scope:

Scope

An elastomeric foam deforms when a force is applied and recovers when a force is removed. The recovery, however, is not immediate; the deformation lags behind the applied force which gives rise to hysteresis or damping effects. These effects are important in seating foams since they affect vibration frequency and the transmissibility of forces through the foam. (Hysteresis, in a sense, is the direct opposite (or inverse) of resilience; e.g., 30 % hysteresis is equivalent to 70 % resilience.) This procedure consists of subjecting a test specimen of the foam material to a number of ILD* load (65 % identation-deflection) and unloading cycles under closely controlled conditions. The ratio of the energy absorbed to the total energy expended during the loading of the sample, obtained with the last cycle, is used to calculate the percent hysteresis (resiliency) of the material.