A force F or a torque M, acting on an rubber-metal mount deforms it by a spring deflection s or a twisting angle α . The degree of deformation depends on the magnitude of the Force F or the torque M, the elastomer hardness H and the geometric shape of the MEGI mount.
The ratio of force F to spring deflection s or the torque M to the twisting angle α is referred to as the spring rate or characteristic c or the torsional spring rate cv.
The geometric shape of the rubber-metal mount and the type of stress (pressure, shearing, tensile stress) influences the shape of the deflection curve. It can be progressive, linear or degressive. The spring rates c or cv for linear characteristic curves remain constant over the entire spring range. The spring rates depend on spring deflection in the case of progressive or degressive characteristic curves.
In these cases, the spring rate is determined by plotting the tangent so that it touches the characteristic curve at working point A. The degree of slope of the tangent yields the value for the spring rate c. It is calculated on the basis of the following formulas:
MEGI mounts subject to pressure tend to have progressive characteristic curves, those subject to shearing and tensile stress tend to have a degressive characteristic curve. The degree of progressivity or degressivity depends on the geometry of the rubber-metal mount and the magnitude of the deformation. Linear characteristic curves result from a superimposition of pressure- and shear-related stress over large deformation ranges.