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- Retrofitting of welded structures by TIG and Plasma DressingPublication . Ramalho, Armando; Antunes, F.V.; Ferreira, J.A.M.Due to economic and environmental constrains, the currently trend is to use the welded structures beyond their design lives. The predominant cause of in service failure of these aged structures is the fatigue of the welded joints. The use of improvement techniques in welded joints, as a repair technique, has been suggested by several authors. TIG dressing is one of the most promising of these repair techniques. However, the effectiveness of TIG remelting is closely linked to the depth of the repaired crack. The use of strain gauges can be effective to detect the presence of fatigue cracks in their initial phase of propagation, however their effectiveness in inspection programs on jobsite needs to be proven. Some TIG variants associated to recent technological innovations of fusion arc welding, are appointed to improve the penetration and the sustainability of the remelting process. In this article are presented some results of the work developed by the authors in the last years, relevant to assess the efficiency of sustainable repair, by TIG and plasma dressing, of welded structures. Relevance is given to the repair, complete or defective, of deep cracks, as well as the possible advantage of using TIG variants.
- Simulation of crack growth in residual stress fields of pre-fatigued T-welded joints repaired by tungsten inert gas: a 3D approachPublication . Ramalho, Armando; Antunes, F.V.; Ferreira, J.A.M.In this article, a three-dimensional finite element model (FEM) is used to predict the crack growth at the weld toe of a pre-fatigued T-joint that was repaired with a remelting technique. The numerical models were developed using the MSC.Marc software. Fatigue life is estimated by integrating the Paris-Erdogan law. The stress intensity factors are obtained by the virtual crack closure technique (VCCT). The T-welded joints, made of S355 steel, are obtained by covered electrode process and pre-cracked by fatigue. These welded joints were repaired by TIG dressing. The stress field generated by this dressing technique was estimated using a FEM model, presented in authors’ previous works. For the crack growth was used the VCCT three-dimensional model recently presented by the authors to predict the effect of overloads. The pre-existence of an elliptical crack at the weld toe, with a depth of 0.5 mm was considered. It is also studied the growth of pre-existing cracks which have been poorly repaired. It was observed that the TIG dressing produce residual compression stress fields on the weld toe that causes a delay in crack growth. The obtained results are compared with experimental ones. The fatigue’s lives obtained by simulations with the numerical model presented in this paper allows to evaluate the application conditions of TIG remelting technique in the repair of pre-cracked welded joints.
- Residual stress analysis in TIG welded jointsPublication . Ramalho, Armando; Ferreira, J.A.M.; Branco, C.M.Abstract. Fatigue strength of welded joints is significantly influenced by the presence of residual stresses due to welding, of flaws and notch sharpness at the weld toe. Compressive residual stresses enhance the fatigue behavior of the structure, while tensile ones impair it. TIG dressing at the weld toe is frequently used to remove flaws to lessen the notch sharpness at the weld toe and to introduce compressive residual stresses. This paper presents a 2D finite element model to predict the residual stresses generated in a TIG dressing at the weld toe of a T joint. The welded T joints are made in St 52-3 steel and are obtained by covered electrode process. The analysis was developed with the Marc finite element code. The modeled stress field is compared with some measurements of residual stresses obtained using X-ray diffraction and the strain gauges technique.
- Previsão da resistência à fadiga em juntas soldadas reabilitadas por técnicas de refusãoPublication . Ramalho, ArmandoNeste trabalho realizou-se um estudo de fadiga no qual se analisou o efeito das técnicas de refusão TIG e plasma na reabilitação de juntas soldadas em T, fissuradas no pé do cordão. Os resultados obtidos para as juntas como soldadas, melhoradas por refusão TIG, melhoradas por refusão plasma, reabilitadas por refusão TIG e reabilitadas por refusão plasma são apresentados em curvas S-N com intervalo de confiança de 95%. Os benefícios na vida de fadiga das juntas reabilitadas pelas duas técnicas de refusão, foram avaliados através dos resultados experimentais e através de um modelo de estimação baseado na Mecânica da Fractura Linear Elástica. Foram avaliados, pela técnica do furo e por difracção de raios X, os valores das tensões residuais gerados nas diversas juntas, como soldada, melhoradas por refusão TIG ou Plasma e reabilitadas por refusão TIG ou plasma. Foi desenvolvido e validado um modelo de estimação das tensões residuais nas juntas melhoradas por refusão TIG ou plasma, utilizando o programa de elementos finitos MARC.