Mechanical behaviors of CFRP cross-ply laminates with central hole under biaxial tension

The biaxial tensile mechanical properties of carbon fiber reinforced polymer(CFRP) cross-ply composite laminates with central hole were experimentally studied using the uniform thickness cruciform specimens with slots in the arms. Three biaxial load ratios were applied to study the effects of load ratio on the biaxial tensile strength and failure characteristics of CFRP cross-ply laminates. The results show that under the biaxial tensile loads, the interfaces between the plies with fibers cut off and their adjacent plies with continuous fibers are prone to delaminate, and resulting in the reduction of load bearing capacity of CFRP cross-ply laminate. Under an equal biaxial tensile load, the cracks initiate at the matrix between the cutting-off and the continuous fibers along the hole edge, resulting from the combined load of the transverse tension and longitudinal shear. Under an unequal biaxial tensile load, matrix crack initiates in the plies perpendicular to the load direction with a higher tensile velocity, and appears at the hole edge with a high stress concentration. With the increasing of the load ratios, the microstructure damage in the regions with a higher tensile velocity develops more rapid, and so does the corresponding stiffness reduction. The propagation direction of the main crack tends to be perpendicular to the tensile direction with a higher tensile velocity. The analysis of the strength envelope of the CFRP cross-ply laminate with central hole shows that the tensile strength in the direction with a higher tensile velocity increases gently with the increasing of load ratio.