Craze density based fatigue-damage analysis in polyethylene methacrylate

The S-N curve, also known as the Wöhler curve, is well acknowledged and widely used in the prediction of fatigue life of engineering materials. In this study, we present a craze density model, as an alternative approach, to predict the fatigue life of polymer material-polyethylene methacrylate (PMMA). Our experiments show that craze grows rapidly with the increase of fatigue loadings after their initiation on the surface of PMMA till to the failure of specimens. Dynamic measurements indicate that the growth rate of craze density reaches a stable stage after a rapid accumulation at the beginning, and dominates the fatigue life of PMMA. Both initiation time of crazing and deformation energy of PMMA are probed through the recorded fatigue stress-strain curves and the optical microscope (OM) observations on crazing evolutions. The critical growth rate of the craze density is correlated with the yield stress and strain of PMMA at quasi-static loadings. On the basis of the craze density, an experimental model is established to predict the fatigue damage and life of PMMA. The predication shows good agreement with that from both experiments and traditional S-N curves in a broad range of fatigue loadings.