Journal of Sound and Vibration, Volume 333, Issue 23, 24 November 2014, Pages 5939–5952 DOI: 10.1016/j.jsv.2014.05.042 1 Effect of ultrasonically-assisted drilling on carbon-fibre-reinforced plastics Farrukh Makhdum, Vaibhav A. Phadnis, Anish Roy, Vadim V. Silberschmidt* Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough, LE11 3TU, UK *Corresponding author: Vadim V. Silberschmidt, Tel: +44 (0) 1509 227 504, Email: v.silberschmidt@lboro.ac.uk Abstract This research focuses on the effect of ultrasonically-assisted drilling (UAD) on carbon fibre- reinforced plastics. High-frequency vibration was used to excite a drill bit during its standard operation. An extensive experimental study of drilling forces, temperature, chip formation, surface finish, circularity, delamination and tool wear, was conducted using Ø3 mm drill and presented here. UAD showed a significant improvement in drill quality when compared to conventional drilling processes. A finite-element study was also conducted to understand the nature of drilling-force reduction in UAD. Keywords: Ultrasonic vibration; drilling; force reduction; tool wear; delamination; CFRP; finite-element analysis 1. Introduction Carbon-fibre-reinforced plastic (CFRP) composites have strong but brittle carbon fibres embedded into a weaker plastic matrix. The carbon fibres support the load, while the matrix serves to hold and protect the fibres and transmit the load to them. CFRP composites have many superior properties including low density (lower than aluminium), high strength (as high-strength steels), high stiffness (stiffer than titanium), good fatigue and creep resistance, and excellent dimensional stability (close to zero coefficient of thermal expansion). Thus, it is of no surprise that CFRP composites are widely used as structural and functional components in aerospace, biomedical, sports, automotive and defence applications amongst others. Though every attempt is made to manufacture CFRP components to near-net shape, in order to facilitate their assembly, machining of CFRP is unavoidable. For example, to join structures, holes need to be drilled to facilitate riveting and bolting. Thus, drilling in