Yield Strength Of Metal Research Articles

Experimental evaluation of multiple-component residual stress distribution in a dissimilar metal repair joint of ferritic/martensitic steel using the asymmetric-cut and the symmetric-cut contour method

A thick multi-pass butt-welded ferritic/martensitic steel (P91) joint is prepared and the local region of the weld is repaired with an ENiCrFe-3 nickel-based alloy using the manual metal arc welding method. The repair weld including part of the base metal is then subjected to ultrasonic impact treatment (UIT). A three-cut contour method, including two asymmetric cuts and one symmetric cut, is developed in the present study to obtain the two-dimensional residual stress distributions at different locations, and the stress release after multiple cuts is considered to get the original stress distribution before cuts. The measurement procedure is introduced in detail. The longitudinal stresses in the repair weld and the initial weld of the P91 steel joint, as well as the transverse stress at the weld center, are finally obtained. The effects of the dissimilar metal repair weld at the local region on the longitudinal and transverse welding residual stresses are investigated. In addition, the applicability of UIT to mitigate the surface stress in nickel-based alloy repair weld is analyzed. The results show that the transverse and longitudinal stresses in the nickel-based alloy repair weld are both tensile stresses, the maximum longitudinal stress is close to the yield strength of the B91 weld metal and occurs in the heat-affected zone of the repair weld located in the initial weld. Repair welding causes the internal transverse compressive stress region to be narrower than in the original weld. UIT can be used to introduce compressive stress to the surface layer of the nickel-based alloy repair weld.

A multiscale model to understand the interface chemistry, contacts, and dynamics during lithium stripping

A reversible Li-metal electrode, paired with a solid electrolyte, is critical for attaining higher energy density and safer batteries beyond the current lithium-ion cells. A stable stripping process may be even harder to attain as the stripping process will remove Li-atoms from the surface, and naturally reduce surface contact area, if not self-corrected by other mechanisms, such as diffusion and plastic deformation under an applied external stack pressure. Here, we capture these mechanisms occurring at multiple length- and time- scales, i.e., interface interactions, vacancy hopping, and plastic deformation, by integrating density functional theory (DFT) simulations, kinetic Monte Carlo (KMC), and continuum finite element method (FEM). By assuming the self-affine nature of multiscale contacts, we predict the steady-state contact area as a function of stripping current density, interface wettability, and stack pressure. We further estimate the exponential increase of overpotential due to contact area loss to maintain the same stripping current density. We demonstrate that a lithiophilic interface requires less stack pressure to reach the same steady-state contact area fraction than a lithiophobic interface. A “tolerable steady-state” contact area loss for maintaining stable stripping is estimated at 20 %, corresponding to a 10 % increase in overpotential. To constrain contact loss within the tolerance, the required stack pressure is 0.1, 0.5, and 2 times the yield strength of lithium metal for three distinct interfaces, lithiophilic Li/lithium oxide(Li2O), Li/lithium lanthanum zirconium oxide(LLZO), and lithiophoblic Li/lithium fluoride(LiF), respectively. The modeling results agree with experiments on the impact of the stack pressure quantitatively, while the discrepancy in stripping rate sensitivity is attributed to the simplifying interface interaction in our simulations. Overall, this multiscale simulation framework demonstrates the importance of electrochemical-mechanical coupling in understanding the dynamics of the Li/SE interface during stripping.

Postweld Heat Treatment of 15Cr-6Ni-2Mo-1Cu Supermartensitic Stainless Steel Welds

Supermartensitic stainless steels with 15Cr-6Ni- 2Mo-1Cu and 135 ksi minimum yield strength (15Cr- 135 SMSS) offer high strength and good toughness through a complex hierarchical microstructure of nanoscale precipitates, tempered martensite, and reverted austenite. Upon welding and postweld heat treatment, substantial changes to heat-affected zone microstructure and hardness may occur. Here, we reveal spatially heterogeneous microstructure and microhardness in the HAZ of 15Cr-135 SMSS; correlate these changes to measured phase transformation temperatures; and demonstrate that HAZ hardness changes depend strongly on postweld heat treatment (PWHT) temperatures. Furthermore, we demonstrate that PWHT may lead to undesired reductions in base metal yield strength and formulate a design guide for PWHT that quantifies the trade-offs in desired reductions of HAZ hardness with undesired changes to base metal yield strength. These findings have important practical implications for welding procedure design and qualification.

Artificial Neural Network-Based Modelling for Yield Strength Prediction of Austenitic Stainless-Steel Welds

This study aimed to develop an artificial neural network (ANN) model for predicting the yield strength of a weld metal composed of austenitic stainless steel and compare its performance with that of conventional multiple regression and machine learning models. The input parameters included the chemical composition of the nine effective elements (C, Si, Mn, P, S, Ni, Cr, Mo, and Cu) and the heat input per unit length. The ANN model (comprising five nodes in one hidden layer), which was constructed and trained using 60 data points, yielded an R2 value of 0.94 and a mean average percent error (MAPE) of 2.29%. During model verification, the ANN model exhibited superior prediction performance compared with the multiple regression and machine learning models, achieving an R2 value of 0.8644 and a MAPE of 3.06%. Consequently, the ANN model effectively predicted the variation in the yield strength and microstructure resulting from the thermal history and dilution during the welding of 3.5–9% Ni steels with stainless steel-based welding consumables. Furthermore, the application of the prediction model was demonstrated in the design of welding consumables and heat input for 9% Ni steel.

Quantification of the local mechanical behavior in dissimilar metal welds using digital image correlation instrumented cross-weld tensile testing

The local yielding behavior in base metal, heat-affected zone, fusion boundary region, and weld metal of low-alloy steel/Alloy 625 filler metal welds was quantified using digital image correlation instrumented cross-weld tensile test. The tested welds exhibited undermatching, matching, or overmatching weld metal yield strength with significant gradients in the local yielding behavior. An undermatching weld yielded at 69 MPa below the base metal yield stress, accumulating to 0.72% total strain. The base metal in an overmatching weld had 110 MPa lower yield strength than the weld metal. The strong strain hardening response in the Alloy 625 weld metal, within the uniform elongation range, and its constraining effect on the fusion boundary region and heat affected zone, led to extensive strain accumulation, necking, and final failure in the base metal of all tested welds. The yielding behavior of the tested welds was compared to stress-based criteria, utilizing minimum specified and as-delivered yield and ultimate tensile strength, and to strain-based criteria. The capability of digital image correlation instrumented cross-weld tensile testing to quantify local yielding and strain accumulation demonstrates potential application in proving conformity to stress-based and strain-based design criteria of dissimilar and matching filler metal welds.

Alloying systems for modern flux-cored wires for mechanized welding in shielding gases of high-strength shipbuilding steels

An analysis of the domestic market for flux-cored wire used for welding low-alloy high-strength shipbuilding steels has been carried out. It has been established that to ensure a guaranteed value of the yield strength of the weld metal from 420 to 620 MPa, alloying systems such as Mn–Si, Mn–Si–Ni and Mn–Si–Ni–Mo are taken as a basis. The influence of alloying elements used in these systems on the formation of the microstructure and properties of welds was experimentally established.

Generation and distribution mechanism of welding-induced residual stresses

Welding-induced residual stresses (WIRS) can have influence on the performance and service life of the welded structures. The present study experimentally and numerically investigates the reason and mechanism behind the generation and distribution of WIRS concretely. The results show that the thermal shrinkage process and phase transformation process are the main sources generating welding-induced longitudinal residual stress (σLRS). Nevertheless, except for these two processes, the quenching process would be another source producing transverse residual stress (σTRS). In the current work, it is found that the maximum σLRS generally reaches the yield strength (σy) of base metal (BM) at ambient temperature (TRT) for both transforming and non-transforming materials but located at different areas. In the single-pass weldments without external restraint, σTRS profile on the top surface is usually always M-shaped for the non-transforming materials but W-shaped instead for the transforming materials. The distribution mechanism behind the M-shaped or W-shaped σTRS profile is systematically clarified here.

The effect of crystalline structure on the mechanical behavior in Zr-based amorphous materials: A molecular dynamics simulation

The structure relaxation in the Zr-based amorphous phase affects the microstructure and mechanical properties of metallic glasses. To clarify the mechanical properties and deformation mechanism of amorphous crystallization, the compression and tensile deformation of the Zr90Cu10 amorphous model with different levels of ordered lattice structure were studied by molecular dynamics simulation. The influence mechanism of crystals on the deformation and mechanical properties of amorphous alloys was investigated using atomic-scale stress‒strain curves, atomic structures, and dislocation line distributions. The results show that the in situ crystallization of amorphous alloys has a positive effect on enhancing the elastic modulus and yield strength of amorphous metals. The high-stress regions in the model are predominantly concentrated within the amorphous phase. The phase dislocation entanglement under stress will improve the plasticity of the amorphous state. This work also discusses the deformation mechanism of nanocrystalline amorphous alloys at the atomic level.

Application of Digital Image Correlation in Cross Weld Tensile Testing: Test Method Validation

This study addresses the limitations of cross weld tensile testing (CWTT) in quantifying local mechanical properties across microstructural and compositional gradients in dissimilar– and matching–filler metal welds. A digital image correlation (DIC) methodology was validated for application in CWTT by direct comparison of stress-strain curves generated using conventional and virtual DIC extensometers in tensile testing of homogeneous steel samples. DIC-instrumented CWTT of dissimilar weld metal Alloy 625 filler metal on F65 steel demonstrated capability in quantifying the local yield strength, strain-hardening kinetics, and strain at failure in the base metal, heat-affected zone (HAZ), fusion boundary (FB) region, and weld metal in dissimilar and matching filler metal welds. It was shown that the high strain-hardening capacity in Alloy 625 weld metal led to base metal failure in CWTT despite the lower Alloy 625 weld metal yield strength. It was also shown that DIC-instrumented CWTT can be used for determining weld metal undermatching and overmatching conditions in compositionally matching- and dissimilar-metal welds. Furthermore, by quantifying local strain distribution (both elastic and plastic) in the HAZ, FB region, and weld metal, DIC-instrumented CWTT provides an additional method for evaluating hydrogen-assisted cracking susceptibility in dissimilar-metal welds.

Variation Coefficient of Metal Yield Strength in New and Long-Used Building Structures

Introduction. Non-destructive methods are most often used to assess the condition of the metal structure. Dangerous stress is determined by the value of the yield strength. This approach has weaknesses. This is, firstly, the probabilistic nature of the methodology (the minimum value of the indicator obtained during laboratory tests is entered into the regulatory and technical documentation). Secondly, the limitations on the number of samples should be overcome. Thirdly, the different duration of operation causes a significant difference in the mechanical characteristics of the metal, which to a certain extent complicates the long-term prediction of the condition of the structure. The presented work is designed to solve these problems within the framework of the study of new and long-operated facilities in the Rostov region. The scientific research objective is to analyze fatigue changes and determine possible degradation of the metal.Materials and Methods. The mechanical characteristics of the material under study were reliably described by the Weibull distribution law through the shear parameter (the minimum possible value of the characteristic) and the shape parameter (magnitude dispersion). For scientific research, the indentation method based on a modified Rockwell hardness estimation method was used as part of the work. A conical indenter was embedded in the surface, then the reaction of the metal was analyzed. To implement the method, an analog-to-digital converter and a laptop were used. For correlation analysis, intermediate characteristics were taken: depth, maximum and minimum velocities, maximum and minimum acceleration of cone insertion. A correlation was established with the mechanical characteristics determined by standard tensile and hardness tests of the metal.Results. Objects with zero and long-term operation were studied. The measurements were carried out in a warehouse, production site, stadium, bridge, Palace of Sports and on a power line support. From the group of new and used structures, one was selected for a detailed fixation of the values of yield strength. So, before the start of operation, the condition of three metal trusses of the warehouse was analyzed. It was established that the lowest value of the yield strength here was 240 MPa, the maximum was 345 MPa. On the power transmission line poles, which have been in operation for 43 years, the lowest recorded value of the yield strength was 235 MPa, the highest was 384 MPa. For each of the six structures, the minimum and average distribution of the metal yield strength values was given, and the coefficients of variation of this indicator were given. The recorded values were summarized in the form of a table. The average values for all new and used designs were calculated. Graphically presented data illustrate the growth of the coefficients of variation of the yield strength with increasing service life.Discussion and Conclusion. A comparative analysis of the obtained values of the yield strength of building structures of approximately the same strength class suggests that the influence of operating time can both increase and decrease the studied indicator. At the same time, long-term operation is a factor that increases the average value of the coefficient of variation. To monitor the strength capabilities of the structure, it is advisable to use a non-destructive method, selectively monitoring the mechanical characteristics of the elements before and during operation.

Effect of strain rate on tensile behavior of tailor welded blanks

The demand for weight reduction, cost savings, more fuel efficiency, and reduced greenhouse gas has led to the increasing application of tailor welded blanks (TWBs) in the automotive industry. The purpose of this study is to investigate the strain rate effect on the tensile behavior of TWB consisting of dissimilar thickness sheets. Hence, a fiber laser was used for welding St14 steel sheets. The weld zone was examined using metallographic and microhardness tests. For investigating the tensile properties, uniaxial tensile tests were performed at strain rates ranging from 0.001 to 10 s−1. It has been found that the presence of Bainitic microstructure in the weld zone increases its hardness. Tensile test results indicate that yield strength and ultimate tensile strength of base metals and TWB enhanced with increasing strain rate. The yield and ultimate tensile strength of TWB are higher than base metals at different strain rates. As the strain rate increases, the total elongation of the TWB decreases, but in base metals, it decreases first and then increases at higher strain rates. In TWB and base metals, by increasing strain rate, uniform elongation decreases, but post-uniform elongation increases. For analysis of plastic deformation of thick and thin parts of TWB, indexes of limiting thickness ratio and difference of ratios (DR) were used. DR decreases with increasing strain rate, which indicates a decrease in the plastic deformation of the thick part of TWB and is consistent with the experimental findings.

Analyze the Effect of Weld Heat Input on Mechanical Properties of Nitrogen Alloyed Stainless Steel by GMAW Process

GMAW process in the recent research work investigates the effect of heat input, feed rate, voltage, current (controlled by GMAW Process) on the tensile strength, micro-hardness and microstructure of nitrogen alloyed stainless steel (JT grade). The base material used for the investigation was Nitrogen Grade austenitic stainless steel (JT Grade) with the low percentage of nickel content. JT grade steel has good resistance to oxidation, easy fabrication, and excellent toughness even in the low temperatures. It is not expensive as lower cost nitrogen and manganese are added as partial alternative for nickel. The yield and ultimate tensile strength of the base metals and welding filler was to be calculated to get the best desirable properties of the welding process. The microstructure, macro-structure and chemical test on the metal plates were done to study about their properties. The numbers of trials are to be done for getting the best and appropriate parameters. And the last testing were done on the best parameters( heat input, voltage, current) on the base metal of JT grade to test the micro- hardness and tensile strength of the metal and welding. The 3 types of filler metal ER308L, ER309L, and ERNiCrMo3 were used during the welding process in GMAW to study these effects. The hardness were tested at the HAZ area and WELD area and the location of fracture from welding area were consider during the testing to get the tensile strength of the weld.

Finite Element Simulation of Multi-Pass Welding of AA6061-T6 Plate-Sleeve: Effect of Different Yield Strengths of Weld and Base Metals

Finite Element Simulation of Multi-Pass Welding of AA6061-T6 Plate-Sleeve: Effect of Different Yield Strengths of Weld and Base Metals

Refinement of the Process Capability Index Сalculation

The variability of product performance is the reason for the introduction of special methods to ensure product quality, particularly statistical methods. These include introducing statistical process control (SPC) in production and calculating the process capability index to determine the manufacturing ability to meet the product’s quality requirements. To a large extent, the ability of a process to meet the requirements was determined by the location of the process or the mathematical expectation of the controlled quality characteristic value. Process setup center variability within the boundaries of the Shewhart control chart of the average values was supposed to be the natural state for a statistically controlled process. However, the calculation of the process capability index did not consider the possibility of a shift in the actual value of the process setup center for a controlled characteristic from its mathematical expectation. It was proposed to adjust the process capability index for the setup center’s possible deviation. It demonstrated the possibility of critical errors in determining the ability of a production process to meet requirements without considering the process setup center. The effectiveness of the proposed solutions was also demonstrated by the example of determining the ability of the welding wire manufacturing process to meet the requirements for metal yield strength of the welded joint of metal bridge span constructions.

Measurement and simulation of residual stresses in transient liquid phase bonded ferritic steels

Ferritic steel bars—25 mm in diameter—were welded by transient liquid phase bonding (TLPB) using Fe-based amorphous metallic foils as filler material. The resulting residual stress (RS) field shows a low peak magnitude—of 147 MPa—as measured by neutron diffraction. The most distinctive feature of TLPB is the heat input delivered simultaneously at the whole joint that allows much lower cooling rates compared with arc welding (AW). Therefore, the elapsed time between 800 and 500 °C (t 8/5) was particularly long reaching 390 s. As a result, a low RS peak magnitude (147 MPa) was obtained in the as-welded condition. This value is well below the RS peak magnitude obtained with AW which typically attain the yield strength of the base metal (276 MPa). The numerical simulation of RS at the welded bars was performed by a thermal and mechanical analysis. It shows that TLPB produced a large austenized region, low cooling rates and a remarkable t 8/5. Consequently, the large volume in which the heat input is delivered is the driving force to reduce RS peak magnitudes. From the mechanical analysis, it was found that the simulated RS was in good agreement with the measured RS. Therefore, the proposed numerical simulation model can be used to predict RS in TLPB weldments.Graphical abstract

Cold Compaction and Macro‐Porosity Removal in Rubble‐Pile Asteroids: 2. Applications

AbstractModels of asteroid collisional evolution suggest that many asteroids are gravitationally‐bound rubble piles. Although rubble piles may be expected to retain large void fractions, compaction may reduce the porosity. We apply models for cold compaction of rubble‐pile bodies developed in a companion paper toward observations of asteroid densities. The model for chondritic boulders is applied to S‐type (stony) and C‐type (carbonaceous) asteroids. The relation between density and size of S‐type asteroids is largely explained by cold compaction of rubble piles through fracturing of boulders, under the assumption that boulder size distributions are narrow before fracturing and fractal‐like afterward. The density variation of C‐type asteroids can only partly be explained by this mechanism, and the removal of micro‐voids inside the boulders would be required to match observations. The model for metal boulders is applied to M‐type asteroids, and the results suggest that, because of cold welding between metal boulders and the high yield strength of metal for either ductile or brittle‐like deformation, metallic rubble piles can preserve large (≳50%) porosities if the boulders are ∼1 m in size. This implies that M‐type asteroids such as Psyche and Kleopatra may be purely metallic, even though their densities are less than half that of iron. We also consider the hypothesis that Psyche is a primitive body of a CB chondrite‐like material. Assuming that the strength of CB chondrite is controlled by a silicate matrix, we predict that the density of a Psyche‐sized rubble pile of CB chondrite is higher than that of Psyche.

Microstructural Features, Tensile Properties, and Impact Toughness of Linear Friction Welded High-Temperature Alloy Joints for Blisk Assembly Applications

The main objective of this investigation is to analyze the microstructure, tensile properties, and impact toughness of Ti6Al4V alloy joints developed using optimized parameters of linear friction welding (LFW) for gas turbine blisk assembly applications. The 6 mm thick plates of Ti6Al4V alloy were joined using a friction time of 40 sec, a friction pressure of 20 MPa, a forging pressure of 10 MPa, a forging time of 3 sec, and an oscillating frequency of 14 Hz. The different regions of joints were analyzed using a stereo zoom microscope. Optical and scanning electron microscope (SEM) was used for analysing the microstructural features of joints. The room temperature tensile properties, hardness, and impact toughness of LFW-Ti6Al4V alloy joints were evaluated and correlated to the microstructural features of weld region. The fractured sections of tensile and impact toughness specimens of joints were analyzed using SEM and the failure of joints was correlated with the hardness survey. Results showed that the LFW-Ti6Al4V alloy joints developed using the optimized parameters exhibited a tensile strength (TS) of 1015 MPa, a yield strength (YS) of 940 MPa, and an elongation (EL) of 8%. The joints revealed 98.54%, 95.91%, and 66.67% of tensile strength, yield strength, and ductility of the parent metal. The LFW joints disclosed impact toughness (IT) of 17.2 J which is 89.77% impact toughness of the parent metal. The superior tensile properties and impact toughness of LFW-Ti6Al4V alloy joints are mainly attributed to a greater degree of refinement of α + β grains in the weld interface, which offers greater resistance to tensile deformation and crack propagation.

Effects of PWHT on the Residual Stress and Microstructure of Bisalloy 80 Steel Welds

Quenched and tempered (Q & T) steels have numerous applications, particularly in the defence industry with welding as the main fabrication route. Since welding imparts stresses due to thermal gradients development during welding, plus the fact that the Q & T fabricated structures are expected to function in a complex loading environment, it is critically important to relax the welding stresses before exposing the parts to service conditions. The present study reports on the generated residual stresses when Bisalloy 80 is welded by pulsed gas metal arc welding (GMAW-P) and verifies the effects of post-weld heat treatment (PWHT) on the microstructural changes, removal or reduction of residual stresses and the resulting mechanical properties of the welded Q & T steel joints. Neutron diffraction was utilized to measure the residual stresses in the as-welded and after PWHT of the Bisalloy 80 steel weldments. High levels of tensile residual stresses reaching to the yield strength of the weld metal were present (642 ± 24 MPa) in the as-welded joints but were substantially reduced after PWHT (145 MPa ± 21 MPa, which is ~23% of the yield strength of the weld metal). PWHT led to microstructural changes in different regions of the parent and weld metals, including the formation of coarsened polygonal ferrite grains and bainitic ferrite laths. This finding is in line with hardness measurements, where hardness reductions were evident in the heat-affected zone (HAZ) and the weld metal (WM) of the heat-treated specimens.

Plastic anisotropy of sheet metals under plane strain loading: A novel non-associated constitutive model based on fourth-order polynomial functions

Constitutive modeling of sheet metals under plane strain state is important but challenging. Recent studies report that the yield strength and plastic strain rate of sheet metals in the plane strain mode exhibit strong anisotropy. To address the plane strain anisotropy, fourth-order polynomial functions (Poly4) of the stress tensor were applied to the yield stress and plastic potential functions under the non-associated flow rule (NAFR-Poly4). The yield stresses under near-plane strain (NPS) measured along three angles from the sheet rolling direction were used for an analytical determination of the parameters of the yield stress function and the commonly applied yield stresses under uniaxial tension (UT) and equi-biaxial tension (EBT). In addition, the plastic strain rates under UT, NPS, and EBT were used to determine the parameters of the polynomial plastic potential. Compared with experimental results under a wide range of loading conditions, the proposed NAFR-Poly4 model predicts the anisotropic NPS deformation of a dual-phase steel and an aluminum alloy with remarkably improved accuracy over the other existing models. The NPS yield stresses of the dual-phase steel are accurately predicted with a reduced average plastic flow deviation of 2.8° by NAFR-Poly4 compared to 7.1° by the Yld2k-2d model under AFR.

Network science approach to predict the yield strength of metals containing soft particles and pores

Local fluctuations in particle size and spatial distributions can substantially affect the yield strength of metals containing soft particles and/or porosities. The phenomenon can be studied via computational homogenization techniques, which, however, can be highly computationally demanding when large representative volume elements are needed. A more efficient approach to model the plastic deformation that controls the yield strength of metals containing pores has recently been proposed by the author and co-workers. The key idea is to treat the material as a network rather than as a continuum. In fact, plastic deformation in porous metals occurs via the formation of shear bands connecting the pores, and it can thus be modelled as a time-evolving network where the nodes represent the pores and the links represent the shear bands. So far, the applicability of this new approach has only been tested against 2D synthetic microstructures. The present work takes it a step further by applying the approach to real spheroidal graphite iron. Based on strain data collected in-situ via digital volume correlation, it is shown that the new network approach can explain the spatial variations of the plastic deformation that arise from local variations of the particle distribution throughout a tensile specimen.