Rotordynamic Crack Diagnosis: Distinguishing Crack Depth and Location

Abstract

The goal of this work is to establish simple condition monitoring principles for diagnosing the depth and location of transverse fatigue cracks in a rotordynamic system. The success of an on-line crack diagnosis regimen hinges on the accuracy of the crack model, which should account for the crack's depth and location. Two gaping crack models are presented; the first emulates a finite-width notch typically manufactured for experimental purposes, while the second models a gaping fatigue crack. The rotordynamic model used herein is based upon an available overhung rotordynamic test rig that was originally constructed to monitor the dynamics of a mechanical face seal. Eour degree-of-freedom, linear equations of motion for both crack models are presented and discussed. Eree and forced response analyses are presented, emphasizing results applicable to condition monitoring and, particularly, to diagnosing the crack parameters. The results demonstrate that two identifiers are required to diagnose the crack parameters: the 2X resonance shaft speed and the magnitude of the angular 2X subharmonic resonance. Eirst, a contour plot of the 2X resonance shaft speed versus crack depth and location is generated. The magnitude of the 2X resonance along the desired 2X frequency contour is then obtained, narrowing the possible pairs of crack location and depth to either one or two possibilities. Practical aspects of the suggested diagnostic procedure are discussed, as well as qualitative observations concerning crack detection.

On the mechanics of beams and shafts with cracks: A standard and generic approach

“…Crack detection in rotating shafts by vibration measurements remains a challenging problem for engineers and scientists ((El Arem, 2019b), (Spagnol et al, 2018), (Dotti et al, 2016), (Liu and Wang, 2016), (Varney and Green, 2013)). The analysis of the vibrational behavior of a rotating shaft aims at providing parameters that could help in early crack detection.…”

Crack localization in stepped rotors based on Bayesian fusion of multiscale superharmonic characteristic deflection shapes

“…Among these investigations, vibration‐based methods are widely investigated and recognized as useful tools. PHM for cracked rotors can be categorized into four levels 3 as crack detection, 4–10 crack localization, 11–13 crack identification 14–17 and remaining useful life prediction 18,19 . These four stages can provide information required when making a reasonable maintenance strategy, which is of great significance to guarantee the safe operation and reduce maintenance cost of key rotating machines.…”

A Practical Method to Detect a Transverse Cracked Rotor Using Transient Response

“…Therefore, various kinds of diagnosis system have been developed to detect a crack in the rotating machinery. Verney and Green presented an on-line crack diagnosis regimen hinging on the accuracy of the crack model which should account for the crack's depth and location [1]. Silani et al introduced a new finite element (FE) approach to detect small cracks and calculated the flexibility matrix of crack elements with modified integration limits [2].…”