Determination of shear strength of unidirectional composite materials withthe Iosipescu and 10 degrees off-axis shear tests

The purpose of this research was to determine the shear strength of a unidi rectional carbon-fibre/epoxy composite by means of the 10 degrees off-axis and 0 degrees Iosipescu specimens subjected to shear. Detailed non-linear f inite-element computations of these two tests were conducted, taking into a ccount the actual non-linear material behavior of the composite. The tests were compared in terms of stresses and strains at failure. It was found tha t the shear strength of the composite can be very accurately determined by using the two independent testing techniques only if fully non-linear finit e element computations of the tests are performed. The stresses and strains at failure in the 10 degrees off-axis specimen closely match. the, stresse s and strains at the onset of intralaminar damage near the roots of the not ches in Iosipescu specimens. Owing to the difficulties associated with the measurement of the shear strength of the composite using the Iosipescu test , and in particular, with the interpretation of the experimental data, this test was found to be almost impractical for the determination of shear str ength. The test can only be used if fully non-linear finite element computa tions of uncracked and axially cracked Iosipescu specimens are conducted in conjunction with the continuous monitoring of intralaminar damage near the roots of the notches during testing. In addition, the shear strength resul ts obtained from the Iosipescu specimen should be independently verified by using another method, such as the 10 degrees off-axis test. (C) 2000 Elsev ier Science Ltd. All rights reserved.