Effect Of Residual Stress Research Articles

Effect of Surface Roughness and Compressive Residual Stress on the Fatigue Performance of TC4 Titanium Alloy Subjected to Laser Shock Wave Planishing

ABSTRACTThe milled surface of TC4 titanium alloy was treated by laser shock peening (LSP) and laser shock wave planishing (LSWP) to investigate the effect of compressive residual stress (CRS) and surface roughness (SR) on the vibration fatigue performance. The results demonstrate that although the amplitude of CRS induced by LSWP is lower than that of LSPed specimens, the vibration fatigue life of LSWPed specimens increased by 63.78% due to a significant reduction in SR from Sa 14.1 μm to Sa 4.21 μm. When the SR is low, increasing the amplitude of CRS is more advantageous to enhance fatigue life. The fractographic analysis further confirmed that compared with LSPed and T0.2‐LSWPed specimens, T0.1‐LSWPed specimens have considerably less initial fatigue crack initiation, and the crack initiation location is deeper. The fatigue striation spacing of T0.1‐LSWPed specimens is the smallest (0.25 μm), greatly lowering the fatigue crack growth rate.

Investigation of the influence of initial residual stress and toolpaths on milling deformation of titanium alloy

Titanium alloy structural components are widely used in the aerospace industry due to their excellent physical properties. However, their susceptibility to machining deformation during milling, attributed to the presence of initial residual stress, poses a significant challenge. Therefore, this paper proposes a finite element model for predicting milling deformation in Ti6Al4V titanium alloy structural parts, considering initial residual stress. The methodology involves establishing the initial residual stress field of titanium alloy components based on a mathematical model of annealing heat transfer and a theoretical study of thermal elasto-plastic constitutive relation, with experimental confirmation of model accuracy. Based on the initial residual stress, a finite element model was developed to predict the maximum deformation under different toolpaths. Finally, a comparative analysis with milling experiments validated the proposed models. The experimental results demonstrated a remarkable alignment with the finite element model, showcasing the correctness of the developed models. The maximum deviation in deformation observed was within the range of 0.003 mm–0.011 mm. This study is the first to comprehensively consider the effects of initial residual stress and toolpaths on titanium alloy milling deformation, and to experimentally verify the proposed model’s accuracy and practicality. It provides a new theoretical basis and technical guidelines for titanium alloy milling deformation.

The effect of residual stress on the multi-step multi-point straightening with the three-dimensionally deformed linear guideway

The Multi-Step Multi-Point (MSMP) pressure straightening method is widely recognised for its effectiveness in manufacturing linear guideways. However, current theoretical analyses are limited to two-dimensional models, which oversimplify the complex nature of the straightening process. In reality, this process involves three-dimensional deformation and results in residual stress, adding complexity to the theoretical understanding of MSMP straightening. To address these challenges, this paper introduces an innovative MSMP straightening method specifically designed for three-dimensionally deformed linear guideways. It integrates both straightening and residual stress theories to thoroughly examine the impact of residual stress in various directions. Moreover, the paper develops a stroke-based straightening model that accounts for residual stress effects. Theoretical analyses are validated through comprehensive experiments, including bending and straightening tests. This research establishes a solid foundation for the study of pressure straightening three-dimensional deformed components.

Seismic design and analysis of truss‐confined buckling‐restrained braces

AbstractThe truss‐confined buckling‐restrained brace (TC‐BRB) with a varying or constant section truss confining system was proposed for applications of long span and large force capacities. Their feasibility and hysteresis behavior were examined through experimental investigations. This paper presents an original formulation of the elastic buckling resistance of the novel restraining system, considering the shear reduction effect. The findings indicate that the chord predominantly contributes to the flexural rigidity in the restraining system, while the post primarily contributes to the overall shear rigidity. Subsequently, the ultimate compressive strength of a TC‐BRB is evaluated, incorporating the effects of chord residual stress, length differences between the restrainer and entire brace, and initial in‐plane flexural deformation, based on available experimental data. A numerical procedure employing finite element model (FEM) analysis is introduced to simulate the mechanical characteristics of TC‐BRBs. The critical loads are verified through FEM analyses and test results. The failure mode observed in the numerical models is the instability of the chords near the midspan, as expected. A simplified approach for determining the ultimate compressive strength and design recommendations for TC‐BRBs are provided for engineering practice.

Effects of ultrasonic shot peening followed by surface mechanical rolling on mechanical properties and fatigue performance of 2024 aluminum alloy

Aiming to improve the mechanical properties and fatigue performance of 2024 aluminum alloy, the experimental investigations on composite treatment consisting of ultrasonic shot peening (USP) followed by surface mechanical rolling (SMR) were carried out. The experimental results were compared with the specimens only treated by USP or SMR in terms of surface roughness, microhardness gradient and microstructure observation. The uniaxial tension test and low cycle fatigue test were conducted on the as-received specimen and the ones treated by USP, SMR and USP/SMR composite treatment, respectively. The tensile mechanical properties were effectively improved by USP. The introduction of SMR following USP can significantly increase the number of cycles to failure. Combining fracture morphology analysis and DEM-FEM coupling simulation of USP/SMR composite treatment, it was concluded that the improvement of tensile mechanical properties is mainly attributed to the synergistic effect of the compressive residual stresses and gradient-structured layer produced by USP, and the decrease in surface roughness resulting from SMR is the main reason for the significant improvement of fatigue performance. This work could provide an insight into the surface strengthening mechanism for USP/SMR composite treatment of materials with respect to the improvement of mechanical properties and fatigue performance.

Nanoindentation creep response of Ti–6Al–4V ELI alloy manufactured via laser powder bed fusion

The anisotropic creep response in both the XY and XZ planes of Ti–6Al–4V ELI manufactured by powder bed fusion (PBF) was examined under nanoindentation creep loading at room temperature, ranging from nm to μm scales. The stress exponent values of 4.06–4.30, rationalised through threshold stress, indicate that the creep behaviour is primarily dominated by dislocation gliding. Creep displacement results show that the anisotropic creep behaviour in the XY and XZ planes of the as-built, and heat treatment enhances the creep resistance of the XZ plane, while there is no significant difference in creep displacement between the as-built and heat-treated XY planes. Due to the higher dislocation density and compressive residual stress in the XY plane compared to the XZ plane, the creep resistance is higher in the XY plane for the as-built. It is highlighted that compressive residual stress is more relieved in the XY plane than in the XZ plane through heat treatment. The heat treatment results in improved creep resistance due to the formation of the Widmanstätten structure and β precipitates, which can impede dislocation movement under creep loading. The combination of residual stress and microstructural effects leads to anisotropic creep behaviour, suggesting that the anisotropy is inherited from the additive manufacturing process at micron scales.

Effect of residual stress and microstructure on mechanical properties of sputter-grown Cu/W nanomultilayers

The combination of the high wear resistance and mechanical strength of W with the high thermal conductivity of Cu makes the Cu/W system an attractive candidate material for heat sinks in plasma experiments and for radiation tolerance applications. However, the resulting mechanical properties of multilayers and coatings strongly depend on the microstructure of the layers. In this work, the mechanical properties of Cu/W nanomultilayers with different densities of internal interfaces are systematically investigated for two opposite in-plane stress states and critically discussed in comparison with the literature. Atomistic simulations with the state-of-the-art neural network potential are used to explain the experimental findings of Young’s modulus and hardness. The results suggest that the microstructure, specifically the excess free volume associated with porosity and interface disorder interconnected with the stress state, has a great impact on the mechanical properties, notably Young’s modulus of Cu/W nanomultilayers.

Improvement of gradient microstructure and properties of wire-arc directed energy deposition titanium alloy via laser shock peening

Wire-arc directed energy deposition (WADED) technology has been widely used in the remanufacturing of titanium alloy structural components benefited from with the advantages such as high deposition efficiency and low cost. However, due to the coarse and anisotropic microstructure, the complex internal stresses and processing-induced rough surface significantly reduce fatigue performance and reliability of the remanufactured structural components. In this work, surface modification of titanium alloy WADED repair component was carried out via laser shock peening (LSP), and its gradient structure, microhardness, residual stress and fatigue performance and enhancement mechanism were systematically investigated. Results indicated that the different microstructure of each region led to different responses under the action of LSP, which was related to the change of dislocation density. LSP induced crystal defects such as high-density dislocations, twins and stacking faults on the surface. A variety of crystal defects gradually decreased with the depth from the strengthened surface, formed a gradient microstructure and significantly affected the microhardness and residual stress of the repaired components. The surface hardness and compressive residual stress of the repaired components were greatly increased after LSP and the hardened layer and compressive residual stress depth affected layer were 600 μm and 800 μm, respectively. The average fatigue life of the additive repair component increased by 197 % under the synergistic effect of compressive residual stress and gradient microstructure.

Influence of residual stress on the high-temperature tribological performance of nickel-based superalloy

This study introduces a method for generating residual compressive stress by utilizing differences in thermal expansion coefficients of materials. A corresponding experimental device has been developed. Using this method, experiments were conducted to investigate the effects of residual compressive stress on the tribological properties of the nickel-based superalloy Ni16Cr13Co4Mo. The results indicate that residual stress significantly affects the friction behavior and wear resistance of the superalloy. The stabilization time of the friction coefficient as well as the wear rate reaches a minimum under moderate residual compressive stresses. Moderate residual compressive stress can facilitate the formation of a tribo-oxide layer and enhance its bonding strength with the substrate, thereby shortening the time for stabilization of the friction coefficient and reducing the wear rate. Finite element simulation of static ball-on-disc contact model also shows that residual stress alters the internal stress distribution inside the alloy, and changes its yield and plastic behavior. Under moderate residual compressive stress, a reduction in maximum von Mises stress can be achieved, which is consistent with the variation rule of friction coefficient and wear rate in the tests.

The effect of residual mechanical stresses and vacancy defects on the diffusion expansion of the damaged layer during irradiation of BeO ceramics

The paper presents the results of a study on the application of Raman and UV spectroscopy methods to determine the structural damage kinetics in the near-surface layer of BeO ceramics caused by high-dose irradiation with He2+ ions. Interest in this type of ceramics is due to the combination of its structural and thermophysical parameters, making these ceramics one of the promising classes of materials for microelectronics and structural materials for nuclear reactors, with the possibility of operation in conditions of heightened radiation background. According to the conducted studies, it was established that with the irradiation fluence growth, changes in the nature of deformation structural distortions associated with the accumulation of residual mechanical stresses of tensile and compressive types are observed. At irradiation fluences of 1016-5×1016 Не2+/cm2, tensile stresses play a dominant role in structural distortions, while the value of compressive stresses at fluence growth makes up a small share in the overall nature of the deformations. Moreover, an elevation in the irradiation fluence above 5×1016 He2+/cm2 leads to a rise in the concentration of defects caused by the formation of oxygen vacancies, as well as He-VO type complexes, the presence of which is indicated by the halo intensity growth in the Raman spectra, as well as a change in the intensity of the absorption bands. Analysis of changes in thermophysical parameters revealed that a rise in structural distortions associated with the accumulation of complex defects results in thermal conductivity reduction and a deterioration in heat transfer processes associated with partial amorphization of the damaged layer. Moreover, the established direct relationship between the value of residual mechanical stresses and the degradation of thermal conductivity indicates the cumulative effect of destructive changes caused by irradiation, as well as the influence of diffusion mechanisms on the damaged layer thickness growth.

Effect of Residual Stresses on the Fatigue Stress Range of a Pre-Deformed Stainless Steel AISI 316L Exposed to Combined Loading

AISI 316L austenitic stainless steel is utilized in various processing industries, due to its abrasion resistance, corrosion resistance, and excellent properties over a wide temperature range. The physical and mechanical properties of a material change during the manufacturing process and plastic deformation, e.g., bending. During the combined tensile and bending loading of a structural component, the stress state changes due to the residual stresses and the loading range. To characterize the component’s stress state, the billet was bent to induce residual stress, but a phase transformation to martensite also occurred. The bent billet was subjected to combined tensile–bending and fatigue loading. The experimentally measured the load vs. displacement of the bent billet was compared with the numerical simulations. The results showed that during fatigue loading of the bent billet, both the initial stress state at the critical point and the stress state during the dynamic loading itself must be considered. Analysis was demonstrated only for one single critical point on the surface of the bent billet. The residual stresses due to the phase transformation of austenite to martensite affected the range and ratio of stress. The model for the stress–strain behaviour of the material was established by comparing the experimentally and numerically obtained load vs. displacement curves. Based on the description of the stress–strain behaviour of the pre-deformed material, guidelines have been provided for reducing residual tensile stresses in pre-deformed structural components.

Structural Design and Mechanical Properties Analysis of Laminated SiAlON Ceramic Tool Materials

Based on finite element simulation analysis, laminated ceramic tool materials with different structures were designed and the effect of laminated structure on tool state was investigated. Residual stresses in ceramic tool materials increase with the number of layers and layer–thickness ratio. Based on the simulation results, SiAlON-SiC-SiCw/SiAlON-Al2O3 ceramic tool materials (SCWAs) were prepared using the spark plasma sintering process, and the influence of residual stress on the mechanical properties and microstructure of laminated ceramic tool materials was studied. The mechanical properties of ceramic materials were significantly improved under the effect of residual stresses. The fracture toughness of SCWA4 with 7 layers and a layer–thickness ratio of 6 was 6.02 ± 0.19 MPa·m1/2, and the front and side flexural strengths were 602 ± 19 MPa and 595 ± 17 MPa, 36.3% and 39.0% higher than homogeneous SiAlON ceramics, respectively.

The effect of cold forming residual stresses in local fatigue approaches: A numerical perspective

Thin-walled structures generally rely on cold-formed mild steel profiles. Due to cold forming, a significant formation of residual stresses impacts their overall fatigue behaviour. In this work, a state-of-the-art framework for fatigue life prediction is proposed and applied to both roll-formed and press-braked full-scale profiles. In summary, the profile’s manufacturing process is numerically simulated to obtain a representative residual stress field. These results are then used as the initial state during a subsequent structural and fatigue analysis. A clear detrimental residual stress effect is verified. Importantly, however, is to note that prediction accuracy increases significantly when these effects are considered.

Finite element simulation of the effect of particle shape and thermal residual stress on the tensile properties of NbCp/Fe composites

To optimize the microstructure and properties of NbCp/Fe composites, this study considered factors such as load transfer, plastic strain, matrix damage, and interface debonding. A two-dimensional finite element model was constructed using ABAQUS software. Random adsorption algorithm was used to realize the random distribution of particles within the representative volume element, and interface damage was described using a cohesive zone model. The effects of particle shape and thermal residual stress on the tensile properties of NbCp/Fe composites were investigated. The results show that circular particles uniformly distribute the stress during the tensile process, effectively enhancing the tensile properties of the composites. Conversely, triangular particles, with obvious sharp corners, reduce their tensile properties, particularly in the presence of thermal residual stresses, which further aggravates the stress concentration between the particles and the matrix. This leads to a decrease in the strength and toughness of the material.

Wet shot peening effects on surface integrity and very high cycle fatigue of TC17 titanium alloy

With the increasing reliability requirements of aerospace equipment, very high cycle fatigue of TC17 titanium alloy has gained significant attention. This study investigates the effects of different wet shot peening treatments on the surface integrity and very high cycle fatigue performance of TC17 titanium alloy, elucidating the underlying mechanisms. Experimental results show that wet shot peening exacerbates surface defects, increases roughness, creates a plastic deformation layer, and induces compressive residual stress and work hardening. The combined effect of these factors reduces the fatigue performance. However, post-peening polishing significantly enhances the very high cycle fatigue performance by reducing stress concentration from surface defects while retaining the beneficial effects of compressive residual stress. Therefore, polishing after wet shot peening is concluded to be the most effective method for improving the very high cycle fatigue performance of TC17 titanium alloy.

Effects of stress-relief and natural aging on the geometric tolerances and functional requirements of ferritic nitrocarburized gray cast iron brake rotors

Gray cast iron (GCI) brake rotors are prone to corrosion, particularly in electric vehicles (EVs), owing to their regenerative braking systems. Ferritic nitrocarburizing (FNC) heat treatment has been used to improve the corrosion resistance and cleanability of GCI rotors. However, pre-existing residual stresses in the rotors can lead to distortion after FNC processing, thereby affecting the functional and tolerance requirements. This study investigated the effects of stress-relief (SR) heat treatment and natural aging (NA) on the natural frequency, damping properties, surface roughness, and geometric tolerances of GCI brake rotors before and after FNC treatment. The GCI brake rotors were subjected to SR and NA processes, followed by FNC treatment. The natural frequency, damping Q-factor, surface roughness, and geometric tolerances were measured and analyzed using two-way ANOVA at a 95% confidence level (α = 0.05). The results showed that SR heat treatment significantly reduced the effect of residual stresses and improved geometric tolerances compared to NA. The FNC treatment increased the surface roughness and slightly improved the damping properties but had an insignificant effect on the natural frequency. The combination of SR and FNC treatments provided the best overall performance in terms of quality, geometric tolerance, and surface finish. This study highlights the importance of SR heat treatment for optimizing the manufacturing process of FNC-treated GCI brake rotors for EVs.

Fatigue and fracture in dual-material specimens of nickel-based alloys fabricated by hybrid additive manufacturing

The integration of additive manufacturing with traditional processes, termed hybrid additive manufacturing, has expanded its application domain, particularly in the repair of gas turbine blade tips. However, process-related defects in additively manufactured materials, interface formation, and material property mismatches in dual-material structures can significantly impact the fatigue performance of components. This investigation examines the low cycle fatigue and fatigue crack growth behaviors in dual-material specimens of nickel-based alloys, specifically the additively manufactured STAL15 and the cast alloy 247DS, at elevated temperatures. Low cycle fatigue experiments were conducted at temperatures of 950 °C and 1000 °C under a range of strain levels (0.3%–0.8%) and fatigue crack growth tests were conducted at 950 °C with stress ratios of 0.1 and −1. Fractographic and microscopic analyses were performed to comprehend fatigue crack initiation and crack growth mechanisms in the dual-material structure. The results consistently indicated crack initiation and fatigue fracture in the additively manufactured STAL15 material. Notably, fatigue crack growth retardation was observed near the interface when the crack extended from the additively manufactured STAL15 material to the perpendicularly positioned interface. This study highlights the importance of considering yield strength mismatch, as well as the potential effects of residual stresses and grain structure differences, in the interpretation of fatigue crack growth behavior at the interface.

Effects of Aluminum Plate Initial Residual Stress on Machined-Part Distortion

Effects of Aluminum Plate Initial Residual Stress on Machined-Part Distortion

Effect of residual stress on mechanical properties of Triply periodic minimal surface lattice structures in Additive manufacturing

Due to its special porous structure with smooth continuous surface and high specific surface area, the triply periodic minimal surface (TPMS) lattice structure exhibits excellent properties such as strong bearing capacity, high energy absorption rate and good fatigue performance. The residual stresses generated during the additive manufacturing (AM) process can have a significant impact on the mechanical properties of the TPMS structure. In this paper, the AM process of four typical TPMS structures are investigated by the thermal–mechanical coupling model. The mechanism of residual stress generation is analyzed, and an optimized preparation process scheme is proposed to reduce the residual stress. Furthermore, the effects of residual stresses on the mechanical properties of TPMS structures are investigated for different types, volume fractions and compression directions. Results show that the influences of scanning speed and hatch spacing on the residual stress are not significant with constant laser power, but the deposition thickness should be adjusted according to the characteristics of the structure. The residual stress will reduce the elastic modulus and yield strength, while no obvious effect on the plastic behavior is observed. Importantly, the residual stress has the greatest influence on the mechanical properties of I-WP-type among the four investigated types, which becomes more pronounced with the increase of volume fraction. Moreover, the influence of residual stress on the mechanical properties of TPMS structures depends on the compression direction. Our results give a comprehensive understanding of the residual stress distribution and impact on the mechanical properties of TPMS structures, providing guidance to the rational design and optimization of TPMS structures in engineering applications.

Combined effects of local residual stresses, internal pores, and microstructures on the mechanical properties of laser-welded Ti-6Al-4V sheets

Laser-welded Ti-6Al-4 V is prone to severe residual stresses, microstructural variation, and structural defects which are known detrimental to the mechanical properties of weld joints. Residual stress removal is typically applied to weld joints for engineering purposes via heat treatment, in order to avoid premature failure and performance degradation. In the present work, we found that proper welding residual stresses in laser-welded Ti-6Al-4 V sheets can maintain better ductility during uniaxial tension, as opposed to the stress-relieved counterparts. A detailed experimental investigation has been performed on the deformation behaviours of Ti-6Al-4 V butt welds, including residual stress distribution characterizations by focused ion beam ring-coring coupled with digital image correlation (FIB-DIC), X-ray computerized tomography (CT) for internal voids, and in-situ DIC analysis of the subregional strain evolutions. It was found that the pores preferentially distributed near the fusion zone (FZ) boundary, where the compressive residual stress was up to -330 MPa. The removal of residual stress resulted in a changed failure initiation site from the base material to the FZ boundary, the former with ductile and the latter with brittle fracture characteristics under tensile deformation. The combined effects of residual stresses, microstructures, and internal pores on the mechanical responses are discussed in detail. This work highlights the importance of inevitable residual stress and pores in laser weld pieces, leading to key insights for post-welding treatment and service performance evaluations.