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ΔK ol level effects on fatigue crack propagation

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Abstract

In order to determine the effects of ΔK ol level on fatigue life, a single peak load was applied at distinct ΔK levels of 7.8×10.3 and 9.8×103 p.s.i. in1/2. Here the ΔK ol level was defined to be a ΔK level at which overload was applied. Three different overload ratios of 1.5, 2.0, and 2.5 were used to determine the overload ratio effect on the recovery factor. The result showed that the recovery factor, Z, was linearly related to ΔK as Z = qΔK+Z o, where q was a function of overload ratio. The value of q decreased as the overload ratio increased in a given ΔK ol level and seemed to be an important factor as well as retardation cycles in determining the fatigue life. For the same overload ratio, specimens that underwent overload at a smaller ΔK ol level showed more improved fatigue life.

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Abbreviations

a :

Crack length

a * :

Overload affected zone size

B :

Specimen thickness

(da/dN)ca :

Crack growth rate due to constant amplitude fatigue load

(da/dN)ol :

Crack growth rate after overload is applied

E :

Young's modulus

K :

Stress intensity factor

K min :

Minimum stress intensity factor

K max :

Maximum stress intensity factor

ΔK ol :

ΔK level at which overload is applied

N :

Number of cycles

N D :

Number of delayed cycles

N f :

Number of cycles needed for a specimen to be completely fractured

r p :

Assumed plastic zone size

S :

Load

σys :

Yield stress

W :

Width

Z :

Recovery factor

References

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Authors and Affiliations

  1. Agency for Defense Development, P.O. Box 35, 305-600, Yuseong, Korea

    Kyong Y. Rhee

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  1. Kyong Y. Rhee
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Rhee, K.Y. ΔK ol level effects on fatigue crack propagation. JOURNAL OF MATERIALS SCIENCE 29, 6501–6504 (1994). https://doi.org/10.1007/BF00354011

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  • DOI: https://doi.org/10.1007/BF00354011

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