Figure 4a Tuning of rig Figure 4b Tuning of rig Figure 4c Rig tuned Figure 5 Tuning weights installed on the shaker armature and the impact position It was found on the tuned test rig that the amplitude of the resonance of the specimen, as shown in Figure 6 was (black curve), 77% higher than the one measured when the rig is not tuned, as shown in Figure 6 (red curve). The excitation was produced using an impact hammer and the shaker armature was not active as the shaker amplifier was turned off during the measurement. Figure 6 Increase of the response level of mode-5 before (red) and after (black) the tuning of the test rig The experiment of tuning the rig was also performed by stepped sine test around the resonance of the rig and adding weights until the frequency match was found. Figure 7a shows the responses measured at the armature and at the sample during the tuning process. Figure 7b shows the response measured at the specimen only. It is interesting to notice that when the shaker is armed the response measured at the armature seems more heavily damped than when the shaker is not armed. This can be explained by the change of the dynamics of the armature because of the electromagnetic field produced. Measuring the responses before and after the tuning the level of amplitude at the sample increased by only 33%. X 508
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