the effect of loading in bending. To predict the development of these plane defects, the delamination threshold and low crack growth rate were studied experimentally in double cantilever beam type specimen calibrated by compliance. In fact, a delamination threshold exists below which a plane crack does not propagate in Mode I testing. Fatigue loading may cause the growth of delamination between adjacent plies at a strain energy release rate Gth five times lower than the fracture energy Gc. This difference is relatively insignificant by comparison with metals since in numerous alloys the difference can be as high as 100. This demonstrates the importance of determining a delamination threshold to evaluate the damage tolerance of the composite. Our tests showed clearly the Gth of test bars. They were sensitive to load ratio R.

Keywords:

composite material , carbon-epoxy , fatigue , delamination , fracture mechanic , threshold