VOL. 7, NO. 6, JUNE 2012 ISSN 1819-6608 ARPN Journal of Engineering and Applied Sciences © 2006-2012 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com 696 EVALUATION OF DYNAMIC PARAMETERS OF ADHESIVELY BONDED STEEL AND ALUMINUM PLATES Sourabha S. Havaldar 1 , Ramesh S. Sharma 1 , V. P. Raghupathy 2 and Moortheesha Adiga 2 1 Department of Mechanical Engineering, RV College of Engineering, Bangalore, India 2 Department of Mechanical Engineering, PES Institute of Technology, Bangalore, India E-Mail: shsourabha@rediffmail.com ABSTRACT Weight reduction remains one of the key factors for various industries. Inevitably this will result in multi-material designs where the most appropriate material is selected for each part. A key enabler for such a multimaterial design is joining two materials with optimized weight which is balanced with the need to keep manufacturing costs down. Further, it is well known that these parts are subjected to dynamic load while in service conditions, and in order to evaluate dynamic parameters for design purpose an adhesively bonded dissimilar joint between Aluminium and Mild steel plates has been investigated experimentally through traditional “strike method” of modal testing. FE simulation is also carried out and are compared with experimental results and found to be in good agreement. Keywords: weight reduction, material joining, steel, aluminium plates, natural frequencies, mode shapes, cantilever, dynamic testing. 1. INTRODUCTION In the last decade, there is a growing interest in dissimilar material combinations as an integrated unit so as to achieve the best combinations of properties. In all the industrial sectors, the main goal of these developments is weight reduction and increased functional performance, even corrosion resistance of combined material is also appreciably high. However, flexible structures usually have low flexible rigidity and low material damping ratio. A little excitation may lead to destructive large amplitude vibration and long settling time. These can result in fatigue, instability and poor operation of the structures. Vibration control of flexible structures is an important issue in many engineering applications, especially for the precise operation performances in aerospace systems, satellites, flexible manipulators, etc. Experimental modal analysis is the process of determining the modal parameters (Natural Frequencies, damping factors, modal vectors, and modal scaling) of a linear, time-invariant system. The modal parameters are often determined by analytical means, such as finite element analysis. One common reason for experimental modal analysis is the verification/correction of the results of the analytical approach. Often, an analytical model does not exist and the modal parameters determined experimentally serve as the model for future evaluations such as structural modifications. Predominately, experimental modal analysis is used to explain a dynamics problem (vibration or acoustic) whose solution is not obvious from intuition, analytical models, or previous experience. After this many numerical methods are often adopted to predict the behavior of the dissimilar systems under dynamic loading conditions, both for scientific and practical applications. The driving force for joining aluminum and steel arises from the need for weight savings, thus essentially, from a need for energy-efficiency in automobile industry [1] and [2], and the requirement for chemical plants and cryogenic and also they have many applications in engineering fields, however, dynamic characteristics is of major concern and it is difficult to predict the dynamic response for dissimilar material combination using well established empirical relationships for normal isotropic simple structures like plates, beams etc. as provided by D Blevins [3]. 2. PROPERTIES OF MATERIALS The properties of aluminum and mild steel are listed in Table-1. Table-1. Mechanical properties of aluminum and mild steel. Properties Aluminium Mild steel Elastic modulus E(GPa) 65 200 Shear modulus G (GPa) 26 77 Density ρ (Kg/M 3 ) 2700 7900 Poisson’s ratio υ 0.28 0.3 3. EXPERIMENTATION An 8 channel FFT analyzer has been used for Modal Testing. Experiment is conducted with a roving hammer test where the accelerometer is fixed at a location (Figure-1) where there is maximum displacement and the structure is impacted at as many DOFs as desired to define the mode shapes of the structure. Post-processing is done to obtain the required FRFs. By these FRFs natural frequencies, mode shapes and damping ratio were obtained. Experimental and FEA values were then compared. This software is a complete, integrated solution for tested-based engineering, combining high speed multiple-channel data acquisition with a suite of integrated testing, analysis and report-generation tools. LMS Test is designed to make testing more efficient and more convenient for each and every user. In this work, LMS Test Lab Impact Testing software has been used with FFT