Maximum Compressive Residual Stress Research Articles

Gradient nanostructure enabled exceptional fretting fatigue properties of Inconel 718 superalloy through submerged abrasive waterjet peening

Submerged Abrasive Waterjet Peening (SAWJP) shows great application potential in augmenting the fatigue properties of metallic parts. Thus, the present work aims to investigate the influence of SAWJP on the Surface Integrity (SI) and Fretting Fatigue (FF) properties of Inconel 718 (IN718) superalloy and illustrate the microstructural evolution, FF life improvement, and fretting wear mechanism. First, the SI of the IN718 specimen was examined following treatment via SAWJP. Results showed that the specimen subjected to SAWJP formed a total plastic deformation layer of 56 μm. The maximum microhardness and Compressive Residual Stress (CRS) measured across the depth of the SAWJP-treated specimens exhibited an increase in values ranging between 522 and 541 HV and 1171–1380 MPa, respectively. The FF test results of the specimen before and after SAWJP treatment at ambient temperatures indicated that the FF life of the SAWJP-treated specimen surpassed that of the as-received specimen by a factor of 2.81. The examination of the FF fracture, contact surface, and crack propagation behavior revealed the crucial factors contributing to the enhanced FF resistance of the IN718 specimen, including the gradient nanostructure characterized by ultra-refined grains, substantial CRS, and elevated microhardness, which were all induced by the SAWJP treatment.

Study on the fatigue performance and Residual Stress of subsurface fluid flow of 2519a aluminum alloy based on water jet peening

In this study, the influence mechanism of water jet (WJ) strengthening on the surface integrity and fatigue properties of 2519 aluminum alloy was investigated by using finite element software Abaqus 2023 and fatigue analysis software Fe-safe. The effects of jet velocity and transverse velocity on the development of surface roughness and residual stress in different strengthening stages were studied, and the fatigue properties of WJ strengthened samples were analyzed by Fe-safe fatigue software. Finally, the fatigue life and fracture morphology of WJ strengthened specimens were analyzed by fatigue test, and the accuracy of finite element analysis was verified. Results indicate that surface roughness post-WJ enhancement displays a “W” shaped distribution, positively correlated with jet velocity. Conversely, increased roughness negatively correlates with higher traverse speeds, with optimal values recorded between 400 and 600 mm/min at WJ-290 mm/s, ranging from 1.10322 to 1.41167 μm. Additionally, the study reveals that maximum residual compressive stress during the WJ-Ip phase correlates positively with jet velocity, peaking at 302 MPa for WJ-290 mm/s. The research also notes that while higher jet velocities enhance residual compressive stress, they simultaneously elevate surface roughness, potentially introducing damage and increasing the variability of stress magnitudes. The study underscores the necessity of meticulously calibrating WJ parameters to enhance surface quality effectively while minimizing adverse effects. This balance is critical to optimizing the treatment process and achieving desired material properties.

Effect of continuous and random multi-particle impaction on the aluminum coating and copper substrate in cold spraying

In this study, the process of multi-particle cold spraying has been numerically simulated and compared with the actual cold spraying results. The results show that in the continuous multi-particle models, the maximum depths of compressive residual stress reached 4.90 μm, 3.99 μm, 4.78 μm, and 5.19 μm for each increment in particle number. The penetration depth of residual stress increases then decreases, due to two opposite factors effects on the penetration depth of residual stress. the maximum compressive residual stresses on the substrate are 438.14 MPa, 293.57 MPa, 286.19 MPa, and 279.30 MPa respectively, declining as the number of impacting particles grows. With the subsequent deposition of particles, the further deformation of the substrate causes the stress on the side to gradually homogenize, and the peak value decreases. Surface stress of the workpiece alleviates after multiple Al particles impact Cu substrate. In all random multi-particle models of different gas pressure, the residual stress begins to disappear at about 100 μm from the surface, and basically disappear at about 300 μm. As the collision speed of particles increases, the substrate deformation increases, but the growth rate of deformation decreases. The influence of coating thickness on the substrate deformation gradually decreases with the increase of coating thickness.

Fatigue performance of a fastener hole treated by a novel electromagnetic strengthening process

In this study, a novel non-contacting electromagnetic cold expansion process was proposed to improve the fatigue performance of hole component using a single power supply and a single coil. The stress state and deformation of the 6063-T6 aluminum alloy hole component during the electromagnetic strengthening process were investigated through numerical simulation. The residual stress around the hole edge was measured using XRD. Fatigue testing was performed to verify the effectiveness of the process on improving the fatigue life of the hole component. Results showed that the proposed electromagnetic strengthening process could effectively improve the fatigue life of the hole component. Fatigue life of the specimen via electromagnetic treatment is 3.42 times of that of the original specimen at a maximum stress of 120 MPa. Simulation results indicated that the generation of compressive residual stress was attributed to the falling stage of the pulse current, and the maximum compressive residual stress was −102 MPa.

Effect of laser shock peening on tribological properties of 55SiMoVA bearing steel

Wear is an important factor limiting the service life of 55SiMoVA bearing steel. In this work, laser shock peening (LSP) technology is used to improve the tribological properties of 55SiMoVA bearing steel, and the corresponding underlying mechanism is systematically discussed. After LSP, the kurtosis (Sku) of surface roughness asperities reduced from 10.355 to 5.488, and no new phase was generated. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) analysis suggested LSP induced the generation of dislocation structures and deformation twins, leading to a decrease in the average grain size and an increase in the fraction of high-angle grain boundaries. Due to the work-hardening and fine-grain strengthening, the microhardness increased by 16.6 %, the maximum residual compressive stress amounted to −793.1 MPa, and the coefficient of friction (COF) and wear volume were significantly reduced. Scanning electron microscopy (SEM) results indicated that the wear mechanism of 55SiMoVA bearing steel before and after LSP was not transformed. However, the abrasive wear and delamination wear of the LSPed specimens were significantly improved, which was mainly attributed to grain refinement, increasing microhardness and constructing a residual compressive stress layer in the subsurface layer of 55SiMoVA bearing steel. During the sliding process, the increase in microhardness limits micro-plowing on the wear surface, and the residual compressive stress inhibits the crack formation and expansion, improving the wear resistance of 55SiMoVA bearing steel.

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.

Surface integrity and fatigue performance of Ti6Al4V alloy peened by sinking bead abrasive jet

Exploring a green, low-cost peening process to improve the surface integrity of titanium alloys, increasing fatigue life, and breaking through the limitations in large-scale applications is an urgent need at present. The study presents a novel peening method using sinking beads as the shot, combined with the low dust pollution and water film cushioning advantages of waterjet peening. The impact of the process on the surface integrity of titanium alloys is meticulously discussed to elucidate the microstructural evolution. Constant stress fatigue tests are performed to evaluate the effectiveness of the proposed method. It was found that the jet pressure and feed rate determined the energy density and the number of peening for sinking bead abrasives, which were the key factors affecting the surface material properties of the peening specimen. By optimizing the process parameters, the maximum surface residual compressive stress can reach 875.5 MPa, the microhardness can attain 481.7 HV, and the surface roughness can be reduced to 1.594 μm. The surface of the peened specimen is covered with impact craters, exhibiting a plastic deformation layer with evident grain refinement and lattice distortion. The ductility of the peened specimen decreased, with axial deformation reducing from 0.278 mm to 0.260 mm under constant cyclic stress. Due to the increase in microhardness and the introduction of residual compressive stresses, the fatigue cycles of the specimen were increased from 20692 to 33615, improving the fatigue life by 62.45%.

Interpass temperature strategies for compressive residual stresses in cladding low-transformation-temperature material 16Cr8Ni via wire arc additive manufacturing

Low-transformation-temperature (LTT) materials induce compressive residual stresses within an effective depth in wire arc additive manufacturing (WAAM), which is well suited for cladding applications. However, this role was found to be sensitive to the phase transformation sequence. We developed an LTT material—16Cr8Ni (16Cr8Ni-LTT)—and to explore its potential, it was clad onto a KA36 substrate via WAAM. Three different interpass temperature strategies were designed as follows: (1) no interpass temperature control; (2) interpass temperature controlled at approximately 270 °C above the martensite transformation start temperature (Ms = 200 °C) for simultaneous phase transformation; and (3) interpass temperature controlled at approximately 50 °C below the martensite transformation finish temperature (Mf = 60 °C) for sequential phase transformation. A thermal elastic-plastic numerical model considering the phase transformation-induced plasticity (TRIP) was developed using in-house software, JWRAIN-Hybrid, to reproduce the temperature field and residual stresses of 16Cr8Ni-LTT cladding. X-ray diffraction (XRD) and contour methods were employed for residual stress measurements. The high accuracy of the model was validated in terms of the temperature, deformation, and residual stress. The reproduced maximum historical temperature distributions were combined with hardness tests to identify the depths and temperatures of the heat-affected zone (HAZ). The measured maximum compressive residual stresses induced by the three interpass temperature strategies for cladding 16Cr8Ni-LTT were −503, −420, and −720 MPa. Moreover, irrespective of the adopted interpass temperature strategy, both longitudinal and transverse residual stresses were compressive in the 16Cr8Ni-LTT cladding. This study provides scientific insights into LLT-induced compressive residual stresses and highlights the superiority and flexibility of cladding LTT materials via WAAM for improving the resistance of large metal components to fatigue and corrosion.

Effect of power density on microstructure characterization and fatigue behavior of laser shock peened Rene-80 Ni-based superalloy

The microstructure plays a crucial role in determining the mechanical properties and performance of materials, particularly in high-strength alloys such as Rene-80. This study focuses on the microstructure characterization of Rene-80 nickel-based superalloy after undergoing Laser Shock Peening (LSP), an advanced surface treatment technique imparting beneficial residual stresses and improving fatigue life. The primary objective of this research is to investigate how varying power densities during the LSP process affect the microstructure of the Rene-80 superalloy. The power density in LSP is a critical parameter that influences the intensity of shock waves imparted onto the material’s surface, consequently impacting the microstructure. Through advanced microscopy techniques and analysis, the study explores the resulting microstructural changes, including surface roughness, dislocation density, and the presence of defects like dislocations and dislocation cells. These alterations are vital indicators of the material’s mechanical properties, such as tensile and fatigue strength. LSP samples were characterized using various techniques, including field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) analysis. Additionally, the mechanical performance of the samples was assessed through low-cycle fatigue tests and tensile tests, both conducted before and after LSP treatment. The optimal power density for Laser Shock Peening is determined to be 2.5 HEL. At this power density, the shock wave generated does not create a molten layer on the surface but accumulates defects, resulting in maximum compressive residual stress at the surface. LSP induces intense plastic deformation in the sample, distorting γ’ precipitates. Higher power densities lead to the formation of cross-linked sets of slip bands, highlighting defect slip as the main mechanism of plastic deformation in the LSP process. Understanding these effects is essential for optimizing the LSP process parameters to achieve desired mechanical properties and enhance the performance and longevity of components made from Rene-80 nickel-based superalloy in high-stress applications. It was found that the fatigue life of the samples increased by 500% and optimizing the effect of power density on the LSP process led to an improvement in the fatigue life of the Rene 80 samples.

Evidence of microstructural evolution linked to non-monotonic distribution of micromechanical properties induced by shot peening

The residual stress field induced by surface strengthening processes such as mechanical shot peening and other forms of plastic deformation does not generally exhibit a simple “monotonic” distribution trend. Some researchers have analyzed this fact from a mechanical perspective based on Hertz theory. However, the micro/nano-scale microstructural changes corresponding to the distribution of residual stress fields still appear to be lacking. In this study, we focused on a widely used material in aviation manufacturing, namely nickel-based superalloy GH4169, as our experimental material. We subjected GH4169 alloy to mechanical strengthening treatment using a shot peening intensity of 0.25 mmA, followed by quantitative testing of micromechanical performance indicators such as microhardness and residual stress. To thoroughly investigate the relationship between micromechanical properties and microstructure changes, we utilized transmission electron microscopy (TEM) to observe and analyze shot-peened materials at different depths. Our findings revealed that the most severe microstructural distortion induced by mechanical shot peening in GH4169 alloy was likely to occur within a depth range of 25 to 75 µm. This observation aligns with the actual phenomenon that the maximum microhardness and maximum residual compressive stress did not manifest on the outermost surface of the material. By presenting a detailed analysis of deformation defects such as dislocations, stacking faults, and twinning in different depths of mechanically strengthened layers, our study contributes to a deeper understanding and practical application of post-processing technologies based on plastic deformation.

Effect of multifunction cavitation on microstructure and plane bending fatigue properties of low-alloy steel

Multifunction cavitation (MFC) has potential as an environmentally friendly surface-modification method. In the present study, the modified surface layer and the fatigue properties for MFC-processed low-alloy steel were investigated. When the processing time was longer than 2 min, the surface roughness increased and the surface potential decreased. The maximum compressive residual stress was induced after a processing time of 2 min, and decreased for longer processing times. Electron backscatter diffraction analysis of a cross section of a sample subjected to MFC for 30 min showed that the modified layer was thicker than that for samples processed for shorter times. The fatigue life at high cycle numbers increased for the specimens processed by MFC under the conditions corresponding to the greatest compressive residual stress. MFC processing was shown to be effective in improving the fatigue properties of steel, and therefore has potential as a next-generation surface-modification method.

Composite effects of residual stress and hardness gradient on contact fatigue performance of rough tooth surfaces and optimization design of detailed characteristic parameters

Residual stress and hardness gradient significantly affect the contact fatigue failure process of rough tooth surfaces, and the meticulous design of their characteristic parameters can help improve the fatigue resistance of gears. In this paper, an efficient computational method for rough tooth surface contact is established based on the reconstruction modeling of asperities and mixed lubrication analysis. By comprehensively considering the effects of residual stress and hardness gradient, the Dangvan multiaxial fatigue criterion is adopted to predict and analyze the contact fatigue life of the gear surface. The correlation between the surface residual stress, maximum residual stress depth, surface hardness, and effective hardening layer depth, among other characteristic parameters, and the contact fatigue performance of tooth surfaces is established. The results show that: (1) Increasing the magnitude of surface residual compressive stress and surface hardness can significantly reduce the risk of fatigue failure in the near-surface layer of the gear. To achieve the same fatigue performance, there is a linear negative correlation between the design values of the two parameters. (2) Affected by the double stress peaks in the rough tooth surface stress field, the maximum residual stress depth significantly affects the depth at which the highest failure risk occurs. With changes in roughness, the optimal design value of the maximum residual compressive stress depth changes from about 0.5 times the Hertzian contact half-width depth in the subsurface layer (Sa < 0.2 μm) to about 15 μm in the near-surface layer (Sa > 0.4 μm). (3) Considering both process cost and gear surface fatigue resistance, the design threshold for the effective hardening layer depth should be greater than the Hertzian contact half-width. This paper establishes a composite correlation between the meticulous characteristic parameters of residual stress, hardness gradient, and the contact fatigue performance of tooth surfaces, providing theoretical support for optimal design of tooth surface anti-fatigue performance.

Comparison of the effects of induction heating composite shot peening and conventional shot peening on residual stress, microhardness, and microstructure of 20CrMnTi gear steel

As a commonly used surface strengthening technology, shot peening, which can significantly improve the fatigue strength of mechanical parts, is widely used in the fields of vehicles and aviation. To obtain a larger residual compressive stress and further refine the grain size under normal shot peening intensity and coverage, this study proposes an induction heating composite shot peening (IHCSP) surface strengthening method, aiming to utilize the coupling effect of temperature and stress fields to promote the shot peening strengthening effect. An IHCSP test plan was designed and an IHCSP test bench was created to achieve simultaneous induction heating and shot peening. This study compares the surface integrity parameters and microstructures under three processes: un-peened, conventional shot peening, and IHCSP. The results show that the maximum axial and radial compressive residual stresses increase by 72.41 and 75.4 MPa respectively; the depth of the hardened layer increases by 0.3 mm, the martensitic transformation more complete, the grain size decreases by 483 nm, the dislocation density increases significantly, and nanocrystals are obtained on the surface of the material. These results verify the superiority of IHCSP surface strengthening.

Hybrid modeling prediction of residual stresses in turned Ti6Al4V considering frictional contact

Residual stress plays a pivotal role in assessing the surface quality of machined components, influencing characteristics such as fatigue performance, corrosion resistance, and mechanical strength. Ti6Al4V, a critical material in the nuclear sector, the generation of residual stresses during machining has attracted significant attention. A model for variable friction coefficient model is proposed to accurately characterize the complex plastic deformation behavior of the material. This model takes into account variables such as the relative sliding velocity, contact pressure, and temperature. A subroutine has been developed using the VFRIC interface to enhance precise cutting simulation and modeling. Using the friction model, a new hybrid prediction model for surface residual stresses is developed by integrating finite element analysis and analytical methods. The reliability of both the hybrid and friction models is confirmed through the evaluation of cutting forces, chip morphology, and residual stress. The findings suggest that the novel friction model produces simulation results with higher accuracy compared to traditional Coulomb friction models. The variations in cutting force amount to 5.8% and 13.7%, the error in chip serration is 12.4%, and the deviation in predicting the maximum residual compressive stress is 10.3%. This study contributes to the advancement of friction models and methodologies used in predicting residual stress.

Study on CFRP-Strengthened Welded Steel Plates with Inclined Welds Considering Welding Residual Stress.

Welded steel plates are widely used in various structural applications, and the presence of inclined welds is often encountered in practical scenarios. Carbon fiber reinforced polymer (CFRP) has been proven to be effective for strengthening steel structures. However, the behavior of CFRP-strengthened welded steel plates with inclined welds, particularly considering the influence of welding residual stress, is limited. This paper aims to investigate the tensile behavior of CFRP-strengthened welded Q355 steel plates with inclined welds considering welding residual stress (WRS). First, WRS data were obtained by the X-ray diffraction (XRD) method at different locations. The maximum tensile and compressive residual stresses are 0.39 and 0.14 times the yield strength of the steel, respectively. Then, finite element models were established to investigate the effects of weld angles, weld width, and height on the WRS distribution of welded steel plates. Finally, the tensile performance of CFRP-strengthened welded plates with WRS was studied by numerical simulation. The results showed that the weld angles have little effect on the distribution pattern of residual stress but significantly affect the peak tensile WRS. When the weld angle changes from 0° to 60°, the peak tensile WRS decreases significantly from 0.32 to 0.06 times the yield strength of steel; furthermore, the influence of weld width and height on WRS is relatively limited. Under tension loading, the maximum stress occurs near the weld. The ends of the weld enter the yielding state later than the middle part of the weld due to the distribution of the WRS. As the weld angle increases and the length of the weld increases, the stress in the weld zone decreases, while the stress in the base material zone correspondingly increases. In addition, CFRP strengthening can reduce the magnitude of stress. This study provides preliminary references for understanding the tensile behavior of CFRP-strengthened welded steel plates with inclined welds.

A comprehensive study on the effects of surface post-processing on fatigue performance of additively manufactured AlSi10Mg: An augmented machine learning perspective on experimental observations

In this study, the efficacy of 21 distinct surface post-processing methods on the fatigue behavior of an additively manufactured (AM) material was investigated. Various treatments, encompassing single-step processes like sand blasting (SB), conventional shot peening (CSP), severe shot peening (SSP), gradient severe shot peening (GSSP), ultrasonic shot peening (USP), severe vibratory peening (SVP), ultrasonic nanocrystal surface modification (UNSM), laser shock peening (LSP), laser polishing (LP), tumble finishing (TF), chemical polishing (CP), electro-chemical polishing (ECP), and machining (M), as well as hybrid treatments, were systematically investigated for their impact on the fatigue behavior of hourglass laser powder based fused (LB-PBF) AlSi10Mg specimens. A comprehensive series of experimental tests were carried out, covering surface texture analyses, microstructural characterizations, porosity measurements, hardness, residual stresses (RS), monotonic tensile tests, and rotating bending fatigue tests at four stress levels. Following the experimental investigations, the acquired data were leveraged to develop a machine learning (ML)-based model to correlate the fatigue life with the influencing factors and conduct parametric and sensitivity analyses. The model utilized a deep learning approach to predict the fatigue response of LB-PBF AlSi10Mg, incorporating various artificial neural networks (ANNs) and considering input parameters such as yield strength, ultimate tensile strength, elongation to fracture, porosity, depth of pore closure, surface hardness, depth of hardness variation, surface RS, maximum compressive residual stresses (CRS), depth of the CRS field, top surface grain size, surface layer mean grain size, surface roughness, and stress amplitude. Depending on the life regime, the factors influencing fatigue behavior can vary significantly. In higher stresses, dominated by plastic strains, surface residual stress emerges as the primary factor. Conversely, in lower stresses, dominated by elastic strains, the significance of surface roughness becomes more pronounced, followed by surface residual stress, surface hardness and other factors. These findings underscore the contextual importance of different influencing factors for enhancing fatigue resistance based on varying loading conditions.

Reliability evaluation for shot-peening conditions affecting durability life of automotive suspension coil springs

Shot peening (SP) is a cold working method used to improve the fatigue life and corrosion resistance of metallic materials subjected to repeated loading. However, optimal SP conditions can only be found through experiments with actual operating parts. In addition, studies on the effective SP conditions and ensuring safety for improving the durability of parts are lacking. In this study, SP of various conditions were applied to automobile suspension coil springs (ASCS). Consequently, the process factors, damage assessment, and microstructure were analyzed to determine the factors that exerted a dominant effect on durability life. The durability life of springs applied with stress SP (SSP) was evaluated to be approximately 3.8–4.8 times higher compared to that of springs applied with other SP conditions. In addition, by analyzing the process factors affecting the durability life, the absence of a direct effect of the arc height and Vickers hardness was observed. Moreover, the effect of surface roughness was observed to be small. However, the durability life in response to the change in maximum compressive residual stress (MCRS) exhibited a tendency to change linearly, and this relationship was expressed in an equation through regression analysis. The fracture surface of spring with a high durability life tended to have a large number of spiral shapes, and that of spring with a low durability life tended to have a large number of flat shapes. Before conducting the durability test, a circumferential metal flow was observed in the work-hardened layer below the spring surface upon shot peening. After conducting the durability test, partial crack initiation and propagation and delamination were observed in these areas. Despite the varying SP conditions, the surface microstructure of each spring was observed to be similar before and after the durability test. In this study, it was confirmed that SSP is the most effective method to improve the durability life of ASCS, and it was possible to understand through damage evaluation and microstructure analysis that MCRS affects the durability life by delaying the initiation of cracks in the spring. The analysis method and results of this study are expected to be useful for improving the reliability of not only ASCS but also SP-applied components in the future.

Effect of process parameters on residual stresses in SLM-formed bionic porous titanium alloy structures

Bionic porous titanium alloy structures have demonstrated broad application prospects in the field of biomedicine, and selective laser melting (SLM) has become one of the main methods for preparing porous titanium alloy structures due to its high degree of forming freedom. Residual stress is a crucial indicator for evaluating the forming quality of SLM parts, thus its control methods have garnered significant attention. Therefore, it is important to understand the process parameters' influence on the generation and regulation of residual stresses in SLM-formed bionic porous titanium alloy parts. In this paper, finite elements and experiments are employed to research the relationship between process parameters and residual stresses in the SLM process, and a method for controlling residual stresses in the key sensitive areas is proposed. It is found that increasing the laser scanning speed is conducive to reducing the residual stress of the porous structure and alleviating the phenomenon of stress concentration. Appropriately increasing the laser power can reduce the residual stress in the Z direction of the porous structure, with the optimal range being from 200 W to 250 W. Using a medium laying powder thickness (0.03 mm∼0.04 mm) results in uniformly distributed residual stress on the surface of the porous structure, leading to the attainment of maximum residual compressive stress. Building upon this foundation, the experimental verification of forming quality established stability, while the derived parameter optimization method and forming mechanism offered theoretical support for process optimization in fabricating porous titanium alloy structures through SLM.

Effect of surface strengthening by ultrasonic shot peening on TC17 alloy

This paper investigates the effects of ultrasonic shot peening (USP) on surface morphology, microstructure, and residual stress field distribution of TC17 alloy under different process parameters. The aim is to reveal the surface strengthening mechanism of TC17 alloy caused by USP. The results suggest that the use of the 2.5 mm projectile diameter leads to an increase in surface roughness, plastic deformation, and a deeper grain refinement layer compared to the 1.5 mm projectile diameter. Additionally, it results in a greater depth of the compressive residual stress layer and maximum compressive residual stress. The crack initiation sites under two projectile diameters are located below the compressive residual stress layer. The USP treatment introduces compressive residual stress on the surface, inhibiting the initiation of surface cracks, and the deeper compressive residual stress layer offsets the early fatigue failure caused by higher roughness.

Modelling and researching the evolution of stress during arc-directed energy deposition (ADED) hybrid inter-layer hammering

ABSTRACT Hybrid manufacturing of arc-directed energy deposition (ADED) and inter-layer hammering can build components with low detrimental residual stress (RS) and warping. Inter-layer hammering with lower load demand has proved to be a promising technology to improve the microstructure and mechanical properties. In this paper, a finite element model of the ADED hybrid inter-layer hammering was constructed for the first time. The accuracy of the model is evaluated by comparing thermal history, RS, and warping. The results show that the maximum compressive RS -25Mpa appears at 3 mm from the top of the wall after a single inter-layer hammering. The RS of the inspection position is reduced by 74.6% after six layers of hammering compared with the wall manufactured by ADED alone, and low-stress distribution with a value of -30Mpa appears in the range of 7 mm to 15 mm from the substrate surface. The warping of the wall in the building direction was completely suppressed (from 0.21 mm to 0 mm). In addition, the plastic strain introduced by the hammering at the wall top exacerbates the “misfit” between the regions of the wall top, resulting in tensile stress at the wall top.