Study on Fatigue Fracture Mechanism of Short Glass Fiber Reinforced Plastic

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The fatigue properties of short glass-fiber reinforced polyphenyleneether (GFPPE), polyphenylenesulfide (GFPPS), syndiotactic polystyrene (GFSPS), and glass-bead reinforced polyoxymethylene (GBPOM) were studied through uni-axial and multi-axial fatigue tests. It was found that the numbers of cycles to failure were strongly dependent on the duration of the interval time. In the case of uni-axial fatigue tests, the interval time resulted in greater numbers of cycles to failure. In multi-axial fatigue tests, however, the interval time resulted in smaller numbers of cycles to crack initiation and ultimate failure. The failure mechanism was investigated through acoustic velocity measurements and optical microscope (OM) observations. The results of those measurements suggested that the different behaviors in fatigue tests under different conditions are attributable to the differences in mechanisms of damage zone development, which consisted with breakage of glass fibers, micro-voiding, changes in the orientation of glass fibers, and plastic deformation of matrix depending on the test conditions such as loading mode (uni-axial and multi-axial) and interval times between loading. Experimental results suggested that the difference in the damage development mechanisms were caused by the different elastic response to the loading resulting in the localized or delocalized damage accumulation depending on the loading mode and interval time. The different damage development mechanisms, in turn, affect the absorption of loading energy resulting in the different fatigue life