Glossary

Tensile strength is the maximum amount of tensile (pulling) stress that a material can withstand before it breaks or fractures. It represents the point on a stress–strain curve where the material reaches its ultimate ability to resist stretching under load. Beyond this limit, the material begins to neck, deform irreversibly, and eventually fail.

In fasteners such as bolts, screws, and rods, tensile strength is one of the most critical mechanical properties. It defines how much tension the fastener can endure before breaking and is usually expressed in megapascals (MPa) or pounds per square inch (psi). For example, a steel bolt with a tensile strength of 800 MPa can withstand a maximum stress of 800 million newtons per square meter before fracturing.

The tensile strength of a fastener is determined through testing, where a sample is gradually pulled apart in a tensile testing machine until it fails. During this process, the material first deforms elastically (it stretches but returns to its original shape), then plastically (it stretches permanently), and finally fractures when the tensile strength is exceeded.

Tensile strength is often used alongside yield strength and proof load to describe a material’s behavior under stress. While proof load represents the maximum stress a fastener can handle without permanent deformation, tensile strength marks the absolute breaking point. For high-strength fasteners—such as those made to grades 8.8, 10.9, or 12.9—the tensile strength can range from 800 MPa to 1,200 MPa or higher, depending on the material and heat treatment.

In summary, tensile strength is a measure of how much pulling force a material can sustain before failure. It is a fundamental indicator of mechanical performance, reliability, and safety in fasteners and structural components, ensuring that parts can resist breaking under load in service conditions.