Shear strength determining mechanism of a +/−45 laminate under tensile loading

Abstract

The shear strength of a composite material is determined as a result of a complex damage and failure process, but the detailed progression has not been clearly elucidated. Here, the mechanism of determining the strength of a ±45 laminate under tensile loading is revealed from exquisitely designed experiments in conjunction with high-fidelity numerical simulation. Synchrotron radiation computed tomography is employed for extremely high-resolution images of damage status inside the composite just before its catastrophic failure. The ex situ observations discover the unique and consistent failure progression; one major matrix crack is initiated either in the +45 or −45 layer and delamination follows after the initial crack completely grows along both the fiber and transverse directions. After the delamination failure is triggered, remaining intact layers start to fail with multiple transverse matrix cracks. The failure of the intact layers is represented as a load drop in the global stress–strain curve. This sequential and interactive failure progression determines the shear strength of the ±45 laminate. The numerical analysis finds that the location of the initial matrix crack is dependent on the microstructure. Once the matrix crack is initiated, the numerical simulation exactly reproduces the experimentally observed failure process.