On the determination of mechanical properties of composite laminates using genetic algorithms
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n the determination of mechanical properties of composite laminates using genetic algorithms C. MALETTA and L. PAGNOTTA* Department of Mechanical Engineering, University of Calabria, Ponte P. Bucci Cubo 45C, 87030 Arcavacata di Rende (CS), Italy *Author for correspondence (E-mail: [email protected]) Received 6 May 2003; accepted in revised form 10 June 2004 Abstract. This paper describes a method which combines finite element analysis and genetic algorithms (GAs) for identifying the elastic constants of composite laminates by using vibration test data. A procedure updates the elastic constants in a numerical model so that the output from the numerical code fits the results from vibration testing. In this approach, the elastic constants can be readily identified in a single test without damaging the structure. The GA, developed on a personal computer using the language MATLAB, applies the general-purpose numerical code MSCNASTRAN to carry out the modal analysis. Key words: composite materials, elastic constants, genetic algorithm, vibration tests
1. Introduction The use of composite materials in mechanical, aerospace, automotive, ship building, and other branches of engineering, is constantly increasing (Gibson, 1994). Because of reductions in manufacturing costs and improvements in product quality, the demand for these materials is expected to rise considerably in the near future. Knowledge of the elastic properties of composite materials is essential for design and application and the measurement of these properties during manufacturing offers the potential for improvements in quality control. Traditional test procedures based on static loading of test specimens tend to be slow and expensive. At least three separate static tests are required to measure the four elastic constants describing the linear-elastic stress–strain relationship of thin uni-directional laminates (Carlsson and Byron Pipes, 1997). Moreover for properties such as shear modulus, these tests often yield poor results. As an alternative to tensile testing, mixed numerical experimental techniques are increasingly being used. One approach to a rapid and inexpensive characterization of the elastic properties of anisotropic composite materials involves modal vibration testing. When a plate is forced to vibrate, its dynamic response is a function of the plate geometry, the plate boundary conditions, the density and the elastic properties of the material. Usually, the response of a numerical model of the plate is correlated with experimental observations of the structural behaviour of the real structure. Unknown material parameters in the numerical model are updated until the computed structural behaviour matches the experimental observations as closely as possible. The values of the parameters used in the numerical model in the last computation are the results of the identification procedure and yield the elastic properties of the plate. In principle, the approach makes it possible to identify all the elastic properties simultaneously from a single experimen
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