An environmental scanning electron microscopy investigation of fatigue crack initiation and propagation in elastomers

Interrupted fatigue testing has been performed on silicone rubber and carbon-black-filled natural rubber samples. The samples have been examined after each test in an environmental scanning electron microscope that has allowed the fatigue crack evolution processes to be studied in new detail. Environmental scanning electron microscopes allow insulating samples to be examined without the need for a conductive coating and this allows the crack evolution in a single sample to be studied and new insights into the fatigue crack evolution processes to be obtained. Thus, the initiation and propagation of cracks in two different elastomeric samples (silicone rubber and carbon-black-filled rubber) has been followed in order to determine the factors that influence the fatigue life of such samples. Cracks were found to initiate at defects associated with the sample geometry and sample processing. The cracks propagated initially on the surface of the sample followed by propagation through the sample thickness. The crack propagation was found to be associated with ligaments that formed in the rubber and the crack front advanced once these ligaments failed. The cracks did not propagate uniformly through the thickness of the specimen and were found to grow from the corners and along the specimen surface before propagating through thickness. Fatigue cracks were found to initiate from features less than 30 pm in size, which is smaller than the calculated threshold for flaws to initiate failure in these samples. (c) 2006 Elsevier Ltd. All rights reserved.