Stress Concentration Reduction

Stress Concentration Reduction

Improving Fatigue Resistance

It is good mechanical design practice to reduce as far as possible the risk from fatigue loading.   This will involve the following:

• Reducing /Eliminating cyclic loads - (Rotating Loads - Vibration etc).
• Reducing operating cycles- (Using lower rotating speeds /Regular part replacement)
• Selecting materials which are tolerant to cyclic loading (ductile /tough materials )
• Reducing/eliminating the stress severe concentrations - (no sharp corners or sudden size changes )
• Specifying manufacturing processes to provide fatigue resistance (Peening /shot blasting/Cold Working )
• Specifying heat treatment to provide fatigue resistance- (Carburising /Nitriding )
• Overdesigning part to reduce stress levels
• Preloading to convert cycling load to steady load (bolt preloading)

Below are illustrated a number of methods of reducing stress concentrations....

Shafts

Screw Threads

Welds

Reduce weld created stresses by heat treatment (stress relieving /anealing).
Welds to be high quality with no cracks, porosity and slag inclusions.
Welds to have smooth profiles with no sharp corners at interface with parent metal. (Concave not convex weld surfaces...

Useful Links..

1. Metal Improvements ...->Shot peening - specialist in improving metal fatigue performance
2. Fatigue Basics -epi_eng ...Useful set of notes