Weld Failure Research Articles

Fault Diagnosis for PV Modules Based on AlexNet and Symmetrized Dot Pattern

Faults in solar photovoltaic (PV) modules often result from component damage, leading to voltage fluctuations and decreased stability in the power system. In this study, the original voltage signals of different PV modules show little variation. Therefore, a solution that combines symmetrized dot pattern (SDP) and AlexNet for fault detection in PV modules was proposed. This solution investigates three common faults: poor welding, cracking, and bypass diode failure, which can be applied to fault-free modules. First, a high-frequency signal was input into the PV module, and the raw signal was captured using an NI PXI-5105 high-speed data acquisition card. Next, we used SDP to process the signal and create images with specific snowflake-like features. These images were used as a basis for fault diagnosis. Finally, deep-learning algorithms were used to perform status detection on the PV module. This research also used 3200 training samples and 800 test samples (200 for each type) to evaluate a new method for diagnosing faults in PV modules. The results show that the accuracy of the new method reached 99.8%, surpassing traditional convolutional neural networks (CNN) and extension neural networks (ENN), whose accuracies were 99.5% and 91.75%, respectively. Furthermore, this study compares the proposed method with more traditional numerical fault diagnosis methods. SDP effectively extracts fault signals and presents them as images. With AlexNet used for fault identification, the method excels in accuracy, training time, and testing time, thereby enhancing the stability and reliability of future energy systems.

Experimental study on seismic behavior of high strength steel flange-plate connections with box columns

The flange-plate beam-to-column connections are a promising option for reinforced moment-resisting connections in ductile steel frames and have potential applicability in high strength steel frames. However, there have been few investigations on flange-plate connections with high strength steel box columns. In this study, experiments were conducted to evaluate the seismic behavior of high strength steel flange-plate connections with box columns. Seven specimens were designed and tested under anti-symmetrical cyclic loads, comprising three different combinations of Q355 or Q460 steel beams and Q460 or Q690 steel columns. While the expected beam failure mode was observed in five specimens, two specimens experienced ESW joints failure, and one specimen experienced CJP weld failure. These findings highlight the possible impact of welding quality defects in engineering applications. The test results about bearing capacity, rotation stiffness, deformation capacity, and energy dissipation were reported and analyzed. Under the similar design conditions, the use of higher strength steel members results in a decrease in the initial stiffness of the specimens, as well as changes in yielding modes, deformation proportion, and energy dissipation capacity. Six flange-plate connections met the deformation and bearing capacity requirements for special moment frames in AISC 341 with the ultimate story drift angle not less than 0.06 rad. The proposed criteria for determining the minimum size of flange plates was verified in this study, and design recommendations were made for flange-plate connections in high strength steel frames.

Fabrication of thin-walled hat-shaped beams from ultrahigh strength steel by laser-assisted robotic roller forming

Laser-assisted robotic roller forming (LRRF) can be applied to forming ultrahigh strength sheets to products with high geometrical accuracy. In this study, the geometrical profiles and three-point bending performance of thin-walled hat-shaped beams formed by LRRF and robotic roller forming (RRF, i.e., without laser heating) were experimentally investigated. It is found that the geometrical distortion resulted from the accumulation of longitudinal tension during multi-pass roller forming is significantly alleviated by LRRF. In addition, the bending performance of LRRF beam assembly is ameliorated at the initial deformation stage of three-point bending. The improvement is ascribed to a smaller bending radius and the alter of mechanical properties at the laser heat-affected zone. The lower geometrical precision of beams formed without laser heating results in early failure of spot welds of the beam assembly during three-point bending. LRRF beam assembly exhibits larger displacements at failure, and the failure mode is cracking at the edge of the laser-irradiated region. The pronounced microstructure differences on both sides of the crack suggest that the obvious laser-induced mechanical property gradients are responsible for the failure of LRRF beam assembly during three-point bending.

Examination on joining of 2 mm thick dissimilar stainless steel plates using resistance spot welding

In the present study, dissimilar metals such as austenitic stainless steel (ASS) and duplex stainless steel (DSS) with a thickness of 2 mm are joined by resistance spot welding process to investigate the welding metallurgy and failure behavior under different heat inputs. Non-uniform electrode impressions are observed on ASS and DSS sides due to their different thermal conductivity and electrical resistivity. The microstructure of the Fusion Zone (FZ) shows that higher heat input accelerates the growth of Intra Granular Austenite (IGA) due to faster cooling. Scanning electron microscopy (SEM) - Energy Dispersive x-ray (EDX) investigation at FZ showed that Chromium & Molybdenum decrease with increasing heat input due to a decrease in ferrite content. X-ray diffraction analysis confirmed that ferrite formation is limited at higher heat input. Microhardness study revealed that the higher hardness is in the middle of the weld nugget, which is due to the presence of equiaxed grains and IGA. The lowest hardness on the ASS side of Heat Affected Zone (HAZ) is due to the phenomenon of grain growth, and the HAZ DSS side has a higher hardness than DSS Base Metal (BM) due to the mechanism of solid solution strengthening. The tensile shear test showed that the tensile shear strength increases with the addition of heat. SEM Examination of the fracture surface revealed the presence of an equiaxed dimple structure on the ASS side, confirming ductile fracture, and torn bonds on the DSS side, confirming quasi-gap fracture due to the work-hardening ability of both plates. This study is carried out to understand the relationship between mechanical, metallurgical, and failure behaviours, because, researches on joining of dissimilar (AISI 316 L and DSS 2205) stainless steel sheets using Resistance Spot Welding process is very limited and need to be studied in detail.

A REVIEW ON THE INFLUENCE OF COOLING APPLICATIONS IN FRICTION STIR WELDING PROCESS

Welding, despite being the most efficient joining process, has significant negative impact on the environment and worker health. This paper presents the environmental impact of various conventional welding processes and sustainability of Friction Stir Welding–a Green technology which requires no filler material, no shielding gas, no flux and involves no gas emissions. It is an energy-efficient process that saves significant amount of power and energy when compared to conventional welding processes. The defect-free welds produced have better mechanical and metallurgical properties than other processes. The higher temperature distributed due to the friction heat is established as the source of weld failure. Cooling the weld joint controls the heat conduction thus further enhancing the weld properties. This review paper explores the different cooling techniques employed for cooling the joint during Friction Stir Welding process. The changes in temperature distribution and microstructure caused by the cooling applied and the consequential transformation in material flow, tensile strength, hardness, corrosion, wear, residual stress are discussed. The changes in weld properties obtained by using different cooling media on different materials are reviewed.

Evolution mechanism of interfacial microstructure and its effect on failure in dissimilar metal welds containing ferritic heat resistant steels

This study investigated the behaviour and mechanism of interfacial microstructure evolution during long term high temperature exposure and the effect of interface structure on creep failure in the dissimilar metal welds (DMWs) involving ferritic heat resistant steels with nickel-based filler metal. The welding of nickel-based and ferritic materials led to the formation of interfacial martensite layer in the ferritic steel side of DMW. During long term high temperature exposure, interfacial martensite transformed to ferrite due to C diffusion and migration in the micro-region near the BCC/FCC interface between the martensite layer and the weld metal. The martensite-ferrite transformation was attributed to the large C chemical potential gradient caused by chemical composition gradient. Under creep condition, the failure of DMW was prone to occur along the weld metal/ferritic steel interface, which was related to strain concentration around the interfacial ferrite formed during service. Hence, the relationships between interface structures before and after service and interfacial failure in the DMWs were clarified.

Deformation behaviour of high‐strength steel welds using DIC

AbstractThis paper focuses on the deformation and strength behaviour of high‐strength steel (HSS) transverse fillet welds. The behaviour of six lap‐welded fillet joints made of high‐strength steels (HSSs) is investigated under tension load through experiment. Due to some weaknesses in the deformation measurement using traditional techniques, the digital image correlation technique (DIC) is used to measure the deformation of transverse fillet weld connections. The development of the deformation on the specimen throughout the loading process was analysed using DIC measurement. The deformation of transverse fillet lap‐welded connections from HSS is always less than 1 mm. The strength calculated from the weld's fracture surface area shows better results than the theoretical weld area because it provides the real strength of the weld. In most cases, the weld failure did not occur along the throat section. Moreover, it is confirmed that the analytical models offered by prEN 1993‐1‐8:2020 are conservative for all the specimens.

Improved Mechanical Properties of SUS304/AA5083 Dissimilar Joint by Laser Ablation Pretreatment in Vortex- Friction Stir Lap Welding

To obtain a high-quality Al/steel dissimilar joint, a micro-groove-assisted vortex-friction stir lap welding (MG-VFSLW) process was developed. Through prefabricating micro-grooves on the steel plate surface by laser ablation, high-quality mechanical interlock and metallurgical bonding were obtained simultaneously in the MG-VFSLW process. The weld formation, interface microstructure, mechanical properties, and failure mode in MG-VFSLW were studied by comparing them with those in VFSLW. The results showed that a line load of the AA5083/SUS304 dissimilar joint up to 485.9 N/mm was obtained by MG-VFSLW, which is 40.1% higher than that in VFSLW. Remarkable intermetallic compound layers and cracks were found in VFSLW. The cracks were closely related to the oxides on the interface. However, in MG-VFSLW, cross-riveting aluminum rivets and steel rivets were formed on the interface due to the micro-grooves and flashes made by the laser ablation. Good metallurgical bonding was also formed between AA5083 and SUS304. No remarkable intermetallic compound layers and cracks occurred. During the tensile shear tests, the aluminum rivets were cut off and some dimples and tear ridges existed on the fracture surface. In short, the high strength of the Al/steel lap joint in MG-VFSLW was attributed to the high-quality mechanical interlock and metallurgical bonding.

Failure Risk Prediction Model for Girth Welds in High-Strength Steel Pipeline Based on Historical Data and Artificial Neural Network

Pipelines are the most economical and sensible way to transport oil and gas. Long-distance oil and gas pipelines consist of many steel pipes or pipe fittings joined by welded girth welds, so girth welds are an essential part of pipelines. Owing to the limitations of welding conditions and the complexity of controlling weld quality in the field, some defects are inevitably present in girth welds and adjacent weld areas. These defects can lead to pipeline safety problems; therefore, it is necessary to perform failure risk assessment of pipeline girth welds. In this study, an artificial neural network model was proposed to predict the failure risk of pipeline girth welds with defects. Firstly, many pipeline girth weld failure cases, pipeline excavation, and inspection data were collected and analyzed to determine the main factors influencing girth weld failure. Secondly, a spatial orthogonal optimization method was used to select training samples for the artificial neural network model to ensure that the training sample set could cover the feature space with a minimum number of samples. Thirdly, a prediction model based on BP neural networks was established to predict the failure risk levels. The training dataset/testing dataset was 602/4215, and the prediction accuracy for all risks of girth welds achieved an acceptable level. This study can provide a valuable reference for pipeline operators to prevent pipeline accidents.

Synergy of carbon fiber fabric-based heating element and h-BN modified insulated film on resistance welding of thermoplastic composites

A sandwich-structure heating element (HE) of hexagonal boron nitride (h-BN) decorated polyetherimide (PEI) and plain weave carbon fiber fabric (CFF) of different fabric weight was fabricated to bond carbon fiber reinforced polyetherimide (CF/PEI) laminates by resistance welding. The effects of fabric weight of CFF and thermal conductivity of insulating films on the lap shear strength (LSS) of resistance welding joints and failure mode of CF/PEI composites were investigated. The LSS of the composite joints increased by 31.4% due to the improvement the thermal conductivity of PEI composite film, as well as the reduction of the current leakage during welding process. Intralaminar failure of joints and breakage of carbon fibers of CFF in HE was observed.

Transition in Interfacial Failure Mechanism of Resistance Spot Welds during Tensile–Shear Loading: Role of Fusion Zone Hardness

The failure of resistance spot welds through the fusion zone along the sheet/sheet interface (i.e., interfacial failure) is critical for automotive crashworthiness. This paper investigates the effect of fusion zone hardness on the interfacial failure behavior of resistance spot welds during the tensile–shear test. AISI 1040 medium carbon steel, producing a high level of hardness mismatch during resistance spot welding, was selected as the base metal. By ex situ tempering heat treatment, various levels of fusion zone hardness are achieved in the welds with constant fusion zone size. It is shown that the interfacial failure of the spot welds is a competition between ductile shear failure and rapid crack propagation. It is found that there is a critical fusion zone hardness beyond which the interfacial failure mechanism transitions from ductile shear failure to rapid crack propagation. In welds with high fusion zone hardness, the mechanism of interfacial failure is rapid crack growth, and fusion zone fracture toughness is the governing factor for the interfacial failure load. Conversely, in welds with low FZ hardness, the mechanism of interfacial failure is a ductile shear failure, and fusion zone hardness would be the governing factor for the interfacial failure load.

Systematic investigation of wear-induced cold welding in ultrahigh vacuum piezoelectric motors with non-metallic coatings.

Piezoelectric motors are widely used in various applications where both precision positioning and miniaturization are required. Inertial or quasi-static motors are commonly employed because of their high accuracy, which demands consistent sliding friction between moving sliders and their static counterparts for reliable operation. In general, slider wear is unavoidable after long-term use. This wear can often lead to more serious cold welding in vacuum, which is also referred to as friction welding induced by direct contact between similar metal surfaces. Non-metallic coatings can prevent such unwanted cold welding in ultrahigh vacuum (UHV) applications. However, the practical reliability of available coatings under UHV conditions still remains to be elucidated. Here, we systematically investigate the practical reliability of commonly used, UHV-compatible lubricant coatings for piezoelectric motors in vacuum. We demonstrate that polytetrafluoroethylene (PTFE) shows the most reliable long-term operation in vacuum, while other coatings eventually lead to wear-induced cold welding and motor failure. Our findings provide a simple and effective method to improve the long-term performance of UHV piezoelectric motors by coating the slider surface with PTFE.

Numerical investigation of branch plate-to-CHS connection under eccentric shear loading

Circular Hollow Section (CHS) columns are usually used in high-rise buildings. International design specifications usually overestimate the design of the beam-to-CHS column branch plate connections. This paper numerically investigates the behavior and strength of beam-to-CHS column branch plate connections using a finite element (FE) model. The FE model is verified using different experimental results available in previous literature. A parametric study is carried out on specimens subjected to eccentric shear loading on the branch plate with a constant column length and end conditions. The parameters included the CHS column diameter, wall thickness, branch plate length and the effect of load eccentricity. A notable effect of these parameters is observed on the connection capacity. The mode of failure of the studied specimens ranged from chord plastification for small thicknesses followed by chord face punching to excessive column ovalization at the vicinity of the connection followed by either chord punching or tearing out in the weld. For CHS columns with large thicknesses, punching failure in the column face or premature weld failure is observed. Finally, the results of the parametric study indicated a prominent effect of load eccentricity on the in-plane bending capacity. Therefore, a proposed improvement to the current design guidelines for the strength of CHS column branch plate connection subjected to in-plane bending is presented in this paper.

Investigation of resistance spot weld failure in tailor hot stamped assemblies

A novel experimental method, dubbed the “Mode I Caiman test”, is introduced to characterize spot weld failure and propagation within spot weld groups. The test configuration comprises a partially welded pair of channel sections subjected to Mode I tensile loading through an opening mode loading applied at the un-welded end of the channels. Experiments were performed considering hot stamped USIBOR® 1500-AS in a fully hardened condition (fully quenched) or in a tailored condition in which the strength of the welded flanged regions was altered using in-die heating (IDH). Both static and dynamic loading conditions are considered. The static loading utilized a conventional tensile frame while the dynamic experiments were performed on an instrumented crash sled at velocities of 7.5 m/s.A high speed thermal imaging camera was utilized to detect the temperature rise associated with plastic work during individual weld failure. This proved to be a rather novel and effective technique to detect weld failure and enabled tracking of weld failure propagation through the weld group for the different parent metal (flange) conditions.The experiments served to demonstrate the complex interaction between weld nugget, heat affected zone (HAZ) and parent metal strengths. For high parent metal strengths (fully quenched, martensitic condition), the welds exhibited interfacial and weld pull-out failure modes with rapid unzipping of the weld group resulting in relatively low energy absorption. In contrast, the lower strength tailored flanges exhibited a more stable (slower) failure propagation through the weld group and considerably higher energy absorption which is largely attributed to greater dissipation through deformation of the flange itself. Numerical simulations of the experiments were performed using spot weld models calibrated from single weld lap shear, cross tension, and coach peel experiments. The models captured the peak loads rather well, but predictions of rate of failure propagation within the weld line exceeded that seen in the experiments, pointing to the need for improved post-failure models for spot weld simulation.In automotive structures in which numerous welds are present, the amount of energy absorbed in weld failure can significantly affect the impact response of the structure. The Mode I Caiman test presents a new opportunity to calibrate the energy release rate of spot weld damage models to improve their accuracy when modelling spot welded connections involving multiple spot welds.

Experimental and numerical investigation of the damage characteristics of a ship side plate laterally punched by a scaled raked bow indenter

Experimental and numerical simulation studies are conducted on a scaled ship side-shell quasi-statically punched at the mid-span by a raked bow indenter to investigate its damage characteristics from deformation to a large opening. A scaled stiffened panel and a raked bow indenter are designed in model tests. Numerical simulation is performed to simulate the indentation responses. The experimental and numerical results are compared well in terms of resistance-penetration curves, final damage shapes and especially the three failure models, i.e., initial fracture, model “I” crack and model “III” crack. In addition, the whole damage process, the energy dissipation characteristics of the specimen and failure related parameters in three specific failed elements corresponding to the three failure models are analyzed through numerical simulation. The results demonstrate that the energy dissipated by the stiffener and frictional effect is substantial during the crack propagation process. In addition, shell elements involved with three failure models prior to fracture are mainly subjected to tension and bending effects, as shell elements cannot satisfactorily simulate the transverse shear effect. Finally, the influences of collision parameters, the failure sequence of integration points, modeling of weld seams, mesh resolution and failure criteria on the numerical simulation results are discussed.

Fatigue Resistance of Fillet Welds of Traction Rod Brackets on a Locomotive Bogie Based on International Union of Railways Standards and Improvement Measures Adopted

To solve the problem of fatigue failure in fillet welds of traction rod brackets on locomotive bogies of a given model, the cause for failure and the improvement method were studied. The results show that when there is maximum clearance at weld roots, maximum incomplete fusion of sidewalls, maximum incomplete fusion at weld roots, and maximum pores allowable in the ISO 5817 standard, the stress amplitude separately increases by 70~97%, 53~55%, 40~46%, and 19~34%. Despite this, when various types of defects of the maximum size are present in the weld alone, the static and fatigue strengths of fillet welds with a throat depth of 6 mm on the traction rod bracket can still meet the requirements in the UIC615-4 standard. In practical fillet welds, defects including clearance at weld roots, incomplete fusion, and pores are very likely to occur at the same time, which may induce fatigue failure in fillet welds of traction rod brackets within the original design life. According to the size of the frame and the traction rod brackets, a strengthening scheme for increasing the throat depth of fillet welds of traction rod brackets to 8 mm was designed. Calculation results of the strengthening scheme show that for new structures subjected to overall post-weld stress-relief thermal treatments, the maximum stress amplitude decreases by 5~29% when increasing the throat depth of fillet welds from 6 to 8 mm. For structures in service with the throat depth of fillet welds increased from 6 to 8 mm through repair welding, peak residual stress at the weld root after repair welding can reach 383 MPa. Because overall stress-relief thermal treatments cannot be performed on repair-welded structures, the fatigue strength of repair-welded fillet welds cannot meet the requirements of UIC615-4; therefore, local stress-relief treatments have to be performed in the welded zone. The results are of guiding significance for the treatment of locomotives in service and performance improvement of new locomotives and suggest that the current standard is relatively conservative.

Comparison of RSW technologies on DP steels with modified instrumented Charpy impact test

In recent decades the toughness of welded structures becomes more and more important. This trend is particularly valid for the advanced high-strength steels (AHSS), which have reduced toughness comparing to the low-strength structural steels. Dynamic characteristics of the welded joints of the newly developed high-strength steel sheets required by the automotive industry have been neglected, with welding procedures being optimized on the static joint properties, mainly on the tensile-shear force. Up to the present time, testing of dynamic properties of the spot-welded joints has been performed by increased testing speed during tensile testing. The authors have developed a new dynamic testing method and designed new testing equipment for impact bending, which can give a numeric result to characterize the resistance of spot-welded joints against dynamic load. In this paper, this method will be used to evaluate resistance spot-welded joints made on DP600 and DP800 steels with three different technological parameters, comparing long-time welding, short-time welding, and two-pulse welding. The different parameters cause different weld nugget sizes, failure modes, impact energies, and force–time diagrams. All test results show that bigger weld nugget diameters cause better impact energies and impact forces, but the differences are not perfectly correlated.

Fatigue behaviour of butt-lap friction stir welded joints used with aluminum bridge decks

This paper presents the results of experimental tests and a numerical investigation of the fatigue behavior of butt-lap friction stir welded (FSW) joints used in highway bridge decks made from aluminum extrusions. A large-scale fatigue experiment was designed to initiate fatigue failure in the butt-lap FS welds joining two full-scale aluminum extrusions used for highway bridge decks. Ten fatigue tests were carried out on an MTS servo-hydraulic press. Test results were used to analyze the fatigue failure mode of this unique joint type and to derive the S-N curve useful for the characterization and design of fatigue-sensitive details. The fatigue data was assessed using the effective notch stress (ENS) approach as recommended by the International Institute of Welding (IIW). Results show that the IIW design ENS IIW FAT-71 curve derived from fatigue tests on fusion-welded joints is conservative in assessing the fatigue behavior of butt-lap friction stir welded (FSW) joints, especially in the high cycle regime.

Advances and Challenges in Design of Connections in Steel-Braced Frame Systems with In-Plane Buckling Braces

A new type of connection has been developed for steel-braced frame systems that allows the brace members to undergo compression buckling in the in-plane direction. In addition to the inherent benefits of in-plane buckling (IPB) braces that help in reducing the extent of damage to the non-structural components, the IPB brace system is also considered to be an efficient way of retrofitting existing seismically deficient structures. The use of the compact and thicker gusset plate prevents the distortion of the free edges and the additional torsional force demand on beams and columns. However, IPB braced frame systems are not frequently used in practice, primarily due to the absence of limit state design criteria. As a result, some prominent failure modes observed in IPB frame systems are out-of-plane brace buckling, yielding of gusset plates, interface weld failure, and fracturing of knife plates. Recent studies on the IPB braced system have resolved some of these problems, such as design criteria being developed to prevent OOPB (out-of-plane buckling) of the IPB braced system. Other challenges need to be studied to achieve reliable performance of the braced frame system. This study focuses on recent advances and potential areas of improvement to achieve an efficient IPB braced system in highly seismic areas.

Axial compression performance and optimum design of round-cornered square CFST with high-strength materials

This study investigates the axial compressive behaviour and optimum design of round-cornered square concrete-filled steel tubes (CFST) with ultra-high performance concrete (UHPC) and high-strength steel (abbreviated as RSUCFST). 11 RSUCFST specimens are designed with various steel strength grades, steel thicknesses and cross-sectional sizes for axial compressive experiments. The results show that the RSUCFST stub columns typically experience shear, mid-height buckling, multiple local buckling and weld failures. The load-displacement curves are quantitated into 5 types based on different confinement indices. Utilizing appropriately thicker and higher-strength steel tubes could likely better match the inner UHPC in designing RSUCFST stub columns, while simply enlarging the cross-sectional size considerably improves the ultimate bearing capacity but weakens the ductility of RSUCFST. The optimum steel ratio (αsc) of 0.09–0.4, width-to-thickness ratio (B/t) less than 45(235/fy)0.5 and confinement index (ξ) of 1.0–2.5 are recommended for RSUCFST stub columns by considering axial compressive behaviour, material efficiency and current code suggestions. Lastly, an analytical predicting model of axial bearing capacity of RSUCFST stub column is proposed according to the confinement in round-cornered square cross-section and well validated by experimental results.