Väänetugevus

Väänetugevus is a mechanical property describing a material’s or component’s resistance to twisting under an applied torque. It covers both the stiffness to twist (torsional rigidity) and the strength to withstand twisting before plastic deformation or failure. The concept is especially important for rotating parts such as shafts, drive systems, and fasteners, where torsion can govern performance and safety.

Torsional stiffness, or rigidity, is the torque required per unit angle of twist. For a homogeneous shaft of length L and polar moment of inertia J, the relation is T = (G J / L) · θ, where G is the shear modulus of the material and θ is the angle of twist. The quantity T/θ is often referred to as the torsional rigidity. The maximum shear stress under torque T is τ = T r / J, where r is the radial position in the cross-section; the highest stress occurs at the outer surface (r = c, the outer radius). For a solid circular shaft with diameter d, J = π d^4 / 32, and the surface stress simplifies to τ_max = 16 T / (π d^3).

Väänetugevus can also denote torsional strength—the maximum torque that a member can sustain before yielding or fracturing. This is determined by the material’s shear yield strength and by geometric factors through the same J and cross-section relationships.

Measurement typically uses a torsion test, where torque is applied to a specimen and the resulting twist is measured. From the slope of torque versus angle, G can be determined; the yield torque and corresponding angle indicate torsional strength.

Applications and design considerations include choosing suitable cross-sections, materials, and heat treatments to achieve adequate torsional stiffness and strength while avoiding excessive torsion or fatigue under service conditions. See also torsion, shear modulus, and polar moment of inertia.