Whole-field assessment of the effects of boundary conditions on the strainfield in off-axis tensile testing of unidirectional composites

The objective of this paper is to present an experimental assessment of the effects of boundary conditions on the strain field in 10 degrees off-axis tensile tests on unidirectional carbon/epoxy composites. It is shown experi mentally by using a whole-field phase stepped grid technique that oblique t abbing of off-axis coupons results in a homogeneous strain field over the w hole specimen, thus preventing premature failure near the tabs. A numerical sensitivity study reveals that the oblique angle is not very sensitive to the elastic moduli values. Therefore only estimates of the moduli are neede d to derive the oblique angle. It is also shown by finite-element analysis that a 3 degrees error on the oblique angle is acceptable in terms of stres s concentrations near the tabs, but that a 7 degrees error leads to signifi cant stress concentrations for this material. (C) 1998 Elsevier Science Ltd . All rights reserved.