Fillet Welds Research Articles

Study on Blowhole Detection in Fillet Welded Sheet of Lap Joint by Laser Ultrasonic Technique

Study on Blowhole Detection in Fillet Welded Sheet of Lap Joint by Laser Ultrasonic Technique

Line-Structured Light Fillet Weld Positioning Method to Overcome Weld Instability Due to High Specular Reflection

Fillet welds of highly reflective materials are common in industrial production. It is a great challenge to accurately locate the fillet welds of highly reflective materials. Therefore, this paper proposes a fillet weld identification and location method that can overcome the negative effects of high reflectivity. The proposed method is based on improving the semantic segmentation performance of the DeeplabV3+ network for structural light and reflective noise, and, with MobilnetV2, replaces the main trunk network to improve the detection efficiency of the model. To solve the problem of the irregular and discontinuous shapes of the structural light skeleton extracted by traditional methods, an improved closing operation using dilation in a combined Zhang-suen algorithm was proposed for structural light skeleton extraction. Then, a three-dimensional reconstruction as a mathematical model of the system was established to obtain the coordinates of the weld feature points and the welding-torch angle. Finally, many experiments on highly reflective stainless steel fillet welds were carried out. The experimental results show that the average detection errors of the system in the Y-axis and Z-axis are 0.3347 mm and 0.3135 mm, respectively, and the average detection error of the welding torch angle is 0.1836° in the test of a stainless steel irregular fillet weld. The method is robust, universal, and accurate for highly reflective irregular fillet welds.

Experimental and numerical investigation on the dynamic response and damage of large-scale multi-box structure under internal blast loading

Internal blast is different from external or air blast for the reason of internal blast load is much more complicated and more destructive to target structures. The present work presents a large-scale experiment on multiple steel box structure under confined blast loading. A multi-box structure specimen with a dimension of 7.5 m × 2.9 m × 2.2 m was designed and field blast test with 1.782 kg TNT detonated inside this model was carried out. The damage features and dynamic response of the specimen were analyzed. The plates near the explosive suffer from strong impact and result in some fragments with high velocity which are destructive to other structural members. Meanwhile, the dynamic response processes were recorded by using the high-speed photography system. The response process of the whole model can be divided into two different stages, namely, localized damage response stage and integral vibration stage. In addition, numerical model considering both double-sided and single-sided fillet welding of this large-scale experiment were built, the dynamic response and the propagation of internal blast wave were analyzed. The numerical studies show that, to achieve a good consistency with the experiment, the failure strain for double-sided and single-sided fillet welding should be set to 0.1 and 0.08 respectively for such large-scale structure under explosive load. Finally, several suggestions for the design of multi-box structure are put forward based on the experimental and numerical investigations.

A State of the Art Review of Fillet Welded Joints.

Fillet welded joints are commonly used in steel structures for various engineering applications such as buildings, bridges, railways, ships, and marine structures. Fillet welded joints are generally subjected to static and fatigue loading, resulting in failures of such welded joints. A number of experimental and numerical investigations on the strength and failure behaviour of fillet welded joints have been published. This paper presents a comprehensive review of research results on the static strength, fatigue life, and thermal performance of fillet welded joints. The review covers the various influential factors, such as loading direction, weld geometry, grades of steel, filler materials, welding process, weld penetration, strength mismatch of weld metal, and post-welded treatment. In total, 100 papers were critically reviewed, which were published from 1970 till date. The key findings and research developments on fillet welded joints are summarised. It was found that the transverse fillet welded joints have a higher static strength than the longitudinal fillet welded joints. Filler materials, post-welded treatment, and penetration of weld metal can offer significant strength enhancements in terms of their static and fatigue strength. Lastly, research gaps have been found in the existing body of knowledge, which will help guide future research.

Direction-independent laser-GMA hybrid welding with coaxial wire feed and annular beam

Conventional laser gas metal arc hybrid welding (LB-GMA hybrid welding) is used as an efficient joining process in several high-tech steel processing production facilities. However, the use of the LB-GMA hybrid welding is often limited to the joining of linear weld seams as the welding process has a preferred welding direction due to lateral positioning of the laser beam and welding wire electrode. Reorienting the welding direction, therefore, often results in weld defects since changing the welding direction also requires a geometric manipulation of the GMA torch in relation to the laser beam optics. This means a considerable additional effort that is necessary if this efficient welding process is to be used for geometrically complex weld seam contours. Furthermore, the conventional LB-GMA hybrid welding process has a high adjustment complexity. Within this work, a direction-independent laser GMA hybrid welding head with an annular beam and coaxial wire feed is used. The annular laser beam with homogenous intensity profile is formed by a special processing head, split and reassembled around the coaxial wire. Due to the coaxial arrangement of the wire electrode to the annular beam, the hybrid process is in theory direction independent. As a result, there should not be any irregularities in the weld seam, when the welding direction is changed. The annular beam considerably reduces the complexity of adjustment and improves reproducibility. The focus of this work is to qualify the process for joining geometrically complex weld contours and to investigate possible advantages of the directional independence of the coaxial LB-GMA hybrid welding process. For this purpose, fillet welds in lap joint configuration with a sheet thickness of 2 mm each at different weld contours (different direction changes, corners, radii) are discussed. By performing a DoE-based sensitivity analysis, influencing factors on the quality of the generated weld are analysed.

Weld toe versus root fatigue failure mode and governing parameters: A study of aluminum alloy load-carrying fillet joints

In load-carrying fillet welded connections, two fatigue failure modes are possible i.e. weld toe cracking and weld root cracking. The fatigue life associated with weld root cracking is typically much lower than weld toe cracking, exhibiting a wider scatter band, especially for welded aluminum alloys. This paper examines fatigue failure mode transition behaviors in load-carrying fillet welds made of aluminum and their governing parameters, among plate thickness, weld penetration, joint misalignment, weld material, and ultrasound impact peening(UIP). Through both experimental and theoretical studies, a quantitative fillet weld sizing criterion was proposed for avoiding weld root cracking in fillet-welded aluminum connections.

Review of the Definition of Weld Penetration, Depth of Fusion and Throat Thickness on Fillet Welds

In this study, definitions of Weld Penetration (WP), Depth of Fusion (DOF) and Throat Thickness (TT) in fillet welds according to related standards are evaluated. Each standard makes its own definition related to WP, DOF and TT. Moreover, when looking at these standards, it is seen that definitions are always made in terms of unit of length. In many studies, assessment of fusion or penetration (FOP) rate on fillet welds is performed as the ratio of the maximum FOP depth to the material thickness. Depth assessment taking into consideration unit of length is not ideal for accurate evaluation of FOP rates especially on fillet welds. In the evaluation made in terms of unit of length, FOP rate can be approximately 50 percent more than the evaluation made in terms of unit of area. Method taking into consideration unit of area will be more suitable as it allows accurate assessment of FOP rates in welded joints. In this review, in addition to evaluation of the definitions of standards, it is also suggested that the evaluation of FOP rate on fillet welds should be determined in terms of unit of area rather than length.

Dynamic behaviors of butt welds and fillet welds under intermediate strain rate

Dynamic properties of widely used butt welds and fillet welds would affect the behavior of welded joints in steel structures under dynamic loading. In the open literature, there are very limited studies on the behavior of butt welds and fillet welds under dynamic loads, such as impact and blast. In this study, a compression-tension conversion experimental facility was specifically designed for dynamic testing of butt welds and fillet welds at intermediate strain rates. The steel plate (SP), butt weld (BW), tensile fillet weld (TFW), and shear fillet weld (SFW) at different strain rates were tested. The corresponding quasi-static tests were also performed for comparison. The strength, failure mode, and fracture strain of the BW, TFW and SFW under static and dynamic loads were compared and analyzed. The effects of weld strength matching or overmatching on butt welds and fillet welds were also investigated. The results showed that with the increase in strain rate, the strength of the BW, TFW, and SFW increase; the fracture strain of the BW also increases but those of the TFW and SFW decrease. The failure modes of the BW and TFW were significantly influenced by the weld strength matching, whilst that of the SFW was less affected. Two empirical formulae were proposed to predict the dynamic strength of different steel materials and butt welds as well as fillet welds.

Mechanical behaviour of high strength steel T-stubs at elevated temperatures: Experimental study

At elevated temperatures, an experimental study on 28 high strength steel (HSS) T-stubs specimens was carried out by tensile tests, to reveal the mechanical performance of HSS T-stubs. The mechanical property and failure mode of each HSS T-stub specimen is obtained from the tensile tests. Further, the applicability of Eurocode 3 Part 1–8 both at ambient and elevated temperatures is verified with experimental results of HSS T-stubs. The experimental study includes 28 HSS T-stub specimens varying in flange strength, flange thickness, bolt strength, bolt diameter, bolt location, and temperature, to explore the effects of various influencing factors on the mechanical properties of HSS T-stubs. Compared with the deformation of the ambient-temperature experiments, the plasticity of the flange is not fully developed and the flexural deformation of the flange is small at elevated temperatures. When the bearing capacity of the flange is slightly lower than that of other components, the experimental results indicate that the predictions of Eurocode 3 Part 1–8 on failure modes are applicable for HSS T-stubs at elevated temperatures, while its theoretical predictions on the HSS T-stubs with large d (the distance between the bolt centre and the fillet weld) are inaccurate at ambient temperature. When e/d (e is the distance from the flange edge to the bolt centre) is less than 1, the initial stiffness and tensile load-bearing capacity will be significantly reduced by increasing d, because the increasing d will significantly improve flexural deformation and reduce flexural stiffness of the flange. Moreover, the initial stiffness of HSS T-stubs is overestimated by Eurocode 3 Part 1–8 both at ambient and elevated temperatures, especially the T-stubs with thick flanges, while the tensile load-bearing capacity of HSS T-stubs is conservatively predicted.

Investigation of fatigue strength of root of lap fillet welds of thin sheet and improvement method

This study investigates the dominant factors of fatigue strength at the root of thin-sheet lap fillet arc welds, which are frequently used in automobile chassis components. A method to improve the root fatigue strength was investigated. The direction of fatigue crack propagation at the root coincided with the direction of maximum circumferential stress range. The circumferential stress was reduced by increasing the distance from the toe to the root (penetration width). Fatigue strength originating from the root was improved in welded joints where the penetration width was increased by adjusting the welding aim point and heat input.

Research on robust laser vision feature extraction method for fillet welds with different reflective materials under uncertain interference

Welding seam tracking is an important means to improve welding quality and realize intelligent welding, among which, laser vision feature extraction for weld seam is one of the important research fields of welding seam tracking. However, current laser vision weld feature extraction methods often target single-material weldments. For weldments of different materials (different reflections), the generality and robustness of the existing methods are insufficient. To address this problem, the fillet welds of different reflective materials such as carbon steel (weakly reflective material), stainless steel (medium reflective material) and aluminum alloy (strongly reflective material) are used as research objects, and the feature extraction method of fillet welds of different reflective materials under interference is studied. According to the morphological characteristics of noise in laser stripe images, the noises are divided into four types. A prior morphological judgment method (PMJM) is proposed to filter out these four kinds of noise. The method is mainly divided into four steps, each step removes one kind of noise, and finally completes the removal of all noises. Since PMJM is greatly affected by the extraction accuracy of the initial frame, a fillet weld feature extraction method based on dual-slope judgment and double least squares fitting is proposed, which can accurately extract the characteristics of the fillet weld in the first frame when there has no arc noise. The experimental results show that the error of the proposed method is within ± 0.13 mm in the X-axis and Y-axis directions under three different reflective materials, and the average computation time of the three materials is 88 ms. The results show that the method has the advantages of strong robustness and high precision, and can meet the requirements of real-time welding.

Fatigue assessment of fillet weld in steel bridge towers considering corrosion effects

Field inspection shows that the fillet weld in steel bridge towers may be subjected to corrosion and fatigue loading simultaneously. To ensure the structural safety in the service life, corrosion effects on the fatigue life of the fillet weld in steel towers were investigated in this study. A prediction procedure of the fatigue life of the weld was firstly proposed based on the fracture mechanics method and verified by the test results. Three types of corrosion effects, pitting corrosion at the initial crack, pitting corrosion near the initial crack, and the corrosion fatigue crack growth were considered. Three corrosion levels were also defined under different corrosive environments. By taking the Third Nanjing Yangtze River Bridge as an example, a modified finite element (FE) model integrated with the local shell model was established to analyze the stress variation of the fillet weld in steel towers. Based on the stress influence lines, the maximum stress range was obtained under the vehicle load. Fatigue assessment of the fillet weld was finally performed considering the corrosion effects. The result shows that the remaining fatigue life of the fillet weld was greatly reduced by the corrosion pits at the initial crack or the interactions of corrosion and fatigue. However, since the tensile stress range was small in the steel bridge towers, the fatigue performance of the fillet weld considering the corrosion effects can still meet the requirements of the code specification.

A new orthotropic steel deck system incorporating two novel structural details

The fatigue and fracture of orthotropic steel decks (OSDs) have compromised the toughness and life of steel bridge. The low fatigue resistance of structural detail design is the primary factor to result in the fatigue fracture of OSDs. To develop OSDs with a high fatigue resistance, two novel structural details for OSDs including rib-to-deck welded joint and rib-to-floorbeam welded joint were proposed in this study. Novel rib-to-deck welded joint was formed with a double-side fillet weld seam, which improves the fatigue performance of rib-to-deck welded joint by eliminating the crack-like defects at the weld root of traditional rib-to-deck welded joint. Novel rib-to-floorbeam welded joint is proposed with an uninterruptible weld seam and a smiley cutout, which relieves the cyclic stress from out-of-plane bending of floorbeam and transfer the potential large stress ranges from the weld seam to the smiley cutout. The comparisons of traditional and novel structural details were carried out by the finite element analysis and fatigue tests. The nominal stress method was used in this study to evaluate the fatigue performance. The results indicate that fatigue resistance corresponding to 2 million cycles (FAT) of novel rib-to-deck welded joint is higher than the traditional rib-to-deck welded joint (FAT = 95 MPa), and FAT of novel rib-to-deck welded joint is over 116 MPa. The fatigue strength of the novel rib-to-floorbeam welded joint with a smiley cutout (FAT > 140 MPa) is higher than that of traditional rib-to-floorbeam welded joint (FAT = 98 MPa). The proposed novel structural details can be effective to improve the fatigue resistance of OSDs.

Fatigue Tests and Analysis on Welded Joints of Weathering Steel.

To investigate the fatigue performance of vertical web stiffener to deck plate welded joints in weathering steel box girders, six specimens of the weathering steel (WS) Q345qNH, four specimens of WS Q420qNH, and four specimens of the plain carbon steel (CS) Q345q for comparison were tested by a vibratory fatigue testing machine, considering different steel grades, yield strengths, stiffener plate thicknesses, and weld types. The fatigue strength was evaluated based on S-N curves and the crack propagation was analyzed by linear elastic fracture mechanics (LEFM). The results show that the fatigue crack of the welded joints was initiated from the end weld toe of the deck plate and subsequently propagated both along the thickness of the deck plate and in the direction perpendicular to the stiffener plate. The fatigue crack initiation and propagation life of WS Q345qNH specimens were longer than those of CS Q345q specimens. The fatigue crack propagation life of WS Q345qNH specimens was longer than that of WS Q420qNH specimens, while the initiation life bore little relationship to the yield strength. Increasing the stiffener plate thickness effectively delayed crack initiation and slowed down its propagation. Compared with fillet welds, full penetration welds extended the fatigue crack propagation life, while no significant improvement was implied for the initiation life. The WS and CS specimens could be classified as having the same fatigue strengths by nominal stress, hot spot stress, and effective notch stress approaches, which were FAT 50, FAT 100, and FAT 225, respectively. Meanwhile, their material constants for LEFM were relatively close to each other.

Obliquely Loaded Welded Attachments Fatigue Categorization in Steel Bridges

The detail category for base metal at the toe of transverse stiffener-to-flange and transverse stiffener-to-web fillet welds is defined as Category C' in the current AASHTO LRFD Bridge Design Specifications (2020, 9th Ed.) and as Category C in the AREMA (2020) Manual for Railway Engineering and the AISC Steel Construction Manual (2017, 15th Ed.). These are often referred to as short attachments due to their very short length (< 2 in.) in the direction of the primary stress range. Sometimes it is necessary to place a stiffener or a connection plate at an angle different than perpendicular to the web, such as in skewed bridges. Increases in the effective length of the stiffener along the flange in the longitudinal direction are seen as the plate is rotated away from being perpendicular to the web. The other extreme occurs when the stiffener is rotated completely 90° and is perfectly parallel to the web and the longitudinal stress range. In this instance, this is identical to the long attachment and classified as Category E (length > 4 in.). The current specifications and manuals, on the other hand, do not have classification on how to address the potential effects on fatigue performance of angles in between these two extremes. This paper summarizes finite element analysis studies based on local stress and structural hot-spot stress approaches that were conducted to investigate and classify welded attachments placed at angles other than 0° (transverse) or 90° (longitudinal) for a variety of stiffener geometries and thicknesses. This study includes new classification for incorporating the findings into the AASHTO LRFD Bridge Design Specifications, AREMA Manual for Railway Engineering, and the AISC Steel Construction Manual.

Experimental Investigation into the Capacity of Concentrically Loaded Steel Connections with Pretensioned High-Strength Bolts and Longitudinal Fillet Welds in Combination

This paper presents the results of an experimental study aiming to investigate the behavior of steel connections that combine pretensioned high-strength bolts and longitudinal fillet welds on a common faying surface. A total of 75 double-shear tension splices were tested under direct tension loading to quantify the effect of various connection variables on the load-deformation behavior of the connection. These variables include the (1) bolt pattern (2×2 and 2×3), (2) bolt size (3/4 in. and 1 in.), (3) bolt grade (ASTM F3125 Grade A325, A490, and F1852), (4) bolt pretensioning method (turn-of-nut and tension control bolts), (5) faying surface class (Class A and B), and (6) weld/bolt strength ratio. The variation in the connection characteristics covered a wide range of weld/bolt strength ratios from 0.50 to 2.00. The bolts were installed in oversized holes, and the specimens were assembled in a negative bearing condition to allow for a maximum slip distance. The load-deformation behavior of the combination connections was recorded and compared to that of the bolted- and welded-only control specimens. In all tests, the addition of welds increased the capacity of the connection. The investigation shows that the capacity of the combination connection with pretensioned high-strength bolts and longitudinal fillet welds can be computed by adding the capacities of the individual connecting elements while considering the strain compatibility.

Interlayer behavior investigation of box profile shear connectors in steel-concrete-steel sandwich structures

The present study introduces box profile (BP) shear connectors for steel-concrete-steel sandwich composite structures. The shear connectors were joined to steel faceplates using slot and fillet welding. The advantages of this shear connector include unlimited thickness, easy application, high strength, and low cost compared to other available shear connectors. A total of eight experimental specimens were fabricated to evaluate the interlayer shear behavior of BP shear connectors. The effects of geometric parameters, including the BP thickness, BP width, concrete thickness, and BP configuration, on the shear behavior of the BP shear connectors were studied. The results of experiments and comparison with other shear connectors show that BP shear connectors have improved the composite behavior and interlayer shear strength. Also, the effect of geometrical parameters was analyzed on the shear strength. The BP shear connector is dependent on its width. A 20-mm rise in the width of the BP connector increased the ultimate strength and energy absorption by 76% and 41%, respectively. The use of BP shear connectors in a V-WEB configuration reduced ductility by 52% (from 501.4 to 239 kN.mm) and initial strength by 43% (from 192 to 109 kN). Therefore, V-WEB BP shear connectors are not recommended. Then, a model was offered to predict the load-slip behavior of BP shear connectors and was compared with the relations of previous researchers. Finally, the proposed shear connector was compared with different available shear connectors in terms of strength and load-slip behavior. It can be concluded that the BP shear connector had higher stiffness and ultimate strength than other shear connectors, e.g., stud bolt, bi-steel, J-hook, CSC, and headed stud shear connectors.

Effect of local heat treatment on residual stresses in an in-service repair welded pipeline

Abstract The multi-pass fillet welds of casing pipe were welded onto the in-service pipeline, which is widely used in pipeline repairs. However, the residual stress of repairing welded joints is larger, and it is easy to cause cracks in the heat-affected zone. In this paper, the local heat treatment was used to adjust the residual stress of the repaired welded joint of the in-service pipeline. The results show that the local heat treatment is very useful for reducing the residual stress of the repair welding joint of the in-service pipeline.

Research on Automatic Welding Technology of Vertical Fillet Weld

In this paper, the key automatic welding technology of one-time forming the opposite fillet weld is deeply studied. With the help of the gas electric vertical welding technology and its innovation, it was successfully applied to the test and exploration of the one-time forming technology of automatic welding and equipment of the vertical fillet weld. Major breakthroughs have been made in tackling the key automatic welding technologies of one-time forming vertical fillet welds, filling the gap in this technology in the welding field and accumulating valuable experience for further research and progress of this technology.

Design of Single-Sided Fillet Welds under Transverse Load

Design of Single-Sided Fillet Welds under Transverse Load