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Prediction of crack opening stress levels for 1045 quenched and tempered steel under service loading spectra
Author(s) -
KHALIL M.,
TOPPER T. H.
Publication year - 2006
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.1460-2695.2006.00930.x
Subject(s) - materials science , crack closure , stress intensity factor , structural engineering , stress (linguistics) , stress concentration , paris' law , crack growth resistance curve , crack tip opening displacement , fracture mechanics , composite material , forensic engineering , engineering , linguistics , philosophy
ABSTRACT The opening stresses of a crack emanating from an edge notch in a 1045 quenched and tempered steel specimen were measured under two different Society of Automotive Engineers (SAE) standard service load histories having different average mean stress levels. The two spectra are the Grapple Skidder history (GSH), which has a positive average mean stress, and the Log Skidder history (LSH), which has a zero average mean stress. To capture the behaviour of the crack opening stress in the material, the crack opening stress levels were measured at 900X using an optical video microscope, at frequent intervals for each set of histories scaled to two different maximum stress ranges.A crack growth analysis based on a fracture mechanics approach was used to model the fatigue behaviour of the steel specimens for the given load spectra and stress ranges. Crack growth analysis was based on an effective strain‐based intensity factor, a crack growth rate curve obtained during closure‐free loading cycles and a local notch strain calculation based on Neuber's rule.The crack opening stress ( S op ) was modelled and the model was implemented in a fatigue notch model, and the fatigue lives of the specimens under the two different spectra scaled to several maximum stress levels were estimated. The average measured crack opening stresses were between 6 and 12% of the average calculated crack opening stresses. In the interest of simplifying the use of S op in design, the average S op was correlated with the frequency of occurrence of the cycle reducing the S op to the average crack opening stress level. The use of an S op level corresponding to the cycle causing a reduction in S op to a level reached once per 10 cycles gave a conservative estimate of average crack opening stress for all the histories.