Size effects in unnotched tensile strength of unidirectional and quasi-isotropic carbon/epoxy composites

A series of fully scaled tests on unidirectional and quasi-isotropic carbon fibre-epoxy has been carried out. Unidirectional specimens showed a decreasing tensile strength with increasing specimen size, with a reduction of 14% over a factor of 8 change in linear dimension. Quasi-isotropic specimens increased in strength with size when the thickness was changed by repeating the sublaminate stacking sequence, with a 10% increase from a single to four stacked sublaminates. However, strength decreased when the thickness was increased by changing the ply block thickness, with a 62% reduction from 1 to 8 blocked plies. None of the laminates reached the equivalent strength of the unidirectional material, indicating that transverse cracking and edge delamination caused premature failure in all cases.