Fatigue stress concentration factor (Kf)

[kajalschopra]

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?

 

[jrmichler]

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.

 

[kajalschopra]

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.

 

[jrmichler]

Google is your friend. Use search terms fatigue notch sensitivity.