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What is the Difference Between Yield Strength and Ultimate Tensile Strength?


Understanding the different terms used to define metals is crucial to implementing them correctly in assemblies, two of the most important physical properties are Yield Strength and Ultimate Tensile Strength, but what are these and critically, what is the difference between the two?

What is Yield Strength?

Yield strength is the point at which a material stops deforming elastically (temporary deformation), and begins to deform plastically (permanent deformation) when subject to stress.

Elastic deformation is where a material is bent, stretched, twisted or compressed but returns to its original shape after the load is removed. Plastic deformation is permanent deformation, leaving the part or material in a different shape than before the force was applied.

Yield Strength is often used to define the strength of a material, as in most cases once a part has bent out of shape, it is no longer functional. In terms of mechanical properties, yield strength is one of the most important when specifying materials for a project or part.

What is Ultimate Tensile Strength?

Ultimate tensile strength, often abbreviated to UTS, is a measure of the amount of stress a material can withstand before breaking, for steel, this is often around 130-140% of the yield strength.

The UTS point is not where the material breaks but where the strain in the material transforms from general, uniform deformation to localized deformation, witnesses in the stretching and narrowing of the part (if failing in tension).

What is the difference between Yield Strength and Ultimate Tensile Strength?

Yield Strength is the point at which a material deforms plastically AKA bends or stretches, ultimate tensile strength is the maximum amount of stress a material can withstand.

Whilst both factors are important, Yield Strength is most commonly used when specifying a material for a component as no material can function after it has passed the point of plastic deformation, a well designed part will only experience around 50% of its yield strength in service, depending on the use and its factor of safety.

Is The Ultimate Tensile Strength Higher than Yield Strength?

In materials such as mild steel, the Yield strength is lower than the Ultimate Tensile Strength by around 30-40%, but this is not the same with all metals. In brittle materials such as high carbon steel, the ultimate tensile strength is not much higher than the yield strength, as the material lacks ductility, and as such does not deform far before breaking.

How are Yield and Tensile Strength Measured?

Tensile and Yield strength is an engineering stress, measured in force per unit area, in North America lb/in² or psi is usually used, the SI unit is Pascal or Mega Pascal. Standardized testing is commonplace, using either a flat or round test piece.

A hydraulic or screw-type tester pulls the sample whilst logging the stress and strain experienced. Most homogenous metals have a linear stress-strain relationship until the point of yield strength.

What is The Yield Strength of Common Materials?

The strength of a material depends highly on the specific alloying elements it contains, here are some examples of common engineering materials.

Material Yield Strength MPa Ultimate Tensile Strength MPa
Aluminum 35 90
Copper 69 200
Brass 75 300
Low Carbon Structural Steel 355 490
1095 High Carbon Steel 800 1270
Stainless Steel 304 241 586
Molybdenum 565 655

It can be seen that more ductile materials such as aluminum and copper, have a large gap between the yield and ultimate tensile strength, the opposite is true with brittle materials such as high carbon tool steel.

Facts about Tensile Strength

  • Tungsten has the highest tensile strength of any metal, at around 980 MPa
  • Certain metals that are very ductile, such as Gold, have a yield strength that is higher than their ultimate tensile strength, as they kneck at a much lower stress, but can elongate significantly more than metals like steel
  • Even though it only has a tensile strength of 1.5 GPa, pound for pound spider’s silk has a tensile strength 5 times that of steel

Get Your High Strength Materials From Metals Supermarkets

Whether you need a high strength steel for a structural application, or a very ductile material for something different, Metals Supermarkets has a wide range, from Aluminum to Tool Steel and Stainless Steel to Brass.

Find a store near you and have the material cut to size too.


Metal Supermarkets

Metal Supermarkets is the world’s largest small-quantity metal supplier with over 130 brick-and-mortar stores across the US, Canada, and United Kingdom. We are metal experts and have been providing quality customer service and products since 1985.

At Metal Supermarkets, we supply a wide range of metals for a variety of applications. Our stock includes: mild steel, stainless steel, aluminum, tool steel, alloy steel, brass, bronze and copper.

We stock a wide range of shapes including: bars, tubes, sheets, plates and more. And we can cut metal to your exact specifications.

Visit one of our locations today.

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