Fatigue tests determine the long-term behavior of foam under constant mechanical load. For example, it represents the load applied to a vehicle seat when a car is being driven.
A fatigue test is described in ISO 3385, ASTM D3574 and in many factory standards. First, the indention hardness and specimen thickness of a cushion when no load is applied is measured. Then a load is applied to the foam tens of thousands of times. This load can be applied under normal climate conditions or under defined humidity and temperature conditions. Following continuous load application and after a holding period, the specimen thickness and compressive stress value are measured again. The results are the hardness and thickness loss.