Cryogenic machining of carbon fiber reinforced plastic (CFRP) composites and the effects of cryogenic treatment on tensile properties: A comparative study

Carbon fiber reinforced plastics (CFRPs) are prone to damage locally during machining due to the applied cutting forced and generated heat. Cryogenic machining can reduce the heat generated damages of CFRPs by utilizing cryogenic liquids instead of conventional cutting fluids. The goal of this study is to investigate milling performance of CFRPs in cryogenic medium. For this, a new cryogenic machining approach was adopted to slot milling of CFRPs by submerging the workpiece within a cryogenic liquid. The CFRPs were fabricated via vacuum assisted resin transfer method by using woven carbon fiber fabric as a reinforcement and epoxy as a matrix. Machining performance was evaluated based on the resulting cutting force, delamination factor, surface roughness, and surface damage. Moreover, the influences of cryogenic coolant on the tensile properties, fracture surface microstructure, and machined surface of the CFRP laminates were analyzed with scanning electron microscopy (SEM). SEM analysis revealed that combination of different damage modes such as debonding, micro matrix crack, fiber pull out, and bundle pull out, delamination, and fiber breakage were observed. The results showed that cryogenic machining approach provided less damage formation on the machined surface, reduced delamination factor and surface roughness but increased resulting cutting force during machining of the CFRPs. On the other hand, there was a slight improvement (about 3%) of the tensile properties for the CFRPs exposed to cryogenic coolant due to matrix hardening and increasing in the fiber strength and shear strength.