Material fatigue in fasteners occurs when its under cyclic loading
Material Fatigue and Stress
What is Material Fatigue?
It is a weaking of material which happens due to repeated or fluctuating cyclic loads. Due to repeated stress micro cracks start developing in the material. Fatigue causes up to 90% of all fastener failures in critical applications.
We can prevent it using below measures:
- Wind Tunnel Testing
- Stiffening the Structure
- Structural Dampers
View improper fasteners installation techniques
Improper Installation Techniques
There are several common improper installation techniques
- Over tightening of bolts or nuts which is known as excess torque.
- Under tightening of bolts or nuts also causes fastener failure
- Misalignment when threading a bolt or nut
- Lack of lubrication can cause threads to seize or strip.
- Improper or No washers
Corrosion and Environmental Damage
Corrosion or environmental damage occurs when material get affected due to chemical or electrochemical reactions. Moisture, salt, chemicals, and temperature cycling plays important role in environmental damage of fasteners.
Below are several types of corrosion which effects fasteners:
Galvanic Corrosion: Mixed metal fasteners which are not compatible with each other when comes in contact within a corrosive environment, It accelerates a corrosion of fastener.
General Corrosion: It happens due to exposure of moisture and oxygen.
Stress Corrosion Cracking: It happens due to mechanical stress and corrosive attack on fasteners. Stainless steel fasteners are more susceptible to it in chloride environments.
Material and Size Selection Errors
Selecting wrong size fasteners for application creates a condition of early failure. Using low strength or wrong material can face a issues like galvanic corrosion, fatigue cracking or excessive wear or deformation.
Size selection is also important to prevent fasteners failures, Undersized or Oversized fasteners may not fit properly and can lead to uneven load distribution or bending.
Inaccurate Load Calculations
If actual load exceeds the design capacity fasteners can fail. Overloading occurs when calculated working load lacks the sufficient margin.