Tensile strength: resistance of materials to pulling forces
Tensile strength measures how much pulling stress a material can take before it deforms or breaks. It is determined by tensile testing and reported in several related ways (yield, ultimate, fracture).
Overview
Tensile strength is a fundamental mechanical property that quantifies the load a material can withstand when pulled (tension) before it fails. Engineers and scientists use this property to compare materials and to design components that must resist stretching, bending, or breaking under tensile loads. Examples of items for which tensile strength matters include rope, wire, and structural elements made from different materials.
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How it is measured
The standard way to determine tensile strength is a tensile test: a specimen with a defined cross section is gripped at both ends and pulled at a controlled rate until it yields and eventually fractures. Engineers record the applied force and the elongation. Stress is calculated as force divided by the original cross-sectional area, and the result is reported in pressure units (for example pascals or megapascals).
Common definitions
- Yield strength — the stress at which a material begins to deform plastically and will not return to its original shape when unloaded.
- Ultimate tensile strength (UTS) — the maximum stress the specimen attains on the engineering stress–strain curve; it marks the highest load-carrying capacity before necking begins.
- Fracture or breaking strength — the stress at which the specimen actually breaks; this can be lower than UTS for ductile materials after necking and reduction of area.
Stress–strain behavior and distinctions
Tensile tests produce a stress–strain curve that reveals stiffness (the initial slope, Young's modulus), yield behavior, strain hardening, and ductility (elongation at break). Distinguish tensile strength from related properties such as compressive strength (resistance to squeezing) and shear strength (resistance to sliding planes). Also note the difference between engineering stress/strain and true stress/strain, the latter accounting for the changing cross section during deformation.
Factors affecting tensile strength
Measured tensile strength depends on material composition and microstructure, manufacturing processes, temperature, strain rate, and the presence of defects or surface flaws. Treatments such as heat treating, work hardening, or composite reinforcement can substantially change strength. For fibers and lightweight materials, tensile strength per unit weight is often a critical figure of merit.
Applications and historical context
Tensile strength underpins safety and performance in fields from civil engineering and aerospace to textiles and electronics. The practice of measuring tensile properties developed alongside industrial testing standards in the 19th and 20th centuries and is now codified by national and international standards bodies so designers can compare materials reliably. Accurate tensile data guide material selection, factor-of-safety calculations, and quality control in production.
Useful notes
When reading tensile data, consider the specimen geometry, testing temperature, and whether values are quoted as engineering or true strengths. For complex components, designers combine tensile properties with fatigue, creep, and impact data to predict real-world performance.
Nominal and true tensile strength
A distinction is often made between the "nominal" stress σ 
("engineer voltage") and the "true" voltage σ 
.
The (nominal) stress values (tensile strength, yield strength) read from the stress-strain diagram do not correspond to the true stress in the material. This is due to the fact that when calculating the nominal stress, the tensile force is related to the initial cross-section.
In the tensile specimen, however, the true cross-section is smaller than the initial cross-section due to transverse contraction or necking; this deformation (elongation and necking) is visible and measurable after the test in the case of elastic-plastic deformation, i.e. specimens made of ductile materials. The true tensile strength is therefore not equal to the nominal stress in the specimen at the moment of fracture, but is higher.
However, since real loads are mostly applied forces that have an absolute magnitude and are not cross-sectional area related, the nominal tensile strength is usually the governing factor when dimensioning components.
For dimensioning in engineering, the yield strength is used instead. The tensile strength plays a role, for example, in manufacturing during forming or machining. Brittle materials, on the other hand, are dimensioned according to tensile strength, but with these materials there is also no relevant necking and therefore no difference between nominal and true stress. In short: technically, a component has long since failed when the tensile strength is reached, with or without necking.
The maximum true stress occurs in the necking area of the specimen. Here, the deformation and, at best, the strain hardening increases until fracture occurs.
In the instrumented tensile test, the specimen cross-section is measured continuously and the force is related to the true cross-section. Specimens examined in this way show a continuous increase in true stress until failure (blue curve in Fig.). However, the value determined in this way is only of theoretical significance.
Tensile strength as name component
Tensile strength has often been used in the past to characterize materials. An example of this is the designation of structural steels. Steel 52 (St52, today S355), for example, was designated according to its tensile strength of 52 kp/mm² (510 N/mm²).
Due to the harmonization of European and international standards, many steels are now designated according to yield strength, which is a better characteristic value for the load-bearing capacity of a material from a design point of view.
Example values
| Material | Tensile strength inN/mm² |
| 7–70 | |
| 10 to 15 | |
| 15 | |
| 45 | |
| 45 to 64 | |
| 150 till 350 | |
| Aluminum alloys | mostly 200 to 450; rarely up to 640 |
| Cast iron with lamellar graphite | 100 till 350 |
| human hair | 200 |
| Titanium alloys | 290 till 1200 |
| Structural steel | 310 to 690 |
| Alloy steel | 1100 till 1300 |
| Dyneema | 3000 |
| up to 63.000 |
Questions and answers
Q: What is tensile strength?
A: Tensile strength is the amount of force needed to pull an object like a rope, wire, or a structural beam until it breaks.
Q: What is the maximum amount of stress that can be sustained by a material before its failure?
A: The maximum amount of stress that a material can endure before failure is known as its tensile strength.
Q: Can you give examples of objects that are tested for tensile strength?
A: Yes, objects like rope, wire, and structural beams are tested for tensile strength.
Q: How many different definitions of tensile strength are there?
A: There are three typical definitions of tensile strength.
Q: What is the first definition of tensile strength?
A: The first definition of tensile strength is that it is the force required to break a material when it is pulled.
Q: What is the second definition of tensile strength?
A: The second definition of tensile strength is that it is the maximum amount of stress that can be sustained by a material before its failure.
Q: What is the third definition of tensile strength?
A: The third definition of tensile strength is that it is the measure of a material's ability to resist breaking under tension.
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AlegsaOnline.com Tensile strength: resistance of materials to pulling forces Leandro Alegsa
URL: https://en.alegsaonline.com/art/97027