Delamination analysis of laminated composites in drilling and quasi-static penetration

Drilling of composite materials is highly important from aspects of operation capacity and safety of structures; especially because these materials are mostly used in transportation industry. One of the main damages observed after drilling composite materials is the delamination, which refers to a damage bonder around the machined holes. This type of damage causes poor assembly tolerance, reduce the structural integrity and has the potential for long-term performance deterioration under fatigue loads. Drilling-induced delamination occurs both at the entry and the exit of the drilled holes and accounts for 60% of all part rejections during final assembly of composite products. In this paper, the effect of machining parameters, feed rate and cutting speed, on delamination in drilling process and quasi-static penetration were investigated. For this purpose, two sets of experiments, drilling and quasi static penetration, were designed based on full factorial design. Using analysis of variance, optimum cutting condition for minimum delamination was determined. A correlation between feed rate and cutting speed with the delamination factor was established by second order linear regression. According to the results, delamination increases with feed rate; whereas it decreases with cutting speed. Finally, a comparison between the delamination in drilling process and quasi-static penetration by conical-nosed projectile was made. According to the results, the difference is significant so that the average value of delamination for each level in quasi-static penetration is about two times greater than drilling process.