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MEASUREMENT OF STRETCH ZONE HEIGHT AND ITS RELATIONSHIP TO CRACK TIP OPENING DISPLACEMENT AND INITIATION J ‐VALUE IN AN AISI 316 STAINLESS STEEL
Author(s) -
Sreenivasan P. R.,
Ray S. K.,
Vaidyanathan S.,
Rodriguez P.
Publication year - 1996
Publication title -
fatigue and fracture of engineering materials and structures
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.887
H-Index - 84
eISSN - 1460-2695
pISSN - 8756-758X
DOI - 10.1111/j.1460-2695.1996.tb01021.x
Subject(s) - charpy impact test , crack tip opening displacement , materials science , fracture toughness , displacement (psychology) , structural engineering , fracture (geology) , composite material , toughness , metallurgy , fracture mechanics , crack closure , engineering , psychology , psychotherapist
Abstract— An accurate method using SEM for the measurement of stretch zone height (SZH) on fracture surfaces has been established. This method does not make any assumption regarding crack blunting angle θ, and for 316 stainless steel in the present investigation θ was in the range of 50 to 67°, contrary to the common assumption of 45°. The semi‐empirical equations, SZH( T ) = 2.5 SZW (stretch zone width) and SZW = 89( J/E ), reported in the literature were found to give very conservative predictions of initiation toughness J i for an AISI 316 stainless steel. Lowerbound values of the coefficient m in the equation, J = m σ y δ, relating J to CTOD, δ, is found to be 1.5–1.7 for the 316 SS used in this investigation; the upperbound value for m is found to be 2.6. The plastic CTOD values (δ max ) corresponding to the maximum load‐point on the instrumented impact test traces are not sensitive to the aging conditions and as they incorporate significant crack growth effects they cannot be used for predicting J i , by a procedure similar to that discussed above. The ratio t 1 / t T , where t i is the time to crack initiation and t i is the time to total fracture, in precracked Charpy tests of unaged and aged 316 SS used in this investigation ( a/W =0.55 to 0.8) corresponds to 0.15 to 0.17.