Pseudo-ductile compressive behaviour of unidirectional thin-ply carbon /glass fibre-epoxy hybrid composites

Favourable pseudo-ductile behaviour under compressive loading with a knee-point was achieved for unidirectional (UD) interlayer hybrids made of thin-ply high modulus carbon/epoxy (CF/EP) layers sandwiched between standard thickness glass/epoxy (GF/EP). The UD thin-ply hybrids were tested under two loading scenarios: 1. Direct compressive loading, 2. Four-point bending loading. In both cases, the damage mechanisms responsible for the pseudo-ductile behaviour are fragmentation of the carbon layer and localised delamination, which later propagates unstably. The final failure of the UD thin-ply hybrid composites examined in four-point bending loading occurs at a higher strain than that under direct compressive loading. This is due to the strain gradient in bending, which results in a lower energy release rate than in direct compression. An increasing carbon layer thickness reduces the final delamination failure strain of the UD thin-ply hybrid composites in compression, but the knee-point strain is not affected.