Thermoelastic behavior of a small bearing cage
The full field non contact measurement of objects undergoing testing is one of interest for manufacturers of parts which are graded on their longevity. Unfortunately, for homogenous small parts with irregular geometries, such as bearing cages, the solution for testing is typically to use only a FEA model and compliment the testing of the model with simply cyclically loading the sample until failure. To better understand the stresses and behavior of a small object Thermoelasticity can be employed in order to see in a full field technique what stress patterns exist and their correlation to a FEA model.
The FEA model was measured separately from a real bearing cage and simulated in Commercial Ansys™. Two cases of the FEA simulation were used in order to first calibrate the thermoelastic constant to the stresses in a simple case which included no weld seam in both experimental and simulation and then in a more complex case with a weld seam compare the calibrated data with simulation data.
The loading for the samples involves the utilization of a MTS machine with a cyclic sinusoidal loading scheme of 10 Hz, while the samples are loaded in 20lbf increments from 20-140 lbf with an initial load of 10 lbf. These tests are carried out for two separate cases, the first for the thermoelastic constant calibration is carried out in a simple case with the weld seam of the bearing cage at a 9pm position, outside the region of maximum stress, the second is a more detailed test with the weld seam located inside the field of view at the 6pm position.
The preprocessing method utilizes software correction for uniformity in the picture adjusting for emissivity, while the post processing adjusts the thermoelastic constant as well as shifting within the image during captures and spatial averaging to reduce noise. The hardware setup shown has a stress resolution of 25 MPa and is able to resolve stresses under real time loading condition. The resulting stresses can be shown as a 3D stress map across the imaged plane and compared to the simulation data.
0794: Materials science