The delamination effect of drilling and electro-discharge machining on the tensile strength of woven composites as studied by X-ray computed tomography

摘要

The presence of stress concentration especially from any induced delamination around a hole causes substantial perturbation of the stress and strain field in the structure under service loads. Therefore; it is of great practical interest to accurately analyse and quantify any delamination and its effect to the load bearing capacity of the structure. Two types of open-hole machining; drilling and electro-discharge machining (EDM); were applied in order to examine their effect on the tensile strength of carbon/epoxy laminates. Pulse durations of 100 μs 200 μs and 300 μs with a current of 3 A and voltage 100 V were used for the EDM. An X-ray computed tomography (CT) was employed to examine the delaminations; while three delamination factor models provided the measuring quantities for assessment. An infrared thermography was used for monitoring the fracture behaviour of the carbon/epoxy open-hole specimens during tensile testing. A finite element model (FEM) computed the stress concentrations around the holes; while the Whitney-Nuismer point stress criterion employed successfully in order to predict the failure strengths of the laminates. The results indicate that the CT process is a very effective tool for capturing the delaminations from open-hole machining and showed that the 100μs pulse duration induce lower delaminations; slightly comparable with the ones of the drilling procedure.