Improving the interface in carbon fibre reinforced composites with variable stiffness

Polystyrene-interleaved carbon fibre reinforced epoxy composites with controllable stiffness have been manufactured that exhibit reductions in flexural stiffness of up to 99% when heated above the T_g of the interleaf layers. Flexural tests at room temperature indicate that improvements in adhesion between the polystyrene and CFRP layers are required to prevent premature flexural failure of the composites at low shear stresses. In this study we investigate how changing the interleaf layer can improve the flexural strength of the laminates through modification of the interleaf/CFRP interface. Two styrene maleic anhydride (SMA) films with different maleic anhydride content were chosen. Flexural tests showed that composites containing SMA interleafs had more than twice the flexural strength of composites containing pure polystyrene layers at 25°C and yet still undergo significant reductions in stiffness at elevated temperature.