We often deal with objects made of materials such as steel, aluminum, or plastic. Have you ever wondered how experts determine how much stress a material can withstand? This is where two essential material properties, yield strength and tensile strength, come into play. Many people confuse these two terms since they both relate to strength. This confusion often leads to debates about yield strength vs. tensile strength.
Yield strength and tensile strength only sound similar. However, they describe very different stages of material behavior under stress. That’s why, when dealing with any metal or plastic, knowing the differences between the two is critical. If this is your first time learning about these concepts, don’t worry! In this guide, I will explain the key difference between yield and tensile strength in the simplest possible way. So let’s get started!
Overview of Yield Strength and Tensile Strength
Let’s first understand what yield strength is.
Yield strength is the amount of stress at which a material starts to deform permanently. In other words, at the yield point, a material begins losing its elasticity without breaking. After this point, the material will not return to its original shape.
Let me explain it in simpler words. When you stretch a material, it hits a point where it begins to lose its elasticity. However, it doesn’t lose it entirely. This is the exact point, which is called the yield point. This means that before reaching the yield point, a material can still return to its original shape when the stress is released. However, after the yield point, the material will not return to its original shape and will deform permanently.
Tensile strength is the maximum amount of force a material can handle before breaking. In simple terms, it’s the point at which the material fractures and can no longer return to its original shape. It permanently fails or fractures under stress.
As I said above, at the yield point, a material starts to bend or deform. Before the yield point, the material can still bear some stress. But tensile strength represents the ultimate limit of a material’s ability to resist breaking under tension. At the tensile strength, the following conditions happen to a material:
- It stretches elastically.
- It yields (permanent deformation begins).
- It stretches more.
- It reaches maximum stress.
- It breaks
The maximum stress a material can withstand before breaking is its tensile strength.
Unit of Tensile Strength & Yield Strength
Interestingly, both tensile and yield strengths are measured in the same units. Those include:
- Pascals (Pa)
- Megapascals (MPa)
- Pounds per square inch (psi)
Yield Strength vs. Tensile Strength: Key Differences
Now you have a basic understanding of the tensile and yield strength of materials. Right? Let’s compare tensile and yield strength head-to-head and see what sets them apart.
1- Stage of Material Behavior
The main difference between yield strength and tensile strength is the stage at which they occur under stress. If we discuss yield strength, we can say it occurs at an earlier stage when a force is applied to the material. In other words, at the yield stage, the material begins to deform permanently. Before the yield point, the material can return to its original shape when the stress is removed.
Once the yield stage is reached, the material will no longer fully recover. On the flip side, the tensile strength comes much later after the yield strength. Basically, it is the final stage of a material’s behavior under stress. At this point, the material has already reached its yield point and finally undergoes permanent deformation. The material reaches its maximum resistance to a pulling force and breaks.
2- Type of Deformation
Yield strength and tensile strength differ in the type of deformation they cause in the material. Deformation refers to a change in shape caused by applied stress. Remember, this change can be permanent or temporary depending on the force you apply. For example, at the yield strength, the material is initially in the elastic deformation stage.
It means that if you release the stress, it returns to its original shape without breaking. Once the yield point is crossed, the material undergoes permanent deformation. But at the tensile strength point, the material undergoes extreme deformation. When a material reaches its tensile strength, it has already deformed. Even if the stress is removed, it will not return to its original shape and will ultimately fracture.
3- Position on the Stress-Strain Curve
The stress-strain curve is a graph that shows how a material responds to an applied force. On this curve, yield strength and tensile strength appear at different positions. How? Actually, the yield strength in the stress-strain curve is found near the end of the straight part of the curve. This position indicates that the material is under stress but is not permanently deformed.
It shows the elastic behavior of certain materials, and it can be returned to its original shape. However, the tensile strength on the stress-strain curve is at the very top of the curve. The curve’s height indicates that the material is under very high stress and is about to break. It shows that the material is about to break and is under permanent deformation.
4- Role in Engineering Design
In engineering design, yield strength and tensile strength play different but essential roles. Engineers use both of these values to ensure a material is safe for a specific job. For example, yield strength is used primarily as a design limit. Simply put, for engineers, the yield strength is the safe boundary that they must not cross.
When designing any material, they ensure that the applied stress remains below the material’s yield strength. This keeps the material from bending or permanently changing shape. Conversely, tensile strength is primarily used to understand the maximum failure limit of a material.
Knowing the tensile strength, engineers can determine the maximum stress a material can withstand before breaking. It helps them determine the point of ultimate failure and safety checks for specific materials. Knowing this value, the engineer begins exploring ways to prevent the material from breaking.
5- Testing & Identification Method
Both yield strength and tensile strength are measured using tensile tests. A tensile test is an experiment that measures how a material behaves when pulled or stretched. It helps engineers understand the strength, elasticity, and breaking point of materials. The machine used for this experiment is called a tensile tester.
It is testing equipment that has two clamps: one holds the top of the sample, and the other holds the bottom. When you switch on the tensile tester, it pulls the sample slowly. Over time, it records the stress applied and the material’s elongation.
After that, the tester automatically generates the stress–strain curves. From this curve, you can read the tensile and yield strengths of a material. To ensure accurate, consistent results, tensile tests follow international testing standards. Those include:
- ASTM (American Society for Testing and Materials) standards: ASTM E8 for metals.
- ISO (International Organization for Standardization) standards: ISO 6892.
6- Importance of Material Selection
Both tensile and yield strength help choose the right material, but in different ways. How? For example, yield strength is critical when the shape of a material matters. Engineers pick materials with high yield strength. This ensures the part won’t deform permanently under normal conditions.
In contrast, tensile strength helps you choose the material that does not break under extreme stress. Through tensile testing, engineers determine a material’s maximum breaking strength. As a result, they are confident that the material won’t suddenly break under severe conditions. In short, tensile strength ensures the material doesn’t break. However, yield strength ensures the material keeps its shape.
7- Use in Real-World Applications
Yield strength and tensile strength are not just theoretical concepts. Both are used in various applications, helping manufacturers choose the most reliable material. For example, if we discuss the applications of yield strength, they include:
- Building beams and bridges: Yield strength helps choose the steel used in the structure so that it does not deform.
- Automobile frame: Yield strength helps ensure that vehicle parts remain in shape while driving.
- Machine parts: Shafts, gears, and levers must withstand heavy loads without deforming. The yield strength helps ensure the reliability of these machine parts.
Now, let’s discuss the applications of tensile strength in various sectors.
- Cables and ropes: Tensile strength helps ensure that cables used in elevators and cranes do not break.
- Fasteners and bolts: Tensile strength helps ensure fasteners keep parts together without breaking.
- Aircraft parts: The materials used are safe and capable of withstanding heavy loads.
Why Does Yield Strength Have More Importance Than Tensile Strength?
Yield strength is more important because it determines when a material begins to bend or permanently change shape. In the real world, engineers focus mainly on the shape and function of the materials. If a material deforms, it can cause serious problems even if it does not break. Therefore, engineers and experts give importance to a material’s yield strength.
As a result, they make sure that the stress applied to certain materials is below their yield points so that they do not deform. Moreover, the tensile strength is much higher than the yield strength. Materials in normal conditions rarely reach that point. That’s why tensile strength is less critical for regular design materials. In short, tensile strength matters only in emergencies. This helps maintain safety, stability, and long-term performance.
Conclusion
Tensile strength and yield strength are key terms in materials science. But many get confused and often consider them the same. Hence, in this article, I have explored the main differences between tensile and yield strength. For example, yield strength is the point at which a material starts to deform. Before this point, the material can return to its original shape.
Once the yield strength is exceeded, the material can’t go back to its original shape. In contrast, tensile strength is the maximum stress a material can withstand before it breaks. It shows the maximum stress a material can withstand. This point comes much later than the yield strength. At this point, the material cannot return to its original shape. Knowing the difference between tensile and yield strength helps you pick the right material.