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Yield Strength - Definition, Example, Formula, FAQs

Yield Strength - Definition, Example, Formula, FAQs

Team Careers360Updated on 02 Jul 2025, 04:44 PM IST

Introduction
In this article, our focus will be on yield strength, yield stress, yield strength of steel, yield point, the tensile strength of steel, etc.

This Story also Contains

  1. What is Yield Strength?
  2. Formula of Yield Strength
  3. Difference between Yield Strength and Tensile strength
Yield Strength - Definition, Example, Formula, FAQs
Yield Strength

What is Yield Strength?

The yield strength determines whether an object is rigid or pliable. It is the moment at which an object becomes plastic rather than elastic. Yield strength aids in the selection of appropriate construction materials based on the requirements. Because it would have been impossible to mould metals into the unorthodox shapes that we so passionately love, the toys that we so dearly love were constructed from something as pliable as plastic rather than metals.

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What Does Yield Strength Mean?

Yield strength is a measurement of the greatest stress that a material can withstand without deforming plastically. It is a practical approximation of the elastic limit and is the pressure by which the object shows a definite deformation.

Yield strength is critical in engineering structural design. When constructing a component, for example, it must be able to withstand the force applied during operation and not distort plastically. To put it another way, a material with adequate yield strength should be used.

The yield strength is frequently used to calculate the upper limit of forces that can be applied without producing permanent deformation since it reflects the upper limit of forces that can be applied without generating permanent distortion.

The yield strength of an object determines whether it is difficult to shape or not. The upper yield strength of a material is the point at which it ceases to be elastic and becomes plastic. These upper and lower yield points assist us in determining the best materials for the job. Toys, for example, are typically constructed of plastic since moulding them into the many shapes required to produce them is impractical.

Commonly Asked Questions

Q: What is yield strength in materials science?
A:
Yield strength is the stress at which a material begins to deform plastically, meaning it won't return to its original shape when the stress is removed. It marks the transition from elastic to plastic deformation.
Q: Can yield strength be negative?
A:
No, yield strength cannot be negative. It represents the minimum stress required to cause plastic deformation and is always a positive value.
Q: What is the 0.2% offset yield strength?
A:
The 0.2% offset yield strength is a convention used when materials don't have a clear yield point. It's defined as the stress that produces a plastic strain of 0.2% and is used as a practical approximation of yield strength.
Q: How does alloying affect yield strength?
A:
Alloying typically increases yield strength by introducing impurity atoms that impede dislocation movement in the crystal structure. This makes it harder for the material to deform plastically.
Q: What's the difference between yield strength and yield point?
A:
Yield strength is the stress at which a material begins to deform plastically, while the yield point is the exact moment this occurs. Some materials have a clear yield point, while others transition more gradually.

Formula of Yield Strength

The 0.2 per cent offset rule is the most frequent engineering approximation for yield stress. Assume a yield strain of 0.2 per cent and multiply by Young's Modulus for your material to apply this rule. Then the yield strength formula is given by:

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It is also called the yield stress formula. Although the offset method can be used to calculate stress along a single axis, some applications require a formula that can handle two axes. Use the von Mises criteria to solve these issues:

1638875194979

stress-strain graph

The Stress-Strain Graph has certain unique characteristics. The following are some of them:

  1. Proportional limit: Hooke's Law is preserved at the proportional limit of the stress-strain curve. As a result, the stress-to-strain ratio yields a proportionality constant known as Young's modulus. The proportionate limit is the point on the stress-strain graph OA.
  2. Elastic Limit: This is the point at which the material returns to its original state once the load operating on the body is eliminated. The material does not return to its original state after reaching this limit, resulting in plastic deformation of the material.
  3. Yield Point: The yield point definition is given as, the point at which a material begins to deform in its current state and, in most cases, turns into plastic. After the point is passed, the object undergoes a permanent distortion in one of two ways. One could be a lower yield point, while the other could be higher.
  4. Ultimate Stress Point: The ultimate stress point is the point at which the material can endure the most stress before deforming. If the material is pushed past this point, it will fail.
  5. Breaking or Fracture Point: This is the point at which the material fails

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Yield Stress of Steel

Yield strength is the maximum force that may be given to an object before it changes its shape or structure. The tensile test is used to determine the strength of any material. The material is stressed and pulled aggressively in both directions during this test. A graph, also known as a stress-strain graph, can be generated as a result of this test.

Yield strength of mild steel: 250MPa

Tensile Strength

Tensile strength is the force required to pull an object, such as a structural beam, wire, or rope, to its breaking point. The largest amount of tensile stress that a material can withstand before breaking into little pieces is its tensile or yield strength. The largest stress a material can endure before breaking down is referred to as tensile ultimate strength.

Tensile Strength of Steel

By definition, tensile refers to the ability of steel to be drawn out. Tensile strength is the steel's ability to resist breaking under tensile force. It's used to describe the moment at which steel changes from an elastic to a plastic state. It's commonly expressed in terms of force per area cross-section. The steel rips apart when it is moved away from its stress point.

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Tensile Strength of Mild Steel

The maximum amount of stress that any material can bear when pushed or stretched is known as tensile strength. Any tensile strength is put to the test by placing samples of a material with a defined area of cross-section within a tensometer and increasing the force until it breaks.

Few materials break down without deforming, whereas more ductile materials stretch just slightly and shrink when under great stress. Tensile strength is thus quantified in Pascal, pounds per square inch, or Megapascal as a force per unit of area.

Mild steel, on the other hand, is less ductile than other steels because it contains less hardening alloy and carbon. It has a tensile strength of 400MPa, which is relatively low.

Commonly Asked Questions

Q: What is the yield strength formula?
A:
The yield strength formula is σy = F / A, where σy is the yield strength, F is the yield force, and A is the original cross-sectional area of the sample.
Q: How does grain size affect yield strength?
A:
Generally, smaller grain sizes lead to higher yield strength. This is described by the Hall-Petch relationship, where yield strength is inversely proportional to the square root of the average grain diameter.
Q: How does yield strength relate to Hooke's Law?
A:
Yield strength marks the end of the linear elastic region described by Hooke's Law. Below the yield strength, stress is proportional to strain; above it, this relationship no longer holds.
Q: What is the yield ratio?
A:
The yield ratio is the ratio of yield strength to ultimate tensile strength. It provides information about a material's ductility and its behavior under load.
Q: What is meant by "yielding" in materials science?
A:
Yielding refers to the onset of plastic deformation in a material. It's the point where a material transitions from elastic (reversible) to plastic (permanent) deformation under applied stress.

Difference between Yield Strength and Tensile strength

Yield strength
Tensile strength
1. The highest stress that a material can sustain while deforming is referred to as yield strength.1. The utmost strength that any solid substance may withstand before failing is called ultimate strength.
2. Under any tensile loading, it is the maximum stress that coincides with the yield point in the stress-strain curve.2. In the curve below tensile loading, it is referred to as the stress that corresponds to ultimate tensile strength.

Also check-

NCERT Physics Notes:

Commonly Asked Questions

Q: How does yield strength differ from ultimate tensile strength?
A:
Yield strength is the point where a material begins to deform plastically, while ultimate tensile strength is the maximum stress a material can withstand before failing. Yield strength occurs before ultimate tensile strength in a stress-strain curve.
Q: Why is yield strength important in engineering design?
A:
Yield strength is crucial in engineering design because it determines the maximum stress a material can withstand without permanent deformation. Designers use it to ensure structures and components remain safe and functional under expected loads.
Q: How is yield strength measured?
A:
Yield strength is typically measured through tensile testing, where a sample is stretched until it yields. The stress at the yield point is calculated by dividing the force applied by the original cross-sectional area of the sample.
Q: Can yield strength change with temperature?
A:
Yes, yield strength typically decreases as temperature increases. This is because higher temperatures increase atomic vibrations and reduce the force needed to cause plastic deformation.
Q: How does strain hardening affect yield strength?
A:
Strain hardening increases yield strength by creating more dislocations in the material's crystal structure. These dislocations interact and impede each other's movement, requiring more stress to cause further deformation.

Frequently Asked Questions (FAQs)

Q: How does yield strength relate to the concept of "plastic collapse" in structural engineering?
A:
Plastic collapse occurs when a structure develops enough plastic hinges to form a mechanism. The yield strength of the material determines the load at which these plastic hinges begin to form, influencing the overall structural behavior.
Q: What is the significance of the yield strength to elastic modulus ratio?
A:
The ratio of yield strength to elastic modulus (σy/E) is important in determining the elastic strain limit of a material. It's particularly relevant in applications requiring high elastic deformation, such as springs.
Q: How does yield strength relate to the concept of "strain energy"?
A:
Strain energy is the energy stored in a material due to elastic deformation. The area under the stress-strain curve up to the yield point represents the elastic strain energy per unit volume that the material can store.
Q: What is meant by "yield locus" in sheet metal forming?
A:
A yield locus is a two-dimensional representation of the yield surface, often used in sheet metal forming to describe the onset of plastic deformation under different stress states.
Q: How does yield strength relate to the concept of "plastic zone" in fracture mechanics?
A:
The plastic zone is the region near a crack tip where the local stress exceeds the yield strength, causing plastic deformation. The size of this zone is inversely related to the yield strength of the material.
Q: What is the relationship between yield strength and dislocation pinning?
A:
Dislocation pinning increases yield strength by creating obstacles that impede dislocation movement. This can be achieved through various mechanisms such as solute atoms, precipitates, or other dislocations.
Q: How does yield strength relate to the ductile-to-brittle transition?
A:
The ductile-to-brittle transition is characterized by a change in fracture behavior, often accompanied by an increase in yield strength. This transition is temperature-dependent and is particularly important in materials like steel.
Q: What is meant by "yield surface" in multiaxial stress states?
A:
A yield surface is a mathematical construct in stress space that defines the combination of stress components that will cause yielding in a material under multiaxial loading conditions.
Q: How does yield strength relate to creep resistance?
A:
While not directly related, materials with higher yield strengths often have better creep resistance. However, creep involves time-dependent deformation and can occur below the yield strength at elevated temperatures.
Q: What is the Bauschinger effect and how does it relate to yield strength?
A:
The Bauschinger effect is the phenomenon where plastic deformation in one direction reduces the yield strength in the opposite direction. It's important in cyclic loading scenarios.
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