# Stress in Strength of Material

In this blog we will study the definition of stress, scalar quantity or zeroth order tensor, vector quantity or first-order tensor, Tensor that is also called a second-order tensor, we will discuss the examples of scalar, vector, and tensor quantity. We will also answer the question like can we measure stress? What is the difference between stress and pressure?, What is Strength? Not only this we will also discuss many key points related to stress in the strength of material.

### Stress (σ)

When an External Influence (that includes force, moment, torque, etc.) acts on a material, a resisting force is produced within a body. The internal resistance force per unit area acting in a particular plane is known as Stress. Stress is a Tensor quantity because it depends on direction, magnitude and plane.

Scalar quantities are zeroth-order tensor since only magnitude is needed to specify them, Vector quantities are first-order tensor because along with magnitude, the direction is also needed and if you talk about second-order tensor then other than magnitude, direction, and plane both are needed.

• Example of scalar quantity: volume, density, speed, energy, mass, and time
• Example of Vector quantity: Force and Velocity
• Example of Tensor: Stress and Strain

## Can we measure the Stress?

No, We cannot measure stress. It is not a measurable quantity. But strain is a measurable quantity. Using Strain gauge, you can easily measure the strain. We know that stress is a function of strain so we can calculate stress mathematically with the help of strain.

## Points to ponder

• Engineering Stress is also known as Nominal or conventional stress. In the strength of material and machine design (Theory of elasticity), we will always use engineering stress and engineering strain.
• In the theory of plasticity (Metal forming), we have to use true stress and true strain.
• SI unit: Pascal
• Common symbols: σ
• In SI base units: Pa = kg⋅m−1⋅s−2
• Stress is only developed when a body is restricted.
• Stress is independent of Material Properties whereas strength is a property of the material. But here the question arises that what is strength? The maximum amount of stress that a material can withstand without failure is called Strength.

## What is the difference between Stress and Pressure?

Since the unit of stress and pressure is the same so it creates confusion between these two terms. Now let us compare the definition of both terms. The pressure is an external normal force per unit area whereas stress is an internal resistance force per unit area in a particular plane.

The pressure is always normal to the area whereas stress needs not be normal to the area. Pressure s a scalar quantity whereas stress is a second order tensor. Pressure is a measurable quantity whereas stress can be calculated but cannot be measured.

## Strength

As we have already discussed that strength is the maximum amount of stress that a material can withstand without failure (yielding, fracture, buckling, etc). The unit of strength is the same as that of the stress. For no yielding, the value of applied stress should be less than the value of yielding stress. For no fracture condition, the value of applied stress is less should be less than the value of ultimate stress.

Let us understand the concept of strength with the help of an example: Let 750 MPa be the strength of Material – A. If you apply 100 MPa, Material- A will not fail, If you apply 500 MPa then also Material- A will not fail. Even If you apply 749 MPa to it then also it will not fail. But as soon as you apply 750 MPa or greater than that then the material will fail. Since 750 MPa is the strength of Material- A.

### What is Stress?

When an External Influence (that includes force, moment, torque, etc.) acts on a material, a resisting force is produced within a body. The internal resistance force per unit area acting in a particular plane is known as Stress. Stress is a Tensor quantity because it depends on direction, magnitude and plane.

### What is Strength?

The maximum amount of stress that a material can withstand without failure is called Strength.

### What is the difference between Stress and Pressure?

The pressure is an external normal force per unit area whereas stress is an internal resistance force per unit area in a particular plane. The pressure is always normal to the area whereas stress needs not be normal to the area. Pressure s a scalar quantity whereas stress is a second-order tensor. The pressure is a measurable quantity whereas stress can be calculated but cannot be measured.

### Can we measure stress?

No, We cannot measure stress. It is not a measurable quantity. But strain is a measurable quantity. Using Strain gauge, you can easily measure the strain. We know that stress is a function of strain so we can calculate stress mathematically with the help of strain.

stress in strength of material

### What is Stress?

When an External Influence (that includes force, moment, torque, etc.) acts on a material, a resisting force is produced within a body. The internal resistance force per unit area acting in a particular plane is known as Stress. Stress is a Tensor quantity because it depends on direction, magnitude and plane.

### What is Strength?

The maximum amount of stress that a material can withstand without failure is called Strength.

### What is the difference between Stress and Pressure?

The pressure is an external normal force per unit area whereas stress is an internal resistance force per unit area in a particular plane. The pressure is always normal to the area whereas stress needs not be normal to the area. Pressure s a scalar quantity whereas stress is a second-order tensor. The pressure is a measurable quantity whereas stress can be calculated but cannot be measured.

### Can we measure stress?

No, We cannot measure stress. It is not a measurable quantity. But strain is a measurable quantity. Using Strain gauge, you can easily measure the strain. We know that stress is a function of strain so we can calculate stress mathematically with the help of strain.