Compressive Residual Stress Distribution Research Articles

Study on the effects of bilateral laser-assisted cutting on surface integrity and fatigue life of FeCoCrNiAl0.6 alloy

This study investigates the impact of various cutting parameters in both unilateral and bilateral laser-assisted cutting processes on the surface integrity and fatigue life of FeCoCrNiAl0.6 high-entropy alloy. By utilizing ABAQUS/FE-SAFE simulations and conducting laser-assisted cutting and fatigue tensile tests, differences in surface quality and fatigue life cycles of FeCoCrNiAl0.6 alloy samples under different cutting scenarios were evaluated. The results indicate that in high-speed laser-assisted cutting, an increase in laser speed leads to a progressive decline in surface quality for both unilateral and bilateral methods. Nevertheless, at a laser speed of 4000 mm/s, optimal surface quality is achieved in both approaches, with the bilateral method consistently providing superior results across varying speeds. Regarding residual stress, unilateral laser-assisted cutting at 4000 mm/s produces a surface residual compressive stress of 532 MPa, which is twice as high as that observed at 10000 mm/s. The bilateral method shows a symmetric distribution of residual compressive stress, with peak values of 567 MPa and 528 MPa on the front and back surfaces, respectively. In terms of fatigue life, bilateral laser-assisted cutting demonstrates enhanced performance at 4000 mm/s, achieving a fatigue life cycle that is 4.72 times longer than that of the unilateral method. Overall, bilateral laser-assisted cutting improves the fatigue life of the material through symmetric thermal effects and higher residual compressive stress, particularly at lower laser speeds and optimal cutting depths.

Effects of laser non-uniform shock peening on the microstructure and fatigue performance of SUS 304 stainless steel welded joints

Residual tensile stresses and microstructural heterogeneity in welded joints are primary factors that degrade fatigue performance. As an effective post-weld strengthening method, Laser Shock Peening (LSP) can address these issues. Given the personalized demands of different regions, this paper proposes a Laser Non-Uniform Shock Peening (LNUSP) technique. This approach involves applying high pulse energy to the weld zone (WZ) and heat-affected zone (HAZ), and low pulse energy to the base material (BM) to achieve a more uniform residual compressive stress distribution and refined microstructure, thereby improving overall performance and service life. Results indicate that LSP transforms residual tensile stresses on the weld surface into compressive stresses. Compared to original samples, uniformly LSP-treated samples, and locally LSP-treated samples, LNUSP-treated samples exhibit more uniform residual stress and hardness distribution. LSP significantly increases surface hardness, with LNUSP-treated samples achieving a maximum hardness of 308.3 HV. Additionally, LSP induces martensitic transformation in the BM and WZ areas, alters grain orientation, and promotes dislocation movement, resulting in dislocation tangling, dislocation networks, and twin structures, which refine grain size. Consequently, LSP markedly improves joint fatigue performance, delaying fatigue crack propagation. The fatigue life of LNUSP-treated samples is increased by 25.41 % compared to original samples, reaching levels comparable to high-energy large-area impacts. This enhancement is attributed to the uniform residual stress and refined grain structure.

An analytical model for predicting residual stress in shot peening with strain energy method

In this study a model by novel analytical approach is developed and experimentally verified for shot peening residual stress distribution. The residual stress field induced by single shot impact is calculated by using Glinka–Molski energy-based method and kinematic hardening model. The formulation of the compressive residual stress (CRS) distribution is often based on plane strain or plane stress. It can be determined from the derived relation presented in this paper, the final residual stress in the full coverage conditions is the average of the two strain and stress plane expressions proposed by previous researchers. The distribution of residual stress is one of the key differences between the profiles produced by the results of the current model. There is a significant distinction between surface residual stress and maximum CRS, because the CRS profile near the surface is more curved compared to profiles obtained in earlier analytical models. The experimental data obtained by XRD analysis indicate the correctness and precision of the current model. Another goal of this study is to increase the fatigue life of GTD-450 stainless steel by shot peening at two different peening intensities. The fatigue life of samples were obtained by rotary bending test. Analytical results that confirmed by experimental findings shown bigger maximum compressive residual stresses occurred in higher shot peening intensities. This incident can improved fatigue life by deeper plastically deformed layer.

Comparative analysis of geometric imperfections and residual stresses on the global stability behavior of cantilever composite alveolar beams

Few studies addressed the influence of geometric and structural imperfections of steel alveolar I-sections on the stability behavior of composite beams under hogging moment. Therefore, this paper aims to study the sensitivity to geometric imperfection amplitude and residual stress distribution on their global stability. The research primarily focuses on comparing numerical results with experimental data in detail, which addresses four tests involving cantilever composite beams with castellated and cellular I-sections. It includes applying various residual stress patterns and geometric imperfection values to advanced numerical analyses as documented in the literature. Linear buckling analyses (LBA) and geometrically and materially nonlinear analyses with imperfections (GMNIA) are carried out using the ABAQUS software. Regarding the first positive eigenvalue from LBA analyses, the eigenvectors presented Web-Post Buckling (WPB) with a slight compressed flange lateral curvature, inserted as the initial geometric imperfection in the GMNIA analyses. However, when the residual stresses were implemented in the GMNIA analyses, some finite element models had different failure modes regarding the deformed configurations from LBA analyses, in which the failure modes were characterized by Lateral-Distortional Buckling (LDB), which was in agreement with the test results. As the beams reached LDB in an inelastic regime, residual stresses significantly affected their resistant capacity. This way, the distribution of compressive residual stresses in the flanges had the most critical influence on the global stability behavior of the analyzed beams, as these residual stresses favor the LDB occurrence. Finally, higher geometric imperfection amplitudes did not provide only lower ultimate loads, as when the instability phenomena are reached in an inelastic regime, the effect of global geometric imperfections becomes highly complex.

Investigating the Dynamic Mechanical Properties and Strengthening Mechanisms of Ti-6Al-4V Alloy by Using the Ultrasonic Surface Rolling Process.

The demand for titanium alloy has been increasing in various industries, including aerospace, marine, and biomedical fields, as they fulfilled the need for lightweight, high-strength, and corrosion-resistant material for modern manufacturing. However, titanium alloy has relatively low hardness, poor wear performance, and fatigue properties, which limits its popularization and application. These disadvantages could be efficiently overcome by surface strengthening technology, such as the ultrasonic surface rolling process (USRP). In this study, the true thermo-mechanical deformation behavior of Ti-6Al-4V was obtained by dynamic mechanical experiment using a Hopkinson pressure bar. Moreover, USRP was applied on the Ti-6Al-4V workpiece with different parameters of static forces to investigate the evolution in surface morphology, surface roughness, microstructure, hardness, residual stress, and fatigue performance. The strain rate and temperature during the USRP of Ti-6Al-4V under the corresponding conditions were about 3000 s-1 and 200 °C, respectively, which were derived from the numerical simulation. The correlation between the true thermo-mechanical behavior of Ti-6Al-4V alloy and the USRP parameters of the Ti-6Al-4V workpiece was established, which could provide a theoretical contribution to the optimization of the USRP parameters. After USRP, the cross-sectional hardness distribution of the workpiece was shown to initially rise, followed by a subsequent decrease, ultimately to matrix hardness. The cross-sectional residual compressive stress distribution of the workpiece showed a tendency to initially reduce, then increase, and finally decrease to zero. The fatigue performance of the workpiece was greatly enhanced after USRP due to the effect of grain refinement, work hardening, and beneficial residual compressive stress, thereby inhibiting the propagation of the fatigue crack. However, it could be noted that the excessive static force parameter of USRP could induce the decline in surface finish and compressive residual stress of the workpiece, which eliminated the beneficial effect of the USRP treatment. This indicated that the choice of the optimal USRP parameters was highly crucial. This work would be conducive to achieving high-efficiency and low-damage USRP machining, which could be used to effectively guide the development of high-end equipment manufacturing.

Prediction of residual stress distribution induced by ultrasonic nanocrystalline surface modification using machine learning

Ultrasonic Nanocrystalline Surface Modification (UNSM) offers an efficient and cost-effective approach for enhancing material mechanical properties by inducing Severe Plastic Deformation (SPD). It leads to grain refinement and substantial residual stress generation beneath the workpiece surface. This study investigates the influence of key modification parameters, specifically static load, vibration amplitude, and strike tip size on compressive residual stress (CRS) distribution. A Finite Element Method (FEM)-based model for the UNSM process is developed, and validated against experimental outcomes, yielding a dataset of 45 unique cases across various modification scenarios. The Balancing Composite Motion Optimization (BCMO), as a meta-heuristic algorithm is used to optimize the hyperparameters of the Support Vector Regression (SVR) model. Additionally, the performance of Artificial Neural Network (ANN), Polynomial Chaotic Extension (PCE), and Kriging algorithms is evaluated in parallel. Among these Machine Learning (ML) models, the SVR-BCMO emerges as a pioneer for its accuracy in estimating residual stress. A sensitivity analysis employing Sobol’ indices further clarifies the distinct impact of each input parameter on residual stress distribution resulting from UNSM. In essence, this research offers a tool for rapidly estimating residual stress, even in cases of limited datasets. Furthermore, the findings help in making prompt decisions regarding of UNSM conditions. This is achieved by elucidating the effect of each input parameter and facilitating the determination of residual stresses in specific scenarios.

Surface morphology improvement and residual stress distribution of SiCp/Al composites using high-power fiber laser-CNC milling cooperative machining strategy

This work proposes a novel high-power fiber laser-CNC milling cooperative strategy for cutting SiCp/Al composites, which aims to machine MMCs with high efficiency and limited damage, and achieve compressive residual stress distribution within machined surface layer in order to subsequently improve service performance of composite components. Experimental results shows that the cooperative machining strategy has a sufficient improvement in machining efficiency with limited surface defects compared to conventional methods. Completely removal of laser cutting induced surface defects, including striations, combustion and cataphracted dross, was achieved under high speed milling with small cutting depth down to 0.2 mm. Additionally, it was found that the roughness of final machined surface was impacted by the parameters of both laser cutting and milling process. The surface roughness decreased by 35 % with the laser power increased from 4.0 kW to 4.5 kW, while decreased by 60 % when milling speed decreased from 180 m/min to 90 m/min. Compressive residual stress was prevalent within the surface layer during fiber laser-CNC milling cooperative machining process. The experimental findings in this work verified the feasibility and advantages of the cooperative machining strategy for processing difficult-to-cut metal matrix composites.

Modelling and optimization of residual stress induction on laser-worked X12Cr turbine blades

The energy and power industry conventionally depends on large-scale turbomachinery to meet the ever-growing global energy demands. However, unplanned in-service failures remain a threat to sustainability with safety and economic consequences. The laser shock surface treatment technique is being considered a competitive alternative in mitigating crack initiation and growth, wear and fatigue of industrial components such as turbine blades. This paper presents the modelling and optimization of laser shock treatment parameters using numerical methods and commercial codes such as ABAQUS® and MATLAB®. Model-based process optimization parameters for the induction of global optimum compressive residual stress distribution in laser-worked Chromium-12 based high strength steel alloy (X12Cr) turbine blade is established, showing parametric combinations of inputs variables within the domain under investigation, yielding maximized CRS outputs. A hierarchy of significance of the input parameters to the laser shock peening process for stress induction has also been put forward as an outcome of this study. The capacity to predict and analyze outcomes before actual treatment of the components is beneficial and imperative to cutting costs, downtimes and other economic losses associated with unplanned failure of these components.

Effect of Laser Shock Peening on the Fatigue Life of 1Cr12Ni3Mo2VN Steel for Steam Turbine Blades

In the present study, laser shock peening (LSP) was employed to enhance the rotating bending fatigue life of 1Cr12Ni3Mo2VN martensitic stainless steel used in steam turbine blades, addressing the issue of insufficient fatigue performance in these components. The aim of this study was to investigate the effect of LSP on the microhardness, residual stress, and rotating bending fatigue life of 1Cr12Ni3Mo2VN steel samples. The microhardness of LSP-treated samples was increased by 10.5% (LSP-3J sample) and 15.3% (LSP-4J sample), respectively, compared to high-frequency hardening samples. The residual compressive stress of the LSP-4J sample was the largest, reaching −689 MPa, and the affected layer depth was about 800 μm. Fatigue tests showed that the number of cycles at the fracture point for the LSP-3J and LSP-4J samples increased by 163% and 233%, respectively. The fatigue fracture morphology of the four samples showed that the microhardness and residual compressive stress distribution introduced by LSP could effectively inhibit the initiation of surface cracks, slow down the crack growth rate, and improve the rotating bending fatigue life of 1Cr12Ni3Mo2VN.

Improving the Wear and Corrosion Resistance of Aeronautical Component Material by Laser Shock Processing: A Review.

Since the extreme service conditions, the serious failure problems caused by wear and corrosion are often encountered in the service process for aeronautical components. Laser shock processing (LSP) is a novel surface-strengthening technology to modify microstructures and induce beneficial compressive residual stress on the near-surface layer of metallic materials, thereby enhancing mechanical performances. In this work, the fundamental mechanism of LSP was summarized in detail. Several typical cases of applying LSP treatment to improve aeronautical components' wear and corrosion resistance were introduced. Since the stress effect generated by laser-induced plasma shock waves will lead to the gradient distribution of compressive residual stress, microhardness, and microstruture evolution. Due to the enhancement of microhardness and the introduction of beneficial compressive residual stress by LSP treatment, the wear resistance of aeronautical component materials is evidently improved. In addition, LSP can lead to grain refinement and crystal defect formation, which can increase the hot corrosion resistance of aeronautical component materials. This work will provide significant reference value and guiding significance for researchers to further explore the fundamental mechanism of LSP and the aspects of the aeronautical components' wear and corrosion resistance extension.

Different responses of wheel–rail interface adhesion and wheel surface damage induced by an out–of–round wheel tread

The out–of–roundness of wheel treads are an inherent degradation characteristic of the wheels of railway vehicles, and the interface behaviour of the wheel and rail caused by out–of–roundness features has essential research value in high–speed train running safety and quality. Sliding–rolling contact wear testing was conducted to evaluate the effect of the out–of–round wheel on the wheel–rail damage behaviour, by using a twin–disc setup. The effects of four wheels, three wheels of different eccentricities and one normal wheel were taken as a control group. The characteristics of the wheel–rail interface adhesion, wheel surface damage and compressive residual stress (CRS) distribution were compared and analysed. The results showed a dramatic increase in the fluctuation amplitude of the wheel–rail vertical force of the eccentric wheels, and the adhesion coefficient of the wheel–rail interface significantly decreased. Furthermore, eccentric wheels dramatically accelerate the wear loss of the rail used as a counterpart during wheel–rail rolling contact. The surface damage behaviour of the eccentric wheels is obviously different along the circumferential direction, and non–uniform wear was observed. The damage mechanism of the worn surface presented varying characteristics, which could be divided into a severely damaged zone (located at the maximum of the rolling radius rmax) and a slightly damaged zone (located at the minimum of the rolling radius rmin). The surface contact stress of the severely damaged zone was high, this finding can be explained by the extremely rough worn surface caused by the severe fatigue delamination characteristics and the initiation and propagation of fatigue cracks in the severely damaged zone. Furthermore, the values of surface hardness and residual stress were relatively low. By contrary, an adhesion layer was observed on the worn surface of the slightly damaged zone. The adhesion layer protects worn surface in the slightly damaged zone was relatively flat, and the CRS was relatively high.

The interactions between incoming shot flow and structural target in a Flap Shot Peening process

A novel numerical modeling approach capable of computing and simulating the Flap Shot Peening (FSP) dynamic process of industrial interest was proposed by the coupling of the Discrete Element Method (DEM) and Finite Element Method (FEM). During the process of shots impacting the metallic target, the shot flow and the target were respectively modeled by DEM and FEM, and the interaction between the shots and structure was efficiently evaluated by DEM-FEM. This approach can be employed to rationally control and regulate the FSP multiple parameters, which would induce an appropriate distribution of Compressive Residual Stress (CRS) within the target to provide additional resistance to the treated component. In this paper, a benchmark was first performed to verify the computational method successfully. Further, the influence of variant mass flow rates on the target was also investigated. The result shows that low mass flow rates can be replaced by a higher mass flow rate in case both were able to generate a similar shot effect.

The Grey-Taguchi method analysis for processing parameters optimization and experimental assessment of 42CrMo steel treated by ultrasonic surface rolling

Static force, ultrasonic amplitude, feed rate, and rolling spacing parameters of 42CrMo steel treated by the ultrasonic surface rolling process (USRP) were optimized by the Grey-Taguchi method. Nine sets of experiments based on an orthogonal array design and grey relational analysis were used to obtain the optimum combination of mechanical properties for USRP. The influence of processing parameters on mechanical properties was investigated based on the grey relational analysis. The results indicated that the feed rate is the dominant parameter affecting the mechanical properties, followed by rolling space, ultrasonic amplitude, and static force. The effects of plastic strain caused by USRP on the compressive residual stress and microhardness were investigated. The effects of the dislocation and cementite evolution on the mechanical properties were investigated to determine the origin of the best and worst mechanical properties. For the best mechanical property, the level and depth of distribution of compressive residual stress and tensile strain hardening capacity are the highest, which is benefited from the optimum synergistic of the elastic-plastic deformation, dislocation evolution, gradient distribution, and cementite evolution. For the worst mechanical property, a large amount of cementite is distributed within and around martensitic laths, increasing brittleness and the lowest comprehensive mechanical properties. These findings can provide a reference for accurately controlling the processing parameters of USRP and improving their mechanical properties.

An internal cooling grinding wheel: From design to application

The cooling and lubrication conditions during the grinding process significantly impact the nickel-based superalloy's final service performance. The existing jet cooling and heat pipe technology can solve the heat conduction problem in the grinding process of superalloy. Still, managing cooling, lubrication, and chip removal are difficult. This paper describes the design and fabrication of a novel central fluid-through internal cooling slotted grinding wheel with an ordered grain pattern to improve the grinding machinability of a nickel-based superalloy. The pressurized grinding fluid was ejected into the grinding zone via the pipe and tool holder from the lower-end face of the inner cooling wheel. The structure of the grinding wheel was optimized using computational fluid dynamics (CFD). The flow field in the grinding area achieved the highest overall flow rate, distribution homogeneity, and effective exit flow when the internal flow channel had four through-holes. The exit for the inner runner is located at the abrasive edge and diamond staggered pattern. Single-layer brazing was used to create cubic boron nitride (CBN) abrasive rings with various abrasive patterns. The internal cooling wheel matrix and various components were prepared according to the optimized grinding wheel geometry model. A grinding test bench was built to conduct an experimental study of grinding the nickel-based alloy GH4169. The results show that, under the same conditions, a diamond-shaped staggered pattern obtains lower grinding temperature, lower surface roughness, better surface morphology, and more significant residual compressive stress distribution than an abrasive cluster diagonal circular staggered pattern or disordered pattern. The average effective flow rate calculated by CFD is increased by 42.3% when compared to the disordered pattern. In the experiment, compared to the disordered arrangement, with the increase of grinding wheel’s rotating speed and coolant pressure, the average grinding temperature of abrasive grain with diamond-interleaved arrangement decreases by 58.2% and 51.7% respectively, and its surface hardening degree decreases by 11.1% and 11.7% respectively.

Surface Microstructure Refinement and Mechanical Properties of GCr15 Steels Improved During Ultrasonic Surface Rolling Processing

In this paper, ultrasonic surface rolling processing (USRP) was used to strengthen GCr15-bearing steel. A finite element three-dimensional model of USRP was established to analyze the residual compressive stress and equivalent plastic strain distribution on the bearing steel surface. The microstructure, hardness, surface roughness, and corrosion resistance before and after USRP treatment were characterized by SEM, EBSD, X-ray diffraction (XRD), and electrochemical techniques. Results indicated that USRP treatment can significantly improve the material's surface microstructure and residual compressive stress distribution and obtain a plastic strain layer of about 60μm. After USRP treatment, the Kernel Average Misorientation (KAM) increased, and the dislocation activity was more intensive, resulting in aggregation near grain boundaries, and the percentage of LAGBs increased to 38.8%. Under the combined effect of surface grain refinement, residual compressive stress, and high glossy surface, the self-corrosion current density is reduced by two orders of magnitude, and the corrosion resistance is significantly improved. This investigation suggests a solution to the bearing failure problem and has implications for understanding the deformation mechanism of ultrasonic surface rolling processing.

Fretting fatigue mechanism of 40CrNiMoA steel subjected to the ultrasonic surface rolling process: The role of the gradient structure

In this research, a gradient nanostructure (GNS) of 40CrNiMoA steel prepared by the ultrasonic surface rolling process (USRP) is investigated. The results show that the USRP sample surface is equiaxial nanocrystalline and has a high-density nanolamellar gradient structure, and excellent compressive residual stress (CRS) and hardness gradient distribution are observed. In this study, the fretting fatigue (FF) limit of the USRP-treated specimen is 550 MPa, which is about 67 % higher than that of the untreated specimen. It is found that the equiaxed nanocrystalline top layer can effectively delay FF crack initiation. The high-density nanolamellar martensite structure is almost parallel to the surface, reduces the FF crack initiation angle, and increases the crack propagation path. High-strength CRS increases the crack growth resistance and changes the crack growth path. In addition, the improvement in surface hardness, CRS, and surface quality enhances the resistance to fretting wear and FF crack initiation. It is concluded that these factors effectively improve the FF limit of the material.

Investigation of wet shot peening on microstructural evolution and tensile-tensile fatigue properties of Ti-6Al-4V alloy

Ti–6Al–4V (TC4) alloy was treated by wet shot peening (WP) using ceramic beads compared with dry shot peening (SP). The effects of shot peening on surface integrity, microstructural evolution, fatigue crack initiation behavior and tensile-tensile fatigue performance were investigated applying multiple characterization techniques. The result exhibited that the surface plastic deformation caused by WP and SP treatment resulted in microstructure changes near the surface. Surface morphology was distinctly changed by shot peening treatment. The roughness value increased from 0.596 μm (Ra) to 1.594 μm (Ra). Microhardness gradients and compressive residual stress (CRS) distributions along the depth were induced by shot peening. The maximum hardness reached 373.5 HV, 407.8 HV and 445.3 HV. The maximum value of CRS reached 884 MPa, 1038 MPa and 1207 MPa with the corresponding depth at 21 μm, 25 μm and 40 μm. The fatigue life was significantly improved by shot peening treatment. Cracks tended to initiate at the subsurface layer instead of the treated surface after shot peening. The reason for crack initiation position altering was tentatively explained by the CRS stable zone. The competition mechanism between the surface stress concentration and local strengthening factors were discussed based on the analysis of stress concentration factor, Kt.

Effect of laser shock peening on tensile properties and microstructure of selective laser melted 316L stainless steel with different build directions

316L stainless steel tensile samples were fabricated via selective laser melting (SLM), wherein the build directions (BD) deviated from the tensile directions by 0°, 45°, and 90°. The effects of BD and laser shock peening (LSP) on compressive residual stress distribution, microstructure, texture, and tensile properties were investigated. The intensity and volume fraction of strong <110> fibre texture decreased after LSP, and the sample with a build angle of 90° had the weakest intensity and the least volume fraction. A tensile test was conducted at 25 °C temperature to investigate the effects of the BD and LSP on strength and ductility. LSP resulted in a noticeable improvement in the strength of all the samples, but the ductility of the samples with 0° and 45° build angles declined. Additionally, it was found that 316L fabricated via SLM with a build angle of 90° and subjected to LSP had the optimal combination of strength and ductility.

Attainment of favorable microstructure for residual stress reduction through high-temperature heat treatment on additive manufactured inconel 718 alloy

Mitigation of residual stress in additive manufactured metal parts through post-heat treatment helps enhancement of life during service. The present work aims to investigate the effect of stress-relieving heat treatment (SRHT) at 1065 °C on microstructural changes, residual stress patterns, and mechanical properties of Inconel 718 (IN718) blocks fabricated through use of the laser-based powder bed fusion (L-PBF) process. The X-ray diffraction technique known as cos α method was used to capture the Debye ring for the measurement of surface residual stress. Dissolution of the columnar dendrites along with laves phases in the interdendritic region was seen after SRHT. The resultant microstructure showed partially recrystallized grains along with the formation of annealing twins and strengthening phases such as γ’, γ’’, and tiny metal carbides. The residual stress on the top surface of as-built sample was found to be 77% higher on the corners compared to the center region. The distribution of residual stress was seen as not uniform in the as-built condition. The SRHT sample showed uniform distribution of compressive residual stresses in all the locations. This phenomenon was due to the diffusion of atoms present in the high-stress regions migrated to low-stress regions until attaining their equilibrium. The combination of face centered cubic (FCC) and hexagonal lattices in as-built microstructure led to misfit strain between the grains. After SRHT, microstructure of IN718 experienced relaxation of residual stresses due to the transformation of hexagonal structured laves phase into the body-centered tetragonal (BCT) γ’’and FCC-structured γ’ phases. Furthermore, SRHT significantly alters the mechanical properties of IN718 alloy causing a 23.03% increase in average hardness and a 21.04% increase in tensile strength.

Theoretical study including physic-based material model to identify underlying effect of vibration amplitude on residual stress distribution of ultrasonic burnishing process

The potential of distribution of compressive residual stress at deep surface layers caused by ultrasonic-based surface sever plastic deformation (SSPD) has attracted researchers' attention to deeply study the mechanism of the process by simulation models. In majority of the researches, macro-mechanical Johnson-Cook (JC) model was utilized to govern material constitutive behavior. However, the large differences between measured and predicted values of residual stress of some materials imply that the underlying mechanism is still unclear and merits further studies. In the present work, a new physics-based constitutive equation incorporating micromechanics of initial grain size, dislocation evolution, dislocation drag and acoustic softening has been developed to obtain plastic flow stress. Then, the mechanic of the ultrasonic burnishing process incorporating superposition of static and dynamic loads was simulated using concept of expanding cavity model (ECM). The residual stress has been further calculated through combination of developed models aiming to discover the undying mechanism of vibration amplitude effect on stress fields. In order to confirm the obtained results, series of ultrasonic burnishing experiments have been carried out on AA6061-T6 under different vibration amplitude. The obtained results revealed that the developed analytical models of residual stress field are considerably more accurate than those previously established that took the macro-mechanical constitutive models to calculate plastic flow stress. Through the developed simulation model, it was studied in depth that how the vibration amplitude as the most adjustable ultrasonic vibration parameter determine variation of residual stress field. It has been demonstrated that the acoustic softening because of presence of ultrasonic energy field has the greatest impact in generation of compressive residual stress in surface and beneath layers.