Residual Strength and Fracture Path for Drilled Epoxy-Glass Composites

Abstract

Aircraft composite structures are mostly joined by mechanical fasteners like bolts, pins or screws. However, the effect of the presence of holes in the remaining strength of the composite structures is still being studied extensively. In this work, epoxy/glass laminates with drilled holes of different sizes were tensile tested and from these results, the residual strength was plotted. Strength vs. hole’s diameter at different fiber orientation was obtained. The fracture path and failure mechanism were identified by fractographic examination. The Point Stress Criterion (PSC) was used, in order to establish the stress intensification due to the presence of a drilled hole. A numerical model by Finite Element Method was carried out to verify the experimental results and the analytic failure predictions. A reduction of 50% in laminate strength was observed when diameter-width ratio was 0.12. The principal fracture mechanism observed in composite laminates was interface breakup. FEM results and analytic results by PSC show accuracy of 90% for predicting the damage in drilled composites.

Drilling in carbon/epoxy composites: Experimental investigations and finite element implementation

“…The process implies destruction of fibre continuity with generation of large stress concentration in the material and delamination at the hole entry and exit [2][3][4][5][6][7]. The damage caused can significantly reduce the fatigue strength of the component, thus degrading the long-term performance of composite laminates [8][9]. Previous studies have shown that machining fibre-reinforced polymer (FRP) composites materials differs significantly in many aspects from machining conventional metals and alloys primarily due to the underlying heterogeneity and anisotropy of FRP materials [2][3][4][5][6][7][8][9].…”

Ultrasonically Assisted Drilling of Carbon Fibre Reinforced Plastics

“…Conventional drilling (CD) implies large distribution of stress concentration in the materials and also delamination and surface quality degradation (Keonig, et al,1985;Davim and Reis, 2003;Zitoune et al, 2005). This reduces the fatigue strength of components, hence, the long-term performance decreases (Torres et al, 2009;Persson et al, 1997). Stress generated during drilling process can be reduced with the help of UAD because UAD lower level of drilling forces is encountered by workpiece and drill bit.…”

Analytical and experimental investigation of the effects of the machining processes on the mechanical behaviour of carbon epoxy composite laminates

“…Even though the CM process is utilized very frequently in today's manufacturing by selecting suitable cutting parameters and tool geometry, but most of the problems mentioned above remain the major cause of producing surface damage [11]. Such damages can cause significant reduction in tensile and compressive strength and it also decreases stiffness [2], consequently reducing the performance of the entire structure [11] which adds to huge economic burden, as 60% of the rejected components during manufacturing owe to the inferior hole quality [1,11,18,20]. Nonoptimal cutting tool designs, rapid tool wear, and machining conditions can be considered for the above mentioned problems.…”