An approach to evaluate delamination factor when drilling carbon fiber-reinforced plastics using different drill geometries: experiment and finite element study

Delamination is one of the major damages associated with drilling carbon fiber-reinforced plastics (CFRP), Peel-up and Push-out are two recognizable delamination mechanisms, while drilling without using a back-up plate under the workpiece complicates the delamination mechanism even more. Minimizing delamination is dependent on many factors such as cutting parameters, geometry and type of drill bits used. The objective of this study is to present a new approach to measure the equivalent adjusted delamination factor (Feda) when drilling unidirectional CFRP laminates without using a back-up plate and comparing it experimentally and numerically with conventional delamination factor (Fd) and adjusted delamination factor (Fda). A polycrystalline diamond (PCD) twist drill and a special diamond coated double point angle drill was used for drilling in this study. The 3D finite element model was developed in ANSYS-Explicit to simulate the drilling process using the ply-based modeling method instead of a conventional zone-based concept. Experimental drilling validation process was implemented by utilizing a CNC machining center. Results show that the Feda obtained is suitable to estimate the drilling induced damages, damage analysis shows that good agreements were obtained from the experiments and finite element method (FEM) simulation, while the special diamond coated double point angle drill seemed to provide a better hole quality, and drilling induced damage is highly affected by feed rate which is considered one of the important parameter.

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