Axial Residual Stress Research Articles

Residual stress relief mechanisms of 2219 Al–Cu alloy by thermal stress relief method

Abstract Monolithic thin-wall components of 2219 Al–Cu alloy are widely used in aerospace and military fields, and usually treated with solution and quenching to improve their comprehensive performance. However, a high magnitude residual stress is introduced into the components during the quenching process, which is unfavorable to the subsequent manufacturing process and service performance. Therefore, residual stress relief is essential to enhance the performance of the components. A conventional effective method is thermal stress relief (TSR). However, the underlying mechanisms of TSR still remain unclear and lack a quantitative interpretation. In the present work, the evolution and distribution laws of the residual stresses, tensile properties, Vickers hardness, dislocations, precipitated phases, and metallography during TSR were investigated. Based on the experimental results, dislocation theory and strengthening mechanisms were applied to reveal the underlying mechanisms of the residual stress relief by TSR. The results showed that the circumferential and axial residual stress relief rates can reach 86.37 and 85.77% after TSR, respectively. The residual stress relief after TSR is attributed to the dynamic evolution of dislocation configuration and density. The improvement in the mechanical properties mainly depends on the precipitated phases and is also affected by the stress orientation effect caused by the residual stress.

Numerical Simulation and Experimental Verification of Residual Stress in the Welded Joints of Weldolet-Branch Pipe Dissimilar Steels.

It is well known that welding dissimilar metals can play the advantages and characteristics of those different metals, but it is easy to encounter some problems. In this paper, the thermomechanical behavior of the weldolet–branch dissimilar steel joints in different welding cases is analyzed by establishing a three-dimensional finite element model, and the predicted thermal cycling and residual stresses are verified using experimental tools. The results show that the high temperature area and the heat affected zone on the side of the branch pipe are larger, and there is a large stress gradient at the fusion line on both sides of the weld. Too high or too low temperature between welding layers will cause large residual stress, thus, 200 °C is more suitable for the welding of weldolet–branch joints. The residual stresses of path-1, path-2 and path-3 have similar distributions at 0° and 180° sections, and the circumferential and axial residual stresses on the inner surface are larger than those on the outer surface. The residual stress on the inner and outer surfaces of path-3 is smaller than that of path-1 and path-2 at the 90° and 270° sections as a whole, and the residual stress at the 90° section reaches the minimum.

AN EVALUATION OF PARTS’ FATIGUE RESISTANCE AFTER SURFACE THERMO CHEMICAL MACHINING

In order to raise a fatigue resistance the calculation-experimental method of parts surface thermo chemical machining efficiency has been carried out. The employment of two types of reference specimens in experiments has been substantiated. The employment of smooth reference specimens for a determination of residual stresses in a surface layer and of corset reference specimens for fatigue tests has been recommended. The results of experimental study of two types of thermo chemical machining (cementation and nitriding) influence on a fatigue resistance of corset specimens made of high-strength allows ВКС-5 и ВНС-17 have been used in the work. . The calculations of the study have been carried out by the Finite Elements Modeling method using the calculation complexes ANSYS and PATRAN/NASTRAN. The residual strained state modeling is carried out by thermo elasticity method. On grounds of conducted calculation its been stated that an axial residual stresses distribution in a dangerous (smallest) section of a corset specimen doesnt practically differ from a similar distribution in smooth specimens. An endurance limit increment due to corset specimens hardening was determined with use of the average integral residual stresses criterion. Carried out results let also maintain that the optimal regimes of thermo chemical machining are the regimes under which average integral residual stresses are maximum.

Determination of residual stresses in a single FBG fiber/epoxy composite system

A new approach to determine residual fiber and matrix stresses in single fiber Bragg grating (FBG) fiber polymer matrix composites is developed based on the earlier work by Hoffman et al., 2020 [( Hoffman et al., 2020) 1] and Khadka et al., 2020 [( Khadka et al., 2020) 2]. In this new study, our already measured fiber strains in the composites based on room temperature (RT) and higher temperature (HT) epoxies were used to determine the stresses in the fibers. The total manufacturing residual stresses in the fibers were also separated for the curing and cooling parts of the manufacturing cycles. The cooling stresses for both epoxy systems were then independently verified through single fiber thermal numerical models. Subsequently, using our new methodology based on the Eshelby misfit approach and the single fiber thermal models, the total residual stresses in the matrix were found and then separated into the curing and cooling stresses. The maximum axial stresses at the matrix/fiber interfaces were found to be increasing with an increase in the curing temperature of the RT epoxy. For the highest curing temperature of the RT resin (70 °C), the residual axial stresses in the matrix (20 MPa) were close to the stresses in the HT epoxy (25 MPa) at the curing temperature of 121 °C. The curing matrix stresses were observed to be significant for both epoxy systems with their contributions to the total stress ranging from 28% to 48% depending on the resin type and curing conditions.

Residual stress analysis and measurement in multi-layer bellows

Because large plastic deformation occurs in hydroforming bellows there is a residual stress distributing in the metal after forming, which is complex and not easy to be measured. The existence of residual stress might have an effect on the corrosive property and bulking performance of bellows. A finite element model was established to simulate the forming residual stress of the nickel alloy multi-layer bellow. The distribution of residual stress was calculated out and validated by cosα X-ray diffraction measurement. Thus the forming mechanics and the effects of layer number and forming pressure on the residual stress in the hydroforming bellow were both discussed in detail based on the established model. It was shown that the calculated residual stress had the same trend with the experimental results. The axial and circumferential residual stresses at the outer surface of the peak were both compressive. There existed the maximal Von Mises stress at the inner surface of the peak of the bellow. At this position the radial and axial residual stresses were both tensile. When applying multi-layer bellows and less forming pressure a lower forming residual stress could be obtained because of the narrow plastic strain region during forming.

Finite Element Welding Residual Stress Analysis of CRDM Penetration Nozzles

Abstract This article investigates numerically welding residual stress distributions of a tube with J-groove weld in control rod drive mechanisms of a pressurized nuclear reactor vessel. Parametric study is performed for the effect of the tube location, tube dimensions, and material's yield strength. It is found that residual stresses increase with increasing the inclination angle of the tube, and the up-hill side is the most critical. For thicker tube, residual stresses decrease. For material's yield strength, both axial and hoop residual stresses tend to increase with increasing the yield strength of Alloy 600. Furthermore, axial stresses tend to increase with increasing yield strength of Alloys 82/182.

Effects of residual stresses on the bending stiffness of shafts strengthened by enveloping de-formation

The aim was to study the effects of technological residual stresses on the bending stiffness of cylindrical parts of shafts and axes. Experiments were conducted for elongated cylindrical specimens made of steel grade 35 with a diameter of 30 mm using boring and turning methods. Specimens were annealed in a protective medium to remove initial residual stresses. Experiments were carried out using an Amsler laboratory hydraulic testing machine and VK8 grade hard-alloy matrices. The experiments showed that, for an extremely low degree of relative crimping of 0.1 to 0.5%, the size of the layer with tangential residual compression stresses gradually decreases. The stiffness of such cylindrical workpieces remains almost unchanged. An increase in relative crimping (from 0.5 to 1.2%) leads to a decrease in resi dual compression stresses on the part surface. The layer thickness with tangential residual compression stresses starts to increase. This leads to a decreased residual buckling and an increased bending stiffness. It was found that the degree of relative crimping has no effect on the variation of distribution depth of axial residual stresses. Optimal distribution of tangential residual compression stresses can be reached by increasing their depth. A linear relationship was found for relative crimping of 0.1 to 1.0%. The highest bending resistance was recorded for specimens strengthened by residual crimping of about 1.0%. By processing workpieces using enveloping deformation with crimping of 0.1% and loading them with a transverse force of 0.6 kN, bending distortion can be decreased and the strength of parts can be increased by 5 times. It was found that the bending stiffness of cylindrical shafts is greatly affected by residual compression stresses. The bedding depth of residual stresses has various effects on the stiffness of cylindrical parts. Thus, correct use of strengthening enveloping deformation can form a high-quality surface layer on parts with the pre-defined distribution of residual stresses.

Experimental investigation on microstructure, mechanical properties, and residual stresses of dissimilar welded joint of martensitic P92 and AISI 304L austenitic stainless steel

In this study, microstructural characteristics and mechanical properties of martensitic steel P92 and AISI 304L austenitic stainless steel (ASS) dissimilar metal weld (DMW) have been examined. The welding was performed using the multipass gas tungsten arc welding (GTAW) process. The ERNiCrMo-3 (Inconel 625) filler metal was used due to its excellent compatibility with the P92 and AISI 304L ASS metals. The microstructure characterization performed with an optical microscope and scanning electron microscope revealed the presence of an unmixed zone in the form of beach, peninsula, and island at the base metal and weld fusion zone interface. Secondary phases enriched with Nb and Mo, and migrated grain boundaries (MGBs) were also observed at the weld fusion zone. The microstructural characterization at the P92 side revealed the presence of a soft ferrite zone and delta ferrite at the weld and P92 interface. The different peak temperature experienced by the P92 metal during the welding process results into the formation of three distinct zones with diverse mechanical and microstructural properties namely coarse grain heat affected zone (CGHAZ), fine grain heat affected zone (FGHAZ), and inter-critical heat affected zone (ICHAZ). The post weld heat treatment (PWHT) at 760 °C for 2 h followed by air cooling was performed to homogenize this heterogeneous microstructure formed toward the P92 side. It was observed that this PWHT does not have any significant effect on weld fusion zone and 304L SS heat affected zone (HAZ) microstructure. But, PWHT modifies the microstructure of P92 side HAZ. The tensile test, Vickers micro-hardness test, and charpy impact test were carried out to determine the mechanical properties of the DMW. The tensile strength was found as 587.709 MPa in the as-welded condition and 594.515 MPa in PWHT condition. The tensile test results indicated that specimens were failed from 304L stainless steel (SS) base metal (BM) in as-welded and PWHT condition. The charpy impact toughness test results showed that the toughness of the weld joint was very low in as-welded and PWHT condition (47J) compared to the P92 (190J) and SS 304L (285J) BM. From the microhardness examination, it was observed that the ICHAZ was the weakest zone among all the other regions due to its lower micro-hardness value compared to the other regions. After welding process, residual stresses were measured in as-welded and after PWHT condition at the center of the weld and at the HAZ of P92 and SS 304L (through the thickness of the plate) using experimental-based deep hole-drilling (DHD) strain-gauge method. The results showed that both circumferential (hoop stress) and axial (longitudinal stress) welding residual stresses were decreased after PWHT.

3D FE modeling and experimental analysis of residual stresses and machining characteristics induced by dry, MQL, and wet turning of AA6061-T6

The present research study aimed to investigate the influences of turning environments and parameters on machining temperature (MT), machining forces (MFs), and axial surface residual stresses (ASRS) in turning operation of AA6061-T6. Turning environments included DRY, minimum quantity lubrication (MQL), and WET modes, and turning parameters consisted of cutting speed (), feed rate (), depth of cut (), tool nose radius (), side cutting edge angle (SCEA), and back rake angle (BRA). A 3D finite element (FE) model was developed to predict MT, MFs, and ASRS for different turning environments and parameters and was validated by experimental measurements. The results showed that increasing feed rate led to a higher tensile ASRS while using tools with a nose radius of 0.4 resulted in lower ASRS. In addition, the deviation of SCEA from 0° to positive or negative values caused higher tensile ASRS. ASRS increased with decreasing BRA from 0° to –15°. The variation of ASRS was found to be more sensitive to thermal effects than to mechanical ones. The results further confirmed that in a turning process, the competition between the machining forces and temperature was the fundamental factor that determined the extent of residual stresses.

Use of a True Material Constitutive Model for Stress Analysis of a Swage Autofrettaged Tube Including ASME Code Comparison

Abstract This work reports results from a new finite element analysis (FEA)-based user programmable function (UPF) featuring true material constitutive behavior with proper algorithms for accurate stress analysis of swage autofrettage of high-strength thick-walled cylinders. This material model replicates an existing Bauschinger-effect characterization (BEC). This incorporates elastoplastic material behavior during loading. Reversed loading includes a reduced elastic modulus and nonlinear plasticity resulting from the Bauschinger effect (BE), both depending upon the maximum level of loading plastic strain. This case study identifies the difference in stress distributions based on two different material models, a bilinear kinematic hardening model, and the BEC model. Near-bore residual stresses for the BEC case are noteworthy and reported in detail, e.g., axial residual stress is tensile and hoop residual stress exhibits a distinct slope reversal, unlike hydraulic autofrettage. This indicates the possible need to re-assess the ASME pressure vessel code (correction for BE) regarding swage autofrettage.

Effects of surface curvature on residual stress field of 316L stainless steel subjected to laser shock peening

To improve the application of laser shock peening (LSP) to curved surfaces, the effects of surface curvature on tri-directional (radial, axial, and depth) residual stress distributions in the LSPed 316L stainless steel specimens were investigated in the present work. Both residual stress fields of convex and concave surfaces were experimentally and theoretically measured and compared using finite element analysis. Results showed that the compressive residual stress decreased with increasing the surface curvature, and the surface curvature had a significant influence on the thickness of plastic deformation layer. Furthermore, a mathematic model of compressive residual stress as a function of surface curvature was proposed to predict the compressive residual stress fields of LSPed curved surfaces.

Experimental and mathematical methods for calculation of residual stresses in production of welded pipes

The results of physical and mathematical modeling of the stress-strain state of metal and residual stresses during plastic deformation of a sheet blank and welding of large-diameter pipes are generalized. One of the analytical methods for calculation of residual stresses during elastoplastic deformation of a rectangular bar and a wide strip is described. From the standpoint of continuum mechanics, it is shown that under the action of a bending moment, tensile stresses appear in the outer layers, and compressive stresses appear in the inner layers, which change sign during unloading and residual stresses remain in the metal, compressive stresses in the outer layers, and tensile stresses on the inner surface. As a result of the studies carried out, the authors for the first time obtained a picture of residual stresses distribution and found that at each technological operation of the formed pipe billet after its completion, tangential and axial residual tensile stresses σостmax/σв ≤ 0,31, act along the entire outer perimeter and length, which after expansion-calibration of pipes decrease to the magnitude σт σост/= 0,23σв and σост∞/= 0,18σв. Ii was established that the value and distribution of residual stresses are significantly influenced by the blank shape, the order of welds imposition, welding modes and mechanical properties of the metal. This conclusion was also confirmed by experimental studies of residual stresses, which were obtained by X-ray diffractometry and sequential etching of surface layers using the MerCulon «Tensor-3» system. The results of experimental studies have shown that during plastic deformation of the sheet blank and after welding, residual tensile stresses are observed on the outer surface in the pipe metal and in the weld, which can cause pipeline failure. The paper describes the results of numerical modeling of non-uniformity of the stress-strain state and residual stresses in the metal of pipe processing at all stages of production according to the JCO scheme: bending of the sheet edges → forming on a step-forming press → re-forming of the «spline pipe» - a pipe profile with divorced edges → calibration - pipe expansion. Based on the results of modeling by the finite element method, it is shown that the required geometric shape of the pipe and the dimensional accuracy of the LDP diameter are achieved when expanding the workpiece with an ovality of no more than 5 mm, while ensuring high-quality assembly and welding of edges of pipes to be joined in the line of the pipeline system.

Effect of length in rotational autofrettage of long cylinders with free ends

Thick-walled cylindrical and spherical pressure vessels are often subjected to autofrettage, a process in which the vessel is loaded at the inner wall to cause a partial or complete plastic deformation emanating from the inner wall, followed by unloading. This introduces the beneficial compressive residual stresses in the vicinity of the inner wall. Depending on the type of the loading, there are five different types of autofrettage processes— hydraulic, swage, explosive, thermal and rotational. This article analyzes the rotational autofrettage, in which the cylinder to be autofrettaged is loaded by rotating it about its longitudinal axis. The centrifugal forces cause the required plastic deformation in the cylinder. Hence, when the cylinder is unloaded by bringing it to rest, compressive hoop residual stresses are introduced in the vicinity of its inner wall. When long cylinders are rotated about their axes, the distribution of axial stress changes with length of the cylinder and affects the generation of the residual stresses in the autofrettaged cylinder. This effect is investigated here by a finite element method (FEM) analysis of rotational autofrettage of cylinder made up of A723 gun steel. The FEM analysis using ABAQUS® package reveals the presence of tensile axial residual stresses in the vicinity of the inner wall of the cylinder, which increase with length. The tensile residual stresses can be mitigated by constraining the ends of the cylinder during the rotational autofrettage.

Effects of segmented thermal-vibration stress relief process on residual stresses, mechanical properties and microstructures of large 2219 Al alloy rings

Large 2219 Al-Cu alloy transition rings are extensively employed in propellant tanks of heavy launch vehicles. These rings have a diameter exceeding 5 m or even reaching 10 m, with a less than 2% thickness-to-radius ratio, and low stiffness which can cause machining deformation due to the residual stress. Thus, residual stress relief of these rings is necessary in their extreme manufacture. A novel effective method is thermal-vibration stress relief (TVSR), which integrates the conventional thermal stress relief (TSR) and vibratory stress relief (VSR); however, the existing TVSR equipment cannot meet the requirements of large rings, and the underlying mechanisms of TVSR remain unclear and a quantitative interpretation is still lacking. Therefore, a segmented TVSR (STVSR) process suitable for large rings was proposed and the corresponding experiment was carried out with a self-made STVSR experiment platform. Then this study investigated the evolution and distribution laws of the residual stresses, tensile properties, Vickers hardness, dislocations, precipitated phases and metallography during STVSR. Based on the experimental results, multi-scale mechanics theory and strengthening mechanisms were applied to quantitatively reveal the underlying mechanisms of residual stress relief by STVSR. The results showed that the circumferential and axial residual stress relief rates can reach 44.43% and 45.14% after STVSR, respectively. The residual stress relief after STVSR is attributed to the dynamic evolution of dislocations and precipitated phases in the material. The improvement of mechanical properties mainly depends on the precipitated phases and is also affected by the residual stress. The findings confirm the significant effects of STVSR on metal plasticity and provide valuable insight into the underlying mechanisms of TVSR.

Analysis of Residual Stress Distribution in Rods after Drawing Process with Regard to Process Variables

Currently, many researchers pay attention to studying the influence of process variables on the quality of metal products after manufacture. The most common methods of metalworking are forming processes, in which a high degree of deformation, uneven plastic deformation, and elevated temperatures are utilized. In most cases of manufacturing using these methods, a self-balanced system of residual stresses is formed that significantly affects the accuracy, strength, durability, reliability, corrosion resistance, and fatigue strength of machine parts after manufacture and processing. At the same time, the level of technological residual stresses depends on the main process variables. And in this regard, the analysis of the residual stress calculation for the deformation of rods will identify the effect of process variables, mechanical properties of the material, the geometry of the workpiece on the level and distribution of formed residual stresses. The object of the study is distributions of residual stresses formed after plastic deformation in rods and wire. In the work, experimental data on the distribution of residual stresses in rods after drawing were investigated. The residual stress calculation method takes into account parameters of technology, geometry and mechanical constants of material. Dependencies of axial and circumferential residual stresses in steel rods and wires after drawing were found.

Influence of boss-backing welding to ERW pipe

Station and valve chamber design often encounter the situation of drilling hole at the main pipeline and welding boss-backing to connect the branch pipe. Boss hole location should generally be at least 100 mm away from the longitudinal weld or spiral weld. However, because the electric resistance weld (ERW) is difficult to distinguish in practice, some bosses mounting position coincide with ERW or close to. In this paper, the influence of boss-backing welding directly on the longitudinal weld to the original residual stresses of ERW pipe was studied. The microstructure of pipe body and longitudinal weld after welding was also analysis. The testing results showed that the overall residual stresses of ERW pipe were relatively small. Residual stress at the longitudinal weld region were smaller than those at the pipe body region. After the boss-backing welding, the axial residual stress at the longitudinal weld and the circumferential residual stress at the pipe body region near the intersection increased sharply to 2.5 (444 MPa) and 3.8 (433 MPa) times, respectively. The invaded width and depth to the ERW pipe after welding were about 15.167 mm and 3.376 mm. Granular bainite with necklace type M-A constituents could be observed at the invaded zone. It is suggested that small welding heat input should be adopted for boss-backing welding.

Neutron Diffraction Study of Residual Stresses in a W–Ni–Co Heavy Alloy Processed by Rotary Swaging at Room and High Temperatures

Residual stresses were studied in tungsten heavy alloy bars produced by powder metallurgy and deformed by rotary swaging at room temperature (RT) and at 900 °C. Neutron diffraction technique was used to scan the residual stresses across the bars. Both tungsten particles and NiCo2W solid solution matrix were analysed. Maximum axial stresses of ~ 300 MPa and ~ 200 MPa were observed for the tungsten phase at the centre in the RT and in the high-temperature deformed samples, respectively. Compressive residual axial stresses were found close to the sample surface, showing that rotary swaging is a suitable deformation method for tungsten heavy alloys to provide an appropriate surface modification for its use in metallic parts undergoing, e.g., fatigue. Residual stresses developed in the NiCo2W-phase are larger than those found in the tungsten particles although with a secondary role in the overall equilibrium conditions due to its lower strength and smaller volume fraction. Total stresses for each phase were separated into macro- and microstresses. Macrostresses can be mainly influenced by the incompatibility of the elliptical cross-section of the sintered sample with the head of the rotary machine while microstresses are mainly developed by the elastic mismatch between the constituent phases.

Elastic and elastic-plastic stress release due to material removal in measurement of in-depth residual stresses

Elastic stress release is mostly considered during material removal while measuring in-depth residual stresses inside a structure. It can give rise to large measurement errors in the case of high residual stress where plasticity effect is involved. This paper focuses on analysis of elastic-plastic stress release due to material removal and the induced error in measurement of residual stress. Simulation of electropolishing prepared for XRD analysis and contour method process is performed on a shot peened 316L cylindrical specimen by accounting for the work hardening effect. Results show that elastic-plastic stress release can occur in iterative electropolishing when the initial yielding relation is broken. However, the induced error is acceptable with a maximum error of 1.67%. In comparison, significant release of residual stress after cutting in contour method activates obvious plastic flow, and induces a much larger deviation of the measured axial residual stress. Influence of the initial work hardening is discussed by analysing the plastic flow mechanism in the two material removals. It is concluded that occurrence and the influence extent of plastic flow rely on the stress release amount and the initial state of yielding relation which is defined by residual stress, work hardening, and material behaviour.

Effect of a Multiple Reduction Die on the Residual Stress of Drawn Materials.

Residual stress may influence the mechanical behavior and durability of drawn materials. Thus, this study develops a multiple reduction die (MRD) that can reduce residual stress during the drawing process. The MRD set consists of several die tips, die cases, and lubricating equipment. All the die tips of the MRD were disposed of simultaneously. Finite element analysis of the drawing process was performed according to the reduction ratio of each die tip, and the variables in drawing process with the MRD were optimized using a deep neural network to minimize the residual stress. Experiments on the drawing process with the conventional die and MRD were performed to evaluate the residual stress and verify the effectiveness of the MRD. The results of X-ray diffraction measurements indicated that the axial and hoop residual stresses on the surface were dramatically reduced.

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.