Matthias Klaerner

Simulative measures for structure borne sound radiation of composites

Due to the high stiffness-to-weight ratio, composite structures tend to be acoustic sensitive. The sound emission of such radiating components is commonly measured by the sound power requiring the determination of the sound intensity in normal direction and—in numerical simulations—the sound pressure on the radiating surface. Assuming a unit radiation efficiency all-over the surface and neglecting local effects, the equivalent radiated power (ERP) is a common approach for an upper bound of structure borne noise. Therein, the sound power finally results from the squared velocity integrated over the radiating surface and the fluid impedance. As ERP usually requires extra post processing to consider the velocity in normal surface direction, the kinetic energy is essential in common FEA results including all velocity components apart from the normal direction, too. Moreover, ERP necessitates the knowledge of the radiating surfaces increasing the effort especially for complex geometries. Thus, the possibilitie...

Spectral Representation of Uncertainty in Experimental Vibration Modal Data

It is well known that structures exhibit uncertainty due to various sources, such as manufacturing tolerances and variations in physical properties of individual components. Modeling and accurate representation of these uncertainties are desirable in many practical applications. In this paper, spectral-based method is employed to represent uncertainty in the natural frequencies of fiber-reinforced composite plates. For that, experimental modal analysis using noncontact method employing Laser-Vibrometer is conducted on 100 samples of plates having identical nominal topology. The random frequencies then are represented employing generalized Polynomial Chaos (gPC) expansions having unknown deterministic coefficients. This provides us with major advantage to approximate the random experimental data using closed form functions combining deterministic coefficients and random orthogonal basis. Knowing the orthogonal basis, the statistical moments of the data are used to estimate the unknown coefficients.

FEA-Based Design of Experiment for the Damping Determination of Thermoplastic-Rubber Compounds

In terms of recycling, polymer blends with rubber crumb filler material offer a high potential in adjusting both static and dynamic material properties. While the influence on stiffness and strength is considerably treated in literature, there are minor examinations on the damping of such compounds. Combining the properties of thermoplastics and elastomers, these materials tend to show a wide range of nonlinear influences such as frequency, temperature and amplitude dependency. Especially the amplitude dependency is critical due to the transferability of the results between different stress states, loads and part geometries as well as the applicability in FEA simulations. In detail, the average strain energy per volume has been chosen as a physical measure for the amplitude dependency. This study provides extensive results of the influence of recycled rubber crumb filler on the stiffness and damping of Polyamide 6. A FE-based experimental design was developed to assure the comparability of the strain energy related dynamic properties. For the different testing conditions the average strain energy is not directly measurable and thus needs to be determined numerically. Cyclic tension and bending in a dynamic mechanical analyses, free decay of cantilever beams as well as modal analysis of plates have been analysed experimentally and numerically for validation. In addition, the boundary conditions have been varied to generate different stress states in the specimens. The results show perspectives and limits of the transferability of the results.