ANALYSIS OF ROLLER-INDUCED RESIDUAL STRESSES IN CIRCULAR DISCS AND THEIR EFFECT ON DISC VIBRATION.

摘要

Rotating circular discs are the basic elements of many different machine types such as steam turbines, computer memories and circular saws. Transverse vibrational instability of such discs can lead to serious operational problems, and so a large disc thickness is often used to ensure adequate disc stiffness and natural frequencies. However, this approach is not always acceptable, and in this study an alternative procedure is described where the stiffness and natural frequencies of a thin circular disc are modified by means of in-plane roller-induced residual stresses.;The deformation of the material in the roller path was measured for a range of rolling conditions. As predicted from an idealized model, the cross-sectional area of the roller path indentation increased with repeated roller traversals over the same path, but was independent of disc thickness.;A three-region mathematical model of the stress distribution in a rolled disc was developed which accurately predicts the sharp radial stress change which occurs across the roller path and the initially-tensile radial stresses in the central disc region. These effects are important in describing the "detensioning" phenomenon which occurs when a disc is rolled close to its periphery. Disc natural frequencies were calculated using the Rayleigh-Ritz method with the disc stress distribution predicted from the three-region mode, and excellent agreement with the measured disc frequencies was obtained.;In an investigation of optimal rolling conditions, it was found that specification of the roller path indentation area is the most important factor, while choice of roller path radius or use of multiple roller paths are less crucial. The required roller path indentation area varies over a wide range for different roller path radii and must be carefully controlled so that the desired disc natural frequency characteristics are achieved. The results from this study show how this deformation can be accurately predicted from theory and realized in practice. An example was given where a 33% reduction in disc thickness was achieved by controlled rolling, when compared with an unstressed disc with the same minimum backward travelling wave frequency.;Disc rolling around a narrow circular path has been used in the wood industry for many years for the "tensioning" of circular saws, but the relationship between the rolling process specifications and the resulting changes in saw operational stability has not been established. This relationship, which encompasses the connections between the process specifications, the roller path deformation, the induced stresses, the changes in disc natural frequencies and the effect on operational stability, is considered in this study.