1. All the models used in numerical analysis share a common representation of the viscoelastic layer using solid CHEXA element. The lower layer and constraining layer are both modeled by solid element. First by using modal analysis of individual CLD beam, the frequency of bending modes are obtained and then the harmonic analysis corresponding to frequency of bending modes is performed . Numerical results in terms of the modal strain energy (MSE) are illustrated and the damping effects are emphasized. In the method of MSE, the system loss factor (system damping), ηr is directly proportional to the ratio of the energy dissipated in the viscoelastic elements to the energy stored in the entire system through one cycle of vibration.
2. This ratio is then multiplied by the Loss factor of the viscoelastic material as explained in equation (1) ηr=ηv Uvr UTotr (1) By using above equation(1), the modal loss factor corresponding to mode 3 of three sandwich CLD beams are found and shown in Table 3. 5. Experimental investigation The damping performance of CLD beams is often quantified in terms of system loss factor and it is determined by ASTM beam test method.
3. The symmetrical sandwich beam as shown in Fig. 2 is composed as per ASTM standard E-756(05). It consists of two layers of aluminum and the viscoelastic material in the core composed of a 3M 300 LSE High-Strength Acrylic double-face Adhesive.
4. (a) (b) Fig. 2 Sandwich CLD beams The dynamic responses of the beams were measured by using accelerometer during a free vibration test performed by employing instantaneous hammer impact as excitation. The main features of the used equipment and the data acquisition are: accelerometer model uniaxial type 4515 (B&K) make, Impact Hammer 8206-002 (B&K) make and FFT Analyzer: 4 channel (B&K Photon +All in one). The result of beam FRF response are shown in RT Pro software.
5. The typical experiment setup is shown in Fig. 3 Fig. 3 Experimental test setup Fig. 4 Comparison of frequency response curves By analyzing the resonant peaks for a particular mode, the loss factor, a measure of damping, is obtained from the real part of the response spectrum as shown in Fig. 4. These curves are presented using Matlab software.