EXPERIMENTAL INVESTIGATION OF POROSITY EFFECTS ON MACHINABILITY AND RESIDUAL STRENGTH IN BRITTLE MATERIALS

Three commercially available tooling materials for composite component manufacturing were chosen for evaluation of their machinability and surface integrity as it fulfills the lightweight and coefficient of thermal expansion requirements of polymer matrix composite. All three of these materials (CB1100 ceramic tooling block, AAC-4/500 and Cfoam (TM) carbon foam) are brittle and porous in nature. End milling machining tests were conducted in order to study the effects of porosity on cutting forces and surface integrity. Measured cutting force profiles were found to be random in magnitude and shape reflecting the variation in pore size and distribution as well as chipping and fracture of the material. It was found that the damage induced during the machining of Cfoam and AAC-4/500 was small in comparison to the size of the pores and had no significant effect on the surface integrity and transverse rupture strength of the materials within the experimental conditions. Therefore, porosity had a positive benefit to the surface integrity and tolerance to machining induced damage. However, damage introduced during the machining of CB1100 was discovered to be significant in comparison to the pore size and was shown to decrease characteristic strength by approximately 16% according to the conducted Weibull analysis.