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The preferred fatigue crack propagation mode in a M250 maraging steel loaded in shear
Author(s) -
Pinna,
Doquet
Publication year - 1999
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 - 10.1046/j.1460-2695.1999.00161.x
Subject(s) - materials science , crack closure , stress intensity factor , crack tip opening displacement , paris' law , maraging steel , fracture mechanics , composite material , coalescence (physics) , torsion (gastropod) , structural engineering , stress concentration , mechanics , medicine , physics , surgery , astrobiology , engineering
Macroscopic torsional fatigue cracks are shown to propagate in shear, in plain tubular specimens, in the M250 maraging steel, for stress ranges from 90% down to 40% of the yield stress. This cannot be explained in terms of microcrack coalescence for the smallest stress range, for which microcracks are scarce. The kinetics and mechanisms of mode II fatigue crack growth are thus investigated, using precracked CTS or tubular specimens. For a high Δ K II , slowly decelerating mode II propagation takes place for a distance that increases with Δ K II before branching occurs. Friction stresses along the crack flanks shield the applied load and explain this deceleration. An inverse analytical procedure is used to derive the effective stress intensity factor, allowance being made for friction effects, from displacement profiles measured from microgrids using a scanning electron microscope. The measured crack growth rates correlate much better with the effective stress intensity factor than with the nominal Δ K II value. The crack paths observed in torsion are discussed in terms of maximum crack velocity.