THE EFFECT OF CRACK TIP RADIUS ON INITIATION FRACTURE TOUGHNESS

PDF

Authors
  1. MacKay, K.
  2. Karis Allen, K.
  3. Lee, G.M.C.
Corporate Authors
Technical Univ of Nova Scotia, Halifax NS (CAN) Dept of Mining and Metallurgical Engineering;Defence Research Establishment Atlantic, Dartmouth NS (CAN)
Abstract
Fracture standards maximize crack tip constraint by including a mandatory fatigue precracking procedure prior to determining initiation fracture toughness. This procedure is time consuming and may introduce considerable scatter and uncertainty in the determined toughness values. A mechanical or electrical means of manufacturing defects would provide a significant economic benefit as well as a more reproducible initial crack tip profile. The objective of this research is to evaluate various alternative methods of producing defects by determining the relationship between lower bound initiation fracture toughness and crack tip radius. A review of the literature indicates that a critical crack tip radius exists below which the apparent fracture toughness becomes independent of any further decrease in radius. Preliminary tests using low alloy steel fatigue precracked specimens (a/W = 0.60) and electric discharge machining (EDM) notched specimens (a/W = 0.45, with crack tip radii 60 - 75 mm) generate average apparent toughness values of 232 kJ/m square and 400 kJ/m square, respectively. EDM notched specimens provide greater reproducibility of the apparent toughness values compared to the fatigue precracked specimens. From the limited data obtained to date, it is uncertain whether the increase in toughness for the a/W = 0.45 specimens results from the decrease in crack depth or from the increase in crack tip radius.
Report Number
DREA-NAMT-93-4-PAP-16 — CONTAINED IN 99-00578
Date of publication
30 Apr 1993
Number of Pages
18
DSTKIM No
99-00595
CANDIS No
510321
Format(s):
Hardcopy;Document Image stored on Optical Disk

Permanent link

Document 1 of 1

Date modified: