Effect Of Residual Stress Relaxation Research Articles

Fatigue crack growth prediction for shot-peened steel considering residual stress relaxation

The compressive residual stress field (CRSF) relaxes during the fatigue crack growth (FCG) process, and the pattern of this relaxation remains unclear. Residual stress (RS) relaxation leads to a change in residual stress intensity factor (RSIF), which significantly affects the fatigue crack growth rate (FCGR) and thus affects the assessment of fatigue crack growth rate. To this end, this work designed a series of experiments to explore the FCG behaviour in compressive residual stress fields (CRSFs) by considering RS relaxation. Firstly, shot peening(SP) treatments were conducted on the specimens. Then, residual stress fields (RSFs) at different crack propagation stages were measured to analyse the relationship between surface RS and inner RSF distribution. The derived weight function and the real-time RSF are combined to calculate the RSIF with/without considering RS relaxation. Finally, the effect of RS relaxation on the accuracy of FCGR assessment was investigated. The results show that the positive effect of CRS on the fatigue performance of the peened specimens is primarily embodied in the early stage of the FCG process. With the continuous relaxation of the CRSF, the difference in FCGR between the peened and unpeened specimens gradually decreases and tends to disappear. When the applied SIFs are large enough, the CRS would completely relax, and the inhibiting effect of CRSF on FCGR would fail. The proposed method in this work can effectively predict the FCGR of the peened specimen when considering the RS relaxation. This work could provide some meaningful insights for the assessment method of FCGR prediction in CRSF induced by surface strengthening treatment.

Effect of Welding Residual Stress on Along-Wind Fatigue Life of Welded Joints in Guyed Mast

On the premise of only considering along-wind effect on guyed mast, the influence of welding residual stress on the fatigue life of welded joints is evaluated in this paper. Since the sum of residual stress and along-wind-induced dynamic stress exceeds the yield strength of structural steel, the effect of residual stress relaxation is included in the numerical analysis. The multiscale finite element analysis of guyed mast is developed in order to capture accurately stress field distribution of welded joint for the “welding-wind-induced” case in which both residual stress and along-wind-induced stress are taken into consideration, and the stress response characteristics at fatigue critical point of welded joints are pointed out. It is found that the “welding-wind-induced” stress field of welded joint can be approximately considered as multiaxial proportional loading state and hence the stress-based von Mises criterion can be adopted to evaluate the fatigue life of welded joints. Based on the S-N curve of stress fatigue life for welded specimens with structural steel commonly used in guyed masts, the fatigue damage of key welded joints is predicted, and as a consequence, the influence of welding residual stress on the fatigue life of welded joints is discussed.

Effect of residual stress relaxation by means of local rapid induction heating on stress corrosion cracking behavior and electrochemical characterization of welded Ti-6Al-4V alloy under slow strain rate test

In this study, a welded Ti-6Al-4V alloy was treated by means of local rapid induction heating in order to relax the residual stress existed in the weldment. The welded samples were heat treated at the different temperatures. The stress corrosion cracking behavior and electrochemical characterization of the as-welded samples before and after the post weld heat treatment as a function of residual stress were investigated. Electrochemical impedance spectroscopy measurements of the samples under slow strain rate test were performed in a LiCl-methanol solution. The results demonstrated that the residual stress in the as-welded sample was dramatically reduced after the post weld heat treatment, and the residual stress decreased with the increase in the heat treatment temperature. The stress corrosion cracking susceptibility and electrochemical activity of the as-welded sample were significantly reduced after the heat treatment due to the relaxation of the residual stress, which gradually decreased with the decreasing value of the residual stress distributed in the heat treated samples.

Analysis of second harmonic generation and deformation of a KDP crystal based on residual stresses of the supporting frame

The residual stress of KDP crystal supporting frame, deformation and stress of KDP crystal caused by the residual stress of crystal frame, as well as the influence rule of the second harmonic conversion efficiency were studied. On the basis of the analysis of the mechanism of grinding machining producing residual stress, through the calculation of power and thermal loads, a two-dimensional finite element model of grinding was established, and the internal and surface stress distribution in the grinding process and after cooling were obtained. The hole drilling method was used to test the surface residual stress of the crystal frame specimens. Based on the results of two-dimensional finite element method of grinding, the effect of residual stress relaxation on surface accuracy of crystal frame was calculated, and according to which a three-dimensional equivalent model and an integrated finite element model of the crystal holder assembly considering the influence of residual stress relaxation were established to calculate the residual stress-induced crystal deformation and stress-induced refractive index. On this basis, the phase match and the second harmonic conversion efficiency considering phase mismatch were obtained. The results showed that residual stress of different symbol and magnitude had diverse effects on the second harmonic conversion efficiency.

Experimental investigation of the effect of residual stresses and interfacial adhesion on rapid crack propagation in bilayered polypropylene/polyethylene (PP/PE100) pipes

Rapid crack propagation (RCP) resistance of bilayered pipes consisting of a polyethylene core and a polypropylene skin was investigated using the ISO 13477 Small Scale Steady State “S4” test. It was found that bilayered pipes met all the RCP requirements, but the addition of a thin (0.4–1.5 mm) skin slightly increased the S4 critical temperature. This embrittlement effect is attributed to increased constraint, which is mainly influenced by the elastic moduli of the skin and core and the adhesion between them. Because the elastic moduli of the skins were very similar, the investigation focused on the effect of adhesion and residual stresses. It was found that higher adhesion leads to higher constraint and higher S4 critical temperature. However, when both adhesion and residual stresses were modified during annealing, the effect of residual stress relaxation was more significant on RCP performance than that of increasing adhesion. Annealed pipes in which residual stresses had relaxed by ∼40%, showed better RCP resistance even though adhesion was almost doubled. It was found that in some cases, bilayered pipes may even present better RCP resistance than monolayered ones when the adhesion falls below a threshold at which the skin no longer constrains the pipe. POLYM. ENG. SCI., 57:458–463, 2017. © 2016 Society of Plastics Engineers

The effect of residual stress relaxation by the vibratory stress relief technique on the textures of grains in AA 6061 aluminum alloy

The textures and crystallographic orientations beneath the treatment area in AA 6061 aluminum alloy after vibratory stress relief (VSR) process were investigated by combining the electron backscatter diffraction analysis of the misoriented low- or high-angle boundaries, the (inverse) pole figures, the line scans and the various grain orientations. The relaxation effect caused by compressive residual stress in the intermediate region is superior to that of tensile residual stress on both sides of the cantilever by means of X-ray diffraction techniques. The residual stress relaxation that occurs due to vibrational stress excitation accompanies the “orientation of banding” disintegration, the decreases in the dislocation density, the strain energy, and the fraction of low-angle boundaries within each type of grain orientation, such as Copper {112} 〈111〉, S {123} 〈634〉, Goss {110} 〈001〉, and Brass {110} 〈112〉, excepting the Cube (or near-Cube) {100} 〈001〉 grain orientation. The maintained invariance in the Cube texture can be attributed to the maximum number of active primary slip systems, resulting in an interaction that results from hindered slip on intersecting families of the planes.

Neutron Diffraction Residual Stress Measurements in Electron Beam Welded Compact Tension Specimens

In a study to investigate the effect of residual stress relaxation on Creep Crack Growth (CCG) a novel fracture mechanics specimen has been designed. Compact Tension, C(T), specimens are fabricated from blocks with Electron Beam (EB) welds such that residual stresses induced during welding are retained in the specimen. Finite element analyses of EB welding and machining processes have been developed to predict the stresses in such C(T) specimens which will drive crack growth in future CCG studies. The residual stresses and strains in these samples have been quantified using the neutron diffraction measurement technique at various stages of the fabrication process and have been used to validate numerical simulations of the fabrication processes.

Residual stress relaxation in typical weld joints and its effect on fatigue and crack growth

Many factors influence the fatigue and crack growth behavior of welded joints. Some structures often undergo fairly large static loading before they enter service or variable amplitude cyclic loading when they are in service. The combined effect of both applied stress and high initial residual stress is expected to cause the residual stresses relaxation. Only a few papers seem to deal with appropriate procedures for fatigue analysis and crack growth by considering the combined effect of variable amplitude cyclic loading with residual stresses relaxation. In this article, some typical welded connections in ship-shaped structures are investigated with 3-D elastic-plastic finite element analysis. The effect of residual stress relaxation, initial residual stress, and the applied load after variable amplitude cyclic loading is revealed, and a formula for predicting the residual stress at hot spot quantitatively is proposed. Based on the formula, an improved fatigue procedure is introduced. Moreover, crack growth of typical weld joints considering residual stresses relaxation is studied.