Tensile Strength vs Yield Strength – Analyzing the Differences

Tensile strength and yield strength are two different terms. However, knowing when to determine each variable and why it is important is critical.

That’s exactly what we will focus on in this article.

What is Tensile Strength?

Tensile strength is the amount of forces materials can withstand before breaking start. Usually, we examine this when you subject the material to a stretching force,by using a metal wire strength tester .

That is to say, it is the point on a stress-strain curve where the material gets to the furthest point in which it can withstand the tension.

Units of measurements are:

• Megapascals(MPa)
• Pounds per square inch(Psi)

These units are based on force per area.

More importantly, this property is critical in applications where materials are subjected to pulling or stretching forces.

What is Yield Strength?

At yield strength, all materials stop being elastic and possibility of plastic deformation starts.

Usually, the measurement units are:

• Megapascals(MPa)
• Pounds per square inch(psi)

Remember, yield strength helps in designing many structural components. With a knowledge on yield strength, it will prevent significant deformation of materials under load.

Exploring Differences in Tensile Strength and Yield Strength

Magnitude and Units of Measurement

They are both measured in megapascals (MPa). Alternatively, you can use pounds per square inch (psi).

Remember, these units represent the force applied per unit area. Despite the above similarities, the magnitudes of these two strengths are different in a significant manner.

Tensile strength is usually higher compared to yield strength.Take for example structural steel:

Its tensile strength might be around 400-500 MPa, whereas its yield strength is typically lower, around 250-300 MPa.

This difference is very significant because it indicates the material’s ability to tolerate higher stress before failure. That is, beyond just the point of permanent deformation.

Point of Measurement

For yield strength, you will determine its value at a point where the material changes from elastic deformation.  That is, where it is reversible to plastic deformation. At the same time, you cannot reverse material to its original shape or size.

Elastic deformation is a stage that applies Hooke’s law where stress is proportional to strain. This stage is predictable.But more importantly, yield strength helps to indicate the limit for safety.

It is important you measure the tensile strength at a point where any material cannot withhold any degree of stress. You should remember, higher forces may cause fracture.

Fracturing causes the material’s ability to carry the load which may reduce significantly after necking begins. Necking is where there is a localized reduction in cross-sectional area predicting looming failure.

On the other hand, tensile strength highlights the end point of failure.

Loading

Yield strength describes higher stress levels. Usually, this is a loading point just before permanent deformation starts.

In engineering design, yield strength is very crucial because it helps ensure that materials can carry loads without deforming irreversibly.

Engineers design structures to operate within the elastic region, which is below the yield strength to avoid permanent deformation.On the other hand, tensile strength focuses more on the maximum loading. That is, the load any material can handle before breaking.

Tensile strength is crucial for understanding the ultimate load-bearing capacity. However, it is  more relevant when considering safety margins and failure conditions rather than day-to-day operational limits.

Behavior under Stress

If the load is removed, a material can return to its original shape. This is because the material deforms elastically at the beginning, since you will be subjecting it increasing stress.

Beyond the yield strength, a material cannot return to its original form. Therefore, at yield strength, the elasticity ends. You will realize that permanent plastic deformation begins.

As you subject any material to more stress, it will get to the tensile strength point. That is, it will be close to breaking.

This behavior is necessary in forecasting how a certain material will perform in the real world. A higher tensile strength bears larger loads and resists permanent deformation better.

Stress-strain Curve

In a stress-strain curve, the yield point is described as the place where a curve diverges from the straight line. The deviation is very minimal and requires accurate measurement.

But more importantly, the peak of the curve represents the tensile strength. On the other hand, the material’s fracture is represented by the highest point before the curves start dropping.

The curve offers a visual representation of the transition of a material from when it is elastic to when it fails.

Now, the area under the curve to the yield point indicates its possibility recover the elastic energy. On the other hand, the area beyond the yield point up to the tensile strength indicates fracture due to plastic deformation.

Importance in Engineering Applications

In engineering design, yield strength is an important factors you must consider when choosing materials for structural components.

You should ensure that under normal conditions, plastic deformation does not occur. This is because it will compromise the structural integrity of parts.

In civil engineering, the yield strength of steel and concrete materials is critical for building designs and other infrastructure. To ensure there is no permanent deformation that could lead to collapse, beams and columns are designed to operate below their yield strength.

Engineers utilize yield strength to incorporate safety factors into their designs. This is done by ensuring the maximum operational stress is lower than the yield strength of the material. This approach keeps a record of material imperfections and unanticipated loads.

Yield strength also impacts the durability and service life of elements. In the automotive industry, maintaining the yield strength ensures automotive parts can endure repetitive loads without deforming.

Tensile strength on the other hand is crucial when assessing the maximum load, a material can withhold before total failure. Therefore, understanding tensile strength helps in predicting how and when a material might fail due to overload conditions.

It will help you to design a fail-safe mechanisms to prevent material failure.

Tensile strength is a primary criterion when selecting high-performance applications. High tensile strength withstands internal pressure such as in transportation of liquids under high pressure. Materials with high tensile strength remain intact and functional in extreme conditions.

Intermolecular Forces

Yield strength relates closely to the internal structure of a material. It specifically relates to the resistance in its molecules or atoms during the first stages of plastic deformation. Plastic deformation is the point where a material’s shape begins to permanently change.

In this case, resistance is influenced by factors like the dislocation density. That is to say, the higher the dislocation density the higher the yield strength since it obstructs dislocation movement.

This makes it more complex for the material to plastically deform.

The size of the grain is another factor that affects resistance. Smaller grains, implies more grain boundary, which may hinder possible movements and dislocations. It is a phenomenon called the Hall-Petch effect.

Conversely, tensile strength is impacted by the ability of the cohesive forces within a material to retain its structural integrity when subjected to tension. Cohesive forces are controlled by atoms bonding in the material.

Eventually, at tensile strength cohesive forces are surpassed causing material failure. In metals, tensile strength is impacted by the forces that cause bonding between atoms. It is necessary to break these forces for the material to fracture.

Conclusion

Tensile and yield strength are very distinct. But more importantly, analyzing the two variable will help you choose a suitable material for any application.

Whether a material can withstand any loading effect depends on careful analysis of these variables.

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