Creep, Fatigue and Wear Flashcards
What is Creep?
Creep is when a material is plastically deformed over a long period of time.
Under what circumstances does creep occur?
Occurs when a material is loaded below its yield stress and at a high temperature.
Why does creep occur?
Creep occurs because of dislocations moving in the material structure over time.
During creep in amorphous materials, do atoms or molecules move past each other?
Atoms.
During creep in thermoplastics, do atoms or molecules move past each other?
Molecules.
What are some examples of consequences of creep?
Electric cable extension.
Turbine blade extension.
Car tyres going flat after long period of time.
What is Fatigue?
Fatigue occurs when a stress below a materials yield strength is applied and removed.
Is fatigue easy or difficult to predict?
Difficult even in ductile materials.
What are some examples of stress raisers?
Cracks, notches or indentations.
What affect does temperature have on rate of fatigue?
Rate of fatigue increased in a high temperature environment.
When does Wear occur?
When components are in contact with each other.
Describe the 4 types of wear.
Adhesive wear - Parts of component break away and increase wear.
Abrasive wear - Hard small particles (grit) get caught between components and increase wear.
Corrosive wear - Chemical damage combined with adhesive or abrasive wear.
Surface fatigue - e.g roller bearing on surface
