EVALUATION OF FRACTURE TOUGHNESS OF HIGH STRENGTH STEEL FROM STRETCH ZONES

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Authors
  1. Bassim, M.N.
  2. Smith, J.V.
  3. Matthews, J.R.
Corporate Authors
Manitoba Univ, Winnipeg MAN (CAN) Dept of Mechanical and Industrial Engineering;Defence Research Establishment Atlantic, Dartmouth NS (CAN)
Abstract
High strength steels exhibit elastic-plastic fracture behavior at the crack tip even at low temperature and/or high strain rates. Characterization of their fracture toughness under these conditions by means of standardized JIC tests is extremely difficult. This is particularly the case at very high strain rates such as those obtained using Split Hopkinson Bar devices. Alternatively, measurements of the stretch zone ahead of the crack on the fracture surface allows evaluation of the fracture toughness. It was found, however, that the stretch zone, which is indicative of the plasticity at the crack tip is affected by several factors such as the level of loading during fatigue precracking, the extent of strain hardening which occurs at the crack tip, the length of the crack and the corresponding a/w ratio and the occurrence of transverse and compressive strains ahead of the crack. In this study, the effect of these factors of the measured stretch zone width and the corresponding JIC is evaluated systematically. Factors examined are a/w values, delta K fatigue, temperature and strains ahead of the crack. The results emphasize the importance of using stretch zone measurements for fracture toughness evaluation.
Report Number
DREA-NAMT-95-1-PAP-4 — CONTAINED IN 99-00779
Date of publication
30 May 1995
Number of Pages
24
DSTKIM No
99-00783
CANDIS No
510347
Format(s):
Hardcopy;Document Image stored on Optical Disk

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