What Is a Tensile Strength?

Tensile strength is the maximum pulling (tensile) stress a material can withstand before it breaks. It is measured in a tensile test, in which a standard specimen is stretched until it fails, and is reported in megapascals (MPa) or pounds per square inch (psi). It is also called ultimate tensile strength (UTS).

In short: tensile strength tells you the stress that will break a part; yield strength tells you the lower stress that will permanently bend it.

How Is Tensile Strength Measured?

In a tensile test, a specimen is pulled slowly while the machine records the applied force and how far the specimen stretches. Dividing the force by the specimen's original cross-sectional area gives stress; dividing the stretch by the original length gives strain. Plotting one against the other gives the stress-strain curve, and the tensile strength is read from it.

• Metals: stress rises through the elastic region, past the yield strength and up to a maximum, where the specimen starts to neck (thin locally) before it fractures. That maximum is the tensile strength. A widely used test standard is ASTM E8/E8M, which covers yield strength, tensile strength, elongation and reduction of area.
• Plastics: tested to ASTM D638 (or ISO 527-1, which covers the same subject with different technical details) using dumbbell-shaped specimens up to 14 mm (0.55 in) thick. Many plastics show a peak at yield and then a separate stress at break, which can be higher, equal or lower, so plastic datasheets often report tensile strength at yield and at break separately.

For conversion, 1 MPa ≈ 145 psi.

Tensile Strength vs Yield Strength

	Yield strength	Tensile strength
What it marks	Where permanent (plastic) deformation begins	The maximum stress reached before fracture
Where on the stress-strain curve	Where the curve leaves its straight elastic line; for metals usually found by the 0.2% offset method	The highest point, where necking begins (metals)
What happens beyond it	The part no longer springs back; it stays bent or stretched	The part necks down and breaks
Metals	Lower than tensile strength	The higher of the two
Plastics	Often the peak stress just after the elastic region	Stress at break, which may be above or below yield
Used for	Sizing parts that must keep their shape	Comparing materials and judging margin against breaking

How to Use Tensile Strength in Material Selection

• Don't design to it. For most parts, a permanent bend is already a failure, so working stresses are kept below the yield strength with a safety margin. Tensile strength tells you how much reserve remains before fracture.
• Know the material class. The tensile strength of some polymers can rival some ceramics, but it is no match for even the softest metals. A plastic part replacing a metal one usually needs thicker sections or ribs.
• Treat plastic data with care. ASTM D638 notes that plastic tensile results vary with specimen preparation, test speed and environment, and that data are not valid for loading times or environments very different from the test. Compare only values from the same standard and conditions, and allow for temperature and long-term load.
• Ask for proof when it matters. For regulated or load-critical parts, request material certifications with the delivery.

NICE Rapid provides material certifications on request, and on LSR molding projects tensile strength, elongation, Shore hardness and critical dimensions are inspected on every batch.

Frequently Asked Questions

What is tensile strength?

Tensile strength is the highest pulling stress a material can take before it breaks. It is measured by stretching a standard specimen to failure in a tensile test and is reported in MPa or psi. It is also called ultimate tensile strength (UTS).

What does tensile strength mean in simple terms?

It is how hard you can pull on a material, per unit of cross-section, before it snaps. A higher tensile strength means a bar of the same size can carry a larger pulling load before breaking.

What is the difference between tensile strength and yield strength?

Yield strength is the stress at which a material starts to deform permanently; tensile strength is the maximum stress it reaches before breaking. For metals, yield strength is the lower value, which is why designers keep working stresses below yield, not below tensile strength.

Related Services at NICE Rapid

• CNC Machining — metals from aluminum 6061 and 7075 to stainless steel and titanium Ti-6Al-4V, plus engineering plastics such as PEEK and nylon.
• LSR Molding — silicone parts with tensile strength, elongation and hardness inspected per batch.
• Request a Quote — share your load requirements and our engineers will help shortlist materials.

Sources

1. Penn State University, MATSE 81: Materials in Today's World, Lesson 4 "Stress-Strain Testing" — tensile test: specimen slowly pulled while force and change in length are recorded, then converted to a stress-strain diagram using original length and area — courses.ems.psu.edu
2. Penn State University, MATSE 81, Lesson 4 "Plastic Deformation" — tensile strength is the maximum stress on the stress-strain curve, at the onset of noticeable necking; yield strength by the 0.002-strain offset — courses.ems.psu.edu
3. Penn State University, MATSE 81, Lesson 4 "Mechanical Behavior of Polymers" — for polymers, yield stress is the peak after the elastic region and tensile strength is the stress at fracture, which can be greater than, equal to or less than yield; polymer tensile strengths can rival some ceramics but are no match for even the softest metals — courses.ems.psu.edu
4. ASTM E8/E8M-24, Standard Test Methods for Tension Testing of Metallic Materials, scope — covers determination of yield strength, yield point elongation, tensile strength, elongation and reduction of area — store.astm.org
5. ASTM D638-22, Standard Test Method for Tensile Properties of Plastics, scope and significance — dumbbell-shaped specimens, thickness up to 14 mm (0.55 in); ISO 527-1 addresses the same subject with different technical content; results vary with specimen preparation, speed and environment and are not valid for widely different load-time scales or environments — store.astm.org