Murtumispiste

Murtumispiste, or fracture point, is the stress or strain level at which a material fails by fracture under load. It is a property determined in mechanical testing, most commonly in a tensile test, and marks the end of the material's usable life in that loading configuration. The fracture point differs from the yield point (the onset of plastic deformation) and from the ultimate tensile strength (the maximum engineering stress before necking in ductile materials).

In practice, the fracture point is where a stable crack propagates and leads to complete separation of the specimen. For brittle materials, fracture occurs with little plastic deformation; for ductile materials, significant necking may precede fracture. The precise fracture stress depends on material, temperature, strain rate, microstructure, flaws, and environment (corrosion, hydrogen embrittlement, etc.).

Influence and use: Designers use fracture-related data alongside fracture toughness to assess safe operating loads and durability. Fracture toughness (K_IC) describes resistance to crack growth, while fracture point describes the stress level at failure. Standards such as ISO and ASTM specify how to determine fracture strength in tests for metals, plastics, and composites. The term is common in Finnish engineering literature; in English it is often called fracture strength or fracture stress.