This work deals with numerical investigations on nonlinear wave propagation in order to detect micro-damage in composite material. For this purpose two models are under consideration. First, a wave guide with linear-elastic material behavior with and without a crack is analyzed. The nonlinearity of this model is due to the strain tensor as well as the contact of the crack surfaces. Secondly, a hyper-elastic waveguide with a nonlinear constitutive description is considered. It is shown, that the nonlinearity gives rise to second harmonic wave modes which which may be considered as an indicator of micro-damage and material deterioration.
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A single sleeper, two adjacent sleepers and a track segment are investigated experimentally in order to get a basic knowledge of the dynamic response of a vertically loaded railway track up to 800 Hz. Since voids are often observed between sleepers and the underlying ballast, special emphasis is laid on investigations of partially unsupported sleepers. Detailed information on the dynamic displacement field is obtained by the holographic interferometry which is used beside conventional accelerometers to record the oscillations. The results show that deviations from optimal coupling to the ground result in significant changes of the dynamic behavior.
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