chapter 9
Elasticity of Solids
Deformation: Changes in shape or size of an object through the application of external forces.
Elasticity: Property which allows a material to regain its shape after being distorted.
Elastic Limit: The maximum amounts by which an object or a material can be stretched and still regain its original shape after the distorting forces are removed.
An object or a material which returns to its original length or size after being distorted suffers elastic deformation, i.e. it behaves within the elastic limit.
Plastic deformation occurs when a material is deformed beyond its elastic limit.
Stress and Strain
The elastic properties of solids are discussed in terms of stress and strain.
Stress, s is the force acting on a unit cross-section area.
Stress,
The unit of stress is N m-2 or Pascal (Pa)
There are three types of stress, they are:
(i) Tensile stress
(ii) Compressive stress
(iii) Shear stress
Strain, e is defined as the extension per unit length.
Strain,
Where = extension/elongation = original length
There are two types of strain, they are:
(i) Tensile strain =
=
(ii) Compressive strain = =
Strain is the ratio of the change in length to the original length, therefore it is a dimensionless quantity or it has no unit.
Force and Elongation
When a wire is being stretched, an elongation will occur. During this process, the attractive force between the atoms will increase (up to a point) and this will prevents the elongation process from occurring. When the wire is being
Deformation: Changes in shape or size of an object through the application of external forces.
Elasticity: Property which allows a material to regain its shape after being distorted.
Elastic Limit: The maximum amounts by which an object or a material can be stretched and still regain its original shape after the distorting forces are removed.
An object or a material which returns to its original length or size after being distorted suffers elastic deformation, i.e. it behaves within the elastic limit.
Plastic deformation occurs when a material is deformed beyond its elastic limit.
Stress and Strain
The elastic properties of solids are discussed in terms of stress and strain.
Stress, s is the force acting on a unit cross-section area.
Stress,
The unit of stress is N m-2 or Pascal (Pa)
There are three types of stress, they are:
(i) Tensile stress
(ii) Compressive stress
(iii) Shear stress
Strain, e is defined as the extension per unit length.
Strain,
Where = extension/elongation = original length
There are two types of strain, they are:
(i) Tensile strain =
=
(ii) Compressive strain = =
Strain is the ratio of the change in length to the original length, therefore it is a dimensionless quantity or it has no unit.
Force and Elongation
When a wire is being stretched, an elongation will occur. During this process, the attractive force between the atoms will increase (up to a point) and this will prevents the elongation process from occurring. When the wire is being