Redistribution Of Residual Stresses Research Articles

Creep rapture of plastic pipes: Effect of eccentricity, residual stress, and circumferential orientation

Plastic pipes made of high density polyethylene material with known geometric eccentricities and residual stresses were subjected to long term hydrostatic stress until rupture at different stresses and temperatures. Cooling and crystallisation rates of the pipe wall during the extrusion process were simulated along the production line. Crystallisation profile and circumferential orientation of polymer chains were measured at different angular locations and thicknesses around the circumference. It was shown that the plasticity-controlled rapture times of plastic pipes are significantly depended on geometric eccentricity as a result of re-distribution of residual stresses and circumferential orientation.

A Study on the Residual Stress of Seam Pipe Cutting and Girth Welding

Seam pipes are easier to manufacture and cheaper than seamless pipes, and are widely used in the manufacture of pipe spools for marine plant facilities. The manufacturing and assembly of seam pipes involve welding and cutting. The localized heating and cooling that occur during these processes may change the existing residual stress and cause deformation. Uncontrolled deformation can accumulate as assembly errors at the next step, potentially delaying the entire process and causing economic losses. Therefore, characteristics of residual stress redistribution caused by cutting and girth welding of seam pipes need to be studied further. In this study, we performed thermo-mechanical analysis of the manufacturing, cutting, and girth welding processes of seam pipes using the commercial finite element analysis (FEA) software MSC Marc and analyzed the characteristics of residual stress. Furthermore, we measured the residual stress in each process using the hole drilling method, analyzed the characteristics of redistributed residual stress, and ensured reliability. Based on the results of FEA and measured residual stress redistribution, we can provide a basis for reasonable mitigation when performing structural integrity evaluation if there is a defect in the weld of the pipe.

The performance transition of C/SiC composites induced by redistribution of residual stress

The residual stress generated from temperature changes and interference fit of rivet plays a significant role in the performance of C/SiC composites. To gain a thorough understanding of the residual stress evolution mechanisms and their influences on C/SiC composites, this work carries out comprehensive experimental research combined with simulation analyzes. The results of quasi-static tension tests present that as the environmental temperature rises from room temperature to 800 °C, the stiffness of structure increases a lot, while the strength of riveted joints significantly decreases. Furthermore, it is found that the microscopic failure modes are also changed. The cyclic unloading-reloading tests for calculating the residual stress quantitatively are conducted to explain the failure evolutions of structures. The obtained results reveal an important connection between the residual stress states and the microscopic failure modes of C/SiC composites. The environmental temperature and interference riveted joint both can affect stress state around the open hole, which are significant factors determining the damage modes and structural performance. In the process of C/SiC composites design, it is necessary to pay attention to the processing parameters of rivet interference fit to meet the performance optimization under service conditions.

Thermal redistribution of compressive residual stress introduced by interlayer laser shock peening in hybrid additive manufacturing

The objective of this research was to quantify the change in magnitude and depth of compressive residual stress (CRS) retained in the subsurface by interlayer coldworking when subjected to localized annealing that superimposed tensile stress. The approach was to hybridize additive manufacturing of AlSi10Mg alloy by coupling powder bed fusion (PBF) with laser shock peening (LSP) and characterize the resultant residual stress state by the hole-drilling method. The research found localized annealing from layer deposition formed two distinct regions in the subsurface, which was driven by localized and bulk stress redistribution. The experiments also showed that residual stress redistribution from LSP reached 550 µm into the subsurface, whereas local annealing from the deposition of layers extended only to a depth of 160 µm. Hence, compressive stress imparted by LSP was not entirely canceled by local annealing from PBF. This work provides the first quantification of the stress state response of hybrid additively manufactured parts to thermal loads and is fundamental to improving part performance through increased functional reliability, fatigue life, and corrosion resistance.

Re-Distribution of Welding Residual Stress in Fatigue Crack Propagation Considering Elastic–Plastic Behavior

The welding residual stress re-distribution behavior during fatigue crack propagation in butt-welded high-strength steel plates for ship construction is investigated based on experimental test results and numerical analyses. The specimens’ initial welding residual stresses are obtained from X-ray for middle tensile (MT) specimens cut from butt-welded high-strength steel plates. Then, fatigue crack propagation experiments on MT specimens are conducted, and a strain gauge is used to measure the residual stress re-distribution field around cracks. A practical fatigue crack propagation simulation procedure is developed with a dynamic update of in-situ welding residual stress, where the residual stress intensity factor Kres of the MT specimen is deduced. The stress ratio effect on Kres during fatigue crack propagation is analyzed and a good agreement between experimental and numerical results is achieved.

Method for processing experimental data when investigating residual stresses by drilling probe holes and digital image correlation

This paper investigates the cutting forces arising when using a single abrasive grain. Analytical studies were carried out using a model of a single abrasive grain in the form of a rod with a radiused apex acting on the workpiece material. The slip-line method (method of characteristics) was used to calculate the deformation intensity of a plastically edged workpiece material under the action of a single grain. Mathematical models were developed for the following factors: plastic deformation of the material, edging of the stagnated zone and its friction against the grain surface when moved upwards in the form of chippings, grain friction against the plastically deformed material, and the action of the dynamic component of plastic deformation. The significance of the dynamic component in the overall balance of forces related to plastic deformation was established by determining the ratio of dynamic stress on the break line and shear yield point. This dependence calculated for D16T and 30HGSA materials showed the feasibility of accounting for the dynamic component subsequently processed by free orthogonal cutting and rolling contact deformation using a special machine with numerical control. Further, using the same machine, drilling of probing holes was performed with video recording of the surface image prior to and following drilling. By varying the speckle images, the displacements of material particles on the sample surface were determined by the digital image correlation method, following which the radial deformations were determined by differentiating the obtained displacement values. Statistical analysis of a sample of radial deformations equidistant from the centre of the hole while varying the rotation angle by Fourier transformation with the calculation of the distribution period showed that the distribution is periodic. It is established that the periodograms constructed using experimental data have local maxima at a period value close to 180 degrees. This determines that the main calculated components of the residual stresses and the angle of their rotation be constant when selected to calculate the values of radial deformations at arbitrary points around the hole. The paper presents an approach that allows residual stresses to be determined by drilling probing holes and assessing the displacement of material particles on the sample surface due to the redistribution of residual stresses. For the analytical description of experimental data, it is proposed that an approximating periodic function be used, and the physical meaning of its coefficients is determined.

Effect of residual stress redistribution on fatigue crack growth pertinent to crack closure and applied load

Clarifying residual stress (RS) redistribution and its effect on fatigue crack growth (FCG) is essential to evaluate the fatigue life of a welded joint. In this study, initial RS distribution along FCG path is calculated based on FCG measurements of as-welded and heated-treated specimens. Subsequently, RS redistribution with crack growth is studied by two groups of specimens with gradually decreased distances between notch tip and weld centerline, and its influence on FCG is linked to crack closure and applied load. The results show that RS redistribution mainly depends on the distance from crack tip to weld centerline, and RS at a crack tip is always compressive during fatigue cycling. In addition, the length of contacted crack wake gradually increases at the beginning of FCG (crack closure effect), which decreases FCG rate together with compressive RS at a crack tip.

Stress-Induced Deformation of Thin Copper Substrate in Double-Sided Lapping

Double-sided lapping is an precision machining method capable of obtaining high-precision surface. However, during the lapping process of thin pure copper substrate, the workpiece will be warped due to the influence of residual stress, including the machining stress and initial residual stress, which will deteriorate the flatness of the workpiece and ultimately affect the performance of components. In this study, finite element method (FEM) was adopted to study the effect of residual stress-related on the deformation of pure copper substrate during double-sided lapping. Considering the initial residual stress of the workpiece, the stress caused by the lapping and their distribution characteristics, a prediction model was proposed for simulating workpiece machining deformation in lapping process by measuring the material removal rate of the upper and lower surfaces of the workpiece under the corresponding parameters. The results showed that the primary cause of the warping deformation of the workpiece in the double-sided lapping is the redistribution of initial residual stress caused by uneven material removal on the both surfaces. The finite element simulation results were in good agreement with the experimental results.

Application of Temperature Cycles to Austenitic Steel and Study of the Residual Stresses Distribution in HAZ

This paper presents the results of research dealing with assessing the welding effect (temperature–stress cycles) on the residual stresses in these steels. Residual stresses, remaining in the material after technological processing, pose a risk, especially at the areas of local stress peaks. During the real welding, residual stresses achieve their highest values in the heat-affected zone (HAZ), which is very narrow and therefore quite problematic to be studied in detail. Therefore, a methodology of temperature–stress physical simulations has been developed to study residual stresses in the HAZ over a 6.5 times larger section of the test sample. Thus, temperature cycles corresponding to the real welding were applied to the samples in the thermo-mechanical simulator, Gleeble 3500. Subsequently, the residual stresses were determined by the X-ray diffraction method. At the same time, the influence of annealing temperature on the residual stress reduction and redistribution was also investigated. Obtained results were compared and discussed with the similar studies about HSLA and duplex steels.

Effect of heat treatment on the anisotropy in mechanical properties of selective laser melted AlSi10Mg

Anisotropy in mechanical properties is one of the critical issues in metal additive manufacturing (AM) impeding the wider application of parts fabricated using this manufacturing technique. In this work, the anisotropy in mechanical properties of an AlSi10Mg alloy fabricated by AM was investigated in terms of grain morphology, microstructure and residual stress distribution, with a focus on changes occurring during post-AM heat treatment by isochronal annealing. It was found that microstructural inhomogeneity is the major factor that weakens the melt pool boundaries, and leads also to anisotropic mechanical properties. Volumes in the vicinity of melt pool boundaries are characterized by coarse Al–Si eutectic networks and high residual stresses, where the former are the main reason for the plastic anisotropy, and the latter increase the local strength. Post-AM heat treatment can alleviate the presence of anisotropy due to homogenization of the microstructure and a redistribution of residual stresses. The overall effect of heat treatment on mechanical strength is a balance between improvement through precipitation strengthening and weakening of grain boundary strengthening, solid solution strengthening and dislocation strengthening. Through an appropriate heat treatment process (annealing at 280 °C for 2 h), the anisotropy in mechanical properties can be effectively reduced and a good strength-elongation synergy can be obtained (strength of 350 MPa and elongation of ∼9%). This study provides new ideas for understanding and mitigating anisotropy of additively manufactured AlSi10Mg, and also has implications for the study of anisotropy of other materials.

Residual Stress Redistribution Analysis in the Repair Welding of AA6082-T6 Aluminum Alloy Joints: Experiment and Simulation.

Residual stress has a three-dimensional scale effect (length, depth, and width) in the process of repair welding, which has a detrimental impact on the service of the aluminum alloy welded structures in high-speed trains. This paper aims to systematically analyze the effects of the repair welding dimension on the residual stress redistribution and obtain the optimal repair welding principles. A combination of blind-hole drilling method and stress linearization in BS7910 was adopted to investigate residual stress redistribution under various repair welding dimensions. The results indicate that repair welding dimension was in accordance with the principle of “SNL (shallow, narrow and long)” and the optimal repair length, depth, and width of butt joints in this study were 15t, 0.25t, and t, respectively (t is the plate thickness of butt joints).

The effects of the cold expansion degree on the fatigue crack growth rate in rail steel

This study investigates the effects of the cold-expansion degree on the fatigue strength of rail steels. Two degrees of cold-expansion, 2% and 4%, and two stress levels were investigated. Results indicate that cold-expansion postpones crack initiation and extends fatigue life, especially with higher degrees of cold-expansion and lower stress levels. Linear superposition principle coupled with the weight function method results in an overestimated fatigue life of cold-expanded specimens, suggesting that reliable predictions can be achieved if both the residual stresses redistribution due to propagating crack and the crack closure effects due to plastic wake generation are considered in the simulations.

Gradient microstructure and foreign-object-damaged fatigue properties of Ti6Al4V titanium alloy processed by the laser shock peening and subsequent shot peening

A dislocation-gradient microstructure layer with large depth and high compressive residual stress (CRS) value on the surface of Ti6Al4V titanium alloy is processed by laser shock peening and subsequent shot peening (LSP + SP). The microstructure evolution and its foreign-object-damaged fatigue properties were investigated by scanning electron microscope, transmission electron microscope, X-ray diffraction, microhardness tests, finite element numerical simulation and vibration fatigue tests. Foreign object damage (FOD) was introduced through the indentations of hardness testers, which can lead to the increase of stress concentration and redistribution of surface residual stress around craters. However, the dislocation-gradient microstructure layer can prolong crack initiation and propagation lives by 184% and 45% for specimens with FOD, respectively. The median fatigue life of (LSP + SP) specimens with FOD even shows longer than that of untreated specimens without FOD. Furthermore, a synergistic strengthening mechanism, involving dislocation strengthening, grain refinement and CRS, was clearly revealed.

The study on the overloading effect on fatigue crack growth considering residual stress relaxation in Al 5456-H38

A numerical and experimental study was conducted on fatigue crack growth (FCG) of metallic components to investigate the effect of redistribution of mechanical residual stresses induced by overloading in notched specimens. The compact tension (CT) specimens of an aluminum alloy were used, and mechanical residual stresses were introduced in them by applying tensile overload (OL). Then, the specimens were subjected to fatigue loading. In the calculations of finite element method (FEM), the modified cyclic J-integral was used as the crack growth parameter. Good agreement was observed between the numerical and experimental results. The FEM results demonstrated a clear redistribution of residual stresses during FCG process. It was observed that after a few cycles, the residual stress field reached a lower magnitude value confining in a small zone around the around the crack tip. Furthermore, the effects of stress ratio, load amplitude, and OL ratio (OLR) on the redistribution of residual stresses are studied in this research. It was observed that the residual stresses are considerably released during the initial cycles of fatigue loading.

Fatigue Crack Propagation of Welded Steel Pipeline under Cyclic Internal Pressure by Bézier Extraction Based XIGA

Residual stress and cracks after welding are widespread mechanical defects in gas and oil pipelines. Internal pressures cause crack propagation and reduce the fatigue life of pipelines. This study developed a new procedure, based on an extended isogeometric analysis (XIGA) to investigate the effect of welding residual stress and cyclic internal pressure on the crack propagation rate and fatigue life. A new approach based on a thermo elastic-plastic equation is introduced for residual stress analysis. The fundamental aspect of this approach is determining the redistribution of residual stress while the crack is growing, and computing the stress intensity factor (SIF) in the residual stress field. Grid points around the crack surface and crack front are identified by the level set method. Then, discontinuous enrichment functions are added to the XIGA approximation. Thus, remeshing is not required in this method. The residual stress results calculated by the presented numerical method are in good agreement with the hole-drilling strain-gage method results. The interaction integral method was used to extract SIF. The superposition method was employed to consider the effect of welding residual stress and cyclic internal pressure on the SIF. Also, the modified Walker equation was used to calculate the fatigue life caused by cyclic internal pressure and welding residual stress. To validate the results, the same analysis was performed using the finite element method. The results of the presented method are in good agreement with finite element method (FEM) results.

Effects of Welded Pipe-cutting on the Residual Stress Re-Distribution and Engineering Critical Assessment

Welded rolled up steel pipe plates undergo more roundness deformation than seamless pipes. The main reason is that the existing residual stress after welding was re-distributed by the cutting process. The objective of this research is to investigate the effect of the constraint on the cutting process through finite element analysis (FEA) to minimize deformation. To include the effect of the cutting simulation, the external constraint was used as the mechanical restraint, and a welded pipe without constraints was used for comparison purposes. The results show that the cutting deformation and residual stress were both significantly reduced under the effect of external constraints. Moreover, the method of reducing conservatism in engineering critical assessment (ECA) was proposed using residual stress re-distribution.

A coupled hydro-mechanical model for subsurface erosion with analyses of soil piping and void formation

A coupled hydro-mechanical erosion model is presented that is used for studying soil piping and erosion void formation under practical, in-situ conditions. The continuum model treats the soil as a two-phase porous medium composed of a solid phase and a liquid phase, and accounts for its elasto-plastic deformation behaviour caused by frictional sliding and granular compaction. The kinetic law characterizing the erosion process is assumed to have a similar form as the type of threshold law typically used in interfacial erosion models. The numerical implementation of the coupled hydro-mechanical model is based on an incremental-iterative, staggered update scheme. A one-dimensional poro-elastic benchmark problem is used to study the basic features of the hydro-mechanical erosion model and validate its numerical implementation. This problem is further used to reveal the interplay between soil erosion and soil consolidation processes that occur under transient hydro-mechanical conditions, thereby identifying characteristic time scales of these processes for a sandy material. Subsequently, two practical case studies are considered that relate to a sewer system embedded in a sandy soil structure. The first case study treats soil piping caused by suffusion near a sewer system subjected to natural ground water flow, and the second case study considers the formation of a suffosion erosion void under strong ground water flow near a defect sewer pipe. The effects on the erosion profile and the soil deformation behaviour by plasticity phenomena are elucidated by comparing the computational results to those obtained by modelling the constitutive behaviour of the granular material as elastic. The results of this comparison study point out the importance of including an advanced elasto-plastic soil model in the numerical simulation of erosion-driven ground surface deformations and the consequent failure behaviour. The numerical analyses further illustrate that the model realistically predicts the size, location, and characteristic time scale of the generated soil piping and void erosion profiles. Hence, the modelling results may support the early detection of in-situ subsurface erosion phenomena from recorded ground surface deformations. Additionally, the computed erosion profiles may serve as input for a detailed analysis of the local, residual bearing capacity and stress redistribution of buried concrete pipe systems.

Efficiency of using vibration treatment of welded stainless steel structures at the welding stages and after its completion

Vibration treatment of welded structures is a tool for relaxation of residual welding stresses, used to stabilize the dimensions over time. The use of this advanced technology in different periods of production has its own characteristics. The traditional performance of vibration action after welding is carried out at resonant or near-resonant frequencies; the result of this action can be estimated by the change in the amplitude-frequency characteristic that occurs due to deformations during relaxation of residual stresses. Another method involves combining welding with vibration, performed at frequencies that ensure the formation of high-quality penetration, the efficiency of this processing is determined, among other things, by reducing residual stresses; in addition, the values of residual deformations are reduced, the shape of the penetration is optimized. The problem of choosing the optimal period of exposure to welded stainless steel structures manufactured using argon arc welding is reduced to comparing the efficiency according to various criteria: redistribution of residual stresses, influence on residual deformations, suitability for control, change in mechanical properties.

A meta-reinforcement learning method by incorporating simulation and real data for machining deformation control of finishing process

Finishing determines the final dimension and geometric accuracy of parts, and the finishing process directly affects the stiffness and residual stress redistribution of the workpiece, so the optimisation of the finishing process plays a very important role in deformation control. At present, existing data-driven methods for deformation control need a large amount of labelled training data, which is always a challenge in the manufacturing area, especially for machining deformation. To address the above issues, this paper presents a meta-reinforcement learning model incorporated by simulation and real data, which is trained in a simulation environment with a piecewise sampling strategy for data collection, and can be updated in a real machining environment through a very small number of real monitoring data. The finishing process optimisation for deformation control can be realised using the proposed approach. Finally, the effectiveness of the proposed method is verified both in simulation environment and actual machining, and better results are obtained compared with other existing methods.

Precise machining based on Ritz non-uniform allowances for titanium blade fabricated by selective laser melting

Selective laser melting (SLM) is an increasingly concerned trend in Ti-6Al-4V blade manufacturing, while the SLMed Ti-6Al-4V blade cannot be used directly because of poor surface integrity and high residual stresses. Precise machining after SLM is a feasible solution but also a challenge. The low rigidity of the blade will lead to deformation when machining. The deformation can lead to surface error and may make defect parts. Two-step machining processes to address the problems were proposed in this paper. First, a non-uniform allowances distribution was allocated and optimized in semi-finishing based on Ritz solution to elastic deformation. The blade was simplified as a cantilever thin plate with various thicknesses, and the thicknesses of finishing allowances were designed and optimized on the premise of ensuring the thin-wall stiffness of the blade, so as to realize the design of Ritz non-uniform allowances. Then, finishing machining was conducted to achieve precise parts. A blade deformation model was established to evaluate part distortions with cutting force moving and changing. Finite element analysis (FEA) and experimental validation in ball-end milling of a blade were conducted. FEA results and experimental results showed dimensional errors have been reduced up to 50%. Further surface tests demonstrated that the mean surface roughness reduced from 7.88 to 0.815 μm. And the residual surface stresses of the SLM samples changed after semi-finishing machining due to the residual stresses relaxation and redistribution. The results demonstrated that the proposed method enhanced the surface quality of the blade fabricated by SLM.