Figure 3 Test rig with the sample mounted in the holding block 4 Tuning of test rig The method for tuning the rig, introduced earlier, is to design a push rod of correct dimensions which connects the shaker armature and the holding block. The armature of the shaker combined with the push rod should resonate at the same frequency as the target mode of the tested structure. Although the simplified parametric model helped to calculate the correct dimensions, the test rig required an additional fine-tuning to match the rig and specimen resonances precisely. A technique for tuning the rig can be to increase the mass of the shaker armature. This fine tuning can also be done by fine adjustement of the rod dimensions but this approach can be very time-consuming because of repeated dismantling of rig. Resonances were measured using impact testing, as shown in Figure 4a and 4b. The frequency distance between the specimen and the rig were measured at every modification applied. The tuning technique considered for this work consisted in adding small weights on the armature and measuring the resonant frequencies until the correct weight was found as shown by plots depicted in Figure 4c. Figure 5 shows the shaker armature with the additional tuning weights and the position of the impact, indicated by a black mark. 507
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