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SURFACE MICRO‐CRACKS IN BLOCK AND RANDOM FATIGUE CYCLING OF 500 MPa STRENGTH STEEL AND WELD METAL
Author(s) -
Iida K.,
Shimamoto H.,
Itoh N.
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.tb01309.x
Subject(s) - materials science , base metal , cycling , welding , amplitude , composite material , metal , structural engineering , metallurgy , engineering , physics , archaeology , quantum mechanics , history
— Crack density, main crack length and the sum total length of micro‐cracks, which initiated and extended on the surface of a 500 MPa strength steel and its weld metal, were investigated by a replica technique applied during fatigue tests. The base and weld metal specimens were subjected to constant amplitude, random and block strain cycling. The base metal specimens were further tested under 4 kinds of block cycling and 2 kinds of incremental strain cycling. All the cumulative cycling patterns in random and block modes followed the so‐called p ‐distribution. As a result of an analysis of micro‐cracks, it was shown that the most useful parameter to estimate the accumulated fatigue damage was the sum total length of micro‐cracks in a unit area, which increased exponentially with cycle ratio. Empirical formulae were obtained expressing the increasing tendency as a function of the cycle ratio for three groups of the equivalent strain amplitude. The formulae were applicable to all strain cycling patterns investigated in the present study.