Welded Steel Plates Research Articles

Thermo-mechanical toner transfer for high-quality digital image correlation speckle patterns

The accuracy and spatial resolution of full-field deformation measurements performed through digital image correlation are greatly affected by the frequency content of the speckle pattern, which can be effectively controlled using particles with well-defined and consistent shape, size and spacing. This paper introduces a novel toner-transfer technique to impress a well-defined and repeatable speckle pattern on plane and curved surfaces of metallic and cement composite specimens. The speckle pattern is numerically designed, printed on paper using a standard laser printer, and transferred onto the measurement surface via a thermo-mechanical process. The tuning procedure to compensate for the difference between designed and toner-transferred actual speckle size is presented. Based on this evidence, the applicability of the technique is discussed with respect to surface material, dimensions and geometry. Proof of concept of the proposed toner-transfer technique is then demonstrated for the case of a quenched and partitioned welded steel plate subjected to uniaxial tensile loading, and for an aluminum plate exposed to temperatures up to 70% of the melting point of aluminum and past the melting point of typical printer toner powder.

Systematic investigation of the fatigue performance of a friction stir welded low alloy steel

A comprehensive fatigue performance assessment of friction stir welded DH36 steel has been undertaken to address the relevant knowledge gap for this process on low alloy steel. A detailed set of experimental procedures specific to friction stir welding has been put forward, and the consequent study extensively examined the weld microstructure and hardness in support of the tensile and fatigue testing. The effect of varying welding parameters was also investigated. Microstructural observations have been correlated to the weldments’ fatigue behaviour. The typical fatigue performance of friction stir welded steel plates has been established, exhibiting fatigue lives well above the weld detail class of the International Institute of Welding even for tests at 90% of yield strength, irrespective of minor instances of surface breaking flaws which have been identified. An understanding of the manner in which these flaws impact on the fatigue performance has been established, concluding that surface breaking irregularities such as these produced by the tool shoulder’s features on the weld top surface can be the dominant factor for crack initiation under fatigue loading.

조선 및 해양플랜트 구조물의 불안전 파괴방지 설계기술

Recently, there have been the increase of ship size and the development of oil and gas in arctic region. These trends have led to the requirements such as high strength, good toughness at low temperature and good weldability for prevent of brittle fracture at service temperature. There has been the key issue of crack arrestability in large size structure such as container ship. In this report for the first time, crack arrest toughness of thick steel plate welds was evaluated by large scale ESSO test for estimate of brittle crack arrestability in thick steel plate. For large structures using thick steel plates, fracture toughness of welded joint is an important factor to obtain structural integrity. In general, there are two kinds of design concepts based on fracture toughness: crack initiation and crack arrest. So far, when steel structures such as buildings, bridges and ships were manufactured using thick steel plates (max. 80~100mm in thickness), they had to be designed in order to avoid crack initiation, especially in welded joint. However, crack arrest design has been considered as a second line of defense and applied to limited industries like pipelines and nuclear power plants. Although welded joint is the weakest part to brittle fracture, there are few results to investigate crack arrest toughness of welded joint. In this study, brittle crack arrest designs were developed for hatch side coaming of large container ships using arrest weld, hole, and insert technology.

Investigation of Clamping Effect on the Welding Sub-surface Residual Stress and Deformation by Using the Ultrasonic Stress Measurement and Finite Element Method

In this study, sub-surface residual stress and deformations, produced by the welding process, are investigated by using ultrasonic stress measurement method and finite element (FE) simulation. The FE analysis is employed to evaluate the residual stresses and deformations caused by the tungsten inert gas welding of 304L stainless steel plates. Residual stresses obtained from the FE analysis are then used to validate results of the ultrasonic stress measurement method, which is fulfilled by employing longitudinal critically refracted ( $$L_{CR})$$ waves. By using four different frequencies of ultrasonic probes, the sub-surface residual stress fields are mapped in four different depths of the examined material. Two different plates are welded with and without the use of clamp to investigate the clamping effect on the residual stress and deformation. By employing the through-thickness measurement of residual stresses, the clamping effect on the sub-surface distribution of the residual stresses is also studied. As a result, the $$L_{CR}$$ ultrasonic method is accurate enough to distinguish the surface and sub-surface residual stresses in the clamped and non-clamped welding plate. Consequently, the longitudinal residual stresses have been increased by using the clamp during the welding of stainless steel plates. However, using the clamp significantly influences the amount and distribution of longitudinal residual stress in the base metal. Regarding the welding deformation results, it has been concluded that employing the clamp considerably decreases the deformations of the stainless steel plates.

Experimental Investigation of Fatigue Crack Propagation in Residual Stress Fields

This work is on the interaction of residual stresses and fatigue cracks in welded steel plates. A longitudinal dummy weld was used to create high tensile residual stresses in axial loading direction. The fatigue crack was trained to start at an artificial notch and propagated through a field of high tensile residual stresses. The fatigue crack propagation as well as the re-distribution of residual stresses were studied in detail by combined experimental methods. The mean stress was varied as well as the residual stress state of the samples used. Samples were tested as-welded as well as stress-relieved at R = (σmin/σmax) = 0, R = -1 and R = -3. The materials used were a typical fine grained construction steel S355J2+N as well as a high strength quenched and tempered steel S960QL.It is shown how residual stress are degraded and in which way moderate residual stresses affect the fatigue strength of welded steel plates. The combined effect of residual stresses and load mean stresses is discussed.

ステンレス鋼の高輝度・高出力レーザ溶接時の溶融池内湯流れに及ぼす溶接速度の影響の三次元X線透視その場観察法による解明

This research was performed with the objective of clarifying the effect of welding speed on melt flows during melt-run welding of SUS304 stainless steel plates with a 6-kW power laser beam on the basis of three-dimensional X-ray transmission in-situ observation. As welding speed increased from 25 mm/s to 250 mm/s, three kinds of welds characterized by porosity formation, no defects or underfilling due to spatters were produced. The average and the maximum values of measured melt flow velocity were three and ten times higher than the welding speed, respectively. Two kinds of circulation flows at the inlet or the tip of a keyhole were confirmed to control heat transfer in a molten pool. It was found that the circulation flows were so sensitive to the welding speed that bubbles resulting in porosity or spatters were often formed. Accoriding to the X-ray observation of the spatters formation with tungsten carbide (WC) tracers, as the melt flow rose along the keyhole wall, the velocity was accelerated from 0.24 m/s to 0.54 m/s near the keyhole inlet. Consequently, the melt flows made the convex surface behind the keyhole grow higher, resulting in spattering.

Oblique laser irradiation technique for vertical welding of thick steel plates employing hot-wire laser welding

Oblique laser irradiation technique for vertical welding of thick steel plates employing hot-wire laser welding

A novel hybrid intelligent optimization model for twin wire tandem co-pool high-speed submerged arc welding of steel plate

In order to solve the welding formation defects of undercut and hump caused by the irrationality selection of parameters at a high welding speed more than 100cm/min in twin wire tandem co-pool submerged arc welding, a novel hybrid intelligent optimization model for twin wire tandem co-pool high speed submerged arc welding is proposed. This model combines local mean decomposition (LMD), energy entropy, back propagation neural network (BPNN) and particle swarm optimization algorithm (PSO). LMD is employed to decompose the collected welding current signal, excavate the underlying arc feature information related to the rationality of parameters and welding quality of welding seam formation appearance and sectional morphology. The energy entropy is used as the quantificational parameter to describe the rationality of parameters and welding quality. The relationship between the welding parameters and the energy entropy is established by BPNN, and the welding parameters are automatically obtained by the PSO. The application shows that the model is able to reliably achieve the optimization selection of welding parameters to guarantee welding quality.

A novel inverter twin wires high effect submerged arc welding equipment for steel plate welding

A novel inverter twin wires high effect submerged arc welding equipment for steel plate welding

Prediction of GMA Welding Characteristic Parameter by Artificial Neural Network System

Nowadays, demand for automated Gas metal arc welding (GMAW) is growing and consequently need for intelligent systems is increased to ensure the accuracy of the procedure. To date, welding pool geometry has been the most used factor in quality assessment of intelligent welding systems. But, it has recently been found that Mahalanobis Distance (MD) not only can be used for this purpose but also is more efficient. In the present paper, Artificial Neural Networks (ANN) has been used for prediction of MD parameter. However, advantages and disadvantages of other methods have been discussed. The Levenberg–Marquardt algorithm was found to be the most effective algorithm for GMAW process. It is known that the number of neurons plays an important role in optimal network design. In this work, using trial and error method, it has been found that 30 is the optimal number of neurons. The model has been investigated with different number of layers in Multilayer Perceptron (MLP) architecture and has been shown that for the aim of this work the optimal result is obtained when using MLP with one layer. Robustness of the system has been evaluated by adding noise into the input data and studying the effect of the noise in prediction capability of the network. The experiments for this study were conducted in an automated GMAW setup that was integrated with data acquisition system and prepared in a laboratory for welding of steel plate with 12 mm in thickness. The accuracy of the network was evaluated by Root Mean Squared (RMS) error between the measured and the estimated values. The low error value (about 0.008) reflects the good accuracy of the model. Also the comparison of the predicted results by ANN and the test data set showed very good agreement that reveals the predictive power of the model. Therefore, the ANN model offered in here for GMA welding process can be used effectively for prediction goals.

Roadmap proposal for determining the variables of pulsed TIG welding process applied to welding of thin plates

In pulsed TIG welding, the current varies between two well-defined energy levels in a given frequency, thus being necessary to regulate a set of variables consisting of the peak current, peak time, background current, background time and the welding speed. Yet despite being a widespread technique, in practice, these welding variables are often regulated arbitrarily. This can lead to inefficient use of the pulsed current regarding the end result of the weld and aspects of productivity. This paper aims to present a roadmap developed in order to meet the practical need to establish criteria to assist in the determination of pulsed TIG welding variables, taking as its premise the desired width of the weld bead, overlap between the weld points comprising the weld bead and the welding speed. Finally, one application of this roadmap is presented in bead on plate welding of stainless steel plates with 1.2-mm thickness.

Numerical and Experimental Determination of the Residual Stress State in Multipass Welded API 5L X70 Plates*

Abstract Residual stress distributions in multipass welded API 5L X70 steel plates were determined by numerical and experimental methods. SYSWELD finite element software was used for numerical simulations. Microstructure variations were also considered for calculation of residual stresses. The continuous cooling transformation diagram was obtained via JMatPro software. The results showed that residual stress distribution is sensitive to number of weld passes, and microstructure changes. The simulation results were compared with those obtained by Magnetic Barkhausen Noise measurements on the welded plates. Simulation and experimental results gave qualitatively similar tendencies for the variation of the residual stress state.

Effect of chemical composition on microstructure and mechanical properties of laser weld metal of high-tensile-strength steel

Laser beam welding (LBW) and laser-arc hybrid welding are expected to be applied to welding of high-strength steel plates over 780 MPa, because they have advantages such as low distortion and a narrow heat-affected zone. This research examined the relationship between the chemical composition of high-strength steel plates and the microstructure and mechanical properties of the weld metal with the aim of improving the toughness of welded joints of high-strength steels by the LBW process. The results revealed that weld metal toughness is strongly dependent on the carbon (C) content of the steel plates, and excellent toughness can be obtained in weld metals with low C contents having an almost fully lower bainite structure without formation of slender martensite austenite constituent (MA). Based on these results, a guideline for appropriate alloying element design for high-strength steels for LBW was proposed, targeting mechanical properties of tensile strength ≥980 MPa and toughness vE−40 °C ≥ 47 J.

Review on the possible tool materials for friction stir welding of steel plates

The friction stir welding (FSW) process is mainly used in industrial applications for joining low melting temperature materials such as aluminium and magnesium. FSW has many advantages in comparison with conventional fusion arc welding. Therefore the interest to use this technique for joining steel plates has grown. However such usage is still limited because of the lack of adequate tool materials. This review gives an overview of possible tool materials for FSW of steels focussing on tungsten, tungsten carbide, pcBN and a few ultra-high temperature ceramics.

Relationship between the Microstructure of the Welded Steel Plates and the Efficiency of Vibration Stress Relief

Welded components of low alloy steels are widely used in various applications. Stress reliving is very important to these welded structures. Vibration stress relief (VSR) is an relatively new method for this purpose. In this study, Q235 and Q345 steel plates were welded. Then they were treated by VSR. The microstructure of the welded lines were investigated and the residual stresses in two directions in these welded structures were measured. The difference of the efficiency of VSR on the two materials were investigate. It is found that, the decreasing amplitude of the residual stress in the Q235 welded structures significantly exceeded that in the Q345 welded structures. The grain size in the area near the weld lines is the main factor that affects the efficiency of the VSR treatment.

High speed TIG–MAG hybrid arc welding of mild steel plate

A TIG–MAG hybrid arc welding process was proposed to achieve high speed welding. The influences of hybrid arc welding parameters on welding speed and weld appearance were studied through orthogonal experiment and the microstructures and mechanical properties of weld were tested and compared with that of the conventional MAG weld. The TIG–MAG hybrid arc welding speed could reach up to 3.5m/min for bead-on-plate welding of 2.5mm thick mild steel plate under the condition of high quality of weld appearance and 4.5m/min for butt welding of 2mm thick mild steel plate, respectively. The mechanical properties of hybrid arc weld were not lower than that of the conventional MAG weld. The assistant TIG arc could effectively stabilize the MAG welding current and MAG arc voltage in high speed TIG–MAG hybrid arc welding process. The stable hybridization obtained by balance between TIG and MAG welding current and proper wire-electrode distance was a key factor to stabilize the welding process.

신경망 알고리즘을 이용한 차체용 강판 아크 용접 조건 도출

Famous artificial neural network (ANN) is applied to predict proper process window of arc welding. Target weldment is variously combined lap joint fillet welding of automotive steel plates. ANN's system variable such as number of hidden layers, perceptrons and transfer function are carefully selected through case by case test. Input variables are welding condition and steel plate combination, for example, welding machine type, shield gas composition, current, speed and strength, thickness of base material. The number of each input variable referred in welding experiment is counted and provided to make it possible to presume the qualitative precision and limit of prediction. One of experimental process windows is excluded for predictability estimation and the rest are applied for neural network training. As expected from basic ANN theory, experimental condition composed of frequently referred input variables showed relatively more precise prediction while rarely referred set showed poorer result. As conclusion, application of ANN to arc welding process window derivation showed comparatively practical feasibility while it still needs more training for higher precision.

X-Ray diffraction technique applied to study of residual stresses after welding of duplex stainless steel plates

Duplex stainless steel is an example of composite material with approximately equal amounts of austenite and ferrite phases. Difference of physical and mechanical properties of component is additional factor that contributes appearance of residual stresses after welding of duplex steel plates. Measurements of stress distributions in weld region were made by X-ray diffraction method both in ferrite and austenite phases. Duplex Steel plates were joined by GTAW (Gas Tungsten Arc Welding) technology. There were studied longitudinal and transverse stress components in welded butt joint, in heat affected zone (HAZ) and in points of base metal 10 mm from the weld. Residual stresses measured in duplex steel plates jointed by welding are caused by temperature gradients between weld zone and base metal and by difference of thermal expansion coefficients of ferrite and austenite phases. Proposed analytical model allows evaluating of residual stress distribution over the cross section in the weld region.

Numerical simulation of full penetration laser welding of thick steel plate with high power high brightness laser

Full penetration laser welding was carried out on a 10mm steel plate using a 16kW maximum power continuous wave thin disk laser. Upper surface and lower surface of molten pool were observed synchronously with two high speed CCD cameras during the welding process. The lower surface was much longer and more unstable than the upper one. A three dimensional laser deep penetration welding model in which volume of fluid (VOF) method was combined with a ray-tracing algorithm was used to simulate the dynamic coupling between keyhole and molten pool in laser full penetration welding. The calculated weld cross-section morphology and molten pool length on both upper side and lower side agree well with experimental results. Evolution of molten pool in lower side during full penetration laser welding was analyzed, periodical features of energy coupling, molten pool behavior and keyhole dynamics in laser full penetration welding were identified and discussed.

맞대기 이음 용접의 피로수명에 베벨 각도가 미치는 역할

This study aims to investigate the influence of bevel angles on the fatigue life of V-groove butt-welded joints with back-plates made by SM490A steel material, generally used for excavators, because changes in the geometry, material and surface properties of welded regions affect the fatigue life of welded structures. Butt type test specimens were prepared by the <TEX>$CO_2$</TEX> welding of rolled steel plates (SM50A steel) with a thickness of 13.5 mm at a welding speed of 30 cm/min and these Butt type test specimens had two different groove angles, which are <TEX>$40^{\circ}$</TEX> (A type) and <TEX>$30^{\circ}$</TEX> (B type). In order to investigate differences in fatigue life between two types, 4-point bending fatigue tests were conducted with a stress ratio of R=0.1 under the cyclic loading environment at a frequency of 5 Hz at room temperature. The fatigue life of A type specimens was approximately 7% higher than that of B type specimens. The stress concentration factors calculated by finite element analysis were 2.16 for A type and 2.25 for B type, whose difference was caused by the influence of the back-plates of butt-welded structures. The current results could provide important guidelines to determine the V-groove angle of butt-welded joints with a satisfactory fatigue life, although under severe operating conditions.