An experimental study on the ratcheting and fatigue behavior of polyacetal under uniaxial cyclic loading

Abstract

This paper presents an experimental study on the behavior of polyacetal or Polyoxymethylene (POM) under uniaxial cyclic loading. All experiments were performed in the stress-controlled mode. The tests were divided into nine groups, where different combinations of the mean stress or stress amplitude were used. Uniaxial fatigue or cyclic testing of polymeric materials is performed on specimens with geometry according to ASTM D638-03 or its equivalent, ISO 527-1. In this study, the diameter of the polyacetal test specimens was 20 mm. The specimens were prepared using a CNC lathe. The gage length of the specimens was 30 mm, and the diameter of the specimens was 10.1 mm. The stress–strain data were recorded during each cycle of the experimental tests. Based on the obtained stress–strain data, quantitative analysis of the mechanical parameters were done in which the strain ratcheting, strain range, strain energy density and the slope of the stress–strain hysteresis loops were calculated. The experimental data showed that the ratcheting strain and strain rate ratcheting are sensitive to the applied stress amplitude and the mean stress. Mean stress functions were used in the equivalent damage parameter and included the mean stress effect on the fatigue life of the polyacetal. The material constants were calibrated using the stress, strain and energy approaches. Finally, it was found that the stress and energy approaches were more successful in predicting the fatigue life of polyacetal.