FRACTURE TOUGHNESS STUDY OF ASTM A515 GRADE 70 STEEL

C. M. BRANCO        

Anales de la Mecánica de la Fractura, nº 8 . 1991 . Pág. 141 -148
Ver (.pdf): Anales08-025

Resumen: The presents paper reports the results of a fracture toughness study of a ASTM A515 Grade 70 steel using Fracture Mechanics ductile parameters such as COD and J integral.The specimens were taken at different locations and orientations from shell disks with the same curvature and thickness of a pressure vessel used in thermal power stations. The objectives of the work are to evaluate and analyse fracture toughness of this steel as a function of loading orientation,level of straining,thickness and temperature. In this paper COD and JR data is presented refering to the influence of initial a /w ratio and thickness.Two values of a/w and thickness were considered (a0 /w=0.15 and 0.5) and thickness B=l2 and SOmm.The results were obtained for base metal and weld metal. A discussion is presented refering the variation of CTOD with initial crack length,attributed to variability in the location of the rotational point.A preliminary assessment of this effect is given. CTOD toughness in the weld metal was found to be independent of specimen orientation and location along the shell thickness.The CTOD-R curve for the weld metal líes above the curve for the base metal. The CTOD values at maximum load,Omaxobtained in normalised specimens of 12mm thickness can be fitted in a single scatter band valid for weld and base metal results. Application of ASTM and EGF criteria for assessment of toughness measured by J showed that for the thickness of 12 and SOmm majority of data fall outside the validation lines of these criteria.Hence no valid J0 2values were obtained. A recommendation is made so that the validation criteria should be reviewed for high toughness materials.

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Professor, CEMUL ,UNIVERSIDADE TECNICA DE LISBOA, l096 LISBOA, CODEX,PORTUGAL