IntermediateTopic 70 of 106Engineering Mechanics
Creep
Slow permanent deformation under steady load at high temperature.
In depth
Creep is time-dependent deformation under constant stress, important above 0.4 of the melting temperature (in kelvin). Three stages: primary, steady secondary and tertiary leading to rupture. Larson-Miller parameter correlates temperature and time.
Key points
- Turbine blades and boiler tubes
- Stress relaxation is related
- Polymers creep at room temperature
ExampleLead pipes sag over decades; nickel superalloys resist creep in jet engines.
Creep is the slow deformation under constant load at high temperature, so it limits turbine blades, boiler tubes and some polymers.
What is Creep?
Slow permanent deformation under steady load at high temperature.
Why is it important to understand creep?
Creep is the slow deformation under constant load at high temperature, so it limits turbine blades, boiler tubes and some polymers.
At what temperature does creep matter for metals?
It becomes significant roughly above 0.4 times the absolute melting temperature, which is why it limits high-temperature metal design.
How is creep different from plasticity?
Plasticity happens when the stress exceeds yield at any temperature, while creep is time-dependent and can occur below yield at high temperature.
How is Creep used in practice?
Typical applications include selecting an alloy for a turbine blade operating near its melting point, estimating the sag of a plastic pipe hanging under its own weight over years and designing the wall of a steam pipe to survive decades at high temperature.
What should I learn before Creep?
Study "Fracture mechanics" first (topic 69 of 106 in Engineering Mechanics). It covers the groundwork this topic builds on.
What are the key points of Creep?
Turbine blades and boiler tubes. Stress relaxation is related. Polymers creep at room temperature.
Can you give an example of Creep?
Lead pipes sag over decades; nickel superalloys resist creep in jet engines.
What comes after Creep?
The next topic is "Plasticity and yielding", which builds directly on this one.
How difficult is Creep?
It is classed as Intermediate in Engineering Mechanics (topic 70 of 106). It is an intermediate topic. Work through the beginner topics in Engineering Mechanics first.