Tensile strength is the maximum amount of pulling force a material can withstand before it breaks, divided by its cross-sectional area. It tells you, in precise terms, how much stress something can handle when stretched. Engineers, doctors, and materials scientists all rely on this single number to predict whether a material will hold up or fail under load.
How Tensile Strength Is Measured
To find a material’s tensile strength, you take a sample, clamp both ends, and pull until it breaks. The maximum force recorded during that test, divided by the original cross-sectional area of the sample, gives you the tensile strength. The result is expressed as force per unit area. In the metric system, that’s usually megapascals (MPa) or gigapascals (GPa). In the U.S. system, it’s pounds per square inch (psi).
A thin wire and a thick cable made from the same steel have identical tensile strengths, because the measurement accounts for size. It’s a property of the material itself, not the object.
What Happens Inside a Material Under Tension
When you first pull on a material, it stretches slightly and snaps back when you let go, like a rubber band. This is the elastic phase. The atoms in the material shift apart but return to their original positions. Every material behaves this way up to a certain point.
Push past that limit and you reach the yield point, where permanent deformation begins. The material bends, stretches, or warps in a way it won’t recover from. Yield strength is the minimum force needed to cause that permanent change. It’s a lower number than tensile strength for any given material, because the material hasn’t broken yet, it’s just damaged.
Keep pulling and the stress climbs to a peak. That peak is the ultimate tensile strength. Beyond it, the material enters a phase called necking, where one spot thins dramatically as the material concentrates all its deformation into a narrow band. Fracture follows quickly. Think of pulling taffy: it stretches evenly for a while, then one thin spot forms and snaps.
Yield Strength vs. Tensile Strength
These two numbers answer different questions. Yield strength tells you how much force a material can take before it permanently deforms. Tensile strength tells you how much force it can take before it breaks entirely. A bridge designer cares deeply about both: yield strength sets the safe working limit, while tensile strength sets the absolute failure point.
For structural steel, yield strength might be around 250 MPa while tensile strength sits near 400 MPa. That gap between the two numbers is actually useful. It means the steel will visibly bend and deform before it snaps, giving warning signs of overload. Brittle materials like glass or ceramics have almost no gap; they skip straight from elastic behavior to catastrophic fracture.
Tensile Strength Across Common Materials
The range is enormous. At the low end, soft plastics and biological tissues measure in the tens of megapascals. At the high end, engineered nanomaterials reach into the hundreds of gigapascals.
- Human tendon: About 100 MPa at the point of fracture, though during normal activity tendons experience only about 25 MPa. That gives them a safety factor of roughly 4, meaning your tendons are built to handle about four times the stress of maximum muscle contraction.
- Human cortical bone: Around 130 to 150 MPa in tension, though bone is notably stronger in compression (around 210 MPa for the femur). The collagen fibers in bone provide most of its tensile resistance, while the mineral content handles compressive loads.
- Structural steel: Typically 400 to 550 MPa, varying by alloy.
- Spider dragline silk: About 1.1 GPa (1,100 MPa), which puts it in the same range as some steel alloys while weighing a fraction as much.
- Carbon fiber composites: Around 2,300 MPa at room temperature for high-quality unidirectional sheets.
- Graphene: A theoretical maximum of 130 GPa, the highest of any material ever discovered. That’s roughly 250 times stronger than structural steel.
How Temperature Changes Tensile Strength
Heat weakens most materials, sometimes dramatically. Carbon fiber reinforced polymer (CFRP), widely used in aerospace and high-performance cars, loses about 68% of its tensile strength at 200°C compared to room temperature. The reason is straightforward: the polymer resin holding the fibers together softens as it approaches its glass transition temperature, the point where it shifts from a rigid, glassy state to a rubbery one. Once the resin softens, the fibers can no longer transfer load effectively between each other.
Metals also weaken with heat, though usually more gradually. Cold does the opposite in some materials, making them stronger but more brittle. This is why engineers designing structures for extreme environments, from jet engines to Arctic pipelines, test tensile strength across a range of temperatures rather than relying on a single room-temperature number.
Tensile Strength in Medicine
Surgeons choose suture materials partly based on how long they maintain tensile strength inside the body. Absorbable sutures are designed to lose strength on a predictable schedule as tissue heals. A common braided absorbable suture retains 70% of its initial tensile strength at 10 days and drops to 30% by day 20, fully dissolving within 60 to 90 days. A slower-absorbing monofilament option holds 50% of its strength at 35 days and takes about 180 days to disappear completely.
Fast-absorbing sutures used for superficial wounds lose essentially all their strength by 21 days. Surgeons match these timelines to how quickly the tissue they’re repairing can bear load on its own. A deep fascial closure needs sutures that hold for weeks; a skin closure might only need a few days of support.
The body’s own tissues have their own tensile properties that matter during recovery. Healing tendons and surgical wounds regain tensile strength gradually, which is why rehabilitation timelines exist. A repaired tendon doesn’t reach full strength for months, and loading it too early risks re-rupture at the weakest point in the healing tissue.
Why Tensile Strength Isn’t the Whole Picture
A material can have impressive tensile strength and still be wrong for a given job. Ceramics are extremely strong in compression but shatter under tension. Glass fibers have high tensile strength but zero tolerance for surface scratches, which act as stress concentrators that trigger cracks. Rubber has low tensile strength but extraordinary elongation, making it ideal for applications where flexibility matters more than raw load capacity.
Engineers also weigh toughness (how much energy a material absorbs before breaking), fatigue resistance (how it handles repeated loading cycles), and ductility (how much it stretches before failure). Tensile strength is one critical number in a larger profile that determines whether a material will perform safely in the real world.