Papers by Author: Misa Zrilić

Abstract: In this paper the micromechanical approach to ductile fracture was applied in a study of constraint effect on crack growth initiation in mismatched welded joints. The single-edged notched bend specimens (precrack length a0/W=0.32) were experimentally and numerically analyzed. The coupled micromechanical model proposed by Gurson, Tvergaard and Needleman was used. Constraint effect was tested by varying widths of the welded joints (6, 12 and 18mm). Highstrength low-alloyed (HSLA) steel was used as the base metal in a quenched and tempered condition. The flux-cored arc-welding process in shielding gas was used. Two different fillers were selected to obtain over- and undermatched weld metal. The micromechanical parameters used in prediction of the crack growth initiation on precracked specimen were calibrated on a round smooth specimen. The difference in fracture behavior between over- and undermatched welded joints obtained in experimental results was followed by numerical computations of void volume fraction in front of the crack tip.

Abstract: Structural integrity and service reliability depend on the fracture resistance of a material. Cracks in the material are the locations of stress concentration, and elastic-plastic deformation can occur causing the development of mixed-mode type of fracture ahead the crack tip. Crack behavior in the elastic-plastic region is analyzed applying numerical and analytical simulation based on fracture mechanics parameters, characterizing the response of the material at the crack tip. Numerical and analytical results are compared with the corresponding experimental results obtained in previously performed fracture mechanics tests with standard single-edge notch bending – SEN(B) specimens. The comparison shows an acceptable level of agreement, enabling application of the proposed numerical model of crack growth in the mixed-mode fracture analysis for structural integrity assessment.

Abstract: Considering the conditions to which steels used for the manufacture of steam pipelines are exposed, the micromechanism of their destruction in exploitation is exclusively the ductile one. In order to make an estimation of the level of the damage that occurs in exploitation, in this paper a combined experimental and numerical procedure has been developed based on micromechanical or local approach to the fracture mechanics of metallic materials. After the analysis of the results obtained for micromechanical criterion of failure for virgin steel and that used in the steam pipeline, a proposal for prolongation of the working life of tested steel for steam pipelines until the next overhaul is given.