Fatigue stress concentration factor (Kf)

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SUMMARY

The fatigue stress concentration factor (Kf) is consistently lower than the geometric stress concentration factor (Kt) due to the inherent ductility present in most materials, which mitigates peak stress concentrations. Kt is based on the assumption of a perfectly elastic and brittle material, while Kf accounts for the material's behavior under cyclic loading conditions. This distinction is crucial as Kf reflects the material's notch sensitivity, which is essential for predicting fatigue failure before reaching the yield point. Understanding the relationship between Kf and Kt is vital for accurate fatigue analysis in engineering applications.

PREREQUISITES
  • Understanding of fatigue analysis in materials engineering
  • Knowledge of stress concentration factors (Kt and Kf)
  • Familiarity with material ductility and its effects on stress distribution
  • Basic principles of elastic and plastic deformation
NEXT STEPS
  • Research "fatigue notch sensitivity" to understand its impact on Kf
  • Study the differences between elastic and plastic deformation in materials
  • Explore methods for calculating Kf in various materials
  • Investigate case studies on fatigue failure in ductile materials
USEFUL FOR

Engineers, materials scientists, and researchers focused on fatigue analysis and stress concentration in structural components will benefit from this discussion.

kajalschopra
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Hi,

I had been reading about the fatigue stress concentration factor (Kf) which is reduced compared to the geometric stress concentration factor (Kt). The reduction in turn dpends upon the material's sensitivity to notches.

https://moodlearn.ariel.ac.il/pluginfile.php/456050/mod_resource/content/0/Stress-consentration.pdf

I'm not able to sense why the fatigue stress concentration factor (Kf) is reduced compared to the geometric stress concentration factor (Kt).

What is the reason?
 
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Simplified explanation: Kt assumes a perfectly elastic perfectly brittle material. In the real world, most materials have at least a little ductility, if only on a microscopic scale. That ductility reduces the stress at the point of peak stress.
 
Simplified explanation: Kt assumes a perfectly elastic perfectly brittle material. In the real world, most materials have at least a little ductility, if only on a microscopic scale. That ductility reduces the stress at the point of peak stress.

I know. Also, for static loading for ductile materials we do not compute kt. The question is for fatigue we do compute kt because failure in fatigue can be anticipated before material reaches elastic limit / yield point.

Why kf is lesser than kt ? Ductility has no role to play in the reduction of kf than kt.
 
Google is your friend. Use search terms fatigue notch sensitivity.
 

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