Abstract:
Machine elements and structures often encounter random or non-periodic cyclic loads over their operational lifetime due to the inherent occurrence of random vibrations, which may lead to premature fatigue failure. Therefore, estimating and anticipating fatigue failure of machine element is crucial. This study aims to analyze and correlate the effect of random vibration on the occurrence of fatigue failure in a rotating beam specimen. A fatigue testing device featuring a rotating beam is designed and constructed, wherein the principal source of vibration is provided by the motor’s rotation. The secondary reason can be ascribed to rotational imbalance, misalignment, and looseness. Fatigue life is analyzed and estimated for three particular cases: static case, single axis vibration consideration and multiple axes vibration consideration. Static case analysis considers no vibration and the latter two cases are termed as dynamic cases considering random vibration along single axis and multiple axes, respectively. The dynamic cases are analyzed with the acquired acceleration data from MEMS-based accelerometers, namely the ADXL345 model, which are placed on bearings. Single axis vibration consideration is already in practice. However, for multiple axes vibration consideration, the cross section of the specimen is divided into a numberof finite elements and bending moment and consequently, bending stress is calculated for each finite element. Finally, fatigue life estimation is accomplished and compared using the rainflow cycle counting algorithm and the Palmgren-Miner rule for the dynamic cases. Notably, the analysis considering multiple axes evaluating cumulative damage on finite elements yields a more precise fatigue life estimation and shows strong correlations when representing the vibratory environment. Therefore, this study concludes that the multiple axes vibration consideration is preferable for estimating fatigue life and correlating random vibration of a rotating beam.
