The Stress Fatigue Behavior And Notch Sensitivity Of Polymer ABS Under Symmetry Circle Loading

With the development of materials science, as one of the new engineering materials, polymer is applied in engineering widely. The fatigue failure of the engineering components made of polymer occurs often, and become an important mode of failure. The research on the fatigue behavior of polymer is lack relatively when compared with metal materials. Because many component of polymer have some notches and they are subjected to cyclic loading, The research on the fatigue behavior and notch sensitivity of polymer under cyclic loading has obvious Significance. The stress fatigue behavior and notch sensitivity of Acrylic nitrile -Butadiene-Styrene (ABS) under cyclic loading are studied in this paper. Two experimental methods are used, One is the "up and down method" by which the fatigue strength of finite life (the number of set cycles is 5×10~5) is determined. Another is the "fitting S-N curve method", by this method the number of cycles-to-failure with some different stress amplitude of cyclic load are determined, and the stress fatigue formula and the S-N diagram are fitted, and the fatigue strength is estimated accord to the formula.First, the fatigue strength of finite life of polymer ABS is determined by above two methods, and the fatigue strength formula with three parameters and the S-N curve are given; the fatigue strength determined by two methods are close to each other, the error is 0.36 percent only. Then, the fatigue strength of finite life under cyclic loading with three different frequencies are determined by "up and down method", and the fatigue Strength under cyclic loading with eight different frequencies are determined by "fitting S-N curve method". It is show by experimental results that the fatigue Strength of finite life of polymer ABS is not affected by the frequency of the cyclic loading. For the notch sensitivity of polymer ABS, the fatigue strength of notched specimens with seven arc radius of notch bottom are determined by "up and down method" and "fitting S-N curve method". The fatigue strength of notched specimens are obviously smaller than the fatigue strength of smooth one, the fatigue behavior of polymer ABS is significantly influenced by the notch, and the fatigue notch factor is used for expressing this influence. The fatigue notch factors of the seven notched specimens determined by experimental results are between 1.40 and 1.75, and it is proved that Neuber formula- the representative formula for calculating fatigue notch factor is applicable to polymer ABS, in which the material constant "a" is equal to 2.5.The possibility of the fatigue calculation for notched specimens of polymer ABS with the finite element computers software ANSYS is discussed in this paper. The calculation process, control and steps are set for simulation the stress fatigue curve of the notched specimens and calculating the fatigue notch factors of polymer ABS. The fatigue strength and fatigue notch factors of the notched specimens of polymer ABS are calculated, and conform to the corresponding experimental results, the error between the calculate value and experimental value is small.