J. Braz. Soc. Mech. Sci. & Eng. vol.29 número1

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The aim of this work is to propose a methodology to estimate the fatigue limit of cylindrical contacts under a partial slip regime. Taylor’s point stress method, usually applied to estimate fatigue limit for notched structures, was associated with the Modified Wöhler Curves to define the fretting crack initiation threshold methodology. Twenty nine tests on cylindrical contacts were selected from the literature and considered to evaluate the quality of the estimates. The results agree well for twenty three experimental data. As the fatigue limit under fully reversed bending is the fatigue parameter usually available for most metallic alloys, it was also showed how the second fatigue limit needed to calibrate the proposed procedure could be estimated by taking full advantage from other standard predictive methodologies previously devised to estimate the mean stress effect under uniaxial fatigue loading.

Keywords: fretting fatigue, notch fatigue, multiaxial fatigue, short cracks, critical distance, size effect.

Introduction

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a9Contact semi width.

a09Maximum non propagating crack length a0= Specimen width

c = Stich zone half width at the instant of maximum or minimum shear load.

d = Stick zone half width at an intermediate load step.

e = Stick zone offset from the centre of the contact at the instant of maximum or minimum shear load.

e’9Stick zone offset from the centre of the contact at an intermediate load step.

E = Young’s modulus

F = Geometrical correction factor for the stress intensity factor m1,λ= Constants depending on the material fatigue strength l9Specimen thickness

L = Characteristic material length constant (:= 1) P = Normal load.

p0 = Peak pressure. Q = Shear load.

Qmax= Amplitude of the shear load.

:= Load or stress ratio. R = Pad radius

t9Time instant. w = Load frequency.

Kth= Range of the threshold value of the stress intensity factor

ρ= Stress ratio on the plane of maximum shear stress amplitude

σ1= Range of the linear elastic maximum principal stress

σ−1= Fully reversed uniaxial plane fatigue limit ( range)

σ1 =Fully reversed uniaxial plane fatigue limit (amplitude)

σ0 =Uniaxial fatigue limit under zero to tension (repeated) loading.

σa=Amplitude of normal stress.

σB(t) = Bulk stress at time instant t. σBmax= Amplitude of the bulk stress.

σm= Mean normal stress. σ

σ σ

σn₉_{Stress tensor due to the normal load}

σn,max= Maximum stress normal to the critical plane σ

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σys = Yield stress.

σus = Ultimate tensile strength.

σ′f = Fatigue strength coefficient.

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τa= Maximum shear stress amplitude among the material planes

Fatigue Damage and Structural Volume

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The theory of critical distances (TCD) and the modified Wöhler curve method (MWCM)

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The Procedure to Apply the MWCM in Terms of the TCD for Fretting Fatigue

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References

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