Auswahl der wissenschaftlichen Literatur zum Thema „Electrodynamic test bench“

High-cycle fatigue behaviour of structures can be obtained through vibratory tests using frequency response functions or transmissibilities. To this end, this study deals with the qualification of the vibratory fatigue bench developed at the Laboratory of Mechanic of Normandy. This bench uses an electrodynamic shaker which can reach excitation frequencies that are higher than conventional fatigue machines. To carry out relevant tests, the capacities of the test bench must be well known. Correlations between excitation and response were investigated to determine the allowable setpoints to maintain linearity between the input and output signals to validate our system. The difficulties related to the experiments were presented and discussed.

When fatigue tests are carried out using a shaker, dynamic phenomena often appear and lead to a non-linear behaviour in the experiment. In this paper, the dynamic response of the specimen is studied in order to evaluate the impact on the results. The experiment consists in a notched beam fixed on the armature of an electro-dynamic shaker. The transfer function between the center of the armature and the tip of the beam is obtained with a swept sine near the first resonance frequency of the specimen. The drive is a constant acceleration amplitude. An evolution in the transfer function of the beam is observed when the drive is modified: the resonance frequency decreases and the damping increases. This non-linearity is investigated by studying the movement of the shaker, the fixture and the beam. The results show that the beam close to its resonance disrupt the imposed movement. An experimental setup correcting those defects is proposed.

The magnetic levitation technology is principally categorized as electromagnetic suspension and electrodynamic suspension, both now practically implemented in maglev trains in China, Korea, Japan and other countries. The magnetic field to levitate a vehicle can be provided by either normal conducting electromagnets, or superconducting magnets, or high-coercivity permanent magnets. With the technology advancing in superconductors and magnetic materials, hybrid configurations that employ different types of magnets become promising for commercial application. Magnets synergy results in better performance and lower energy consumption as justified by virtual prototyping and measurements on sub-scale models. Stable levitation of a loaded platform has been demonstrated on a test bench. A series of parametric simulations (performed with the use of software developed in RF) and magnetic measurements enabled validation of computational and physical models of all magnets and adjustment of numerical procedures for scaling parameters with respect to the practical load capacity and other operational characteristics. The established approach will be used for full-scale modelling of realistic maglev vehicles, particularly, a 50-ton flat freight car.

This master's thesis deals with data processing for an electrodynamic test bench. The thesis presents a theoretical overview of signal distribution, determination of fatigue damage from random vibrations and a description of test benches. The next part deals with setting up the test time reduction in GlyphWorks software. The aim of this thesis is to process and create a procedure for an accelerated fatigue test from data measured during an operational test on a polygon. The data are then verified on an electrodynamic test rig using a Skoda Auto dynamic test room. The final part of the thesis contains data evaluation and a guide explaining how to easily create a test in the relevant software.

Dans le but de fournir des données expérimentales pour alimenter les modèles numériques développés au Laboratoire de Mécanique de Normandie, nous avons mis en place un banc d'essais uniaxiaux en fatigue vibratoire permettant de tester des structures à grand nombre de cycles. Après la rédaction d’un cahier des charges pour définir les caractéristiques d’excitations et de mesures, une étude de qualification de ce moyen d’essais est présentée afin d’obtenir les plages de performance basée sur l’hypothèse de linéarité du système. Ensuite, pour vérifier la faisabilité en fatigue, nous avons réalisé une étude visant à établir une courbe de caractérisation d’un acier bas carbone. Néanmoins, ce banc d’essais ne permet pas de distinguer les phases d’initiation de fissure, de propagation et de rupture. Nous avons donc proposé quelques pistes pour évaluer le nombre de cycles à fissuration : la première est basée sur la variation de pente de l’amplitude de déformation mesurée à partir de jauges de déformation et la seconde utilise le décalage de la fréquence de résonance. Nous avons ainsi proposé un modèle simple de dommage non linéaire basé sur la variation de la fréquence de résonance qui permet également d'évaluer les nombres de cycles à la rupture des spécimens. La durée de vie en fatigue expérimentale obtenue par ce modèle est confrontée avec celle en fatigue obtenue par un modèle de dommage issu de la littérature
The aim of Laboratory of Mechanics of Normandy is to provide experimental data to enhance the numerical models developed for structural design. Therefore, we have set up a vibration-based uniaxial bending bench for testing structures under a high cycle fatigue. After setting up specifications to specify the characteristics of the excitations and measurements, a qualification investigation of this test bench is presented in order to obtain the performance ranges based on the assumption of the system linearity. Then, to verify the feasibility in fatigue, we conducted a study to establish a characterization curve of a low carbon steel. Nevertheless, this test bench does not distinguish the phases of initiation, propagation and fracture of the crack. We have therefore proposed some ways to assess the cycle number of crack initiation: the first one is based on the slope variation of the strain amplitude measured from strain gauges and the second one uses the resonant frequency drop. We have thus proposed a simple model of nonlinear damage based on the variation of the resonant frequency which also makes it possible to evaluate the cycle number at fracture of the specimens. The experimental fatigue life obtained by this model is compared with the fatigue life obtained by a damage model provided by the literature

One of the most important parameters evaluated by racing and trekking cyclists is vibrational comfort: as generally accepted, it is closely correlated to the response of bicycle components in combination with the cyclist’s characteristics. Vibration transmissibility of wheels and saddles was recently studied during lab tests using a wooden dummy bottom resting on the saddle or in road tests on an instrumented racing bicycle at different speeds on different surfaces. The use of shakers is also well established in the evaluation of cyclist’s posture effects on the overall bicycle behaviour. In fact, in previous works, either a servohydraulic actuator was applied to the seatpost of a bicycle frame hinged at the front wheel axle with a cycling tester, or two electrodynamic shakers were applied under the wheels of a fully equipped bicycle, with a cyclist sitting statically on the saddle. In the present study, the combination of a servohydraulic actuator and a roller type bench allowed to overcome the limitations of the former experiences. Random vibrations were input to the bicycle-cyclist complex by means of rollers supporting the rear wheel while cyclists were cycling unrestrained on the rollers. The test bench setup and tuning approach are presented for comparison with results available from previous bench and road tests.

In the present works, we examine experimentally and theoretically the dynamic behavior of linear oscillator strongly coupled to a nonlinear energy sink under external periodic forcing. The nonlinear oscillator has a nonlinear restoring force realized geometrically with two linear springs that extend axially and are free to rotate. Hence, the force-displacement relationship is cubic. The linear oscillator is directly excited via an electrodynamic shaker. Experiments realized on the test bench consist of measuring the displacement of the oscillators while increasing and decreasing frequencies around the fundamental resonance of the linear oscillator. Many nonlinear dynamical phenomena are observed on the experimental setup such as jumps, bifurcation, and quasiperiodic regimes. The retained nonlinear model is a two degree of freedom system. The behavior of the system is then explained analytically and numerically. The complexification averaging technique is used to derive a set of modulation equation governing the evolution of the complex amplitude at the frequency of excitation, and a stability analysis is performed.