Open hole compressive elastic and strength analysis of CFRE composites for aerospace applications

This paper presents an experimental and analytical study of hole-size effect on the compressive properties of woven carbon fiber-reinforced epoxy composites. The composite laminates were cut into the standard dimensions of compression after impact specimens with different center hole sizes using abrasive waterjet machine to avoid thermal and mechanical defects that were associated with conventional drilling processes. Damage development was monitored using instrumented specimens with 8-strain gauges. For the first time, the strain transverse to the hole edge thickness and perpendicular to the loading axis is measured, which has important contribution to interpreting the damage free at this position with the aid of scanning electron microscope images. In addition, a new analysis about increasing the slope (stiffening) of axial surface strain with the applied load was proposed. The predicted strain distribution in the vicinity of the hole has acceptable agreement with the experimental measurements. The compressive strength was measured and predicted by several two-parameter fracture models. Three-parameter fracture models are employed to improve the predicted compressive strength. The results showed that the critical stress intensity factor increased with the hole size and vice versa for the compressive strength and stiffness. An excellent agreement is found between the measured and predicted compressive strengths using three-parameter fracture models (R2≥99.5%). Damage initiation was effectively detected at about 77% of the ultimate stress using the instrumented specimens.