Mixed-Mode delamination failure criteria in carbon fibre/composite under quasi-static and cyclic loading

Abstract

The aim of this study is to establish delamination failure criteria under mixed (I+II) mode loading for a carbon/epoxy composite (T300-914). This is achieved under quasi-static and cyclic loading. The criteria are planned to be used to assert non propagation of delamination in a composite structure panel. Concerning quasi-static loading, temperature (i.e.:−55°C, Room temperature and +70°C) and humidity (i.e.: at moisture saturation or without moisture ageing) effects have been taken into account to determine which conditions are the most critical in terms of crack propagation. Results show that moisture ageing up to saturation has beneficial effects on composite fracture toughness. Though effects of temperature are more delicate to analyse, it appears that room temperature is the most critical one. A mixed mode failure criterion of interaction type is then determined and results of pure and mixed modes are discussed. Delamination propagations under cyclic loading have been achieved to measure crack propagation thresholds and rates. Mode II and mixed mode (i.e. 50% of mode I) test results show the existence of a propagation threshold in a Paris' law type curve. Though Mode I results tends to fit a Paris' law, there is no evidence of a propagation threshold. A mixed-mode criteria under cyclic loading is then established; it also takes into account moisture ageing.