Strength degradation and fractographic analysis of carbon fiber reinforced polymer composite laminates with square / circular hole using scanning electron microscope micrographs

In this article, experimental study has been carried out to obtain comparative information intended for designing and assembly of structural components made of carbon fiber reinforced polymer (CFRP) composite. Investigation on tensile strength has been done on unidirectional CFRP composite laminates with hole. Effect of stacking sequence, hole size, and hole shape on tensile strength has been examined independently by open hole tensile (OHT) test. Reduction in OHT strength is observed when stacking sequence is changed from 0]₈ to 0/90]_2s and when the hole size is increased. However, OHT strength is noticed to get increased when hole shape is changed from circular to square. Laminates containing square shaped hole demonstrate less sensitiveness towards tensile strength and show negligible effect of stacking sequences on the normalized strength than the circular hole. Fractographic analysis figures out the failure mechanism of tested specimens by correlating their mechanical properties. SEM micrographs and data analysis reveal that axial splits and local delamination effectively blunt the stress concentration around the hole resulting in higher OHT strength and less notch sensitiveness towards tensile strength.