A multi-strain-rate damage model on fracture prediction in single-point diamond turning process

Single-point diamond turning (SPDT), which cuts the workpiece with a single crystal diamond tool, is considered as a promising manufacturing technology in modern industry. In SPDT, it is found that the surface roughness near the center of the workpiece is poor when the cutting depth is small or the feed rate is large. In order to obtain better surface quality, the spindle speed must be increased, which thus reduces the productivity and causes the unnecessary abrasion of the cutting tool. Meanwhile, the influence of feature size effect to the fracture formation in SPDT has not yet been mentioned. In tandem with this, this paper has provided a hybrid damage model to predict appropriate feed rate, cutting depth, and cutting speed of SPDT. Based on the Johnson Cook model, a revised function to quantify the influence of size effect is introduced, and the pre-strained method using the split Hopkinson pressure bar (SHPB) is conducted to calculate the unknown coefficients of the model. The experimental result shows that feature size effect will cause surface rough patterns when feed rate and cutting speed are lower than the predicted critical speed. By implementing the critical energy, which is calculated by the hybrid damage model with different strain rates and heat treatment conditions, the multi-strain-rate fracture diagram (MFD) is carried out and the fracture caused by size effect in SPDT is revealed and predicted. This paper has thus provided an in-depth understanding of the influence of size effect in SPDT.