Development Of Residual Stresses Research Articles

Experimental investigation of residual stress distribution on girth welds fabricated at proximity using neutron diffraction technique

Maintaining minimum distance between repair and existing welds often becomes impractical due to the presence of compact layouts, original welds of branches, nozzles, etc. on offshore structural elements, pipelines, and piping. Although some international codes and standards provide criteria for maintaining a minimum distance between proximity welds, most of them lack technical justification in relation to their effect on the structural integrity of welded components. The development of residual stresses has a significant effect (i.e., a negative effect on tensile stresses and a positive effect on compressive stresses) on the integrity of the welds fabricated at proximity. Hence, it is important to investigate the residual stress distribution on welds fabricated at proximity, especially at a distance away from the weld toe. This study presents findings on the characterization of residual stresses by neutron diffraction at the proximity region between two girth welds. The two welds were fabricated at proximity, using two different welding procedure specifications and at three different distances, on a structural steel pipe, grade S355. The three different welding distances between weld toes were maintained at 5, 10, and 15 mm respectively. The neutron diffraction-based residual stress distributions were investigated at the POLDI neutron instrument at the Swiss spallation source SINQ in Switzerland. The axial, hoop, and radial components of the residual stresses were experimentally investigated between proximity welds. The findings revealed that residual axial stresses at a 5-mm proximity distance were increased beyond the yield strength of the structural steel, grade S355. The findings of this study enable practitioners to take remedial actions to minimize the residual stresses developed in girth welds fabricated at proximity. Also, the findings enable us to derive technical justification for maintaining a minimum distance and developing welding procedure for welds fabricated at proximity.

Improved corrosion resistance of Ni-base Alloy 600 welded joint by laser shock peening

Stress corrosion cracking (SCC) of welded joint is one of the salient problems influencing the safety of nuclear power structure. In this work, laser shock peening (LSP) was introduced to enhance the corrosion resistance of Ni-base Alloy 600 welded joint. The corrosion behavior was evaluated by electrochemical corrosion and SCC tests, and its anti-corrosion mechanism was analyzed in terms of the residual stress and microstructure evolution. The results indicate that LSP treatment could significantly reduce the electrochemical corrosion rate and SCC sensibility of the weldments by 81 % and 14 %, respectively. The enhanced corrosion resistance of the welded joint was attributed to the compressive residual stress and high-density dislocation tangles induced by LSP. The maximum compressive residual stress of ~460 MPa in weld zone could be obtained with the laser power of 25 J. The microstructure evolution of LSP for weld zone and base metal is dominated by the dislocation activities.

Thermo-mechanical modelling to evaluate residual stress and material compatibility of laser cladding process depositing similar and dissimilar material on Ti6Al4V alloy

• 3D finite element modelling of laser cladding process has been developed to predict residual stress at clad, substrate and interface. • Effect of Similar and dissimilar materials on the development of residual stress during laser cladding. • Benchmarking the model with experimental results. • Laser materials interaction of alloy and ceramic materials, and their effect on generation of residual stress. • Use of commercial software for any material system to select appropriate clad materials with minimised residual stress. The formation of residual stresses due to thermo-mechanical effect and microstructural transformation in the Laser Cladding process predominantly affects the final product integrity and service life. A 3D finite element transient thermo-mechanical model has been developed to predict thermal profile and residual stress distribution for repair application of Ti6Al4V alloy using a moving heat source. Then the developed model was applied for the deposition of ceramic materials Al 2 O 3 and TiC on Ti6Al4V alloy substrate. The outcome of this model is to predict temperature distribution, cooling rate, melt pool depth, heat affected zone and residual stress. This study mainly highlights the thermal effect on the residual stresses for similar and dissimilar clad/substrate materials and suggests the suitable cladding material with minimum residual stress.

Selective Laser Melting of CuSn10: Simulation of Mechanical Properties, Microstructure, and Residual Stresses

In this study, the evolution of mechanical properties, microstructure, and residual stresses during selective laser melting of CuSn10 components was studied. To provide a proper material model for the simulations, various CuSn10 parts were manufactured using selective laser melting and examined. The manufactured parts were also used to validate the developed model. Subsequently, a sequentially coupled thermal–mechanical FEM model was developed using the Ansys software package. The developed model was able to deliver the mechanical properties, residual stresses, and microstructure of the additively manufactured components. Due to introducing some simplifications to the model, a calibration factor was applied to adjust the simulation results. However, the developed model was validated and showed a good agreement with the experimental results, such as measured residual stresses using the hole drilling method, as well as mechanical properties of manufactured parts. Moreover, the developed material model was used to simulate the microstructure of manufactured CuSn10. A fine-grain microstructure with an average diameter of 19 ± 11 μm and preferred orientation in the Z-direction, which was the assembly direction, was obtained.

Research on welding-induced inhomogeneous stress in thick plate EH40 butt joint considering phase transformation

In this work, the inhomogeneous residual stress distribution and evolution of thick plate in single-pass full penetration laser welding are systematically investigated using phase transformation model. The material constitutive model considering solid-state phase transformation according to the actual weld microstructure is proposed to predict the inhomogeneous stress distribution of the welded joint. The inhomogeneous stress distributions along the longitudinal, transverse and thickness direction surfaces of the welded joint are systematically analyzed and deeply discussed, respectively. The results show that there is an obvious inhomogeneous distribution of the temperature field between the start-welding, middle section and end-welding position of the weld. It is obviously observed that the top and bottom surfaces of welded joint produce remarkably high stress areas and high stress gradients. The maximum longitudinal and transverse stress gradient values in the top surface are up to 1240.1 MPa and 1175.7 MPa, respectively. It is found that martensitic transformation is the main reason for the inhomogeneous stress distribution including high stress areas and high stress gradients in thick plate welded joint. The current research is beneficial to reduce the detrimental effects of welding-induced inhomogeneous residual stress on thick plate welded joints.

Evolution of material properties during the solvent-assisted recycling of thermosetting polymers: to reduce the residual stress and material inhomogeneity

Primary recycling of thermosetting polymers is shown to be enabled by depolymerizing the material in a suitable organic solvent and then re-polymerizing it into near-identical networks with equivalent mechanical properties. The re-polymerization process involves sophisticated coupling among solvent diffusion, chemical reaction, and stress field development. Specifically, solvent evaporation leads to restrained volume shrinkage of the resin and residual stress development within the re-polymerized materials. Nonuniform curing degree and material properties are also developed in the direction of solvent diffusion. These impose grand challenges to identify the optimal processing conditions to recycle thermosets with high quality and high speed. In this paper, using an integrated experimental and theoretical approach, the evolutions of the stress field and material properties during the re-polymerization of thermosetting polymers are studied. It shows how to tune the processing temperature to mitigate the residual stress and material inhomogeneity of recycled thermosets. The influencing mechanisms of sample thickness and catalyst content are also revealed. The fundamental understanding is finally extended to study the manufacturing of composites with particle reinforcements using the depolymerized solution, with a particular emphasis on the minimization of the stress concentration around particles. Overall, this study provides a guideline to design material and processing conditions for homogeneous network structure and mechanical properties of recycled thermosets, which will promote the applications of the green recycling method for thermoset wastes and benefit society.

Effect of crystallization and packing pressure on the development of residual stresses on injection molded polypropylene samples

Effect of crystallization and packing pressure on the development of residual stresses on injection molded polypropylene samples

Effect of residual-stress evolution during curing process on fatigue-life of fiber-reinforced polymers

The fabrication process of Fiber-reinforced polymer (FRP) composite leads to the formation of residual stresses. The effect of these stresses may be insignificant on the monotonous properties like tensile strength etc. However, residual stresses can significantly affect the fatigue performance of the FRP composites. There is lack of rigorous analysis on connecting the evolution of residual stress and the fatigue life of FRPs. A multi-physics analysis was performed to model the evolution of residual stresses in the curing process under different process and material conditions for unidirectional Glass Fiber Reinforced Polymers. The viscoelastic model also accounted for percolation in the matrix and thus gave realistic estimates of residualstress compared to the past elastic models. It was found that the residual-stress varied by over 25% by just changing the cure thermal cycle. The stress prediction results were found to be in-line with the experimental results reported in the literature. A numerical model was developed to obtain a change in the fatigue life (fiber-dominated failure mode in High Cycle fatigue (HCF)) from residual stresses under the simulated circumstances. This numerical model was validated with the experimental fatigue data using two different cure cycles. Fatigue life for HCF was found to be improved by upto 4% under such conditions. Thus, this study gives insight on various processes and material property handles for manipulation of the residual stresses. Accurate numerical prediction of such stresses can be cardinal in composites processing.

Residual stress evolution and tailoring of cold pilgered Ti-3Al-2.5V tube

Cold pilgering has been considered as one of the preferred fabrication technologies for high-strength titanium alloy tube. However, the complex multi-pass thermo-mechanical loading histories in whole cold pilgering, viz., multi-stroke rolling and annealing as well as surface strengthening treatment might significantly influence the inhomogeneous deformation and residual stress which closely related to the fatigue and other service performances of tube products. The objective of this manuscript was to clarify the residual stress evolution characteristics in cold pilgering of high-strength titanium alloy tube while to propose an efficient approach for the tailoring of the residual stress. The residual stress distribution features at different deformation zones during cold pilgering were numerically investigated base on the verified finite element model. On account of the coordination of inhomogeneous deformation along the tube wall, the cold pilgered tube exhibited residual tensile and compressive stress on outer and inner surface, respectively. The effects of key process parameters on the residual stress of the cold pilgered tube were explored as well as the relevant inhomogeneous deformation features were discussed, the results showed that the value of residual stress could be affected by the variation of the Q value and area reduction but independent with other parameters. By combining the experiment, it can be also concluded that the residual stress states of the cold pilgered tube were maintained with the variation of the process parameters of cold pilgering and annealing. Furthermore, aiming at the residual stress tailoring and service performances improvement of the tube, the magnetic abrasive finishing (MAF) was introduced while the measurement results indicated that large residual compressive stress could be generated on the outer and inner surface of the tube simultaneously.

Fatigue improvement and residual stress relaxation of shot-peened alloy steel DIN 34CrNiMo6 under axial loading

Shot-peening treatment was applied to a quenched and tempered DIN 34CrNiMo6 steel to improve its high-cycle R: −1 axial fatigue strength. Compared with the machined condition, the increase in the fatigue limit was 21.8%. S-N curves for shot-peened and the as machined condition were presented and compared with those obtained in previous research for rotating bending fatigue, including curves for mirror-polished specimens.The applied shot-peening treatment in this work (Isp: 8A and 200% coverage) for quenched and tempered (Q + T) DIN 34CrNiMo6 steel introduced a compressive residual stress field and an increase in surface roughness, as well as minor variations in microstructure, hardness and the FWHM (full width of the diffraction peak at half maximum intensity) parameter.The introduced compressive residual stress field tended to reduce when an external stress is applied. This was due to the onset of plastic strain. In this paper, two types of quasi-static tests were conducted by applying an axial stress with six different magnitudes and in the two directions (compressive or tensile). This was in order to assess their influence on the relaxation of surface residual stresses. Due to the introduced compressive residual stresses, if the applied stress was compressive, the onset of plastic deformations was achieved with a lower stress magnitude.In addition, surface residual stress relaxation under cyclic applied stress was evaluated at four different stress magnitudes. Due to the cyclic-softening behaviour of this Q + T steel, its cyclic mechanical properties must be considered to assess the onset of plastic strains. With the experimental data, a logarithmic model to predict the evolution of surface residual stresses with the number of cycles for different applied stress magnitudes was presented.

Evolution Behaviors and Reduction Mechanism of Curing Residual Stresses in GLARE Laminates under a Hot-Pressing Condition.

Nowadays, variable preparation, forming and processing methods of fiber metal laminates are constantly developing to meet the requirements of different application fields, hence the characteristics and evolution of residual stresses under different manufacturing conditions deserve more attention. In this work, the evolution behaviors of curing residual stresses in GLARE under a hot-pressing condition were studied, and the residual stress reduction mechanism was also explained. Results suggested the FE prediction models of the entire cure process, verified by the fiber Bragg grating (FBG) sensors, were more precise than the traditional elastic model. Moreover, the stress evolution during the cure process mainly occurred in the cooling stage, in which the different coefficient of thermal expansion (CTE) of aluminum and GFRP played a major role. Meanwhile, curing shrinkage stress in the GFRP layer during the holding stage at curing temperature obviously influenced the final stress level. The residual stresses in GFRP layers differed by 9.6 MPa under a hot-pressing and autoclave condition, in which the convection heat transfer condition played a major role as it caused lower thermal stress in the holding stage and a smaller temperature gradient in the cooling stage. Considering this, a lower cooling rate could be a feasible way to obtain GLARE with lower residual stress under a hot-pressing condition.

A combined heat source model for the prediction of residual stress post extreme high-speed laser material deposition

Extreme high-speed laser material deposition (EHLA) can be utilized for mass customization owing to its enhanced process speed and productivity. Although EHLA has multiple similarities with additive manufacturing techniques such as conventional laser metal deposition (LMD), the variation in the process speed causes different phase transformations and residual stress distributions. Therefore, a combined heat source model is proposed to evaluate the performance of structures repaired by EHLA and optimize process strategies. The model considers the unique energy input associated with the densification process compared with that of the conventionally used Gaussian heat source model. The parameters within the model were calibrated based on the residual stress distribution and molten pool morphology. The evolution of temperature and residual stress was investigated under various process conditions such as scanning speed and power input using the model. The consistency between the simulation and experimental results verified the viability of the model for determining EHLA parameters and improving the performance of repaired parts.

Effects of Laser Shock Peening on Surface Roughness and Residual Stress of AA 7050-T7451

Surface treatment techniques such as laser shock peening (LSP) represent a consolidated strategy to induce the presence of compressive residual stresses beneath the surface of various metallic alloys. However, surface roughening caused by the process must be monitored, since it may negatively affect fatigue life, resulting in earlier crack initiation. For this reason, the interplay between the key factors affecting both the surface roughness and the development of residual stresses was experimentally examined. The surface roughness was assessed through the determination of roughness average and roughness total height values, whereas residual stresses were assessed using the x-ray diffraction technique and hole drilling method to obtain information about the stress status of the components. Higher values of laser power density resulted in higher values of maximum compressive stress both along scanning and stepping direction and residual stresses remained approximately constant up to a depth of about 0.7-0.8 mm beneath the treated surface. No substantial difference was observed between the residual stress components in the two main LSP directions. Moreover, it was found that the approach to use lower values of nominal power density together with a higher number of layers allows obtaining the same stress condition determined by the use of the highest value of nominal power density but a significantly lower impact on the surface roughness.

Residual stress evolution for tooth double-flank by gear form grinding

In gear form grinding, the complexity of tool-workpiece geometries affects the grinding force and heat distribution along the tooth profile, thus resulting in difficulties in the calculation of residual stress. Specifically, the stress and heat generated on the newly machined tooth flank were influenced by the former grinding passes. Unfortunately, this issue was ignored in the previous research. To fill this gap, this paper presents a thermal-mechanical coupling calculation model considering the differences in gear double-flank, and a new heat source optimization algorithm is proposed. Firstly, according to the kinematic analysis of gear form grinding, the Lagrange interpolation method is used to solve unevenly distributed moving heat sources on the curved surface. Secondly, based on the theory of plastic increment combined with the von Mises yield criterion considering work hardening, the relationship between the temperature and the grinding stress on the first grinding tooth flank and the second grinding tooth flank is obtained through load cyclic loading. Finally, the residual stress field in the final state of all tooth flanks is obtained through the release procedure. The gear grinding experiments were conducted to verify the model, and the comparison results showed good consistency. The influence of unevenness in gear form grinding is not only reflected in the stress distribution along the tooth profile, but also on the different flanks. Based on the correlation law between the processing parameters and the residual stress on the tooth flanks, the optimal machining parameter range is obtained. The study provides an important reference for the understanding of gear form grinding mechanisms and the optimization of the grinding process.

Investigating residual stress evolution in the deposition process of diamond-like carbon film through molecular dynamics

Diamond-like carbon (DLC) films possess excellent tribological properties, such as low friction and high wear resistance. However, DLC films detach easily owing to the high residual stress, which limits their application on mechanical sliding surfaces. To overcome this problem, it is crucial to clarify the residual stress generation mechanism in DLC films. In this study, molecular dynamics simulations were conducted on the deposition process of a DLC film to clarify the residual stress generation mechanism. The results suggest that sp3 hybridization clusters are nucleated in the sp2 formed on the film surface, and sp3 clusters grow in the sp2 carbon through the sp2 → sp3 bond change during the film growth process. The bond length of sp3 was approximately 8.5% larger than that of sp2 under stress-free bulk conditions. Thus, when the sp2 → sp3 bond change occurs under construction by surrounding atoms, compressive stress is generated in the sp3 cluster, which increases with the growth of the sp3 cluster. Based on the results, we conclude that the nucleation and growth of sp3 clusters in sp2 result in residual compressive stress in the DLC film. We believe that the present mechanism clarification of the stress development process in DLC films will facilitate the development of new methods for residual stress reduction.

Gaseous carbonitriding of high carbon chromium bearing steel: Correlation between composition, microstructure and stability

Gaseous carbonitriding of AISI 52100 steel was investigated under various processing conditions. The process parameters studied involve ammonia content (2.5–7.5 vol%), carbon potential (0.8–1.2%), and temperature (780–880 °C). The carbon/nitrogen concentration-depth profiles that developed during carbonitriding were determined by light element analysis. The microstructural and residual stress evolution, and the thermal-mechanical/dimensional stability, associated with the dissolving of carbon and nitrogen, were studied by reflected light microscopy, X-ray diffraction, hardness indentation and dimensional analysis, respectively. The resulting carbon/nitrogen concentration depth-profiles and microstructure of the carbonitrided layer vary with the combination of parameters applied, associated with the carbonitriding thermodynamics. The content of retained austenite and the state and distribution of residual stresses in the carbonitrided specimen depend strongly on the total content (distribution) of carbon and nitrogen dissolved in the carbonitrided surface layer. Carbonitriding leads to exceptional tempering resistance over conventional treatment (austenitization and quenching), but results in inferior dimensional stability due to the higher content of retained austenite.

Mechanics of droplet flow/solidification and film deformation/fracture

In industrial applications, the coatings of materials are an important consideration, particularly the fracture and elastic-plastic mechanics of coating materials. This is an area of focus for researchers in the Inoue Sakaguchi Laboratory, Tokyo Institute of Technology, Japan, where Associate Professor Motoki Sakaguchi and the team are investigating the stress and strain evolution during the solidification and adhesion process of coating materials. They are doing this by conducting model experiments using paraffin wax, which is enabling them to investigate the individual effects of different experimental variables, including droplet materials, droplet temperature, droplet kinetic energy, substrate temperature and substrate roughness. In a current project, Sakaguchi is exploring the fundamental processes involved in residual stress development in thermal barrier coatings during thermal spray procedures. For this, he and the team have developed a model experiment that allows them to simplify the thermal spray using a paraffin wax with a low melting point and, in doing so, the researchers can monitor and precisely record the deposition process of each splat in the thermal spray. Sakaguchi hopes the research will help improve thermal spray technology and, ultimately, lead to improved, longer-lasting components and equipment in industrial products.

Research on the evolution of residual stresses in the manufacturing process of TC4 alloy profile rolled ring

The residual stresses generated during the manufacturing process of titanium alloy rolled ring parts, which is an important factor affecting the dimensional accuracy and operational stability of the casing parts. The research object is the TC4 titanium alloy profiled aerospace rolling ring. The optimized process is proposed by introducing bulging technology to control the residual stresses. Firstly, the stress evaluation index and comprehensive evaluation function of ring parts were established. Secondly, a multi-step continuous simulation model of the rolled ring manufacturing process was established. Finally, experimental measurements of the rolled ring parts under different process conditions were completed using the hole-drilling method. The experimental measurement results are consistent with the evolution of residual stresses obtained from the simulation results. For casing parts, the introduction of the bulging technique into the optimized process for ring parts provides an effective improvement in the uniformity of residual stresses.

Effects of a thermal-ultrasonic stress relaxation process on the residual stress, mechanical properties and microstructures of C19400 copper alloy strips

With the development of 5G communication, more demanding requirements have been specified for copper alloy strips applied in lead frames. Thin copper alloy strips with high residual stress always warp during the etching process, so they do not meet the requirements of industry. Therefore, it is essential to reduce the residual stress in these strips. In this work, a novel effective technique suitable for thin strips, the thermal-ultrasonic stress relaxation (TUSR) method, which integrates conventional thermal stress relaxation (TSR) and ultrasonic stress relaxation (USR), is proposed. The equipment used to conduct TUSR and TSR experiments on C19400 copper alloy was produced in this laboratory. The residual stress evolution was investigated using X-ray diffraction (XRD). The microstructure evolution of the strips was analyzed by using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The mechanism of the relaxation of residual stress was revealed. The maximum residual stress relaxation values in the transverse and rolling directions after TUSR treatment were 80.56 and 89.39%, respectively, which were better than the results obtained after TSR treatment. After TUSR treatment, the grain sizes were smaller, and the percentage of low-angle grain boundaries (LAGBs) was higher than that before the treatment. The dislocation morphology was converted to ordered dislocation cells and dislocation walls and macroscopic plastic deformation of the grains released elastic strain energy, which was the main reason for residual stress relaxation in the C19400 alloy strips. In addition, the increase in tensile strength was mainly due to the enhancement of a precipitate pinning effect and grain refinement. These findings can provide guidance for future work related to the relaxation of residual stress in copper alloy strips for lead frames.

Evolution of residual stress through the processing stages in manufacturing of bore-chilled sand-cast aluminum engine blocks with pressed-in iron liners

To minimize the carbon footprint of the transportation industry, manufacturers and engineers are continuously trying to improve the efficiency of the combustion engine. However, due to the presence of iron cylinder liners in the engine block, high tensile residual stresses are generated during the manufacturing process which leads to a large reduction of the alloy’s useable strength. Thus, the present study utilized neutron diffraction to study, for the first time, the evolution of residual stress of sand-cast aluminum engine blocks that have eliminated the iron cylinder liners from the casting process and mechanically inserted them after heat treatment and machining operations. Moreover, this study also examined the effects that cylinder bore chills have on the resulting residual stress profiles. The replacement of the iron liners shifted the stress mode from purely tension to purely compression until the bore chills were removed. Following the removal of the bore chills, the maximum tensile stress at the top of the cylinder bridge was ~ 70% lower than the engine’s predecessor which was produced with iron liners. Moreover, in the production-ready state (i.e., T7 heat treated and press-fit liners inserted), the stress mode maintains the partially compressive nature, thereby lowering the material’s susceptibility to crack growth and propagation.Graphical Abstract