Fatigue stress concentration factor (Kf)

Click For Summary

Discussion Overview

The discussion revolves around the fatigue stress concentration factor (Kf) and its relationship to the geometric stress concentration factor (Kt). Participants explore the reasons for the reduction of Kf compared to Kt, particularly in the context of material properties and fatigue loading.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant notes that Kf is reduced compared to Kt due to the material's sensitivity to notches.
  • Another participant suggests that Kt assumes a perfectly elastic and brittle material, while real-world materials exhibit some ductility, which may reduce peak stress.
  • A different participant emphasizes that for static loading of ductile materials, Kt is not computed, but Kt is relevant for fatigue since failure can occur before reaching the elastic limit.
  • One participant questions the role of ductility in the reduction of Kf compared to Kt, implying that ductility may not influence Kf as it does Kt.
  • A suggestion is made to search for information on fatigue notch sensitivity for further understanding.

Areas of Agreement / Disagreement

Participants express differing views on the factors influencing the reduction of Kf compared to Kt, indicating that multiple competing perspectives remain without a consensus.

Contextual Notes

There are unresolved aspects regarding the definitions and assumptions related to Kf and Kt, particularly concerning the role of material ductility and notch sensitivity in fatigue analysis.

kajalschopra
Messages
40
Reaction score
0
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?
 
Physics news on Phys.org
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.
 

Similar threads

Graduate What is the fatigue limit for copper pipe with a factor of safety of 5?
  • · Replies 2 ·
Replies
2
Views
1K
Effects of notch's position along a rod that is in tension
  • · Replies 2 ·
Replies
2
Views
2K
Fatigue life hand calculations based on static FEA results
  • · Replies 4 ·
Replies
4
Views
3K
Understanding Stress Concentration Factor in FEA for Stepped Shafts
  • · Replies 3 ·
Replies
3
Views
2K
Confidence in FEA stress values?
  • · Replies 9 ·
Replies
9
Views
4K
Calculating time to reduce alcohol in wine using heating method
  • · Replies 131 ·
5
Replies
131
Views
11K
What is the maximum mean stress in a bolted joint?
  • · Replies 12 ·
Replies
12
Views
14K
Fatigue strength of 304, cold worked versus annealed
  • · Replies 4 ·
Replies
4
Views
8K
What is the purpose of a stress concentration factor?
  • · Replies 3 ·
Replies
3
Views
14K
Graduate Stress-energy tensor for a single photon
  • · Replies 5 ·
Replies
5
Views
5K