When a material is deformed, a certain amount of energy is required to achieve deformation. Recovery from deformation also takes a certain amount of energy. For polyurethanes, the ratio of energy returned during recovery to the energy required to cause the deformation is called polyurethane resilience.
A material that is perfectly elastic will return all the energy during recovery. A more viscous material will return less energy upon recovery because some of the input energy was lost in the form of heat. The energy loss is due to internal friction within the elastomer and is called Hysteresis; it’s equal to the per cent energy loss per cycle. A material with high resilience will be very lively, think bouncy ball because all the energy that is input during deflection is returned on the rebound. A material with low resilience will feel dead because the input energy is lost in the form of heat during deflection.
Polyurethane resilience is typically measured in a variety of ways with the most common probably being the Bashore Rebound Test. Resilience is measured on a scale of 0 to 100%. A 100% resilient material would return all of the input energy upon recovery.
Shown here are tables containing the polyurethane resilience for a variety of Gallagher Corporation compounds. Resilience is a property that can vary widely among the compounds independent of the hardness. Polyurethane resilience will also vary widely based on the temperature of the material. When a polyurethane part is heated, it’s able to flow more easily, thus reducing the internal friction and increasing the resilience.
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Bashore Resilience Summary Tables