Abstract
This work describes a new testing system for applying a coupled/uncoupled bendingtorsion loading in vibratory tests by a tri-axis shaker. The system is composed of a cylindrical specimen with eccentric tip masses, excited by horizontal and/or vertical base accelerations. The specimen tip is constrained by a lateral thin and flexible plate which impedes any bending when the specimen is excited horizontally, but which permits the specimen torsional rotation. This layout then allows torsional and bending deformations to be produced and controlled independently, when vertical and horizontal base accelerations are applied simultaneously. A finite element model is first used to estimate the system dynamic response and the stresses in the notched specimen section. The model is then validated through experimental tests under harmonic base accelerations. The strains at clamping system are also monitored to indirectly estimate the bending and torsion moment in the specimen. Comparison of numerical and experimental results showed a close correlation and proved that bending-torsion loading are truly uncoupled. Preliminary fatigue tests with harmonic bending loading (vertical base excitation) are finally compared to the constant amplitude S-N curve, showing a quite satisfactory agreement.
Highlights
Mechanical systems and structures are often subjected to vibratory excitations, which generally induce a local multiaxial random stress
Laboratory experiments with multiaxial loading are normally performed in two different ways: by servohydraulic machines that impose a force and/or torque, or by shaker tables that apply a base vibratory excitation
The specimen is fixed to the shaker table and excited by a base acceleration
Summary
Mechanical systems and structures are often subjected to vibratory excitations, which generally induce a local multiaxial random stress. A simple way to obtain a bending-torsion loading by a uniaxial shaker is the use of a cantilever specimen with eccentric mass at the free extremity, as suggested in [10]. The eccentricity of the tip masses induces a torsion loading (combined to bending), even when the specimen is excited by uniaxial vertical acceleration. The nodes lying on the bottom surfaces of the clamped base (base 1 and base 2 in Fig. 1) were fully constrained Both the specimen extremity and the base of the cantilever beam are constrained by a thin plate. A horizontal base excitation could cause only a torsional loading induced by the eccentric tip masses, whereas the horizontal bending is completely impeded by the thin plate. In order to verify this system behaviour, a finite element model was first developed
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