Generation Of Residual Stresses Research Articles

On the interaction of microstructural morphology with residual stress in fiber laser welding of austenitic stainless steel

The development of compressive residual stress is governed by the metallurgical transformation and associated microstructure, which in turn influences the mechanical properties of a welded structure. In the present work, the microstructural interaction with the thermo-mechanical performance of Yb-Fiber laser-welded austenitic stainless steel (SS304) is evaluated at different heat inputs and varying defocus distances. The interrelation between microstructural morphology and the typical pattern of residual stress is systematically investigated. The development of the thermal-metallurgical-mechanical model particularly considers the effect of solid-state phase transformation (SSPT) such that the model predicts the phase fraction and its influence on residual stress distribution. The present study exclusively focuses on the mechanism of residual stress generation as a consequence of dual-phase microstructural evolution during solidification. Low heat input (45J/mm) leads to a high cooling rate, excellent tensile strength, and low tensile residual stress. The finite element-based thermo-mechanical model predicts the residual stress with a maximum deviation of ±50 MPa compared to the experimental value. The Ferritic-austenitic (FA) mode of solidification results in the combination of skeletal and lathy δ-ferrite morphology. Increasing peak intensity of δ {110} with a cooling rate confirms the enhancement of δ-phase within the austenite matrix and restricts the complete transformation to the austenitic phase. A relatively high amount of δ-ferrite due to enriched Cr and lean Ni content at the dendritic core with fine or acicular morphology at a high cooling rate reduces the longitudinal and transverse residual stress significantly. Besides, the increasing trend of primary dendritic arm-size of δ-ferrite yields a gradual increase in residual stress.

Size effect on residual stress in low transformation temperature welded joints

It has been reported that low transformation temperature (LTT) weld metals are beneficial to generation of compressive residual stress around weld zone. In this study, the relationship among residual stress, size effect of LTT welded joints with different plate width and thickness as well as martensite start (Ms) temperatures was investigated by experimental and finite-element analysis. It was found that heat dissipation and thermal expansion coefficient of LTT weld metal had a significant impact on residual stress. Welded joint with a small plate width led to greater compressive residual stresses in the LTT weld, which was due to the lower heat dissipation and smaller thermal expansion coefficient of the LTT weld metal in due course of cooling process. Additionally, the finite-element analysis revealed that increasing plate width mainly affected the longitudinal residual stress, while increasing the plate thickness influenced all the residual stress components in the LTT weld. Furthermore, the LTT weld with a lower Ms temperature of 191 °C resulted in greater compressive residual stresses, and was less sensitive to the LTT joint size, as against the Ms temperature of 398 °C.

Nano-lubricant influence on surface residual stresses in hard milling

Residual stress could be induced by machining processes like milling which can greatly affect the fatigue life of fabricated parts, especially in dynamic loading conditions. In metal cutting operations, machining induced residual stresses can be explained in the terms of machining forces and temperatures of the cutting zones. This thermo mechanical loading along with the resulted metallurgical changes are the main sources of residual stresses generation at the surface of machined workpiece. Researchers have proved the superior properties of nanofluids over the conventional coolants to reduce the intensity of thermo mechanical loading in machining process which will affect the residual stresses caused by machining. Therefore, in this paper, silver nanoparticles in the water-soluble oil have been used for reducing the mechanical and thermal loads in the milling process. The cutting forces, temperature of the cutting zone, surface roughness and the residual stress of machined surface have been measured experimentally in milling of hardened steel AISI 4140 for various nanoparticle’s concentration, feeds and cutting speeds. Results show that increasing the concentration of Nano-particles in base fluid from 0.5 to 3.0% wt., will make machining surface residual stresses more compressive averagely by about 66.67% compared to conventional cutting fluid.

Simple and Versatile Analytical Method for Monitoring the Deposition of Thin Layers by Optical Measurement and Calculation of Residual Stress

This paper develops a simple and versatile analytical method for characterizing residual stress associated with the deposition of thick, thin, single and multilayer coatings. This study is of great importance, since the generation of residual stress can lead to the formation of significant defects in the coating. To illustrate the effectiveness of our analytical method, two different processes were characterized. The coatings formed are intended for anti-corrosion applications. The first is a Physical Vapour Deposition (PVD) involving a High Power Impulsed Magnetron Sputtering (HiPIMS), the second is a sol-gel process. The approach is based on the optical recording of the curvature of a thin substrate, followed by its assessment using a fit of the digitalized image by a parametric model. The results provide experimental data on the development of stress during deposition. Both coatings studied have a low level of residual stress, which explains why they are flawless and which is interesting for the targeted anti-corrosion application. For the PVD coating, it was possible to link the development of the stress to the evolution of the film structure during growth. For the sol-gel process, the study of the stress allowed us to highlight the drying reaction mechanisms involved during the sol-gel transition and their influence on the gel structure.

Development of residual stresses by infeed rotary swaging of steel tubes

Additionally to the achievable tight geometrical tolerances, rotary swaging can influence intrinsic material properties by work hardening and residual stresses generation. Although residual stresses should be usually avoided, they can be used on purpose to improve the performance properties of a produced part. To find prospective process settings, 2D FEM simulation of the rotary swaging process was developed and revealed the development of residual stresses distributions in E355 steel tubes in the whole longitudinal section. Besides the closing time, also geometric features of the dies were varied. It was found that the closing time affects the residual stresses significantly at the surface, but not in the depth of the part. By shortening the calibration zone, the axial tensile residual stresses near the outer surface could be lowered, while compressive residual stresses near the inner surface remained almost unaffected. By applying a higher die angle, the tensile axial residual stresses were increased while reducing the compressive axial residual stresses. Experimental investigations of residual stresses were performed by X-ray diffraction which revealed a good agreement between simulation results and physical measurements. With these findings, the rotary swaging process can be optimized for shaping residual stresses profiles to improve the performance properties of the produced parts.

Review on Quality Control Methods in Metal Additive Manufacturing

Metal additive manufacturing (AM) has several similarities to conventional metal manufacturing, such as welding and cladding. During the manufacturing process, both metal AM and welding experience repeated partial melting and cooling, referred to as deposition. Owing to deposition, metal AM and welded products often share common product quality issues, such as layer misalignment, dimensional errors, and residual stress generation. This paper comprehensively reviews the similarities in quality monitoring methods between metal AM and conventional metal manufacturing. It was observed that a number of quality monitoring methods applied to metal AM and welding are interrelated; therefore, they can be used complementarily with each other.

Prediction of residual stresses in turning of pure iron using artificial intelligence-based methods

Residual stresses (RS) induced in machined components have substantial impact on the quality and lifetime of the final products. There are several cutting parameters and conditions that affect the generation of RS, so understanding the relationship between the RS generation and those parameters to minimize the induced tensile RS is a crucial issue. This paper presents a study on the utilization of artificial intelligence-based methods to model the RS generation during dry turning of DT4E pure iron. The experiments were designed based on central composite design method. The effects of the cutting parameters such as cutting speed, feed and cutting depth on the generated RSes in both circumferential and radial directions are investigated. Two hybrid artificial neural network (ANN) models are used to predict the process responses after training them using the experimental results. The prediction accuracy of the two models are enhanced via integration with two different metaheuristic optimization algorithms, namely particle swarm optimization (PSO) and flower pollination algorithm (FPA). These optimization algorithms are used as subroutine algorithms to determine the optimal parameters of the ANN model. The predicted results by the proposed models were compared with the experimental results as well as those obtained by standalone ANN. The accuracy of all models was evaluated using different statistical measures. The ANN-FPA had the best prediction accuracy followed by ANN-PSO. The coefficient of determination of ANN-FPA has high values of 0.996 and 0.997 for radial RS and circumferential RS, while they were 0.971 and 0.992 for ANN-PSO and 0.649 and 0.815 for standalone ANN.

Turning parameters effects in residual stresses of AISI 1045 steel

The main objective of this work was to evaluate the influence of turning parameters on the generation of residual stresses in AISI 1045 steel bars. Therefore, effects of four main parameters as feed rate, cutting velocity, tool nose radius, and rake angle were analyzed. Residual stresses investigation through X-ray diffraction (XRD) was carried out at different depths (surface, 5, 10, 20, 50, and 75 μm). As the samples showed distinct roughness patterns with variable amplitude and shape, and based in a previous work, samples were classified in two main groups accordingly with surface finishing (regular and irregular). The current results showed that feed rate and cutting speed played the major influence on residual stress distributions. Moreover, the tool nose radius affected surface residual stresses, whereas the rake angle did not significantly change it. Finally, samples could be divided in two residual stress groups, showing a direct relation of surface finishing quality and residual stresses.

Investigation of the Residual Stress in a Multi-Pass T-Welded Joint Using Low Transformation Temperature Welding Wire.

We investigated whether low transformation temperature (LTT) welding materials are beneficial to the generation of compressive residual stress around a weld zone, thus enhancing the fatigue performance of the welded joint. An experimental and numerical study were conducted in order to analyze the residual stress in multi-pass T-welded joints using LTT welding wire. It was found that, compared to the conventional welded joint, greater tensile residual stress was induced in the flange plate of the LTT welded joints. This was attributed to the reheat temperature of the LTT weld pass during the multi-pass welding. The formerly-formed LTT weld pass with a reheat temperature lower than the austenite finish temperature converted the compressive residual stress into tensile stress. The compressive residual stress was generated in the regions with a reheat temperature higher than the austenite finish temperature, indicating that LTT welding materials are more suitable for single-pass welding.

Parameter Identification for Thermo-Mechanical Constitutive Modeling to Describe Process-Induced Residual Stresses and Phase Transformations in Low-Carbon Steels

Reinforcing steel bars (rebars) are widely manufactured using the Tempcore™ process. Several studies have been conducted analyzing the effect of the heat treatment route on the strength and corrosion resistance of rebars, but knowledge of its effects on the residual stresses of the finished product are largely lacking. This paper presents experimental investigations to identify the material parameters necessary to simulate the Tempcore™ process using thermo-elasto-plastic constitutive modeling in order to study the generation of residual stresses during the manufacturing process. Mechanical parameters such as yield strength at elevated temperatures and elastic constants were determined experimentally. A continuous cooling transformation diagram needed to model the phase transformations was also identified and is presented here. Residual stress distributions in the surface region of the rebar were characterized using X-ray diffraction. Further characterizations of microstructure, chemical composition, and hardness were carried out. The constitutive modeling approach for the numerical simulation is briefly described for which the experimentally determined parameters are required as input.

Experimental and numerical study to minimize the residual stresses in welding of 6082-T6 aluminum alloy

One of the most important negative consequence in the fusion welding processes is the generation of tensile residual stresses in welded joints. The main goals of this work are to determine the optimal combination of welding parameters to minimize the residual stress level and the influence of each welding parameter in that feature to weld 6082-T6 aluminum alloy plates using the GMAW welding process. To achieve these goals was implemented the Taguchi orthogonal array (L27) to define the design of numerical and experimental tests. All combinations were simulated in the Simufactwelding 6.0 software, from which it was possible to obtain the values of maximum residual stresses. The data treatment was carried out, reaching the combination of levels for each parameter. With ANOVA analysis was found that the parameter with the greatest influence in the residual stress generation was the welding speed, while the parameter with the least influence was the torch angle. Also, to minimize the residual stresses it was observed that the optimal combination of welding parameters is welding current intensity of 202 A, welding speed of 10 mm/s, and 30° of inclination of the angular torch. The two simulations that resulted in the highest and lowest residual stresses were validated experimentally by the hole drilling method to measure the residual stresses.

Research on the water cavitation peening process and mechanism of TC4 titanium alloy

Cavitation water shot peening is a new processing method of surface strengthening and modification that utilizes the cavitation bubbles in the cavitation water jet to destroy high-energy shock waves, causing the cavitation groups to collapse on the surface of the material. Strengthening research on TC4 titanium alloy cavitation water jet peening is limited. The process of cavitation water shot peening strengthening is small, and the mechanism of residual stress generation is not yet clear. Therefore, five typical shot peening strength tests of TC4 titanium alloy are taken as examples in this paper. Experiments and mechanistic studies are carried out through macro-micromorphology, metallographic structure and XRD analysis, microhardness, and residual stress methods. The research results are as follows: as the shot peening strength increases, the surface roughness Ra and the depth of the plastic deformation layer gradually increase, and the depth of the plastic deformation layer is saturated at 55–60 μm; the depth of the influence of the microhardness and residual stress reaches 130 μm; and the surface grains gradually refine and develop to the nanometre level.

A thermodynamic framework for additive manufacturing, using amorphous polymers, capable of predicting residual stress, warpage and shrinkage

A thermodynamic framework has been developed for a class of amorphous polymers used in fused deposition modeling (FDM), in order to predict the residual stresses and the accompanying distortion of the geometry of the printed part (warping). When a polymeric melt is cooled, the inhomogeneous distribution of temperature causes spatially varying volumetric shrinkage resulting in the generation of residual stresses. Shrinkage is incorporated into the framework by introducing an isotropic volumetric expansion/contraction in the kinematics of the body. We show that the parameter for shrinkage also appears in the systematically derived rate-type constitutive relation for the stress. The solidification of the melt around the glass transition temperature is emulated by drastically increasing the viscosity of the melt. In order to illustrate the usefulness and efficacy of the constitutive relation that has been developed, we consider four ribbons of polymeric melt stacked on top of each other such as those extruded using a flat nozzle: each layer laid instantaneously and allowed to cool for one second before another layer is laid on it. Each layer cools, shrinks and warps until a new layer is laid, at which time the heat from the newly laid layer flows into the previous laid layer and heats up the bottom layers. The residual stresses of the existing and newly laid layers readjust to satisfy equilibrium. Such mechanical and thermal interactions amongst layers result in a complex distribution of residual stresses. The plane strain approximation predicts nearly equibiaxial tensile stress conditions in the core region of the solidified part, implying that a preexisting crack in that region is likely to propagate and cause failure of the part during service. The free-end of the interface between the first and the second layer is subjected to the largest magnitude of combined shear and tension in the plane with a propensity for delamination.

A validated modelling technique for incorporating residual stresses in glass structural design

This paper presents the development of a simple parabolic residual stress depth profile model for characterising residual stresses in construction-sector glass. The proposed model requires only the knowledge of the surface residual stress, which is usually available from glass manufacturers. Unlike the complex computational techniques reported in the literature, such as modelling physical, microstructural and mechanical phenomena of glass at different temperatures during manufacturing, the proposed model obviates the need for modelling multi-physics phenomenon of the generation of residual stresses. The proposed model also eliminates the need of sophisticated experimental equipment, such as Scattered-Light-Polariscopes (SCALP), which are usually not available among practicing engineers, in order to characterise the residual stresses. Residual stress predictions from the proposed parabolic model were validated against experimental results reported in the literature. Using the concept of eigenstrains, the paper also extends the results of the proposed parabolic residual stress depth profile model for incorporating the effects of residual stresses in stress analysis of glass structures.

Effect of fire exposure on residual stresses relief in welded high strength Q690 steel sections

Welding induced residual stresses in steel sections can be reduced by high temperatures in fire conditions and thus affect the load bearing capacity and stiffness of structural steel members. This paper presents effect of high temperature exposure on residual stresses relief in welded high-strength Q690 steel sections by experimental and numerical studies. The distribution and magnitude of the residual stresses in three Q690 steel H-sections and three Q690 steel box-sections after exposure to 600 °C and 800 °C were investigated by cutting method. In the numerical studies, finite element analysis software ANSYS was employed to simulate residual stress generation and relief in the entire welding and high temperature exposure stages, including the heating and cooling phases. The predicted results of the residual stresses after an exposure to high temperature obtained by the finite element analysis agree well with the test results. Parametric studies were conducted to investigate the influence of exposed temperature, high temperature duration, and creep strain in steel on residual stresses after being exposed to high temperature. For welded Q690 steel H- sections and box-sections, equations to evaluate the corresponding residual stress reduction factor at elevated temperatures and after high temperature exposure were proposed based on the results of finite element analysis.

Efficient analysis of welding thermal conduction using the Newton\u2013Raphson method, implicit method, and their combination

Finite element analysis is commonly used to investigate the thermal-mechanical phenomena during welding. To improve the computing efficiency of finite element analysis for welding thermal conduction, a novel Newton–Raphson method (NRM) without the computation of inverse matrix and a hybrid method combing the NRM and conventional implicit method (IMP) were developed. Comparison of computing time between the hybrid method implemented in an in-house software JWRIAN and the IMP used in a commercial software ABAQUS indicated that the computing speed of the former was about 4.5 times faster than that of the latter. Additionally, compared to the conventional IMP, the NRM exhibited higher computing efficiency in the analysis of transient thermal conduction during the welding heating process. Meanwhile, a combined hybrid method of the NRM and IMP was verified to be more efficient in analyzing the welding thermal conduction throughout the heating and cooling processes. Moreover, the thermal cycles computed by the hybrid method were consistent with those from experimental measurement, indicating the high accuracy of the hybrid method. Furthermore, the hybrid method was used to predict the temperature field of the corner boxing fillet joint welded by a low transformation temperature weld metal for generation of compressive residual stress.

Applicability of Solid Lubricant Coatings in Cold Rod Extrusion of Stainless Steels

Cold extrusion is an established technology for the production of dimensionally accurate components in large series. Due to the high material and energy efficiency, a resource-saving manufacturing of high-performance parts is possible. Forming at room temperature leads to an advantageous grain structure and work hardening of the material, resulting in components with favorable operating characteristics. Nevertheless, a challenge is the generation of residual stresses during forming, which are influencing the fatigue behavior. The modification of the tribological conditions is one method for influencing the parts’ residual stress state. However, the high strength and work hardening of the materials formed at room temperature leads to high tribological loads between billet and die. These challenges are intensified by the increasing use of stainless steels due to growing demands for corrosion resistant components. The aim followed within this paper is therefore to investigate the applicability of typical lubricant coatings in the forward rod extrusion of stainless steels. For this purpose, the ferritic stainless steel X6Cr17 (DIN 1.4016) and the ferritic-austenitic stainless steel X2CrNiMoN22-5-3 (DIN 1.4462) are extruded with an equivalent plastic strain of ε̅ ≈ 1. The research is performed with a molybdenum disulfide (MoS2), a soap and a polymer-based lubricant coating. For reproducing different contact conditions, the die geometry is varied with die opening angles of 60°, 90° and 120°. The suitability of the lubricants is evaluated using the integrity of the lubricant coating after forming. From the correlations between process forces, temperatures and surface integrity, recommendations for the application of the researched lubricants are derived.

Exploration of irreversible residual stresses in a carbon/epoxy composite

Residual stresses in composite material may rise from several sources; difference in thermal straining between fibre and matrix, chemical shrinkage of the matrix material. The presented paper explores an irreversible Eigen-strain in the material which is shown to change and be removed by a thermal treatment above the Tg of the matrix material. This has been observed though TMA measurements of a carbon/epoxy unidirectional sample. The local Eigen-strain is translated into stresses using a visco-elastic constitutive relation. Further exploration indicates that cooling rate influence the generation of residual stresses in the material.

Elaboration and mechanical properties of monolithic and multilayer mullite-alumina based composites devoted to ballistic applications

Both monolithic and multilayer mullite-alumina ceramic composites dedicated to ballistic applications were produced by uni-axial pressing and tape casting before being sintered at 1510 °C. The compositions combining andalusite and kaolin in addition to α-alumina exhibit the more promising mechanical properties, reaching the performances of pure ballistic alumina. However, for a given bulk density value, a significant improvement of the performances (Young's modulus and ballistic impedance) only by varying the composition of the monoliths is limited. The second approach reported in this work has consisted in the development of judicious multilayer materials based on the generation of internal residual stresses in thinner layers. Compared to the monolithic materials, the most efficient multilayer configurations exhibit a failure stress improved by +35% and a fracture energy increased by +60%. Indeed, the layers subjected to compressive stress promote a significant crack bifurcation during rupture.

Wear mechanism in high-speed superabrasive grinding of titanium alloy and its effect on surface integrity

Single-layer electroplated cBN wheels offer several advantages over conventional wheels when grinding difficult-to-cut materials, in terms of improved workpiece surface integrity issues, such as lower grinding burn, fewer surface defects, and generation of compressive residual stresses. However, grinding behaviour e.g., grinding forces, temperature, and surface integrity, changes with wheel use while employing single-layer wheels due to progressive wheel wear as dressing is not conducted for them. Therefore, wheel wear and associated grindability studies like grinding forces and surface integrity are essential for the implementation of these wheels in the industry. The present study evaluates the wear mechanism of the electroplated cBN wheel and its effect on the grindability of Ti–6Al–4V. High grinding speeds (40 & 60 m/s) were employed under different cutting fluids environments (water-based soluble oil emulsion in minimum quantity cooling lubrication (MQCL) as well as in flood cooling modes and neat oil in MQCL regime). A lower cutting speed of 20 m/s is also chosen for benchmarking purpose. Grit fracture is found to be the primary mode of wheel wear. An elaborate discussion on the mechanism of cBN grit fracture is presented. It is observed that thermal shock-induced fracture has a dominant effect on wheel wear, and consequently, water-based fluid provided 2–4 times higher radial wear than neat oil up to 40 m/s. Because of lower radial wear, neat oil provided only 0–10% increase in grinding forces, 0–10% decrease in compressive residual stress, and almost the same level of surface redeposition with the progression of cumulative material removal. On the other hand, water-based fluid yielded 30–100% rise in grinding forces, 10–75% decrease in compressive residual stress, and a higher level of surface redeposition.