0 0.00005 0.0001 0.00015 0.0002 0.00025 0.0003 0.00035 300 320 340 360 380 400 Fr equency [Hz] LDV no masses Ar mnomass LDV 1 mass Arm1mass LDV 2 mass Ar m2mass LDV mass 3 Ar mmass 3 LDV mass 4 Ar mmass 4 Figure 7a Tuning of the rig using, armature and specimen response 0 0.00001 0.00002 0.00003 0.00004 0.00005 0.00006 0.00007 300 320 340 360 380 400 Frequency [Hz] Amplitude [m] LDV no masses LDV 1 mass LDV 2 mass LDV mass 3 LDV mass 4 Figure 7b Tuning of the rig using, specimen response 5 Performance of the tuned test rig The previous section presented two methods for tuning the designed test rig so that it could be capable of amplifying the response of the tested structure. This section will present an additional experiment to assess if the test rig is capable of performing efficiently the excitation when the level of the output force is increased. In fact, it was suspected that the test rig would present an impedance mismatch to the shaker. A sine-step around the resonance of mode 5 was performed for 7 levels of gain generated by an electronic output card, the gain of the amplifier was kept constant during all the experiments. Figure 8a presents the acceleration measured at the armature for the highest level of force at the resonance of mode5 while Figure 8b shows the logarithm of the frequency spectrum of the response. Before commenting these plots, it is important to say that the shaker used 509
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