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• The synergetic effect of shot peening (SP) and laser shot peening (LSP) on the fatigue behavior of 30CrMnSiA steel compared with a baseline SP treatment was investigated. • A fatigue life transition was observed in the S N curves, which indicates different fatigue mechanisms and the enhancement of SP and SP + LSP specimens in HCF and LCF. • Different microstructural evolutions of SP and SP + LSP spceimens were observed. • The short crack incubation and initial propagation were retarded explaining the fatigue life transition behavior. The synergetic effect of shot peening (SP) and laser shot peening (LSP) on the fatigue behavior of a medium carbon steel was investigated. A fatigue life transition was observed in the S N curve, where the fatigue performance of the SP + LSP specimen was improved only at lower stress levels. This result is consistent with the short crack propagation behavior observed in the near-threshold region. The heterogeneous structures comprised by ultra-fine grains, dislocation tangles, and more high-angle grain boundaries were responsible for this behavior which effectively retard the short crack propagation. [ABSTRACT FROM AUTHOR]

Laser shock processing of 6061-T6 aluminium alloy is carried out. Temperature and stress fields are simulated in line with the experimental conditions. Metallurgical changes due to the laser shock and microhardness in the laser treated region are examined using analytical tools that include scanning and transmission electron microscopes and microhardness tester. The depth of shock affected region, plastic strain, and dislocation density are determined numerically and experimentally in the laser treated region. It is found that the temperature attains high values at the centre of the irradiated spot resulting in high rate of evaporation at the surface. The recoil pressure formed, due to high evaporation rate, at the laser treated surface results in plastic deformation of about 500 mm below the surface. A dislocation density of the order 2 × 1013 to 4 × 1013 cm-2 occurs in the surface region. Although high temperature gradients result in high stress levels in the region below the surface vicinity, high recoil pressure results in crack free surface with compressive stress. [ABSTRACT FROM AUTHOR]

• The effects of load ratios on the gain of AA2524′s fatigue life after laser shot peening were thoroughly studied. • The crack closure model has been used to eliminate the R -effect of the peened specimens' FCGR. • The data driven approach has been used to predict the fatigue crack growth behavior, an ANN model and a SVR model based on particle swarm optimization algorithm were trained by FCGR data, and the fatigue crack growth life is predicted through these well-trained models. Laser shot peening is a relatively novel surface treatment technology generating deep compressive residual stress and further retarding fatigue crack growth rate (FCGR). Meanwhile, the load ratio, R , plays an important role in fatigue crack growth behavior. Evaluating the remaining life of components accurately is essential to damage tolerance design, many efforts have been applied to correlate the R -effect. In this paper, the effect of load ratio on the gain of AA2524′s fatigue life after laser shot peening have been thoroughly studied. Initially, the fatigue crack growth rate of AA2524 after laser shot peening was measured under different load ratios. Subsequently, a comparative analysis between the FCGR for AA2524 before and after laser shot peening was thoroughly conducted. Then, the crack closure model has been applied to correlate the R- effect of peened specimens, but the results are unsatisfied due to the ignore of compressive residual stress. To address this issue, a novel method of predicting crack growth life considering compressive residual stress was proposed. The artificial neural network model and support vector regression model based on particle swarm optimization algorithm were trained by the FCGR data, and the fatigue crack growth life is predicted by a cycle-by-cycle method. The result shows the artificial neural network model is more accurate than the support vector regression model, and this intelligent algorithm can be a potentially effective way to predict fatigue crack growth behavior. [ABSTRACT FROM AUTHOR]

The aim of this paper is to study the effect of microstructure heterogeneity upon elasto-plastic wave propagation generated during laser shot peening. We consider a simplified elasto-plastic laminate specimen subjected to uniaxial strain. The microstructure is composed of two phases alternating periodically and perfectly bonded together. The associated PDE system is solved using a high-resolution Godunov scheme, allowing to study the wave propagation in the heterogeneous structure. It is found that, even for a small mechanical contrast between the two phases, the considered laminate microstructure has a significant effect on the distribution of plastic strain. In addition, an elasto-plastic homogenization of the laminate has been carried out, and the resulting Homogeneous Equivalent Medium (HEM) has been used to decrease the computation time of the wave propagation. The HEM-based model is able to reproduce accurately the full-field solution in terms of distribution of mean plastic strain within the specimen and its fluctuation between the two phases. [ABSTRACT FROM AUTHOR]

Abstract: Mechanical properties of engineering material can be improved by introducing compressive residual stress on the material surface and refinement of their microstructure. Variety of mechanical process such as shot peening, water jet peening, ultrasonic peening, laser shot peening were developed in the last decades on this contrast. Among these, lasers shot peening emerged as a novel industrial treatment to improve the crack resistance of turbine blades and the stress corrosion cracking (SCC) of austenic stainless steel in power plants. In this study we successfully performed laser shot peening on precipitation hardened aluminum alloy 6061-T6 with low energy (300mJ, 1064nm) Nd:YAG laser using different pulse densities of 22pulses/mm2 and 32pulses/mm2. Residual stress evaluation based on X-ray diffraction sin2 ψ method indicates a maximum of 190% percentage increase on surface compressive stress. Depth profile of micro-hardness shows the impact of laser generated shock wave up to 1.2mm from the surface. Apart from that, the crystalline size and micro-strain on the laser shot peened surfaces have been investigated and compared with the unpeened surface using X-ray diffraction in conjunction with line broadening analysis through the Williamson–Hall plot. [Copyright &y& Elsevier]

Massive laser shot peening (LSP) is a promising surface modification technology to improve the properties of metallic materials. In this work, with the established FEM model, the dynamic propagation characteristics of stress waves by single round and square impact were investigated. The effect of three critical LSP parameters such as scanning patterns, overlapping rates and spot shape on the residual stress and the displacement deformation (U3) of 7075 aluminum alloy were further investigated under same spatial energy input. The simulation results were compared and validated with the reported research results. The spot shape has little effect on the residual stress field after a single impact while a better LSP treatment could be achieved by the massive square spot impact strategy. The snake scanning pattern was proved to be an optimized advancing pulse sequence compared with other two scanning patterns. The uniformity of compressive residual stress field and the displacement deformation (U3) curve were improved with the increase of overlapping rate. [ABSTRACT FROM AUTHOR]