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In this paper, the laser shot peening (LSP) technology of H13 steel is studied to improve the friction and wear performance of shield machine hob. And to utilize the LSP experiment and simulation analysis, the influence of LSP parameters on the friction and wear performance of H13 steel after strengthening is studied. The numerical simulation study reveals the variation law of laser parameters on residual stress and stress layer depth. Study on friction and wear characteristics of H13 steel after LSP. The results show that the maximum residual stress of H13 steel is 911 MPa, and the hardness is 650.7 HV, when there are three times of black paint absorption and LSP. Compared with the raw material, the residual stress is increased by 125%, and the hardness is increased by 18%. And its friction coefficients and wear volume were relatively lower than other schemes. The average friction coefficient and wear volume were reduced by 10.8% and 57.2% respectively. [ABSTRACT FROM AUTHOR]

Confined deformation, e.g. mechanical twinning, shear banding, and Lüders banding, etc. was extensively observed in metals and alloys with low stacking-fault energies, especially under complex loadings, governing the mechanical properties. It is often accompanied with gradient microstructures to accommodate the stress concentrations. Understanding the micromechanical behaviors of structural materials having confined deformation is important for evaluating the structural stabilities of engineering components. Synchrotron-based techniques provide powerful tools for multiscale microstructural characterization owing to their good resolution in real/reciprocal space, fast data collection/processing and flexible application scenarios. In this paper, the synchrotron-based high-energy X-ray diffraction (HE-XRD) and microdiffraction (μXRD) techniques in combination with traditional characterization methods are used to reveal the deformational gradient structures/stresses under different loading modes in multiscale. The structure/stress gradients induced by laser shot peening treatment and the deformation twins generated during uniaxial tensile loading in pure titanium were systematically studied by HE-XRD and μXRD, in order to elucidate the accommodating role of the deformational structures subjected to various confined scenarios. The new finding regarding the micromechanical behaviors related to confined deformation contributes to the in-depth understanding of related complex deformation behaviors.

• 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]

Based on theoretical analysis, finite element software ABAQUS and MSC.Fatigue were used to establish the forecasting model of fatigue life for laser shot peening (LSP) process. By using a standard stretch test sample of 6061-T6 aluminium alloy, the residual stress field induced by LSP was analyzed with ABAQUS code firstly, and then the stress field model was imported into MSC.Fatigue code for the crack growth analysis. The residual stress distribution and its effect on crack propagation life induced by LSP are numerical studied, and the fatigue life is predicted. The results show that numerical simulation approach is valuable for analyzing the fatigue crack growth and influence of process parameters on fatigue life. [ABSTRACT FROM AUTHOR]

Abstract: The results on laser shot peening of Inconel 600 are presented. A brief description of the physical processes involved in the pressure generation mechanism is given. Using an X-ray diffraction technique we show that the residual compressive stresses can be successfully induced in Inconel 600 with parameters of laser peening, which are close to that of 316L stainless steel. We found that the laser spot scanning of the surface during processing results in a system of column-like microstructure, which is tilted in the direction of scanning. The light reflected from this microstructure is predominantly scattered at angles which are different from the incidence angle. We revealed that the base material injected into the confining water due to laser ablation is transformed into spherical nanoparticles with diameter as small as 60nm. [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]