S. Mall, Air Force Institute of Technology, Wright-Patterson AFB, OH
In this study, a systematic investigation of the fretting fatigue behavior of nickel alloy, IN-100 was carried out at room temperature and elevated temperature of 600 0C. The study includes both experiments and the analyses of the contact conditions, and the latter is accomplished using the finite element method. Fretting fatigue tests were performed over a wide range of axial stresses to examine both low and high cycle fretting fatigue under constant contact load and the influence of two cylindrical pad geometries was also explored. It was observed that fretting reduced the fatigue strength of IN-100, and that increasing cylindrical pad radii does not have the any effect. The crack initiation location and orientation along the contact surface were determined using the Optical and Scanning Electron Microscopy (SEM). In all experiments, cracks were found to initiate near the trailing edge at the contact surface, and at an orientation of 45° with a scatter of +/-10°. Finite element analysis was conducted to obtain the contact region state variables such as stress, strain and displacement. These state variables were used to compute the critical plane based parameters. These parameters were evaluated based on their ability to predict the crack location, crack initiation angle and fatigue life without dependence on contact geometry. The comparison of the analytical and the experimental results showed that fretting fatigue life is not only governed by shear stress on the critical plane, but also the normal stress on the critical plane plays a role in the crack initiation mechanism. A modified shear stress range parameter is capable of predicting crack location, crack initiation angle and fatigue life in IN-100.
Summary: In this study, a systematic investigation of the fretting fatigue behavior of nickel alloy, IN-100 was carried out at room temperature and elevated temperature of 600 0C. The study includes both experiments and the analyses of the contact conditions, and the latter is accomplished using the finite element method. Fretting fatigue tests were performed over a wide range of axial stresses to examine both low and high cycle fretting fatigue under constant contact load and the influence of two cylindrical pad geometries was also explored. It was observed that fretting reduced the fatigue strength of IN-100, and that increasing cylindrical pad radii does not have the any effect. The crack initiation location and orientation along the contact surface were determined using the Optical and Scanning Electron Microscopy (SEM). In all experiments, cracks were found to initiate near the trailing edge at the contact surface, and at an orientation of 45„a with a scatter of +/-10„a. Finite element analysis was conducted to obtain the contact region state variables such as stress, strain and displacement. These state variables were used to compute the critical plane based parameters. These parameters were evaluated based on their ability to predict the crack location, crack initiation angle and fatigue life without dependence on contact geometry. The comparison of the analytical and the experimental results showed that fretting fatigue life is not only governed by shear stress on the critical plane, but also the normal stress on the critical plane plays a role in the crack initiation mechanism. A modified shear stress range parameter is capable of predicting crack location, crack initiation angle and fatigue life in IN-100.
