Stress concentration in mechanical design occurs when a geometric discontinuity causes local stress to rise above the nominal stress calculated from a simple section.
Common causes
- Sharp internal corners
- Holes and slots
- Sudden changes in section thickness
- Keyways and grooves
- Threads and notches
Why sharp corners matter
A sudden change in geometry forces load paths to change rapidly. This creates a local stress peak. Increasing the corner radius can often reduce the concentration and improve fatigue performance.
Stress concentration factor
The stress concentration factor, commonly written as Kt, relates peak elastic stress to nominal stress for a particular geometry and loading case. Charts, handbooks and validated analysis can be used to obtain appropriate values.
Practical design solutions
- Increase fillet radius.
- Use gradual section transitions.
- Move holes away from highly loaded edges when possible.
- Add relief geometry carefully around grooves and shoulders.
- Improve surface finish where fatigue is important.
Stress concentration and FEA
FEA can reveal local stress concentrations, but a sharp theoretical corner may produce a mathematical singularity. Do not automatically interpret an extremely high single-node stress as a real material stress. Refine the mesh and evaluate the stress field away from singular geometry.
Fatigue design
Stress concentration becomes especially important under cyclic loading. A component that survives a static load may still fail after repeated cycles if local alternating stress is high.
Learning stress concentration in mechanical design helps engineers create stronger brackets, shafts, frames and machine components without simply adding unnecessary material.