Fatigue crack initiation and propagation behavior in Al – 7075 alloy under in-phase bending-torsion loading

•Fatigue crack nucleation on the plane of maximum shear stress.•Mix-mode crack propagation with inverted S-shaped trajectory for pure bending load.•Crack path include mode I, transition & mode II region in combined bending-torsion.•Microscale features indicate nucleation is a brittle cleavage fr...

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Bibliographic Details
Published in:International journal of fatigue 2019-09, Vol.126, p.346-356
Main Authors: Singh, Abhay K., Datta, Siddhant, Chattopadhyay, Aditi, Riddick, Jaret C., Hall, Asha J.
Format: Article
Language:English
Subjects:
Aluminum base alloys
Bend tests
Bending fatigue
Bending-torsion
Crack initiation
Crack propagation
Fatigue failure
Fractography
Fracture mechanics
Fracture surfaces
Materials fatigue
Multiaxial fatigue
Propagation
Shear stress
Stress propagation
Torsion
Trajectories
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Summary:•Fatigue crack nucleation on the plane of maximum shear stress.•Mix-mode crack propagation with inverted S-shaped trajectory for pure bending load.•Crack path include mode I, transition & mode II region in combined bending-torsion.•Microscale features indicate nucleation is a brittle cleavage fracture.•Striations, intergranular and transgranular fracture observed in stage II growth. Fatigue crack initiation and propagation behavior were investigated on a tubular specimen of Al 7075 alloy subjected to multiaxial mixed mode bending-torsional loadings. Tests under pure bending and pure torsional loadings were also conducted to segregate the effect of multiaxiality. A single crack nucleated on the plane of maximum shear stress in all the tests, except for pure torsion. For pure bending, crack propagated on the plane of maximum shear stress in a mixed mode condition tracing an inverted S-shaped trajectory; whereas, crack trajectory under combined bending-torsional load consisted of mode I dominant region, transition region, and pure mode II region. Furthermore, analyses of fracture surfaces were conducted to determine the micro-mechanisms governing crack initiation and propagation behavior.
ISSN:0142-1123
1879-3452
DOI:10.1016/j.ijfatigue.2019.05.024