Parametric study on drilling induced damage in thick unidirectional carbon-epoxy composite laminates

Abstract

The growing application of carbon fiber-reinforced polymer (CFRP) composites in aerospace, automotive, marine, and structural engineering demands reliable, damage-controlled machining approaches, particularly for drilling operations critical to assembly and mechanical fastening. This investigation examines drilling-induced damage in a hand-layup high-strength carbon fiber/epoxy laminate with a thickness of 50 mm. The objective of this work is to understand the influence of drilling parameters such as spindle speed (165–1250 RPM), drill tool diameter (4–10 mm), and drill tool selection (HSS or Carbide) on the nature of damage in the laminate structure. Partial-depth drilling from the top surface (30 mm depth), allowing for comprehensive damage assessment at both entry and through-thickness locations in the laminate, and thickness drilling from the side surface were performed to examine damage under different conditions. A systematic experimental approach was made right from the manufacturing of the laminate, establishing the drilling methodology and examining the post-behavioral studies. Through systematic one-factor-at-a-time variation, the individual influence of each drilling parameter on laminate damage was identified and analysed. Drilling-induced damage was quantified using the damage factor, and samples were assessed through optical microscopy and radiographic non-destructive testing. The results suggest that drilling settings need to be adjusted carefully to reduce damage when working with thick CFRP layers. The study identifies preferred parameter combinations of these settings and offers useful advice for drilling CFRP materials in industrial situations.