murtolujuuden

Murtolujuuden (fracture strength) is a term used in materials science to describe the maximum nominal stress a material can withstand before crack propagation leads to fracture. In Finnish literature the base term is murtolujuus, with murtolujuuden serving as the genitive form used to refer to the material’s fracture strength. It is a stress-based property that provides a practical measure of a material’s resistance to sudden failure when a crack is present.

Measurement of murtolujuuden is done under controlled fracture tests using specimens with a pre-existing flaw or notch. Common methods include three-point bending with a notch, single-edge notch bending, and compact tension tests. The result is typically reported as a stress value in megapascals (MPa) and is highly dependent on flaw size, geometry, and loading conditions. Because real materials contain flaws whose size and distribution vary, fracture strength is often tied to specific specimen configurations rather than representing an absolute intrinsic material constant.

Murtolujuuden is related to, but distinct from, fracture toughness. Fracture toughness (often expressed as K_IC) quantifies resistance to crack growth per unit crack extension and has units of MPa·m^0.5, whereas fracture strength is the stress at which fracture occurs for a given crack size. The relationship between the two can be described by fracture-mechanics concepts such as energy release and the presence of flaws, and is influenced by the Griffith criterion in brittle materials.

Several factors influence murtolujuuden, including temperature, loading rate, environment, microstructure, and flaw characteristics. It is used across engineering fields—metals, ceramics, polymers, composites, and geological materials—to assess safety margins and design components that may contain flaws.