SYNERGISM BETWEEN LAYER CRACKING AND DELAMINATIONS IN MULTIDIRECTIONAL LAMINATES OF CARBON-FIBER-REINFORCED EPOXY

Photographs of different crack modes are shown giving insight into the damage behaviour of composites fabricated of T300/914C plies of 0.125 mm thickness. An increase in the damage tolerance was observed for la minates stacked by quasi-unidirectional [+/-2] angle plies. For cross- ply laminates under tension fatigue loading, test results, supplied fo r the spacings of layer cracks, are used to generate formulae for the residual layer stiffnesses. As an extension to the common energy relea se rate (ERR) concept an ERR tenser is established. The first invarian t of this tenser and its mean values describe the energy release rate and its partitioning into different crack modes, respectively. From th e complete set of invariants a first estimation of a crack condition f or the delamination growth is proposed which includes the effect of fi bre orientation.