NUMERIC AND EXPERIMENTAL COMPARISON OF FATIGUE CRACK GROWTH RATE IN WELDED VIRTUAL SPECIMENS Marcos Roberto Dariva e Walter J. Paucar Casas
Resumo: The presence of welding residual stresses close to cracks in structures involves modifications in the field of stresses, when they are submitted to some loading effect. The modifications in the level of stresses obviously affect the structure with respect to its fatigue behavior. This work develops computational simulations for determination of the crack growth rate of the soft martensitic stainless steel CA6NM, material commonly used in the manufacturing of hydraulic turbines, in homogenous and as welded conditions. The objective of this work is to evaluate the influence of the field of welding residual stresses or the error due to the lack of this field in the computational results. For this purpose, it is considered the existence of experimental data in CT specimens for determination of the fatigue crack growth rate with this alloy, according to the ASTM E647-95 standard. The finite element method is used for stress evaluation and the experimental results serve to calibrate the simulation in virtual geometric CT specimens. It is verified that the results are in agreement with the theory; the numerical values are lower than the experimental ones, because the field of residual stresses are absent in the computations, showing the maximum error when the pre-crack is at the heat affected zone (average of 67%) if compared to the weld metal region (average of 21%), local where probably traction residual stresses are higher (heat affected zone).
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