A novel experimental technique for biaxial testing of a composite laminate with matrix damage

Abstract

Matrix damage, in the form of cracks parallel to the fiber, is a common failure mode for composite laminates, yet little is known concerning the associated shear modulus degradation. This study proposes a novel experimental technique to study shear modulus degradation under biaxial loading. An Iosipescu coupon was modified that induced transverse tension and compression loads while applying shear loading. The axial loads were induced using unbalanced layups with coupled normal–shear response. An analytical, closed-form solution was generalized to include unbalanced layups under a shear loading boundary condition. It was observed that the shear modulus degradation depends on the normal stress acting on the matrix transverse cracks. While compressive normal stress increased the effective shear modulus, the tension normal stress reduced the shear modulus, compared to pure shear loading.