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SEMI‐ELLIPTICAL FATIGUE CRACK GROWTH UNDER ROTATING OR REVERSED BENDING COMBINED WITH STEADY TORSION
Author(s) -
Fonte M. A.,
Freitas M. M.
Publication year - 1997
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.1460-2695.1997.tb01533.x
Subject(s) - materials science , torsion (gastropod) , fretting , composite material , crack closure , structural engineering , paris' law , bending , mechanics , fracture mechanics , engineering , physics , medicine , surgery
— An analysis of the influence of steady torsion loading on fatigue crack growth rates under rotating or reversed bending is presented. Mixed‐mode (I + III) tests were carried out on cylindrical specimens in DIN Ck45k steel and results are compared for two different testing machines: rotary bending and reversed bending obtained by cyclic Mode I (Δ K 1 ) with or without superimposed static Mode III ( K III ) loading, simulating the real conditions on power rotor shafts where many failures occur. The growth and shape evolution of semi‐elliptical surface cracks, starting from a chordal notch on the cylindrical specimen surface, was measured for several Mode III/ Mode I ratios. Results have shown that the steady Mode III loading superimposed on the cyclic mode I leads to a significant reduction in the crack growth rates. It is suggested that this retardation is related to an increase of plastic zone size near the cylindrical surface in association with the interlocking of rough fracture surfaces, friction and fretting debris, leading to a decrease of the ΔK effective at the crack tip profile due to the “crack closure effect”. This work provides a contribution to a better understanding of crack growth rates under mixed‐mode load conditions thereby allowing one to predict remaining lifetimes and to estimate the risks of pre‐cracked rotor shafts.