Residual Stress Measurements Research Articles

Effects of thermo-chemical treatment and grinding process of external cylindrical surfaces on residual stresses in 13CrMo4-5 steel

This paper presents a study aimed at determining the effect of the carburizing treatment process and the subsequent grinding process on the residual stresses occurring in ring-shaped specimens made of 13CrMo4-5 steel.During the tests, vacuum carburizing was used, achieving an effective case depth ECD = 0.5 mm. Subsequently, the cylindrical outer surfaces of the samples were ground by conventional plunge grinding and with innovative kinematics using a test stand based on a conventional flat-surface grinding machine. As part of the study, microhardness and residual stresses were measured before and after grinding. Measurements were carried out to a depth of 1 mm. The main component of the stand is an original special device that allows the cylindrical specimen to be clamped. Then the angle between its axis of rotation and the axis of rotation of the grinding wheel is set with respect to the plane of the grinding machine’s magnetic table. In the described tests, the axis of rotation of the cylindrical specimen was deviated from its original position by 15 and set at an angle of 75 to the axis of rotation of the grinding wheel. The specimens were ground with a grinding wheel of noble electro-corundum marked 38A60K8V. In both kinematic cases of the grinding process, a machining allowance of 0.01 mm was removed.Grinding using innovative kinematics did not cause any significant changes in the microhardness distribution, either for vacuum or conventional carburizing. In addition, residual stress measurements using the Dawidenkov-Sachs method showed that innovative grinding enables a more favourable distribution than those obtained after conventional plunge grinding.Further research will focus on, among others, selecting the angular settings of the workpiece axes relative to the grinding wheel axes depending on their dimensions. Grinding guidelines should include coverage ratio, infeed value, grinding time, and peripheral speeds. In addition, the plan for future research includes measuring the components of the grinding force and the geometric structure of the surface.Grinding process is a crucial stage of steel treatment in almost every industrial branch. In sustainable manufacturing, it is extremely important to produce high-quality items while reducing the cost of manufacturing and taking care of the environment and workers’ health.The proposed test stand, together with the authors’ device, makes it possible to conduct machining of the external surfaces of cylindrical workpieces on a flat surface grinder. In this case, the innovation of the grinding process consists of the non-parallel alignment of the cylindrical rotational axis of the specimen and the rotational axis of the grinding wheel with respect to the plane of the magnetic grinding table.

(High-Temperature Energy, Materials, & Processes Division Subhash Singhal Award) From Electrochemical to Mechanical Modeling of SOFCs and Their Experimental Validation

Due to the asymmetric structure with multiple materials, SOFCs are subjected to various modes of mechanical stress, resulting in a risk of failure. Of particular importance are thermal and chemical strains, which depend on the micro- and macroscopic distribution of electrochemical reaction sites. Therefore, SOFC modeling must include electrochemistry, mass and charge transport, thermo-fluid dynamics, and structural analysis. In addition, appropriate experiments must be performed to validate the modeling results. This research group is working to develop a comprehensive environment for modeling and validation in order to evaluate the mechanical reliability of SOFCs.Electrochemical modeling of cathode was made based on the defect chemistry and mass transport of (La,Sr)CoO3 (LSC) and (La,Sr)(Co,Fe)O3 (LSCF). An empirical equation for the surface reaction of the porous electrode was determined by electrochemical analysis of a dense film electrode taking into account the difference between the dense film and porous electrodes [1]. Anode reaction rate on a unit length of triple phase boundary of Ni-YSZ-gas was determined using circular Ni model electrodes of various size [2]. Evaluation of 3D oxygen potential distribution inside the constituent oxides was made using an in-house code called SIMUDEL where mixed ionic/electronic conduction and oxygen nonstoichiometry were taken into consideration [3,4]. It was combined with commercial software to make structural analysis. Mechanical properties used for calculation were obtained from measurements by the resonance method and the small punch method or collected from the literature. Non-linear stress-strain behaviors were observed with Ni-YSZ cermet [5] and inelastic behaviors were found in most nonstoichiometric oxide materials. Large ferro-elasticity emerged in the LSC and LSCF [6] and in Sc stabilized ZrO2 electrolyte at elevated temperatures. Chemical strain in vacancy formation was formulated with a linear function of the defect concentration as an independent factor from the thermal expansion. In the structural analysis, it was treated as the additional temperature change of the local material. Volume change of Ni-YSZ cermet on red-ox operation was a difficult factor to formulate because of its complex dependence on composition, temperature, and atmosphere. As expected, Ni-YSZ showed expansion when oxidized, but under certain conditions at an intermediate temperature range, it rather contracted on oxidation [7].In reality, the calculated stress distribution does not always match the actual behavior of the cell since there often are unconsidered factors. Thus, experimental validation is essential. For this purpose, we have developed methods for in-situ or operando measurements of cell shape and the residual stress. Long-focus laser profilometer was used to measure the warping of a planar cell during heating, operating, and cooling operations. For the change in the diameter of a tubular cell, the laser projection type dimension meter was employed. Residual stress measurements were made with a handy X-ray analyzer (μ-X360s, Pulstec Industrial. Co. Ltd.) combined with a newly developed one- or two-chamber cell holder [8,9]. Anode-supported cells from multiple sources were analyzed, showing different stress histories in red-ox operations depending on the microstructure of the anode support layer.Currently, we are developing a protocol for testing robustness of planar SOFCs. Here, temperature distribution is intentionally applied on a cell with segmented heater allays on the top and the bottom of the cell. Severe condition tests will be performed, and the results will be analyzed with the above-mentioned simulation.AcknowledgementThis study was supported by the New Energy and Industrial Technology Development Organization (NEDO) .[1] T. Kawada, Current Opinion in Electrochemistry, 21, 274-282 (2020) DOI: 10.1016/j.coelec.2020.03.016[2] M. Takeda, Master’s thesis, Graduate School of Environmental Studies, Tohoku University (2016) : M. Takeda, et al. Submitted to J. Electrochem. Soc.[3] K. Terada, et. al., ECS Trans. 35(2 part2), 923-933 DOI: 10.1149/1.3570073[4] M. Sato, et. al., Trans. Jpn. Soc. Comp. Eng. Sci. 2017, 14 (2017) DOI: 10.11421/jsces.2017.20170004[5] S. Watanabe et al., J. Mater. Sci. 55, 8679-8693 (2020) DOI: 10.1007/s10853-020-04624-4[6] Y. Kimura et al., J. Electrochem. Soc. 161(11), F3079- F3083 (2014) DOI: 10.1149/2.0131411jes[7] Y. Morishita et al. , ECS Trans., 91(1) 1979-1984 (2019). DOI: 10.1149/09101.1979ecst[8] K. Yashiro et al., submitted to J. Power Sources[9] K. Oshima et al.,ECS Trans. 103(1), 1251-1260 (2021) DOI: 10.1149/10301.1251ecst

Electrochemical Performance and Mechanical Stress Evaluation of Metal-Supported Solid Oxide Fuel Cells Fabricated By Plasma Spray Method

At present, the most common type of SOFC is anode-supported SOFC (AS-SOFC), in which the cell is mechanically supported by the thick fuel electrode layer. Recently, Metal-supported SOFCs (MS-SOFCs) have attracted attention because of their potential for low cost and high mechanical robustness. However, the fabrication process of MS-SOFCs has not been established. The mechanical behavior of the cells under high temperature operation has not been clarified. In this study, we fabricated prototype MS-SOFCs using the plasma spray method. The cell was tested by electrochemical measurements, residual stress measurements, and SEM/EDX to clarify the mechanical behavior of MS-SOFCs under high temperature operation.The layers of anode (NiO-YSZ), electrolyte (LSGM9182), and cathode (LSCF6428) were formed on a metal substrate (SUS430) by atmospheric pressure plasma spraying (APS) to fabricate a single cell of MS-SOFC.Open circuit voltage, AC impedance, and I-V measurements were performed at 600°C, 650°C, and 700°C. The residual stress of LSGM9182 electrolyte was evaluated by cosα method [1] under the cell operation condition using specially designed chamber.The MS-SOFC with thicker electrode layers showed the much lower OCV than that of theoretical. In addition, the electrolyte had vertical cracks between cathode and anode after the 2nd thermal cycle. However the MS-SOFC with thinner electrode layers showed the higher OCV, which was nearly theoretical value, and much better I-V characteristics than the cell with thicker electrodes. Electrochemical impedance measurement revealed the plasma sprayed electrodes showed acceptable performance even though its microstructure was not optimized. The residual stress of LSGM electrolyte in the cell did not change so much during the cell operation. This might be caused by existence of small cracks in the electrolyte layer.This research was financially supported by NEDO.[1] K.Tanaka, Journal of the Society of Materials Science,japan,vol.66,No.7 (2017) 479-487

Quantification and Analysis of Residual Stresses in Braking Pedal Produced via Laser-Powder Bed Fusion Additive Manufacturing Technology.

This study focuses on the experimental verification of residual stress (RS) in a 3D-printed braking pedal using the Powder Bed Fusion (PBF) method with SS316L material. The RS was measured at two representative locations using the hole drilling method (HDM) and the dividing method, which are semi-destructive and destructive methods of RS measurement, respectively. The finite element method (FEM) was used with Ansys Workbench 2020R2 and Simufact Additive 2021 software to determine the magnitude of RS. The results provide insights into how RS is incorporated into metal 3D-printed components and the available tools for predicting RS. This information is essential for experts to improve the accuracy and functionality of SLM parts when post-subtractive or additive manufacturing processes are used. Overall, this study contributes to the advancement of knowledge on the effects of RS on 3D-printed metal components, which can inform future research and development in this area.

A study on the effect of plasticity on the measurement of residual stresses using ultrasound technique

Residual stresses can have detrimental effect on the life cycle of engineering components and can affect the accuracy of the fatigue life prediction models. Accurate measurement of these stresses are therefore crucial. . However, destructive and semi-destructive methods of measuring residual stresses often cause damage to the components. In contrast, the non-destructive ultrasonic method allows for intact measurement of residual stresses even, in situation where portability is not feasible. Various waves can be utilized in the ultrasonic method for measuring residual stresses. In this study, longitudinal critically refracted (LCR) waves were employed due to their higher sensitivity, larger scanning area, and lower sensitivity to texture effect, making them preferable over other waves. The purpose of this study was to investigate the influence of plasticity on the measurement of residual stresses using the ultrasonic method. To achieve this, two stainless steel disks were subjected to quenching at temperatures of 300 °C and 700 °C to induce different levels of residual stresses and plasticity. The material properties of the disks were determined through standard tensile tests to facilitate numerical simulations. Tensile test specimens were extracted from the initial sheet to measure the yield stress and modulus of elasticity. The coefficient of acoustoelasticity, was determined by subjecting the tensile test specimens to different stress levels and recording the wave flight time. The coefficient of acoustoelasticity for stainless steel 316Lwas obtained using the slope of and (E(t-t0))/t0,. Residual stresses were experimentally measured using both the ultrasonic method and the center-hole drilling method, and the results were compared with those obtained from numerical analyses. The findings from center-hole drilling method, ultrasonic method, and numerical simulation were then compared and discussed. Different levels of plasticity were considered, and the accuracy of measuring residual stresses was analyzed and evaluated.

A Digital Twin Based Residual Stress Prediction Method for Turbine Blades

The investment casting process is the conventional method for manufacturing turbine blades, and the residual stress generated through this process is widely regarded as a critical factor that markedly impacts the quality and serviceability of turbine blades. However, real-time measurement of residual stress is extremely complex and expensive, especially for single-crystal turbine blades. Current experimental measurement techniques such as X-ray or neutron diffraction can only measure residual stresses at specific points or within a very small area. Studies on residual stress of turbine blades are mainly performed by finite element (FE) simulation, but the accuracy is difficult to guarantee due to the inability to establish accurate mathematical models for complex physical systems. To address this issue, this paper proposes utilizing a digital twin (DT) model to predict residual stresses in turbine blades. By combining real-time sensor and FE simulation data, the DT model is able to update and correct the mathematical models, resulting in more accurate predictions compared to traditional FE simulations.

Characterization of Residual Stress in SOI Wafers by Using MEMS Cantilever Beams.

Silicon-on-insulator (SOI) wafers are crucial raw materials in the manufacturing process of microelectromechanical systems (MEMS). Residual stresses generated inside the wafers during the fabrication process can seriously affect the performance, reliability, and yield of MEMS devices. In this paper, a low-cost method based on mechanical modeling is proposed to characterize the residual stresses in SOI wafers in order to calculate the residual stress values based on the deformation of the beams. Based on this method, the residual strain of the MEMS beam, and thus the residual stress in the SOI wafer, were experimentally determined. The results were also compared with the residual stress results calculated from the deflection of the rotating beam to demonstrate the validity of the results obtained by this method. This method provides valuable theoretical reference and data support for the design and optimization of devices based on SOI-MEMS technology. It provides a lower-cost solution for the residual stress measurement technique, making it available for a wide range of applications.

Experimental and numerical investigation of the deep rolling process focussing on 34CrNiMo6 railway axles

Deep rolling is a powerful tool to increase the service life or reduce the weight of railway axles. Three fatigue-resistant increasing effects are achieved in one treatment: lower surface roughness, strain hardening and compressive residual stresses near the surface. In this work, all measurable changes introduced by the deep rolling process are investigated. A partly deep-rolled railway axle made of high strength steel material 34CrNiMo6 is investigated experimentally. Microstructure analyses, hardness-, roughness-, FWHM- and residual stress measurements are performed. By the microstructure analyses a very local grain distortion, in the range < 5 µm, is proven in the deep rolled section. Stable hardness values, but increased strain hardening is detected by means of FWHM and the surface roughness is significantly reduced by the process application. Residual stresses were measured using the XRD and HD methods. Similar surface values are proven, but the determined depth profiles deviate. Residual stress measurements have generally limitations when measuring in depth, but especially their distribution is significant for increasing the durability of steel materials. Therefore, a numerical deep rolling simulation model is additionally built. Based on uniaxial tensile and cyclic test results, examined on specimen machined from the edge layer of the railway axle, an elastic–plastic Chaboche material model is parameterised. The material model is added to the simulation model and so the introduced residual stresses can be simulated. The comparison of the simulated residual stress in-depth profile, considering the electrochemical removal, shows good agreement to the measurement results. The so validated simulation model is able to determine the prevailing residual stress state near the surface after deep rolling the railway axle. Maximum compressive residual stresses up to about -1,000 MPa near the surface are achieved. The change from the induced compressive to the compensating tensile residual stress range occurs at a depth of 3.5 mm and maximum tensile residual stresses of + 100 MPa at a depth of 4 mm are introduced. In summary, the presented experimental and numerical results demonstrate the modifications induced by the deep rolling process application on a railway axle and lay the foundation for a further optimisation of the deep rolling process.

Nondestructive Evaluation of Residual Stress in Shot Peened Inconel Using Ultrasonic Minimum Reflection Measurement.

Shot peening is a process wherein the surface of a material is impacted by small, spherical metal shots at high velocity to create residual stresses. Nickel-based superalloy is a material with high strength and hardness along with excellent corrosion and fatigue resistance, and it is therefore used in nuclear power plants and aerospace applications. The application of shot peening to INCONEL, a nickel-based superalloy, has been actively researched, and the measurement of residual stresses has been studied as well. Previous studies have used methods such as perforation strain gauge analysis and X-ray diffraction (XRD) to measure residual stress, which can be evaluated with high accuracy, but doing so damages the specimen and involves critical risks to operator safety due to radiation. On the other hand, ultrasonic testing (UT), which utilizes ultrasonic wave, has the advantage of relatively low unit cost and short test time. One UT method, minimum reflection measurement, uses Rayleigh waves to evaluate the properties of material surfaces. Therefore, the present study utilized ultrasonic minimum reflectivity measurements to evaluate the residual stresses in INCONEL specimens. Specifically, this study utilized ultrasonic minimum reflection measurements to evaluate the residual stress in INCONEL 718 specimens. Moreover, an estimation equation was assumed using exponential functions to estimate the residual stress with depth using the obtained data, and an optimization problem was solved to determine it. Finally, to evaluate the estimated residual stress graph, the residual stress of the specimen was measured and compared using the XRD method.

Residual stress measurement system of the general purpose powder diffractometer at CSNS

Neutron diffraction has become a well-established technique for the determination of residual stresses in various structural materials and bulk industrial products because of the unique deep penetration, three-dimensional mapping capability, and volume averaged bulk measurements characteristic of the scattering neutron beam. To conduct experiments in this research area, a residual stress measurement system was established on the general purpose powder diffractometer (GPPD) at the China Spallation Neutron Source (CSNS), which diffractometer now combines both powder diffraction and residual stress measurement conditions. The best d-space resolution of the diffractometer of medium-angle detector bank is Δd/d ≈ 0.33%. The gauge volume is precisely controlled by the four-blade slits, neutron Kirkpatrick–Baez (KB) mirror and radial collimators, and the general gauge volume is φ2*2 mm 3. The intelligent scanning positioning system established by GPPD achieves high-precision sample positioning, with an accuracy of up to 100μm. Until now, it has completed measurements on standard cycle samples of VAMAS shrink fit rings and plugs with known residual stress distributions, the results confirming the diffractometer’s high sensitivity and high accuracy to stress/strain gradients in materials or components. A large number of beam times are dedicated to user researches including residual stress studies of superalloys, high-entropy alloys, engineering steels, welds, and more. This demonstrates that the GPPD’s residual stress test system and the established test methods are feasible and effective.

Experimental and numerical investigations of S960 ultra-high strength steel welded I-section beams with in-plane flexural failure

A testing and numerical modelling programme was performed to investigate the in-plane flexural behaviour and cross-section bending capacities of S960 ultra-high strength steel welded I-section beams and presented in this paper. The testing programme included material testing, membrane residual stress measurements, initial local geometric imperfection measurements and eight in-plane four-point bending tests, with four performed about each of the cross-section minor and major principal axes. This was followed by the numerical modelling programme, where finite element models were developed and validated against the test results and then used to perform parametric studies to generate further numerical data over a wide variety of cross-section dimensions and span lengths. The obtained test and numerical data were used to evaluate the applicability of the design rules for cross-section classification and bending capacities, as prescribed in the European code, Australian standard and American specification, to S960 ultra-high strength steel welded I-section beams. The evaluation results revealed that all codified slenderness limits were safe (though conservative to different extents) when used for classifying the constituent plate elements of S960 ultra-high strength steel welded I-sections in bending. Moreover, all three considered design codes were shown to result in accurate and consistent bending capacity predictions for Class 1 and 2 (or compact) S960 ultra-high strength steel welded I-sections, but conservative bending capacity predictions, to different extents, for Class 3 (or non-compact) and Class 4 (or slender) S960 ultra-high strength steel welded I-sections.

Prestrain in the eardrum investigated using laser-ablation perforation: A proof of principle study on the New Zealand white rabbit

While the presence of residual stress (also called prestress) in the tympanic membrane (TM) was hypothesized more than 150 years ago by von Helmholtz (1869), little experimental data exists to date. In this paper, a novel approach to study residual stress is presented. Using a pulsed laser, the New Zealand white rabbit TM is perforated at seven predefined locations. The subsequent retraction of the membrane around the holes is computed using digital image correlation (DIC). The amount of retraction is the so-called prestrain, which is caused by the release of prestress due to the perforation. By measuring the prestrain using DIC, we show that residual stress is clearly present over the entire rabbit TM surface. In total, fourteen TMs have been measured in this work. An automated approach allows tracking the holes’ deformation during the measurement process and enables a more robust analysis than was previously possible. We find similar strains (around 5%) as reported in previous work, in which slits were created manually using flattened surgical needles. However, the new approach greatly reduces measurement time, which minimizes dehydration artifacts. To investigate the effect of perforation location on the TM, the spatial decrease of the prestrain (α) around the perforation was quantified. Perforations inferior to the umbo showed the least negative α values, i.e., the most gradual decrease around the hole, and were the most consistent. Perforations on other locations showed more negative α values, i.e., steeper decrease in strain, but were less consistent across samples. We also investigated the effect of the holes’ creation sequence but did not observe a significant change in the results. Overall, the presented method allows for consistent residual stress measurements over the TM surface. The findings contribute to our fundamental knowledge of the mechanics of the rabbit TM and provide a basis for future work on human TMs.

Residual stress assessment for dissimilar metal welds in nuclear power plant

The European Network on Neutron Techniques Standardization for Structural Integrity (NeT) aims to develop experimental and numerical techniques and standards for the reliable characterization of residual stresses in structural welds. NeT has developed over 20 years and involves over 30 organizations including industrial, academic, and research facilities around the world. The network tackled each specific problem by creating a dedicated Task Group (TG), which undertakes both measurement and modelling studies. NeT TG8 follows on from the successful TG1 and TG4 benchmarks, which studied the dissimilar metal welds (DMW) between 18MnD5 and Alloy 52. The material properties characterization, residual stress measurements and modelling have been conducted for NeT TG8. This paper only presents the NeT TG8 benchmark residual stress measurement in the as welded condition and preliminary simulation results.

Residual Stress Analysis of Additive Manufactured A356.2 Aluminum Alloys using X-Ray Diffraction Methods

The physical properties of metal-based structural materials, such as hardness, strength and toughness, are directly or indirectly affected by residual stress inside or on the surface of the given part. Repeated rapid heating and cooling during the additive manufacturing process causes thermal gradients and expansion and contraction in the material, which causes residual stress. Tensile residual stresses are known to exist on the surface of additive manufactured products and should be kept to a minimum as they affect the mechanical properties and lead to product deformation and product failure. Therefore, it is important to evaluate the residual stress after making the product and to control it under the desired conditions. There are limitations to using the destructive method commonly used for residual stress evaluation with additive manufacturing products, due to difficulties in repeated measurements, product size, and cost issues. Therefore, it is necessary to apply a non-destructive evaluation method and verify the validity of the method. In this study, A356.2 aluminum alloy powders were used for additive manufacturing using the powder bed fusion process, and the surface residual stress generated during the process was measured. X-ray diffraction (XRD) methods were used to observe the surface residual stress. After XRD measurement, analyses were performed using the Williamson-Hall plot, sin2ψ, and cosα methods. The residual stress measurement results of samples manufactured through the LPBF process and the characteristics and limitations of each method were discussed.

Stress Relieving Heat Treatment Technology of Oil and Gas Pipeline Based on Stress Detection

Through heat treatment tests and the measurement of residual stress in oil and gas pipelines, the relationship between stress distribution and heat treatment is discovered in this study. The distribution rules of the tensile strength of the pipes under various heat treatment temperatures and heating temperatures were discovered by examining the tensile strength of the samples after heat treatment and the tensile characteristics of the pipes at high temperatures. Finally, it is suggested that the stress removal heat treatment temperature of the pipeline should be 350 °C and the holding time should be 3 hours. Through the research on the stress-relieving heat treatment process of pipelines based on stress detection and control, the service performance of the pipeline is not affected, but the residual stress caused by various reasons can be effectively reduced and the safe operation quality of the pipeline can be improved.

Comparison of Mechanical Properties Obtained for Armor Steels: Conventional Methods vs. Nanoindentation

Abstract The mechanical properties of three armor steels, namely Ramor 500, Ramor 550, and Armox Advance, were acquired by nanoindentation and conventional methods, and then the results were compared. To this goal, samples were extracted from different (e.g., undeformed and deformed) zones of the ballistically tested armor plates. Then, nanoindentations were performed at 10-mN maximum load and different maximum indentation depths (50–150 nm). In addition to the hardness and modulus of elasticity values of the examined materials, residual stress values of the samples were calculated through the equations suggested in the literature. These values were then compared with the residual stress measurements obtained with the conventional x-ray diffraction (XRD) - sin2ψ method. Moreover, Charpy V-notch impact tests were performed to calculate the fracture toughness of armor steel samples. Microstructural analysis (e.g., optical microscope, scanning electron microscope, atomic force microscope), surface roughness, and micro-hardness (micro-Vickers) measurements were also obtained. It was noted that hardness values for the Ramor 500 and Ramor 550 armor steels were in the range of 5.5–9 GPa, whereas the hardness values of Armox Advance samples were obtained in the 8.6–10.2 GPa range at a 50-nm indentation depth. The residual stress values obtained with nanoindentation were found to be in quite good agreement with the one obtained through XRD. It was proven that nanoindentation can be used to acquire several mechanical properties through considerably less sample preparation procedure, in an automated, and a more representative manner because of the measurements obtained at multiple points.

Residual stresses in austenitic thin-walled pipe girth welds: Manufacture and measurements

Determining residual stresses in thin-walled pipes is challenging. They are potentially difficult targets for simulation, because they may not behave as simple axisymmetric structures during welding. Thin-walled pipes are more sensitive to changes in the welding heat input than thick-walled pipes. They are also under-represented in the existing population of residual stress measurements used to generate upper bound residual stress profiles for structural integrity assessments. In this paper, residual stress characterisation of two thin-walled austenitic girth welded pipes is presented. The overall geometries of the two mock-up designs were the same; they differed in the linear heat input per pass and the total number of weld passes. The residual stress characterisation was carried out using two independent measurement techniques; the contour method and neutron diffraction. The multiple-cut contour strategy was implemented to measure the cross-sectional maps of hoop and axial stresses on axial-radial and hoop-radial planes respectively. The contour method results are compared with stresses measured using neutron diffraction and specific residual stress distribution signatures observed are discussed.

Experiments and proposed model for residual stresses in hot-rolled wide flange shapes

This paper proposes a new residual stress model for hot-rolled wide flange steel cross sections. For this purpose, a dataset of 85 residual stress measurements is first assembled. The dataset is comprised of prior measurements available in the literature that are complemented by additional ones as part of the present study. A constrained optimization problem is then formulated by assuming parabolic residual stress distributions for both the flanges and the web of hot-rolled wide flange cross sections. The parameters of the developed residual stress model are inferred from the results of the optimization method and from rigorous statistical analyses. The results demonstrate that the cross-sectional area and the depth-to-width ratio strongly influence the residual stress distributions in the flanges and the web of a hot-rolled wide flange profile. The results suggest that there is no evidence that the yield strength of the material influences the developed residual stresses within a cross section. Contrary to available residual stress models in the literature that may be applicable for a limited range of cross-sectional geometries, the proposed model reduces the mean error between all available measurements and predictions by 60%–70%. The variance of the error is also reduced by a factor of two to four across all known cross-sectional properties.

Tuning residual stress in electrodeposited nickel films via pulse current

The pulse current electrodeposition has proved to be effective in the preparation of metal films with a low residual stress, while the formation mechanism of residual stress under the pulse current remains unclear. In this study, in situ measurements of residual stress in electrodeposited nickel films was performed. Nickel films with the lowest average stress were obtained under the frequency of 800 Hz, average current density of 1 A/dm2 and duty cycle of 50%. Based on X-ray diffraction and TEM analysis, the relationship between dislocation density and residual stress was studied, revealing that a high dislocation density contributed to the formation of cross slip, as well as the release of residual stress. Furthermore, charge time of the electric double layer was measured by multi-current step tests, and the possible mechanism for residual stress formation under pulse currents was proposed. The results indicated the stress was modulated by two competing factors: overpotential and fraction of the charge time. The overpotential played a leading role on average stress at low frequency and high current density, while fraction of the charge time played a dominant role at high frequency and low current density (less than 1 A/dm2). Our study provides a valuable insight to understand how pulse current parameters influence the residual stress in electrodeposited nickel films.

Membrane residual stresses and compressive behaviour of laser-welded stainless steel T-sections

This paper reports experimental and numerical investigations into the membrane residual stresses and compressive behaviour of laser-welded stainless steel T-sections. An experimental programme was firstly conducted on eight T-sections and included tensile coupon tests, membrane residual stress measurements, initial local geometric imperfection measurements and sixteen stub column tests. On the basis of the measured data, a new membrane residual stress predictive model was proposed for laser-welded stainless steel T-sections. Following the experimental programme, a numerical modelling programme was performed, with finite element models developed and validated against the test results and then employed to perform parametric studies to generate additional numerical data over a wide range of cross-section dimensions. The obtained test and numerical data were used to evaluate the relevant local buckling design rules specified in the European code and American specification. The evaluation results revealed that (i) the codified slenderness limits were generally accurate when used for cross-section classification of laser-welded stainless steel T-sections in compression and (ii) both design codes resulted in slightly conservative and scattered cross-section compression resistance predictions.