Thick Welding Research Articles

Influence of pores on the fatigue life of welded joints and investigation of acceptance criteria defined in standard documents

AbstractInner defects in welded joints constitute concurrent sites for fatigue failure in welds, especially when high fatigue resistance is enforced at weld toe and root. Existing standards limit the size of pores and other inner defects in proportion to the sheet or weld thickness, but for larger dimensions cutoff values are in place. This leads to overly high acceptance criteria when it comes to thicker sheets, as for example those used for wind turbine towers. To analyze the influence of pores on the fatigue life, specimens with targeted pore sizes larger than the usually accepted were tested under fatigue loading. In the present study, a numerical model for fatigue assessment was developed based on the experimental results, which allowed further variance of pore sizes and locations. It is shown, that for larger weldments the acceptable pore size can be increased by up to 87.5 % without the necessity to reduce the applicable design curve. But, the location of the pore with regard to the specimens surface has a large influence, with pores in a distance to the surface smaller than 13 % of the sheet thickness leading to a reduction in the applicable design curve by up to 4 FAT classes — an effect that is currently not considered in common weld quality documents.

Predicting the Effect of RSW Parameters on the Shear Force and Nugget Diameter of Similar and Dissimilar Joints Using Machine Learning Algorithms and Multilayer Perceptron.

Resistance spot-welded joints are crucial parts in contemporary manufacturing technology due to their ubiquitous use in the automobile industry. The necessity of improving manufacturing efficiency and quality at an affordable cost requires deep knowledge of the resistance spot welding (RSW) process and the development of artificial neural network (ANN)- and machine learning (ML)-based modelling techniques, apt for providing essential tools for design, planning, and incorporation in the welding process. Tensile shear force and nugget diameter are the most crucial outputs for evaluating the quality of a resistance spot-welded specimen. This study uses ML and ANN models to predict shear force and nugget diameter responses to RSW parameters. The RSW analysis was executed on similar and dissimilar AISI 304 and grade 2 titanium alloy joints with equal and unequal thicknesses. The input parameters included welding current, pressure, welding duration, squeezing time, holding time, pulse welding, and sheet thickness. Linear regression, Decision tree, Support vector machine (SVM), Random forest (RF), Gradient-boosting, CatBoost, K-Nearest Neighbour (KNN), Ridge, Lasso, and ElasticNet machine learning algorithms, along with two different structures of Multilayer Perceptron, were utilized for studying the impact of the RSW parameters on the shear force and nugget diameter. Different validation metrics were applied to assess each model's quality. Two equations were developed to determine the shear force and nugget diameter based on the investigation parameters. The current research also presents a prediction of the Relative Importance (RI) of RSW factors. Shear force and nugget diameter predictions were examined using SHapley (SHAP) Additive Explanations for the first time in the RSW field. Trainbr as the training function and Logsig as the transfer function delivered the best ANN model for predicting shear force in a one-output structure. Trainrp with Tansig made the most accurate predictions for nugget diameter in a one-output structure and for shear force and diameter in a two-output structure. Depending on validation metrics, the Random forest model outperformed the other ML algorithms in predicting shear force or nugget diameter in a one-output model, while the Decision tree model gave the best prediction using a two-output structure. Linear regression made the worst ML predictions for shear force, while ElasticNet made the worst nugget diameter forecasts in a one-output model. However, in two-output models, Lasso made the worst predictions.

Intelligent Perception and Seam Tracking System for Thick Plate Weldments Based on Constant-Focus Optical Path

To achieve efficient and accurate thick plate welding, as well as to precisely extract and plan the paths of complex three-dimensional weld seams in large steel structures, this study introduces a novel vision-guided approach for robotic welding systems utilizing a constant-focus laser sensor. This methodology specifically targets and mitigates several critical shortcomings inherent in conventional vision-guided welding techniques, including limited detection ranges, diminished precision in both detection and tracking, and suboptimal real-time performance. For preprocessed weld images, an improved grayscale extreme centroid method was developed to extract the center of the light stripe. Furthermore, a sophisticated feature point extraction algorithm, which integrates a maximum distance search strategy with a least-squares fitting procedure, was developed to facilitate the precise and timely identification of weld seam characteristic points. To further optimize the outcomes, a cylindrical filtering mechanism was employed to eliminate substantial discrepancies, whereas local Non-Uniform Rational B-Spline (NURBS) curve interpolation was utilized for the generation of smooth and accurate trajectory plans. A spatial vector-based pose adjustment strategy was then implemented to provide robust guidance for the welding robot, ensuring the successful execution of the welding operations. The experimental results indicated that the proposed algorithm achieved a tracking error of 0.3197 mm for welding workpieces with a thickness of 60 mm, demonstrating the method’s substantial potential in the manufacturing sector, especially in the domain of automated welding.

Effects of plunge depth on the intermetallic compounds and mechanical properties of Al/Cu joints fabricated by micro friction stir welding

0.5 mm thick 6061-T4 Al and T2 Cu were butt-joined by micro friction stir welding (μFSW) at different plunge depths (D1=0.04 mm, D2=0.08 mm, D3=0.12 mm), the temperature distribution was studied by numerical simulation. The results showed that the control of thickness reduction and intermetallic compounds (IMCs) are the keys to obtain a joint with excellent performance. When the plunge depth is 0.04 mm, the peak temperature and residence time are both minimum, the reduction rate of the weld thickness and the proportion of agglomerated IMCs are minimum, which are 4 % and 9 % respectively, the average thickness of IMCs layer is only 112 nm. The tensile strength is the largest (94.1 % of Al base material), the joint fails in the heat-affected zone (HAZ) of Al side due to lowest hardness. Agglomerated IMCs (including Al2Cu and Al4Cu9) are formed in the upper nugget zone (NZ), and IMCs layer (including Al2Cu, AlCu and Al4Cu9) are formed in the lower NZ. As the plunge depth increases, the proportion of agglomerated IMCs and the thickness of IMCs layer increases. So, preferential sites of crack nucleation appear at the agglomerated IMCs. Subsequently, crack growth is exacerbated by the inherent brittleness of AlCu, resulting in ductile fracture in the upper NZ and cleavage fracture in the lower NZ.

Nonuniformity of Fatigue Properties of Two‐Sided Electron Beam Welded Joint of Superthick Titanium Alloy

ABSTRACTThe TC4 titanium (Ti) alloy has been widely utilized in various industries such as aerospace and shipbuilding, owing to its numerous advantages. Its exceptional properties have made it a material of choice for applications requiring high performance and reliability. The total weld thickness was 140 mm, and microstructures and high‐cycle fatigue properties were investigated at three different layers within the 140‐mm section. Experimental results show that the overlap area at two weld roots has the highest microhardness and largest nonuniformity of the overall joints, so the area is found to have the poorest high‐cycle fatigue properties. The microstructures in every layer of the weld metal of the joints were analyzed to determine the causes of the poor fatigue properties in the overlapping area at the weld roots. Significant amounts of α′ acicular microstructure are present in the weld metal of joints, while the overlap area at weld roots contains more α′ acicular microstructure with a finer size. Compared with other layers, the weld metal and base metal in Layer 2 (overlap area) have the largest microhardness gradient, where the stress concentration is more serious in the fatigue experimental process. Heat dissipation conditions was a critical factor for the inhomogeneity of microstructure and mechanical properties along the thickness direction of 140‐mm double‐sided electron beam welding joint. Fatigue damage (micropore) is formed at β phases in priority, and fatigue cracks propagate via series connection of micropores, indicative of transgranular ductile cracks.

Passive vision based three-dimensional seam tracking using a stereo vision system with a single HDR camera

Seam tracking is a crucial feature that an automatic welding system must have. The laser tracking algorithm offers high accuracy but faces challenges in identifying seams with extremely narrow gaps, as the deformation of the laser stripe becomes difficult to detect in such cases. In contrast, the passive vision-based algorithm can effectively capture narrow gap information from the welding scene, making it more suitable for recognizing narrow seams. However, most of proposed passive vision-based seam tracking is based on “teaching and playback” mode and can only realize planar tracking. In medium and thick steel plate welding, the workpieces are so large that the “teaching and playback” based control algorithm is unsuitable. Therefore, in this paper, a stereo vision system with a single camera and the corresponding calibration algorithm are developed to achieve three dimensional seam tracking. Compared to stereo system with dual camera, the proposed system is cheaper and easier to synchronize acquisition. Moreover, to get out of the “teaching and playback” control strategy, a vector control algorithm without cumulative error is proposed. Results of nine experiments show that the average error of the proposed seam tracking system is less than 1.0662mm and the maximum error is 1.8030mm.

Achieving microstructural homogeneity in the stir zone across thick AA6061 welds using self-reacting bobbin tool friction stir welding

This study focuses into strategizing the usage of self-reacting bobbin tool friction stir welding (SRBT-FSW) to obtain consistent microstructural homogeneity along the thickness of AA6061 aluminium alloy (AA) thick plates during welding. The SRBT-FSW technology, distinguished by its dual-shoulder design, represents a significant step forward in FSW by eliminating the requirement for a backing anvil and promoting balanced heat distribution. This study seeks to address the issues of maintaining uniform microstructural characteristics throughout the weld zone, which is crucial for the mechanical performance and durability of welded joints in structural applications. The experimental study entails the systematic welding of AA6061 plates of 6 mm thickness using a self-reacting bobbin tool under a fixed processing condition. Electron backscatter diffraction (EBSD) was used to characterize the grain structure and phase distribution over the weld. Mechanical parameters like as tensile strength and hardness were determined to establish correlations between microstructure and mechanical performance. The results demonstrated that SRBT-FSW significantly enhances microstructural homogeneity across the weld zone, leading to improved mechanical properties. In the Bottom Zone (BZ), a refined grain structure with an average grain size (AGS) of 3.53 µm and a random or weak texture was observed, contributing to enhanced hardness and mechanical performance, with an ultimate tensile strength (UTS) of 220 MPa. In contrast, the Top Zone (TZ) exhibited a coarser AGS of 4.33 µm with a pronounced {111} crystallographic texture, resulting in a slightly lower UTS of 205 MPa. The Middle Zone (MZ), influenced by the greater heat input from both the TZ and BZ, showed an intermediate AGS of 3.99 µm, predominantly oriented along the {101} plane, and achieved a UTS of 194 MPa, with a slight reduction in ductility. This study highlights the potential of self-reacting bobbin tool friction stir welding as a reliable method for making high-quality, homogeneous welds in thick aluminium plates and paving way for their wider application in the aerospace, automotive, and shipbuilding industries, where homogeneous microstructural qualities are of significant importance.

Intelligent Grinding System for Medium/Thick Plate Welding Seams in Construction Machinery Using 3D Laser Measurement and Deep Learning

With the rapid development of the construction machinery industry, thick plate welds are increasingly needing efficient, accurate, and intelligent processing. This study proposes an intelligent grinding system using 3D line laser measurement and deep learning algorithms to solve the problems of inefficiency and inaccuracy existing in traditional weld grinding methods. This study makes use of 3D line laser measurement technology and deep learning algorithms in tandem, which perform automated 3D measurement and analysis to extract key parameters of the weld seam, in conjunction with deep learning algorithms applied on image data of the weld seam for the automatic classification, positioning, and segmentation of the weld seam. The entire work is divided into the following: image acquisition, motion control, and image processing. Based on various weld seam detection algorithms, the selected model was MNet-based DeepLab-V3. An intelligent trimming system for welding seams based on deep learning was constructed. Experiments were conducted to verify the feasibility and accuracy of the 3D line laser measurement technology for weld seam inspections, and that the deep learning algorithm can effectively identify the type and location of the weld seam, thus predicting the trimming strategy. With an accuracy far superior to conventionally based methods in accurate detection and regrinding of weld surface defects, the system proves advantageous for improved weld regrinding productivity and quality. It was determined that the system presents significant advantages in reinforcing weld regrinding when it comes to efficiency and quality, thus initiating a paradigm of using intelligent treatments for medium/thick plate welds in the construction machinery industry.

Effects of welding displacement and energy director thickness on the ultrasonic welding of epoxy-to-polyetherimide based hybrid composite joints

This study aimed to develop robust thermoplastic-to-thermoset composite joints upon an ultrasonic welding process. The carbon fiber/epoxy composite was topped with a layer of polyetherimide (PEI) film by a co-curing process, making it “weldable” with the carbon fiber/PEI composite. The effects of welding displacement and thickness of the energy director (ED) on the welding process of the epoxy-to-PEI hybrid composite joints were investigated. The experimental results demonstrated that an optimal welding displacement existed for the best welding quality, whose value depended on the ED thickness. Given a certain ED thickness, the lap-shear strength (LSS) of the hybrid joints increased to a maximum value and then decreased as the welding displacement increased. By optimizing the displacement and ED thickness, a maximum LSS of 39.4 MPa was obtained for the hybrid joints. In which case, the level of the defects within the welding line was minimized, and the joints failed cohesively within the composite substrates.

Recrystallization behavior and strengthening mechanism of friction stir welded T-joint of Ti80 titanium alloy

In this study, Ti80 titanium alloy T-joints were produced by friction stir welding (FSW), and the joint temperature and residual stress distribution of the joints were analyzed by numerical simulation based on the ABAQUS platform, and the correlation between microstructure and performance of FSWed T-joint was investigated. The results show that the SZ is lamellar α grains due to the fact that the peak temperature of all joints exceeds β phase transus. The deformation and dynamic recrystallization behavior take place in the β phase region. During the subsequent cooling stage, the acicular α/α' phase is precipitated from refined prior β phase. The non-uniform heating and cooling results in the significant microstructure differences in the weld thickness direction. The top and middle of the SZ are composed of basketweave structure, while the bottom of the SZ shows a bimodal structure. The microhardness distribution along the skin shows a higher value in the weld area, and the weakest area is located in the HAZ due to recovery, resulting in a significant reduction in dislocation density of the weld. The tensile specimen breaks in the HAZ when it is stretched along the skin direction, while it breaks in a direction parallel to the skin when it is stretched along the stringer. The fracture mechanism of the joint changes from a hybrid mode of ductile and brittle fracture to ductile fracture as the rotation speed increases from 600 rpm to 750 rpm.

Determination Of Weld Thickness In Hollow Section Connection Under Local Buckling Effect

Hollow section profiles are widely used in the structural steel industry. An important point to take into consideration in such connections is the continuous transfer of internal forces from element to element. One of the measures taken to ensure this continuity is to use end plates. The connection between plates and elements is mainly provided by welds. The aim of this study is to determine an optimum weld thickness for connections subjected to local buckling of box-beam-columns under bending. Corner and circular fillet welds were used to join the designed plates with box columns and beams. Hollow section profile connections were experimentally studied in the Steel Structure Laboratory of the Department of Civil Engineering of Süleyman Demirel University. Results were used to develop numerical models. Ansys Workbench was used in numerical models to analyze the corner welds of different thicknesses and lengths depending on plate dimensions and to examine their behavior.

Microstructure and mechanical properties in VPPA keyhole welding of thick aluminum alloy

In this study, the 16 mm thick aluminum alloy was successfully welded using variable polarity plasma arc (VPPA) keyhole welding. The microstructure and microhardness distributions of the weld were systematically measured along its thickness and width. To evaluate tensile strengths along the weld thickness, tensile specimens were divided into upper, middle, and lower sections. The surface temperature distribution of the weld pool, along with the temperature profile through its thickness, was measured using thermometers and thermocouples. Numerical simulations were employed to calculate the pressure oscillations along the keyhole boundary and to analyze the temperature and flow field distributions of the VPPA. The findings initially revealed a homogeneous and refined microstructure distribution within the weld seam. The weld zone exhibited higher microhardness compared to the base metal (BM). The weld demonstrated a tensile strength of 187.86 MPa and an elongation of 24.76%, corresponding to 95.57% and 78.65% of the BM, respectively. The tensile strengths and elongations of the upper, middle, and lower sections displayed a similar distribution to that of the entire weld. The mechanism underlying the microstructure distribution of the weld was significantly influenced by the temperature distribution of the weld pool, dynamic pressure oscillations in the mushy zone, and fluid flow of the weld pool. Specifically, the mechanism whereby pressure oscillations fracture existing nuclei and generate multiple new nuclei has been proposed to explain the refined microstructure distribution. These findings provide crucial insights for optimizing VPPA keyhole welding technology, ensuring stable and high-quality welding of thick aluminum alloys.

Application of Convolutional Neural Networks for Classifying Penetration Conditions in GMAW Processes Using STFT of Welding Data

For manufacturing components with thick plates, such as in the heavy equipment and shipbuilding industries, the gas metal arc welding (GMAW) process is applied. Among the components that apply the thick plate GMAW process, there are groove butt joints, which are fabricated through multi-pass welding. Various welding qualities are managed in multi-pass welding, and the root-pass weld is controlled to ensure complete joint penetration (CJP). Currently, the state of complete joint penetration during root-pass welding is managed visually, making it difficult to confirm the penetration condition in real time. Therefore, there is a need to predict the penetration condition in real time. In this study, we propose a convolutional neural network (CNN)-based prediction model that can classify penetration conditions using welding current and voltage data from the root pass of V-groove butt joints. The root gap of the joints was varied between 1.0 and 2.0 mm, and the wire feed rate was adjusted. During welding, the current and voltage were measured. The welding current and voltage are transformed into a short-time Fourier transform (STFT) representation depicting the arc and wire extension lengths. The transformed dynamic resistance STFT information serves as the input variable for the CNN model. Preprocessing steps, including thresholding, are applied to optimize the input variables. The CNN architecture comprises three convolutional layers and two pooling layers. The model classifies penetration conditions as partial joint penetration (PJP), CJP, and burn-through, achieving a high accuracy of 97.8%. The proposed method facilitates the non-destructive evaluation of the root-pass welding quality without expensive monitoring equipment, such as vision cameras. It is expected to be immediately applied to the thick plate welding process using readily available welding data.

Establishing theoretical foundations for predicting the structural and morphological characteristics of diffusion-welded joints of the beryllium–copper composite

The paper presents the results of theoretical and experimental studies regarding the quality of diffusion welding of the beryllium–copper composite. Numerical investigations of the parameters of heterodiffusion of diffusants and the thickness of the Be–Cu pair welded joint under varying temperature-time conditions were conducted. The analytical examinations revealed that the thickness of the diffusion weld at the Be–Cu joint varies between 26 and 345 µm, with the temperature increasing from 800 to 1000 °C and the holding time ranging from 20 to 120 min. The calculated layer thickness during the diffusion welding of a Be–Cu pair at 800 °C for 2 h is 65 µm, with 15 µm on the beryllium side and 50 µm on the copper side. Notably, a CuBe3 intermetallic compound zone can form in the diffusion weld, which should be considered an adverse factor that reduces the mechanical properties. To theoretically substantiate the modification of the structure and properties of the diffusion zone, a numerical study of welding was carried out using a 10 μm thick nickel foil spacer, which is readily soluble in beryllium. It was demonstrated that after exposure to temperature-time conditions at 900 °C for 20 min, a 50 µm wide diffusion-bonded joint is formed. Its structure includes two single-phase zones of solid solutions based on copper and beryllium, as well as two two-phase regions consisting of solid solutions hardened with intermetallic compounds. Since the weld lacks structural zones consisting solely of intermetallic compounds (unlike when welding the Be–Cu diffusion pair), there are grounds to anticipate a reduction in the embrittling effect on the weld. The results obtained from the analytical studies can serve as the foundation for a theoretical prediction method for assessing the quality of diffusion welding of the beryllium–copper composite.

Metallurgical Characterization of Micro Friction Stir Spot Welding (μFSSW) Parameters on Similar Materials AA1100

The Micro Friction Stir Spot Welding (μFSSW) process is a metal plate welding technique with a relatively thin plate thickness. The advantages of this welding are the higher quality of the weld and the relatively low deformation. This study aimed to determine the effect of depth of penetration, dwell time, and tool geometry on the trend of material flow on the macro-structure of the welds produced in μFSSW technique using AA1100 thin aluminum plates. In this study, the parameters that are changed are the depth of the chisel, dwell time, and tool geometry. In this study, the parameters of the penetration depth were divided into 500 microns, dwell time was split into three lengths of time (300 ms, 500 ms, and 700 ms), and tool geometry was divided into two types of tool geometries (tool-1 and tool-2). In addition, the macro test was carried out to determine the depth of the weld, contour profile, and stretch macrostructure. The results of the macro test will be used to analyze the material flow relationship in each weld zone on the welding results of all existing parameters. Based on the results of the study, the effect of depth of penetration, dwell time, and tool geometry on the weld depth and metallography (hook width, hook height, and effective top sheet thickness) of welds using AA1100 thin plates is influential along with various tool geometries and the deeper the weld penetration and the longer stirring time, although the results are not always directly proportional.

Numerical investigation on stress concentrations of circular steel X joints

The most important reasons for the usage of steel as a building material are its high strength and ductile behavior, which can be defined as inelastic deformation or displacement capacity under a certain load. Steel frames are required to sustain the horizontal loads during an earthquake. The steel frames are classified as moment-resisting steel frames, concentric steel braced frames, eccentric braced steel frames, and buckling restrained braced frames. These steel frames can be designed with a high ductility level frame, limited ductility level frames, and ductility level mixed frames. In this study, stress concentrations due to the maximum compression force that may occur during an earthquake have been examined by the finite element method at the connection point of the circular cross-sectional braces of the central X-type braced steel frame with a high ductility level. Stress concentrations in the X-type brace were investigated depending on the variation of the cut surface required for the connection plate due to the change in the angle between the braces and the differences in the weld thickness applied in this region. In the models, the angle between the braces is designed as 60°, 75°, and 90° and the weld thicknesses are defined as 3.5 mm, 5 mm, and 7 mm. The results are obtained by applying the same compressive and tensile forces to the braces under the same boundary conditions and compared for these different models. It is obtained that the highest stress values occur along the direction of the tensile force in the tension profile and nearly at a distance of 5 mm after the cut. The maximum stress values decrease when the intersection angle between the braces increases from 60° to 90°.

Influence of physical properties of weld metal on hydrogen diffusion into the heat affected zone of heterogeneous welded joints

The paper presents the analytical solution of one-dimensional problem on hydrogen diffusion in butt heterogeneous welded joints. Such parameters as welded joint thickness, weld thickness, diffusion coefficients, solubilities and initial concentrations of hydrogen in the weld metal and base metal have been taken into account. The effects of microstructure on hydrogen kinetics in homogeneous and heterogeneous welded joints are considered. It is shown that hydrogen concentration in the heat affected zone (HAZ) to a great extent depends on the ratios of the initial concentrations, hydrogen diffusion coefficients and solubilities in the weld metal to those in the base metal. The concentration of hydrogen in the HAZ decreases by three orders of magnitude when welding martensitic steel with austenitic electrodes as compared to homogeneous joints.

A novel zero tool defect accelerated friction stir thin sheet welding technique for automotive light-weight structural component fabrication with dissimilar material

Frequent tool failure and rupturing pose significant challenges in friction stir welding (FSW) of thin dissimilar material sheets with diverse thermal and mechanical properties. These issues exacerbate at higher welding speed (ν), demanding greater precision in welding methodology. This paper presents a novel approach to weld 300 μm thin SS304 and 500 μm thick commercially pure aluminum sheets at ν up to 2400 mm/min using H13 tool without wear, obviating the necessity for expensive high-strength tool materials. Furthermore, the use of a pinless tool negates the requirement for an additional pinhole filling step, which is a prevalent challenge associated with pinned tools. The study unveils that higher tool tilt angle (α) reduces flash formation, leading to a higher effective weld thickness, thereby enhancing weld strength. The increased material extraction (2.048 mm3) from the weld center and higher heat generation (7.6%) compared to the pinless tool imposes a speed limit of 300 mm/min for the pinned tool. The thicker layer (4.9 μm) of inter-metallic compounds (IMC) formed at lower ν showed maximum joint strength (70.03% of base Al). The fracture behavior indicates cleavage facet formation becomes more frequent at higher ν, diminishing joint ductility. With a distortion-free, high lap shear strength and enhanced ν, this novel joining method meets the needs of industrial mass production.

Guided wave-based crack detection in U-shaped flexural plate butt welds

Based on the guided wave, a crack detection method for U-shaped flexural plate (UFP) butt welds is established to realize damage localization and quantitative identification. Firstly, the semi-analytical finite element (SAFE) method was used to obtain the dispersion curve in a plate with weld by discretizing the cross-section and then solving the characteristic equation. Subsequently, numerical studies were performed to investigate the mode conversion and energy transfer efficiency in weld bending. Then the method was determined after the wave packet analysis of voltage responses under different damage conditions. Finally, a validation experiment was conducted in an actual UFP butt weld. The result indicates that there exist 10 guided wave modes in a plate with weld at 150 kHz, while only 2 modes in a flat plate; For curvature radius of weld bending substantially greater than the weld thickness, the guided wave energy mainly passes through the bending in the form of transmitted waves and the reflected wave formed in the bending can be ignored; The damage can be located with the defect echo of the specific guided wave and the error distance only accounting for 1.5% of the total weld length. It is effective to take wavelet energy as an indicator to characterize the damage degree. The method significantly improves crack detection efficiency and provides a scientific basis for monitoring similar structures.

Nonlinear mechanical behavior and stress amplification effect correction of thin plate welded structure considering initial deformation

With the continuous development of light weight of ships, thin plate welded structures are widely used in superstructure of large hull structures and high-speed boats. However, the thin-plate welded structure has a special nonlinear mechanical behavior because of its small stiffness, more complicated welding deformation. The nonlinear mechanical behavior of thin plate welded structure is mainly caused by large slenderness ratio and complex initial buckling deformation, which can be characterized and quantified by defining global deformation angle αG and local deformation angle αL. Because of the welding angle deformation and welding dislocation, there is obvious stress amplification effect at the welding corner, but the traditional stress amplification correction formula is only suitable for thick plate welding structure. Aiming at the nonlinear mechanical behavior and secondary bending moment effect of thin plate welded structure, an analytical model of thin plate welded structure with initial deformation is established by combining theoretical derivation and numerical method. The results show that the additional bending moment effect caused by local welding deformation angle cannot be ignored. Finally, combined with a series of fatigue tests, the additional bending moment caused by bending deformation and angular deformation of typical welded joints is analyzed, and the notch stress field and fatigue strength correction of thin plate welded structures with initial defects are realized.