2023 Volume 49 Issue 6 Pages 183-190
The interlaminar strengths of cross-ply carbon fiber-reinforced plastic (CFRP) laminates were evaluated experimentally by combined out-of-plane tensile and in-plane shear stress tests. Spool-shape CFRP laminate specimens glued to T-shape jigs were prepared, and a tensile load or torsional torque was applied to the specimens using a combined tension-torsion testing machine. Uniaxial out-of-plane tensile and interlaminar shear tests were then carried out to obtain the nominal interlaminar tensile and shear strengths of the cross-ply CFRP laminates. The fracture surfaces of the specimens were thereafter observed using a digital microscope and a scanning electron microscope. Smooth fracture surfaces were observed in the out-of-plane tensile tests, whereas rough fracture surfaces with hackle-like fracture patterns were observed in the interlaminar shear tests. The combined out-of-plane tensile and in-plane shear stress tests were subsequently performed on the specimens for five nominal stress ratios. The critical nominal out-of-plane tensile stress decreased as their nominal in-plane shear stress increased. In contrast to uniaxial tests, combined stress tests showed complex fracture surfaces. The critical nominal stresses obtained could be approximated by an ellipse as a failure criterion for interlaminar areas of cross-ply CFRP laminates.
