Microstructural evolution and performance analysis of WC-11Co reinforced iron matrix composites

Residual weld stresses in stiffener-to-deck plate weld of an orthotropic steel deck

The stress corrosion cracking(SCC) of austenitic stainless steel and nickel-based alloy is a primary concern for stable operation in Boiling Water Reactors(BWRs) and Pressurized Water Reactors (PWRs). Laser peening is one of the promising technologies for prevention of SCC initiation to induce compressive residual stress near the surface region. However, the compressive residual stress by laser peening is likely affected due to applied stress. In this study, the effect of mechanical loading on the compressive residual stress by laser peening was investigated. The specimens of low carbon austenitic stainless steel (Type316L), nickel-based alloy (Alloy600) and their weldments were prepared, and several levels of cyclic loading were applied to their specimens. The surface residual stress at surface was measured by X-ray diffraction method before and after loading. The relaxation behaviour of the compressive surface residual stress by laser peening was evaluated at the base metal and heat affected zone (HAZ) of the weldment. It was confirmed that compressive surface residual stress remained after stress loading which corresponds to 0.2% proof stress, and that the relaxation of the surface residual stress remarkably observed after initial loading during cyclic loading test. These relaxation behaviour were similar in Type316L, Alloy600 and their HAZ.

Optimization of residual stress field in ultrasonic assisted burnishing process

Residual stress field and thermal relaxation behavior of shot-peened TC4-DT titanium alloy

Investigation of residual stress formation mechanism with water jet strengthening of CoCrFeNiAlx high-entropy alloy

Tensile residual stresses at the surface of welded components are known to compromise fatigue resistance through the accelerated initiation of microcracks, especially at the weld toe. Inducement of compression in these regions is a common technique employed to enhance fatigue performance. Transformation plasticity has been established as a viable method to generate such compressive residual stresses in steel welds and exploits the phase transformation in welding filler alloys, that transform at low temperature to compensate for accumulated thermal contraction strains. Neutron and X-ray diffraction have been used to determine the stress profiles that exist across the surface of plates welded with low transformation temperature welding alloys, with a particular focus on the stress at the weld toe. For the first time, near-surface neutron diffraction data have shown the extent of local stress variation at the critical, fusion boundary location. Compression was evident for the three measurement orientations at the fusion boundaries. Compressive longitudinal residual stresses and tensile trans- verse stresses were measured in the weld metal.

Laser shock peening (LSP) is a powerful technique for improving the fatigue performance of metallic components by customizing compressive residual stresses in the desired near-surface regions. In this study, the residual stress distribution characteristics of 6061-T6 aluminum alloy induced by LSP were identified by the X-ray diffraction method, and their dependent factors (i.e., LSP coverage, LSP energy, and scanning path) were evaluated quantitatively by numerical simulations, exploring the formation mechanism of LSP residual stresses and the key role factor of the distribution characteristics. The results show that LSP is capable of creating anisotropic compressive residual stresses on the specimen surface without visible deformation. Compressive residual stresses are positively correlated with LSP coverage. The greater the coverage, the higher the residual stress, but the longer the scanning time required. Raising LSP energy contributes to compressive residual stresses, but excessive energy may lead to a reduction in the surface compressive residual stress. More importantly, the anisotropy of residual stresses was thoroughly explored, identifying the scanning path as the key to causing the anisotropy. The present work provides scientific guidance for efficiently tailoring LSP-induced compressive residual stresses to improve component fatigue life.

This study aims to compare the influence of residual tensile and compressive stresses resulting from welding on the fatigue crack propagation. The development of fatigue fractures within zones characterized by residual tensile and compressive stresses is investigated using numerical simulations. A quantitative evaluation of the impact of residual stresses on the crack propagation is conducted by comparing the crack opening loads in cases with and without residual stresses. A series of comparative analyses of crack closure parameters is performed to examine the effects of changes in the load level (e.g., load ratio, maximum load, and overload ratio) on the release and redistribution of welding residual stresses. The research findings indicate that the influence coefficients for residual tensile stress and compressive stress on the fatigue crack propagation are 0.65 and 1.5, respectively. Increasing the cyclic loading amplitude and overloading are beneficial for reducing the difference in crack closure parameters between cases with residual stress and those without, weakening the influence of welding residual stress on the crack growth.

ABSTRACTTo understand the cause of compressive residual stress in welded joints, we analysed by numerical analysis the effect of welding pass sequence using low transformation temperature (LTT) welding materials on residual stress around the weld toe of boxing fillet welded joints. It was determined by numerical analysis that the produced compressive residual stress and the influence of the stiffeners are reduced in the equivalent position of the weld toe in a fillet welded joint because of the influence on the behaviour of the stiffener in the weld being due to residual stress distribution around the weld toe. The residual stress reduction method of extending the length of the welded bead and releasing the weld toe from the stiffener, similar to the concept of discarding a bead to reduce tensile residual stress, was effective in fillet welded joints. Numerical analysis of the relationship between residual stress around the weld toe and width of the weld bead in the bead-on-plate welding model clarified that compressive residual stress can be introduced around the weld toe by having a wide width weld bead. In addition, a fully penetrated welded joint was very effective for causing compressive residual stress around the weld toe.

The benefits of applied compressive residual stress on fatigue properties of materials is a well-known phenomenon, but not well described in all respects. The fatigue life and the fatigue limit could be improved by targeted created compressive residual stress in the surface layers therefore, diversified surface compressing methods are developed and used in the engineering industry. The relaxation of the compressive residual stress state during a cyclic and static load is determinative for the life time of a componenet. Compressive stress relaxation was experimentally determined during the cyclic and static load. The compressive residual stress was induced by shot penning on the surface of stainless steel, micro alloyed high strength steel and hardened steel specimens. The residual stress state was investigated nondestructively by X-ray diffraction method then these specimens were load. After a certain number of cycles the fatigue load was stopped and the residual stress state was recorded again and again until fracture. To investigate the relaxation process during static load a four-point bending bench was used. The compressive residual stress relaxation was correlated to the applied fatigue stress level, the cycle number the quality of alloys.

Abrasive waterjet peening (AWJP) is a new mechanical surface treatment where particles are delivered by a waterjet to induce plastic deformation and achieve surface strengthening effects on a workpiece. Although fatigue strength can be improved by inducing compressive residual stress, the prediction of residual stress distribution remains challenging because particle–workpiece interaction occurs with randomicity, superposition, and overlapping. In this paper, a theoretical model is proposed for predicting workpiece plastic deformation and compressive residual stress by analysing i) the non-uniform energy distribution of the AWJP beam caused by the non-uniformity of the abrasive size, spatial distribution, and impact velocity; ii) material hardening among multiple impacts by abrasive particles; and iii) overlapping traces induced by the changing position of the AWJP beam. The AWJP experiments were conducted in single-pass/multiple-pass/multiple-overlapping footprints with different pump pressures, traverse speeds, and jet centre distances of the adjacent traces to validate the model. The results showed good agreement with the predicted surface roughness and compressive residual stress. Compressive residual stress increased with the pump pressure, whereas the effect of pump pressure change rate decreased when the pump pressure was increased; further, residual stress is nearly constant with the variation in traverse speed and jet centre distance of the adjacent traces when it decreases to a certain value. These results can act as references for the control of residual stress and the prediction model can aid industrial manufacturing in AWJP parameter optimisation (e.g. pump pressure, traverse speed, surface roughness, compressive residual stress, and centre distance between two adjacent traces).

In this study, nanoindentation was employed to determine residual stresses in copper after compression and tension deformations with different deformation levels. Rectangular and cylindrical compression specimens were prepared in order to produce residual stresses parallel or perpendicular to the stress direction. For the compression deformation, with the increase in compressive strain, the residual compression stress parallel to the compression direction increased and exhibited a linear relationship with the compressive strain, σcompression resparallel=−1.56εrectangle compression, while the residual compression stress perpendicular to the compression direction were as follows: σcompression resperpendicular=−0.20εcylinder compression. For the tension deformation, with the increase in tensile strains, the residual tension stress parallel to the tension direction increased and exhibited a linear relationship with the tensile strain, σtension resparallel=1.03εplate tension, while the residual tension stress perpendicular to the tension direction were as follows: σtansion resperpendicular=0.65εcylinder tension. The residual stresses parallel to the stress direction exhibited significant anisotropic characteristics, while the residual stresses perpendicular to the stress direction exhibited significant isotropic characteristics. Based on the above results, the relationship between strains and residual stress were successfully determined, providing valuable data reference for engineering applications.

800x600 The short and long Japanese swords “WAKIZASHI” (back up sword of the main sword, “KATANA”) were made by one sword craftsman. The short and long swords “WAKIZASHI” were machined by rough grinding and final hand polishing, respectively. The microstructure, carbon content and hardness of short sword were measured experimentally on the cross section of sword blade. The 2θ-sin2ψ diagrams from Fe-211 plane using Cr-Kα radiation on the ground and polished blade were measured. An influence of final hand polishing process on the surface residual stress field of sword blade was examined. As a result, biaxial principal compressive residual stresses were generated and had constant stress gradients in depth on the ground and polished surfaces because the ψ-splitting was not observed and the measured 2θ vs. sin2ψ relations could be approximated as a parabolic curve. Large compressive residual stresses more than −1.0 GPa were distributed on the ground surface from “HASAKI” to “HAMON” of short sword. The surface compressive residual stress and its gradient were diminished gradually from “HAMON” to “MUNE” (the ridge of sword). On the other hand, compressive residual stresses more than −650MPa were distributed on the pol­ished surface from “HASAKI” to “HAMON” of long sword. The surface compressive residual stress and its gradient were also diminished gradually from “HAMON” to “MUNE”, and the residual stress gradient in the transverse direction were greatly degraded in comparison to the short sword. Additional compressive residual stress field induced by rough grinding was superimposed on the residual stress field after tempering process. The residual stress field near the blade surface after rough grinding was released partly by final hand polishing. Normal 0 21 false false false DE X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Century","serif";}

Fatigue tests with three different stress ratios were carried out on shot-peened SUS316L steel, and in situ X-ray stress measurements were performed to analyze the behavior of the residual stress change and related factors. The compressive residual stress decreased during tensile loading and increased during compressive loading. The reduced compressive residual stress was caused by the tensile yielding of the core region, whereas the increase in compressive residual stress was caused by the compressive yielding of the core region. This behavior was observed when the yield strength of the surface layer was significantly increased by shot peening, and the compressive yielding of that layer and the resulting relaxation of compressive residual stress were prevented. In this case, the behavior of the residual stress change during cyclic loading was contingent on the stress ratio. It is because the compressive residual stress, which decreased during tensile loading, increased under subsequent compressive loading, and the amount of increase is based on the magnitude of the applied compressive loading.

Fatigue tests with three different stress ratios were carried out on shot-peened SUS316L steel, and in situ X-ray stress measurements were performed to analyze the behavior of the residual stress change and related factors. The compressive residual stress decreased during tensile loading and increased during compressive loading. The reduced compressive residual stress was caused by the tensile yielding of the core region, whereas the increase in compressive residual stress was caused by the compressive yielding of the core region. This behavior was observed when the yield strength of the surface layer was significantly increased by shot peening, and the compressive yielding of that layer and the resulting relaxation of compressive residual stress were prevented. In this case, the behavior of the residual stress change during cyclic loading was contingent on the stress ratio. It is because the compressive residual stress, which decreased during tensile loading, increased under subsequent compressive loading, and the amount of increase is based on the magnitude of the applied compressive loading.