Tensile, compressive, and fatigue strength of a quasi-isotropic carbon fiber reinforced plastic laminate with a punched hole.

The mechanical properties of a quasi-isotropic carbon fiber reinforced plastic (CFRP) laminate with a punched hole were investigated. During the punching process, pressure was applied to the laminate through the upper and lower blank holders of a punching machine; the clearance between the punch and blank holders was set to be small to suppress damage in the CFRP laminates. Due to the dragging of plies encountered during punching, the surface of the punched hole was relatively uneven as compared to that of the drilled hole. However, the effect of the uneven surface created during the punching process was not as significant on the tensile and compressive strength of the open hole as compared to the manufacturing damages generated by drilling processes. The stress-number of cycles to failure curves for the open-hole tension-tension fatigue tests also showed comparable results between the punched- and drilled-hole specimens. These results indicate that there were no significant differences in the mechanical properties of CFRP laminates with a punched hole, and thus present the possibility of a highly productive hole-making process using the punching method.