Open-Hole Compressive Strength and Fracture Morphologies of Punched and Drilled CFRP Laminates

Abstract

Piercing is an essential process for composite structures because they are usually near-net-shape manufactured to reduce further machining operations. Although drilling is commonly used to increase productivity, punching by out-of-plane shear loading is also used. This study analyzes the open-hole compressive (OHC) strength and fracture morphologies of carbon fiber reinforced plastic (CFRP) laminates with punch-and drill-pierced holes (CFRP-PPH and CFRP-DPH, respectively).The damage in CFRP-PPH and CFRP-DPH was evaluated using the delamination factor. The OHC failure process was experimentally assessed by in-situ observation during the OHC test. The results showed that the OHC strength of CFRP-PPH and CFRP-DPH was not correlated with the delamination factor. It was observed that micro-buckling was initiated in the middle layer of CFRP-PPH owing to the roughness of the characteristic machining surface induced during punching. In contrast, for CFRP-DPH, micro-buckling was initiated in the upper layer because of the tear and matrix cracks generated during drilling.