DISSERTATION TITLE: DRILLING BEHAVIOUR OF COMPOSITES AND HYBRID FIBER COMPOSITES AT VARYING DRILLING PARAMETERS

Nowadays, fiber composites and hybrid fiber composites are widely used in aerospace industry to replace conventional materials due to weight to strength ratio and resistance to corrosion. These attractive properties resulted in increased machining fiber composites and hybrid fiber composites such as drilling. However, drilling fiber composites and hybrid fiber composites are very problematic compared to that with conventional materials because they are non-homogenous material. The problems encountered during drilling fiber composites and hybrid fiber composites include damage at hole interface, and damage at the drilled holes wall. The aim of this research was to investigate the influence of drilling fiber composites and hybrid fiber composites at various cutting speed, feed rate, different types and thickness of composites materials on damage factor (Fd), surface roughness (Ra), and surface microstructure. The fiber composites used in this research were glass fiber reinforced polyester (GRP) and glass fiber reinforced epoxy (GRE). The hybrid fiber composites used in this research were glass fiber and carbon fiber reinforced polyester (GCRP) and glass fiber and carbon fiber reinforced epoxy (GCRE). Fiber composites and hybrid fiber composites were fabricated using hand lay-up technique. Each composite was fabricated in two different thicknesses (3 mm and 10 mm). 55% fiber volume fraction (FVF) was used to fabricate the fiber composites and hybrid fiber composites to expedite the wear process of the drill bit. In order to maintain the properties of the composites for two different thicknesses, stepped structure design was used to fabricate the fiber composites and hybrid fiber composites. In this research the drilling parameters used to drill fiber composites and hybrid fiber composites were cutting speed (from 1000 rpm to 3000 rpm) and feed rate (from 0.05 mm/rev to 0.2 mm/rev). The damage of the drilled holes was evaluated based on three different evaluations; damage factor (Fd), surface roughness of the drilled holes (Ra) and surface microstructure. The damage factor (Fd) for GCRP (hybrid) fiber composites was lower than GRP fiber composites for 3 mm and 10 mm thickness. The damage factor (Fd) of
vii
GCRE (hybrid) fiber composites was lower than GRE fiber composites for 3 mm thickness and 10 mm thickness. The surface roughness of GCRP (hybrid) fiber composites was lower than GRP fiber composites for 3 mm and 10 mm thickness. The surface roughness (Ra) of GCRE (hybrid) fiber composites was lower than GRE fiber composites for 3 mm thickness. The surface roughness (Ra) of GRE fiber composites was lower than GCRE (hybrid) fiber composites due to matrix smearing occurred during drilling of GRE fiber composites for 10 mm thickness. Scanning electron microscopy (SEM) evaluation showed that the damage occurred during drilling of fiber composites and hybrid fiber composites were due to fiber pull-out, fiber-matrix debonding and delamination. It can be concluded that drill GCRP (hybrid) fiber composites at 3 mm thickness with lowest cutting speed and feed rate were more suitable compare to GRP fiber composites. On the other hand, it was more suitable to drill GRE fiber composites at 10 mm thickness with lowest cutting speed and feed rate compare to GCRE (hybrid) fiber composites.