Multiaxial and Uniaxial Fatigue Failure Evaluation Using Modal Velocities
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RESEARCH PAPER
Multiaxial and Uniaxial Fatigue Failure Evaluation Using Modal Velocities K. Kersch1
· E. Woschke2
Received: 22 April 2020 / Accepted: 10 September 2020 © The Society for Experimental Mechanics, Inc 2020
Abstract The presented work aims at evaluating the results of uniaxial and multiaxial fatigue failure tests using velocity and acceleration measurements. A specimen containing damaging modes at different eigenfrequencies is introduced. The tests are conducted on an electrodynamic 3D-shaker system using a random vibration environment. Different fatigue times are observed between uniaxial and multiaxial excitation. Based on the velocity and acceleration measurements, fatigue damage values are calculated for each test. While the fatigue damage values of velocities are similar between uniaxial and multiaxial tests, large deviations can be detected when using accelerations as base for the calculation. Thus, experimental verification for recently proposed multiaxial fatigue damage calculations based on different vibrational quantities is made possible. Keywords Multiaxial fatigue · Multi-axis testing · Electrodynamic shaker · Stress-velocity relationship
Introduction Vibration testing is of crucial importance for the approval of newly developed machines and structures. Measured field data is considered as a base for meaningful load collectives that have to be extrapolated to the expected total service time. Vibration tests are mainly conducted on uniaxial shakers where loads are applied to each axis sequentially. This way of testing is not able to reproduce a real vibrational environment with all multiaxial characteristics that may be measured in the field. While multiaxial shakers can be used to overcome this issue, due to their high complexity, they are not widely available standard equipment. The difference in fatigue damage caused by a sequence of uniaxial tests, and (the same) uniaxial tests introduced simultaneously, has been extensively discussed in literature. Early investigations concluded that the difference in overall fatigue damage for aerospace structures in the former case is twice than it is in the latter [1]. Nonlinear effects K. Kersch
[email protected] 1
Robert Bosch GmbH, Powertrain Solutions, Center of Competence for Vibration, 71701 Schwieberdingen, Germany
2
IFME Institute of Mechanics, Otto von Guericke University Magdeburg, 39106 Magdeburg, Germany
have been investigated on simple plate structures, resulting in either higher or lower response energy depending on the excitation levels [2]. Similar nonlinearities were investigated in real electronic components [3]. Furthermore, differences in maximum stresses and their respective locations were examined for a simple specimen, showing the inherent theoretical difference between uniaxial and multiaxial excitation [4]. The difference in fatigue failure was proven experimentally in [5], performing end of life tests with a statistically sufficient number of test specimens in the form of quadratic rods with rectangular
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