PhD - Characterisation of machining induced damage in composite materials

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Carbon fibre reinforced polymers (CFRP) are widely used in the aerospace and automotive industry due to their superior mechanical proprieties such as a good strength to weight ratio, high resistance to corrosion and excellent fatigue resistance. Machining of CFRP is important as the manufactured part needs to meet geometrical constraints having an excellent surface quality required for specific engineering applications. Typical machining induced problems such as delamination, fibre pull-outs, matrix cracking and fibre breakage arise due to the incorrect configuration of machining parameters in correlation with material properties. To avoid the machining induced damage, a better understanding of the tool-material interaction is needed, which in literature is investigated experimentally through orthogonal cutting tests. The present work proposes a new perspective in analysing the orthogonal cutting process of UD CFRP laminates using an on-line, in situ analysis method: High Speed Digital Image Correlation (HS-DIC) and a specially designed rig for experimental cutting tests. The creation of strains, which is known to affect the integrity of the newly finished surface is monitored and strain maps are generated and correlated with the cutting force and chip formation mechanism. The material properties such as compression strength, shear modulus and shear strength are strain rate dependent properties which governs the plastic deformation during cutting. An in-depth assessment of the relation between strain values and cutting forces, chip formation and cutting parameters is done to optimize the cutting process and safeguard against the premature failure of machined parts under in-service loading conditions.