Brief Discussion On Stress-Strain Index

Stress is the measure of force acting on a body per unit of its area to change the body’s volume, length, or shape – the SI. The unit of stress is N/m2 (Newton per square metre).

Strain is the measure of the extent to which a body has deviated from its initial condition after the action of stress on the body. Because the strain is the ratio of the final condition of the body to its initial one, it is a dimensionless entity.

The ratio of stress to strain for a body is its stress-strain index. 

Stress-Strain Index

A stress-strain index is the ratio of the stress acting over a body to the strain or deformation that it has gone through. The stress-strain index is also referred to as Young’s modulus. The unit of this index happens to be N/m2, the same as stress. 

The Stress-strain index for a body is the extent to which a body will be able to undergo stress without bringing about a permanent deformation in the body’s shape. This index provides the measures of resistance of a body against this change. 

Stress-strain index = Stress(σ) / Strain(ε).

For a body to have a greater stress-strain index, it means that the body will be able to undergo a large amount of force before any change in shape takes place. 

Three-Point Bending Test

The three-point bending point for metal or an object represents the properties of a body to signify whether the material will be suited for the given task or not. The three-point bending test gives measures of the following properties of a body:

• The stress on the body
  It states the extent to which a body will be able to endure an amount of force before it breaks or becomes unable to be of use again.

• The body’s strain
  This is the degree to which a change can be brought in the shape, length, or volume of a body compared to the conditions that the body had in its initial state.

• The elasticity of the body
  Elasticity is the property of a material that determines the extent of the body’s return to its initial state after the exertion of a deforming force on the body. Bodies with high elasticity can completely regain their former state after the applied force over them is removed.

Only after considering all of these properties regarding a material, can the proper use of that material be determined. This is one of the best ways to determine the longevity of a metal or its durability under extreme conditions.

Peripheral Quantitative 

Peripheral quantitative is the set of the properties that a body displays when it reaches the breaking point or yielding point. The yielding point is related to the stress-strain index in the following way:

• Breaking the stress on a body
  This is the amount of stress on a body that, when applied, cannot sustain its purpose properly and breaks down. Breaking the stress on a body is the extent to which a body can bear a certain amount of stress before giving way to the burden.

Breaking stress = Force / Area.

• Yielding strain on a body
  This is the limit to which a material can bear the change in its shape or volume. When the body is pushed beyond the limit of strain that the body can bear, it will be torn apart or severely damaged. This gives tensile strength or the point to which a material can be pushed.

Yielding strain of the body = {(Final length of the material – initial length of the material) / initial length of the material}.

• The elastic limit of a body
  This is the point for a body beyond which it will lose its elastic character. This means it will not be able to return to its original state after the force applied over it is removed.

F = k × x 

Where k is the elastic constant of the body, and x is the distance to which the material was deformed. 

Conclusion

The relation between stress and strain under various conditions and operations brings about the life of different materials to be put to use. These factors state the very applicability of a material for a particular task. Therefore, the stress-strain index has a high significance in physical fields.