Through-thickness Residual Stresses Research Articles

Small-quantity cooling lubrication in creep-feed grinding: Surface quality and residual stress analysis

Small-quantity cooling lubrication (SQCL) has emerged as a promising eco-friendly alternative to conventional flood cooling in creep-feed grinding processes. This study delves into the influence of various cooling conditions (dry, SQCL, and flood cooling) on the creep-feed grinding dynamics of 420 stainless steel specimens. Key parameters, including friction coefficient, surface texture, and through-thickness residual stresses, are investigated. Both SQCL and flood cooling exhibit marginal reductions in the friction coefficient compared to dry conditions, owing to their lubricating properties. With a smoother surface finish, SQCL grinding exhibits an average roughness of 42 % lower than that of dry grinding. Furthermore, increasing cutting depth and feed rates lead to elevated residual stresses on the specimen's surface, with SQCL cooling demonstrating substantial reductions compared to dry conditions. The SQCL cooling condition yields surface residual stresses 46–48.28 % lower than those observed in the dry condition. This study sheds light on the efficacy of SQCL as an alternative cooling method in enhancing surface quality and mitigating residual stresses in creep-feed grinding processes.

An in-depth comparative FEA on through-thickness residual stresses in press-braked cold-formed steel section

The finite element (FE) is one of the techniques implemented to predict residual stresses. The selection of the proper FE technique is essential to achieve accurate results. This study investigated the prediction of residual stress distribution in pressed-braked thin-walled cold-formed steel sections using the 3D-Shell finite element (FE) technique. Cold-forming processes produce residual stresses and affect the structural capacity of thin-walled cold-formed steel sections. Previous studies have used and recommended the 3D-Solid FE technique to predict residual stresses; however, limited studies have applied this 3D-Shell FE technique. Therefore, the results showed this study had compared the longitudinal/transverse residual stresses and the neutral axis shift obtained by the 3D-Shell FE technique with the results from the literature using the 3D-Solid FE technique. It is also revealed that there are limitations in the 3D-Shell FE technique for predicting residual stresses.

Residual stresses and distortion in additively-manufactured SS316L-IN718 multi-material by laser-directed energy deposition: A validated numerical-statistical approach

In the present work, a numerical-statistical approach was used to study the distortion and residual stress in the additive manufacturing (AM) of SS316L-IN718 multi-material structure. Also, the structure was fabricated by laser-directed energy deposition (L-DED), and experimental measurements via thermocouple and micro X-ray diffraction were performed to validate the numerical results. In a good agreement with the experiments, the thermomechanical modeling of the process showed that through-thickness residual stresses (build direction) are distributed as a large accumulation of compressive residual stress in the mid-length of the structure-substrate interface and the maximum tensile residual stress at its two free ends. The critical development of longitudinal residual stresses (scanning direction) at the interface of the structure due to the sudden change in properties has caused the formation of the maximum tensile residual stress (up to 475 MPa) in this area and immediately changed its nature to compressive that can easily lead to localized cracking. Besides, Von Mises stress distribution indicated the concentration of stress at the interfaces of structure-substrate and base alloys, in such a way that it causes yielding in the SS316L section. On the contrary, less (plastic) strain occurred in the IN718 section due to higher yield strength. The results of the statistical modeling using multiple response analysis in the response surface method (RSM) also determined the desirable minimum level of longitudinal strain and stress of the structure (about 0.013 and 320 MPa, respectively) in the laser power range of 300–380 W and the powder per unit length of 5–25 g/m. In addition to minimization, it was demonstrated that sharp changes in longitudinal strain and stress at the interface of multi-material structure can be effectively reformed to mild changes by designing compositional gradients through thermodynamic calculations, owing to the approximation of the properties of adjacent layers.

Study on evaluation of through-thickness residual stresses and microstructure-mechanical property relation for dissimilar welded joint of modified 9Cr–1Mo and SS304H steel

Gas Tungsten Arc Welded dissimilar joint of modified 9Cr–1Mo (P91) and SS304H steel plate is prepared using Ni-based ERNiCrCoMo-1 super alloy filler and are post-weld heat treated (PWHT) at 760 °C for 2 h. In particular, joints are investigated for metallurgical and mechanical properties in different heat-affected zones. Furthermore, an attempt has been made to understand the following: (i) Is there any effect of mixing of Ni-based superalloy filler material on the joint? (ii) How does the PWHT process change the metallurgical and mechanical properties of joints and different sections? (iii) Does the PWHT process beneficial as compared to as-welded (AW) joint? Experimental results indicate that improper mixing of filler materials led to the formation of an unmixed zone near the weld metal and HAZ interface. The hardness, residual stress, and impact energy results confirmed the variation in mechanical properties along the weldments. The tensile strength varied from 539 MPa in as-joint to 516 MPa in PWHT, and impact energy varies from 165 J in as-joint to 40 J in PWHT condition. The maximum hardness of 375 H V is observed in P91 CGHAZ. The maximum longitudinal residual stress is estimated as 200 MPa at the top surface of the welded plate, i.e., about 2 mm depth, while the maximum magnitude of the transverse residual stresses is observed as 109 MPa at the same depth of 2 mm. In P91 HAZ, the longitudinal and transverse residual stress magnitudes are found to be in a range of 0 to ˗70 MPa. The SS304H HAZ shows the maximum value of longitudinal and transverse residual stress level at a depth of 3 mm, and it was 144 MPa and 92 MPa, respectively. The PWHT showed a drastic reduction in residual stress value in a different zone of the weldments.

Evaluation of through-thickness residual stresses and microstructure in SA516 Gr. 70 steel welds

The critical working condition of nuclear power plant equipment necessitates meticulous determination of the welding process and parameters. In this work, some major influential factors of welding were investigated to observe their effects on the through-thickness residual stress distribution in multipass pressure vessel steel welds. In this regard, experiments were conducted to find the characteristics of residual stresses dispersed in SA516 Grade 70 steel welds of different groove geometries with distinct welding conditions. Three-dimensional finite element models of the weldments were developed considering a moving heat source with temperature-dependent material properties to simulate the welding thermal cycles and corresponding residual stress fields. Effects of weld groove geometry, number of weld passes, external constraints, and preheating on the through-thickness residual stress fields were studied. Additional attention was given to the evaluation of the heterogeneous microstructure and microhardness across the weld cross-section associated with their weld thermal history. Finally, the evolution of the through-thickness residual stresses attributed to subsequent weld passes was elaborated.

Distortion and residual stresses in thick plate weld joint of austenitic stainless steel: Experiments and analysis

Abstract The present work aims to evaluate distortion and residual stresses in thick plate weld joints of austenitic stainless steel. Quantification of residual stresses in thick austenitic stainless steel weld joint is important because it is not desirable to carry out stress relieving after welding owing to the susceptibility to sensitization in the heat-affected zone. Therefore, systematic studies were carried out to predict and measure distortion and residual stresses in the austenitic stainless steel plate weld joint. Variables influencing the generation of residual stresses such as heat input, welding speed, constraints during welding were considered. 20 mm thick plate weld joint of austenitic stainless steel material was prepared using gas tungsten arc welding (GTAW) in unclamped condition and distortions were measured during welding after each pass. Sub-surface and through-thickness residual stresses were measured using blind hole drilling (BHD) and deep hole drilling (DHD) techniques respectively. Thereafter, the weld joint was modeled using the finite element method and analyzed for residual stresses and distortions. Thermal analysis was carried out using actual welding parameters and temperature-dependent material properties to generate temperature profile and compare it with the measured values. The temperature profile along with necessary boundary conditions was used for structural analysis to obtain distortion and residual stresses. Experimental and finite element analysis results for distortion and residual stresses compare well. Details of the experimental and numerical analysis results of distortion and residual stresses for thick section plate weld joints have been discussed in this paper. Also, the effects of differences in yield strengths of weld and base metals on distortion and residual stress results have been brought out.

Neutron Diffraction Study of Macrostress and Microstress in Al-Al2O3-Based Corrosion Protection Coating Obtained by Cold Spray (Dynamic Metallization).

Protective coatings based on an Al-Al2O3 metal matrix composite (MMC) were sprayed using dynamic metallization (DM), a low-pressure cold spray variant. A series of samples approximately 1 mm in thickness were sprayed using different spray process parameters (temperature, velocity) and different feedstock powder compositions (Al, Zn, Al2O3). This resulted in MMCs of different phase compositions and slightly different physical conditions of coating formation. The through-thickness residual stresses that accumulate in coatings during the spray process were studied using neutron diffraction in all phases comprising the MMCs. The overall residual stress in the coating (macrostress) was compressive, which is in good agreement with the data on residual stress observed in other cold spray coatings, accumulating as a result of the peening process. However, due to the slightly elevated spray temperature characteristic of DM in comparison with other cold spray variants, thermal stresses are also present and play an equally important role in the accumulation of residual stress in each phase. Because of the multi-phase composition and thermal mismatch between the metal and ceramic components of the MMC, inter-phase microstresses also accumulate. A micro-mechanical explanation of the observed tensile microstress in Al/Zn versus compressive stress in Al2O3 is proposed.

Novel residual stress measurement technique to evaluate through thickness residual stress fields

In this present study, a novel approach of measuring through-thickness residual stresses based on the general strain relaxation methodologies has been described. This new method is an amalgam of the conventional deep hole drilling technique and the contour method with a reduced degree of damage to the component made during measurements. The annular deformation of a reference hole made at the measurement location has been interpreted as the displacement boundary conditions in a two-dimensional finite element model. In this regard, a thick, partially plastic four-point bent bar specimen was used to validate the proposed method. Through-thickness axial residual stresses induced in the bar were measured using the proposed technique and were observed to be in a reasonably close match with the theoretical and DHD results.

Evaluation of through-thickness residual stresses in conventional and narrow grooved stainless steel welds

Thick AISI 304L stainless steel plates were welded using the gas metal arc welding process, and through-thickness residual stresses were evaluated by finite element simulation and the deep hole drilling technique. 3D moving heat source-based thermo-mechanical models were implemented to evaluate through-thickness residual stresses. The effects of the weld groove geometries and external restraints on the pattern of through-thickness residual stresses were studied. The maximum magnitude of locked-in residual stresses was recorded beneath the top surface, at a depth of around 6 mm. In comparison to conventional weld groove, the narrow weld groove configuration exhibited a 20–40% reduction in peak residual stresses. A significant rise in residual stresses was observed in constrained welds. The effect of the yield strength of the filler material on the evaluation of the through-thickness residual stress distribution in the course of finite element modeling was illustrated. The evolution of through-thickness residual stresses was also assessed concerning each weld pass.

Through-Thickness Residual Stresses, Microstructure, and Mechanical Properties of Electron Beam-Welded CA6NM Martensitic Stainless Steel after Postweld Heat Treatment

In this study, the integrity of electron beam- (EB-) welded CA6NM—a grade of 13% Cr-4% Ni martensitic stainless steel—was assessed through the entire joint thickness of 90 mm after postweld heat treatment (PWHT). The joints were characterized by examining the microstructure, residual stresses, global mechanical properties (static tensile, Charpy impact, and bend), and local properties (yield strength and strain at fracture) in the metallurgically modified regions of the EB welds. The applied PWHT tempered the “fresh” martensite present in the microstructure after welding, which reduced sufficiently the hardness (<280 HV) and residual stresses (<100 MPa) to meet the requirements for hydroelectric turbine assemblies. Also, the properties of the EB joints after PWHT passed the minimum acceptance criteria specified in ASME sections VIII and IX. Specifically, measurement of the global tensile properties indicated that the tensile strengths of the EB welds in the transverse and longitudinal directions were on the same order as that of the base metal (BM). Evaluation of the local tensile properties using a digital image correlation (DIC) methodology showed higher local yield strengths in the fusion zone (FZ) and heat-affected zone (HAZ) of 727 MPa and 740 MPa, respectively, relative to the BM value of 663 MPa. Also, the average impact energies for the FZ and HAZ were 63 J and 148 J, respectively, and attributed to the different failure mechanisms in the HAZ (dimples) versus the FZ (quasi-cleavage consisting of facets and dimples). This study shows that the application of PWHT plays an important role in improving the weld quality and performance of EB-welded CA6NM and provides the essential data for validating the design and manufacturing process for next-generation hydroelectric turbine products.

Residual Stresses, Microstructure, and Mechanical Properties of EB-Welded 90-mm-Thick UNS S41500 Martensitic Stainless Steel after PWHT

Abstract UNS S41500 is a grade of 13Cr-4Ni martensitic stainless steel utilized in hydroelectric turbine products. In this study, the microstructural characteristics, mechanical properties, and through-thickness residual stresses of electron-beam (EB) welded butt joints in 90-mm-thick UNS S41500, assembled using a single pass autogenous process, were evaluated after post-weld heat treatment (PWHT). The results of the longitudinal residual stresses, measured using the contour method, indicated that the applied PWHT was effective in stress relieving and reducing the hardness of the weldment through tempering of the “fresh” martensite present in the microstructure after EB welding. The static tensile properties that were evaluated in the directions transverse and longitudinal to the weld seam demonstrated high performance of the joints with conformance to the requirements of not only ASME Section IX, ASME Boiler & Pressure Vessel Code–Section IX: Qualification Standard for Welding and Brazing Procedures, Welders, Brazers, and Welding and Brazing Operators, but also ASTM A240, Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels and for General Applications, for unwelded UNS S41500. The Charpy impact energies indicated that the toughness of the welds greatly surpassed the minimum acceptance criteria specified in ASME Section VIII, ASME Boiler & Pressure Vessel Code–Section VIII: Rules for Construction of Pressure Vessels. Also, bend testing of transverse weld cross sections displayed no discontinuities on the tension side of the bent joints. These results provide the essential data for validating a manufacturing process for assembly of high-performance joints in an important hydroelectric turbine material.

Distribution and formation mechanism of residual stress in duplex stainless steel weld joint by neutron diffraction and electron backscatter diffraction

The residual stress distribution of duplex stainless steel multi-pass weld joint and its formation mechanism still lacks systematic research. In this study, neutron diffraction and electron backscatter diffraction were used to systematically investigate the through-thickness residual stresses. The results show that both the macroscopic and macroscopic plus elastic mismatch residual stresses decrease along the through-thickness direction and the maximum area is located near the weld top surface. The elastic residual stresses in austenitic phase are larger in comparison to those in ferritic phase. In addition, tensile and compressive stress components are generally found in austenite and ferrite, respectively. Furthermore, it shows that higher level of high angle boundaries, Σ3 coincidence-site-lattice and local misorientation, which can generate larger thermal misfit plus plastic misfit residual stresses, are found in austenite. The formation mechanism of the residual stresses in both ferrite and austenite are also discussed.

A Parametric Investigation of the Through-Thickness Residual Stresses in the Thick Weld Plate Considering Back Chipping: Neutron Diffraction and Finite Element Method

Neutron diffraction and finite element method were combined to analyze the through-thickness residual stresses in the thick weld plate considering back chipping. Large residual stresses were generated near the surface. Furthermore, the effect of back chipping width, the heat input of the back weld after back chipping, interpass temperature and plate thickness on the residual stresses were conducted by finite element method. The results showed that larger back chipping width could be helpful to decrease the risk of stress corrosion crack. With the decrease of heat input, the stress variation becomes more obvious. The interpass temperature has an obvious effect on the longitudinal residual stresses but little effect on the transverse residual stresses. Nevertheless, the plate thickness has little influence on the residual stress distribution law. Based on the finite element method results, a formula focused on the 10-40 mm thick plates was fitted to calculate residual stresses with the change of depth through thickness, which was verified by neutron diffraction measurement.

Numerical and Experimental Studies on Subscale Behaviors of Ultrasonic Surface Peening

Displacement-controlled and force-controlled surface-striking conditions were applied for finite element method simulations of the single path ultrasonic nanocrystal surface modification (UNSM) surface peening process. The single path UNSM treatment was done on a 4 mm-thick 6061 T6 Al sheet, and the surface topology and through-thickness residual stresses were measured and compared to the simulation results. Both displacement- and force-controlled simulations predicted maximum compressive residual stresses near the surface and subsurface for the stresses along the strike progression direction and transverse direction, respectively. The experimentally measured through-thickness residual stress profile also showed the maximum compressive residual stress near the subsurface. Both simulation conditions showed a topological pile-up on the surface in front of the leading strike. However, only the force-controlled simulation showed the pile-up breakdown at a critical number of strikes followed by the redistribution of subsurface strain fields, and lead to topological undulations along the edge and valley of the UNSM path, which were confirmed to be consistent with the surface topology measured from the experiment. It was concluded that the actual UNSM strike is close to the force-controlled surface-striking condition.

Experimental and numerical investigation into temperature histories and residual stress distributions of high strength steel S690 welded H-sections

In order to exploit full structural benefits offered by high strength steel materials in construction, it is important to examine and quantify effects of welding on these steel materials for development of effective structural design. A systematic experimental and numerical investigation into thermal and mechanical responses in four S690 welded steel H-sections with different cross-sectional dimensions during and after welding was conducted.During welding, surface temperatures of the welded sections at specific locations in close vicinity of welding lines were measured continuously using thermocouples. After welding, surface residual stresses in these welded sections were measured using an established hole-drilling method. Based on codified data and measured temperatures, three-dimensional finite element models with thermomechanical coupled analyses were established to simulate heat transfer from a welding arc onto the welded sections. After a careful calibration of predicted surface temperature histories of these sections against measured data, both through-thickness temperature and residual stress distributions of these sections were obtained. Predicted and measured surface residual stresses at specific locations of these sections were found to be in a good agreement. Hence, accuracy of the proposed models in predicting temperature histories and residual stress distributions of these welded sections are established. Averaged through-thickness residual stresses are provided as representative residual stress patterns for these sections. It should be noted that the maximum residual stresses in these welded sections are proportionally smaller than those in S355 welded sections.Consequently, the proposed finite element models are demonstrated to be able to predict accurate temperature histories and residual stress distributions of S690 welded H-sections through thermomechanical coupled analyses. The proposed models will be readily employed to investigate welding-induced residual stresses in welded H-sections and I-sections of various steel grades and plate thicknesses with different welding parameters. Predicted residual stress patterns will then be employed for numerical investigation into (i) axial buckling behavior of slender columns made of S690 welded H-sections, and (ii) lateral torsional buckling of unrestrained beams made of S690 welded I-sections. These numerical investigations will be reported separately.

Accuracy Improvement of Through-Thickness Residual Stress Measurement by Deep Hole Drilling Technique for Welds

In this study, the effect of diameters of drilled hole and trepanned cylindrical sample on the through-thickness residual stress measurement at welds was experimentally investigated. The measured through-thickness residual stresses were compared with those calculated using the welding thermo-mechanical analysis with the finite element methods. Also, the distribution of residual stress on the welded surface was measured by X-ray diffraction method to verify the accuracy of the calculated results. Based on the comparison among them, the effect of diameters of drilled hole and trepanned cylindrical sample on the accuracy of through-thickness residual stress measurement at welds by deep hole drilling technique was evaluated. The results showed that diameter ratio of trepanned cylindrical sample to drilled hole was an important factor for more accurately measuring the residual stress at welds. The accuracy of residual stress measurement was improved with increasing the diameter ratio. From the other perspective, meanwhile, the diameter of trepanned cylindrical sample was required to be smaller than the range of residual stress to be measured. Thus, two requirements for more accurately measuring the residual stress at welds were clarified. It is then expected that the deep hole drilling technique becomes to be more broadly applicable for the welds.

Application of multiple analysis methods in optimising complex residual stress characterisation

An accurate characterisation of residual stress plays an important role in the structural integrity assessment of an engineering component. Several techniques and tools are available for measuring and predicting residual stresses. For example, neutron diffraction (ND) and X-ray diffraction (XRD) are non-destructive techniques used for measuring through-thickness and surface residual stresses respectively, while the deep-hole drilling (DHD) and the incremental centre-hole drilling (ICHD) are semi-destructive techniques and measure through-thickness and sub-surface residual stress respectively. In most open literature, a more favoured method is traditionally used over others, with some degree of validation using finite element analysis (FEA) predictive tool. In this paper it will be shown that the different methods and tools available are not contradicting or more superior to the others, but rather, the use of more than one available technique complementary to each other can improve the quality and the confidence in the characterisation of the residual stress state in an engineering component. In particular, the accurate knowledge of the residual stress field for a safety critical component plays a vital role for subsequent structural integrity assessment.

Investigation of residual stresses distribution in equal channel angular rolled aluminum alloy by means of the slitting method

Equal channel angular rolling is a severe plastic deformation process which produces an ultrafine-grained structure and improves the mechanical properties of the samples. In this article, using the slitting method experimentally and finite element simulation, the residual stress distribution in an equal channel angular rolled Al alloy 5083 specimen was investigated. First, by applying the slitting technique on the considered specimen, the produced strains were measured and recorded. Then by employing the series expansion method, the through-thickness residual stresses were calculated. The compliance matrix was obtained by means of finite element analysis and 16 terms of the Legendre polynomial (L2 through L17) were used to get the compliance coefficients. According to the finite element results, the residual stresses were created in the sample because of different plastic strain deformation at the same times in different locations. The residual stress distribution was non-uniform and similar to sine curve. There was a good agreement between the obtained results by slitting method and finite element simulation.

Evaluation of Through-Thickness Residual Stresses by Neutron Diffraction and Finite-Element Method in Thick Weld Plates

Through-thickness distributions of the welding residual stresses were studied in the range of 50–100 mm thick plates by using finite-element modeling (FEM) and neutron diffraction measurements. In order to simulate the residual stresses through the thickness of the thick weld joints, this paper proposes a two-dimensional generalized plane strain (GPS) finite-element model coupled with the mixed work hardening model. The residual stress distributions show mostly asymmetric parabola profiles through the thickness of the welds and it is in good correlation with the neutron diffraction results. Both the heat input and plate thickness have little influence on the residual stress distributions due to the relatively large constraints of the thick specimen applied for each welding pass. A general formula has been suggested to evaluate the distributions of the through-thickness residual stresses in thick welds based on FEM and neutron diffraction experimental results.

An analytical model on through-thickness stresses and warpage of composite laminates due to tool–part interaction

Abstract Tool–part interactions play an important role in the deformation of composite components during forming, especially for thin laminates. In this paper, taking into account the effect of slipping between the tool and composite laminates, an analytical model is proposed to predict the through-thickness residual stresses and warpage of a composite part during the curing process without extensive resin characterization. A parametric study examining the effects of various interfacial shear stresses on warpage is performed and the results are compared with experimental data in the literature. Good agreements are obtained. The results show that warpage is enhanced linearly with the increase of interfacial shear stress and the stress distribution does not take on an exponential form for [90/0] s lay-up. It is also shown that this model could successfully predict part processing deformations without extensive resin characterization.