Reduction Of Residual Stress Research Articles

A New Approach for the Control and Reduction of Warpage and Residual Stresses in Bonded Wafer

A geometrical modification on silicon wafers before the bonding process, aimed to decrease (1) the residual stress caused by glass frit bonding, is proposed. Finite element modeling showed that (2) by introducing this modification, the wafer out-of-plane deflection was decreased by 34%. Moreover, (3) fabricated wafers with the proposed geometrical feature demonstrated an improvement for the (4) warpage with respect to the plain wafers. A benefit for curvature variation and overall shape of the (5) bonded wafers was also observed.

Residual stress reduction in dissimilar metals weld

Conventional methods such as post-weld heat treatment is not capable to reduce residual stress (RS) in dissimilar metals weld (DMW) to the same extent as in similar weld due to mismatch between thermal expansion coefficient of base metals. The objective of this study to understand the effects of a modern in situ technique, called CO2 rapid cooling, on mechanism of RS redistributions in both similar and dissimilar metals welds. More focus of this investigation is given to the DMW. A thermo-mechanical numerical model is developed to investigate the effectiveness of various CO2 rapid cooling parameters such as power, radius, off-center, and location of the CO2 nozzle on RS distribution. The model is tested and validated with experimental data obtained from neutron diffraction measurement. Overall, this study shows that the CO2 cooling application can produce a significant RS reduction in similar weld as well as DMW. It shows that smaller CO2 nozzle can lead to lower RS magnitude considerably; however, it is not always capable to produce favorable RS distribution. In addition, since the RS distribution is asymmetric in a DMW, the implementation of CO2 cooling technique to mitigate RS need not be symmetric or uniform with respect to the weld center line. Based on the results, further recommendations to minimize RS in welded parts are provided.

Photooxidation crosslinking to recover residual stress in decellularized blood vessel.

Decellularization method based on trypsin-digestion is widely used to construct small diameter vascular grafts. However, this method will reduce the opening angle of the blood vessel and result in the reduction of residual stress. Residual stress reduced has an adverse effect on the compliance and permeability of small diameter vascular grafts. To improve the situation, acellular blood vessels were treated with glutaraldehyde and photooxidation crosslinking respectively, and the changes of opening angle, circumferential residual strain of native blood vessels, decellularized arteries and crosslinked blood vessels were measured by means of histological examination, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) in this study. The opening angle of decellularized arteries significantly restored after photooxidation crosslinking (P = 0.0216), while that of glutaraldehyde crosslinking blood vessels reduced. The elastic fibers inside the blood vessels became densely rearranged after photooxidation crosslinking. The results of finite element simulation showed that the residual stress increased with the increase of opening angle. In this study, we found at the first time that photooxidation crosslinking method could significantly increase the residual stress of decellularized vessels, which provides biomechanical support for the development of new biomaterials of vascular grafts.

Towards an holistic account on residual stresses in full-forward extruded rods

An holistic view is attempted towards prediction of the effect of residual stresses induced by full-forward extrusion on fatigue life of workpieces during operation. To study the effect of constitutive model on the accuracy of forming simulations, a combined nonlinear isotropic/kinematic hardening model as well as the isotropic hardening part of the same model are calibrated based on five compression-tension-compression uniaxial stress experiments. A full-forward extrusion finite element model is developed adapting both the aforementioned hardening plasticity models and the predicted residual stress states at the surface of the workpiece are compared against that of a corresponding forming experiment. Results show residual stress predictions of remarkable accuracy by the FE-models with the isotropic hardening model. The effect of residual stresses on fatigue life of the workpiece is qualitatively studied by uncoupled multiscale simulations featuring gradient crystal plasticity at the microscale. While the effective (homogenized) macroscale response indicates elastic response during a macroscopically cyclic loading, plasticity accompanying reduction of residual stresses is still present at the microscale within, e.g. grain boundaries.

Control of residual stresses in roll forming through targeted adaptation of the roll gap

Roll forming is a continuous manufacturing process, which allows for the economical production of a wide range of profile geometries in large batches. When roll formed profiles are cut to length, process related residual stresses are released. This effect, also known as end flare, results in a deformation of the profile ends at the cut-off. However, typical roll formed profiles like linear guides or cable conduits require high dimensional accuracy having tight manufacturing tolerances to guarantee their functionality. Therefore, during process design and set up, countermeasures have to be applied to minimize end flare. In this paper a countermeasure to reduce end flare by targeted adaptation of the roll gap is presented and application limits are discussed. An explanatory model is developed, which shows the creation and reduction of residual stresses due to the reduced roll gap.

Study on a stress-magnetic relationship of DO3 based on first principles

Based on the first principles, in this paper the stress-magnetic relationship model of the Fe3Si (DO3) phase in silicon steel was analyzed, and the band structure and electronic density states were calculated. The experimental results show that the atomic magnetic moment would increases with the increase of tensile stress, and decreases with the increase of compressive stress. The linear compressive strength of the DO3 crystal is stronger than the linear tensile strength, and this phenomenon could be explained by the band structure and electronic density states. In addition, the macro verification experiment is designed. The silicon steel plate is used as the verification experiment sample, the change of silicon steel magnetic properties during the tension and compression process is measured. The experimental results show that the magnetic properties of silicon steel show an increasing trend in the tension process and a decreasing trend in the compression process, which qualitatively proves the correctness of the first principle calculation results. The MFM measurement results confirm that the stress would affect the magnetic domain. The stress-magnetic relationship of DO3 would provide theoretical support for electromagnetic detection and reduction of residual stress in silicon steel.

Research on Magnetic-Vibration Combination Treatment Based on Multifield Coupled Finite Element Analysis

Abstract In this paper, the three-dimensional simulation modeling of the magnetic-vibration combination residual stress reduction device was established based on the multifield coupled finite element analysis, and the residual stress reduction method of magnetic-vibration combination treatment was researched. The placement mode of the electromagnetic device and the factors affecting the effect of the magnetic-vibration combination reduction were comprehensively studied. The results showed that when the electromagnetic device was placed vertically, it was more beneficial to reduce the residual stress. The electromagnetic frequency was the maximal factor to affect the magnetic-vibration combination, and the factors that followed were voltage, material performance, exciting force, and exciting frequency. The greater the electrical conductivity of the material was, the lower the magnetic induction intensity was. The thicker the steel plate was, the easier it was to magnetize, but it was not conducive to vibration, and there was an optimal thickness under a certain set of parameters. Applying tension to the steel plate was beneficial to increase magnetization to reduce stress, and the aforementioned results of the simulation were consistent with the experimental results. The simulation study in this paper provided theoretical support for the process parameter setting of magnetic-vibration combination treatment to reduce residual stress.

The effect of build direction and heat treatment on atmospheric stress corrosion cracking of laser powder bed fusion 316L austenitic stainless steel

Austenitic stainless steels are susceptible to stress corrosion cracking (SCC) when exposed to chloride ions and tensile stresses. For laser powder bed fusion (LPBF) components, high residual tensile stresses exist from the large thermal gradients during solidification. While post fabrication heat treatments can relieve residual stresses, their effectiveness in improving SCC resistance of LPBF material is undetermined. The effects of different heat treatments (i.e. temperature and cooling method) and build orientations on SCC susceptibility of LPBF 316L were explored. Samples were exposed to MgCl 2 and maintained at 75 °C and 70% RH for the test duration. Cracks were highly branched and propagated perpendicularly to build direction even in the presence of an applied perpendicular 60 MPa stress. Vertical as-built specimens exhibited higher cracking densities than horizontal ones, due to higher surface residual stresses. SCC and corrosion favoured one side for horizontal specimens while the distribution was random for vertical specimens. After 750 °C (2 h, furnace cooled) heat treatment, SCC susceptibility reduced for vertical 316L but increased for horizontal 316L. This was attributed to competing effects: reduction in residual surface tensile stresses (beneficial) and loss of non-equilibrium microstructure (detrimental). Encapsulation to prevent oxidation during heat treatment negatively impacted SCC resistance of LPBF 316L, likely due to changes to surface oxide condition. No SCC was observed after 900 °C (0.5 h) heat treatments within the test duration, however, pitting corrosion persisted.

Reduction of residual stress in porous Ti6Al4V by in situ double scanning during laser additive manufacturing

Selective laser melting (SLM) technology plays an important role in the preparation of porous titanium (Ti) implants with complex structures and precise sizes. Unfortunately, the processing characteristics of this technology, which include rapid melting and solidification, lead to products with high residual stress. Herein, an in situ method was developed to restrain the residual stress and improve the mechanical strength of porous Ti alloys during laser additive manufacturing. In brief, porous Ti6Al4V was prepared by an SLM three-dimensional (3D) printer equipped with a double laser system that could rescan each layer immediately after solidification of the molten powder, thus reducing the temperature gradient and avoiding rapid melting and cooling. Results indicated that double scanning can provide stronger bonding conditions for the honeycomb structure and improve the yield strength and elastic modulus of the alloy. Rescanning with an energy density of 75% resulted in 33.5%–38.0% reductions in residual stress. The porosities of double-scanned specimens were 2%–4% lower than those of single-scanned specimens, and the differences noted increased with increasing sheet thickness. The rescanning laser power should be reduced during the preparation of porous Ti with thick cell walls to ensure dimensional accuracy.

Remedies for hydrogen-embrittlement on Grade-91 steel weld joint during long delay in PWHT

This paper discusses the effect of different combinations of preheating and post-heating on the corrosion and hydrogen embrittlement of Grade-91 steel weld joint in the as-welded condition. Though these welds are subjected to post-weld heat treatment (PWHT), there could be long delay in executing this, especially in the case of fabrication of large components, and during this delay, the welds in as-welded conditions are prone to environmental degradations like hydrogen embrittlement and different forms of corrosion. Though recommended minimum preheating and post-heating conditions are already known for welding of this class of steels, marginally increasing the temperature of preheating and post-heating or increasing the duration of post-heating can permit longer delay in the post-weld heat treatment (PWHT), without increasing the risk of environmental degradation. With this objective, a set of thirteen single-V multi-pass gas tungsten arc weld joints of Grade-91 steel fabricated with different preheating and post-heating combinations. Results indicated a significant reduction in residual tensile stresses in the weld metal and reversing into compressive stresses upon preheating and post-heating at 300 °C. Moreover, diffusible hydrogen content and corrosion rate decreased significantly with the preheating and post-heating. However, there are no significant variations in the microstructure, mechanical properties, and hydrogen embrittlement with preheating and post-heating. This study proved that the risk of embrittlement in Grade-91 steel welds due to an indefinite delay in PWHT could be minimized by combined preheating and post-heating.

The effect of low temperature heat treatment on stress corrosion crack initiation in machined 316L stainless steel in high-temperature hydrogenated water

A notable reduction of the stress corrosion cracking (SCC) initiation susceptibility was identified for machined cold-rolled 316L stainless steel that received a 650°C/10 hours heat-treatment prior to slow strain rate tensile (SSRT) testing in high-temperature hydrogenated water. The cracks per unit area of the machined surface of heat-treated specimens decreased by ~50% compared to as-machined surfaces, and by >70% with respect to polished surfaces. The results were ascribed to recrystallization of the ultrafine-grains present in the outer deformation layer of the machined surface, which resulted in a reduction of the tensile residual stress and nano-indentation hardness.

Studying the residual stress homogenization and relief in aerospace rolling ring of GH4169 alloy using ageing treatment

In the manufacturing process of aerospace large ring parts, a large number of exterior materials are removed, which makes the ring parts become a thin-walled structure with low stiffness. In the actual production process of the aerospace industry, the processing deformation caused by a series of internal and external factors is ubiquitous. The studies show that the main factor causing the machining deformation is the initial residual stress (RS) inside the blank ring. The ring rolling process is accompanied by local severe plastic deformation, resulting in large and uneven RS. The homogenization and reduction of initial RS are of great significance to reduce the adverse effect of machining deformation. The research object in this study is a sizeable GH4169 alloy aerospace rolling ring. First, a long-term natural ageing treatment was designed for homogenizing residual stresses in sizeable GH4169 alloy ring. Second, a finite element model was established to simulate the rolling process and the thermal ageing process. The corresponding rolling and thermal ageing experiments were carried out to verify the simulation results. The purpose of this process is to explore and verify the effect of natural ageing and artificial ageing on homogenizing and reducing the RS in the rolling ring. The results show that the homogenization of RS distribution was enhanced significantly by natural ageing treatment, while the RS magnitudes descended by 15~35%. Combined with the subsequent thermal stress relief, the RS is significantly reduced or even eliminated. This study is of great significance to the homogenization and reduction of RS in large GH4169 alloy ring.

Optimization Study of Post-Weld Heat Treatment for 12Cr1MoV Pipe Welded Joint

In order to clarify the role of different post-weld heat treatment processes in the manufacturing process, welding tests, post-weld heat treatment tests, and finite element analysis (FEA) are carried out for 12C1MoV steel pipes. The simulated temperature field and residual stress field agree well with the measured results, which indicates that the simulation method is available. The influence of post-weld heat treatment process parameters on residual stress reduction results is further analyzed. It is found that the post weld dehydrogenation treatment could not release residual stress obviously. However, the residual stress can be relieved by 65% with tempering treatment. The stress relief effect of “post weld dehydrogenation treatment + temper heat treatment” is same with that of “temper heat treatment”. The higher the temperature, the greater the residual stress reduction, when the peak temperature is at 650–750 °C, especially for the stress concentration area. The longer holding time has no obvious positive effect on the reduction of residual stress.

Computationally Efficient Models of High Pressure Rolling for Wire Arc Additively Manufactured Components

High pressure multi-layer rolling is an effective method to reduce residual stress and distortion in metallic components built by wire arc additive manufacturing (WAAM). However, the mechanisms of the reduction in residual stress and distortion during multi-layer rolling are not well understood. Conventional finite element models for rolling are highly inefficient, hindering the simulation of multi-layer rolling for large WAAM components. This study aims to identify the most suitable modelling technique for finite element analysis of large WAAM component rolling. Four efficient rolling models were developed, and their efficiency and accuracy were compared with reference to a conventional large-scale rolling model (i.e., control model) for a WAAM built wall. A short-length transient model with fewer elements than the control model was developed to reduce computational time. Accurate predictions of stress and strain and a reduction in computational time by 96.5% were achieved using the short-length model when an implicit method for numerical solution was employed, while similar efficiency but less accurate prediction was obtained when an explicit solution method was adopted. A Eulerian steady-state model was also developed, which was slightly less efficient (95.91% reduction in computational time) but was much less accurate due to unrealistic representation of rolling process. The applicability of a 2D rolling model was also examined and it was found that the 2D model is highly efficient (99.52% time reduction) but less predictive due to the 2D simplification. This study also shows that the rigid roller adopted in the models is beneficial for improving efficiency without sacrificing accuracy.

Dynamic Performance Evaluation of Concrete Building Using Low‐Yield Point Steel Shear Panels

Steel shear walls are a novel component in the field of construction. It has been of special interest to structural engineers for the reinforcement of steel buildings for the recent decades. Its unique features have attracted more attention, and its features are economical, easy to implement, light weight compared to similar systems, high ductility, fast installation, high energy absorption, and a significant reduction in residual stress in the structure. All the reasons made researchers think about studying its use in the repair of concrete buildings. Because this system has a low weight, it does not add extra load to the structure, and even with its connections, it strengthens the beams and columns around it. The design of this system in concrete buildings does not seem to be economical except in the case of restoration. In this paper, preliminary explanations of the steel shear wall are presented for more familiarity, and in the following sections, the study of reinforcement and repair of concrete structures will be studied and its difference with the low‐yield point will be considered. Finally, the test results will be reviewed. The results of this study show that LYP steel shear panels cause a lot of energy loss and absorption, which is very useful in the safety of buildings exposed to severe earthquakes.

Effectiveness of Welding Residual Stress Reduction Method using Ultrasonic Vibration in Stainless Steel

Effectiveness of Welding Residual Stress Reduction Method using Ultrasonic Vibration in Stainless Steel

A Method of Welding Residual Stress Reduction using Ultrasonic Vibration

A Method of Welding Residual Stress Reduction using Ultrasonic Vibration

Utilization of Optimization of Internal Topology in Manufacturing of Injection Moulds by the DMLS Technology

The present paper is focused on the issue of creating residual stresses in the manufacturing of the moulded parts for injection moulding machines using DMLS technology. Thus, fractures and cracks can cause deformations and geometric inaccuracies in the final part. Moreover, they pose a potential damage risk to the machine itself. The simulation tools for the analysis of the Direct Metal Laser Sintering (DMLS) process were used to expose the critical points of the original monolithic shaped insert in which the highest stresses during the manufacture occur. Subsequently, an alternative solution was created via the optimization of the internal topology. This solution was analysed, and in terms of strength characteristics, compared to the original model in order to ensure the proper function and durability of the manufactured part. The present study was created in cooperation with a company engaged in the production of injection moulds. The internal topology optimization of the part itself is used in combination with the appropriate orientation of the model in the workspace, unlike other research in the given field, where either the model orientation optimization or the support structure is used in this design. However, except for the mentioned reduction of residual stresses, it has a positive effect on mechanical properties, reducing material consumption and savings in time; thus, the obtained results can be applied to other methods of additive manufacturing.

Effect on microstructural and mechanical properties of Inconel 718 superalloy fabricated by selective laser melting with rescanning by low energy density

In this study, the residual stress reduction through low energy density reheating method in selective laser melting (SLM) process and the correlation between microstructure and mechanical properties were investigated. Inconel 718 superalloy specimens were manufactured via SLM and subjected to reheating (RH) strategies with different energy density, which was based on laser rescanning method. The microstructures were characterized by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The microstructure was observed in the vertical section, parallel to the building direction. With a scanning speed decrease in the RH conditions, the low angle grain boundary (LAGB) and average misoriented region fraction progressively increased. RH conditions exhibited higher Vickers hardness, tensile strength, and yield strength than those of the as-built condition, which increased slightly when the scanning speed was increased. Thermal residual stress was generally higher at z-axis than that at the x-axis. The lowest residual stress value was observed in the highest scanning speed RH condition, and as the scanning speed decreased, it became similar to that of the as-built condition.

Post-Weld Heat Treatment of API 5L X70 High Strength Low Alloy Steel Welds.

High Strength Low Alloy (HSLA) steels are the materials of choice in pipeline construction with the API X70 grade as the steel for the majority of pipeline networks constructed during the late 20th and early this century. This paper reports on the influence of Post-Weld Heat Treatment (PWHT) on the reduction of residual stresses, resulting changes in the microstructure, and mechanical properties of a multi-pass, X70 HSLA steel, weld joints made by a combined Modified Short Arc Welding (MSAW) and Flux Cored Arc Welding (FCAW) processes. Neutron diffraction results highlighted high magnitude of tensile residual stresses, in excess of yield strength of both parent and weld metal, in the as-welded specimen (650 MPa), which were decreased substantially as a result of applying PWHT (144 MPa). Detailed microstructural studies are reported to confirm the phase transformation during PWHT and its interrelationship with mechanical properties. Transmission Electron Microscopy (TEM) analysis showed polygonization and formation of sub-grains in the PWHT specimen which justifies the reduction of residual stress in the heat-treated weld joints. Furthermore, microstructural changes due to PWHT justify the improvement in ductility (increase in the elongations) with a slight reduction in yield and tensile strength for the PWHT weld joint.