| Summary: | 博士 === 國立清華大學 === 動力機械工程學系 === 92 === Drilling is the most frequently used secondary machining of the fiber-reinforced composite laminates, while the delamination often occurs during drilling. The drilling-induced delamination threatens the long-term reliability of the composite structure. The evaluation of the delamination damage in the material is rather difficult, particularly for the carbon fiber-based composites, which are optically disadvantageous for the conventional visual inspection. A special technique using the medical equipment of computerized tomography is presented in the current study. It is compared to the ultrasonic technique and is demonstrated a feasible and an effective tool for the evaluation of drilling-induced delamination.
Based on the plate-bending theorem, the linear elastic fracture mechanics (LEFM) is used to describe the composite delamination produced by drills. Based on the earlier proposed concentrated-load model, the thrust force is the main cause for delamination. The central concentrated loading is a special case of the radial circular loading. The radial distributed thrust force the can increase allowable critical thrust force and the drilling quality. In the industrial experience, saw drill, candle stick drill, core drill and step drill show better drilling quality. The current study generalizes the earlier model and describes the effects of the fracture strength, the elastic modulus, the thickness of the workpiece and drill design on the delamination of the composite. It also presents comprehensive experimental results of delamination in use of special drills. The measurements are compared with the theoretical predictions of critical thrust force at the onset of delamination. The well known advantage of industrial use of saw drill, candle stick drill, core drill and step drill is fundamentally illustrated. A guide for drill design can be developed based on the proposed model, and this approach can be extended to examine the effects of special drill or future innovative drill design.
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