Image processing methodology for assessment of drilling induced damage in CFRP

Dissertação para obtenção do Grau de Mestre em Engenharia Mecânica

Composite material components are produced in a near final shape. Machining operations such as drilling are often indispensable, namely for joining of structures. This process introduces damage along the periphery of the hole. Different methods to reduce this induced damage were developed. However, difficulties arise when comparing them since delamination is irregular in shape and in size. The delamination factor and the adjusted delamination factor quantify the damage but none achieved full acceptance since no international standards have been set. The aim of this work is to develop an image processing methodology associated with digital radiography that is capable of assessing the drilling induced damage in CFRP, being easily reproducible and allowing comparison of different drilling approaches. The subtraction of pre and post drill radiographies defined the target image to reach. In the image processing the threshold was found to be the most influential variable causing significant changes to the delamination factors. A new approach to the delamination factor is proposed in order to characterize the drilling induced damage. This approach allows the minimization of the quantified damage for the most irregular delamination shapes while equalling the current delamination factors for regular (crown like) damages.