Abstract
A new testing system for applying coupled/uncoupled bending-torsion loading in vibratory tests by a tri-axis shaker has been recently developed at the Department of Engineering of University of Ferrara. The system is composed of a cylindrical specimen with eccentric tip masses, excited by horizontal and/or vertical base accelerations. A special design of the gripping system for specimen constraint allows torsional and bending deformations to be produced and controlled independently, when vertical and horizontal base accelerations are applied simultaneously by the shaker. The values of accelerations and strains in the tested specimens can be monitored continuously. This paper presents a first set of experimental results under harmonic bending and torsion, and under narrow-band combined random loading. Estimations from two frequency-domain approaches are also discussed.
Highlights
In structural durability of mechanical structures, one of the most challenging goals is durability assessment under random multiaxial loading. Within this complex research field, several numerical and theoretical contributions are present in the literature and, the research group at the University of Ferrara carried out several activities [1,2,3,4,5] in the frequency domain approach to fatigue damage assessment
It is possible to carry out experiments to test the fatigue strength under multiaxial random loading by means of servo-hydraulic machines or shaker tables
Despite the Root Mean Square (RMS) of stress is a useful parameter to compare the frequency content of signals, it has little if no significance in fatigue strength assessment, as – even considering only uniaxial loading – harmonic and narrow-band loadings lead to a different fatigue behaviour even under the same RMS content of stress
Summary
In structural durability of mechanical structures, one of the most challenging goals is durability assessment under random multiaxial loading. Over the last two years, a research activity [11,12] has been pursued with the aim to design an innovative testing system to carry out bending-torsion random loading tests by a tri-axis shaker In this testing device, three independently controlled shakers act on the same table by offering the possibility of controlling the three Cartesian accelerations independently. Three independently controlled shakers act on the same table by offering the possibility of controlling the three Cartesian accelerations independently At this stage of the research, a preliminary testing layout has been developed by considering only two out of three available degrees of freedom, in order to generate independent bending and torsion loading on tested specimens. Random bendingtorsion test results were compared with theoretical estimations by the ‘Projection-byProjection’ fatigue criterion, showing a good agreement
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