FRACTURE MECHANICS PARAMETERS ESTIMATION OF CCT SPECIMENS MADE OF X 5 CrNi 18 10 STEEL

For a reliable operation of structures and their components during exploitation period, it is crucial to monitor continuously or periodically check the integrity of structure. In the production and during exploitation, a certain amount of flaws can be encountered in any structure. It is important to determine how such flaws can influence the safety and reliability of the operation. Since fracture mechanics deals with fracture and fracture behaviour of materials, it gives a methodology which can be used to evaluate structural integrity of components containing such flaws considering cracks in the first place. In assessing the integrity of structures containing cracks, it is important to quantify the relevant crack-driving force, so that the load carrying capacity can be predicted. If it is the case with components made of ductile materials, which generally exhibit slow and stable crack growth and which are able to provide large-scale plasticity near the crack tip, this crack-driving force is frequently described as contour J-integral 1 . It stands for a suitable elastic-plastic fracture mechanics parameter, for materials that possess low strength and high material toughness, but not sufficient enough to fully describe fracture behaviour of such materials 2 especially if crack growth is present, because the basis of J-integral concept considers stationary crack 1 and its value may become inaccurate because of path dependence for the growing crack. Therefore, beside J-integral, the data of crack growth must be obtained to allow construction of crack resistance curve and if certain size and geometrical conditions are fulfilled 3 then constructed crack resistance curve can be considered as one of the material properties. All fracture parameters are generally divided into two groups, one considering local parameters describing the near crack tip fields, like crack tip opening displacement CTOD, and other considering global parameters that usually represent some type of energy, such as J-integral. Since local crack tip generally controls the crack growth, local fracture parameters are more accurate in predicting fracture behaviour than global ones and they are expected to be independent of specimen size and geometry and loading configuration 4 . Therefore, in this paper, which describes fracture