polished metal plates on both sides and, then, clamped the assembly in the holding block. This approach was chosen so as to minimise power loss because of the friction in the clamped areas specifically at high level of vibrations. The mode chosen for the HCF study was mode-5 at 339.15Hz. Hence, Table 2 reports the parameters used for designing the rod. Figure 1 Simplified model of test rig for HCF testing Mode-1 Mode-2 Mode-3 Mode-4 Mode-5 Mode-6 Mode-7 Frequency [Hz] 83.29 217.03 339.15 249.05 634.16 712.68 945.4 Loss factor [%] 0.7 0.5 0.4 0.4 0.4 0.4 0.5 Table 1 Modal properties of test structure Armature mass Young’s modulus Holding block mass Sample modal mass Sample resonance frequency 11.25kg 210E9 86kg 0.2kg 339.15Hz Table 2 Values used for running the parametric model Figure 2 presents the driving rod designed for tuning the rig at the frequency of interest. The rod was manufactured to have a right hand thread at the holding block and a left hand one at the shaker armature so to tighten them together by rotating the rod. The holding block was supported on a three rollers to allow free movements along the direction of the push rod and this set up was decided to minimize possible buckling of the rod, already calculated during the design process. It is important to avoid buckling during the HCF test because of unwanted vibrations occurring on the sample. Figure 3 shows the assembled test rig. Figure 2 Dimensions of the designed push rod 40mm 10mm 560mm 10mm 1” 1” R5mm 40mm 14mm MTS MHB MSA KRod KTS KSA CTS CRod CSA (a) Test Structure (b) Shaker Armature 506
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