Before we go for types of stress in material we should know the definition of Stress. Stress is defined as the internal resistance set up by a body when it is deformed. It is measured in N/m2 and this unit is specifically called Pascal (Pa). A bigger unit of stress is the mega Pascal (MPa).
1 Pa = 1N/m2,
1MPa = 106 N/m2 =1N/mm2.
1.Tensile stress: The stress induced in a body when subjected to two equal and opposite pulls, as a result of which there is an increase to length is known as tensile stress.
Consider a uniform bar of cross sectional area A subjected to an axial tensile force P. The stress at any section x-x normal to the line of action of the tensile force P is specifically called tensile stress pt . Since internal resistance R at x-x is equal to the applied force P, we have,
pt = (internal resistance at x-x)/(resisting area at x-x)
Under tensile stress the bar suffers stretching or elongation.
2.Compressive Stress: The stress induced in a body when subjected to two equal and opposite pushes, as a result of which there is an decrease in length of the body is known as compressive stress.
If the bar is subjected to axial compression instead of axial tension, the stress developed at x-x is specifically called compressive stress pc.
3. Shear Stress: The stress induced in a body when subjected to two equal and opposite forces are acting tangentially across the resistance section, as a result of which the body tends to shear of across the section is known as shear stress.
Consider the section x-x of the rivet forming joint between two plates subjected to a tensile force P as shown in figure.
The stresses set up at the section x-x acts along the surface of the section, that is, along a direction tangential to the section. It is specifically called shear or tangential stress at the section and is denoted by q.
4. Bending Stress: When a beam is loaded with some external forces bending moments and shear forces are set up. The bending moment at a section tends to bend or deflect the beam and internal stress are developed to resist the bending. These stress are called bending stresses.
5. Torsional Stresses: When a machine member is subjected with to equal and opposite couples acting in parallel planes then the member is said to be in torsion. The stress induced by this torsion is called Torsional Stress.