Types of Stress

What are different types of Stresses?

When a beam is loaded, stress is developed in it. Different types of stress that are developed in a loaded beam depend on the type of beam and their loading patterns.

If the stress is more than a permissible limit, it fails to sustain. This permissible limit depends upon (1) type of loading ( i.e. static load, variable load or cyclic load etc. ) and (2) pattern of loading ( i.e. point load, uniformly distributed load or loading of a couple etc. ).

Stress

We know about the elastic behavior of a material. Almost all materials are elastic in nature. When an external force is applied on a body, the body undergoes some deformation. This deformation also depends on the types of stress which may be an elastic deformation or plastic deformation. Because of this deformation, the body material sets up some resistance to oppose deformation and external force. This resistance is called stress.

Therefore, stress is defined as the internal resistance which sets up in a body to resist any deformation by an applied external force.

Mathematically, the stress is defined as – “Force per unit area”

Therefore, \quad f = \left ( \frac {F}{A} \right )

Here ( f ) is intensity of stress, ( A ) is area of cross section of body and ( F ) is applied force or load on body.

Types of Stress in a cylindrical rod

A rod of uniform circular cross section can be used for different purposes in different manners. Such as –

1. It can be used as a vertical pillar or a column. In this case, axis of rod is placed vertical and a vertical load is applied which is co-axial to the longitudinal axis of the rod. The stress developed in this member is called longitudinal compressive stress.
2. The rod can be used as a truss or an inclined structural member. In this case, rod axis is inclined to the vertical and a vertical load is applied which is neither co-axial to the longitudinal axis of rod nor perpendicular to the axis. Thus two or more type of stresses are developed. The stress developed in this member is complex in nature.
3. It can be used as a cantilever beam or simply supported beam. In this case, rod is placed horizontally and a vertical load is applied perpendicular to the longitudinal axis of rod. Stress developed in this member is called bending stress.
4. The rod can also be used as a shaft or an axle of a wheel. In this case it suffers torsion or torque. A torque is applied tangentially to the circumference of cross sectional area or rod. Stress developed in the member is called tangential stress or shearing stress.

Different types of loading and related stresses which develops in members are summarized as follows –

1. Tensile stress.
2. Compressive stress.
3. Superficial Shear Stress.
4. Bending Shear Stress.
5. Torsional Shear Stress.

Consider about the figure as shown below. The figure is self explanatory and tells about above stresses in details.

Tensile Stress

To know in details about tensile stress, consider about the figure ( A ). Here –

Loading pattern

1. Member is subjected to a pair of axial forces which are equal but act in opposite directions.
2. One force acts at each end of the member.
3. Line of action of the forces is parallel to the longitudinal axis of member and passes through the centre point of every transversal cross section.
4. Both forces have tendency to move away from each other.

Effect of stress

Effect of force is to increase the length of member.

Types of stress

Developed stress is called “Tensile Stress”.

USE – Vertical members used for hanging of loads such as, Lifting Tackles, Slings etc. are subjected to tensile stress.

Compressive Stress

To know in details about compressive stress, consider about the figure ( B ). Here –

Loading pattern

1. Member is subjected to a pair of axial forces which are equal but act in opposite directions.
2. One force acts at each end of the member.
3. Line of action of the forces is parallel to the longitudinal axis of the member and passes through the centre point of every transversal cross section.
4. Both forces have tendency to move towards each other.

Effect of stress

Effect of force is to decrease the length of member.

Types of stress

Developed stress is “Compressive Stress”.

USE – Vertical members used for supporting or holding of loads such as, Pillars, Columns etc. are subjected to compressive stress.

Superficial Shear Stress

To know in details about superficial shear stress, consider about the figure ( C ). Here –

Loading pattern

1. Member is subjected to a pair of tangential forces.
2. This force act tangential to the surface of the member.
3. Line of action of applied force is parallel to the transverse cross section of member.

Effect of stress

Effect of force are to slide one layer of transverse cross section over the other layer to deform shape of member.

Types of stress

Developed stress is “Superficial Shear Stress”.

USE – Members subjected to forces in transverse direction such as, Pushing a pile of papers or book etc. are subjected to superficial shear stress.

Bending Shear Stress

To know in details about the bending shear stress, consider about the figure ( D ). Here –

Loading pattern

1. Transverse section of members are subjected to radial forces.
2. Member is supported at one end ( called Cantilever ) or both ends ( called Simply Supported Beam. )
3. Line of action of applied forces is parallel to transverse cross section area of member.

Effect of stress

Effect of force is to slide one layer of transverse cross section over the other layer to deform its shape which causes bending.

Types of stress

Developed stress is “Bending Shear Stress”.

USE – Members which are placed horizontal and loaded with forces in transverse direction such as, Simply supported beams and Cantilevers etc. are subjected to bending shear stress.

Torsional Shear Stress

To know in details about the torsional shear stress, consider about the figure ( E ). Here –

Loading pattern

1. Transverse cross section of member is subjected to a pair of equal but opposite direction tangential rotating moment or torque or torsion.
2. One moment of force acts at each end of the member.
3. Line of action of applied forces is tangential to the circumference of transverse cross section area.

Effect of stress

Effect of forces is to rotate one layer of transverse cross section over the other layer to deform its shape in the form of twist.

Types of stress

Developed stress is “Torsional Shear Stress”.

USE – Horizontal or vertical members subjected to torque or twisting moment such as, Shafts, Axles etc. are subjected to torsional shear stress.