Numerical Modeling of Elastic Wave Propagation in Random Particulate Composites

In this paper, ist was demonstrated how numerical modling techniques like EFIT can be used to investigate the elastic wafe propagation in low- and high-packed composite materials systematically. For the first time, the apperarance of particle resonances and the Kramers-Kronig relationships between attenuation and dipersion could have been shown by a numerical simulation. The results for low-packed composites are in a good qualitative agreement with multiple scattering theories. Therefore, in further studies the simulations can be used to prove mulitple scattering models, especially their two-dimensional versions. The simulations in concrete as a very comples and high-packed composite material also showed significant particle resonances confirming experimental results of PS/PR attenuation measurements. The comparison of porous and nonporous concrete models revealed the dominant effect of cement porosity on the applicability of ultrasonic nondestructive testing methods. In the future, th e concrete model must be designed in a more realistic way. Although the most likely mechanism for the attenuation is the scattering of the waveforms at the aggregates and the pores, further research has to take into account the attenuation due to absorption (which was neglected till now) as well as mechnisms concerning the transition zone around the cement-aggregate interface (e.g. nonlinear effects, imperfect adhesion). This will be the subject of further publication