Yield Strength vs Tensile Strength: What's the Difference?

Yield strength is the stress at which a material stops springing back and starts to deform permanently. Tensile strength (ultimate tensile strength, or UTS) is the highest stress the material can carry before it starts to fail. Yield always comes first: a metal bends for good at its yield strength, then keeps stretching until it reaches its tensile strength, necks down, and breaks.

For most design work, yield strength is the number that matters, because a part that has yielded is already bent out of spec. Tensile strength tells you how much margin is left before it fails. This guide explains both, shows where they sit on the stress-strain curve, and lists typical values for the aluminum, steel, and stainless steel sheet we cut and bend.

Yield Strength vs Tensile Strength at a Glance

What Is Yield Strength?

Yield strength is the amount of stress a material can take without permanently deforming. Imagine you have a metal rod and you start pulling it. At first, the rod stretches, but once you release the load, it returns to its original length. That behavior holds up to a certain point, known as the yield point. Beyond it, the rod stretches permanently.

In other words, yield strength is the stress at which a material changes from elastic (reversible) deformation to plastic (permanent) deformation. It tells you how much load a part can handle before it starts to bend or permanently change shape.

Stress is force divided by cross-sectional area, so yield strength is reported in units of pressure: psi or ksi (thousands of psi) in the US, and MPa elsewhere. 1 ksi is about 6.9 MPa.

Yield point vs 0.2% offset yield strength

Low-carbon steel shows a distinct yield point. The stress rises, drops slightly, and the material stretches at nearly constant stress before it starts to harden again. Aluminum and stainless steel yield gradually with no sharp point, so their yield strength is defined with the 0.2% offset method: draw a line parallel to the elastic part of the curve, starting at 0.2% strain, and read the stress where it crosses the curve. That value is also called proof stress or Rp0.2.

What Is Tensile Strength?

Tensile strength is the maximum stress a material can withstand while being stretched or pulled before it fails. It is the highest point on the stress-strain curve, which plots stress (force per unit area) against strain (stretch as a fraction of the original length).

Think of the same metal rod. As you keep pulling, it gets longer and thinner until it finally snaps. The highest stress it carried along the way is its tensile strength. In ductile metals, that peak comes before the break: the rod starts to neck down at one spot, the load it can carry falls off, and it fractures at a stress below its tensile strength.

"Tensile strength" and "ultimate tensile strength" mean the same thing on a datasheet. "Tensile yield strength" is just yield strength measured in tension.

The Stress-Strain Curve

Both numbers come from the same tensile test. A standard specimen is pulled until it breaks while the machine records load and stretch.

Reading the curve from left to right:

1. Elastic region. Stress and strain rise along a straight line. The slope is the elastic modulus (Young's modulus), a measure of stiffness. Remove the load anywhere on this line and the part returns to its original shape.
2. Yield strength. The line bends over. From here on, some of the stretch is permanent.
3. Strain hardening. The metal keeps getting stronger as it deforms, so the stress keeps rising, but more slowly.
4. Ultimate tensile strength. The peak of the curve. The specimen starts to neck.
5. Necking and fracture. The cross-section shrinks at the neck, the measured stress drops, and the specimen breaks.

The gap between yield and tensile strength tells you how much a metal can strain-harden. The total stretch at fracture, called elongation, tells you how ductile it is.

Typical Yield and Tensile Strength of Sheet Metals

These are published values for the sheet metals Fabworks stocks. Aluminum values are typical properties for the alloy and temper. Steel and stainless values are specification minimums or typical ranges, so material from a given mill run usually tests higher. Use them for comparison and early sizing, and use a mill certificate or your own design standard for anything critical.

G90 galvanized steel is carbon steel with a zinc coating. Its strength comes from the base steel, which for commercial-quality sheet is similar to 1008.

A few things stand out:

• Heat-treated aluminum yields close to its tensile strength. 6061-T6 and 7075-T6 yield at nearly 90% of their tensile strength, and they stretch only about 10–12% before breaking. There is little room between "bent" and "cracked."
• Annealed 304 stainless is the opposite. It yields at roughly half its tensile strength or less and stretches 40% or more. It work-hardens quickly, which is why it takes more force to bend and machine than mild steel.
• A36 has a higher yield than 5052-H32 but a lower one than 6061-T6. Steel is not automatically stronger than aluminum. Compare the actual grades, and see our aluminum vs steel comparison for strength by weight.

Why Yield and Tensile Strength Matter in Design

Design to yield. Most structural parts are sized so the highest working stress stays below yield strength divided by a factor of safety. A bracket that yields has failed for practical purposes even though it hasn't broken.

Check tensile strength for ultimate failure. Tensile strength sets the load at which a part actually separates. It matters for crash or overload cases, for fasteners and welds, and when a part is allowed to deform as long as it holds together.

Use stiffness for deflection. Yield and tensile strength say nothing about how much a part flexes under load. That depends on the elastic modulus and the part's shape. Aluminum's modulus is about one third of steel's, so an aluminum part flexes about three times as much as the same steel part under the same load, even if its yield strength is higher.

Why They Matter for Sheet Metal Bending

Bending only works because metal yields. The press brake pushes the material past its yield strength through the thickness so the bend stays put. Both numbers show up on the shop floor:

• Springback comes from the elastic stretch that recovers after the punch lifts. It grows with the ratio of yield strength to elastic modulus. 6061-T6 has a higher yield than A36 and about a third of the stiffness, so it springs back far more. High-yield materials are overbent to hit the finished angle.
• Bending force scales with tensile strength. Annealed 304 needs noticeably more press tonnage than mild steel of the same thickness.
• Cracking is a ductility problem. Materials whose yield sits close to their tensile strength, with low elongation, crack on the outside of tight bends. 5052-H32 is the aluminum on our sheet metal bending service list, along with 1008 and A36 steel, G90 galvanized, and 304 stainless. 6061-T6 and 7075-T6 are not on it.
• The distortion zone next to a bend is material that yielded as the bend formed. Holes inside it can stretch. See what the distortion zone is and our bending guidelines for the limits by material and thickness.

You don't need to work out springback yourself when you order bent parts from Fabworks. Upload a STEP file and the quote shows each bend on our tooling in the press brake simulation.

How to Choose Material Based on Strength

1. Find the highest working stress in the part and pick a material whose yield strength, divided by your factor of safety, is above it.
2. Check deflection separately. If the part is too flexible, a thicker gauge or a bend that adds a flange usually helps more than a stronger alloy.
3. If the part will be bent, check that the material is on the bending list and that the bend radius suits it.
4. Weigh cost, weight, and corrosion resistance. Our guide to choosing the right material and the mild steel vs stainless steel comparison cover those tradeoffs.

Frequently Asked Questions

Is tensile strength the same as yield strength?

No. Yield strength is the stress where permanent deformation starts. Tensile strength is the maximum stress the material reaches before it necks and breaks. Both come from the same tensile test, and tensile strength is always the higher of the two.

Is yield strength always lower than tensile strength?

Yes. Yield is the start of plastic deformation and tensile strength is the peak of the curve after it, so yield strength can't be higher. In brittle materials the two are almost equal, because they break with very little plastic stretch.

What is the difference between yield strength and ultimate tensile strength?

Ultimate tensile strength is the full name for tensile strength. The difference from yield strength is the same: yield marks permanent bending, ultimate tensile strength marks the maximum load before failure.

Which is more important, yield strength or tensile strength?

For most parts, yield strength, because the part is no longer usable once it has taken a permanent set. Tensile strength matters when you need to know the failure load, when designing fasteners and welds, and when estimating forming force.

What is a good yield strength for steel?

It depends on the job. Mild steels like 1008 and A36 yield at about 20–40 ksi (140–275 MPa) and are easy to bend and weld. High-strength structural steels yield at 50 ksi (345 MPa) and up. Higher yield means a stronger part but more springback and more force to form.

What is yield stress?

Yield stress is the stress at which a material yields. In practice, yield stress and yield strength are used interchangeably.

How does temperature affect yield strength?

Yield and tensile strength both drop as metal heats up. Heat-treated aluminum such as 6061-T6 also loses strength permanently when welded or held at high temperature, because the heat undoes the temper.

Summary

Yield strength tells you when a part will start to bend permanently. Tensile strength tells you the most stress it can carry before it breaks. Design against yield, check tensile strength for ultimate failure, and keep the gap between them in mind when a part will be bent.

Ready to make parts? Upload a STEP or DXF file for an instant quote on laser cut and bent parts in aluminum, steel, and stainless steel.