What is dynamic fatigue and what is it used for?
The dynamic fatigue test predicts the durability of a foam. It allows us to estimate the hardness and thickness loss of a foam sample when it is subject to a cyclical compression force. In other words, it is a test that predicts the behaviour of a foam over time, particularly regarding the loss of hardness (associated to firmness) and thickness.
How does the test work?
Firstly, we measure the thickness and hardness of the samples.
After the cyclical compressions, we measure the thickness and hardness of the samples again and use that to calculate its percentage loss. A foam with 3% thickness loss in the dynamic fatigue test shows greater resistance to fatigue than a foam with 6%, making it more durable.
This test is often used in final products and not in layers of foam that compose that product. In this case, we try to understand how the design and materials that compose that product influence its characteristics.
What is it used for?
These results will help us predict the natural waring of the product over time (for instance, a sofa/chair seat or a mattress). This will poin us in the right direction when picking the right material for the desired application. If we need a foam for a hospital chair seat, which receives thousands of people a day, it needs to have low loss of thickness to ensure it lasts longer.
The dynamic fatigue test also allows us to calculate a higher product life time than the mandatory two years imposed by consumer defense laws.
Overall, foams with good dynamic fatigue resistance have higher quality as they preserve their characteristics with use over time.