340 Ö. Mencek and M. Aykan Fig. 32.1 Representative configuration of test setup for gyroscope A finite element method. The structure is an isolation layer within a gyroscope where the quantitative material properties of the isolation layer are to be identified. The aim is to be able to use the obtained material model in case of different gyroscope geometries. 32.2 Methodology In this study two different gyroscopes, hereafter called gyroscopes A and B, are used with the same isolation panel. The isolation layer is a rubberlike material with unknown mechanical behavior. It is sandwiched between two plates of aluminum as shown in Fig. 32.1. In order to identify the material properties of the isolation layer, a finite element model (FEM) of the gyroscope A with the isolation panel is established and modal analysis is done on this environment. Meanwhile, modal tests are performed on the gyroscope, and then the results obtained from FEM are compared to that of modal tests. Material properties of the isolation layer are set through optimization, such that the natural frequencies from the FEM match the test results. The material is taken as an orthotropic one and is modeled accordingly. Then the same isolation panel is attached to the second gyroscope (gyroscope B). Similarly, modal tests are performed and a FEM is established. Determined material properties from gyroscope A are used in the FEM of gyroscope B. Results from modal tests and finite element modal analysis are compared to observe the validity of the material model. 32.3 Gyroscope A 32.3.1 Preliminary Modal Tests This gyroscope, with its isolation sandwich layer attached, is fixed to a test foundation through bolts as shown in Fig. 32.1 and the accelerometers are located as in Fig. 32.2. Modal tests are performed with a roving hammer and fixed accelerometers. Hammer is applied on various directions (x, y and z) at each accelerometer location. Natural frequencies and mode shapes obtained through the analysis of these tests are presented in Fig. 32.3. The rectangular area formed by the lines represents the upper face of the gyroscope, where colors blue and yellow stand for the undeformed and deformed shapes, respectively. The corners of the rectangle, marked with point numbers, represent the accelerometer locations with numbers being the same as the test setup shown in Fig. 32.2.
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