FEM Explicit Dynamic Simulation of Micro Shot Peening: a Stochastic Approach

Author:  M. Marini, V. Fontanari, M. Bandini, M. Benedetti
Source:  ICSP-13
Doc ID:  2017130
Year of Publication:  2017
Abstract:  
Introduction: At the beginning of the research on the FEM simulation of the shot peening process, the symmetry cell approach, devised in the studies of Meguid [1], was used by many authors to estimate the residual stress (RS) field. The study of Bagherifard [2] underlined the need for a realistic FE model, based on statistical considerations, which was used in the following studies by many authors, such as Bagherifard [3], Gariepy [4], Peñuelas [5]. Numerical investigations undertaken so far have mainly addressed surface treatments using steel shots with a diameter larger than 0.5 mm. On the other hand, several experimental investigations have pointed out that light alloys benefit more from gentle peening treatments employing small ceramic beads with a diameter lower than 0.15 mm, often referred to as micro- or fine-particle shot peening. Indeed, such treatments introduce a compressive RS peak located close to the surface where the cracks are likely to nucleate and induce a less detrimental surface roughening. Clearly, the numerical analysis of micro shot peening represents a tremendous computational challenge given the large number of impacts to be simulated to achieve complete coverage and the very fine mesh required for the FE model to appreciate low surface roughness and thin surface layers affected by the compressive RS. The outcomes of FE models are usually validated by comparison with in-depth RS measurements undertaken with diffractometric techniques, but often the effect of radiation penetration into the sample is overlooked. This can lead to significant errors if the numerically estimated RSs are directly compared with measures taken on light alloys characterized by X-Ray penetration depth (on the order of tens of microns) comparable with the thickness of the surface layer where the compressive RS develops. On the other hand, the simulation of micro-shot peening treatments would be of great industrial interest, as the effects of the fundamental process parameters could be estimated without requiring expensive experimental techniques. In addition, the numerical reproduction of the surface morphology would allow a direct estimation of the stress concentration effect at surface dimples in place of semi-analytical simplified models based on large-scale roughness parameters, whose applicability to micro-shot peening treatments has yet to be validated.