Determination of Full Set Elastic Constants for Composite Materials on Basis of Frequency Response Analysis, FEA, and GA

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The number of engineering problems includes the identification of anisotropic composite elastic constants determination. We developed an experimentally - analytical technique for identification of all elastic constants of orthotropic materials. The offered technique is substantially based on measurement of eigenfrequencies and semi quantitative analysis of natural vibration modes, instead of wave propagation speed and fields of vibrational displacement used by other acoustic methods. The developed method of the elastic composite and piezoelectric materials properties identification is implemented in linked MATLAB – Comsol Multiphysics combining the finite element analysis (FEA) of oscillations dynamics and minimization of some functional, which type is determined by particularity of a solved problem. These techniques complement the early designed by authors’ FEM-based methods for orthotropic composite static tests. The offered dynamic tests include an evaluation of specimen’s frequency response, determination of natural frequencies and vibration modes of specimens both in natural experiments and numerical finite element simulations. The identification process consists of several stages. In series of static tests are determined all allowable modules. Further a complete matrix of elastic constant is constructed, but some modules specified by approximated values (in particular, interlaminar shear modules). A series of dynamic tests executed in which the periodical excitation of samples and the frequency response is recorded by means of piezoelectric actuators and sensors. Then on basis of early defined (in static tests and with use of mix rule) modules of composite and experimentally founded eigenfrequencies by means of FEM the vibration natural modes are identified. By combination of FEM, genetic algorithm (GA) and Levenberg-Marquardt minimization method the specification of composite mechanical properties is evaluated. Application of developed technique to orthotropic composite used in aviation structures (polymeric composite spar of the helicopter main rotor blade) is explicitly illustrated. The obtained results have shown a good efficiency of proposed identification methods. We demonstrate that proposed approach provides best reliability and shows small dependence on metering equipment precision.