7. Microplasticity Analysis for Materials Characterisation

During the last few decades, much research work has been done to develop accurate tool force models for studying the characteristics of the cutting process in ultraprecision machining based on the concept of shear angles in the chip formation, the fluctuation of which leads to fluctuation of the deformed chip thickness and hence the cutting forces. A microplasticity model is developed in this chapter to analyse the variation of the shear angle and hence the cutting force in ultraprecision diamond turning. The model took into account the effect of material anisotropy due to the changing crystallographic orientation of the workpiece being cut and a spectrum analysis technique is deployed to reveal the features of the cutting force patterns. A series of cutting experiments was conducted on a single crystal with different crystallographic cutting plane normals. The complexity of the shear angle formation is further revealed by a microstructural analysis of the chip cross-sections showing plasticity by means of scanning electron micrographs.