When it comes to understanding and evaluating the mechanical behavior of materials, yield strength and tensile strength emerge as two key properties that provide crucial insights. These measures play an essential role in characterizing a material’s response to outside forces and its overall strength under various conditions.
Yield strength refers to the point at which a material undergoes permanent deformation or a significant change in shape due to applied stress, signaling its transition from elastic to plastic behavior. On the other hand, tensile strength represents the maximum amount of stress a material can withstand before it fractures or breaks. Both of these properties offer valuable information about a material’s durability, suitability for specific applications, and overall structural integrity, serving as vital benchmarks in materials science and engineering.
Let’s dive into understanding these two important properties so you can make an informed decision on the SendCutSend materials you choose for your projects.
The Basics: The Stress-Strain Curve
To fully understand what yield and tensile strength actually are and what they represent, it’s important to know what the stress-strain curve is and what it measures.
Stress describes outside forces acting on the molecules in a given material. When a material is not being moved, bent, formed, or otherwise manipulated, the molecules in the material are in their equilibrium state. This state is the lowest demand, lowest energy state possible. Once an outside force begins acting on the material, the molecules making up the material will fight the forces in order to move back to their equilibrium state. Stress, then, is the measurement of the intermolecular forces causing the molecules to be outside their equilibrium state. We calculate stress by measuring the external force on the material and dividing that by the area which the force is being acted upon.
When you stretch a rubber band to the point right before it breaks and then release it, the rubber band will be slightly bigger than before. Strain describes this deformation and measures it by subtracting the original length of the object from the stretched length, and then dividing the result by the original length.
Taking multiple stress measurements and multiple strain measurements, you can make a graph showing how much strain occurs as the stress on the material increases. The resulting chart is known as a Stress-Strain curve, and it’s used to help us understand how different materials will react to different levels of force. Yield strength and tensile strength both exist on this curve.
What is Yield Strength?
Let’s use the rubber band example again. When you stretch a rubber band just a little bit and you stop before it starts to get difficult to stretch it anymore, the rubber band will usually snap back to its original shape and length. Metal and other materials are the exact same way. When you have a sheet of material, there is always some point to which you can bend it or force and when you release it, it will return to its original shape and state. Some are more capable of experiencing force and returning to their original state than others. We say these materials are more “elastic.”
Sometimes, you stretch a rubber band just enough that it doesn’t break, but you release it and it is a bit longer or even deformed in some spots. The force exerted on the band was strong enough to change its shape and state. Metal and other sheet materials behave this way too. When materials experience very little force before they are no longer capable of returning to their original state, we describe them as “plastic.”
The amount of stress that is so strong it permanently deforms the material is known as the yield strength. Yield strength is just the measurement of how much force can be exerted on the material before it bends or deforms. Some materials have such a high yield strength that it’s difficult to bend them on purpose, whereas others have such a low yield strength that they can’t be used in situations where even light force is used because they will deform so easily. Most applications will want materials that are somewhere in the middle of those two extremes.
What is Tensile Strength?
So you’ve stretched the rubber band to the point of permanent deformation. What happens if you stretch it just a little bit more? It becomes difficult to feel any yield in the rubber band and it starts to feel rigid and inflexible. If you continue to exert force past that point, the rubber band snaps. Once again, the same principles are applied to other materials as well. For all materials, regardless of their yield strength, there is a point at which no more force can be exerted on it without it giving way and failing. Whether this is a tear or a break, the amount of force it takes to cause a material to fail and break is called the tensile strength.
Yield vs. Tensile Strength: What Are the Differences?
|Components||Yield Strength||Tensile Strength|
|Definition||Yield strength is the measurement of the amount of force that can be exerted on a material before it permanently deforms.||Tensile strength is the measurement of the amount of force that can be exerted on a material before it breaks.|
|Stress||Yield strength is a minimum measurement, showing the minimum amount of force to permanent deformation.||Tensile strength is a maximum measurement, showing the maximum amount of stress a material can experience.|
|Position in Graph||No matter the material, yield strength is always a lower value and thus comes first in the stress-strain graph.||Tensile strength is the last measurement shown in the stress-strain graph.|
|Intermolecular Forces||The intermolecular forces are stronger than the stress being exerted on the material.||The intermolecular forces are weaker than the stress being exerted on the material.|
Choosing the Best Material for Your Project
It is important to know what amount of stress the material can experience before the point of deformation and breaking before choosing a material for your project. If your project is in a low-stress environment with little outside forces and impact, a low yield strength and low tensile strength measurement is probably okay. But if your project will be experiencing heavy loads, high impact, or extreme stress, it’s important to make sure the yield strength and tensile strength measurements of your chosen material exceed the stress measurements of their intended environment.
To learn more about different materials and their strengths, be sure to check out our overall materials guide. We also have specific guides for choosing a material thickness and choosing the right composites for your project.
FAQs About Yield Strength vs. Tensile Strength
Is yield strength always lower than tensile strength?
Yes, yield strength is always a lower number than tensile strength. This applies to metals, woods, plastics, and composites alike.
Is tensile strength more important than yield strength?
Tensile strength is not necessarily more important to know than yield strength. Both values are important to understand before choosing a material for your project. Since they each measure entirely different things, it’s valuable to know both before putting your projects through heavy testing.
How does yield strength change as a material is heated?
Yield strength decreases with an increase in temperature. The thermal activation decreases the intermolecular forces, increasing the plasticine qualities of the material, making it easier to bend and deform permanently.