New ideas on the measurement of the in-plane shear strength of unidirectional composites

This paper addresses the issue of the measurement of the in-plane shear strength of unidirectional composites. It is shown from recently published material that for both Iosipescu and 10 degrees off-axis tensile tests, failure under a homogeneous stress state is achieved. However, these stress states are not pure shear and it is shown that ignoring the presence of transverse tensile and compressive stresses, respectively in the 10 degrees off-axis and the Iosipescu tests, would lead to important apparent differences in the in-plane shear strength measured from both tests. An analysis using a quadratic failure criterion underlines the role of the transverse stresses and values of 95 and 98 MPa for the shear strength of unidirectional T300/914 are derived respectively from the 10 degrees off-axis and the Iosipescu tests.