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Item type:Publication, Access status: with files , Fatigue life extension of existing welded structures via high frequency mechanical impact (HFMI) treatment(Elsevier, 2021-04-09); ; High Frequency Mechanical Impact (HFMI) is one of the post-weld treatment methods. In this study, comparative axial fatigue tests were conducted on as-welded and HFMI-treated welded transverse attachment details. The test results demonstrated the efficiency of HFMI-treatment in fatigue life extension of cracked welded structures, providing that the existing crack size is less than 1.2 mm. Cracks were created in some specimens through fatigue testing before HFMI-treatment, while other specimens were not subjected to any fatigue loading prior to treatment. Many of the treated specimens ran-out after 10 million cycles of loading when tested at a stress range of 150 MPa. Therefore, the stress range was increased to 180 MPa or 210 MPa. No remarkable difference was found between the fatigue strength of the crack-free and the cracked treated specimens. It was found that the induced compressive residual stress can exceed the material yield limit, and reach a depth larger than 1.5 mm in most of the cases. The induced compressive residual stress, the local material hardening, the increase in weld toe radius, the change in crack orientation and the shallowness of the crack size were the causatives of the obtained long fatigue lives of the HFMI-treated specimens. Besides, linear elastic fracture mechanics calculations were conducted to predict the fatigue lives of as-welded and HFMI-treated details. The results were in agreement with the experiment. Moreover, the calculations showed that the initial crack size, the clamping stress and the induced compressive residual stress were the main factors behind the scatter in fatigue lives.Publicationtype: Journal ArticleScopus© Citations 24 136 519 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Fatigue crack repair by TIG-remeltingFatigue is one of the most detrimental Problems that often limits the service life of steel bridges. Because of that, different post weld treatment methods have been studied to extend the fatigue life and repair any existing cracks resulted from the traffic loading. The aim of this paper is to study the fatigue life extension of cracked structures by means of Tungsten Inert Gas (TIG) remelting. Fatigue tests were conducted at stress ratio of 0.29 on a transverse attachment of 16 mm, thick-walled specimens. The specimens were instrumented with multiple strain gauges along the weld to detect the strain drop caused by crack growth. The specimens were pre-fatigued until a crack of around 1 mm- deep was obtained at the weld toe. After crack detection, the weld toes were treated by TIG-remelting to remove any existing cracks and to reduce the local stress concentration. The weld parameters were controlled so that the fusion depth was always larger than the crack depth. A substantial fatigue life extension could be achieved and the testing led to ran-out after 10 million cycles, which was attributed to the improvement in geometry and residual stress. Weld toe radius were measured before and after treatment by laser scanner. Hole drilling was used to measure the residual stresses in as-welded state and after TIG-remelting. In this paper, a fatigue damage model is also presented. It is shown that the model gives a good prediction of the effect of TIG-treatment in repairing fatigue loaded welded details.Publicationtype: Conference Paper39 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Crack detection via strain measurements in fatigue testing(Wiley-Blackwell, 2021-03-26); ; Fatigue cracks have appeared as a significant issue for joints and connections in existing steel structures in the last decades. Therefore, those are a major inspection and maintenance matter for any steel structure's operator. This emphasises the importance of using a reliable detection method to determine the crack size and assessing the severity of such a crack on the structural integrity of a structure. In this article, the effectiveness of strain measurement in detecting fatigue cracks in transversal non-load carrying welded attachment subjected to out of plane axial loading is studied. Numerical analysis and experimental investigations allowed to correlate the decrease in strain measured by attached gauges to the crack depth at the weld toe. In addition, different strain evolution patterns were found during fatigue testing, and the fracture surfaces of the specimens were observed to interpret these patterns. Moreover, the crack position with respect to the weld toe surface was predicted via strain measurements.Publicationtype: Journal ArticleScopus© Citations 6 107 1202 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A probabilistic study of welding residual stresses distribution and their contribution to the fatigue lifeWelding is a joining process that is associated with heating cycles which leads to considerable change in local material microstructure and the formation of high welding Residual stresses (RS) in the welded joint. Residual stresses can have a detrimental effect on the fatigue strength of welded joints. In this paper, previously published data from measurements of residual stresses in various types of welded joints are compiled. In total, more than 100 test results are studied covering steels with yield strengths between 307 MPa and 1050 MPa in different welded details (butt joints, longitudinal and transverse attachments, cruciform joints, as well as K-joints) with varying thicknesses. The collected data is used to study the distribution of welding residual stresses (regardless of the welding parameters) at weld toe and through the thickness of the welded plate. Probabilistic analysis is then used to arrive at a model that represents the value and distribution of residual stresses in welded joints. This model is used to predict and explain the scatter in fatigue test data from recent fatigue testing of welded samples.Publicationtype: Review Article94 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Fatigue crack repair in welded structures via tungsten inert gas remelting and high frequency mechanical impact(Elsevier, 2020-06-29); ; Rehabilitation of welded structures has gained increasing attention lately. This paper aims at investigating the efficiency of Tungsten Inert Gas (TIG)-remelting and TIG-remelting followed by High Frequency Mechanical Impact treatment (TIG-HFMI) in fatigue life extension. Fatigue tests were carried out on as-welded and cracked specimens after treatment. The lives of the treated specimens increased remarkably by the two methods (TIG and TIG-HFMI). Many of the treated specimens ran-out after 10 million cycles of loading and failed at the clamping location when tested at a higher stress range. The improvement in compressive residual stresses, hardness values and weld toe radii were the reasons behind the life extension. These factors were used for fatigue life estimation in as-welded and TIG-treated specimens using the base metal S[sbnd]N curve. Moreover, the test results together with results from previous tests in the literature demonstrated that these methods can be useful for crack retrofitting as for new structures.Publicationtype: Journal ArticleScopus© Citations 21 209 252