Fracture and Fatigue Failure Behavior of Fluoroelastomers

Abstract

Fluoroelastomers (FEs) are a class of elastomers with very high chemical resistance and wide service temperature which are being used in chemically harsh environments. In the present work, the fatigue failure characteristics of FEs have been studied. Fatigue Crack Propagation (FCP) experiments were conducted on single edge notch (SEN) specimens in displacement control. The strain range was kept constant at about 14% with a frequency of 0.5 Hz. FCP data such as, the number of cycles, crack length, and hysteresis loop, were recorded in order to correlate the crack speed to the energy release rate. In addition, the static behavior of the material has been examined in view of both notched and un-notched specimens. Post failure analysis was performed on the fractured samples using Scanning Electron Microscopy (SEM). The fractographic features associated with different FCP stages were identified. As the FCP speed increased, the roughness of the fracture surface decreased. Multiple cracks and fracture lines, at different fracture planes, are associated with the fatigue failure. The intersection of those fracture lines form fracture islands which are characteristic to FE fracture morphology under fatigue loading. On a microscopic level, the fracture surface exhibits microcracks and microvoids with evidence of void coalescence. The fracture surfaces of both un-notched and notched samples tested under monotonic tensile loading were also examined and compared with those tested under fatigue loading. The origin and features of fracture initiation and propagation for the monotonic type of failure have been identified.