Modal analysis of automotive lighting parts produced from plastic materials and updating of finite elements model

In this study, 4 different pieces of automotive rear lamp lenses which are made of Polymethly Methacrylate - PMMA and have different geometries have been inspected. Free-free natural frequencies and mode shapes of lenses have been estimated by the help of ANSYS WB® Finite Element Analysis (FEA) software. Meanwhile, by the help of Experimental Modal Analysis (EMA) methods; natural frequencies, damping ratios and mode shapes of the lenses have been determined. Finally, mode shapes calculated by FE and measured by EMA were compared and Modal Assurance Criteria matrix (MAC) was determined. This thesis consists of 3 chapters. In the first chapter; application areas of the modal analysis methods today and examples of the studies done recently have been told. In the second chapter; in general, vibration theory and fundamental terms of modal analysis have been mentioned also, modal analysis methods, formulations, characteristics of Frequency Response Functions (FRF), measurement setups used on EMA methods, methods for extracting modal parameters from FRF's have been explained. In the third chapter, in order to determine the dynamic characteristics of the lenses; EMA's have been performed on these lenses. Two different methods of the "modal hammer test" have been applied on a certain lens, and based on results obtain, the most suitable test method has been chosen. This test method has been applied on remaining 3 lenses and dynamic characteristics of all lenses have been determined. At the natural frequencies of the structures, damping ratios have been calculated by the use of half power bandwidth method. In addition, a new elasticity modulus was calculated and this elasticity modulus is used as inputs for FEA. As a result, Finite Element Model has been updated then theoretical modal analysis has been performed. Finally, FEA and EMA results have been compared and MAC matrix has been found.