Modeling and Calibration for Crack Detection in Circular Shafts Supported on Bearings Using Lateral and Torsional Vibration Measurements

摘要

In this paper the requisite foundational numerical and experimental investigations that are carried out, to model the “uncrackedudand cracked” shaft and to identify its bending and torsional vibration responses, are reported. The cylindrical shaft used in this experimentaludstudy is continuous over two spans (with a cantilever span carrying a propeller) with ball-bearing supports. Duringudmodal tests the backward end of shaft (away from the propeller end and connecting it to an electric motor, required for onlineudmonitoring) is fixed to one of the test frame supports; later on this backward end will be connected to an electric motor to carry outudonline modal monitoring for crack identification. In the numerical study, beam elements are used for modeling the bending andudtorsional vibrations of the rotating shaft. The paper describes in detail the numerical “linear spring” models developed for representingudthe effects of “ball bearings and the (experimental test) frame supports” on the vibration frequencies. Shaft responseudparameters are obtained using modal analysis software, LMS Test Lab, for bending vibrations monitored using accelerometers, andudthree “sets” of shear strain gages fixed at three different shaft locations measure the torsional vibrations. Effects of different crackuddepths on bending and torsional frequencies and mode shapes are investigated experimentally and numerically, and the results interpretedudto give better comprehension of its vibratory behavior.