Mechanics of chip, delamination, and burr formation in drilling supported woven GFRP composites

A new approach was used in drilling woven glass fiber reinforced polymer (GFRP) composites to clamping the specimen by a controllable force at drill entry and exit sides. The influence of cutting and support conditions on thrust force, push-out and peel-up delaminations, and burr factor was investigated. A series of ASTM tests were implemented to determine tensile, in-plane shear, Mode I and Mode II fracture toughness properties, which were used to predict the critical thrust force (CTF) at delamination initiation. The delamination and burr areas were accurately measured via inexpensive, easy, and accurate image processing technique. Result from drilling processes revealed that the supported specimens are approximately free from burr accompanied with insignificant peeling within the drill (10 mm)/support hole (12 mm) tolerance. By using support plates, the thrust force was increased up to 8.3% compared to the unsupported conditions. On the other hand, the delaminations were decreased by about 65.5%. The delaminations were dominated by Mode I fracture toughness, which is lower than that of Mode II by 41%. The predicted CTF using concentrated load models are slightly lower than the measured values, which interpret the occurrence of delamination damage on the cutting zone.