Design of Dynamically Loaded Fiber-Reinforced Structures with Account of Their Vibro-Acoustic Behavior

Dynamically loaded structures for high-technology applications generally require high material damping combined with low construction weight and adequate stiffness. Advanced lightweight structures will have to meet not only these dynamic demands but also improved acoustic (low noise) standards. High-performance materials like magnesium, aluminum, or titanium, which are mainly used in today's lightweight applications, reach their limits with respect to these dynamic and especially vibro-acoustic requirements. They offer a high specific stiffness and strength, but a relatively low damping, which leads to intense acoustic radiation. Therefore, composites or compound materials with a dynamically and vibro-acoustically optimized property profile are needed. The structural dynamic and vibro-acoustic behavior of these types of lightweight structures cannot be described by the use of classical models. Here, the advanced methods developed at ILK are considered, which take into account the special mechanical properties of the fiber-matrix compound. Also, sophisticated numerical simulation techniques such as the finite and the boundary element method are successfully applied.     

Frequency response and damping analyses of structures with different damping models

The behavior of structures with different damping models has been investigated using finite element and frequency response analyses. As an example, systems with hysteretic and viscous damping were examined. The damped eigenfrequencies and the corresponding loss factors were computed based on frequency response analysis and then compared to the results obtained from free vibration analysis using the method of complex eigenvalues. Recommendations are given for a more effective employment of frequency response and damping analyses in the structures considered.Institute of Computer Analysis of Structures, Riga Technical University, Kalku, St. 1, Riga, LV-1658 Latvia. Published in Mekhanika Kompozitnykh Materialov, Vol. 33, No. 2, pp. 226–234, March–April, 1997.     

Frequency response analysis of laminated composite beams

Conclusions The modeling of laminated composite beams has been derived systematically from the three-dimensional elasticity relations. The correctness of the solution found by using the present finite element model is verified by comparison with the results obtained by analytical solutions and other results presented in the literature. Numerical results indicate that the present technique can given accurate results for frequency response analysis for laminated composite beams. Loss factors of structures obtained by the method of complex eigenvalues and the direct frequency response method exhibit very good agreement. Optimum design of a laminated composite beam by the finite element method and the method of experiment planning has been successfully presented.Published in Mekhanika Kompozitnykh Materialov, Vol. 30, No. 5, pp. 664–674, September–October, 1994.     

Optimization of sandwich structures with damping properties

Maximum viscoelastic damping characteristics of sandwich structures are designed using finite element and informative planning methods. Two basic design problems were considered: addition of a damping coating to a given homogeneous structure and building a sandwich structure subjected to a given set of constraints. The methods of complex eigenvalues and direct calculation of the frequency characteristics were used. Numerical examples of optimizing sandwich beams are presented for both design problems.Translated from Mekhanika Kompozitnykh Materialov, Vol. 29, No. 5, pp. 653–656, September–October, 1993.