Process-property-performance relationships in CFRP composites using fractal dimension

The present study considers the dependence of the mechanical properties on the fibre architecture for composite laminates. Woven carbon/epoxy fabric composites were manufactured by the resin transfer moulding (RTM) process. Image analysis and fractal dimension (D) were used to quantify fibre distribution and resin-rich volumes (RRV) then correlate these data with the mechanical properties of the fibre-reinforced composites. The static strength of these composite laminates showed a clear dependence on the fibre distribution. Four- point flexural fatigue tests were conducted under load control, at a sinusoidal frequency of 10 Hz under load amplitude control with a stress ratio (R=σmin/σmax) of 0.1. Specimens were subjected to maximum fatigue stresses of 95% to 82.5% step 2.5% of the ultimate flexural strength (UFS). The fatigue properties of the composite laminates are shown to have statistically significant correlations with the fibre distribution and the static properties of the laminates. A loss of 5-6 % in the flexural modulus of the composite laminates predicted an increasing probability of failure of the composite laminates under fatigue loading. This occurs at about 90% of the fatigue life at a particular stress level.