Study on multi-material drilling and defects modelling using a fracture mechanics approach

Abstract

Multi-materials are increasingly used in the automotive and aeronautical industries owing to their high strength-to-weight ratio, besides the high strength and stiffness of metals allied to the lightweight, corrosion resistance, impact, fracture and fatigue properties of composites. Despite being manufactured in near-net shapes, the drilling process remains necessary for component assemblies. However, this process presents significant challenges due to the high abrasiveness of composite fibres and the requirement for tools to cut through different materials simultaneously. These factors contribute to hole damage and rapid tool wear, hindering the efficiency of the machining process. In this paper, multi-material stacks composed of carbon fibre reinforced polymer and aluminium layers were drilled with chemical vapour deposition diamond coated tools to infer on parameter combination (feed and cutting speed) and conditions required to improve the process, as well as reduce/mitigate delamination. A fracture characterization campaign, through the double cantilever beam testing, was performed to correlate the composite's fracture toughness with the maximum force on the onset of delamination, to prevent hole and surface damage. For that the identification of a fracture mechanics peel-up model and its numerical-experimental validation has been performed. Future research includes adding the full fracture envelope (instead of solely pure mode I) as an input to the delamination model, for more accurate portrayal of real conditions.