Laser Peening Effects on High-Cycle Fatigue Properties of Al-Li Friction Stir Welded Joints: Crystal Plasticity Modeling & Quantitative Evaluation

Author:  Maziar Toursangsaraki and Yongxiang Hu* State Key Laboratory of Mechanical System and Vibration, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai, China
Source:  ICSP14 Milan
Doc ID:  2022082
Year of Publication:  2022
Abstract:  
Abstract To optimize surface treatment procedures, their strengthening mechanisms need to be evaluated on the material properties. In this study, physics-based relations were employed with crystal plasticity constitutive equations to quantify the strengthening effects of microstructural attributes on the high-cycle fatigue properties of the AA2195-T6 friction stir welded joints after applying multiple laser peening layers. The developed model quantified the contributions of laser-peening-induced near-surface compressive residual stresses, dislocation density increase, and crystal morphology variations on the evolutions in fatigue indicator parameters. Grain-average fatigue indicator parameters were utilized to evaluate the fatigue property modification trends with depth, while their extreme values estimated the corresponding improvements at grain boundaries in near-surface regions after laser peening. As the crystal plasticity model predicted, the enhancement in joint fatigue properties mainly stemmed from the alleviation of cyclic mean stress under near-surface compressive residual stresses. This effect was followed by the increased resistance to cyclic plastic deformation due to the rise in dislocation density and texture intensity, and the decrease in crystal morphology heterogeneity under the homogenization of crystal morphology after laser peening. The decrease in extreme-value and grain-average fatigue indicator parameters in depth were the mechanisms behind enhancements in joint surface fatigue properties and the relocation of fatigue failure regions from surface to subsurface areas. Moreover, experimental high-cycle fatigue observations revealed the improvement in joint fatigue properties and validated the numerical approaches. Keywords: Crystal plasticity, Laser peening, Friction stir welding.