Performance Of Welded Joints Research Articles

Effects of different post-weld heat treatment conditions on mechanical properties and microstructure of welded joints

Post-weld heat treatment is a standard method to improve the performance of welded joints. Different heat treatment processes have different influences on the performance of welded joints. Therefore, it is of great significance to explore the impact of the heat treatment process on welded joints’ performance. This work applied three different heat treatment processes to the welded joints with three different properties. Then hardness test, impact test, tensile test, metallographic analysis and other means were used to evaluate the performance of welded joints after heat treatment. The following conclusions were drawn through the experiments: The change of phase compositions of the welded joints caused by the post-weld heat treatment was considered as the main reason for changes in mechanical properties of the welded joint. The difference in mechanical properties after different welding process and post-weld heat treatment combination was obtained, which has a guiding significance for practical production.

Influence of Scandium on AA5052-H32/AA5083-H111 TIG welded joint

ABSTRACT In the present work, two aluminum alloys 5052-H32 and 5083-H111 were tungsten inert gas welded using ER5356 filler and scandium added modified ER5356 filler rod. The morphologies of the weld joints were analyzed and characterized for microstructure and physical properties by optical microscopy, scanning electron microscopy, tensile testing and Vickers` microhardness survey. The scandium from the modified filler rod was found to fuse with aluminum of the base alloy plates in the weld zone and enhanced the yield strength of the joint by 46 MPa. The corresponding increase in ultimate tensile strength was observed to be 48 MPa. The improved strength rates were attributed to the formation of aluminum – scandium dispersoids that effectively restrained the recrystallization and growth of grains, greatly enhancing the weld joint performance. The resulting scandium added weld joint had excellent weld geometry while exhibiting active control over intermetallic compound within the material fusion zone. The ultimate tensile strength and microhardness of this joint were enhanced considerably.

Study on welding crack sensitivity assessment method based on thermal elastic plastic finite element analysis

This study presents a new welding crack sensitivity assessment method with the equivalent plastic strain increment as an indicator, and the reliability is verified by comparing the computed results and experimental results of bead-on-plate joint under different welding conditions. Then the proposed method is applied to assess the welding crack sensitivity of multi-pass joints in the bridge rehabilitation engineering. The results show that the equivalent plastic strain increment increases with increasing heat input and constraint degree, and decreases with increasing preheat temperature. The equivalent plastic strain increment can be used as an indicator for assessing welding crack sensitivity assessment of joints. With regard to multi-pass welded joints, the welding crack sensitivity decreases with the increase of number of weld passes in terms of equivalent plastic strain increment. The welding crack sensitivity assessment method proposed in this study is reliable and can provide a practical tool for assessing the performance of welded joints.

Effect of S-curve laser power for power distribution control on laser oscillating welding of 5A06 aluminum alloy

Laser oscillating welding of 5A06 aluminum alloy is widely used in industry. In order to improve the performance of Al-based welded joints and reduce welding defects, this paper details the effects of employing an S-curve laser power which is distributed along the laser oscillating path (sine wave) to improve the microstructure and mechanical properties of the joints. By applying the S-curve and an equal power condition to the 5A06 aluminum alloy, bottom butt sinusoidal path laser oscillating welding was performed. The welding appearance, microstructure and mechanical properties of the welded joints under two laser oscillating welding processes were investigated. Our results showed that laser oscillating welding using the S-curve power allows to obtain good joints when compared to the joints produced with constant power. When the linearly varying laser power of “high-low-high” applied periodically was employed, the grains in the joint structure showed the cyclic “growth-inhibition-growth” phenomenon. This growth mechanism not only refined the grain structure, but also narrowed the columnar region, and improved the mechanical properties of the joint. Compared with the laser oscillating process with constant power, the tensile strength of the joints using the S-curve power was increased by 35.3 %. Moreover, the tensile strength of the welded test coupons with S-curve power was 337 MPa, which is about 99.1% of the base metal (340 MPa). The welded joints using the S-curve power showed larger and deeper dimples, highlighting higher ductility and good plasticity. This paper provides a new approach for the research of laser oscillating welding and the control of laser power to improve the mechanical properties of welded joints.

Research on influencing factors of fatigue performance of cruciform welded joints on offshore platforms

In this study, the fatigue life of load-carrying cruciform welded joints under various plate thicknesses and degrees of penetration was performed. The fatigue assessment results showed a significant “thickness effect.” The fatigue limit of the 25 mm-thick sample was 13.4% lower than that of the 16 mm-thick fatigue sample. Essentially, the fatigue life of the weld toe does not change with the degree of penetration. Plate thickness is the key factor affecting the fatigue life. The thickness effect is determined by both the stress gradient along the plate thickness and the degree of surface stress concentration. The correction result based on the effective notch stress approach is more accurate than the thickness correction formula in the ABS standard, which underestimates the thickness effect of load-carrying cruciform welded joints and may lead to danger. The penetration ratio a/t affects the fatigue failure position of load-carrying cruciform welded joints. The fatigue design of load-carrying cruciform welded joints can be performed by appropriately increasing the degree of penetration while achieving the damage at the weld toe.

Fatigue design of mild and high-strength steel cruciform joints in as-welded and HFMI-treated condition by nominal and effective notch stress approach

According to the Recommendations for Fatigue Design of Welded Joints and Components by the International Institute of Welding (IIW), the fatigue strength of welded steel joints is in general independent of the base material strength. Post-treatment methods, such as the High Frequency Mechanical Impact (HFMI) treatment, can significantly increase the fatigue performance of welded joints especially in case of high-strength steel applications, which is already considered within the IIW Recommendations for the HFMI Treatment. This paper firstly investigates the effect of the base material strength on the fatigue resistance of welded and HFMI-treated steel joints. Therefore, mild steel S355 and high-strength steel S700 cruciform joints are cyclically tested in both conditions and the statistically evaluated S/N-curves are compared. The results reveal an increase of the high-cycle fatigue strength by the HFMI-treatment by a factor of 1.35 in case of the S355, and of 1.59 for the S700 specimens. Secondly, the test results are assessed by the fatigue design curves of the corresponding structural detail within the IIW-recommendations using the nominal stress concept. Moreover, the applicability of the procedure applying the effective notch approach is analyzed. In order to numerically evaluate the effective notch stress, the geometry of the cruciform joint is modelled according to the given guidelines within the recommendations applying a reference radius of 1 mm at the weld toe for both conditions. On the basis of the numerically computed effective notch stress, a local fatigue design is performed for all test series, which reveals sound accordance between the recommended design curves and the statistically evaluated fatigue test S/N-curves.

Influence of assembly procesS condition of A gantry crane on the corrosion resistance of welds

The article presents an analysis of the manufacturing process of gantry crane elements in the unit production regime. Gantry cranes are one of the most important heavy-duty mechanical components designed for lifting and loading heavy and bulky loads. In the analyzed case, the assembly of large-size elements in the form of a welding process was carried out outside. Therefore, there was a problem with the corrosion resistance of the elements produced in this way. In this article, special attention is paid to the performance of welded joints of such large elements and their disadvantages related to the conditions of the assembly process. These joints were made on the basis of typical, low-carbon structural steel (grade S355J2, steel with the number 1.0562) and Nickel alloy (Alloy 59, X2CrNiMoCuN22-5-3, steel with the number 2.4605) using the metal electrode. The weldability of investigated joints was assessed. The aim of the article is to analyze the influence of assembly conditions and subsequent corrosion protection of joints on their corrosion resistance under operating conditions. Appropriate tests have been carried out for this purpose. The tests showed the negative influence of external conditions on the corrosion resistance of the entire gantry crane structure.

GPR-assisted evaluation of probabilistic fatigue crack growth in rib-to-deck joints in orthotropic steel decks considering mixed failure models

Rib-to-deck (RD) welded joints in orthotropic steel decks (OSDs) of bridges demonstrates two major fatigue failure models, including the toe-to-deck (TTD) cracking and root-to-deck (RTD) cracking. Generally, the sole failure model is employed in the fatigue assessment of RD joints, causing a hot dispute on the dominant failure model. In this paper, the fatigue crack growth (FCG) in RD joints has been evaluated considering uncertainties and mixed failure models. A probabilistic fatigue crack growth (PFCG) model is at first established for the RD joint, in which two crack-like initial flaws are assumed at the weld toe and root of the RD joint. After that, the gaussian process regression is used to assist and boost the PFCG simulation. Then, the PFCG model is implemented on a typical OSD with the random traffic model. Finally, the result of the PFCG model is discussed in detail, including the failure model, fatigue reliability and life prediction, and crack size evolution. It is revealed that both the TTD and RTD cracking models have a notable contribution to fatigue failure and could not be ignored. More crucial, a remarkable reduction can be observed in the fatigue reliability of RD joints when considering mixed failure models. This study not only highlights the influence of mixed failure models on the fatigue performance of welded joints, but also provide an insight into the application of novel machine learning tools in solving the traditional structural issue.

The Influence of the Mechanism of Double-Sided FSW on Microstructure and Mechanical Performance of AZ31 Alloy

In the friction stir welding (FSW) process, the final performance of weld joints is determined by microstructures influenced mainly by the heat input and mechanical deformation. In this research, the effects of FSW parameters, rotation speeds, and welding passes, on microstructure and mechanical properties of AZ31 alloy were systematically and comparatively studied. It was found that the microstructure at the joint center with multi-pass FSW could obtain a smaller average grain size compared with the single pass. The differences of the grain size were reduced significantly when the samples experienced the double-side FSW process. The mechanical performance results showed that the optimum strength (315 MPa) was achieved through the double-side FSW process with a rotation speed of 500 r/min and welding speed of 60 mm/min. The mechanism of the parameters and double-sided process on mechanical properties of the joint samples was elaborated.

Computational crack propagation modeling of welded structures under as‐welded and high frequency mechanical impact (HFMI) treatment conditions

AbstractThe fatigue damage assessment of welded structures is of critical importance in the design of many engineering structures. The thermomechanical nature of the welding process leads to undesired tensile residual stresses, which results in fatigue performance degradation of welded structures. High‐frequency mechanical impact (HFMI) technique offers significant potentials to induce compressive residual stresses into the welded joints, thus improving fatigue life of welded parts. In this paper, a new crack propagation modeling approach considering effects of residual stress fields and the crack closure based on a modification of the Forman model is proposed to assess fatigue crack propagation performance of welded joints under as‐welded and HFMI treatment conditions. Experimental residual stress and fatigue data sets of 5083‐H321 aluminum, CSA 350W, ASTM A514, S355, and S960 steel welded joints are used to validate the proposed approach. Both predicted and experimental results show that the fatigue life improvement by the HFMI treatment depends on the applied stress level and material type. The fatigue life improvement is greater at the lower stress levels with a factor of more than 10–30 times, and the fatigue life increase becomes less at the higher stress levels with a factor of two to three times depending on the material type of welded joints. The fatigue life improvement by the HFMI is more significant with a higher material yield strength. Compared results showed that the proposed modeling approach provides efficient and accurate life predictions of the welded joints of five different materials under both as‐weld and HFMI conditions. The proposed modeling framework can be used as an effective analysis technique for fatigue crack propagation life of welded structures under pre‐ and post‐weld treatment conditions to account for residual stress fields.

Fatigue behaviour of non-welded wrapped composite joints for steel hollow sections in axial load experiments

Design and execution of fatigue load dominated circular hollow section (CHS) multi-membered structures, such as offshore jacket and floating structures for wind turbines, truss bridges, etc., is hinged on fatigue performance of critical welded joints. An innovative jointing technology of wrapped composite joint connects steel hollow sections by direct bonding through a fibre reinforced polymer composite wrap, which completely avoids welding and therefore has superior fatigue performance than welded joints. In this study first results on fatigue performance of the wrapped composite joints is presented. Tensile cyclic loading tests on wrapped composite X-joint specimens were carried out to characterise their fatigue performance under different constant amplitude load ranges and compare it to equivalent welded joints. In addition, the influence of surface roughness of steel tubes and re-testing (load history) on fatigue performance of wrapped composite joints, as well as the influence of fatigue loading on residual static resistance was investigated in experiments. Preliminary S-N curves of wrapped composite joints are established. The tests results showed that X45 wrapped composite joints exhibited steadier stiffness degradation and 10–100 times longer fatigue life than their welded equivalents. Through 3D DIC surface strain measurements and post-failure microscopic insights to cut specimens, different failure modes including de-bonding at glass fibre composite-to-steel interface, delamination/fracture of the composite layers and fracture of steel brace are distinguished. The relationship between joint stiffness degradation rates, crack propagation rates and nominal stress ranges in the brace are established, based on which a preliminary fatigue life prediction of wrapped composite joints can be made. The re-tested specimens exhibited superior fatigue performance than virgin ones, while specimens with poor steel surface roughness showed worse fatigue performance. After fatigue loading with 40% of stiffness degradation, the specimens were found to still have the potential to sustain its original static resistance.

Effect of hygrothermal environment on properties of induction welding joint of carbon fiber reinforced polyphenylene sulfide laminate

The carbon fiber reinforced polyphenylene sulfide (CF/PPS) composite laminate was taken as the research object, and the induction welding method was used to weld the CF/PPS laminate. It was focused on the effect of hygrothermal on the welded joint performance of the CF/PPS laminate. The experimental results show that the PPS resin does not undergo chemical changes before and after moisture absorption. At room temperature, the shear strengths of the welded joints gradually decrease with the increase of moisture absorption time, and compared with the dry welded joints, they are reduced by 15%, 18%, 23%, 32%, and 38%, respectively. The wet stress increases at the interface of the stainless steel mesh, resin matrix and carbon fiber, which weakens the bonding performance of the welded joint interface, and affects the failure mode of the welded joint. Under the environment of 120℃, the shear strength values of the welded joints with different moisture absorption times decrease by 12%, 15%, 22%, 37% and 44%, respectively. High temperature and high humidity make the thermal stress and wet stress at the interface of the stainless steel mesh, resin matrix and carbon fiber greater, which aggravates the damage of interface bonding performance. Interface debonding is the main failure form of the welded joints.

Effect of Yield Strength Distribution Welded Joint on Crack Propagation Path and Crack Mechanical Tip Field.

Due to the particularity of welding processes, the mechanical properties of welded joint materials, especially the yield strength, are unevenly distributed, and there are also a large number of micro cracks, which seriously affects the safety performance of welded joints. In this study, to analyze the effect of the uneven distribution of yield strength on the crack propagation path of welded joints, other mechanical properties and residual stresses of welded joints are ignored. In the ABAQUS 6.14 finite element software, the user-defined field (USDFLD) subroutine is used to define the unevenly distributed yield strength, and extended finite element (XFEM) is used to simulate crack propagation. In addition, the static crack finite element model of the welded joint model is established according to the crack propagation path, which is given the static crack model constant stress intensity factor load, and the influence of an uneven yield strength distribution on mechanical field is analyzed. The results show that the crack length of welded joints as well as the plastic deformation range of the crack tip in high stress areas can be reduced with the increase of yield strength along the crack propagation direction. Moreover, the crack deflects to the low yield strength side. This study provides an analytical reference for the crack path prediction of welded joints.

A study on strengthening and toughening mechanism of laser beam welded joint prepared between Ti–22Al–27Nb and Ti–6Al–4V with an interlayer of Nb

In this study, laser beam welding (LBW) between Ti–22Al–27Nb and Ti–6Al–4V was experimented with and without an interlayer of Nb to analyze and compare the effect of Nb on evolution of microstructure in fusion zone (FZ) and its impact on weld joint performance at room as well as high temperature (650 °C). The nucleation and evolution of phases and crystals were examined through X-ray diffraction (XRD), electron probe microanalysis (EPMA), electron back scattered diffraction (EBSD), high resolution transmission electron microscopy (HRTEM) and high angle annular dark field (HAADF) imaging, respectively. The weld joint performance was evaluated through tensile and hardness tests. The adulteration of LBW joint between Ti–22Al–27Nb and Ti–6Al–4V through pure Nb contributed an increase of 28.70% in yield strength (YS), 10.22% in ultimate tensile strength (UTS) and 12.81% in percentage elongation. The evident reason for such an improvement in joint performance was attributed to the suppression of α′ martensite and nucleation of single phase B2 with fine grained structure, which provided greater fraction of high angle grain boundaries (HAGBs) in FZ. The LBW joint between Ti–22Al–27Nb and Ti–6Al–4V with an interlayer of Nb was ruptured from the base material (BM) Ti–22Al–27Nb during tensile straining at room temperature. All the LBW joints between Ti–22Al–27Nb and Ti–6Al–4V, either prepared with or without an interlayer of Nb, were fractured from the BM Ti–6Al–4V during tensile test at 650 °C.

The Influence of Heating Time on the Mechanical Properties of Laser Though-Transmission Welded Polyamide PPA40GF Joint

The goal of this work was to investigate effect of heating time during welding on mechanical properties of High Performance Polyamide thermoplastic composite material PPAGF40. Studies showed that welded joints with shorter heating time from 6.1 s to 6.7 s had a higher amount of pores and burn mark defects compared to the welded joints with longer heating time. Cross-section analysis of welded samples revealed tendency, that samples with higher heating time from 7.4 s to 11.5 s possessed more homogenous weld seam and higher resistance to burst pressure, respectively from 5.1 bar to 7.5 bar, while the resistance to pressure values of shortest heating time range, respectively are varying from 3.3 bar to 3.9 bar. The weld seam defects like pores and burn marks weakened the welded joint. 470 W of laser power energy input influenced fast melt-down of a cover and a housing, which caused material partial evaporation and later on formation of pores inside weld seam. By using lower 450 W of laser power and scanning speed of 1900 – 1700 mm/s, we can observe more homogenous weld seam. The cross-section of the samples were examined by using optical microscope. Mechanical resistance to pressure was performed in order to evaluate the performance of welded joints of different heating time of PPAGF40.

Application of progressive hybrid RSM-WASPAS-grey wolf method for parametric optimization of dissimilar metal welded joints in FSSW process

An eco-friendly high efficiency solid state welding technique, Friction stir spot welding (FSSW) produces the welding lap joints of two dissimilar material of aluminum alloy to a commercially used copper alloy. Generally, Copper has an excellent thermal and electrical conductivity combined with creep resistance and high ductility which are used in the current carrying electrical connection and components in the automobile and electrical Industry. A number of experiments have been carried out in this paper which focus on the maximum force required to break workpiece, maximum stress developed and heat affected zone at the welding joint by changing the different parameters such as rotational speed, pin length and tool tilt angle. In this investigation, tests were completed according to Response Surface Methodology based L15 orthogonal array. The optimum welding parameters were determined by using WASPAS (weighted aggregated sum product assessment) coupled Grey Wolf Optimization method which reported pin length as the most significant constraint. Validation of the output responses was done augmenting the mechanical performances of welded joints.

Welding Joint Performance of Inclined Stationary Shoulder Friction Stir Welding for Aluminum Alloy Sections

Welding Joint Performance of Inclined Stationary Shoulder Friction Stir Welding for Aluminum Alloy Sections

Characterisation of LCF performance of X100 weld-joints: Mechanistic yield strength modelling, finite element analyses and DIC testing

This paper is concerned with the effect of welding on the fatigue behaviour of X100 material for steel catenary risers. The methodology includes both modelling and experimental characterisation. The modelling combines (i) a physically-based yield strength model to capture the thermally-induced microstructural heterogeneity and associated spatial variations in relative contributions of the key strengthening mechanisms due to welding, and (ii) a five-material cyclic plasticity model with a Coffin-Manson strain-life fatigue model for prediction of cross-weld heterogeneity in cyclic plasticity and fatigue response. The combined non-linear isotropic-kinematic cyclic plasticity behaviour of the five weld joint constituent materials (PM, weld metal (WM) and heat-affected zone (HAZ) subregions) is implemented via a user material (UMAT) subroutine, including Kocks-Mecking monotonic-cyclic evolution of yield stress. The experimental methodology consists of tensile tests with digital image correlation (DIC) for X100 PM and cross-weld samples. The results indicate that the primary phenomenon driving the detrimental effect of welding on fatigue is the evolution of cyclic strain localisation in the inter-critical heat-affected zone (ICHAZ), leading to predicted ICHAZ failure.

WITHDRAWN: Challenges and possibilites in the resistance spot welding of dissimilar metals – A review

In order to get a defect free spot weld, both the metals are desired to have the same thermal and electrical conductivity. But when welding dissimilar metals or sheets of different thickness, the fusion zone of both the metals may not experience same heat input due to the difference in material properties. This leads to weld defects such as nugget offset, voids and intergranular cracks in the fusion zone. The existence of weld defects deteriorates the mechanical performance of welded joints. A thorough metallurgical analysis must be carried out to ensure that the weld nugget is free of defects. The resistance spot welding of various dissimilar metals in the recent research publications and its practical outcomes are analyzed.

Finding ways to improve the performance of welded joints based on controlled heat input and use of shock-mechanical treatment

The paper summarizes the study’s results of welded joints fatigue failure obtained by arc welding with controlled and uncontrolled heat input and shock-mechanical treatment. Based on energy parameters of the mode fixed in welding process of samples obtained at various technologies, the experiments on determination of their fatigue life were performed. The results of numerical estimation of fatigue failure of welded joints made of 09G2S steel are presented. The positive influence of shock-mechanical treatment on test samples durability is shown.