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. (C) 2007 Elsevier Ltd. All rights reserved.