Abstract
Delamination is considered as a major problem in drilling of composite materials, which degrades the mechanical properties of these materials. The thrust force exerted by the drill is considered as the major cause of delamination; and one practical approach to reduce delamination is to use a back-up plate under the specimen. In this paper, the effect of exit support plate on delamination in twist drilling of glass fiber reinforced composites is studied. Firstly, two analytical models based on linear fracture mechanics and elastic bending theory of plates are described to find critical thrust forces at the beginning of crack growth for drilling with and without back-up plate. Secondly, two series of experiments are carried out on glass fiber reinforced composites to determine quantitatively the effect of drilling parameters on the amount of delamination. Experimental findings verify a large reduction in the amount of delaminated area when a back-up plate is placed under the specimen.
Highlights
Glass fiber reinforced plastics (GFRPs) have been extensively employed in many engineering applications because of their outstanding advantages over other materials
This paper investigates the effect of back-up plate on drilling-induced delamination both analytically and experimentally
In which dU is the infinitesimal strain energy, dW is the infinitesimal work done by the thrust force Fth and drill displacement of dX and dUd is the infinitesimal strain energy absorbed by crack growth which are as following: dW = Fth · dX
Summary
Glass fiber reinforced plastics (GFRPs) have been extensively employed in many engineering applications because of their outstanding advantages over other materials. Composite materials are difficult to machine due to some particular characteristics of them like non-homogeneous, anisotropic and abrasive fibers. This causes significant damages in drilling process such as matrix cracking, fiber breakage, fuzzing and thermal degradation. In drilling with back-up plate, the thrust force increases suddenly and severely as the chisel edge begins to penetrate into the specimen and it continues until the full penetration of cutting lips. At this point actual material removal takes place and the force reaches its steady state value, until delamination occurs. As the drill bit approaches the last uncut plies, the stress due to the thrust force exceeds its critical value and all the uncut material is burst open [3]
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