Maximum Compressive Residual Stress Research Articles

Tangential Ultrasonic-Vibration Assisted Forming Grinding Gear: An Experimental Study.

This study used a forming grinding wheel to machine an involute spur gear with ultrasonic vibration applied to the gear in order to improve the gear processing technology and enhance the gear processing effect. Conventional grinding and ultrasonic vibration-assisted forming grinding gear (TUVA-FGG) tests were carried out. The effects of grinding parameters, such as spindle speed, feed rate, radial grinding depth, and ultrasonic amplitude, on grinding force, grinding temperature, residual stress, surface roughness, and surface morphology were analyzed. The TUVA-FGG significantly improved processing efficiency. With the increase in spindle speed, the maximum reductions in the normal and tangential grinding forces, grinding temperature, and surface roughness reached 33.6, 24.5, 23.9, and 21.6%, respectively. With the increase in feed rate, the respective maximum reductions were 21.4, 19.7, 20.3, and 16.1%. With the increase in radial grinding depth, these values attained 24.6, 20.3, 21.5, and 17.6%, respectively. Finally, with the increase in ultrasonic amplitude, these reductions reached 21.4, 19.7, 21.5, and 19.4%. The maximum residual compressive stress grew by 30.3, 27.5, 30.9, and 27.5% with the increase of wheel rotation speed, feed speed, radial grinding depth, and ultrasonic amplitude, respectively. TUVA-FGG changed the conventional continuous cutting mechanism between the abrasive grain and workpiece into intermittent cutting, reducing grinding forces, grinding temperature, and surface roughness. Moreover, it increased residual compressive stress and improved the micromorphology of the tooth surface, thus enhancing gear machining efficiency.

Residual Stress Measurement of a Single-step Sintered Planar Anode Supported SC-SOFC Using Fluorescence Spectroscopy

The fluorescence spectroscopy technique was used to measure the residual stress between the cathode and electrolyte of an anode supported planar single-chamber solid oxide fuel cell. The cell was made of (NiO-CGO) :(CGO) :(LSCF-CGO), as anode:electrolyte:cathode and the test was carried out after sintering at room temperature. The measured stress between these layers arises from the sintering stress caused by differential shrinkage from layers during sintering and the thermal expansion co-efficient mismatch between the layers during cooling. Therefore, the residual stress in the cathode and electrolyte layer of the cell due to co-efficient of thermal expansion mismatch during cooling was calculated analytically so as to find sintering stress. According to findings a maximum compressive residual stress of -1084 MPa occurred at the place contiguous to electrolyte layer. The estimated residual stresses in the cell’s cathode and electrolyte layer owing to CTE mismatch for the duration of cooling was calculated as -324 MPa and 15.96 MPa, respectfully. Furthermore, total mean residual compressive stress between cathode and electrolyte was obtained from fluorescence spectroscopy as -703.795. Thus, the main contribution of this residual stress is the stress growth during sintering (-395.755 MPa) due to different shrinkage behavior of adjacent layers.

Tradeoff between the Ion Exchange-Induced Residual Stress and Ion Transport in Solid Electrolytes

Rapid filament growth of lithium is limiting the commercialization of solid-state lithium metal anode batteries. Recent work demonstrated that lithium filaments grow into pre-existing or nascent cracks in the solid electrolyte, suggesting that increasing the fracture toughness of the solid electrolytes will inhibit filament penetration. It has been suggested that introducing residual compressive stresses at the surface of the solid electrolyte can provide this additional fracture toughness. One of the ways to induce these residual compressive stresses is by exchanging lithium ions (Li+) with larger isovalent ions such as potassium (K+). On the other hand, incorporation of too much potassium can alter the lithium-ion diffusion pathway and lower the diffusivity, thus limiting the performance of the solid-state electrolyte. Using multiscale modeling methods, we optimize this tradeoff and predict that exchanging 3.4% potassium ions up to a depth twice the grain sizes in Li7La3Zr2O12 solid electrolyte can induce a maximum residual compressive stress of around 1.1 GPa, corresponding to an increase in fracture strength by ∼8 times, while lowering the diffusivity in the ion-exchanged region by a factor of 5 at room temperature. The reduction of lithium diffusivity is due to K+-induced stress and (mainly) blockage of lithium ion pathways in the shallow ion-exchanged layer.

Exploration of Key Process Parameters and Properties of 40Cr Steel in Ultrasonic Surface Rolling Process

Ultrasonic surface rolling (USRP) is an effective process to improve a workpiece’s fatigue property, in which ultrasonic vibration and static force are applied on the workpiece’s surface. In order to clarify the ultrasonic rolling strengthening mechanism of critical components and optimize the USRP parameters, a theoretical model of ultrasonic rolling was established. Based on the stress-strain curve of 40Cr steel, the USRP parameters were formulated. The compressive residual stress field of single point impact was analyzed by finite element simulation, and the simulation results were validated by conducting an experimental research. In addition, the changes in the surface properties of specimens under different USRP parameters were studied experimentally. The results show that with the increase in depth, the compressive residual stress on the external surface increases firstly and then decreases, and the maximum compressive residual stress is −338 MPa. As the amplitude is 12 μm and the frequency is 20 kHz, the static force of 600 N is optimal for the ultrasonic rolling of 40Cr steel. This study could provide a guide for the key parameters’ selection in USRP.

Effect of the Pre-Shot Peening and Nitrogen Ion Implantation Combined Surface Treatments on the Surface Structure and Properties of Gear Steel 16Cr3NiWMoVNbE

Transmission engineering components need to fulfill requirements for adequate wear resistance and fatigue resistance, which are related to their surface properties. In this paper, we combined shot peening and nitrogen ion implantation to improve the surface properties of 16Cr3NiWMoVNbE gear steel. The average surface roughness decreased slightly after the ion implantation because of the high-speed impact of implanted ions having the surface etching role. The maximum compressive residual stress of the near-surface layer after the surface treatment increased by more than 11.8–15.9% compared with shot peening. The nitrogen ions diffused through the peening deformation channel, and the deformation degree and the implantation temperature were positively correlated with the diffusion process. The surface nano-hardness obtained by ion implantation after shot peening was increased by 124.4% compared to the AR state.

Mechanical Properties Enhancement of Dissimilar AA6061-T6 and AA7075-T651 Friction Stir Welds Coupled with Deep Rolling Process.

The main purpose of this research was to enhance the mechanical properties of friction stir welds (FSW) in the dissimilar aluminum alloys 6061-T6 and 7075-T651. The welded workpiece has tensile residual stress due to the influence of the thermal conductivity of dissimilar materials, resulting in crack initiation and less fatigue strength. The experiment started from the FSW process using the 2k full factorial with the response surface methodology (RSM) and central composite design (CCD) to investigate three factors. The experiment found that the optimal rotation speed and feed rate values were 979 and 65 mm/min, respectively. Then, the post-weld heat treatment process (PWHT) was applied. Following this, the 2k full factorial was used to investigate four factors involved in the deep rolling process (DR). The experiment found that the optimal deep rolling pressure and deep rolling offset values were 300 bar and 0.2 mm, respectively. Moreover, mechanical property testing was performed with a sequence of four design types of workpieces: FSW, FSW-PWHT, FSW-DR, and FSW-PWHT-DR. It was found that the FSW-PWHT-DR workpiece had an increase in tensile strength of up to 26.29% and increase in fatigue life of up to 129.47% when compared with the FSW workpieces, as well as a maximum compressive residual stress of −414 MPa.

Modelling residual stress and residual work hardening induced by surface mechanical attrition treatment

Shot peening induced residual stress is strongly related to residual work hardening which relies on both the process and the target material. In this work, residual stress and coupled residual work hardening are studied in a surface mechanical attrition treatment (SMAT) on a cylindrical structure by combining discrete element method (DEM) and finite element method (FEM). Shot, ultrasonic parameters, chamber structure, sonotrode surface, and cylindrical structure of the target are finely modeled in DEM simulation. On the basis of the DEM results, FEM simulation of the SMAT process is performed on a representative area considering the factual impact parameters and elastic-plastic behavior of the target material, and mechanism of residual stress generation is analyzed. It shows that isotropic hardening and kinematic hardening of the target material play a different role in residual stress generation. The obtained maximum compressive residual stress is mainly determined by residual yield stress, while the residual kinematic hardening is nearly unchanged when the coverage is increased. Further analyses indicate that the mechanisms of residual stress generation should be very different for the Johnson-Cook model and the model that includes kinematic hardening, even though these two kinds of models are reported to be able to well predict the shot peening induced residual stress. The gradient of the residual work hardening can be used for further evaluating mechanical properties of the SMATed cylindrical structure.

Bending fatigue life enhancement of NiTi alloy by pre-strain warm surface mechanical attrition treatment

Many structures like medical stents made of superelastic NiTi shape memory alloy (SMA) are subjected to cyclic bending loads and show a limited fatigue life due to crack nucleation and growth in the surface layers under local tensile stress. Here, we enhance the bending fatigue life of NiTi plates by pre-strain warm surface mechanical attrition treatment (pw-SMAT) where the austenite phase is directly subjected to severe plastic deformation and grain refinement without inducing phase transformation. Amorphous and grain size gradient (5–100 nm) microstructures, as well as a maximum compressive residual stress of 1093 MPa are produced in the surface layer of the NiTi plates via the pw-SMAT. The compressive residual stress notably reduces the surface tensile stress from bending. The grain size gradient layers with improved hardness and reduced hysteresis have high fatigue crack nucleation resistance, while the middle large-grained layers of the plates have high fatigue crack growth resistance. The combined effects of the gradient nanostructure and the compressive residual stress substantially increase the bending fatigue life of the NiTi plates from an original 103 cycles to over 1.3 × 104 cycles. The results open up a new route to improve the bending fatigue life of NiTi plates by heterogenous nanostructures.

Study on the relation between surface integrity and contact fatigue of carburized gears

Surface integrity is critical for gear contact fatigue performance. The relation between gear surface integrity and contact fatigue remains unclear, which is a challenge for gear anti-fatigue design. This study investigates the relation between surface integrity and contact fatigue of 18CrNiMo7-6 carburized gears through fatigue experiments and data-driven modeling. A series of gear contact fatigue tests, with approximately 110 × 106 running cycles in total, has been conducted. P-N curves and fatigue limits of the tested gears are investigated for four typical manufacturing processes: carburizing and grinding, shot peening, barrel finishing, and barrel finishing after shot peening. The influence of different surface integrity components on contact fatigue is explored with a Pearson correlation coefficient analysis and a random forest algorithm. Formulae of gear contact fatigue life and fatigue limit considering surface integrity are proposed. Results show that a high surface integrity state with surface hardness of 686.5 HV, maximum compressive residual stress of −1162 MPa, and surface roughness Sa of 0.36 μm, exhibits the highest gear contact fatigue limit, which is 15.1% higher than the carburizing and grinding state, indicating the benefits of improving surface integrity. For both the gear contact fatigue life and fatigue limit, the most significant surface integrity components are surface hardness, maximum compressive residual stress, and surface roughness. The proposed formulae considering surface integrity illustrate reasonable prediction accuracy, with 1.5 times dispersion band for the predicted fatigue life and a maximum relative error of 2.1% for the predicted fatigue limit.

Numerical Prediction of the Effect of Laser Shock Peening on Residual Stress and Fatigue Life of Ti-6Al-4V Titanium Alloy

Laser shock peening (LSP) is a promising surface strengthening technology to improve the fatigue life of alloy components. In this work, the residual stress field of Ti-6Al-4V titanium alloy induced by LSP was simulated based on finite element method (FEM), and then the fatigue lives of the non-LSP and LSP-treated specimens subjected to four-point bending were predicted using the software Fe-safe. The simulation results were compared and validated with the corresponding experimental results. LSP treatment produces a maximum compressive residual stress (CRS) of up to 800 MPa on the surface of the specimen and a CRS layer with a thickness of 0.623 mm under the upper surface of the specimen. The existence of the CRS layer reduces the maximum principal stress from 608 MPa to 540 MPa and changes its location from the upper surface into the internal position at a depth of about 0.6 mm during the four-point bending process. This results in experimental and predicted fatigue lives 4.2 and 17.24 times longer for the specimens with LSP pretreatment compared to those without LSP.

Study on surface nanocrystallization and dislocation configuration of E690 steel strengthened by laser shock peening

Through the combination of simulation and experiment, this paper explored the direct relationship between laser energy and surface nanocrystallization of E690 high strength steel, and analyzed the indirect relationship between surface residual compressive stress and surface nanocrystallization. The experimental and simulation results showed that when the laser energy reached 10J, grain refinement occurred on the surface of E690 high strength steel, and the maximum residual compressive stress appeared on the sub surface of the material. At the same time, with the increase of laser energy, violent vibration and extrusion occurred between lattices, resulting in a certain micro thermal effect and inducing the climbing of screw dislocations. Therefore, there was a qualitative relationship between the surface nanocrystallization of E690 high strength steel after laser shock processing and the distribution of residual stress, that was, when the maximum residual stress appeared on the sub surface, the surface of material appeared nanocrystallization. This was because surface nanocrystallization consumed a lot of energy, which reduced the surface residual stress. This study was of great significance to predict the dislocation configuration changes of E690 high strength steel after laser shock processing.

Study on the Effects of Multiple Laser Shock Peening Treatments on the Electrochemical Corrosion Performance of Welded 316L Stainless Steel Joints

To study the influence of laser shock peening on the electrochemical corrosion resistance of welded 316L stainless steel joints, welded 316L stainless steel joints are treated with different laser shock peening treatments (i.e., one, two, and three times). Our analysis employs electron backscattering diffraction (EBSD), scanning electron microscopy (SEM), X-ray diffraction (XRD), an X-ray stress meter, and electrochemical corrosion tests to observe and analyze the microstructure, structural composition, residual stress, and corrosion resistance in different areas of the surface of 316L before and after the laser shock peening. The results show that the residual stress distribution of the welded joints is optimized after laser shock peening, with a maximum residual compressive stress near the matrix of 171 MPa. When the number of laser shock peening treatments is two, the corrosion current reaches a minimum of 9.684×10−7 A/cm2, and optimal pitting resistance is obtained. However, when the number of laser shock peening treatments is further increased to three, the corrosion current increase and the pitting resistance decreases. In summary, the electrochemical corrosion resistance of the welded joints effectively improves after laser shock peening, but its performance begins to decline after three repeated shocks, which is related to the combined effects of stress change and microstructure phase transformation.

Surface integrity and transmission performance of spiral bevel gears subjected to shot peening: A comparison between concave and convex surfaces

As a typical surface strengthening method, shot peening can effectively enhance the bending fatigue resistance of spiral bevel gears by improving the surface integrity parameters. Due to the complex geometry of spiral bevel gears, one group of shot-peening parameters can hardly satisfy the performance requirements of concave and convex surfaces. Thus, the effect mechanism of shot peening on both surfaces needs a thorough understanding. Meanwhile, the effect of shot peening on the transmission performance of gears is still somewhat cloudy and controversial, which confuses the optimization of shot-peening parameters. To address this issue, the effect of shot peening on the surface integrity and transmission performance of spiral bevel gears is systematically investigated by experiments. The results show that due to the smaller curvature radius, the surface integrity of the concave surface is better than that of the convex surface before and after shot peening. Specifically, for the shot-peened gears, the dislocation density at the concave surface is 9.1 % higher than that at the convex surface; the intergranular oxidation (IGO) layer for the concave surface is 2.1 % shallower than that for the convex surface; the maximum compressive residual stress for the concave surface in the profile direction is 6.9 % higher than that for the convex surface; the peak value of hardness for the concave surface is 3.5 % higher than that for the convex surface. Furthermore, smoother tooth flanks can lead to better transmission performance of gears, and shot peening has side effects on it. The transmission performance in the drive condition is better than that in the coast condition before and after shot peening.

Improved corrosion resistance of Ni-base Alloy 600 welded joint by laser shock peening

Stress corrosion cracking (SCC) of welded joint is one of the salient problems influencing the safety of nuclear power structure. In this work, laser shock peening (LSP) was introduced to enhance the corrosion resistance of Ni-base Alloy 600 welded joint. The corrosion behavior was evaluated by electrochemical corrosion and SCC tests, and its anti-corrosion mechanism was analyzed in terms of the residual stress and microstructure evolution. The results indicate that LSP treatment could significantly reduce the electrochemical corrosion rate and SCC sensibility of the weldments by 81 % and 14 %, respectively. The enhanced corrosion resistance of the welded joint was attributed to the compressive residual stress and high-density dislocation tangles induced by LSP. The maximum compressive residual stress of ~460 MPa in weld zone could be obtained with the laser power of 25 J. The microstructure evolution of LSP for weld zone and base metal is dominated by the dislocation activities.

Effect of multiple laser peening on microstructural, fatigue and fretting-wear behaviour of austenitic stainless steel

The present work investigates the influence of laser peening without coating (LPwC) on the fatigue and fretting wear behaviour of AISI 304 alloy subjected to one and five peening passes peened at 9 GW cm−2. Laser peened samples were characterised for microstructure, residual stress, phase evolution and hardness. After LPwC, the samples induced maximum compressive residual stress of −380 and −581 MPa for one and five peening passes at 50 μm from the surface. Microhardness was increased to 31 % and 71 % for one and five pass samples at 50 μm depth. The microstructure of laser peening samples was characterised using a transmission electron microscope (TEM) and electron backscattered diffraction (EBSD). Dislocation density was increased after peening with twin-twin interaction observed in both the peening cases and martensite induced at the junction of the twin-twin in five-time peened samples. Low angle grain fraction increased from 29 % (unpeened) to 41 % (one pass) and 63 % (five passes), and grain refinement was observed, where the average grain size reduced from 22.28 μm (unpeened) to 18.36 μm (one pass) and 9.51 μm (five passes) for LPwC samples. Fretting wear behaviour at various loading (5, 10 and 20 N) displayed significant improvement in wear resistance of LPwC samples, as evident from lower wear volume loss. Fatigue testing performed at R = 0.1 exhibited an improvement in fatigue life of 1.4 and 2.4 times for one and five pass samples compared to unpeened samples at a stress amplitude of 450 MPa. Fatigue fractography revealed a decrease in striation spacing for LPwC samples (979 nm/cycle and 565 nm/cycle for one- and five-time peening) with a delay in crack-propagation rate.

Analytical model of residual stress in ultrasonic rolling of 7075 aluminum alloy

Ultrasonic rolling produces large values of residual compressive stress (RCS) in the surface layer of metal part, thereby significantly enhancing the fatigue resistance of the part. Ultrasonic rolling is a complex elastic-plastic deformation process, and it is difficult to accurately predict the residual stress produced by ultrasonic rolling. 7075 aluminum alloy was processed in this work. The elastic-plastic deformation caused by “loading-unloading” during ultrasonic rolling was analyzed based on Hertzian theory and elastic-plastic deformation theory. The residual stress model of ultrasonic rolling was developed by considering the effects of initial surface residual stress and plastic indentation depth. Finally, the model was verified by experiments. The numerical analysis results show that the surface RCS, the value and depth of the maximum RCS and thickness of the RCS layer increase to different degrees with the increment of the static load, the amplitude and the roller radius. The trend of the experimentally obtained surface RCS value with static load is consistent with that of the numerical calculations. The surface RCS increase with the increasing of the static load. The maximum error between the calculated RCS and the experimental result is no more than 10 %. The proposed residual stress model in ultrasonic rolling is relatively reliable.

Research on the Residual Stress of the Machined Surface of Cutting Superalloy under High Pressure Cooling

High pressure cooling assisted cutting has certain advantages in cutting difficult materials such as superalloy. Therefore, the residual stress on the machined surface of superalloy is studied with the application background of high pressure cooling cutting. Firstly, the formation mechanism of the machined surface residual stress was analyzed. Then, the influence mechanism of high pressure coolant on the residual stress of machined surface was studied. Finally, it is concluded that the maximum residual compressive stress in cutting depth direction of cutting superalloy under high pressure cooling should be less than that of dry cutting by theoretical analysis and experimental research.

Analysis of shot peening residual stress distribution based on dislocation configuration

The distribution profile of residual stress on the surface layer of shot-peened materials is often in a hook shape. We analysed the distribution characteristics of residual stress by detecting dislocation configurations. The position of maximum compressive residual stress (MCRS) shifts inward with an increase in shot peening strength. It was found that long-term orderly dislocation pile-up groups frequently appeared in the MCRS region. The location of MCRS is not necessarily related to maximum dislocation density. At low strength, both the maximum dislocation density and the MCRS are on the surface region. At high strength, the surface region structures are composed of sub-grains and dislocation cells. The position of maximum dislocation density is between the surface region and the MCRS.

Strengthening Performance Optimization of Single Ball Impact Treatment by Evaluating Residual Stress.

Residual stress plays an essential role in affecting the strengthening performance by a surface treatment. Studying the impact of a single ball on a target surface is the basis of shot peening technology in order to obtain the distribution of the residual stress, and to optimize the processing parameters. In this paper, a numerical model has been developed to represent single ball impacts on high manganese steel by considering different processing parameters. It was found that by increasing the ball diameter and impact velocity, the depth of maximum residual compressive stress and the depth of the residual compressive stress layer became significantly enlarged due to increasing kinetic energy of the impacting ball. It was also found from simulation that with an increase in ball impact angle, the maximum residual compressive stress, the depth of maximum residual compressive stress and the depth of the residual compressive stress layer were significantly improved; an exception was the surface residual compressive stress, which showed a decreasing trend. Moreover, by employing quantitative analysis with the entropy method, it was found that within the range of processing parameters considered in the simulation, it is recommended to use a ball with a diameter of 0.6 mm to impact the target, with a velocity of 80 m/s and an angle of 90° for the best strengthening performance.

Effect of Mechanical Shock Treatment on Microstructure and Corrosion Properties of Manual Argon Arc Welding Joints of 2205 Duplex Stainless Steel.

Pneumatic chipping hammer and ultrasonic impact peening were used to relieve the welding residual stress of 2205 duplex stainless steel by manual argon arc welding, and the influences of these mechanical shock treatment technologies on the residual stress, microstructure, and corro-sion resistance of the welding seam were studied. Results showed that after pneumatic chipping hammer or ultrasonic impact peening, a small amount of plastic deformation occurred in the welded joint of 2205 duplex stainless steel, which led to an increase in the dislocation density in the microstructure. Meanwhile, the stress state of the welded joint changed from the residual tensile stress to the residual compressive stress. The maximum residual compressive stress could reach −579 MPa. The combined action of the two effectively improved the corrosion resistance of the welded joint. Among them, the best overall effect was the ultrasonic impact peening tech-nology.