Experimental investigations of impact behavior and milling performance of T700-CFRP under cryogenic conditions

The carbon fiber reinforced plastic (CFRP) composite is a reliable body material for modern airplanes, and extremely difficult to cut owing to its complex structure and special mechanical characteristics. In cutting CFRP, fiber breakage and delamination defects very frequently appear on the machined surface. The use of cryogenic cooling in CFRP cutting has proven to be an advanced approach to improving the machined surface quality of CFRP composites. To reveal the mechanism of milling CFRP under cryogenic conditions, this study investigates the impact behavior and cutting performance of T700-CFRP at low temperatures. The impact test of T700-CFRP unidirectional laminates with 0 degrees, 45 degrees, and 90 degrees fiber directions was performed at various temperatures ranging from 20 degrees C to -196 degrees C, to analyze the impact toughness and the fracture morphology. Side milling experiments of CFRP laminates of 0 degrees, 45 degrees, and 90 degrees fiber directions with the PCD endmill were conducted at the same temperatures used in the impact test. Experimental findings revealed that for 0 degrees specimens, the impact toughness increased at lower temperatures, and the impact damage worsened as the temperature dropped from -120 degrees C to -196 degrees C. There were no evident changes in the impact toughness or impact damage of 45 degrees and 90 degrees specimens with the decrease in temperature. The feed force and radial force increased as the cooling medium temperature lowered during milling CFRP. The machined surface of 45 degrees workpieces was the roughest among all the workpieces and covered with numerous pits and craters. The machined surface roughness Ra of 0 degrees workpieces decreased as the cooling medium temperature was lowered from 20 degrees C to -160 degrees C and then increased at -196 degrees C, while the Ra value of both 45 degrees and 90 degrees workpieces rose as the temperature dropped from 0 degrees C to -196 degrees C.