Effects of the End-Tab Constraint on the Off-Axis Tensile Behavior of Unidirectional Carbon-Fiber-Reinforced Composites

Effects of the end-tab constraint on the off-axis tensile behavior of the carbon/epoxy unidirectional fiber composites were studied. We compared two end-tab shaps: the conventional rectangular end-tab and a new oblique end-tab proposed by Sun and Chung. For the specimens with the conventional rectangular end-tabs, the difference between the longitudinal and transverse strains at the center and near the end-tabs of the specimen becomes significant. For the oblique end-tab, such an inhomogeneity of the longitudinal and transverse strain distribution disappears in the linear elastic range. Also in the range of the subsequent nonlinear response, the oblique end-tab can significantly reduce the inhomogeneity of the strain distribution in the longitudinal and transverse directions of the specimens. Because of this reduced end-constraint due to the oblique end-tabs, the nonuniform Poisson's effect has been markedly improved. An undesirable effect of shear coupling on the measurement of the shear modulus was also reduced. Regarding the elastic modulus and the major Poisson's ratio measured at the center of specimens, however, no appreciable effect due to the different tab-shapes was found. The fracture stress has not been subjected to the effect of the tab shape difference.