The Fretting Fatigue Behavior Of 45 Steel At Different Cyclic Loading Stress Ratio

The presence of fretting fatigue is relatively common. It is the main reason that caused failure of some key parts of machine. The fretting damage caused to initiation and propagation crack at the contact areas of machine, which reduces the fatigue life and even causes security accidents.The fretting fatigue life and crack initiation characteristics of the 45 steel were studied by experiment at different axial cyclic loading stress ratios. The finite element simulation was used to analysis the stress intensity, axial stress, transverse stress, shear stress on the contact surface, under different loads, and its effect on crack initiation characteristics. The main work and conclusions are as follows:1. The fretting bridge with cylindrical foot surface and the loading bolt and the loading ring and so on such experimental device were designed for fretting fatigue experiment under cylinder-on-flat contact. The fretting fatigue S—N curves of 45 steel under vertical load of 2000 N and axial cyclic loading stress ratios of 0, 0.25, 0.5 has obtained by fretting fatigue experiments. We can see that fretting fatigue life decreased, under the same stress amplitude, as cyclic loading stress ratio increased. The scar which parallel to the fretting direction, and large area of micro-crack, and long crack, and surface shedding, and corrosion pits have been found in microscopic observation at contact surface. The mechanism of fretting wear under experimental condition has given some analysis. The crack location of fretting fatigue fracture has been measured, which is at the center of contact area and a little biased outboard of bridge foot.2. A finite element model has been established which is as the same as test fretting model. The finite element solution under the same load of test has been calculated. The stress intensity, axial stress, transverse stress, shear stress on contact surface and their effects on crack initiation characteristics has been given some analysis. There is stress concentration in the contact region. The location of maximum stress intensity amplitude is at the center of contact area and a little biased outboard of bridge foot where is easy to initiation crack under the axial load. Under the contrast of the location of maximum stress intensity amplitude to the crack location of fretting fatigue fracture, we can see that the location of maximum stress intensity amplitude on contact surface is the crack location of fretting fatigue fracture.The fretting fatigue life and crack initiation characteristics of 45 steel at different axial cyclic loading stress ratios were studied by experimental analysis and finite element simulation analysis. This topic will have a further study on new materials like composite materials and ceramic materials.