Abstract
Crack fault diagnostics plays a critical role for rotating machinery in the traditional and Industry 4.0 factory. In this paper, an experiment is set up to study the dynamic response of a rotor with a breathing crack as it passes through its 1/2, 1/3, 1/4 and 1/5 subcritical speeds. A cracked shaft is made by applying fatigue loads through a three-point bending apparatus and then placed in a rotor testbed. The vibration signals of the testbed during the coasting-up process are collected. Whirl orbit evolution at these subcritical speed zones is analyzed. The Fourier spectra obtained by FFT are used to investigate the internal frequencies corresponding to the typical orbit characteristics. The results show that the appearance of the inner loops and orientation change of whirl orbits in the experiment are agreed well with the theoretical results obtained previously. The presence of higher frequencies 2X, 3X, 4X and 5X in Fourier spectra reveals the causes of subharmonic resonances at these subcritical speed zones. The experimental investigation is more systematic and thorough than previously reported in the literature. The unique dynamic behavior of the orbits and frequency spectra are feasible features for practical crack diagnosis. This paper provides a critical technology support for the self-aware health management of rotating machinery in the Industry 4.0 factory.
Highlights
The recently emerged conception ‘‘Industry 4.0’’ is one of the most popular manufacturing topics among the industry and academia in the world which was first announced at the 2013 Hannover Fair [1]
An experiment is set up to study the dynamic response of a rotor with a breathing crack as it passes through its 1/2, 1/3, 1/4 and 1/5 subcritical speeds
Focusing on cyber-physical systems (CPS), Industry 4.0 is regarded as the next-generation production framework for the fourth industrial revolution [3] and promises to create the smart factory [4]
Summary
The recently emerged conception ‘‘Industry 4.0’’ is one of the most popular manufacturing topics among the industry and academia in the world which was first announced at the 2013 Hannover Fair [1]. The CPS provides great opportunity to perform online crack detection based on the broad implement of sensors, data acquisition systems, computer networks and cloud computing systems together with the rotor dynamic theory so that the sudden breakdown of production lines due to the cracked shafts can be avoided. It has been shown in the literature that the presence of a crack introduces additional flexibility to the shaft, which reduces its overall stiffness and generates complex orbits and super-harmonic frequency components [15, 16]. This work presents an effective crack detection method based on the dynamic response for the online diagnosis of rotor systems in the future smart factory
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