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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.

The main goal here is to optimise the finite element mesh used to predict plasticity induced crack closure (PICC). A numerical model was developed for a M(T) specimen made of 6016-T4 aluminium alloy. The parameters studied were the size of most refined region perpendicularly to crack flank (ym) and along propagation direction (xr), the size of finite elements near crack tip (L1) and the vertical size of refinement close to crack flank (yA/B). A maximum size of about 1.3mm was found for ym, but a smaller value has a limited impact on PICC. An analytical expression was proposed for xr, dependent on δK and Kmax. An optimum value seems to exist for L1.

Compressive stresses play an important role on tension-compression fatigue which can be attributed to plasticity induced crack closure (PICC). The objective here is to study numerically the effect of compressive stresses on PICC and to discuss the applicability of PICC to explain the effect of negative stress ratios on fatigue crack growth rate. The compression produces reversed plastic deformation at the crack tip, reducing linearly the crack opening level. The incursion to negative stress ratios did not produce sudden changes in the behavior of PICC and no saturation with the decrease of minimum load was observed for δKeff. Crack closure was able to collapse da/dN-δK curves with negative stress ratios, indicating the applicability of the crack closure concept to explain the effect of negative R. The analysis of crack tip plastic strain range with and without contact of crack flanks confirmed the validity of crack closure concept.

No presente trabalho pretende-se efetuar a caracterização mecânica do aço S 355 AR, EN 10025-4, a alta temperatura. A avaliação rigorosa da variação da tensão de cedência, do módulo de Young, do módulo de encruamento, do calor específico e do coeficiente de dilatação térmica, com a temperatura é essêncial na simulação numérica da distorção e das tensões residuais induzidas por campos térmicos. Embora esta informação esteja disponível em alguns códigos estruturais, como o Eurocódigo 3 parte 1.2, ela não inclui o efeito da composição química e da microestrutura. O aço S 355 AR é um material bastante utilizado em estruturas soldadas, onde a avaliação de distorções e tensões residuais é um problema usual. A caracterização mecânica do aço S 355 AR, EN 10025-4, foi obtida através de ensaios de tração isotérmicos realizados a temperaturas até 600 °C, por Calorimetria Exploratória Diferencial (DSC) realizada até à temperatura de 950 °C e por Análise Termomecânica (TMA) conduzida até aos 1350 °C. Os resultados obtidos diferem significativamente dos valores apresentados na parte 1.2 do Eurocódigo 3, para um aço ferrítico genérico.

In this paper is presented a 2D finite element model to predict the residual stresses generated by Tungsten Inert Gas (TIG) dressing at the weld toe of a T-joint. The welded T-joints, made of S355AR steel, are obtained by covered electrode process and improved with TIG dressing. The analysis was developed with the MSC.Marc finite element code. The estimated stress field is validated with experimental stress results obtained using X-ray diffraction. Over the estimated residual stress field is simulated the growth of fatigue cracks. The simulation is performed with the virtual crack closure technique, implemented in the MSC.Marc software. The obtained results are compared with the integration solutions of the Paris-Erdogan law, without influence of residual stresses, where the stress intensity factor is obtained using the Mk factor proposed by Bowness and Lee, included in BS 7910 standard. The numerical predictions are also compared with experimental results.