Welded Steel Components Research Articles

Application of local fatigue approaches on corroded welded joints with consideration of weld geometry and residual stresses

Corrosion can significantly affect the fatigue strength of steel structures. On the one hand, it can cause stress concentrations by changing the surface geometry, and on the other hand, it can lead to embrittlement of the material. In welded steel components, sharp notches are already present due to the weld geometry, which may interact with the notches from corrosion. In addition, residual stresses exist in the fatigue-relevant area, which can also be partially modified by surface preparation methods such as clean blasting. In the current standards, all the mentioned effects are considered by reducing the design stress-life (SN) curves, in which all aforementioned effects are superimposed. One possibility to consider the effects separately is the application of local concepts, with which the influence of the geometry, here obtained from 3D-scans, the influence of measured residual stresses, and the influence of material can be considered individually. For butt and fillet welds investigated in this study, it could be shown that by considering the real geometry via a reverse engineered 3D-solid model, the locations of crack initiation in the fatigue tests, measured by digital image correlation (DIC), matched with the numerically predicted locations in most cases. Moreover, it was shown that by taking into account the real geometry and residual stresses, the use of local approaches can result in a substantially reduction of the scatter in SN-curves from Tσ = 2.17 to Tσ = 1.26, demonstrating the great reliability of the applied method.

Fatigue life prediction of welded joints at sub-zero temperatures using modified Paris–Erdogan parameters

The fatigue life of welded steel components is usually determined by the weldment; in these cases, fracture mechanical approaches are widely used for their prediction. Ferritic steels are known to have a fatigue strength that is dependent on temperature. Therefore, this study evaluates fatigue tests of cruciform joints and transverse stiffeners at different sub-zero temperature levels regarding fatigue life. Simultaneously, the stress intensity factors over the crack length are calculated for the individual experiments using analytical solutions. Then, using the Paris–Erdogan relation with temperature- and material-specific C and m parameters as well as tabular values, the fatigue lives are calculated with analytical solutions and compared with the experimental results. It is shown that the prediction accuracy is significantly increased for the sub-zero temperature range by using temperature-adjusted Paris–Erdogan parameters, as long as the temperature is above the fatigue transition temperature.

Visual-Based Multi-Section Welding Path Generation Algorithm

As an important form of additive manufacturing, welding is widely used in steel components welding work of construction, shipbuilding and other fields. In this study, an intelligent welding path generation algorithm based on multi-section interpolation is proposed in order to deal with non-standard multi-pass welding grooves which are difficult to be handled by automatic welding equipment in the construction site. Firstly, the non-standard grooves are classified and the reasons for their occurrence are discussed. Secondly, an automatic welding additive manufacturing system framework is discussed and an appropriate detection method is selected. Then, combining with the welding standard of non-standard grooves and the characteristics of the welding process, a multi-section interpolation-based welding path generation algorithm is proposed. Finally, a visual experiment platform was built to detection the typical non-standard groove and the welding experiment is implemented to verify the feasibility of the algorithm. According to the path generated by the algorithm, the welded steel components test plate meets the actual engineering standard after quality inspection. The experimental results and simulation results conclude the algorithm can be used to generate the welding path of the non-standard groove.

Review on The Prediction of Residual Stress in Welded Steel Components

Residual stress after welding has negative effects on the service life of welded steel components or structures. This work reviews three most commonly used methods for predicting residual stress, namely, empirical, semi-empirical and process simulation methods. Basic principles adopted by these methods are introduced. The features and limitations of each method are discussed as well. The empirical method is the most practical but its accuracy relies heavily on experiments. Mechanical theories are employed in the semi-empirical method, while other aspects, such as temperature variation and phase transformation, are simply ignored. The process simulation method has been widely used due to its capability of handling with large and complex components. To improve its accuracy and efficiency, several improvements need to be done for each simulation aspect of this method.

Analyzing the Failure of Welded Steel Components in Construction Systems

Failure of welded construction steel components can occur due to inappropriate design, wrong steel choice or quality, substandard welding processes and through defective maintenance. Welded constructional steel joints in particular are highly sensitive to issues of fatigue, weld corrosion and/or weld quality. A key concern is on placing welds in regions of nominal stress. Welded joints are produced to a specification, which is used to minimize the heat-affected zone and any residual stress within the weld. In this article, numerous examples of weld fracture are shown together with the causes and of weld failure.

02.04: Experimental and numerical analyses of butt‐welded S460 joints

ABSTRACTFor the development of reliable calculation approaches regarding the load bearing capacity of welded steel components, knowledge about stress‐strain relations in the weld and the heat affected zone is required. A three dimensional stress state, particularly in case of highly divergent material properties in the spatially concentrated areas of welded connections, mainly influences the response of the structure. This paper presents the experimental and numerical study of single‐pass butt‐welded joints under tensile loading. Furthermore, it depicts the determination of material properties in the weld and heat affected zone by means of miniature tensile tests. Miniature specimens are taken from the base material, the weld and the heat affected zone of connections with matching base and filler material by water jet technology. The varying material ductility, yield stress and ultimate strength, are illustrated experimentally depending on the origin of the miniature specimen (weld, heat affected zone, base material) and using a modified single‐pass butt‐welded joint under tensile load. The stress‐strain‐curves obtained by means of miniature tensile tests are used for the numerical simulation of a welded connection under tensile loading. The comparison of numerical results of welded connections with local strain measurements shows good agreement.

Evaluation of nominal and local stress based approaches for the fatigue assessment of seam welds

In the context of the German joint research project “Applicability of fatigue analysis methods for seam welded components”, fatigue tests were performed by five universities and institutes on welded components, welded parts of larger structures as well as component-like samples of weld details. The sheet thickness t was in the range 1 mm ⩽ t ⩽ 20 mm. The welding parameters for all test coupons and structures tested were chosen according to the industrial production process. Based on the data acquired, nominal, structural and notch stress approaches were analysed with regard to applicability and quality of assessment. The actual weld geometry except the real notch radii was taken into account within the notch stress approach. For the notch radii various values, the reference radii 0.05, 0.3 and 1 mm, were applied. Experimental and numerical results for welded steel components are presented. Approximately equivalent scatter ranges were obtained when applying the various approaches based on the current state of the art. It should be noted that both the nominal and the structural stress approaches are limited in their application compared to the notch stress approach. A comparison of the scatter bands obtained for the various approaches is subject to limitations because it was necessary, in each case, to use different test series as the basis for determining the scatter bands.

An intelligent sensor system for monitoring fatigue damage in welded steel components

A sensor and data storage system that monitors fatigue damage in load-bearing steel components is described. The sensor is a thin steel sheet measuring 50 × 20 mm, with a pre-crack in its centre. It is fixed next to a welded joint on the component under test. It follows the component's flexions in service and begins to fatigue, thereby lengthening its crack. Crack length is measured using a simple circuit and is recorded using a microcontroller. This is achieved by laying electrically conductive tracks on the sensor in a direction perpendicular to that of the crack. They are connected to the microcontroller's analogue to digital converter via resistors in a potential divider arrangement. When the crack propagates past a track, it breaks its continuity, thereby changing the network's output voltage. The crack length is represented by the analogue voltage recorded. The microcontroller is configured to operate in low power mode, waking up at predetermined intervals to read the sensor. In this way, it consumes very little current and can operate over many years. The data are stored in memory and can be remotely downloaded from a distance of up to 30 m using Bluetooth™ technology, to a PC. It can then be analysed to predict the component's useful life.

피로강도해석을 위한 용접잔류응력 이완의 정량적 평가

It is well known that the strength and the fatigue life of welded steel components are affected extensively by welding residual stresses distributed around their weldments under not only monotonic but also cyclic loads. The externally applied loads are to be superimposed with the welding residual stresses, so that unexpected deformations and failures of the components might occur. These residual stresses are not kept constant, but relaxed or redistributed during in service. Under monotonic loads the relaxation takes place when the sum of external and welding residual stress exceeds locally the yield stress of material used. By the way, it is shown that under cyclic loads the welding residual stress is considerably relieved by the first or the early cycles of loads, and then gradually relaxed with increasing loading cycles. Although many investigations in this field have been carried out, the phenomenon and mechanism of the stress relaxation are still not clear, and there are few comprehensive models to predict amount of relaxed welding residual stress. In this study, the characteristics of the welding residual stress relaxation under monotonic and cyclic loads were investigated, and a model to predict quantitatively amount of welding residual stress relaxation was proposed.<br/>

Residual stress relaxation of welded steel components under cyclic load

It is a well known fact that the fatigue strength and the life of welded steel components are affected, to a considerable extent, by residual stresses distributed around their weldments. When externally applied load is superimposed on residual stresses, unexpected deformations and failure of the components can occur. These residual stresses are not constant, but are relaxed or redistributed during in‐service. Under monotonic load relaxation takes place when the sum of external and residual stress locally exceeds the yield stress of material used. It is noteworthy that under cyclic load the residual stress is considerably relieved by the first or the early cycles of load, and then is gradually relaxed with increasing loading cycles. Although many investigations in this field have been carried out, the phenomenon of and mechanism of stress relaxation are still not clear, and only a few comprehensive models have been proposed to predict amount of relaxed residual stress. In this study, the characteristics of residual stress relaxation under monotonic and cyclic load were investigated, and a model for quantitatively predicting the amount of residual stress relaxation is proposed.

Vibratory Stress Relieving Treatment of Welded Steel Components Studied by Barkhausen Noise Method and X-Ray Diffraction

In this study the effectiveness of vibratory stress relieving (VSR) treatment on the residual stresses of axially welded steel tubes made of mild steel was investigated. Residual stresses of the tubes were measured before and after the VSR treatment by Barkhausen noise and X-ray diffraction. Slight, inhomogeneous stress reduction was observed in some of the tubes in the vicinity of the weld seam. Despite of this slight stress reduction, the VSR treated tubes distorted approximately the same amount as untreated tubes during machining. The mechanism behind the observed stress reduction is discussed.

Bulldozers or Ships—What’s the Difference?

This paper explains Caterpillar's approach to maintaining leadership position in designing and manufacturing fabricated structures, and highlights some of the technologies that are used to make welded steel components. Caterpillar's customers continue to look for maximum value from our machines and, to meet their increasing expectations, investment in new technology is a necessity. To build lightweight, high quality, long life structural components, Caterpillar uses state-of-the-art design tools, process simulation technologies and the latest manufacturing processes. It is the authors' perception that there are many synergisms between ship construction and the manufacture of earthmoving equipment. This paper debates networking between the two industries for cross-industry technology development and knowledge transfer. This can potentially improve the competitiveness of the United States in the ever-increasing global marketplace.

Measurement and prediction of residual stresses in thick-section steel welds

Significant levels of residual stress are developed in the production of thick-section steel welds. Residual stress can be measured by a variety of methods, although few offer the ability to determine the spatial distribution completely through the thickness. This paper summarizes recent developments in the deep-hole method for measuring residual stresses in thick-section welds. Experimental results obtained from a variety of welded steel components are described. The measurement method has also been used to provide validation for finite element simulations of residual stresses in a welded cylinder-to-nozzle stainless steel component. The paper describes the finite element weld analysis and compares the results with measurements obtained from several locations in the complex geometry. Overall, there is good agreement between the predicted and measured distributions of residual stress, but the magnitudes of predicted stress tend to be greater.