CHARACTERIZATION OF RESIDUAL STRESS RELAXATION PRODUCED BY CONVENTIONAL AND ADVANCED CUTTING METHODS BY X RAY DIFFRACTION RESIDUAL STRESS MEASUREMENT

摘要

Dynamically loaded components such as gears undergo cyclic stresses in their service life and require high magnitude of compressive residual stresses at critical locations to resist fatigue failure. Due to intricate geometry at areas such as gear flank, component needs to be cut to avoid obstructions in X-ray beam path. The cutting method adopted may affect magnitude of residual stresses. This experimental data on the effect of various cutting methods for the component such as gear is important to choose appropriate cutting technique which will minimize stress change on component. In the present study, residual stress measurement is carried out at identical location i.e. gear flank PCD (Pitch Circle Diameter) for multiple gears processed with same shot peening parameters. These gears are then cut by 4-5 different cutting methods. The residual stresses are measured at same location before and after various cutting methods adopted to evaluated stress change/relaxation caused by these cutting methods. The residual stress measurement is carried out by using multi angle sin~2ψ technique by Cr (Chromium) radiation source. The change in diffraction angle caused due to change in inter atomic spacing in crystal structure of material is measured. The parameters of stress measurement such as Psi angle tilt range, Psi angle oscillation, number of exposures, fitting function are kept identical for all measurements to make the results comparable. Standard value of X-ray elastic constant 5.91x 10~(-6) MPa is used for all measurements. Residual stress change/relaxation caused due to various cutting methods ispresented to compare effect of various cutting methods for causing stress change. Comparison of various cutting methods is useful to choose appropriate method which will give minimum stress change/relaxation after cutting and can also be useful to fairly predict possible residual stress change from each cutting method to anticipate actual stress value present on component. The study is limited to the chosen component and results may vary with geometry and processing of other components. This paper provides the experimentally derived unique data for the gear component. The data can also be useful to fairly predict and give insight on actual residual stress present on component before cutting. Expected stress change/relaxation due to various cutting methods is studied and presented to choose appropriate cutting methodology for stress measurement at critical locations.