Study On The Chip Failure Characteristics And The Constitutive Relation Of High-speed Cutting

In the high-speed cutting process, the materials deformed accompanied by a variety of damage inevitable, the damage will have a huge impact on materials of the dynamic constitutive relations. Currently, most of the researchs on constitutive relations does not take into account of the injury, as a result,the simulations have large errors. Establish an accurate materials’ dynamic constitutive model for the high-speed cutting is the basis for the study of cutting deformation theory and cutting process simulation. In this paper, we aimed at the dynamic destruction characteristics of the materials for the cutting process.By theoretical analysis and experimental study, We got the influence of cutting parameters on the chip morphology and the dynamic constitutive relation equation in account of material damage. Specific studies are as follows:A split Hopkinson pressure bar apparatus was used to measure curve of the true flow stress and true strain for H62 and QAl9-4 alloys at the wide scope of temperature and high rate of strain,analysis the impact of strain, strain rate and temperature on the flow stress of H62 and QAl9-4, we got the Johnson-cook constitutive equation for high-speed cutting through regressive calculation. The material constitutive models with the physical conception have been established, which have high precision in forecasting material flow stress;By observing macro morphology and microstructure of the TC4 chip which got from the orthogonal cutting tests,we come to the conclusion that the degree of chips jagged enhanced with the cutting speed and depth increases,,and the feed has little effect on it;It proved the existence of damage through observing the QAl9-4 SHPB test sample by scanning electron microscopy. On the basis of previous studies, according to the thought that part of the plastic work from local plastic deformation directly into energy for the development of micro-defects, the damage variable D is constructed, and then the constitutive relation equation considering damage is established.The new model was testified more accurate through SHPB and cutting experiments.