Granular mixtures with tailored damping properties

• Applicant: Professor Dr.-Ing. Holger Steeb
• Subject Area: Mechanics
• Term: from 2019 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 424876160

Background: Noise and vibration/resonance constitute a drawback in many industrial and geo-engineering applications. Acoustic waves produced on roads, railways or by earthquakes propagate through “granular” materials (like soil, concrete or asphalt), with the characteristics of the aggregate affecting the velocity, amplitude-damping and frequencies of the arrival wave. What?/novelty/originality: In this innovative project, as a mind-changer, we propose to turn materials/soil into “granular dampers”. By tuning particle properties and species compositions in (bi- and tri-disperse) stiff-soft material mixtures, we will aim to enhance damping, tailor attenuation and to design band gaps in desired frequency ranges, where the damping can be best exploited. How?/Approach: We will attack the problem from two sides: physical experiments on the damping/elastic material behaviour, at a wide range of stress-levels, will be combined with advanced particle-based numerical simulations to inform a comprehensive reduced order theoretical model for granular mixtures that predicts the influence vibrations, and can be applied to test, improve and optimize novel designs for materials, constructions, or landfill/soils. Preliminary work/experience: In the past years, we have been studying wave propagation and damping in granular mixtures made of soft and stiff particles subjected to various hydrostatic stress conditions. Focus was on the elastic and dissipative properties of aggregates made of monodisperse glass and rubber beads and the interplay between applied stress and rubber content. Interestingly, the experiments showed that by an optimal amount of soft inclusions one can obtain an enriched material, with the same (or even higher) stiffness than the original, yet lighter and with considerably stronger damping.Work-plan: First, we will study the combined influence of size ratio, stiffness ratio and soft content on the damping behaviour of granular mixtures. Using frequency-space analysis, we will unravel the relation between particle and system parameters, energy absorbed/damped frequencies and formulate a reduced order stochastic model (master equation) for the evolution of the energy of waves in space and time. Novelty here is to group frequency bands instead of focusing on the low frequency eigen-values only, since especially the higher frequencies might be more relevant for damping applications.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1897: Calm, Smooth and Smart - Novel Approaches for Influencing Vibrations by Means of Deliberately Introduced Dissipation
• International Connection: Netherlands
• Cooperation Partner: Professor Dr. Stefan Luding