Laboratory for Dynamics of Machines and Structures 
Multiaxial Vibration Fatigue - A Theoretical and Experimental Comparison
 M. Mršnik, J. Slavič and M. Boltežar
Mechanical Systems and Signal Processing, Volumes 76–77, August 2016, Pages 409-423

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Abstract
Random vibration excitation is a common cause of failure, especially when the vibration is in the range of natural frequencies, where the stress response is greatly amplified. A vibration-fatigue analysis can be performed for a high-cycle regime consisting of a structural dynamics analysis, a response calculation and a fatigue analysis. The material parameters (S-N curve) are defined for a constant-amplitude, cyclical, uniaxial stress state. However, in real structures the stress state due to the structural dynamics is rarely uniaxial the and direct application of the S-N curve is difficult. The stress tensor is reduced to a more manageable representation using a multiaxial criterion. A multitude of such criteria are available in the literature. In this study, a group of multiaxial criteria are compared theoretically and experimentally, i.e., maximum normal stress, maximum shear stress, maximum normal-and-shear stress, C-S criterion, Projection-by-Projection and the Preumont and Piéfort criterion. A special specimen is used in the experiments that experiences a rich structural response which causes fatigue failure. The experimental comparison of the crack location and the time-to-failure gives comparable results for the tested multiaxial criteria with a reliable time-to-failure estimation. From the research it follows that the crack-location estimation is not accurate enough for either of the compared criteria. The study proves the applicability of the vibration-fatigue analysis procedure (i.e., from excitation, structural dynamics, multiaxial criteria to spectral moment methods) on real vibrating structures with rich structural dynamics.
Authors

Researcher

Matjaž Mršnik, PhD

  Ladisk, Faculty of Mechanical Engineering, University of Ljubljana
  matjaz.mrsnik@ladisk.si
  +386 1 4771 227
matmr    
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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    
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Professor

Miha Boltežar, PhD

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