Generation Of Residual Stresses Research Articles

Surface morphology of API 5L X65 pipeline steel processed by ultrasonic impact peening: An integrated experimental and computational study

Ultrasonic impact peening (UIP) is a highly effective surface engineering technique to improve material durability through peening-induced surface plastic deformation. These improvements are determined by not only the generation of surface compressive residual stresses but also the alteration of surface morphological features. In literature, researchers have focused primarily on the average roughness (Sa) to understand the morphology changes induced by UIP. From the surface engineering perspective, in addition to Sa, other surface morphological characteristics play key roles in determining material durability, particularly surface skewness (Ssk) and surface kurtosis (Sku), which describe the asymmetrical distribution of surface profiles and the sharpness of peak features, respectively. In this study, surface morphological characteristics of API 5L X65 pipeline steel processed by UIP are investigated with a focus on the effects of processing parameters on Sa, Ssk, and Sku. The results indicate that the optimized UIP conditions lead to the preparation of surfaces with valley structures as the dominant feature accompanied by blunt peaks, resulting in the elimination of stress concentration sites towards enhanced material durability. In addition, surface hardness, residual stresses, and peening-induced deformation depth are measured. Furthermore, to gain a comprehensive understanding of the material response and the underlying mechanisms driving surface morphological alterations by UIP, a finite element method (FEM)-based model is developed. By investigating the effect of process parameters (peening amplitude, peening cycles, and pin size) on the surface deformation depth and stress/strain distribution, a correlation between these process variables with surface characteristics is established.

Hybrid Analytical-Numerical Modeling of Surface Geometry Evolution and Deposition Integrity in a Multi-Track Laser-Directed Energy Deposition Process

Abstract Modeling multitrack laser-directed energy deposition (LDED) is different from single-track deposition. There is a temporal variation in the deposition geometry and integrity in a multitrack deposition, which is not well understood. This article employs an analytical model for power attenuation and powder catchment in the melt pool in conjunction with a robust fully coupled metallurgical-thermomechanical finite element (FE) model iteratively to simulate the multitrack deposition. The novel hybrid analytical–numerical approach incorporates the effect of preexisting tracks on melt pool formation, powder catchment, geometry evolution, dilution, residual stress, and defect generation. CPM 9V steel powder was deposited on the H13 tool steel substrate for validating the model. The deposition height is found to be a function of the track sequence but reaches a steady-state height after a finite number of tracks. The height variation determines the waviness of the deposited surface and, therefore, the effective layer height. The inter-track spacing (I) plays a vital role in steady-state height evolution. A larger value of I facilitates faster convergence to the steady-state height but increases the surface waviness. The FE model incorporates the effects of differential thermal contraction, volume dilation, and transformation-induced plasticity. It predicts the deposition geometry and integrity as a function of inter-track spacing and powder feed rate. The insufficient remelting of the substrate or the preceding track can induce defects. A method to predict and mitigate these defects has also been presented in this article.

Effect of natural aging by multifunction cavitation on plane bending fatigue behaviour of heat-treatable Al-Si7Mg aluminum alloys and its fatigue strength estimation

The effect of natural aging by multifunction cavitation (MFC) on the fatigue behaviour of heat-treatable Al-Si7Mg aluminum alloys was examined. Surface observation and plane bending fatigue tests were conducted for the MFC-treated aluminum alloys at a stress ratio, R, of −1. The hardness of aluminum alloy without T6 treatment was significantly increased by MFC due to both the work hardening and natural aging. MFC treatment improved the fatigue lives and the fatigue strength at N = 107 cycles of aluminum alloys due to the generation of compressive residual stress and increasing the surface hardness; however, surface pits were large enough to easily nucleate an initial fatigue crack. In addition, the fatigue strength at N = 107 cycles of MFC-treated aluminum alloys can be estimated considering the residual stress, pit size and surface hardness.

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.

The enhanced strength and radiation efficiency of alumina reticulated porous ceramics via coal gangue addition

Al2O3 reticulated porous ceramics (ARPC) are widely selected for high-temperature porous media burners due to their excellent thermal stability. However, the relatively low mechanical property and infrared emissivity of ARPC led to a low lifespan and radiation efficiency of the burner, limiting its application in high-temperature porous burners. In this work, a novel strategy was proposed to synergistically improve mechanical and radiation properties of ARPC and recycle of coal gangue. ARPC with three-layered struts, including microporous alumina-mullite coating, alumina skeleton and filling layer, were prepared by polymer replica technique and vacuum infiltration method. The addition of coal gangue could obviously strengthen ARPC, because coal gangue was attributed to form mullite, as well as the generation of residual compressive stress in the coating of three-layered struts. The decomposition of organic compounds within coal gangue enhanced the degree of microporosity on the coating, thereby increasing infrared emissivity by 21.8%, which increased the surface temperature of porous burner from 857.4°C to 905.7°C.

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.

Laser deposition of titanium layer to enhance two-way shape memory behavior of Nitinol sheet

One of the long-standing mechanical challenges associated with shape memory alloys (SMAs) is achieving and stabilizing an evolving two-way shape memory effect (TWSME) through thermomechanical training/cycling. In most martensitic NiTi SMAs that exhibit zero TWSME at room temperature, the TWSMEs typically require hundreds of cycling repetitions to track trivial values. This demonstrates a promising solution to overcome this challenge. The surface of NiTi SMA sheets was treated by depositing a certain number of titanium (Ti) powder layers on the NiTi surface using a laser beam. The results showed that a unique TWSME of approximately 12% with good stability was achieved after 100 cycles when the optimum number of five Ti layers was deposited, which was much higher than that of the NiTi sheet (0.3% TWSME) and the sample with a single-time laser path irradiation (1.8%). This was attributed to the low coefficient of thermal expansion of the Ti vs. NiTi sheet, which prevented reverse bending during heating, and the formation of Ti-rich intergranular Ti2Ni(Ox) precipitates, which hindered dislocation movement. Meanwhile, in this sample, owing to the generation of a large residual tensile stress and a large heat-affected zone that led to a reduction in plastic zones, the one-way shape memory effect (OWSME) was retained at values above 90% with good stability over cycling. However, the introduction of additional Ti layers can cause problems in terms of oxygen accumulation within the NiTi sheet, which should be considered when designing a product.

Extensive evaluation of microhardness alterations induced in subsurface layers after hard machining of AISI 4340 steel and process optimization

ABSTRACT Hardened AISI 4340 steel is extensively utilised in engineering industries. Owing to the fact that thermo-mechanical loads are applied to surface layers during the hard machining process, severe changes occur at the surface of the machined workpiece. These changes can affect some mechanical properties of the material, including microhardness, and residual stresses generation in material. Therefore, it is significantly influenced by process conditions and there is not any study in literature to extensively evaluate and optimise different indications of microhardness alteration after hard machining of AISI 4340 Steel. In this study, the influence of machining parameters was firstly studied on the microhardness distribution at machining of hardened AISI 4340 steel by experimental tests. Then, the optimal surface microhardness and depth of the affected layer were assessed using the intelligent techniques. In this regard, the optimal process conditions were simultaneously determined using the combination of the Artificial Neural Networks (ANNs) and Non-dominated Sorting Genetic Algorithm (NSGA-II). The results indicated that, both depth of the affected layer and surface microhardness were obtained in optimal state when the cutting speed changes from 720 to 600 (Rpm) and feed rate and depth of cut are 0.05 (mm/rev) and 0.4 (mm), respectively.

Numerical modeling and statistical analysis of the effect of thermomechanical properties on residual stresses in feldspar‐based ceramic materials after thermal tempering

AbstractThis study focuses on the investigation of the impact of the thermomechanical properties of ceramic materials on residual stresses generated after the thermal tempering process. A sodium feldspar matrix was chosen for numerical simulations, with variations in its thermomechanical properties of up to ± 20%, to encompass a range of properties exhibited by other ceramic materials. The simulations demonstrated that the viscosity of the material had the most significant influence on residual stress generation, while the coefficient of thermal expansion, modulus of elasticity, and effective diffusivity also contributed to residual stress formation. A statistical analysis based on a 24 factorial design revealed that increasing residual compressive stress on the surface was achievable by increasing the coefficient of thermal expansion and modulus of elasticity, as well as the viscosity, while reducing the effective thermal diffusivity. Finally, a mathematical model was proposed to relate the thermomechanical properties of the ceramic material to the residual stresses observed on the surface following thermal tempering.

Residual Stress Generation in Additive Manufacturing of Complex Lattice Geometries

Residual stresses developed during additive manufacturing (AM) can influence the mechanical performance of structural components in their intended applications. In this study, thermomechanical residual stress simulations of the laser powder bed fusion (LPBF) process are conducted for both simplified (plate and cube-shaped) geometries as well as five complex lattice geometries fabricated with Inconel 718. These simulations are conducted with the commercial software package Simufact Additive©, which uses a nonlinear finite element analysis and layer-by-layer averaging approach in determining residual stresses. To verify the efficacy of the Simufact Additive© simulations, numerical results for the plate and cube-shape geometries are analyzed for convergence and compared to experimental residual stress results available in the literature. Numerical residual stress results are subsequently compared for five complex lattice geometries. Results suggest that lattice geometry can play a significant role in the distribution and magnitude of residual stresses, which are significant in some applications.

Multiphysics Study of Thermal Profiles and Residual Stress in Welding.

One of the effects of welding is residual stress. Welding involves complex tests concerning differences in values of the mechanical parameters of its regions as an effect of residual stress. Such multiphysics characteristics of welding pose a challenge in predicting residual stress. In the present study, a thermo-mechanical constitutive model considering phase transformation and transformation plasticity is implemented in the numerical model in ABAQUS user subroutines. In order to consider phase evolution in welding, the metallurgical parameters for Leblond's phase equation were obtained from the calibration of DH36 steel with a CCT diagram. In addition, the effects of welding speed on thermal profiles and residual stress generation were investigated. Analysis has suggested that the width of the heat-affected zone (HAZ) decreases with an increase in welding speed, and the phase fraction is significantly affected by this kind of parameter. Such phase transformation has led to the generation of a compressive stress in the fusion zone (FZ) and HAZ. The volume difference between coexisting phases produces a compressive stress in cooling, and its magnitude was increased with martensite increasing.

A Finite Element Study of Wire Arc Additive Manufacturing of Aluminum Alloy

Analyses in the present work focus on understanding the influence of the WAAM (wire arc additive manufacturing) deposition pattern and travel speed on residual stress and warpage in aluminum alloy. The thermal profiles are analyzed using thermomechanical FE simulations. Analysis shows that the out–in deposition pattern leads to the highest level of residual stress and warpage. It is also found that an increase in the travel speed decreases the peak temperature and thermal gradient during the AM deposition, which results in a lower level of residual stress generation. A comparison of results for the line-type patterns (raster and alternate) suggests that the deposition interval between each deposition has little influence on thermal profiles, residual stress generation, and warpage. However, the contour-type patterns significantly affect the heat transfer, thermal gradient, and cooling rate during the AM deposition.

Effect of surface characteristics on the axial fatigue properties and wear resistance of Ti-6Al-4V alloy nitrided by gas blow induction-heating

The effects of surface characteristics on the axial fatigue properties and wear resistance of the GBIH-nitrided titanium alloy were investigated to improve the fatigue strength and wear resistance of Ti-6Al-4V alloy rapidly nitrided by induction-heating in a nitrogen atmosphere with blowing nitrogen gas (GBIH-nitriding). The fatigue strength of the GBIH-nitrided Ti-6Al-4V alloy was lower than that of the mirror-polished specimen owing to the formation of a brittle nitrogen compound layer and grain coarsening. Fatigue tests using specimens prepared by combining GBIH-nitriding and particle collision treatments revealed that the formation of nitrogen diffusion layers at the outermost surface and the generation of compressive residual stress without forming surface asperities increased the fatigue strength of the GBIH-nitrided Ti-6Al-4V alloy. Moreover, the formation of a nitrided layer and suppression of surface asperities effectively improved the wear resistance of the Ti-6Al-4V alloy. Therefore, formation of a nitrogen diffusion layer and the introduction of compressive residual stress without grain coarsening, a compound layer, and surface asperities increased the fatigue strength and wear resistance of the GBIH-nitrided alloy.

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.

Factors Influencing Residual Stresses in Cold Expansion and Their Effects on Fatigue Life—A Review

Cold expansion technology has been widely used in aviation industries as an effective method of improving the fatigue performance of fastener holes. It can improve the fatigue life several times over without adding weight, meeting the growing demand for lightweight and durable aircraft structures. In recent years, it has been extensively studied through extensive experiments and finite element simulations to analyze the residual stresses around the fastener hole. Appropriate process parameters lead to the generation of beneficial residual stresses that influence the material microstructure, thereby improving the fatigue life of the component. This paper summarized factors influencing residual stresses in cold expansion and their effects on fatigue life, and the strengthening mechanism, parameter optimization, and effect of anti-fatigue are discussed from the point of view of the residual stress and microstructure. The development of new cold expansion technologies and the research directions that can realize anti-fatigue technology efficiently are proposed.

Reducing residual stress in photopolymerized composites by grafting high-mobility polymer chains onto the filler-matrix interface

3D/4D printing of thermosets, composites and hydrogels, lithographic procedures and dental resins are important examples of applications that rely on light-driven polymerization supported on substrates. Adhesion between the polymer and substrate during photopolymerization (and even between printed layers) can restrict the usual polymerization shrinkage, leading to the generation of residual stresses. These residual stresses can result in poor-quality products due to the presence of cracks and occurrence of warpage. In this work, silica nanoparticles were incorporated into photopolymerizable dimethacrylate based networks. These nanoparticles had their surface modified by grafting polymer chains with high mobility at usual room temperatures (low glass transition temperature polymer) and with high affinity towards the polymer matrix in order to test the hypothesis that these high-mobility chains could be helpful in dissipating stress and energy generated during photopolymerization in conditions in which the polymerization shrinkage is restricted. The nanoparticles and composites were analyzed via: electron microscopy (SEM), thermal analysis and mechanical bending tests. The evolution of the monomer-to-polymer conversion during photopolymerization was monitored using real-time infrared (FTIR) spectroscopy. To determine the residual stress generated by the polymerization at restricted contraction conditions, a universal mechanical testing machine was adapted and used. The results showed that silica nanoparticles with grafted high-mobility polymer chains that were able to interpenetrate and interact with the dimethacrylate based networks led to the production of composites having higher mechanical properties and lower polymerization stresses than composites containing only silanized nanoparticles and nanoparticles having immiscible polymer grafts towards the dimethacrylate based network. Results indicate that the modifications of the interface of composites developed in this work can be useful in the formulation of materials with improved mechanical properties and stability regarding polymerization shrinkage and residual stress that can lead to higher-quality products obtained in processes that employ light-driven polymerization supported on substrates or that occur on sequential polymerized layers, such as 3D/4D printing, lithography and in dental applications.

Wire Arc Additive Manufacturing: A Study of Process Parameters Using Multiphysics Simulations

In this work, analyses focus on understanding the effects of the scanning pattern and speed on the thermal profile, phase transformation, and residual stress generation in the WAAM deposition. An FE numerical model is constructed that takes into account the phase evolution and transformation plasticity using the ABAQUS user subroutine, UMAT. The results show that the scanning pattern significantly affects the heat accumulation and the cooling rate during the AM deposition, and, eventually, the generation of residual stresses. According to the simulation results, the highest residual stress is generated in the case of the out–in scanning, while the alternate pattern leads to the lowest residual stress. The influence of the scanning speed on the thermal profiles and residual stress are also examined. The analyses show that an increase in the scan speed leads to a decrease in the peak temperature and an increase in the cooling rate, which result in an increase in the martensite volume fraction of the deposition.

An investigation on the performance of bio-mimicked rake surface structured tool during machining of hard-to-cut materials

The current work seeks to improve the machining characteristics of tool by generation of various geometrical structures on cemented carbide tool's rake face. A total of three different structures: (a) bio-mimicked micro-crescent structure, (b) micro-dimple structure, and (c) micro-groove structure, are generated using laser micro-machining technique on rake surface of tool. Dry turning tests were performed using the structured tool and conventional tool during cutting of AISI 420 workpiece material. The effect of various geometrical textures on chip-tool contact area, surface roughness, cutting force, morphology of chip and residual stress have been compared with respect to conventional tool. Results indicate that crescent-shaped bio-mimicked structured tool indicated better cutting performance in decreasing contact area of chip-tool by 43.6%, tangential force by 15.38%, feed force by 20.22%, and average surface roughness by 8.81% relative to the conventional tool. The machined surface of structured tool also indicated lower generation of residual stress of 419.3 MPa in cutting direction and 316.9 MPa in feed direction relative to 608.3 MPa in cutting and 375.5 MPa in feed direction using conventional tool machined surface. Segmented chips were produced during all machining conditions, and crescent-shaped structured tool indicated least chip reduction coefficient of 1.08 compared to 1.57 in the case of conventional tool. The results of the current study are very essential for expanding the application of bio-mimicked structured cutting tools for cutting different hard to machine materials.

Numerical simulation and experimental study of residual stress in dissimilar aluminum alloy laser composite welding

The study combined experimental and numerical simulation methods to investigate the distribution of residual stress in laser composite welding of dissimilar aluminum alloys 6063 and 5083. Using the Simufact Welding simulation software and a combined volume heat source, the distribution patterns of transverse and longitudinal residual stress fields at different welding speeds were analyzed. The blind hole method was used to test the residual stress after welding. The results showed that the use of a combined volume heat source model for heat source calibration yielded ideal results, and the thermal cycle curve was basically consistent with the simulation and experimental results of residual stress. As the welding speed decreased, the longitudinal residual stress of the parent material on both sides significantly decreased, while the transverse residual stress increased. The majority of tensile and compressive stresses on both sides of the 5083 and 6063 aluminum alloys decreased with a decrease in welding speed. The Von Mises equivalent stress indicated that the cooling process is the main stage for residual stress generation. When the welding speed decreased, the peak value of longitudinal residual stress on the 6063 aluminum alloy side decreased from 230 to 90 MPa, while that on the 5083 aluminum alloy side decreased from 304 to 150 MPa. These findings provide an important basis for controlling and reducing the residual stress and deformation of dissimilar aluminum alloy laser arc composite welded components.

Modeling of local hydrogen concentration on microscopic scale to characterize the influence of stress states and non-metallic inclusions in pipeline steels

Hydrogen as an energy carrier plays an important role in achieving the ambitious climate targets associated with decarbonization. The main challenge is to ensure safe transport of gaseous respectively liquid hydrogen through the already existing natural gas pipelines. Since experimental methods, such as hydrogen-induced-cracking tests, fail to provide quantitative answers to the question of which local effects/mechanisms trigger failure under hydrogen loading, complex numerical multi-scale approaches are needed. In this work, a phenomenological crystal plasticity model based on dislocation slip mechanisms was implemented in Abaqus/Implicit and coupled with a hydrogen diffusion model to investigate the influence of microstructural characteristics in terms of grain size, texture, phase fraction but also lattice defects such as dislocations, grain boundaries, carbides, and non-metallic inclusions on hydrogen-induced-damage behavior. As a driving force for hydrogen diffusion, both hydrostatic stresses and plastic strains associated with mechanically and thermally induced residual stresses under various stress states were investigated. It was found that the impurity degree of the steel in terms of non-metallic inclusions plays an important role in hydrogen susceptibility in two aspects, namely geometrically (notch-effect) and in the generation of residual stresses. The effect of matrix shrinkage on the inclusions and the resulting stress field after cooling leads to the accumulation of hydrogen atoms around the inclusions, resulting in locally high critical concentrations. The simulations performed on microstructures with and without non-metallic inclusions under different stress states demonstrated the notched effect that the presence of non-metallic inclusions increases the local hydrogen concentration up to 28 %.