Numerical Simulation of Micropeening of quenched and tempered AISI 4140

Author:  A. Erz, A. Klumpp, J. Hoffmeister, V. Schulze
Source:  Conf Proc 2014: ICSP-12 Goslar, Germany (pgs.353-358)
Doc ID:  2014102
Year of Publication:  2014
Abstract:  
Numerical simulation of machining processes is a valuable tool for describing and optimizing those processes. In shot peening, numerical simulation is used to predict the residual stress distribution for instance. Due to the huge computing effort required for these simulations, a few years ago only a limited amount of shots could be simulated in a reasonable amount of time. For the simulation of micro-peening however, a much higher amount of shots needs to be considered to represent the process. With the availability of better and more efficient hardware at lower costs, it is now possible to simulate more than 1000 shots without having to accept extremely long computation times. Based on existing simulation models for macro shot peening, new models were created for micro shot peening. The process conditions in micro-peening are different from macro peening, which had to be considered. Comparing the first numerical results to experimental results a qualitative agreement is shown. In order to achieve accordance quantitatively, further optimization of the description of the work piece material AISI 4140 (German grade 42CrMo4) is required to respect the circumstances that occur in micro-peening. That includes very high strain rates, an extreme deformation degree that is concentrated in the first few microns below the surface, as well as the possibility of generation of subgrains or grain refinement. Especially grain refinement has a huge impact on the local material behavior which has not been considered up to date. The optimized and extended material model for AISl4140 now considers also the microstructural changes that occur during the process. It is now possible to achieve a better correlation with experimental data and to predict the surface state with respect to residual stresses and also considering grain size.