Modeling of grain size effect on micro deformation behavior in micro-forming of pure copper

In micro-scaled plastic deformation process such as micro-forming, material grain size effect is difficult to reveal and investigate using conventional material models. Finding a way to study and model the grain size effect on micro-scaled deformation behavior is a non-trivial issue that needs to be addressed in greater depth. In this study, the grain size effect is investigated through micro-compression of pure copper. The deformation behaviors, including inhomogeneous material flow and the decrease of flow stress with the increase of grain size for the same size of specimens, are studied. It is revealed that when the specimen is composed of only a few grains, the grains with different sizes, shapes and orientations are unevenly distributed in the specimen and each grain plays a significant role in micro-scaled plastic deformation and leads to inhomogeneous deformation and the scatter of experimental data. Furthermore, it is found that the decrease of flow stress is caused by the dwindling of grain boundary strengthening effect when the grain size is increased. Based on the experiment results and the proposed composite model, the methodologies to estimate grain properties and model grain size effect are developed. Through Finite Element (FE) simulation, the grain size effect on deformation behavior and the scatter of flow stress are modeled. The results of the physical experiment and the proposed modeling methodologies provide a basis for understanding and further exploration of micro-scaled plastic deformation behavior in micro-forming process.