PSI - Issue 42

Iulian-Ionut AILINEI et al. / Procedia Structural Integrity 42 (2022) 1422–1427 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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An electrodynamic shaker, RMS 45 kN, generated the forced harmonic motion to excite the test specimens. Piezo-electric accelerometers were used to measure the acceleration response during the vibration test. A broadband sine sweep vibration profile was used, ranging from 10[Hz] to 1000[Hz], with a constant acceleration of 1G, having a linear sweep rate of 1Hz/s over the entire spectrum. A close control loop is defined between the shaker, controller and control accelerometer. Complete vibration test setup can be seen in this Fig. 2.b, where (1) represents the fixture that clamps the specimen under test (2). The design is controlled by the drive acceleration sensor (3), and sensor (4) measures the acceleration response of the test sample. One run for each test specimen was performed, and the main results were plotted. The Q-factor of resonance is defined as the ratio of the resonance's centre frequency and the resonance's half-power bandwidth, Ailinei (2022). The Q-factor shows how sharp or steep a resonance is. The Q factor was calculated with equation 1. Damping is an energy dissipation mechanism that causes vibration to diminish over time and eventually stop, Silas (1968). The vibrational energy is converted into sound or heat. The amount of damping depends on the material, the velocity of motion, and the vibration frequency. Structural damping ξ was calculated using equation 2 takes, considering the connection between damping and Q-factor. = −3 ℎ ( ) = 0 [ ] 2 [ ] − 1 [ ] (1) = 2 1 (2) 3. Numerical analysis The numerical analysis was performed using the commercial program Ansys. Steel properties were used for the numerical model. Fix support was introduced in the part and acceleration of 9.806 m/s 2 for all specimens, Fig. 3.a. The sample was meshed with hexahedral elements, summing 11324 elements, Fig. 3.b.

Fig. 3. a) Boundary Condition, and b) Mesh Model.

Damping is the energy dissipation mechanism (conversion to heat, sound or both) that causes the vibration motions to decay over time and eventually stop. In Numerical models, it can be defined by viscous damping (forces proportional to the fundamental frequency of the structure) and material damping (forces balanced to strains) or a combination of both. In this, Rayleigh damping was employed, which inputs the mass (α) and stiffness (β) matrix multipliers within the damping matrix [C], equation 3. [ ] = [ ] + [ ] (3) By extracting the damping ratio ξ and natural frequency ω from the physical test, equation 4 allows computing the (α) and (β) values. = 2 + 2 (4)