Welded Joint Specimens Research Articles

Fatigue damage evaluation of welded joints in steel bridge based on meso-damage mechanics

Welding is a rapid and flexible connection that facilitates the use of a broad range of steel bridge. However, fatigue cracks initiating from various welded connection details are common problems in steel bridges. Therefore, it is vital to accurately evaluate the fatigue damage evolution and fatigue life of welded joints in steel bridge. In this study, a fatigue damage evolution model based on the meso-damage mechanics was proposed to evaluate the fatigue damage of welded joints in steel bridge. The number density of micro-cracks was adopted as the damage variable in the fatigue evolution model. Finite element modelling and user material subroutine (UMAT) in ABAQUS were combined to simulate fatigue damage evolution of welded joints in steel bridge. The fatigue damage evolution model was embedded in UMAT while the UMAT was coupled with the finite element model of the welded joints under cyclic loading. Then, the proposed model was validated by fatigue tests. The fatigue damage evolution model was also used to investigate the fatigue damage evolution process, and fatigue life prediction of the typical welded joints specimens in orthotropic steel decks (OSDs) of steel bridge. The results indicate that the fatigue strengths of nominal stress method were estimated to be 65.7 MPa for typical welded joints. The fatigue cracks mainly initiating at the weld toe and propagating along the weld toe line. The simulation results indicate that the fatigue damage evolution model provides superior ability in evaluating fatigue damage process and fatigue life of welded joints in steel bridge.

Effect of abnormal structure on creep strength of long-term used 9Cr steel welded joint

ABSTRACT Microstructural characteristics of abnormal structure in long-term used Gr.91 steel weldments and its effect on creep strength of welded joint are presented. The abnormal structure is defined as a structure in which the hardness is clearly lower than that in the normal region, and the grain is coarsened. Creep strength of the abnormal structure is significantly lower than that of normal weld metal. There is little effect of abnormal structure formed in the HAZ on creep life of standard welded joint specimensr. In case of abnormal structure formed in the weld metal, times to creep rupture of standard specimens are shorter than those of specimens without abnormal structure. Full-thickness welded joint specimen consisting more than half abnormal structure in the weld metal ruptured at the weld metal before the HAZ. Time to creep rupture decreased with increasing the abnormal structure ratio in thickness direction.

Study on the Effect of Load Frequency on Temperature and Stress States Measured by Infrared Thermoelastic Method

We investigated the effect of load frequency using thermoelastic finite element (FE) analysis on a gusset welded joint specimen commonly used in welded structures. To simulate the thermoelastic effect, we developed a stress field-temperature field thermoelastic FE analysis technique that calculates the heat transfer of heat generation and heat absorption according to compression and tensile stress. The calculated stress distribution showed a good agreement with thermoelastic stress distribution measured using an infrared ray method. The result implies that the developed technique is effective in reproducing the thermoelastic effect. In the case of a load frequency of 1 Hz, a small gradient of temperature distribution appeared. Therefore, when applying the thermoelastic method to the stress concentration field, it is important to consider the influence of the load frequency.

Brittle fracture estimation at ends of groove welded joints under cyclic loading

To prevent brittle fracture in structural components during earthquakes, their cumulative ductility (plastic deformation capacity) should be determined beforehand and appropriate countermeasures applied accordingly. In this paper, a method for estimating the cumulative ductility of welded joints with defects based on the σW–Nf relationship and Miner's rule is proposed for steel structure components to facilitate brittle fracture estimation. To verify its effectiveness, it was applied to the testing of welded joints with defects and compared to experimental results. The experimental tests were conducted under cyclic loading conditions to reproduce brittle fractures starting from the ends of complete joint penetration groove welded joints. The joint models used in this study were part of beam-to-column connections between beam flanges and diaphragms. Defects were artificially introduced into the welded joints before the experimental tests; brittle fractures occurred at these preinstalled defects in the welded joint specimens. The calculated cumulative ductility was obtained from the fracture toughness and Weibull stress of the joint model measured using finite element analyses. The calculated cumulative ductility values corresponded well with the experimental results, albeit with some explicable errors. The results indicate that the proposed method can estimate the cumulative ductility for structural components with defects under cyclic loading independent of their materials, notch types, and connection details. Thus, the findings could contribute to the assessment of defects in welded joints in steel structures subjected to earthquake loadings.

Study and optimize tensile strength of FSW joints using AA5083 filler by Taguchi & Anova

FSW is a cutting-edge technique that eliminates many of the drawbacks of traditional welding procedures, such as the release of hazardous gases and the need for a large amount of energy to complete the process. Experiments are designed using the Taguchi L9 orthogonal array and ANOVA analysis methods. Analyze the gathered data values to see if tool rotation speed of 850 rpm, 1000 rpm, or 1150 rpm, and tool transverse speed of 25, 35, or 45 (in mm/min) have an effect on the tensile strength of weld joint specimens. FSW fabricates aluminium alloys AA5052, AA5083, and AA6063 in this research utilising AA5083 as filler. Nine specimens with different base metal combinations are created during the experiment, using tool rotation speeds of 850 rpm, 1000 rpm, or 1150 rpm and tool transverse speeds of 25, 35, or 45 (in mm/min). The results show that as the TRS is raised, the tensile strength increases. Taguchi's orthogonal system was used to create the Design of Experiment, which allows for better outcomes with the least number of experiments. FSW has application range in the industrial industry, including shipbuilding, aircraft, and automobile production, and is widely employed in the fabrication of aluminium plates and sheets, as well as steel and magnesium.

Interpretation of nature of non-metallic inclusions in assessing the quality of metal products in the industrial conditions

Using an example of the quality assessment of welded pipe joints made of steel 09G2S, the method of processing the results of factory expert opinions has been developed to interprete the origin of non-metallic inclusions detected in the defects of a welded joints. Thermodynamic calculations have been made to assess the possible indigenous origin of these inclusions, the results of which are summarized in the form of radar diagrams of five clusters, which combine similar deoxidation products. According to the same method, more than 136 actual inclusions found on dozens of welded joints specimens are combined in 7 clusters. After a comparative analysis of these two types of radar diagrams, the origin of all real inclusion clusters was determined, three of which are predominantly indigenous and the other ones are predominantly exogenous. None of the clusters contains only indigenous inclusions. Several of the inclusions of one of the clusters contain pure exogenous MgO inclusions. The sources of inclusions in weld discontinuities are conglomerates consisting of exo-indigenous or indi-exogenous inclusions, which were torn off from the refractory surface. The method is implemented as a Thixomet PRO plug-in and allows to automate the process of metallographic conclusions generation under conditions of factory practice, as well as to accumulate all information in the database for subsequent processing and analysis.

Properties of amorphous Fe-based alloy

The paper presents the results of tests for multi-cycle fatigue of laboratory samples of welded joints of exploration drill pipes in a combination of steel s 32-2-Mn of strength group L (pipe body) with 40-Cr-Ni (tool joint part) and solid samples of pipe body material. Welding of the joint part with the pipe body was carried out by rotary friction welding. Multi-cycle fatigue tests were carried out according to GOST 25502 on a test machine with a two-support rotating specimen under constant torque. Mathematical processing of the results of fatigue tests was carried out, linear regression equations were obtained, fatigue curves were constructed, the endurance limits σ-1 of samples with a welded joint and solid samples were determined, taking into account the relative error of the regression equations. On the basis of metallographic analysis, vulnerabilities in welded joints were identified, in which the initiation and development of fatigue cracks occurred. Fractograms are presented that illustrate the mechanism of fatigue fracture of solid and welded samples. It is shown that the development of a fatigue crack in specimens of welded joints occurs with a greater proportion of microplastic deformation. It has been established that rotary friction welding of a pipe body made of 32-2-Mn steel of strength group L and a joint made of 40-Cr-Ni steel contributes to an insignificant decrease in the fatigue limit of welded joints relative to the pipe body, providing its value at the level of 43-47 % of the ultimate strength of 32-2-Mn steel. The data obtained assume trouble-free operation of the welded joint zone in the drill pipe string made of steel 32-2-Mn, strength group L with welded joints made of steel 40-Cr-Ni.The reported study was funded by RFBR, project number 19-38-90079.

Endurance limit and mechanism of fracture of friction welded joints of exploration drill pipes in the conditions of multi-cycle fatigue

The paper presents the results of tests for multi-cycle fatigue of laboratory samples of welded joints of exploration drill pipes in a combination of steel s 32-2-Mn of strength group L (pipe body) with 40-Cr-Ni (tool joint part) and solid samples of pipe body material. Welding of the joint part with the pipe body was carried out by rotary friction welding. Multi-cycle fatigue tests were carried out according to GOST 25502 on a test machine with a two-support rotating specimen under constant torque. Mathematical processing of the results of fatigue tests was carried out, linear regression equations were obtained, fatigue curves were constructed, the endurance limits σ-1 of samples with a welded joint and solid samples were determined, taking into account the relative error of the regression equations. On the basis of metallographic analysis, vulnerabilities in welded joints were identified, in which the initiation and development of fatigue cracks occurred. Fractograms are presented that illustrate the mechanism of fatigue fracture of solid and welded samples. It is shown that the development of a fatigue crack in specimens of welded joints occurs with a greater proportion of microplastic deformation. It has been established that rotary friction welding of a pipe body made of 32-2-Mn steel of strength group L and a joint made of 40-Cr-Ni steel contributes to an insignificant decrease in the fatigue limit of welded joints relative to the pipe body, providing its value at the level of 43-47 % of the ultimate strength of 32-2-Mn steel. The data obtained assume trouble-free operation of the welded joint zone in the drill pipe string made of steel 32-2-Mn, strength group L with welded joints made of steel 40-Cr-Ni.The reported study was funded by RFBR, project number 19-38-90079.

Studies on creep-fatigue interaction behavior of Grade 92 steel and its weld joints

Creep-fatigue interaction (CFI) behavior of 9Cr-1.8W-0.5Mo-VNb steel (Grade 92 steel) base metal and its weld joint has been investigated at 823 K using a constant strain rate of 3 × 10–3 s−1. Both the base metal and the weld joint exhibited continuous softening with an almost equal cyclic stress response. The fatigue life decreased with increasing hold time. The hold applied in the compressive peak strain proved more deleterious compared to the tensile hold, indicating a compressive dwell sensitivity. Besides, the weld joints showed a greater reduction in fatigue life compared to the base metal. Fracture surfaces of the tested specimens revealed the prevalence of secondary cracks and extensive oxidation in the material. Weld joint specimens failed in the base metal region in all the tests. Evidence of dynamic strain aging in the form of serrations in the stress-strain hysteresis loops was also noted.

Experimental investigation and numerical simulation on welding residual stress of innovative double-side welded rib-to-deck joints of orthotropic steel decks

An innovative double-side welded rib-to-deck (RTD) joint has been developed recently to enhance fatigue performance of orthotropic steel decks (OSDs) in steel bridges. The welding residual stresses (WRS) will lead to reduction in fatigue resistance of RTD joints in steel bridges. It is essential to study WRS and its distribution to estimate the fatigue resistance of innovative double-side welded RTD joints accurately. To investigate WRS caused by the double-side welding process, the experimental tests on four specimens of double-side welded RTD joints were carried out by means of longitudinal critical refraction (LCR) wave method. A sequentially coupled three-dimensional thermo-mechanical finite element (FE) analysis model was established to simulate the double-side welding process, and it was validated by the WRS results of experimental investigation. Then, the effects of welding parameters and geometric configuration of RTD joints on WRS and its distribution are analyzed by the validated numerical simulation. The results show a reasonable agreement between WRS simulation and the experimental data. WRS at the surface of weld seam and plate components is strongly affected by the welding speed, but comparatively weakly depends on the weld penetration rate, the assembly gap and the deck thickness.

Investigation on low cycle fatigue properties of CLAM steel electron beam welded joint at 550 °C

The low cycle fatigue (LCF) properties of structural materials at high temperatures are important for operational safety of fusion reactors. In this work, the investigation on LCF properties of CLAM steel joints welded by electron beam was conducted at strain amplitudes varying from 0.2 % to 0.7 % at 550 °C. It is found that the fatigue life and cyclic stress response of welded joints are lower than those of base metal. Continuous cyclic softening is observed in welded joints and base metal during LCF test. A majority of the fatigue cracks initiated at the surface of the the welded joint specimen with several initiation sites and propagated in a transgranular mode. The area of the crack propagation region decreased and the fatigue striation spacing increased with increasing strain amplitude. The cyclic softening is attributed to the coarsening of martensite laths and the reduction in dislocation density.

An investigation of the impact of axial force on friction stir-welded AA5086/AA6063 on microstructure and mechanical properties butt joints

Friction stir welding (FSW) is a method through which frictional heating and plastic deformation normally joined the work pieces at temperatures under the melting temperature of the materials to be united. The aim of this study is to assess the impact of axial force during welding on the dissimilar joints mechanical properties of aluminum alloys (AA5086 and AA6063 aluminum alloy) formed by friction stir welding process. Friction stir welding is done using four different axial forces (Viz 5kN, 6kN, 7kN and 8kN) on the dissimilar aluminum alloys and the impact of these on the mechanical performance of samples were investigated in contexts of tensile and bending. The microstructural investigations of the welded joint specimen are also carried out. The mechanical characteristics of the joints were strongly influenced by the axial force applied during the welding process, based on experimental results.

Effect of change in microstructures due to simulation temperatures on the low cycle fatigue behavior of P91 steel

In this study, the microstructures of the three principal heat-affected zones (HAZs) of the P91 steel weld joint were simulated using appropriate heat treatments at different soaking temperatures ranging from 865 °C to 1200 °C. Low cycle fatigue tests were conducted on the samples of each microstructural zone of the weld joint at 550 °C employing a constant strain amplitude of ±0.6% and strain rate of 3 × 10−3 s−1. In the weld joint’s microstructures, the weld metal exhibits the lowest fatigue life, followed by the inter-critical (IC). However, the actual weld joint specimen failed at the interface between the ICHAZ and the base metal.

The thickness effect of hot spot S-N curves for welded aluminum joints

This study aimed to investigate the design S-N curve on the basis of the hot spot stress (HSS) approach considering proper thickness effect for welded aluminum joints. The effect of the main plate thickness is examined by using the results of fatigue tests in this study and references of fatigue data of previous literature. The fatigue tests are performed on 5083-O welded joint specimens with four kinds of main plate thicknesses, namely 12 mm, 16 mm, 20 mm, and 25 mm. The main plate thicknesses of the fatigue data of the references ranged from 2.8 to 25 mm. We clarify the relationship between fatigue strength and main plate thickness, and propose hot spot design S-N curve for welded aluminum joints with thickness of less than 25 mm based on the research of the thickness effect. Fatigue tests of large-scale model are carried out to test the validity of the proposed design S-N curve for welded structures.

Lowest Fatigue Limit Estimation of Ductile Cast Iron Joints by Considering Maximum Defect Size Toward Replacing Welded Joints

In our earlier study, the authors revealed that the fatigue limit of ductile cast iron (DCI) specimens whose shapes are similar to the welded joint shapes is about three times larger than that of the welded joint specimens. However, since many defects are usually included in the DCI specimens, the fatigue limit of DCI joints decreases with increasing the maximum defect size. In this paper, therefore, the maximum defect size is estimated by using statistics of extremes. Then, the lowest fatigue limit corresponding to the maximum defect size is estimated from the 4 parameter model and compared with the lowest fatigue limit of the welded joint. As a result, it was confirmed that the lowest fatigue limit of the DCI specimens is about twice as large as the welded joint.

Influence of Cooling Time t<sub>8/5</sub> on Impact Toughness of P460NL1 Steel Welded Joints

The results of impact testing of welded joint specimens taken from a welded plate made of P460NL1 steel are presented in this paper, and analysed with regards to the cooling time t8/5, that was previously calculated. The aim was to determine how the cooling times that were measured, some of which were below the minimum required values, affected the toughness, in terms of total impact energy and its components, crack initiation and crack propagation energy. In addition, this analysis included the effects of temperatures measured at the opposite ends of the plate during the welding process, since this had also affected the cooling times for each welding pass. After observing the differences in total, crack initiation and propagation energy between the tested specimens taken from different parts of the welded plate, it was determined that the specimens from the part where the higher temperatures were measured had shown better, more uniform results, whereas the average total impact energy for specimens from both groups were very similar. It was also noticed that the ratio of crack propagation to crack initiation was more favourable (greater) in the case of specimens from the second group (with higher temperature), as the values of crack initiation energy decreased slightly and the crack propagation energy increased.

Comparative evaluation of tensile properties of simulated heat affected zones of P91 steel weld joint

ABSTRACTThe present work aims to understand the contribution made by each heat affected zone (HAZ) to the overall tensile behavior of the P91 steel weld joint. The three principal microstructures of heat-affected zones such as inter-critical (IC), fine grain (FG) and coarse grain (CG) were simulated through isothermal furnace heat treatments at 1138 K, 1208 K and 1473 K respectively. The simulated microstructures predominantly developed tempered martensite after oil quenching followed by tempering. The grain size and hardness across the P91steel weld joint vary in a complex manner. Tensile tests were carried out on each simulated HAZ and actual weld joint at 823K and a strain rate of 3 × 10-3 s-1. The weld joint specimen has failed in the base metal region. An increase in microhardness at the ICHAZ was found after tensile deformation. Higher initial strain/work hardening behavior of soft ICHAZ attributes the shifting of strain localization, consequently failure at the base metal.

Evaluation of the Properties of Alternative Construction Combined Tube Joints from Heat Exchanger Tube Grids Made of Steel 2Cr18Ni10Ti

One of the most effective ways of excluding heat treatment during the manufacture if tube bundles is replacement of arc welding by rotary friction welding. The corrosion resistance of welded joints of 12Cr18Ni10Ti steel, prepared by friction welding and not subjected to heat treatment is evaluated. The corrosion properties of such welded joints, including those not subjected to heat treatment, are evaluated. Measurements of the electrode potential of welded samples are performed to determine zones prone to brittle fracture. It is established that the spread of electrode potential values is small that makes it possible to propose that there is uniform corrosion in a welded joint. Tests for welded joint specimen resistance to intergranular corrosion show that there is no grain boundary breakdown to a depth of more than 30 μm in 12Cr18Ni10Ti steel specimens, which indicates joint intergranular corrosion resistance.

Study on microstructure and fatigue properties of high strength aluminum alloy X-joints

6082 high-strength aluminum alloy was welded by metal inert gas arc welding (MIG), and the welded joint and high-cycle fatigue result were applied to the welded joint and the base metal. The result found that the precipitation and dissolution of the strengthening phase changed the hardness of the welded joint. Fatigue specimens of welded joints were fracture in the weld zone, and the pores inside the welded joint were the main causes of fatigue crack initiation. The fatigue crack propagation was composed of a fatigue crack initiation region, a stable extension region and a fatigue final rupture region. The welds of welded joints were analyzed. It was found that there were metallurgical pores and process pores in the welds. The two types of pores were analyzed respectively. It was found that the crack propagation path near the process pore is fracture along the fatigue striation, and the crack propagation path at the metallurgical pores is mainly through the fatigue striation. The mechanism of crack propagation was found to be caused by slip, and the passivation and sharpening of the crack propagation path in a ‘Z’ shape.

Influence of welded joint microstructures on fatigue behaviour of specimens with a notch in the heat affected zone

In this paper, the results of determining the Paris law coefficients, C and m, are presented, based on the experimental data obtained by three-point bending testing of 8 welded joint specimens. The specimens were taken from a welded plate, with P460NL1 used as the parent material and VAC 65 used as filler material. The specimens had a 1.4 mm notch in the heat affected zone, either in the root or the weld face side. After the fatigue crack growth tests performed using the Fractomat 7609/213 (RUMUL), the obtained crack growth rate vs. number of cycles (da/dN vs. N) diagrams were used to calculate the coefficients. The values of these coefficients were then compared to each other, in order to determine the cause of noticeable differences, which were assumed to be a result of different microstructures in different specimens, caused by the increased temperature measured in the specimens near the end of the welded joint. Since the specimens used in the experiment had differences in terms of notch position and temperature, they were divided into four groups. Analysis of the results involved the comparison of obtained a-N curves with the images of microstructures, as seen on the broken specimens, in order to determine whether the changes in the curve's slope correspond to the changes in microstructures along the specimens' cross-sections. The experimental results confirmed this assumption, and it was determined that the crack growth rate was the highest in the weld metal, whereas the lowest rates (highest resistance to fatigue crack growth) were observed in the parent material, with the heat affected zone being between these two value ranges.