Experimental investigation on fatigue failure characteristics of QP-16 type ball-eye under bending load

Abstract

Abstract In order to ensure the safety and reliability of power delivery systems, the fatigue characteristics and mechanical properties of ball-eyes (BE) are studied by proprietary equipment: bending fatigue test equipment (BFTE), scanning electron microscope (SEM), stereomicroscope, energy dispersive spectrometer (EDS), hardness display equipment. It was found that, compared with the BEs of the annealing process and quenching and tempering process (QTP), the mechanical properties of BE treated by normalizing process are the best under the three different bending fatigue loads, which are 200, 300, 400 MPa. The three kinds of BE with different processes have their own characteristics, in which, the fatigue fracture of BE treated by normalizing process has obvious cowrie pattern and multi fatigue origins. The fatigue extension region is relatively smaller, but the appearance are more smooth and delicate, whose color are black and dark. In final fracture region, there is obvious rust, coarse, a granular surface. The microstructure is fine uniform ferrite and pearlite. The fracture morphology are characterised by transgranular and quasi-cleavage fracture with a few intergranular cracks and the fracture surface contains more impurities. Fatigue fractures of BE from the other two processes of the characteristics of inhomogeneous microstructure, large difference of micromorphology, rough fracture surface and different impurity elements. Under the same stress amplitude, the life of the BE under bending load is lower than that of the BE under tensile load.