Research on the Detection ofa Crack and Its Location Using ModalAnalysis and Signal Processing

由于转子在运行过程中不可避免地受到周期性载荷，旋转机械因疲劳而崩溃是致命的。为了开发故障诊断系统，许多研究人员对裂纹转子的振动特性进行了研究。现有文献大多是由于裂纹的非线性特性而产生的，如简谐共振、亚谐共振、超谐共振等。然而，由于额定转速并不总是与这些共振速度一致，因此很难从这些共振中确实检测到裂纹。在本研究中，我们研究了使我们能够在与共振速度分离的转速下检测裂纹发生并确定其位置的方法。作为第一步，我们用电磁铁在不同的转速下激励转子，研究了裂纹转子与正常转子的响应幅值和频谱的差异。结果表明：(L)裂纹转子产生的共振是对周期激励的响应。(2)由于裂纹引起的参数激励、裂纹引起的非线性和重力的共存，当转速(a、激励频率q和固有频率p)之间存在某种特定关系时，这些共振就会发生。(3)如果我们注意到这些共振，就有可能检测到裂纹。

Since a periodic load to the rotor is inevitable during operation, rotating machinery is fatal to collapse due to fatigue. Many researchers investigated vibration characteristics of a cracked rotor for developing a diagnosis system. Most of the existing literatures crarifted resoannces, such as, harmonic resonances, subharmonic resonances, and superharmonic resonances, which occur due to the nonlinear characteristics mede by a crack. However, because the rated speed does not always coincedes with these resonance speeds, it is difficult to detect a crack from these resonances certainly.In this study, we studied means which enables us to detect the occurrence of a crack and determine its location during the operation at a rotational speed separated from the resonance speeds. As the first step, we excited the rotor by a electrical magnet at various rotational speed and investigated the difference in the magnitude of the response and the spectra between a cracked rotor and a normal rotor. As a result, the following are clarified : (l) Resonances which areunique in a cracked rotor occur as the response to the periodic excitation. (2) Due to the coexistence of the parametric excitation due to a crack, the'nonlinearity due to a crack, and the gravity, these resoances occur when some specific relation holds among the rotational speed(a, the excitation frequency Q, and the natural frequency p. (3) It is possible to detect a crack if we pay attention to these resonances.