Laboratory for Dynamics of Machines and Structures 
Uninterrupted and accelerated vibrational fatigue testing with simultaneous monitoring of the natural frequency and damping
 M.Česnik, J. Slavič and M.Boltežar
Journal of Sound and Vibration, Vol. 331, Issue 24, 19 November 2012, Pages 5370–5382

download pdf   link to publisher
Abstract
A mechanical system's modal parameters change when fatigue loading is applied to the system. In order to perform an accelerated vibration-based fatigue test these changes must be taken into account in order to maintain constant-stress loading. This paper presents an improved accelerated fatigue-testing methodology based on the dynamic response of the test specimen to the harmonic excitation in the near-resonant area with simultaneous monitoring of the modal parameters. The measurements of the phase angle and the stress amplitude in the fatigue zone are used for the real-time adjustment of the excitation signal according to the changes in the specimen's modal parameters. The presented methodology ensures a constant load level throughout the fatigue process until the final failure occurs. With the proposed testing methodology it is possible to obtain a S-N point of the Woehler curve relatively quickly and to simultaneously monitor the changes of the specimen's natural frequency and damping loss factor. The presented methodology with real-time control is verified on an aluminium Y-shaped specimen (1.000.000 load cycles are achieved in 21 minutes) and is applicable to a specimen with arbitrary geometry. Besides the faster completion of the fatigue test the methodology can be adopted for the validation of the vibrational fatigue analysis.
See also related paper:
[Frequency-Domain Methods for a Vibration-Fatigue-Life Estimation - Application to Real Data],
Authors

Researcher

Martin Česnik, PhD

  Ladisk, Faculty of Mechanical Engineering, University of Ljubljana
  martin.cesnik@fs.uni-lj.si
  +386 1 4771 227
Scholar Home Xs

Associate Professor

Janko Slavič, PhD

  Ladisk, Faculty of Mechanical Engineering, University of Ljubljana
  janko.slavic@fs.uni-lj.si
  +386 1 4771 226
jankoslavic     jankoslavic    
Scholar Home Xs

Professor

Miha Boltežar, PhD

  Ladisk, Faculty of Mechanical Engineering, University of Ljubljana
  miha.boltezar@fs.uni-lj.si
  +386 1 4771 608
Scholar Home Xs