Residual Stress Concentration Research Articles

Residual Stress Concentration Due to Nano-Scaled Particulate Contamination at Direct Bonding Interface with Localized Material Inhomogeneity

Residual Stress Concentration Due to Nano-Scaled Particulate Contamination at Direct Bonding Interface with Localized Material Inhomogeneity

Effect of intermetallic compounds on the mechanical properties of Cu/Al clad sheets with an SS304 interlayer

Annealing treatments were conducted on Cu/Al clad sheets incorporating a 304 stainless steel (SS304) interlayer to investigate the impact of intermetallic compounds (IMCs) on the mechanical properties of these clad sheets with an interfacial layer. Additionally, the mechanisms of interfacial strengthening and crack propagation behavior were examined. It was found that the best overall performance was achieved for samples annealed at 200 °C, showing tensile strength, fracture elongation, and peeling strength values of 219 MPa, 7.19 %, and 19.6 N/mm, respectively. For the rolled clad sheet, cracks typically initiated at the edges of the SS304 fragments, accompanied by minor residual holes and stress concentrations. Post-annealing, the Cu and Al layers underwent varying degrees of recovery and recrystallization, and element diffusion increased, leading to improvements in elongation and interfacial bonding strength of the clad sheets. As the thickness of the IMCs grew, the interfacial crack propagation path shifted to the Al2Cu/AlCu interface within the IMC layer, significantly reducing the bonding strength.

Influence of shot-peening treatment on wear resistance of medium manganese steel

The effect of shot peening treatment on dry sliding wear behavior of medium manganese steel in as-hot rolled and solution-aging states were studied. The results show that before shot peening, the wear resistance of the solution-aging sample was better than that of hot-rolled steel. The excellent wear resistance was due to the synergistic effect of Ti (C, N) particle precipitation strengthening and grain refinement in the matrix, resulting in high strain hardening ability. After shot peening, different microscopic evolution mechanisms caused great contrast in properties. The as-hot rolled sample released internal stress by generating deformation twins (DTs) during shot peening. With the increased shot peening time, the DTs thickened and interacted with dislocations, effectively reducing the free dislocation path, releasing residual stress, and significantly improving wear resistance. However, solution-aging steel generated many dislocations, resulting in residual stress concentration at Ti (C, N) particles, promoting crack initiation and propagation, and deteriorated wear resistance.

Pre-softening HIP treatment enabled crack-healing and superior mechanical properties for René 142 superalloy fabricated via laser powder bed fusion

The generation of defects, such as cracks and pores, presents significant challenges for high-strength metals and alloys fabricated by the quick-emerging additive manufacturing technology, and subsequent post-processing treatments are often necessary before their practical applications. In this work, a novel heat treatment approach, involving a pre-softening treatment before hot isostatic pressing (HIP), is developed to facilitate the crack-healing in René 142 superalloy produced through laser powder bed fusion. Results demonstrate that René 142 alloy exhibits a propensity for severe cracking across a wide range of printing parameters, primarily in the form of solidification cracks and liquation cracks. These cracks are formed mainly due to a wide solidification range, the presence of a liquid film, and the concentration of residual stress. The pre-softening solution heat treatment significantly reduces dislocation density and residual stress levels, and the subsequent HIP together leads to a defect-free, dense structure for René 142 superalloy. Consequently, the René 142 alloy processed by the pre-softening HIP treatment achieves an excellent combination of yield strength (850 MPa), ultimate tensile strength (1227 MPa), and elongation (13.7 %), with pseudo-equiaxed grains (120–150 μm) and square γ′ precipitates (approximately 540 nm). These findings provide valuable insights for exploring crack elimination methods in other nickel-based superalloys fabricated through additive manufacturing.

Study on temperature field in the process of induction heat treatment with current assisted weld double side method

At present, in the process of weld induction heat treatment, the common method is to carry out centralized induction heating in the weld area, which will lead to large radial temperature difference of the weld, poor controllability of temperature distribution and easy to cause the defects of residual stress concentration in the weld area. To solve the above problems, this paper adopts the two-sided method to conduct induction heating on both sides of the weld, and at the same time, the auxiliary pulse current is passed into the weld to improve the quality of the weld. ANSYS finite element software is used to establish a multi-field coupling prediction model of electric-magnetic-thermal structure, and explore the distribution law of the auxiliary pulse current and the temperature field of the weld. Finally, an experimental study of pulsed current assisted two-sided induction heating is carried out. Temperature test and metallographic test were carried out respectively to verify the effectiveness of pulsed current assisted induction heating technology.

Investigation of microstructure evolution and electromagnetic shielding mechanism of absorbed MWCNTs-FeCo composites by one-step in situ deposition using high-speed laser cladding

Electromagnetic shielding materials can inhibit or reduce the harm of electromagnetic radiation and have become an important means to protect against electromagnetic pollution. In order to overcome the inconveniences of in situ or conformal manufacturing on the specific equipment, and the resulting assembly errors lead to the reduction of electromagnetic interference shielding effectiveness (EMI SE). As a new technology, high-speed laser cladding can directly design multi-walled carbon nanotubes (MWCNTs)-FeCo alloy composites as absorbents, and it is the first time to realize the rapid manufacturing of electromagnetic shielding materials by one-step in-situ deposition without adding auxiliary materials. According to the temperature field and stress field, it is found that the through-crack defects of electromagnetic shielding coating mainly resulted from the residual stress concentration of microcracks near the bottom fusion line. When the cladding strategy is 1600 W power deposition after preheating at 400 °C, a high-quality cladding layer can be obtained. When the addition of MWCNTs is 1.5 wt%, the material exhibits good electromagnetic shielding performance under the synergistic effect of dielectric loss, conductivity loss, and magnetic loss. And the average EMI SE is 23 dB in the range of 2-18GH. The research shows that high-speed laser cladding can simultaneously meet the requirements of flexible material design and efficient preparation, which realizes the integration of electromagnetic shielding material design and manufacturing.

Hydrogen diffusion simulation of the X80 pipeline steel girth weld zone considering the synergistic effect of the structure–stress–concentration field

Hydrogen embrittlement failure, caused by hydrogen permeation and diffusion in the girth weld zone of pipelines, is the main obstacle to large-scale hydrogen blending transportation. Accordingly, a three-dimensional model of the girth weld zone of X80 pipeline steel was established. Considering the influence of structural inhomogeneity in the weld zone, multi-field sequential coupling simulation technology was used to analyze the diffusion process of hydrogen under the combined action of the residual stress and hydrogen concentration fields. A synergistic mechanism between hydrogen enrichment, structural characteristics, and residual stress in the weld zone was revealed. The results indicated that the structural inhomogeneity in the girth weld zone and residual stress field significantly influenced the hydrogen concentration distribution. Moreover, for the hydrogen diffusion process at the grain boundaries, the impact of the residual stress was greater than that of the structural inhomogeneity. This study further clarifies the spatial distribution of hydrogen atoms induced by multi-field coupling in the weld zone and provides a reference for the safety assessment of girth weld layers from an engineering perspective.

3-D FE modelling of residual stress distribution in 3003 aluminium alloy overlapped joints by ARM laser with beam oscillations

Adjustable Ring Mode (ARM) laser technology combined with Beam Oscillation optics module was introduced to effectively enhance weld quality in joining aluminium alloys. This study developed a three-dimensional (3-D) thermo-mechanical finite element (FE) model to analyze the distribution of thermally induced residual stresses in laser-welded 3003 aluminium alloy. The accuracy of model was validated through comparisons with experimental weld cross-sections and further reinforced by X-ray diffraction residual stress measurements. The transient temperature field and stress distribution during the welding process were investigated using the verified model. Additionally, the hardness and microstructure of the welded samples were examined through micro-hardness tests and scanning electron microscopy. Results showed that welding with beam oscillation resulted in less penetration but higher hardness and finer columnar grain size in the fusion zone. Additionally, the influence of varying standoff distances between two sequential weld beads on residual stress distribution was investigated. Numerical findings revealed that higher residual stress concentrations were located at the weld seam and dominated by tensile longitudinal residual stress and compressive transverse residual stress. As the distance between weld beads increased, transverse and equivalent residual stresses decreased, while longitudinal residual stress away from the bead increased.

Finite Element and Design of Experiments Study on Stresses in Impact-Damaged Hourglass Specimens Subjected to Rotating Bending

Residual stresses and stress concentrations induced by impact-damage may shorten the fatigue life and cause premature failure of aeronautical components. Under cyclic loading, fatigue cracks may initiate at the points where high tensile stresses occur and propagate to failure. In this work, an experimentally validated finite element model was used to assess the stress state in impact-damaged 7075-T6 hourglass specimens subjected to rotating bending. In the first simulation step, the finite element method was used to model residual stresses in the specimens for various impact cases, with different masses of impacting objects and impact speeds and angles. In the subsequent simulation step, the damaged specimens were subjected to rotating bending. The total stresses in the impact region were obtained through the superposition of the residual stresses caused by the impact and the stresses due to the rotating bending load. The design of experiments was applied to the obtained finite element results to identify which impact parameters mostly influence the stress distribution in the damaged specimens. The analysis showed that the most significant parameter is the impact speed, followed by the material and the size of the impacting object while the influence of the impact angle is low.

Investigation of Gallium Arsenide Deformation Anisotropy during Nanopolishing via Molecular Dynamics Simulation.

Crystal orientation significantly influences deformation during nanopolishing due to crystal anisotropy. In this work, molecular dynamics (MD) simulations were employed to examine the process of surface generation and subsurface damage. We conducted analyses of surface morphology, mechanical response, and amorphization in various crystal orientations to elucidate the impact of crystal orientation on deformation and amorphization severity. Additionally, we investigated the concentration of residual stress and temperature. This work unveils the underlying deformation mechanism and enhances our comprehension of the anisotropic deformation in gallium arsenide during the nanogrinding process.

Controlling method of the welding residual stress in support platform of hydrogenation reactor

The support platform is an essential component of a hydrogenation reactor, providing stable support for internal components and ensuring efficient reactions. However, the manufacturing method of overlay welding and complex structure of support platform unavoidably generates welding residual stresses (WRS) and stress concentration, posing a threat to operational reliability. In this paper, the WRS distribution and cracking causes of the support platform of hydrogenation reactor was studied by the finite element method (FEM) combined with experimental research. Four manufacturing processes for the support platform were compared in terms of their residual stresses, and the influence of welding heat input and fillet size on the WRS was discussed. The results indicate that the abrupt increase in residual stresses at the fillet region following the machining of the base layer has enhanced the likelihood of crack occurrence. The cumulative effect of stress concentration resulting from improper welding processes and structural discontinuities, along with the tensile stress during normal operating conditions, renders the surface layers susceptible to cracking during service. The manufacturing process significantly influences the distribution of residual stresses. To obtain a reliable and crack-resistant large-sized hydrogenation reactor support platform, a welding procedure with a certain machining allowance at the support platform location prior to overlay welding should be adopted. The fillet size has a notable effect on the residual stresses at the fillet region of transition layer. Recommended fillet sizes are 15 mm radius for the base layer, 11 mm radius for the transition layer, and 8 mm radius for the surface layer. Additionally, the heat input greatly affects the hoop stresses in the transition layer, in order to avoid the occurrence of cracks, a recommended heat input of approximately 20 kJ/cm is suggested.

Vacuum brazing SiC to Mo using Nb0.74CoCrFeNi2 eutectic high-entropy alloy filler

Joining ceramics and metals is important to expand their application scope in the nuclear industry. The brazing of SiC and Mo was conducted using a Nb0.74CoCrFeNi2 eutectic high-entropy alloy filler. The microstructure and mechanical properties of the joints were examined at different brazing temperatures. As the temperature increased, the eutectic structure gradually disappeared, and a layered structure was formed at the brazed joint. An increase in the MoNi phase content can improve joint strength owing to differences in the thermal expansion coefficient and lattice mismatch between phases. The joints exhibited a maximum shear strength of 62 MPa at 1300 °C. Finite element analysis results demonstrated that the presence of a Cr0.46Mo0.4Si0.14 phase causes the concentration of residual stress. Brittle fracture occurred mainly in the Cr0.46Mo0.4Si0.14 phase, causing the rupture of the joint. This study provides valuable insights into the use of eutectic high-entropy alloys as fillers to establish a strong and reliable connection between ceramics and metals.

Contact-reactive brazing of CoCrFeMnNi high-entropy alloy to Zr alloys using Cu interlayer

Contact-reactive brazing was introduced to obtain the high-quality joints between CoCrFeMnNi high entropy alloys (HEA) and Zr alloys using Cu interlayer in a vacuum furnace. The influence of brazing temperature and holding time on the microstructure evolution and mechanical property of HEA/Cu/Zr-3 brazed joints were studied synthetically. The results displayed that the HEA/Cu/Zr-3 joints brazed at 950 °C for 10 min consisted of HEA/Cr-rich(Mn,Fe)ss/Zr(Cr,Mn)2/Zr2(Cu,Ni) + Zrss+Zr(Cr,Mn)2/Zr-3. As the brazing temperature raised, the Zr(Cr,Mn)2 layer adjacent to HEA thickened, the content of Zrss and blocky Zr(Cr,Mn)2 phases in brazing seam increased whereas Zr2(Cu,Ni) phase decreased. Noticeably, the Cr-rich(Mn,Fe)ss acted as the diffusion barrier at HEA/Zr(Cr,Mn)2 interface increased with the increasing of brazing temperature/holding time. The shear strength of HEA/Cu/Zr-3 joints was increased first and then diminished with the increasing of brazing temperature/holding time. In particular, the joints brazed at 950 °C for 10 min had the maximum shear strength of 140.1 MPa. Moreover, the cracks started at HEA/Zr(Cr,Mn)2 interface, and extended along the bulk Zr2(Cu,Ni) phase in brazing seam. Furthermore, the finite element analysis demonstrated that the primary concentration of residual stress in HEA/Zr-3 joints was at the interface of Cr-rich (Mn,Fe)ss/Zr(Cr,Mn)2, indicating this area was the weaknesses in whole brazed joints.

Modified Maximum Likelihood Estimation Metal Magnetic Memory Quantitative Identifying Model of Weld Defect Levels Based on Dempster–Shafer Theory

Metal magnetic memory (MMM) is a nondestructive testing technology based on the magnetomechanical effect, which is widely used in the qualitative detection of stress concentration zones for welded joints. However, there is inevitable residual stress after welding, which brings the bottleneck of quantitative identification between the weld residual stress concentration and the early hidden damage. In order to overcome the bottleneck of quantitative identification of weld defect levels with MMM technology, a modified maximum likelihood estimation (MLE) MMM quantitative identifying model is first proposed. The experimental materials are Q235B welded plate specimens. Fatigue tension experiments were operated to find the MMM feature laws of critical hidden crack by comparing with synchronous X-ray detection results. Six MMM characteristic parameters, which are, ΔHp(x), Gxmax, Zxmax, ΔHp(y), Gymax and Zymax, are extracted corresponding to the normal state, the hidden crack state and the macroscopic crack, respectively. The MLE values of the six parameters are obtained by the kernel density functions with optimized bandwidth from the view of mathematical statistics. Furthermore, the modified MLE MMM quantitative identifying model is established based on D–S theory to overcome the partial overlap of MLE values among different defect levels, of which the uncertainty is as low as 0.3%. The verification result from scanning electron microscopy (SEM) is consistent with the prediction of the modified MLE MMM model, which provides a new method for quantitative identification of weld defect levels.

Interior micro‐defect induced cracking mechanism and life prediction of carburized Cr−Ni steel based on double nonlinear damage under variable amplitude loading

AbstractThe constant/variable amplitude loading fatigue test with interior inclusion‐fine granular area‐fisheye induced failure under R=0 were carried out on carburized Cr−Ni steel. The results showed that the fatigue life under variable amplitude loading is longer than that under constant amplitude loading in very‐high‐cycle fatigue regime under same maximum stress level, and the surface morphology of fine granular area under variable amplitude loading is coarser than that under constant amplitude loading under same order of magnitude of fatigue life. Simultaneously, it can be determined that the formation micro‐mechanism of fine granular area is caused by the continuous deboning due to stress concentration around interior micro‐defects. Furthermore, the life prediction model based on double nonlinear fatigue damage, which considers the coupling effect of local equivalent stress (surface residual stress and local stress concentration effect), loading sequence, failure mechanism and nonlinear characteristics of fatigue damage under constant/variable amplitude loading is established, and predicted life has good accuracy within the factor‐of‐three lines.

Effects of galvanizing on residual stresses and stress concentrations in RHS X- and T-Connections

Complementary studies showed that post-production hot-dip galvanizing changes residual stress magnitudes and distributions in cold-formed hollow structural section (HSS) members and can affect their behaviours under axial compressive and flexural loads. However, research on the effects of galvanizing on HSS connections is insufficient. Similar to previous research, in this research a comprehensive measurement of residual stresses was performed, using the hole-drilling approach and a total of 144 strain gauge elements at 48 locations of interest on the connection specimens. The experimental program includes two galvanized and two ungalvanized rectangular hollow section (RHS) connection specimens with different branch-to-chord width ratios (β). The effects of fabrication (cold forming and welding) and post-fabrication (galvanizing) processes on residual stresses at various locations of the specimens are investigated and compared. The effects of galvanizing-induced residual stress changes on stress concentrations at the critical locations at different fatigue load levels are studied. The connection specimens were subsequently tested under branch axial compressive forces to failure to compare their performances under static loading.

Effect of pre-welding and welding voltage on thermal fatigue property of parallel gap resistance welded joint between Ag interconnector and Au/Ag back electrode of GaAs solar cell

Thermal reliability of Au/Ag interconnection is a crucial factor for the life of solar cell array during service in space. Although it is known that increasing the heat input can effectively improve the joint thermal fatigue resistance, such welding energy increase has to be achieved by coordination of various parameters to avoid damage to the solar cell matrix. Therefore, clarification of specific strengthening mechanism by different welding parameter is significant for the further improvement of joining quality. In this study, parallel gap resistance welding (PGRW) is used to perform micro-leveled interconnection between Au/Ag back electrode of triple-junction GaAs space solar cell and Ag interconnector. Besides the original parameter set, methods of welding voltage increase and pre-welding are used to improve the joining quality. Subsequently, the samples are subjected to temperature cycling environment between−160 °C and+120 °C for various cycles. According to the tensile-shear test results, although both methods have effectively improved the joint thermal fatigue property, quite different strengthening routes are shown. On one hand, joints strengthened by increasing welding voltage have higher tensile shear force than the ones strengthened by pre-welding. On the other hand, joints optimized by pre-welding show much stabler tensile-shear property. Material characterization by transmission electron microscopy (TEM) has explained the different strengthening routes that increase of voltage actually changes the joining mechanism from original solid-phase diffusion between Au/Ag interface into total melting, while pre-welding keeps the interface with partial solid-phase diffusion interface. Besides, electron back scattered diffraction (EBSD) results indicate that the evolution of residual stress concentration is the intrinsic reason for thermal fatigue failure of the Au/Ag interface.

Effect of local ‘over-growth’ on fracture behaviors of coated titanium fiber fabricated by plasma electrolytic oxidation

The local ‘over-growth’ behavior of plasma electric oxidation (PEO) coating plays a vital role in the fracture of alloy. In this work, the effect of the ‘over-growth’ on the fracture behavior of PEO coating on the titanium fiber substrate was investigated by the tensile and bending. The ‘over-dissolution’ on the surface of fiber occurred by concentrated plasma discharge during the discharge stage, which lead to the ‘over-growth’ behavior and formed a ‘zigzag’ region in the interface between fiber and coating. The ‘over-growth’ behavior induces the concentration of residual stress generated by PEO, which provides a driving force for the crack initiation and propagation. The cracks propagate from the ‘zigzag’ interface to the fiber substrate resulting in the reduction of the tensile strength for the coated fiber by 45%, compared with the original fiber. Besides, the cracks propagate from the ‘zigzag’ interface to the coating surface, which causes coating cracking and peeling off. This work provides a potential application in surface treatment on fibers and the theoretical basis for optimizing ceramic coating.

Dynamic photoelastic study of flexure hinges produced by additive manufacturing technology

There are many challenges in compliant mechanism redesign for additive manufacturing (AM) technologies, and in order to assess their applicability and propose adequate recommendations, the behavior of compliant elements has to be examined. Plastic materials are often used in AM technologies and are well suited for large volume compliant mechanisms due to their flexibility to strength ratio. However, they also have many disadvantages, notably a low fatigue strength and complex material behavior. Therefore, in this paper a photoelastic observations of corner-filleted flexure hinges manufactured from the transparent acrylic based photopolymer using the Digital Light Processing (DLP) AM technology subjected to the dynamic loading have been conducted in order to assess the fatigue strength and potentials of the photoelastic methods for the material behavior modeling. Three-point flexural tests on rectangular beam samples with the standardized dimensions printed in vertical and in horizontal orientation have been performed and the obtained data has been used for numerical simulations of corner-filleted flexure hinges. The specimens printed in different orientations exhibit significantly different anisotropic properties; the horizontally printed samples exhibit brittle behavior, while the samples printed vertically yields and consequently have much higher deformations, the calculated flexural moduli are also very different. Corner-filleted flexure hinges printed in vertical orientation and subjected to dynamic cantilever beam bending tests at relatively high stress amplitudes proved sufficient for the low dynamic compliant mechanisms applications. The qualitative photoelastic observations have shown that the photoelasticity is applicable in dynamic tests and useful in residual stress determination and stress concentration investigations.

Investigation of the Microstructure of Ti6Al4V Alloy by Coaxial Double Laser Metal-Wire Deposition.

Laser metal-wire deposition (LMwD) exhibits a larger molten pool and layer height during printing, compared to powder bed fusion additive manufacturing; in the present study, these features revealed a more inhomogeneous but easily observable microstructure. The coaxial double laser used herein makes the energy distribution of the molten pool more complex than that afforded by a single laser source, and the microstructure of the LMwD parts was more heterogeneous as well. We observed the microstructure of Ti6Al4V by the double LMwD as-built samples by conducting a laboratory experiment and a simulation. The precipitated martensite (α') phase was defined after eliminating the influence of the β element in an X-ray diffraction analysis, which has not been discussed previously in the literature. We also propose a theory regarding the formation of heat-affected zone (HAZ) bands in an environment that includes the α' phase. Our experiments revealed only white HAZ bands, which can be attributed to the solute partitioning caused by sequential thermal cycling and the absence of the β element. The microhardness of the HAZ band areas was lower than that of both the upper and lower sides. The simulation results indicate that the maximum temperature of 2925 °C restrains the generating of HAZ bands in the final two deposited layers, due to its great difference from the β transus temperature. Moreover, the higher heat accumulation in the upper layers promoted the migration of β-grain boundaries, which may explain why the coarse columnar β grains tended to grow at the edge area in the layers deposited later. We also observed that with the use of high temperature, the nucleation of β grains is more easily promoted in the lower layers. We conclude that the concentration of residual stress in the fusion zone and the first layer is favorable to the nucleation of equiaxed grains.