Conference Proceedings Paper
A METHOD FOR PREDICTING THE EVOLUTION OF CRACK GROWTH IN COMPLEX STRUCTURES – A POTENTIAL APPLICATION IN SIMULATING STRESS CORROSION CRACKING
13th International Conference on CANDU Fuel - 2016 Aug. 15-18
D. Wowk (The Royal Military College of Canada)
P. Chan (Royal Military College of Canada)
Iodine induced stress corrosion cracking can occur in the zircaloy sheath surrounding nuclear fuel pellets when a critical combination of iodine concentration and stress levels are present. Predicting the initiation and propagation of these cracks may involve individual analytical models that can predict the thermal-mechanical response of the pellet and sheath, the rate of fission gas release, the rate of diffusion to the crack site, and intergranular and transgranular crack growth. In metallic components, crack growth is often predicted using linear elastic fracture mechanics, which requires knowledge of the stress field at the crack tip, the shape of the crack and the material properties that govern the rate of crack growth. This method makes use of stress intensity factors which combine the effects of the crack geometry and the applied loading. In complex situations such as when the cracked surface is in contact with an adjacent component, or when thermal loads are applied, the stress intensity factors are not readily available in handbooks. This paper focuses on the development of an analytical tool that uses finite element analysis to predict the stress intensity factors for a crack propagating in situations for which handbook solutions are not available. Finite element analysis is a powerful analytical tool that can be used to determine stress intensity factors, and in some complex cases may be the only method available. Three-dimensional simulations are created which can account for the effects of adjacent components and different loading cases, thus enabling the stress intensity factors to be predicted for an unlimited number of scenarios. In order to correctly predict the stress intensity factor, the shape of the crack front must be known. The crack front is typically assumed to be represented by simplified geometry such as a quarter circle or an ellipse. It has been shown than these assumptions can lead to differences in the predicted crack growth when compared to realistic crack shapes. In this paper, an automated technique is presented where successive finite element simulations are used to predict the shape of an evolving crack and ultimately the number of loading cycles until failure. This method may have a potential application in predicting crack growth in fuel elements which is a complex situation involving surface pressure, thermal loads and mechanical interaction. Predictions of crack growth and crack geometry for a notch in a metal alloy under tensile loading is presented.
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