Puolijäykkyys

Puolijäykkyys (literally “half-stiffness”) is a Finnish term used in materials science, engineering and related fields to describe a mechanical behavior that lies between rigidity and pliability. A component or material characterized by puolijäykkyys resists deformation under load more than a flexible material but less than a rigid one. In practice, puolijäykkyys denotes an intermediate stiffness that allows some controlled deformation, energy absorption and damping, while maintaining structural support.

Measurement and interpretation: There is no single universal numerical threshold for puolijäykkyys. It is typically inferred from test results such as the Young's modulus, flexural modulus, or dynamic mechanical analysis data, including storage modulus and loss factor. The concept is often used qualitatively when designing joints, supports, or products that need a balance between stiffness and compliance. In structural engineering, semi-rigid or partially rigid connections can enable rotation or deformation to absorb loads, while in polymers or composites, reduced cross-link density or temperature effects can produce semi-rigid behavior.

Context and examples: The term appears in Finnish-language texts across engineering disciplines, including mechanical design, civil construction, and materials science. Examples include semi-rigid polymer blends, certain filled polymers, and wood-based composites that are stiffer than foam but more compliant than metal. In furniture or consumer products, puolijäykkyys might describe components that resist bending but yield slightly to ensure comfort or fit.

See also: stiffness, rigidity, elasticity, semi-rigid connection, damping.