Types of Stress

Tensile Stress:

Tensile stress (or tension) is the stress state leading to expansion; that is, the length of a material tends to increase in the tensile direction. The volume of the material stays constant. When equal and opposite forces are applied on a body, then the stress due to this force is called tensile stress.

Therefore in a uni-axial material the length increases in the tensile stress direction and the other two directions will decrease in size. In the uni-axial manner of tension, tensile stress is induced by pulling forces.

Compressive Stress:

Compressive stress (or compression) is the stress state leading to shortening; that is, the length of a material tends to decrease in the tensile direction. The volume of the material stays constant. When the length of a material is compressed under the action of the applied force, the restoring force per unit area is known as the compressive stress.

Shear Stress:

Such stresses are created when the forces are transmitted from one part of the body to the other by causing stresses in the plane parallel to the applied force. When a body is subjected to load P consisting of two equal and opposite parallel forces not in same line, it tends to shear off across the resisting section. The stress induced in the body is called shear stress.

Thermal Stress:

When a body is subjected to change in temperature its dimensions get changed. For metals when the temperature of a body is increased there is a corresponding increase in its dimensions. When the body is free to expand no stress develops. 
But, in case the body is constrained to prevent the change in dimensions, the stresses develop in the material. These stresses are called as thermal stress. It may be tensile or compressive depending upon whether the contraction is prevented or extension is prevented.