Yield Point

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What is the Yield Point?

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Yield point meaning in structural engineering is the load at which a solid material that is stretched begins to flow or change shape permanently. It is the point on a stress-strain curve that indicates the limit of stretchability behaviour and the beginning of plastic behaviour. Lower than the yield point, a material will deform stretchability and return to its original shape when the yield stress point is removed.

The Yield Point Definition

Stress crosses the stretchable limit that the material begins to show plastic properties and continues to distort without further pressure, especially tension. For example, Steel offers a yield point methodology. The interstitial atoms lead to the yield point process. More strain at the yield point needs to be applied to make the particles separate evenly around the dislocations for plastic deformation to occur.

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What is Yield Strength?

The yield strength is the determination of an object whether it is stubborn or easily shapeable. The upper yield strength is the point at which a thing is not elastic and changes to plastic. These upper and lower yield points help us determine the suitable materials for the construction. For example, the toys are generally made of plastic because it will be impossible to mould them into different shapes required to make them.

The Relation Between the Two Factors, Stress and Strain, Need to Be Understood in Different Views-

  • Proportional Limit

It is part when the stress-strain curve comes under Hooke’s law. In this limit, the strain ratio with the strain comes to a proportionality constant, also known as young modulus.

  • Elastic Limit

In this part, the material returns to its original shape when the load acting on it is completely removed. After this limit, the material does not return to its original position, and a plastic deformation begins to form.

  • Yield Point

It is the stage at which the material starts to deform plastically. After the yield point is crossed, permanent deformation occurs. There are two divisions in this: the upper yield point and the lower yield point.

  • Ultimate Stress Point

It is the maximum limit of stress that a material can take before failing. After this point, failure occurs.

  • Fracture or Breaking Point

This stage is the point at which the stress-strain relation when the failures of the material take place.

Explain Yield Point About Lower Yield Stress

The yield point of the material is seen when the material changes from stretchability form; when the applied pressure is moved, the material will regain its old form to plastic behaviour where deformation is permanent is the yield point. At the same time, yield stress marks the transition from elastic to plastic behaviour. The minimum stress at which a solid will change permanent deformation or plastic flow without a significant increase in the pressure or force. A few materials flow easily at well-defined stress that falls to a lower yield point as distortion continues. The lower yield point example is in the case of steel. The disconnections are locked in due to the presence of carbon. When the carbon ratio in steel is increased to make high carbon steel, we can see the lower and upper yield point in the process. Some materials start to yield at an upper yield point that will fall very quickly to the lower yield point as deformation. Especially in the case of steel, it has two yield points because the stress-strain curve for low carbon steel shows a double yield point. The material itself deforms at stress 1. But the atoms gather around the disconnections and engage in the slip and increase the yield point. 

FAQ (Frequently Asked Questions)

Q1. What is the Significance and Importance of the Yield Point?

Ans: The Yield point is the point on a stress-strain curve that states the limit of stretchability behaviour and the starting of plastic behaviour. Before the yield point, a material will deform stretchability and return to its original shape when the applied stress is removed. 

The Importance of the Yield Point Explained -

That is essential in designing components, as it is the upper limit of yield strength that determines the load that can be applied. Yield strength helps in controlling many materials production procedures such as forging, rolling and pressing.

It is also essential in constructing structures as the structures can perform in the elastic region under normal servicing conditions. A metal with a higher yield strength is strong and sustains high stress without permanent distortion. A straight line is drawn through a point at the same slope as the stress-strain curve’s initial portion to measure the yield strength. The intersection between the new line and the stress-strain curve is shown on the stress axis. The stress value is pounds per square inch.

Q2. State the Differences Between Stress and Strain?

Ans: Stress is defined as the object’s force, leading to the change in it, while a strain is defined as the change in the shape of an object when stress is used. It is possible to measure stress and have a unit, while a strain is not likely to have no measuring unit. The word stress and strain are derived from the Latin phrase strictures, drawing tight and binding tightly. After studying the differences, it is essential to check out the relation between them. The association between stress and strain is directly proportional to each other up to an elastic limit. As per Hooke’s law, the strain in a solid is proportional to the applied stress, and it should be within the stretchability limit of that solid.