Maximum Tensile Residual Stress Research Articles

Modeling the effects of Undeformed Chip Volume (UCV) on residual stresses during the milling of curved thin-walled parts

With the increasingly popularized curved thin-walled parts, the control of curved surface residual stress in machining has become more and more demanding. However, it remains to be a major challenge to predict and control curved surface residual stress in the present aerospace research areas. Amidst this backdrop, this paper introduces a residual stress volume model to evaluate the effects of sequential cuts for the generated surface and subsurface residual stresses. Additionally, based on the proposed modeling and calculated results, quantified method is used for superposition of residual stress under different machining conditions. The superposition rates in feed, vertical feed and depth of cut directions are about 10%, 11% and 7%, respectively. In addition, this paper presents a newly constructed mathematical model between the curved surface maximum tensile residual stress and the Undeformed Chip Volume (UCV) (fz, R, ap and ae) of the ball end milling cutter. Through polynomial fitting for the proposed mathematical model, the influence coefficients α and β can be obtained, which act as the influence factors of machining parameters on residual stress generation. The values of α vary from 0.0018 to 0.0087, while the values of β vary from −3.99 to 0.72. That means that the depth of cut and tool radius can exert the greatest influence on the curved surface maximum tensile residual stress. Finally, with larger tool radius and smaller depth of cut, an experiment of machining curved thin-walled part proves that curved surface residual stress and deformation can be effectively reduced.

Comparison of residual stress on different three-dimensional multi-layer welding methods of welded hollow sphere joint in large-span structure by considering latent heat

This article quantitatively evaluated the influence of three-dimensional multi-layer welding on the welding residual stress of super-big diameter welded hollow sphere joint in the large-span spatial steel structure considering the influence of material state change using finite element method. First, this article proposed a conception of equivalent state change time—the virtual time of state change in the analysis of welding and cooling—which represents the heat absorbed or released during the change of solid and fluid states in welding material. The equivalent state change time increases the accuracy of the thermal analysis considering the latent heat of fusion in welding and cooling process. Second, this article simulated the numerical experiments of three welding methods including multi-layer symmetric welding, multi-layer sequential welding, and single-layer symmetric welding, which show that multi-layer symmetric welding not only increases the balance of supporting ability of structure but also decreases the value of maximum tensile residual stress, and it is better than the other two welding methods.

Effect of post heat-treatment on the microstructure and mechanical properties of Hastelloy-X structures manufactured by laser based Directed Energy Deposition

This paper reports a systematic investigation of Hastelloy-X (Hast-X) structures built by Laser Directed Energy Deposition in as-built and post heat-treated conditions. The optical microscopy shows microstructures with fine dendrites in as-built condition due to higher cooling rate during deposition, while recrystallized equiaxed grains are observed after post heat-treatment (at 1177 °C) due to recrystallization. X-ray diffraction studies reveal nickel γ-matrix with variation in crystallite size and a peak shift after post heat-treatment, primarily due to change in surface residual stress. Surface topography reveals the reduction in average roughness with post heat-treatment. Further, the maximum compressive residual stress of 350 MPa and maximum tensile residual stress of 252 MPa are observed at the surfaces of post heat-treated and as-built samples, respectively. The average micro-hardness changed from 239 HV1.96N to 208 HV1.96N after post heat-treatment. Single Cycle Ball Indentation studies indicated increase in energy storage capacity by a factor of 1.55 after post heat-treatment. Automated Ball Indentation studies quantify yield strength and ultimate strength as 478 MPa and 765 MPa in as-built samples, while 393 MPa and 630 MPa in post heat-treated samples, respectively. Further, crack propagation studies indicate an improvement in the fatigue life after post heat-treatment, while the specific wear rate increased by a factor of 1.72 with increased delamination in heat-treated samples. Thus, post heat-treatment of Hast-X samples changes the material properties significantly.

Modeling and Prediction of Residual Stresses in Additive Layer Manufacturing by Microplasma Transferred Arc Process Using Finite Element Simulation

Prediction of residual stresses induced by any additive layer manufacturing process greatly helps in preventing thermal cracking and distortion formed in the substrate and deposition material. This paper presents the development of a model for the prediction of residual stresses using three-dimensional finite element simulation (3D-FES) and their experimental validation in a single-track and double-track deposition of Ti-6Al-4V powder on AISI 4130 substrate by the microplasma transferred arc (µ-PTA) powder deposition process. It involved 3D-FES of the temperature distribution and thermal cycles that were validated experimentally using three K-type thermocouples mounted along the deposition direction. Temperature distribution, thermal cycles, and residual stresses are predicted in terms of the µ-PTA process parameters and temperature-dependent properties of substrate and deposition materials. Influence of a number of deposition tracks on the residual stresses is also studied. Results reveal that (i) tensile residual stress is higher at the bonding between the deposition and substrate and attains a minimum value at the midpoint of a deposition track; (ii) maximum tensile residual stress occurs in the substrate material at its interface with deposition track. This primarily causes distortion and thermal cracks; (iii) maximum compressive residual stress occurs approximately at mid-height of the substrate material; and (iv) deposition of a subsequent track relieves tensile residual stress induced by the previously deposited track.

Investigation of laser bending parameters on the residual stress and bending angle of St-Ti bimetal using FEM and neural network

In this paper effects of laser bending process parameters on bending angle and maximum tensile residual stresses was investigated on bimetallic steel-titanium sheet using finite element modeling and neural networks method. For this purpose, after validation of finite element modeling, 43 simulations were performed and the results of bending angle and maximum tensile residual stress were evaluated. The effect of process parameters including laser power, scanning velocity, number of passes, beam diameter and sheet thickness were designed based on response surface methodology. Design-Expert software was used to design experiments and analyze the results. The results showed that bending angle increases with increasing power and number of scan passes. The angle of bending is also inversely proportional to the scanning velocity, beam diameter and sample thickness, and decreases with increasing them. The maximum tensile residual stress increased with increasing laser power and the number of scan passes. By increasing the velocity of scanning, the beam diameter and the thickness of the maximum tensile residual stress sample was decreased.

Experimental and numerical investigation of the characteristics of flash-butt joints used in continuously welded rails

Continuously welded rails are widely used in the Iran railway network, which are generally built using the flash-butt welding process. To accurately model the flash-butt welding process, thermal analysis, and prediction of the welding residual stresses, the influence of upsetting force on the total electrical resistance and a material model with consideration of the influence of temperature on the material properties are included in the numerical modeling. In this paper, numerical and experimental studies, including the finite element method, thermography, metallography, and hardness testing are performed to determine the characteristics of the welded UIC60 rail. By studying the fractured flash-butt welded UIC60 rails, it is shown that the location of the crack initiation and the rail failure in the web and heat affected zone of the welded rails was similar as compared to the maximum tensile residual stress calculated by numerical simulation. According to the numerical and experimental results, it is shown that four key parameters – such as the maximum temperature during the welding process, the total welding time, the upsetting time, and the upsetting force – control the size, microstructure, and the hardness profile of the heat affected zone which directly affects the characteristics and quality of welding.

Effect of solid state phase transformation on the residual stress in multi-pass weld plates of S355J2W steel

The coupling model of temperature-phase transformation-mechanics is constructed in this paper. The effect of solid state phase transformation and different hardening models on the residual stress distribution of S355J2W welded joints have been studied with finite element method (FEM) simulation. The microstructure, micro hardness and residual stress of welded joints are also studied. It has been shown that the microstructure of weld seam is composed of bainite structure with little martensite, while the base metal is ferrites and pearlites. The simulation results by FEM were in good accordance with the X-ray results. The maximum tensile residual stress is 463 MPa in the weld. The tensile residual stress was decreased with the larger distance to the weld.

Residual Stresses in Resistance Spot Welded AZ61 Mg Alloy

The use of magnesium alloys has been rapidly increased due to their ability to maintain high strengths at light weights. However weldability of steels and aluminum alloys by using resistance spot weld (RSW) process is a major issue, because it cannot be directly utilized for magnesium alloys. In this study, a structural-thermal-electrical finite element (FE) model has been developed to predict the distribution of residual stresses in RSW AZ61 magnesium alloy. Thermophysical and thermomechanical properties of AZ61 magnesium alloy have been experimentally determined, and have been used in FE model to increase the accuracy of the model. X-ray diffraction (XRD) technique has been utilized to measure the residual stresses in welded samples, and its results have been used to validate the FE model. Comparison study shows that the results obtained by using FE model have a good agreement with the experimental XRD data. In specific, the results show that the maximum tensile residual stress occurs at the weld center while decreases towards the nugget edge. In addition, the effects of welding parameters such as electrical current, welding time, and electrode force have been investigated on the maximum tensile residual stress. The results show that the tensile residual stress in welded joints rises by increasing the electrical current; however, it declines by prolonging the welding time as well as increasing the electrode force.

Investigation of residual stresses of hybrid normal and high strength steel (HNHSS) welded box sections

In order to obtain high bearing capacity and good ductility simultaneously, a structural column with hybrid normal and high strength steel (HNHSS) welded box section has been developed. Residual stress is an important factor that can influence the behaviour of a structural member in steel structures. Accordingly, the magnitudes and distributions of residual stresses in HNHSS welded box sections were investigated experimentally using the sectioning method. In this study, the following four box sections were tested: one normal strength steel (NSS) section, one high strength steel (HSS) section, and two HNHSS sections. Based on the experimental data from previous studies and the test results of this study, the effects of the width-to-thickness ratio of plate, yield strength of plate, and the plate thickness of the residual stresses of welded box sections were investigated in detail. A unified residual stress model for NSS, HSS and HNHSS welded box sections was proposed, and the corresponding simplified prediction equations for the maximum tensile residual stress ratio (σrt/fy) and average compressive residual stress ratio (σrc/fy) in the model were quantitatively established. The predicted magnitudes and distributions of residual stresses for four tested sections in this study by using the proposed residual stress model were compared with the experimental results, and the feasibility of this proposed model was shown to be in good agreement.

Non-dimensional process maps for normalized dilution limits in laser direct metal deposition

Abstract The quality and integrity of laser direct metal deposition (DMD) processes primarily depend on the substrate dilution and the nature of residual stresses in the deposited layer. An adequate amount of melting of the substrate is required to ensure the formation of sound metallurgical bond between the deposited layer and substrate. Insufficient melting and excessive dilution may lead to adverse effects. Furthermore, the dilution also controls the location of the melt front in substrate where maximum tensile residual stresses occur. The presence of tensile residual stresses in the deposited layer may be detrimental to service life, especially, for components repaired using DMD. These challenges can be overcome by predicting and controlling the dilution and the nature of residual stress as a function of process parameters. To model the direct metal deposition process, a 3D coupled metallo-thermomechanical finite element model is employed to predict the temperature and the residual stress due to thermomechanical interactions and metallurgical transformations and the substrate dilution. Non-dimensional process parameters affecting the dilution in laser DMD have been identified using Buckingham-Π theorem. The metallo-thermomechanical model is used to develop empirical relationships via regression to correlate the dimensionless process parameters with the dilution. These correlations are employed in developing the isopleths in the form of process maps, which could predict regions of inadequate fusion and excessive dilution (unduly large substrate melting). It may be noted that the limiting value of dilution corresponds to the condition where the entire deposited layer (cladding) is under compressive residual stresses. Any dilution higher than this will result in excess substrate melting which is undesirable. The limiting values of normalized dilution are estimated to be 1 and ~1.3 corresponding to complete deposit-substrate fusion and presence of entirely compressive residual stress in deposition, respectively. These process maps are designed to provide a theoretical framework for understanding the influence of process parameters and provide informed decisions on the selection of appropriate process parameters for ensuring the quality and integrity of the deposition.

Effect of preheating on the microstructure and properties of fiber laser welded girth joint of thin-walled nanostructured Mo alloy

Fiber laser girth welding of a thin-walled nanostructured Mo (NS-Mo) alloy tube was conducted. The microstructures, properties, and residual stresses of the welded girth joints achieved at different preheating temperatures were compared. Combining finite element simulation with experimental data, it was found that as the preheating temperature increased, the maximum welding residual tensile stress monotonically decreased while the tensile strength of the joints increased at first and then declined. At the preheating temperature of 673 K, the tensile strength reached a maximum, which was approximately 50% that of the base metal. The results showed that oxygen content was segregated at the grain boundary of fusion zone during welding and further produced Mo oxides. As the preheating temperature increased, vaporized Mo oxides might escaped from the molten pool, so the oxygen concentration at the grain boundary first decreased. However, when the preheating temperature increased over 773 K, the oxygen concentration rose due to the increased oxidation tendency of Mo at high temperatures and grains in the fusion zone coarsened greatly, while the total area of grain boundaries reduced.

Temperature, Stress and Distortion of Ti–6Al–4V Alloy Low-Temperature Friction Stir Welding Assisted by Trailing Intensive Cooling

The low-temperature friction stir welding (FSW) in which peak temperature is lower than the transus temperature of β phase was achieved using rotational speed of 100 rpm and welding speed of 30 mm/min. Trailing intensive cooling with liquid nitrogen was successfully applied to FSW under the low-temperature welding conditions. Comparisons of the temperature field, plastic strain, residual stress and welding distortion between intensive and conventional cooling were investigated by experiment and simulation. Results reveal that trailing intensive cooling is attributed to shrink high-temperature area and reduce the value of peak temperature and plastic strain. Longitudinal residual stress presents M shape, and the reduction of maximum tensile residual stress reaches 4.8%. The welding distortion shows an anti-saddle shape, and the decrement of welding distortion in transverse direction is 34.5%.

Residual stress, tensile strength, and macrostructure investigations on ultrasonic assisted friction stir welding of AA 6061-T6

In recent decades, ultrasonic vibrations are used in manufacturing processes because they can improve tool life, material performance, and quality. One of them which can be integrated with ultrasonic vibrations is friction stir welding called ultrasonic assisted friction stir welding. In previous studies, the effect of ultrasonic vibrations on the mechanical, metallurgical, and thermal properties was investigated and there is not any residual stress investigations on ultrasonic assisted friction stir welding. Since residual stress plays an important role in performance and stability of components, the influence of ultrasonic power on the longitudinal residual stress in friction stir welding is investigated in this work. In spite of residual stress, tensile strength and quality of weldment were investigated as complementary terms to ensure successful performance of ultrasonic assisted friction stir welding. The findings indicated that high-frequency vibrations with power of 200 W can reduce the maximum tensile residual stress about 45% and significantly increase tensile strength. Also, ultrasonic vibrations prevent defect such has voids and tunnel in weld zone due to peening effect in ultrasonic assisted friction stir welding.

Experimental study on the residual stresses of 800 MPa high strength steel welded box sections

This study presents the residual stresses magnitude and distribution of 800 MPa high strength steel welded box sections. The value of residual stresses is investigated using a method of sectioning, and the effect of width to thickness ratio on the magnitude of stresses is considered in the analysis. From the results of experiment, the influence of width to thickness ratio on the tensile residual stresses in welded zone is small, while the effect of width to thickness ratio on the compressive residual stresses located in the center of plates is large. The maximum tensile residual stresses values change from 0.30 fy to 0.56 fy, and the constant compressive stresses ranges from 0.06 fy to 0.26 fy. The residual stresses distributed in all cross-section satisfies the self-balancing requirement. Comparison of distribution and magnitude of residual stresses between test data and existing models are made. A simplified model is suggested to estimate the residual stresses distribution of steel welded box section made of 800 MPa high strength steel.

Numerical Analysis of Residual Stress and Distortion Use Finite Element Method on Inner Bottom Construction of Geomarin IV Survey Ship with Welding Sequence Variations

In the ship fabrication industry, welding is the most critical stage. If the quality of welding on ship fabrication is not good, then it will affect the strength and overall appearance of the structure. One of the factors that affect the quality of welding is residual stress and distortion. In this research welding simulation is performed on the inner bottom construction of Geomarin IV Ship Survey using shell element and has variation to welding sequence. In this study, welding simulations produced peak temperatures at 2490 K at variation 4. While the lowest peak temperature was produced by variation 2 with a temperature of 2339 K. After welding simulation, it continued simulating residual stresses and distortion. The smallest maximum tensile residual stress found in the inner bottom construction is 375.23 MPa, and the maximum tensile pressure is -20.18 MPa. The residual stress is obtained from variation 3. The distortion occurring in the inner bottom construction for X=720 mm is 4.2 mm and for X=-720 mm, the distortion is 4.92 mm. The distortion is obtained from the variation 3. Near the welding area, distortion value reaches its minimum point. This is because the stiffeners in the form of frames serves as anchoring.

Comparison of microstructure, mechanical properties, and residual stresses in tungsten inert gas, laser, and electron beam welding of Ti–5Al–2.5Sn titanium alloy

Electron beam welding (EBW), pulsed Nd:YAG laser beam welding (P-LBW), and pulsed tungsten inert gas (P-TIG) welding of Ti–5Al–2.5Sn alloy were performed in order to prepare full penetration weldments. Owing to relatively high power density of EBW and LBW, the fusion zone width of EBW weldment was approximately equal to P-LBW weldment. The absence of shielding gas due to vacuum environment in EBW was beneficial to the joint quality (low oxide contents). However, less cooling rates were achieved compared to P-LBW as an increase in heat-affected zone width and partial α′ martensitic transformation in fusion zone were observed in EBW weldments. The microstructure in fusion zone in both the EBW and P-TIG weldments comprised of both acicular α and α′ martensite within the prior β grains. Hardness of the fusion zone in EBW was higher than the fusion zone of P-TIG but less than the fusion zone of P-LBW weldments due to the observed microstructural differences. Notch tensile specimen of P-LBW showed higher load capacity, ductility and absorbed energy as compared to P-TIG and EBW specimens due to the presence of high strength α′ martensite phase. Maximum sheet distortions and tensile residual stresses were observed in P-TIG weldments due to high overall heat input. The lowest residual stresses were found in P-LBW weldments, which were tensile in nature. This was owing to high power density and higher cooling rates in P-LBW operation. EBW weldment exhibited the highest compressive residual stresses due to which the service life of EBW weldment is expected to improve.

Modeling and Parameter Optimization for Surface Roughness and Residual Stress in Dry Turning Process

The influence of some turning variables and tool overhang on surface roughness parameters and residual stress induced due to machining 6061-T6 aluminum alloy is investigated in this paper. Four input parameters (cutting speed, feed rate, depth of cut and tool overhang) are considered. Tests are carried out by precision turning operation on a lathe. Design of experiment techniques, i.e. response surface methodology (RSM) and Taguchi's technique have been used to accomplish the objective of the experimental study. Surface roughness parameters are measured using a portable surface roughness device while residual stresses are measured employing deflection-etching technique using electrochemical analysis. The results obtained reveal that feed and rotational speed play significant role in determining the average surface roughness. Furthermore, the depth of cut and tool overhang are less significant parameters, whereas tool overhang interacts with feed rate. The best result of surface roughness was obtained using low or medium values of overhang with low speed and /or feed rate. Minimum maximum tensile residual stress can be obtained with a combination of tool overhang of 37 mm with very low depth of cut, low rotational speed and feed rate of 0.188 mm/rev.

Influence of preheating source on mechanical properties and welding residual stress characteristics in ultra thin ferritic stainless steel hybrid friction stir welded joints

The joining of ultra thin ferritic stainless steel (STS) with thickness of 0.5 mm has been carried out by Hybrid Friction Stir Welding (HFSW) without pin method using additional Gas Tungsten Arc Welding (GTAW) as preheating source. The influence of preheating source on mechanical properties and welding residual stress characteristics has been investigated through mechanical test and numerical analysis. The ultimate tensile strength of HFSWelded joints is approximately 103% of base metal tensile strength which is higher than that of FSWelded joints. From the result of numerical analysis for thermal elastic-plastic analysis, it is founded that the magnitude of residual stress component (σx) of welding direction is in following order: HFSWelded joints (470 MPa) >FSWelded joints (400 MPa). For the stress component (σy) of perpendicular direction to welding line, there is no great difference for maximum tensile residual stress of FSWelded joints (180MPa) and HFSWelded joints (200 MPa). On the other hand, the area of residual stress distributions in HFSW is smaller than FSW method. The overall results obtained in mechanical test and numerical analysis confirmed that HFSW is a distinct possibility to join ultra thin STS.

Research on anti crack mechanism of bionic coupling brake disc

According to the biological function of fatigue resistance possessed by biology, this study designed a Bionic Coupling Brake Disc (BCBD) which can inhibit crack propagation as the result of improving fatigue property. Thermal stress field of brake disc was calculated under emergency working condition, and circumferential and radial stress field which lead to fatigue failure of brake disc were investigated simultaneously. Results showed that the maximum temperature of surface reached 890°C and the maximum residual tensile stress was 207 Mpa when the initial velocity of vehicle was 200 km/h. Based on the theory of elastic plastic fracture mechanics, the crack opening displacement and the crack front J integrals of the BCBD and traditional brake disc (TBD) with pre-cracking were calculated, and the strength of crack front was compared. Results revealed the growth behavior of fatigue crack located on surface of brake disc, and proved the anti fatigue resistance of BCBD was better, and the strength of crack resistance of BCBD was much stronger than that of TBD. This simulation research provided significant references for optimization and manufacturing of BCBD.

Residual stress in high-strength-steel welded circular tube

To determine the distribution characteristics of the residual stress in a transmission tower welded circular tube section fabricated from 690 MPa high-strength steel (HSS), an experimental study using 30 galvanised and non-galvanised 690 MPa HSS specimens was conducted using the sectioning method and the hole-drilling method. Further, the effects of the residual stress measurement method, hot-dip galvanisation and circular diameter-to-thickness ratio on the residual stress were discussed. Finally, two distribution models for galvanised and non-galvanised specimens, and their simplified forms, were established. Comparison with a model of a welded circular tube section composed of normal-strength steel (NSS) showed that, although the maximum tensile residual stress of 690 MPa HSS is consistent with that of NSS, and although both exhibit the desired material yield strength, the maximum compressive residual stress of the HSS specimen is only 57% of that of the NSS specimen.