懸臂樑振動量測與疲勞分析之研究

A Study of Vibration Measuring and Fatigue Analysis for Cantilever Beams

振動大都由於機器內部不平衡受力經結構傳送產生，振動會造成結構疲勞破壞，為分析振動對結構之影響，本研究建立懸臂樑頻率反應函數，結合振動量測與有限元素分析法，分析懸臂樑振動負載，估算疲勞壽命。首先，設計製作一量測用之旋臂樑，利用LabView 撰寫振動量測系統，量測旋臂樑上風扇之振動，依據量測之振動時域、頻域圖，建立風扇振動特徵頻譜，比較驗證結構共振頻率。利用風扇不平衡轉動產生之振動，模擬懸臂樑振動負載，建立結構頻率響應函數，找出加速度和負荷關係，估算風扇在不平衡轉動下之質量偏心矩，提供風扇品質檢測基礎。進一步，用ANSYS 分析懸臂樑應力、模態，找出結構自然頻率，找出旋臂樑在不同振動負荷下之應力振福，結合疲勞壽命與累積損傷估算模式，估算旋臂樑在振動負載下之疲勞壽命，建立振動疲勞壽命估算法。

Mechanical vibration will cause fatigue failure, induced mainly by unbalancedrevolution of rotational parts. In order to analyze the effects ofvibration to mechanical structure, this paper combined vibration measuringwith finite element methods (FEM) to evaluate the fatigue life of cantileverbeams. Vibration is created using a cool fan by setting unbalanced revolutions.The measured values of vibration are applied not only in identifyingthe quality of a fan but also in calculating the dynamic loadings generatedby unbalanced revolutions. A cantilever beam was designed to measure the vibration generated by a cool fan. ANSYS software is used to analyze themodals of the structure for finding out the natural frequencies of structure.The measured system was designed by LabView software for acquiringvibration signals including time and frequency domains. The frequencyresponse function (FRF) of the cantilever beam was derived to formulatethe relationship between the vibration accelerations against the dynamicloadings. The stress amplitudes are evaluated by ANSYS analysis accordingto the dynamic loadings obtained by the FRF. The studied results show thatthe vibration loadings induced by the fan are too small, so that the cantileverbeam would not fail. However, the proposed methods of fatigue life evaluationof vibration may be useful in vibration-based predictive maintenance.