Experimental and analytical examination of multidirectional carbon fiber–reinforced polymers for uncut fibers and their distributions during drilling

Abstract

Drilling is often employed when using carbon fiber–reinforced polymers (CRFPs) to fabricate machine parts. However, CFRP drilling is compromised by uncut fibers and delamination of the final layers of fiber sheets, reducing the quality and strength of the product, increasing fatigue around drilled holes, and rendering product assembly difficult. We used a mathematical model to analyze drilling behaviors at the critical cutting angles 0 < φ ≤ ${\Upsilon }_{0}$+π/2 and ${\Upsilon }_{0}$+π/2 < φ. We used the Euler–Bernoulli beam theory to derive the maximum lengths of uncut fibers; these were determined by reference to half of the maximum deflection of a simply supported beam. Critical cutting angles were calculated by evaluating the hogging and sagging of a cantilever beam after fracture of a maximally deflected single fiber. These analyses were used to validate the experimental data obtained under various machining conditions, employing two tools to drill three different types of multidirectional CFRP sheets. Predictions were derived using an analytical Dexel model that employs self-generating 3D software. During simulation, the drilling tools were moved using NC-code kinematics, or manually, in the X, Y, and Z directions. The model errors for the experimental results were 2–12% in terms of the maximum uncut fiber length. The critical uncut fiber cutting windows of the predictions and experiments indicate approximately 90–95% agreement.