Fatigue of Closed Cell Foams

ABSTRACT: The static properties of foams scale with relative density and scaling can be obtained through various static tests. The same scaling appears to be valid for both crack propagation rates and fatigue properties of the foams. This implies that, once the fatigue behavior of one relative density foam is established, one can predict the fatigue behavior of all other density foams within the same class of materials. This study deals with fatigue of closed cell foams. The main idea is to use a few simple tests to predict tension–tension fatigue properties of foams. The required testing consists of crack propagation rate measurements and one tension–tension fatigue test performed at the yield stress of the foam. This data can then be combined to construct a synthetic S–N curve for the foam. Testing is performed on three densities of Divinycell H-grade and three densities of Rohacell WF-grade foam. A very simple fatigue model, based on an initial flaw approach, is used to link the crack propagation rate behavior of these foams with their unnotched fatigue life. This approach is backed up by the experimental results. The results obtained can be used to form some general conclusions about the fatigue of closed cell foams, at least of the types used herein. KEY WORDS: cellular materials, foam, fatigue, crack propagation