MS18.1: Wave propagation in Mechanical Systems and Nonlinear Metamaterials

Partial replacement of contact wires using splice fittings (splicer) is a cost-saving and labor-reducing technique desired in high-speed railways. However, concerns have arisen due to accidents, such as contact wire breakages at the splicer position. To address this issue, it is necessary to understand the wave interaction caused by splicer installation on the overhead contact line. While some studies have used simulations to analyze the transient response at these points, there is a lack of qualitative knowledge from experimental and analytical studies. Therefore, this study conducted experiments using actual equipment and developed an analytical model using an infinite string with a one-degree-of-freedom system to represent the splicer. This study aims to provide useful guidelines for partial replacement in high-speed railways.

The authors have previously introduced a novel gradient elasticity model for seismic wave predictions. The said model combines (i) the higher-order gradient terms that capture the influence of small-scale soil heterogeneity and/or microstructure and (ii) the nonlinear softening soil behaviour through the use of the hyperbolic soil model. The current study presents an in-depth analysis of the proposed model. The findings indicate that as nonlinearity increases, the bulk of the wave slows down, and its shape becomes more distorted in comparison to the response of the linear system. Furthermore, the wavenumber spectrum of the nonlinear-elastic response presents peaks at large wavenumbers. However, these are eliminated when a small amount of linear viscous damping is added indicating that they are not physically relevant. One model feature that does not disppear with the presence of damping is the formation of small-amplitude waves travelling in the opposite direction to the main wave. These findings shed light on the characteristics of the proposed nonlinear gradient elasticity model and its applicability for predicting the seismic site response.

The study discusses the phenomenon of wave synchronization in a chain of coupled modified Van der Pol (VDP) oscillators. The basic system that was studied consists of a chain of coupled bistable VDP oscillators. This study tries to understand the behavior of the system under varying parameters - focusing on a regime of wave synchronization of a chain of coupled oscillators, and its behavior when the coupling between the oscillators is modified. In addition, we study the system behavior with different number of particles. A similar modulation regime was obtained numerically a, where the energy is transferred periodically from one oscillator to another – in multiple DOF. In addition, analytical methods were devised to predict the synchronized responses.

Wave dynamics of viscoelastic metamaterials, governed by their architecture, is strongly influenced by viscous losses in the constituent materials. These losses have not been properly quantified yet for additively manufactured metamaterials. This work presents a thorough characterization of the viscoelastic properties of additively manufactured polymers and analyzes the dynamics of metamaterial structures made of them, both numerically and experimentally. In particular, we performed the dynamic mechanical thermal analysis and tensile testing for two polymers commonly used in FDM 3D printing and employed the obtained master curves for the complex elasticity moduli in FEA simulations of a simple viscoelastic metamaterial. The calculation results were validated in transmission measurements using non-contact ultrasonic laser vibrometry. Our findings shed light on the peculiarities of wave control in viscoelastic additively manufactured metamaterials and form a basis for reliable prediction of their dynamic behavior at (ultra)sonic frequencies.