Federhärte

Federhärte, in engineering usage, refers to the stiffness or rate of a mechanical spring. It describes how resistant a spring is to deformation under load, i.e., how much force is needed to produce a given deflection. In technical contexts this stiffness is commonly expressed by the spring constant k (units of newtons per meter, N/m). For a linear spring obeying F = kx, doubling the deflection x requires doubling the force F, provided the material remains within the elastic range. A higher Federhärte yields smaller deflections under the same load and influences resonance, vibration isolation, and energy storage.

Practically, Federhärte depends on design and material: wire diameter, coil diameter, number of active coils, and the modulus of elasticity E of the spring material. For a helical compression spring, an approximate expression is k = (d^4 E) / (8 D^3 n), where d is the wire diameter, D the mean coil diameter, and n the number of active coils. Other spring types have different relations.

Measurement is performed with static compression or extension tests using a force sensor and a deflection measurement to determine k, often across a range of deflections to assess linearity. Temperature, aging, and pre-load can affect Federhärte over time.

Applications are broad, including automotive suspensions, machinery actuators, electronics mounts, and consumer products. The term should not be confused with the material’s hardness (Härte) or with damping characteristics.

See also: spring constant, Hooke’s law, preload, stiffness.