Vetolujuus

Vetolujuus, or ultimate tensile strength (UTS) in English, is the maximum stress that a material can withstand in uniaxial tension before necking and eventual fracture. It is obtained from a tensile test and is expressed as stress, typically in megapascals (MPa) or ksi. The value lies at the peak of the engineering stress–strain curve and is distinct from the yield strength, which marks the onset of plastic deformation; in many metals the yield strength is lower than the UTS.

Measurement is carried out by standardized tensile tests, such as ISO 6892-1 for metals or ASTM E8/E8M. A specimen with a known original cross-sectional area is pulled until failure, recording force and displacement. Engineering stress is computed as force divided by the original area, and the UTS is the highest engineering stress reached. Some tests also report true stress for large deformations.

Applications and factors: UTS is a key parameter in material selection and structural design, indicating how much load a material can bear before failing. It depends on composition, processing (such as heat treatment and work hardening), temperature, and strain rate. Typical ranges include mild steel around 400–550 MPa, high‑strength steels 700–1000 MPa, and aluminum alloys roughly 200–550 MPa; polymers and composites may show lower or highly variable values. UTS alone does not reflect ductility or toughness; elongation at break and impact resistance are also important for assessing performance.

Limitations: In brittle materials the UTS may occur near fracture, and environmental conditions can affect results. In design, UTS is used with safety factors to ensure structural integrity. Vetolujuus is a standard reference point for comparing material strength under tensile loads.