AUTOMATED-SYSTEM FOR ANALYZING STRESS INTENSITY FACTORS OF 3-DIMENSIONAL CRACKS - ITS APPLICATION TO ANALYSES OF 2 DISSIMILAR SEMIELLIPTIC SURFACE CRACKS IN PLATE

This paper describes a new automated system for analyzing the stress i ntensity factors (SIFs) of three-dimensional cracks. A geometry model containing one or several three-dimensional cracks is defined using a commercial CAD system, DESIGNBASE. Several focal distributions of node density are chosen from the database of the present system and then a utomatically superposed on one another over the geometry model. by usi ng the fuzzy knowledge processing. Nodes are generated by the bucketin g method, and ten-noded quadratic tetrahedral solid elements are gener ated by the Delaunay method. A user imposes material properties and bo undary conditions onto parts of the geometry model such as loops and e dges by clicking them with a mouse and by inputting values. For accura te analyses of the stress intensity factors, finer elements are genera ted in the vicinity of crack tips, thanks to the fuzzy knowledge proce ssing. The singular elements such that the midpoint nodes near crack f ront are shifted at the quarter-points are automatically placed along the three-dimensional crack front. The complete finite element model g enerated is given to a commercial finite element code, MARC, and a str ess analysis is performed. The stress intensity factors are calculated using the displacement extrapolation method. To demonstrate practical performances of the present system, two dissimilar semi-elliptical su rface cracks in a plate subjected to uniform tension are solved, and t heir interaction effects are discussed in detail. It is shown from the results that ASME Boiler and Pressure Vessel Code, Section XI, Append ix A gives a conservative stress intensity factor for two identical ad jacent surface cracks and for two dissimilar adjacent surface cracks.