Fatigue Cracks In Welded Joints Research Articles

Deep learning-based acoustic emission data clustering for crack evaluation of welded joints in field bridges

To advance the intelligent operation and maintenance of bridges, a deep learning-based acoustic emission (AE) data clustering framework was developed for evaluating fatigue cracks in welded joints under conditions of operational noise interference and complex damage mechanisms. Specifically, a convolutional autoencoder (CAE) model was implemented to extract damage-sensitive features from AE wavelet images. Additionally, a physics-guided single-and-cross-case strategy using Gaussian mixture models (GMMs) was presented to diagnose overlapping microscopic noise and damage mechanisms across different cases with various crack lengths. Field tests demonstrated the efficiency of the proposed framework to distinguish AE data induced by noise, crack propagation, surface fretting, and impact, enabling accurate identification of no-damage, minor-damage, and serious-damage cases according to their characteristic mechanisms. Future work will incorporate long-term monitoring data from additional cases to further refine the damage quantification and enhance the overall robustness.

Coupled propagation behavior of multiple fatigue cracks in welded joints of steel-bridge

Fatigue cracking in welded joints is a critical problem in bridge engineering, especially for aging long-span steel bridges. The crack size and density are increasing gradually with the bridge aging process, where the crack interaction will accelerate the crack propagation or even short cracks merging into a long crack. However, the mechanism underlying the coupled propagation behavior of multiple cracks remains unclear. In this study, the coupling effect of multiple cracks was investigated based on numerical simulations. Subsequently, the numerical result was verified by a full-scale segmental fatigue experiment. In order to overcome the time-consuming iterative computations, the back propagation (BP) neural network was utilized to predict the effective coupling spacing between multiple cracks. Finally, a new crack reconstruction method was proposed to simplify crack merging processes. Results indicate that the coupled propagation behavior is significantly impacted by the effective crack spacing. The coupling effect is more significant at the near-end point compared to other feature points. In addition, the cracks with similar sizes have greater coupled effect, which is the worst-case scenario for the multiple fatigue crack problem. The experimental study demonstrates that the growth rate of the near-end point is 1.53 times that of the far-end point and pre-made cracks merge together successfully. By utilizing the BP neural network, the relative error of predicted effective spacing of two cracks is 3.52%. Compared to existing design specifications, the new reconstruction method provides a more reliable result for the fatigue life prediction of the welding seam with multiple fatigue cracks.

The impact of flow-accelerated corrosion on the crack developing in welded joints of NPP equipment and pipelines

Thermal mechanical equipment or the pipelines of the second circuit of a VVER type NPP are mainly subject to two degradation mechanisms that reduce the strength of structural elements: flow-accelerated corrosion and fatigue damage. As a rule, the aforementioned degradation mechanisms bear no combined impact as they affect different zones of the object. However, welded joints are subjected to the impact of both mechanisms which results in initiation and development of cracks in welded joints and in their local thinning due to the low content of alloying elements or due to hydrodynamic features of the flows arising in back of taps, throttling devices, cone transitions and similar pre-connected sections. The goal of the study is to elucidate the effect of flow-accelerated corrosion on the development of fatigue cracks in welded joints. We used the formulas of fracture mechanics to describe the time-dependent undergrowth of cracks and empirical data to describe the dependence of flow-accelerated corrosion on the operation time and postulated residual defect structure. The proposed approach provided estimation the effect of flow-accelerated corrosion on the rate of crack developing in the equipment or pipeline. It is shown that flow-accelerated corrosion can both reduce and significantly increase the crack growth rate. The distribution of defects versus the operating time is obtained, taking into account the entire set of possible missed defects. The distribution obtained provides for more correct assessing of the reliability and safety of welded joints of the NPP equipment and pipelines.

Results of the experimental study of the fatigue characteristics of the repaired welded joint of the marine stationary oil and gas producing platform

Offshore stationary platforms are actively exploited in the world. The lifespan of some of these platforms exceeds 20 years. Such a significant period of operation leads to the fact that the platforms are exposed to various loads for a long time, causing alternating stresses and, as a result, fatigue damage, including fatigue cracks in welded joints and the base metal of the platform. When fatigue cracks are identified, defect joints are repaired commonly using welding techniques. However, the duration of the subsequent operation of such repaired welded joints is not currently known. The authors conducted an extensive experimental study to understand the life span of welding repair technologies. This approach was for the first time used to repair the welded joint of a platform located in the White Tiger. White Tiger is the Vietnamese offshore oil field, located 200 km east of Ho Chi Minh City on the shelf of the South China Sea. The result of this study was the fatigue diagram and its equation, which were first obtained by the authors.

ДОСЛІДЖЕННЯ ВПЛИВУ ГЕТЕРОГЕННОСТІ ЗВАРНИХ ШВІВ НА РЕСУРС ТРИМАЛЬНИХ СИСТЕМ ПРИЧЕПА

The paper considered the issues of the influence of structural heterogeneity of welds on the life of the trailer design. Mainly in the works on welded structures, the effect of stress concentration during welding on the strength and crack resistance of the weld is considered and the possibilities of reducing temperature differences and deformations, which create the main threat of microcracks, are examined. One of the essential features of welded joints is the structural-mechanical inhomogeneity of the metal. The nature and properties of this heterogeneity as a factor in the destruction of welded joints is not fully determined. Therefore, the object of this study is the structural heterogeneity of welds of the supporting structure of the trailer BMZ-887.General questions are considered regarding the trailer designs and physical properties of welded joints and the peculiarities of heterogeneity of the heat-affected zone or near the suture zone. For the study, we used the following methods: tensometric research, quantitative metallography. The paper presents experimental data that were obtained using the above mentioned methods, and a comparative analysis of these data was carried out. The relationship between the numerical values of the parameters of the weld heterogeneity and the propagation velocity of small and main fatigue cracks in welded joints is established.The numerical values of the heterogeneity parameters and the propagation speeds of fatigue cracks in the welded joints of the following types were obtained: the propagation speed of small cracks decreases slightly with increasing diameter of the second phase particles; particle diameter does not significantly affect the propagation velocity of trunk cracks; the effect of concentration (distance between particles) for small cracks is not significant; for trunk cracks with increasing particle density, the rate of propagation of cracks is somewhat reduced.

Ways of ensuring regulatory resource of bridge spans

The structural features of welded railway bridges of the last century were considered. The basic causes of appearance of fatigue cracks in welded joints of railway bridges were assessed. Structural and technological ways of provision of the design life of operated and new-built welded railway bridges are discussed.

Strengthening fatigue-cracked steel bridge decks

In slender orthotropic decks of steel bridges, the dynamic interaction between vehicle tyres on flexible asphaltic pavement and the deck structure plays an important role on stress amplitudes. This involved interaction mechanism is brought into the discussion on the main causes of the pavement disruption and of the observed cracks in a large steel bridge, which has been frequently damaged by fatigue cracks in welded joints and geometric details under random stresses produced by traffic loading. Numerical modelling and experimental strain measurements performed both in situ and in the laboratory on a prototype scale model of the actual steel deck. Proposed solutions include adding a reinforced concrete pavement, either as a sandwich structure with a visco-elastic layer in between the steel plate and the concrete slab, or as a composite deck formed by fixing the concrete slab to the steel plate with stud connectors. It is shown that visco-damping and composite stiffness properties led to substantial reduction of both longitudinal and transverse bending stresses, enhancing the fatigue performance of these bridge decks.

Strengthening fatigue-cracked steel bridge decks

In slender orthotropic decks of steel bridges, the dynamic interaction between vehicle tyres on flexible asphaltic pavement and the deck structure plays an important role on stress amplitudes. This involved interaction mechanism is brought into the discussion on the main causes of the pavement disruption and of the observed cracks in a large steel bridge, which has been frequently damaged by fatigue cracks in welded joints and geometric details under random stresses produced by traffic loading. Numerical modelling and experimental strain measurements performed both in situ and in the laboratory on a prototype scale model of the actual steel deck. Proposed solutions include adding a reinforced concrete pavement, either as a sandwich structure with a visco-elastic layer in between the steel plate and the concrete slab, or as a composite deck formed by fixing the concrete slab to the steel plate with stud connectors. It is shown that visco-damping and composite stiffness properties led to substantial reduction of both longitudinal and transverse bending stresses, enhancing the fatigue performance of these bridge decks.

Special features of acoustic emission from fatigue cracks in welded joints in oil pipes : Golovinskii, A.G.; Kiselev, A.V.; Kotkis, A.M.; Khokhlov, N.F.: Shiryaev, A.M. Soviet Journal of Nondestructive Testing, Vol. 26, No. 8, pp. 540–544 (Apr. 1991)

Special features of acoustic emission from fatigue cracks in welded joints in oil pipes : Golovinskii, A.G.; Kiselev, A.V.; Kotkis, A.M.; Khokhlov, N.F.: Shiryaev, A.M. Soviet Journal of Nondestructive Testing, Vol. 26, No. 8, pp. 540–544 (Apr. 1991)

Special features of acoustic emission from fatigue cracks in welded joints in oil pipes

Special features of acoustic emission from fatigue cracks in welded joints in oil pipes

Propagation of fatigue cracks in welded joints

Propagation of fatigue cracks in welded joints