International Journal of Students’ Research In Technology & Management Vol 4 (1) Jan-Feb 2016, pg 08-11 eISSN 2321-2543, doi: 10.18510/ijsrtm.2016.413 http://ijsrtm.in 8 Design and Development of Vibration Testing Fixtures Anjali Reddy 1 , Hamsini K 2 Industrial Production 3 rd year, CBIT, Hyderabad, India 1 reddyanjali20@gmail.com 2 kosarajuhoney@gmail.com Harsh. S. Petunias Asst. Professor, Mechanical Engineering Department, CBIT, Hyderabad, India harsh.pothanis@gmail.com Abstract— this paper deals with the Design of Vibration Testing Fixtures for Random Vibration loads as specified by the MIL 810 military standards. Following selection of the right material and configuration of the fixtures, CAD models are generated and numerically checked for natural frequencies and mode shapes using Finite Element Analysis. Based on these results, the response of the fixtures to the MIL 810 standard Random Vibration profile input is measured using Finite Element Analysis and the transmissibility is calculated. Finally, the fixture is tested experimentally for to the MIL 810 standard Random Vibration profile input and based on these values; transmissibility of the fixture is computed. The experimental result is compared to the Finite Element results and thus, found that the fixture can be used for testing missile packages at the Defense Research and Development Laboratory (DRDL), Hyderabad. I. INTRODUCTION Testing of a component for any kind of vibrations involves mounting it on a shaker with the help of an intermediate element called a Fixture. A vibration testing fixture interfaces the package to be tested with the source of vibration. A good fixture must have its natural frequencies lying beyond the operational range of the test frequencies and must possess a transmissibility of 1. Figure 1 shows the schematic representation of the process of vibration testing. It was required to design fixtures for a random vibration load of 0.01 g2/Hz over a frequency range of 50-200 Hz as per the MIL 810 standard for testing against transportation loads. Figure 1 The dimensions of the fixture are usually chosen based on the component to be tested and the size of the shaker (source of vibration). In this particular case dimensions were arbitrarily chosen based on the shaker table diameter of 400 mm. Although many configurations of fixture can be used, the L and T configurations were selected as they offer high stiffness, strength to weight ratio and ease of fabrication. The material for the fixtures was chosen as Aluminum alloy LM 25 as it is a known fact that aluminum and magnesium offer better strength, stiffness, vibration damping properties compared to steel compared to steel fixtures of same geometry and weight. However, fabrication of magnesium fixtures is not feasible from the consideration of casting and welding Hence Easily available aluminum alloy LM 25 is chosen. II. DESIGN PROCEDURE The CAD models of the fixtures were generated using Solid works. The dimensions of the fixtures are shown in Fig: Subsequently modal analysis was performed on the fixtures using a Finite Element Analysis package called FeMAP (developed by Siemens with an integrated Nastran solver). The 10 noded tetrahedral element was used to mesh the geometry. The first five natural frequencies of the L and T fixtures were identified and corresponding mode shapes were determined. They are shown in the table below. TABLE 1: FIRST FIVE NATURAL FREQUENCIES OF L AND T FIXTURES OBTAINED FROM FEA S.No. Natural frequencies of L fixture (Hz) Natural frequencies of T fixture (Hz) 1 900.93 1369.77 2 1043.40 1372.36 3 2038.92 1765.90 4 2061.20 2386.65 5 3102.82 2580.00 It was observed that the natural frequencies of the fixtures were well beyond the test frequency range of 20-500 Hz. Using the mode shapes, the points with maximum amplitude of vibration were determined. Consequently, the random response of the fixtures in X, Y and Z directions to an input of 0.01 g 2/ Hz in X, Y and Z directions (individually) was computed using FeMAP. The gRMS values of the response PSD was compared to the input PSD was measured and plotted as graphs with using MATLAB, with Frequency (20-2000 Hz) on the X axis and the response PSD (in g2 / Hz) on the Y axis. Transmissibility is computed as