Premium
ON THE NUCLEATION OF FATIGUE CRACKS IN PURE POLYCRYSTALLINE α‐IRON
Author(s) -
GUIU F.,
DULNIAK R.,
EDWARDS B. C.
Publication year - 1982
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.1460-2695.1982.tb01240.x
Subject(s) - materials science , grain boundary , nucleation , crystallite , cracking , fatigue testing , metallurgy , crack closure , amplitude , fatigue limit , deformation (meteorology) , composite material , fracture mechanics , microstructure , physics , chemistry , organic chemistry , quantum mechanics
— This paper presents the results of an investigation of fatigue crack initiation in pure polycrystalline α‐iron as a function of testing frequency (0.01–1000 Hz). Three distinct types of fatigue crack initiation mechanisms were identified: (i) At low frequencies, <0.5 Hz, cracks were observed to nucleate at intrusions, extrusions and grain boundaries. However over the frequency range studied the cracks at the intrusions and extrusions were not associated with the final fatigue failure. The results suggest that in pure iron frequencies <0.01 Hz are required for fatigue failure to be initiated at intrusions and extrusions. (ii) At frequencies ≤0.01 Hz at high strain amplitudes, cracks nucleated at the intersection of grain boundaries with the free surface as a result of the incompatable deformation of surface grains. The subsequent propagation of these cracks resulted in fatigue failure. (iii) Tests performed at low strain amplitude at 5 Hz and 1000 Hz initiated surface grain boundary cracking without any significant associated change of grain shape. The results of the present investigation indicate that fatigue failure in pure iron alloys (at frequencies >0.01 Hz) is initiated not at intrusions and extrusions but at grain boundaries.