Abstract
Tensile residual stresses can have a detrimental affect on the safe operating limits of components. In most cases, these residual stress fields can be relieved through various treatments but in some components it is not realistic to completely eliminate these stresses. When considering a nuclear power generation plant (civil or naval), knowledge of fracture within a residual stress field is essential in support of any safety cases. This research has investigated the behaviour of flaws, such as cracks and voids that lie within a residual stress field with emphasis on the influence on fracture toughness. The eventual aim is to provide a benchmarked methodology of how these flaws will behave through the working life of the component/plant. To obtain this information a numerical model has been created in conjunction with a series of experiments to characterise the residual stress field present in a laboratory specimen and its affect on the fracture behaviour. These experiments include low temperature fracture toughness tests and synchrotron X-ray diffraction conducted at the European Synchrotron Radiation Facility (ESRF). By utilising these techniques it has been shown that a tensile residual stress can induce brittle fracture at an apparent stress intensity factor approximately 50% lower than the as-received material. The crack that initiated under initial primary loading was also shown to arrest before the total fracture of the specimen had occurred. Using the numerical analysis it has been shown that the residual stress is at its peak at the crack tip but rapidly dissipates away from the crack tip. The plasticity model used in the numerical analysis will significantly affect the predicted residual stress field distribution. Using data gained at the ESRF it is possible to determine the appropriate plasticity model and initially validate the numerical models although further work is required to improve the accuracy of the plasticity model.