Tensile strength prediction of notched composite laminates using fracture toughness

Strength prediction of a laminate with a hole generally depends on a characteristic length of the hole which is not only related to the properties of its constituent materials but also depends on the laminate lay-up and the hole diameter. In this paper, a new method based on linear elastic fracture mechanics was proposed to predict the tensile strength of a symmetric laminate with hole, which only needs the fracture toughness of a cross-ply composite plate and the tensile strength of the un-notched laminate, and which can significantly reduce the requirement on composite data. In this method, the characteristic length was first expressed as a function of the fracture toughness and the un-notched tensile strength of the laminate. Then, the fracture toughness of a 0° ply (i.e. unidirectional laminate) was determined by a compact tension test on the cross-ply laminate90/0_8s and the virtual crack closure technique. Further, the fracture toughness of laminates with arbitrary symmetric lay-up angles can be calculated from that of the 0° ply. Tensile tests on T300/7901 notched laminates with lay-ups of0/±45/90_2s and0/±30/±60/90_s have been done in this work. Three kinds of hole diameters, i.e. 3 mm, 6 mm and 9 mm, were assigned for each of the laminates. The theoretical predictions for the tensile strengths are in good agreement with the measured values. The maximum difference is 15.2%, which is acceptable in engineering applications.