A Model for Joining the Fatigue Crack Initiation and Propagation Analyses
by
W.-C. Chen
Department of Metallurgy and Mining Engineering
and
F. V. Lawrence
Professor of Civil Engineering and Metallurgy
Abstract
An analytical model for nonarbitrarily defining the crack initiation length (aI) of a notched member on the basis of the minimum total life estimate (Life-calculation method) is proposed. The crack initiation length (aI) is not a fixed value, as usually assumed, but varies with stress level (or life), notch size, notch geometry, and material. The partitioning of crack initiation life (NI) and crack propagation life (Np) can be achieved using this model. This model provides an interpretation of fatigue notch size effect and a powerful means for numerically determining Neuber and Peterson parameters " p1/2" and "a1/2".
On the basis of crack initiation life, K f is determined from the stress-strain parameter (ΔΣI DeI E)1/2 at the crack initiation length (aI). The longstanding problem as to how to join the NI estimate using the local stress-strain approach and the Np estimate using fracture mechanics concepts appears to be solved through the use of a I defined by the proposed model.
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