Residual Stress Modification Research Articles

Modification of Residual Stress and Microstructure in Al-Cu-Mg Alloy by Cryogenic Aging Treatment

Modification of Residual Stress and Microstructure in Al-Cu-Mg Alloy by Cryogenic Aging Treatment

Prediction of Fatigue Crack Growth in Vacuum-Brazed Titanium Alloy

The assessment of fatigue is a crucial concern in welded components and structures. This study investigates the fatigue properties and models for predicting fatigue crack growth in Ti-6Al-4V titanium alloy when processed by vacuum brazing with TiCuNi filler. Fatigue properties and the impact of the stress ratio were determined through constant amplitude fatigue tests. By utilizing the results obtained from variable amplitude fatigue tests, various prediction models for fatigue crack growth were examined: modifications for load interaction, residual stress, and crack closure. The results indicate that the microstructures in the brazed zone consist of numerous fine, elongated needle-like Widmanstätten structures. In terms of cycle counting methods, the rainflow method outperforms the simple-range method. In the stable crack growth rate region, fatigue crack growth rate increases with the rise in stress ratio in a manner similar to high-strength steels. The Paris model without any modification obtains good predictions. For models modified with crack closure, the Elber model yields slightly better prediction results than the Schijve model. Among fatigue crack growth prediction models, the Willenborg model with residual stress modification produces the best results. Fracture surfaces within fatigued specimens’ brazed zones exhibit ductile failure characteristics, where fatigue striations and secondary cracks were observed.

Ultrasonic nanocrystal surface modification (UNSM) of surface properties and residual stress in 300 M steels

The effects of different processing parameters of ultrasonic nanocrystal surface modification (UNSM) on surface properties of 300 M steel were investigated in this study. Experiments were performed using different scanning speeds, scanning intervals and static loads. The surface microhardness, roughness, wettability, appearance and residual stresses were evaluated for every set of processing parameter. The results showed that trenches, visible under microscope, formed in scanning direction indicating the contribution of burnishing effect of sliding motion of tungsten carbide (WC) ball tip on the surface of the specimen. It was observed that the surface roughness increases with a decrease in scanning speed as peening effect overtake the burnishing action of the WC tip and increase in the static load intensifies the peening effects in turn increasing the surface roughness. As static load increases, the surface begins to form microcracks and at very high static load the surface experiences severe surface damage. It was observed that the hardness and surface residual stresses of the processed sample increased with an increase in static load however at high static load the surface damage causes stress relaxation as material experiences localized fracture. Wettability of the processed surfaces was observed to be independent of the processing parameters.

On the high cycle fatigue resistance of austenitic stainless steels with surface gradient microstructures: Effect of load ratio and associated residual stress modification

The effect of gradient microstructure generated by ultrasonic surface mechanical attrition treatment (SMAT) on the fatigue performance of an austenitic stainless steel has been evaluated in the context of localized and general plasticity by comparing two load ratios: fully reversed tension-compression (TC) RTC = -1 and tension-tension (TT) RTT = +0.1, respectively.After identical SMAT processing conditions, the fatigue limit was enhanced by +17% for RTC while it was reduced by -7% for RTT. Under RTC cyclic loading, self-heating of the specimens and sub-surface martensitic transformation occurred but not for RTT. The residual stress measurements have also revealed that while the stress gradient was smoothed after the RTC fatigue loading, it was completely reverted for the RTT one. In turns, the fatigue crack initiation sites and propagation were modified between the RTC and RTT loading conditions.Considering the stabilized surface residual stress after fatigue loading, the use of a Crossland criterion allowed to explain both the effects of load ratio and SMAT on the high cycle fatigue behavior of the stainless steel. It turns out that under the studied loading conditions the modifications of residual stress state can be considered as the primary factor governing the varying fatigue performances and the observed triggering at different initiation sites.

Effect of residual stress modification technique on CTOD test results in heavy thick welded joints

ABSTRACT In order to investigate the effects of residual stress modification on the results of crack-tip opening displacement (CTOD) tests in heavy thick welded joints, experiments using a submerged-arc welding (SAW) joint of an EH47 steel plate with the thickness of 70 mm and residual stress analyses by the finite element method (FEM) were performed. It was confirmed that appropriate reversed bend conditions improved fatigue precrack front shapes, and the low ratio of the fatigue precrack length to the size of the compressive plastic zone induced by reversed bending contributed to the fatigue crack shape improvement. Although the local compression with a large diameter platen was effective in improving the fatigue precrack front shape, small diameter platens were not effective even if they applied to wide ranges of specimens. In addition, specimens treated by the reversed bending showed higher critical CTOD values than those treated by local compression. According to the FEM analysis, the reversed bending introduced tensile residual stress at the mechanical notch root, although the initial residual stress distribution of the welded joint still remained a little away from the notch root. On the other hand, the initial residual stress was almost removed by the local compression with a large diameter platen. It was presumed that the initial residual stress distribution affected fatigue precrack front shapes and the critical CTOD in welded joints. The reversed bending is very useful if appropriate conditions can be used.

Effect of Residual Stress Modification Technique on CTOD test results in Heavy Thick Welded Joints

Effect of Residual Stress Modification Technique on CTOD test results in Heavy Thick Welded Joints

Investigation of Residual Stress Modification Method for Fracture Toughness Test of Multipass Welds in Thick Plates

Investigation of Residual Stress Modification Method for Fracture Toughness Test of Multipass Welds in Thick Plates

Strength and fatigue crack growth behaviours of metal inert gas AA5083-H116 welded joints under in-process vibrational treatment

Abstract Strength and fatigue properties are important design considerations for many aluminium welded structures which are operated under cyclic loadings such as ships, railway vehicles and car bodies. Over the years, various weld treatments have been developed to improve the quality of weld joints through modification of microstructure and residual stress. In the present study, in-process vibrational treatment has been applied to metal inert gas (MIG) welding of 5083-H116 aluminium alloy plates at various frequencies of 100, 300 and 500 Hz in effort to enhance strength and fatigue crack growth resistance of the weld joints. Experimental works including microstructure observation, microhardness and tensile tests, residual stress measurements and fatigue crack growth tests were performed. Results showed that in-process vibrational treatment obviously increased the ultimate tensile strength of the weld joints with the best frequency was achieved at 300 Hz. It was found that the strength of the weld at this condition was increased around 51.3 % higher than the weld in as welded condition owing to grain refinement and increasing amount of equiaxed dendritic microstructure in the weld metal region. These fine grained equiaxed dendritic structures combined with compressive residual stress induced by vibrational treatment could improve fatigue crack growth performance of the welds.

Modification of residual stress and microstructure in aluminium alloy by cryogenic treatment

The effect of cryogenic treatment (CT) combined with solution and ageing treatment on the residual stress and microstructure of 7050 aluminium alloy was investigated. The relationship between residual stress and microstructure was discussed. The results showed that compared to solution–ageing treatment (SA), CT after solution and before ageing (SCA) exhibited lower level and higher uniformity of residual stress. The highest dimensional stability was also obtained by the process of SCA. It was found that CT induced the fine precipitates through the lattice contraction under cryogenic temperature. Furthermore, the execution of CT in advance would also promote the uniform distribution of precipitates in the subsequent ageing by releasing and homogenising the residual stress.

Modification of residual stress distribution in welded joint of titanium alloy with multi electron beam heating

Abstract Welding residual stresses usually have some negative effects on mechanical properties of the welded structure. A multi electron beam heating method was proposed to modify the residual stress of the weld. A finite element model was established to analyze the welding transient temperature and residual stress evolution in the multi electron beam joint of titanium alloy. The computed results were validated by the measurement using blind hole drilling method. The residual stress evolutions during the multi electron beam welding and heating were analyzed to explain the residual stress modification. The effects of multi beam shape and heating group offset on residual stress distribution were discussed based on the established numerical model.

Micro-scale measurement & FEM modelling of residual stresses in AA6082-T6 Al alloy generated by wire EDM cutting

Wire EDM is well-known as a technique for sectioning metallic samples that causes minimal disturbance in terms of residual stress introduction and modification at the macro-scale. Indeed, at the millimetre scale, EDM-induced residual stress can usually be neglected. However, when the dimensions of the machined product are reduced to less than a few millimetres, the structural modification of the EDM affected layer may play a significant role in altering its structural integrity through microstructural changes and induced residual stresses. The surface finish and mechanical properties of the modified surface layer are of great importance for the correct assessment of the in-service life of mechanical components and assemblies.In this study, the EDM-affected layer generated after the primary cut, and also after a subsequent trim cut are analysed. The key advance reported in the present study is the micro- to nano-scale residual stress evaluation and modelling using the FIB-DIC method, supported and validated against non-linear thermo-mechanical FEM analysis of the cutting process. Modelling of such a machining process has a relevant implications in the optimisation of the process parameters.A thin compressive residual stress layer was found at the surface of the sample which was attributed to the Cu and Zn diffusion within the parent material, giving rise to phase transformation. Scanning Electron Microscopy with Focused Ion Beam milling were employed for the exploration of the surface and through-thickness morphology. EDS and EBSD techniques were used to interrogate the material microstructure in terms of elemental concentration and grain orientation. The implications of these findings are discussed.

Experimental and numerical investigation of the effects of the pre-heating in the modification of residual stresses in the repair welding process

In this paper, the application of pre-heating process on the reduction of residual stress in the repair welding of steel pipes is investigated. In this purpose, a thermo-elastic-plastic molding of the repair welding process is developed using finite element method. In order to verify this modeling method, experimental data of repair welds of a carbon steel pipe, measured by deep hole drilling method, were utilized. The verified results indicated that the developed computational method can be beneficially used as an effective tool to predict the residual stress of the pipes undergo the repair welding. The verified finite element model was utilized in the repair welding of carbon steel and stainless steel pipes to consider the effects of preheating. It was observed that by increasing the preheating temperature in the repair welded pipes, longitudinal residual stress on the inner and outer surfaces of the both carbon and stainless steel pipes decreased about 35–50%, respectively, although the compressive residual stresses on the outer surface have small variations. Moreover, by increasing the preheating temperature, tensile hoop residual stresses on the outer surface of both the stainless steel and the carbon steel pipes decreased, but only a small variation was observed on the compressive hoop residual stress. In general, there are no significant effects on the magnitude and distribution of hoop stresses on the inner surface of the repaired stainless steel pipe. Also, high preheating temperature, leads to a wider distribution of axial residual stresses in repair welded pipes.

Modification of Residual Stresses in Laser Additive Manufactured AlSi10Mg Specimens Using an Ultrasonic Peening Technique.

Ultrasonic peening treatment (UPT) has been proved to be an effective way of improving residual stresses distribution in weld structures. Thus, it shows a great potential in stress modification for metal parts fabricated by additive manufacturing technology. In this paper, an investigation into the ultrasonic treatment process of AlSi10Mg specimens fabricated by selective laser melting (SLM) process was conducted by means of experimental and numerical simulation. The specimens were prepared using a SLM machine, and UPT on their top surface was carried out. The residual stresses were measured with an X-ray stress diffraction device before and after UPT. Meanwhile, a finite element simulation method for analyzing the influence of UPT on the residual stress field of specimens was proposed and validated by experiments. Firstly, the thermal mechanical coupling numerical simulation of the SLM process of the specimen was carried out in order to obtain the residual stress distribution in the as-fabricated specimen. Then, the transient dynamic finite element simulation model of the UPT process of the specimen was established, and the UPT effect analysis was implemented. In the UPT simulation, the residual stress was applied as a pre-stress on the specimen, and the specimen’s material mechanical property was described by the Johnson–Cook model, whose parameters were determined by Split Hopkinson Pressure Bar (SHPB) experiment. The residual stress distribution before and after UPT predicted by the finite element model agree well with the measurement results. This paper concludes with a discussion of the effects of ultrasonic peening time, as well as the frequency and amplitude of the peening needle on residual stress.

Surface integrity of turned laser-welded hybrid shafts

For applications like components of vehicle drives, e.g. drive shaft or motor shaft, the increasing amount of CO2 emission becomes a major challenge. Weight reduction of vehicle parts is one possibility to reduce CO2 emission. Therefore functionally adapted components must be designed in order to become smaller and lighter. Consequently monolithic material is not sufficient anymore, so there is a demand for tailored hybrid parts consisting of more than one material. Those tailored hybrid parts have to pass through a processing chain. There is the option of joining different materials in the hybrid part to meet the requirements. The discussed combination is a SAE1020-SAE5120 compound. Laser beam welding is an appropriate joining process due to its reduced heat influence, the resulting narrow welds and a low post-processing effort. Thus semi-finished products for the manufacturing of tailored hybrid shafts with graded properties can be produced efficiently. Further in the process chain there is the need for machining to reach an adequate level of accuracy of shape and dimension. Moreover the residual stress modification by the machining process has a deep impact on the lifespan of hybrid components. Therefore in this paper the machinability of the SAE1020-SAE5120 compound compared with a SAE1020-SAE1020 compound will be examined. The effect of cutting edge micro geometry on the surface and subsurface properties is analysed. Relationships between process forces, residual stresses and surface roughness are investigated. Metallographic cross sections and hardness measurements will show the connection between welded materials. The transition zone—the weld between the monomaterials—is the centre of attention for the investigations.

Residual Stress Modification and Mechanisms of Bearing Steel with Different Microstructures during Water-Jet Cavitation Peening

Abstract Water-jet cavitation peening (WCP) is used to increase the hardness and induce the formation of a compressive residual stress layer on the surface through the shock wave pressure, which is produced by the collapse of small bubbles of a cavitation jet at the surface of materials. In this article, a pressure sensitive paper is applied to determine the pressure field distribution of WCP. WCP is carried out on the bearing steel 100Cr6 with different microstructures, which are heat-treated differently. The hardness, residual stress distribution, and microstructure of bearing steels at the same observation points are compared, respectively, before and after WCP. The research indicates that both the hardness and residual stress are increased with the peening time. It also proves that this method has different strengthening limits for materials with different microstructures because of the different mechanisms of WCP.

Evaluation of macro- and microscopic residual stresses in laser shock-peened titanium alloy by FIB-DIC ring-core milling with different core diameters

The residual stresses in a laser shock-peened (LSP) plate of titanium alloy were measured by means of the ring-core Focused Ion Beam–Digital Image Correlation (FIB-DIC) technique using pillar diameters of 10 μm and 5 μm. A cross-section of the Ti-6Al-4V laser shock peened plate was electrochemically polished to avoid induced residual stress modification due to grinding. FIB-DIC measurements with pillar diameters of 10 μm show that a near-surface compressive residual stress of approximately 350 MPa is present in the direction parallel to the peened surface. This changes to a tensile residual stress of approximately 100 MPa at the depth of 2 mm, and then changes back to a small compressive residual stress on the opposite face. These results are in good agreement with the previously obtained set of measurements using high-energy synchrotron X-ray diffraction. However, FIB-DIC measurements with pillar diameters of 5 μm show strong deviations from this general macroscopic trend that corresponds to the macroscopic average (Type I) residual stresses. The reason for the apparent discrepancy lies in the smaller gauge volume used in the second set of measurements, which causes the evaluated residual stress values to be dominated by the microscopic (Type II + III) residual stress components. These Type II + III residual stresses are the result of the local microstructure and intra- and intergranular interactions. The results demonstrate that the FIB-DIC ring-core technique can be tailored to determine either macro- or microscopic residual stress, by tuning the core diameter with respect to the grain size. Type II + III stresses have significant magnitude sufficient to produce local tensile stress in the region that is subjected to macroscopic compression due to LSP treatment, and vice versa. The implications of this finding are discussed.

Through Process Modeling of the Fracture Toughness Test of Multipass Welds Incorporating Residual Stress Distribution

Weld residual stress inevitably occurs in multipass welds of thick steel plates, and it affects the fracture toughness testing procedure and test results; therefore, it is important to clarify the effect of residual stress on fracture toughness evaluation. However, it is almost impossible to measure the entire residual stress distribution in welded joints and to consider the detailed distribution in fracture toughness testing. Therefore, in this study, a numerical simulation method to model the fracture toughness test considering the weld residual stress is developed. The weld residual stress incorporated into the simulation was validated through experimental measurement. The transition of the residual stress throughout the processes of multipass welding, specimen machining, residual stress modification, precracking, and fracture toughness testing were evaluated using the proposed method. Three-point bend fracture toughness test simulations were performed for the following three cases: (1) base metal, (2) as-welded joint, and (3) residual stress modified (reverse bent) specimen by reverse bending. It was shown that the residual stress distribution in multipass welded joint was effectively modified by reverse bending. Finally, it was demonstrated that residual stress has a considerable influence on the crack-tip opening profile.

Numerical simulation of residual stress modification by reverse bending of notched fracture toughness test specimens of multipass welds

In the fracture toughness tests of multipass welds of thick steel plates, the fatigue precrack front initiating from a machined notch root frequently be non-uniform affected by the welding residual stress distribution. Reverse bending before fatigue precracking could be an effective measure of residual stress modification. However, the effect of reverse bending is not well understood from the viewpoint of the variation of the residual stress distribution at the notch root. Therefore, the transition of the welding residual stress throughout the multipass welding, notch machining, and reverse bending processes is calculated using a numerical simulation model developed in this study. The compressive plastic deformation at the notch root caused by the reverse bending and successive tensile loading during unloading are the major mechanisms of residual stress modification by reverse bending. A flattened residual stress distribution along the thickness can be achieved if the reverse bending condition is properly controlled.

Lateral-Torsional Buckling Resistance of Castellated Beams

AbstractThe existing design expressions for the lateral-torsional buckling behavior of castellated beams conflict. Furthermore, they do not take into account the detrimental effect of the residual stress modification attributable to the fabrication process, which was only recently demonstrated by the authors. This makes these design rules possibly unsafe. In this paper, the lateral-torsional buckling behavior of doubly symmetric castellated beams loaded by a constant bending moment is investigated numerically. The numerical model, including the modified residual stresses, was validated by comparing its results with experimental results. A preliminary design approach is proposed based on the current European guidelines for the calculation of the lateral-torsional buckling resistance of I-section beams. According to the proposed approach, the lateral-torsional buckling resistance of castellated beams can be determined using the cross-sectional properties calculated at the center of the web opening. The modi...

Effect of LASER shock peening on microstructure, mechanical properties and corrosion behavior of interstitial free steel

LASER shock peening (LSP) is an effective process of surface modification. This work is concerned with the effect of LSP on the modification of microstructure, hardness, microhardness profile, residual stress, tensile properties and corrosion behavior of interstitial free (IF) steel. In order to study the effect of pulse energy on hardness, samples were subjected to LSP at pulse energy of 170, 230, 290 and 340mJ respectively. The effect of LSP time on hardness, microhardness profile and tensile properties was investigated by processing the samples for 5, 10, 15 and 20min at pulse energy of 230mJ and there was found to be significant increase in tensile strength. There was grain refinement to nano level in the surface region due to LSP. Hardness was observed to increase by LSP up to 10min and tensile strength increased up to LSP of 5min. However with the increase in LSP time beyond 10min there was prominent ablation and melting. The effect of overlapped (OV) LASER shocks was also studied by comparing their behavior with that of single shock. The potentiodynamic polarization study showed significant increase in corrosion resistance of the LSPed IF steel.