If a large enough force is applied to a solid object the shape of the object can change. This change is called deformation and there are two types – elastic and plastic.
Elastic Deformation
If an object changes shape due to a force but re-gains it’s original shape once the force applied has been removed it’s said to have undergone elastic deformation.
For example, if you exert a force on a spring (i.e. stretch a spring) it is deformed. However, if you remove the force (stop stretching it) and it returns to its original shape it has been deformed elastically. Most materials are ‘elastic’ to a certain point.
Plastic Deformation
If an object doesn’t return to its original shape when it has been deformed it is said to have undergone plastic deformation.
For example, if a steel rod is bent and remains bent once the force has been removed (i.e. it’s permanently changed shape) then it has undergone plastic deformation.
Forces
There are two types of forces that are important when looking at the deformation of an object. These forces are:
Compressive Forces – a force that presses inwards on an object causing it to compact, i.e. squeezing an object
Tensile Forces – a force that causes tension in an object, i.e. stretching an object.
The Deformation of Objects
As mentioned above most materials can be deformed elastically for a certain amount of force. However, if this force is exceeded they undergo plastic deformation.
If we think back to a string, generally when a moderate force is applied, a spring returns to it its original shape. But if we keep stretching it, it gets to a point where it loses its ‘elastic’ property and becomes permanently deformed (‘plastic’).
This point is known as the elastic limit.
Elastic Limit – the maximum force that can be applied to an object before it undergoes plastic deformation.
Key Points
- Elastic Deformation – a temporary change in shape or size when a force is applied to an object
- Plastic Deformation – a permanent change in shape or size when a force is applied to an object
- Compressive Force – squeezes an object
- Tensile Force – stretches an object
- Elastic Limit – the maximum force an object can withstand before undergoing plastic deformation
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