The non-linear response of quasi-isotropic composite laminates

The stress–strain response of quasi-isotropic composite laminates consisting of carbon fiber strands embedded in urethane resin was tested at several load orientations. It was noted that at sufficiently high stresses the above response exhibited angular dependence and deviation from linearity, especially at load orientations intermediate to the fiber directions. Similar results were reproduced for quasi-isotropic carbon/PPS composites, where failure was associated with a most substantial amount of delaminations. The above angular dependence could not be explained by either of two forms of elaso-plastic models, and is probably attributable to damage.