Studies on the effects of lamina thickness and orientation on the shear response of composite laminates

With the growing application of carbon-fibre reinforced polymers (CFRPs) in lightweight aerospace and transportation structures, it is essential and urgent to develop a comprehensive understanding of their response under various loading conditions to determine the design constraints. Under longitudinal tensile and compressive loading, the material behaviour is dominated by the fibre and presents a predominantly linear response. In contrast, transverse and shear loading may result in large nonlinear deformation prior to polymer matrix damage. Compared to fibre dominated behaviour, a response dominated by the matrix under shear loading can considerably limit the load-bearing capability and restrict the utilisation of composite materials. In the design of composite structures, lamina thickness and orientation are specified to meet the requirements of the working environment. In order to attain a detailed comprehension of the shear response of these parameters, an investigation into the effects of lamina thickness and orientation on the shear response of composite laminates was carried out in this work. Different ply thickness and ply orientation were represented by four composite lay-ups to characterise the material response of composite laminates under shear loading. The geometry of a V-notched rail shear specimen and testing method, presented in the American Society for Testing and Materials (ASTM) standard D7078/D7078M-05, was employed to perform the physical compact shear tests. A Digital Image Correlation (DIC) system was used to observe the strain evolution of the compact shear specimens. The load versus displacement and nominal stress versus strain curves were obtained from the experimental data. In addition, the nonlinear shear stress profile was defined using an exponential model based on the calculated nominal stress and measured strain. The shear modulus, shear strength and nonlinear shear response obtained from different composite lay-ups were compared.