Effect of the cooling temperature on the critical thrust force to avoid delamination when drilling carbon fiber-reinforced polymers

Carbon fiber-reinforced polymers (CFRPs) are widely utilized in aerospace and rail transportation industries due to their superior strength-to-weight ratio and structural efficiency. However, the inherent anisotropic properties and relatively low transverse thermal conductivity of CFRPs present substantial challenges during drilling operations. Specifically, the heat generated during machining tends to accumulate within the cutting zone, causing localized temperature increases. This phenomenon leads to softening of the polymer matrix and a heightened risk of delamination-a critical defect that compromised the integrity of components. To mitigate these issues, this study systematically investigated the thermal-mechanical interactions during CFRP drilling through experiments conducted under controlled cooling temperatures ranging from ambient conditions down to -45°C. The research aimed to elucidate the relationships among drilling-induced temperature, axial thrust force, and the critical threshold for delamination initiation. A novel temperature-dependent analytical model was developed to predict the critical thrust force, accounting for temperature-sensitive material properties such as fracture toughness and elastic moduli, as well as the dynamic load distribution between the drill's chisel edge and cutting lips. Experimental findings revealed that cooling temperature significantly affected delamination behavior, with optimal suppression observed at intermediate cooling levels. These results offered valuable insights for optimizing drilling parameters to minimize thermal damage in high-performance CFRP components.