What is an Axial load?

When a bar of the uniform cross-section is acted by a load, such that the load acts along the longitudinal axis of the bar, such kinds of loadings are known as axial loadings. In general terms, a load is an external force acting on a component. An axial load acts perpendicular to the geometric cross-section of the component. Based on the direction of the application of the load, an axial load can be tensile or compressive. The analysis of bodies under the action of axial loads is generally studied under the branch of mechanics, known as statics.

Additionally, the line of application of the forces decides the behavioral nature of the body under the application of such forces.

Line of action of force passing through the centroid

When the line of action of the forces passes through the centroid of the cross-section, such forces cause a deformation in the body. When the forces are applied away from the cross-section, such that the line of action is in the opposite direction of the cross-section, such forces are called tensile forces. If the line of action of force acts towards the cross-section of the body, the force is called compressive force.

The deformation by the tensile forces causes an increase in length and a decrease in the width of the component. However, the deformation by the compressive forces causes a decrease in length and an increase in the width of the component. For example, in the flange used for the interconnection of two bodies co-axially, the bolts that are used for the tightening purpose are subjected to crushing stresses due to the compressive loads' action on them.

Line of action of force passing at a distance from the centroid

When the line of action of force does not pass through the centroid of the body but acts at some distance from the centroid, such forces, along with the effects caused by the tensile forces and compressive forces, tend to cause a moment in the body. This moment gives a rotation to the body. Under such applied forces, the body undergoes rotations about the polar axis.

Shear force and shear modulus

The loads that act parallel to the cross-section of the body and act perpendicular to the longitudinal axis, are known as shear forces. The body under the action of shear forces undergoes cross-sectional changes or deformations. The resistance provided by the body for these deformations caused due to the shear forces is known as the shear modulus of the body. The shear modulus is known as the amount of elastic stiffness provided by the body in response to the shear deformations. For example, in beams, the type of loadings are shear loadings. Under the action of such loads, the beam undergoes deflection. The resistance to such deflection/deformations is given by the shear modulus of the beam.

Thrust load and ball bearings

When there is a relative motion between two bodies such that one of them supports, guides, and carries the load of the other body, the other body is known as a bearing. Angular contact bearings and ball bearings are one such example. The rotations of the angular contact bearing produce both radial loads (loads acting perpendicular to the body) and thrust loads (loads acting along the axis of the body), whereas ball bearings only produce thrust loads. Bearing endurance is often represented by load capacity. It is the load that the bearing can withstand before its races undergo 0.001% of deformations.

Context and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for

• Bachelors in Science (Physics)
• Bachelor of Technology in Civil Engineering
• Bachelor of Technology in Mechanical Engineering

Practice Problems

1. Which of the following forces cause an increase in length and decrease in the width of the component?

1. Tensile load
2. Compressive load
3. Shear load
4. Moment

Correct option- a

Explanation: Tensile load acts away from the cross-section of the body, such kinds of loads causes the width of the body to decrease with an increase in the length of the body.

2. Which of the following statements are true for an axial load?

1. Axial load acts along the longitudinal axis of the body
2. Axial load acts perpendicular to the cross-section of the body
3. Axial load acts along the cross-section of the body
4. Axial load acts perpendicular to the longitudinal axis of the body

Correct option: Both a and b

Explanation: An axial load acts perpendicular to the cross-section of a body or acts along the longitudinal axis of the body.

3. Under which of the following conditions of the applied load the body experiences a moment?

1. The applied load must pass through the centroid of the body
2. The applied load must pass through the center of gravity
3. The applied load must pass through the cross-sectional area of the body at a distance from the centroid
4. None of these

Correct option- c

Explanation: When the axial load acts at a distance from the centroid of the body, the body experiences a moment. The moment tends to rotate the body about the polar axis.

4. Which of the following loads acts on the bolts of a flange?

1. Compressive load
2. Tensile load
3. Shear load
4. Impact load

Correct option- a

Explanation: The flange is used to join two co-axial bodies. The bodies that are to be connected by a flange, are joined together using nuts and bolts. The bolts press the surface of the flange and induce high compressive loads.

5. Which of the following loads are experienced by a ball bearing?

1. Thrust loads
2. Radial loads
3. Both thrust and radial loads
4. None of these

Correct option- a

Explanation: A ball bearing generally supports high-speed rotating shafts, the enter of gravity of the shaft never matches the axis of rotations which causes a shift in the mass center from the axis of rotation. This shift has an eccentricity. Due to this eccentricity, the shafts experience a whirling phenomenon, i.e. lateral vibrations. These lateral vibrations induce thrust loads to the ball bearing.