Stivheden

Stivheden is the Danish term for stiffness or rigidity, describing the resistance of a material, structure, or system to deformation under an applied load. In physics and engineering, stiffness is a property that relates force to the resulting displacement within the elastic range and is distinct from strength, which describes the maximum load a material can bear before failure.

In materials science, stiffness is quantified by elastic moduli: Young's modulus (tension/compression), shear modulus, and bulk modulus. For bending, stiffness is often expressed as flexural rigidity EI, where E is Young's modulus and I is the second moment of area. For torsion, stiffness is GJ. The ratio F/δ gives stiffness, where δ is displacement.

Applications: In design, higher stiffness reduces deflections and shapes dynamic response; designers modify geometry, select stiffer materials, or add reinforcements. In biomechanics, stiffness can describe joints, muscles, and tendons resistance to movement; abnormal stiffness may occur in neurological or musculoskeletal conditions and affects gait and dexterity.

Measurement and factors: Stiffness is determined from load–deflection tests or dynamic tests, and depends on temperature, moisture, aging, and microstructure. It is related to natural frequency and vibration behavior; the interplay with mass determines resonance. Stivheden thus influences performance across mechanical, civil, and biomedical domains.