Mitigation Of Residual Stress Research Articles

Neutron Through-Thickness Stress Measurements in Coatings with High Spatial Resolution

A great variety of techniques are nowadays used to spray coatings with different functionality and properties for the purpose of surface enhancement. Depending on application and design, these can be thermal (plasma or high-velocity oxy-fuel are the most widely used) and warm or cold spraying, which are known to generate considerable residual stresses. This stress is a function of the spaying process as well as the material and thickness of the coating-substrate system. The mechanical integrity of coatings is critical for certain applications, e.g. wear resistant and thermal-barrier coatings, hence residual stress control and mitigation are essential in preventing the coating’s mechanical failure, improving the coating’s performance and the its operational lifetime. Although hole drilling technique or x-ray diffraction combined with layer removal method can be applicable for stress measurements in coatings, the neutron diffraction stress analysis also provides an effective and efficient tool for non-destructive through-thickness stress measurements with a commensurately high resolution, down to 0.1-0.2 mm. The most recent results of neutron diffraction stress measurements in coating systems are presented herein.

A new distributed cooling method for mitigating residual stress in friction stir welding

An analytical and finite element investigation of the effect of different cryogenic cooling nozzle configurations on temperature and residual stress in a model friction stir weld is presented. A new configuration adopting a distributed cooling approach is proposed based on an analytical cooling model. Finite element models are implemented to verify the effect of distributed cooling on welding temperature and longitudinal residual stress. The results presented indicate that new active cooling methods can improve mitigation of welding-induced residual stress.

Characterisation of residual stresses in heat treated, high strength aluminium alloy extrusions

Residual stresses were measured in rectilinear aluminium bars quenched using an aqueous polyoxyethylene glycol (PAG) solution or cold-water. Residual stresses were measured with neutron diffraction and a superposition-based method using mechanical strain release measurements. Three orthogonal stress components were measured along two transverse lines using neutron diffraction. The longitudinal residual stresses were mapped over a transverse cross-section using the contour technique. A primary slice removal technique mapped three orthogonal residual stresses over a transverse cross-section in the PAG extrusion. Residual stresses were found to vary from biaxial compressive in the part boundaries to triaxial tensile in the interiors. There was close correlation between the neutron diffraction and mechanical strain release techniques. PAG quenching demonstrated lower residual stresses.This paper is part of a Themed Issue on Measurement, modelling and mitigation of residual stress.

An assessment of residual stress mitigation strategies for laser clad deposits

Laser cladding can be used for reclamation or for improving the corrosion resistance of engineering components. However, the process introduces substantial levels of residual stress, which can exacerbate corrosion. In this study, the effectiveness of different residual stress mitigation strategies was investigated. Laser clad overlays were produced by melting an austenitic stainless steel powder onto either an austenitic stainless steel or a mild steel substrate. Residual stresses were measured, using the hole-drilling technique, in the as-clad condition as well as after either laser shock peening (LSP) or post-weld heat treatment (PWHT). Samples were then subjected to corrosion testing. In all cases, LSP delayed the onset of corrosion cracks. However, PWHT was only effective when the substrate and overlay materials matched.This paper is part of a Themed Issue on Measurement, modelling and mitigation of residual stress.

Quantifying the metallurgical response of a nuclear steel to welding thermal cycles

Solid-state phase transformations can drastically influence the evolution of stress in welds due to the strains associated with the transformations and related changes in mechanical properties. As such, finite-element predictions of welding residual stresses need reliable materials data including, where applicable, information on phase transformation kinetics and phase- and temperature-dependent material properties. Owing to a scarcity of such data, many authors have used uncalibrated empirical modelling approaches for the prediction of welding residual stresses. This paper addresses this critical shortage for an important nuclear pressure vessel (SA508) steel. Austenite formation, grain growth and decomposition data are presented and subsequently used to calibrate transformation models. These models are shown to accurately predict microstructure and residual stresses for experimental test cases.This paper is part of a Themed Issue on Measurement, modelling and mitigation of residual stress.

Determination of residual stress within complex-shaped coarse-grained cobalt–chromium biomedical castings

Cast ASTM F75 femoral knee implant components distort during manufacture due to residual stress re-distribution or inducement. These castings pose a number of challenges for residual stress determination methods; they have a complex geometry, their microstructure is inhomogeneous, they work-harden rapidly and they have a coarse, elastically anisotropic grain structure. The contour method is anticipated to be the most promising residual stress determination technique. X-ray diffraction is feasible for components which have experienced plastic deformation on their surface which results in refined diffracting domains. Centre-hole drilling is feasible, but the influence of stress induced from drilling and the effect of coarse grain structure is unknown. Neutron diffraction is challenging also due to a coarse grain structure and difficult nuclear material properties.This paper is part of a Themed Issue on Measurement, modelling and mitigation of residual stress.

Numerical and experimental investigation of thickness effect on residual stress measurement

This article studies the effect of thickness on residual stress measurements both numerically and experimentally. First, the released strain of aluminium specimens with different thicknesses subjected to incremental hole drilling is analysed using an efficient finite element model. From these results, the cumulative calibration coefficients and their variations as a function of plate thickness are determined. Then, the residual stress profile of a 1-mm-thick aluminium plate subjected to incremental hole drilling is investigated by in-plane three-directional moiré interferometry. A comparative study between the principle stress data calculated using the special calibration coefficients that match the thickness and the general ASTM calibration coefficients that are designed for thick plates is carried out. The analysis results demonstrate that the thickness significantly influenced the release strain. Moreover, the mismatch between the calibration coefficients and the thicknesses results in a deviation in the stress data of more than 10%, and the deviation increases with decreasing thickness.This paper is part of a Themed Issue on Measurement, modelling and mitigation of residual stress.

Prediction of welding stresses in WIC test and its application in pipelines

In the present study, the Welding Institute of Canada (WIC) restraint test was used to simulate the restraint conditions of full-scale girth welds on energy pipelines to ascertain the influence of welding process parameters on welding stresses. Finite element models are developed, and validated with neutron diffraction measurements, to evaluate the welding stresses for under-matched, matched and over-matched welds. The effects of heat input, wall thickness and variable restraint lengths of WIC sample are systematically investigated. As a practical outcome, this work can help in selection of the appropriate restraint length for WIC tests to simulate the specified stress conditions in the pipeline, and, ultimately, reduce the risk of Hydrogen Assisted Cold Cracking (HACC) in high strength low alloy.This paper is part of a Themed Issue on Measurement, modelling and mitigation of residual stress.

Determination of residual stresses in welded components by finite element analysis

The continued safe and reliable operation of plant invariably has to consider the assessment of defects in welded structural components. This requires some estimate of the residual stresses that have developed during the welding fabrication process. There is an increasing use of computational weld mechanics to evaluate residual stresses and this paper describes the development of guidelines for using finite element analysis, which are now incorporated into the EDF Energy R6 defect assessment procedure, to determine stresses for use in the procedure. Prior to use in assessment the predicted results should be validated by comparison with measurements and the guidelines provide advice on the differing standards of validation which may be applied including the manufacture and testing of validation mock-ups.This paper is part of a Themed Issue on Measurement, modelling and mitigation of residual stress.

Residual stress distributions in laser and gas-metal-arc welded high-strength steel plates

S700 is a high-strength steel recently developed by Tata Steel. This paper describes the residual stress distributions in a multi-pass gas-metal-arc weld (GMAW), a single pass autogenous laser weld (ALW) and a multi-pass ultra-narrow gap laser weld (NGLW) in 13 mm thick high-strength (S700) steel plates, as measured by X-ray diffraction and the contour method. The relationships between microstructural variation and residual stress distributions were investigated. It was found that solid-sate phase transformations from austenite to ferrite, bainite and martensite changed both the magnitude and distribution of residual stresses in the three different welded specimens. The width of the regions sustaining tensile stress in each specimen decreased in the following order: GMAW > ALW > ultra-NGLW.This paper is part of a Themed Issue on Measurement, modelling and mitigation of residual stress.

Residual surface stress: comparing traditional and modulated tool path machining processes

Traditional machining processes, where material is removed by a cutting tool from a workpiece, can introduce residual stresses at the surface of machined pieces. This paper provides an examination of an alternative machining methodology called modulated tool path machining. The ultimate objective of this research is to determine the effects of modulated tooling path machining processes, as applied to control chip geometry, on the surface stress of selected materials. Residual stresses in machined samples were characterised through the use of X-ray diffraction by comparing the modulated path method with a more traditional material removal technique (i.e. constant surface speed and constant contact).This paper is part of a Themed Issue on Measurement, modelling and mitigation of residual stress.

Residual stress of as-deposited and rolled wire+arc additive manufacturing Ti–6Al–4V components

Wire + arc additive manufacturing components contain significant residual stresses, which manifest in distortion. High-pressure rolling was applied to each layer of a linear Ti–6Al–4V wire + arc additive manufacturing component in between deposition passes. In rolled specimens, out-of-plane distortion was more than halved; a change in the deposits' geometry due to plastic deformation was observed and process repeatability was increased. The Contour method of residual stresses measurements showed that although the specimens still exhibited tensile stresses (up to 500 MPa), their magnitude was reduced by 60%, particularly at the interface between deposit and substrate. The results were validated with neutron diffraction measurements, which were in good agreement away from the baseplate.This paper is part of a Themed Issue on Measurement, modelling and mitigation of residual stress.

Time transient validation of residual stress prediction models for aluminium alloy quenching

Finite element models that predict residual stress states in relatively large quenched aluminium alloy products tend to give reliable results. However, even though there is confidence that the predicted stress state is correct, there is no validation indicating that the stress/displacement development during the quench is comparable to the experimental case. Combined with this, finite element predictions for small samples tend to underestimate surface stress. This paper uses a ‘Navy C-Ring’ benchmark design to monitor displacement during quenching. The heat transfer coefficient is found to be the most dominant boundary condition and is critical to ensuring displacement and residual stress predictions that match the experimental case.This paper is part of a Themed Issue on Measurement, modelling and mitigation of residual stress.

The Mitigation of Weld Residual Stress on 304L Stainless Steel by Post Weld Cool Treatment Process

The High Welding Residual Stress is the Main Factors Affecting the Service Life of Welded Structures. Post Weld Cool Treatment (PWCT) is a Novel Method by Introducing Reverse Process Welding Temperature Field to Eliminate the Residual Stress and to Obtain Compressive Stress Layer. the Major Factors Affecting the Effects of Post Weld Cool Treatment (PWCT) is Preheating Temperature, Cooling Time and Cooling Range. in this Paper, a Model to Calculate the Residual Stress was Built Using Finite Element Code ABAQUS, and Different PWCT Processes were Applied on 304L Stainless Steel Specimens. at the same Time, Impact Indentation Method (IIM) was Used to Measure the Residual Stress on the Specimens. the Results Show that the Longitudinal Stress and the Transverse Stress were Reduced Obviously and Compressive Stress was Generated after PWCT in both of the Simulation and the Experiment. the Proposal Preheating Temperature was 400°C and the Cooling Range was 2 Times of Weld Width. Besides, the Cooling Time had Little Effect on the Residual Stress.

Mitigation of residual stresses and distortions in thin aluminium alloy GMAW plates using different heat sink models

This study aims to minimise the residual stresses and distortions in thin butt-welded aluminium alloy 5052-H32 plates during gas metal arc welding process by using three different heat sink models employing thick backing plate and cooling fluids. Experiments are conducted to investigate the efficacy of these models on the temperatures, longitudinal and transverse residual stresses and distortions produced in the welded plates. The results are compared against numerical simulation results obtained using a commercial finite element analysis software ANSYS. Temperature-dependent thermal and mechanical properties of plates are used and coupled transient thermal–structural analysis based on thermo-elastic–plastic approach is conducted. Residual stresses are measured using X-ray diffraction and distortions using a coordinate measuring machine. Temperatures were measured using thermocouples. Results show good conformity between experimental and numerical results and that the heat sink model using a mixture of argon gas and water is the most suitable scheme to achieve the mitigation.

Local residual stress mitigation after curing process by spread fiber tow in carbon fiber-reinforced plastic

The application of the tow spreading technique to wound filaments or woven composites seems promising because of its advantageous strength enhancement mechanism. The effects of tow spreading on the curing progress and the residual stress of the resin were investigated in this study. We hypothesized that the homogeneous distribution of fibers realized by the tow spreading technique suppresses the stress concentration of the resin in the vicinity of close-packed fibers. This hypothesis was examined through finite element simulation using a micro-scale model with the definite separation of fiber and resin. The residual stress and strain after the curing process were investigated using a newly developed simulation system.

Effect of continuously graded functional layer on curvature and residual stress of solid oxide fuel cell in initial reduction process

Solid oxide fuel cell (SOFC) is considered to be a highly efficient device to convert chemical fuels directly into electrical power. Because of multilayer composite arrangement of cells, mismatch of the thermal expansion coefficients, chemical/thermal gradient, or phase change of the materials will result in residual stresses, which are reflected in the pronounced bending of unconstrained cells and cause a reliable problem. Considerable efforts have been devoted to the analysis of residual stresses in an elastic multilayer system, and one of the efforts that are to improve not only electrochemical performance for high energy conversion efficiency but also long term stability, is to process a continuously gradient anode functional layer (CG-AFL) between dense electrolyte and porous anode. Hence to understand the stress distribution and deformation of the multilayer with a CG-AFL is needed for the cell design. As the chemical reduction takes place at the interface between NiO-YSZ and the previously reduced porous Ni-YSZ, a reduced layer, together with the unreduced layer and the electrolyte will cause the residual stresses to be re-distributed. In this paper, taking the CG-AFL into account, the curvature and residual stresses of half-cell during reduction are analyzed. The results show that the curvature of half-cell with a CG-AFL increases as the reduction process. And the curvature would also increase as the thickness of the CG-AFL increases, and decrease with the increase of the index of power function that expresses young's modulus and thermal expansion coefficient of gradient layer. The residual stresses among the layers are correspondingly influenced by the thickness of the gradient layer, the index of power function and reduction extent. When taking power function as a linear function, the gradient layer obviously reduces the residual stress in the electrolyte. However, the increase of the index in power function will cause the increase of electrolyte residual stress. These mentioned analyses reveal that the CG-AFL cannot offer a solution that simultaneously improves the residual stress and curvature in a half-cell in terms of thickness and profile exponent of CG-AFL, i.e., the mitigation of residual stress will give rise to the increase of curvature, and vice versa. On the other hand, for part-reduced half-cell, the maximum tensile stress is found at anode/gradient layer interface in anode layer, which may facilitate structural failure since tensile residual stress is so high that it reaches the fracture strength of anode material. Consequently, it is important to ensure that the anode is fully reduced in practice. In conclusion, the existing gradient layer is helpful for enhancing the cell reliability via suitable design.

원자로 입출구 노즐 Alloy 82/182 이종금속 용접부 Weld Inlay 적용 후 초음파나노표면개질이 잔류응력 완화에 미치는 영향

This study was performed to investigate the effect of ultrasonic nano crystal surface modification (UNSM) on residual stress mitigation after Weld Inlay repair for butt dissimilar metal weld with Alloy 82/182 in reactor vessel In/Outlet nozzle. As-welded and Weld Inlay specimens were made in accordance with design standard of ASME Code Case N-766, and two planes of their weld specimens were peened by the optimum UNSM process condition. Peening characteristics for weld specimens after UNSM treatment were evaluated by surface roughness and Vickers hardness test. And, residual stress for weld specimens developed from before and after UNSM treatment was measured and evaluated by instrumented indentation technique. Consequently, it was revealed that the mitigation of residual stress in weld metal after Weld Inlay repair of reactor vessel In/Outlet nozzle could be possible through UNSM treatment.

A study on residual stress mitigation of the HDPE pipe for various annealing conditions

This paper presents effects of the annealing condition variables such as temperature and time on the residual stress mitigation. The effects were investigated by using the various measurement methods such as hole-drilling method and slitting method. As a result of the investigation, the residual stress mitigation magnitude increases with increasing the annealing time and temperature. Based on the investigation results, the quantitative correlations between the annealing variables and the residual stress mitigation were derived. Finally, the effect of long-term operation under the normal operating temperature conditions on the residual stress mitigation was investigated by referring to the derived equations and performing some additional tests, and it is identified that the residual stresses are not significantly relaxed over the design lifetime of the safety class III buried HDPE pipes.

Effect of Multipass Welding Using a Low Transformation Temperature Filler Metal on Residual Stress and Toughness

Residual stresses in welded components are consequence of stress and/or thermal gradients and influenced by factors such as joint geometry, variation in strength of the material, preheat temperature, heat input, post-weld heat treatment and phase transformation strains. During the 70’s, it was observed that the level of residual stress accumulated in a constrained sample during cooling from austenite could be reduced after transformation to martensite or bainite. Some works have evaluated effect of welding using a low transformation temperature martensitic filler metal on the level of residual stress in single pass joints. According to these studies, martensite start temperature in the range 200–250°C can be extremely effective for mitigation of tensile residual stresses. The outcome of most of these works was on one hand increase of fatigue life due to the mitigation of tensile residual stresses via transformation strains, on the other a significant reduction of the fracture toughness.In the present study, sections of API 5L class B steel tubes were multipass welded using a 12Cr-5Ni low transformation temperature filler metal in addition to a conventional filler metal. Residual stresses in the inner and outer surfaces were measured by X-ray diffraction. Aspects related to the improvement of toughness in the weld metal due to the tempering of one pass by the subsequent were also discussed.