A static load is a force or couple applied to a member that is unchanging in magnitude, and point(s) of application and direction. They cannot change in any manner, We need to examine the relationship between strength and static loading to ensure appropriate material selection.
A dynamic load refers to forces and couples that are not constant across time. Fatigue failure is repetitive exposures to fluctuating stresses. These are often due to cracks developing and causing areas of stress concentration leading sudden failures.
Stress Concentration
Stress concentration is often used for analyzing failures with static and dynamic loads.
For static loads:
- Ductile materials
- Stress concentration is usually not applied to predict critical stress
- Stress concentration is localized and has a strengthening effect
- Brittle materials
- Stress concentration factor is applied to nominal stress before comparing with strength
For dynamic loads:
- Always consider stress concentration effect