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Home  >  Journal list  >  MATERIALS TRANSACTIONS  >  Vol.42  No.8 (2001)  >  pp.1502-1508

MATERIALS TRANSACTIONS
<<Previous article Vol.42  No.8 (2001)   pp.1502 - 1508 Next article>>

Effects of Overload and Frequency on Fatigue Crack Propagation in Nanocrystalline Zr-Based Bulk Metallic Glass

Kazutaka Fujita1), Akihisa Inoue2) and Tao Zhang2)
1) Department of Mechanical Engineering, Ube National College of Technology
2) Institute for Materials Research, Tohoku University


A nanocrystalline (NC) bulk glass Zr55Al10Cu30Ni5(at%) containing nano-scale crystals embedded uniformly in a glassy matrix has both high tensile strength of 1.7 GPa and high ductility. The new alloy is therefore expected to have practical applications in machines and structures. The influences of frequency and overload on fatigue crack propagation behavior of the NC bulk glass were examined. The fatigue crack propagation rate dadn less than 3×10−5 mm/cycle was independent of frequency in the frequency range of 0.1 to 50 Hz at the stress ratio of 0.1 under sine and triangular waves. When the overload ratio (overload/baseline load) was large, a complete crack arrest occurred and the ΔK value just before a crack regrowth was three times larger than the threshold stress intensity factor range ΔKth. The reason for the crack arrest was not explained by the crack closure effect. The overloading induced the kinking and branching of the crack. The stress reduction near the crack tip due to the kinking and branching of the crack and the crack closure effect gave an appropriate explanation for the complete crack arrest and the larger threshold stress intensity factor range. When the overload ratio was small, a temporary crack arrest occurred and the kink and branching of cracks occurred intermittently at the crack front.


Keyword:
fatigue crack, nanocrystal, bulk metallic glass, frequency, overload, delay, arrest, retardation

Received: March 05, 2001
Accepted: June 04, 2001 , Published online: September 06, 2005
Copyright (c) 2005 The Japan Institute of Metals

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