Abstract
Particle simulations are able to model behavior of granular materials, but are very slow when largescale phenomena and industrial applications of granular materials are considered. Even with the most advanced computational techniques, it is not possible to simulate realistic numbers of particles in large systems with complex geometries. Thus, continuum models are more desirable, where macroscopic field variables can be obtained from a micromacro averaging procedure. However, aspects of microscopic scale are neglected in classical continuum theories (restructuring, geometric non linearity due to discreteness, explicit control over particle properties).
The focus of this work is the investigation of elastic and dissipative behavior of isotropic, dense assemblies. In particular, the attention is devoted on the effect of microscopic parameters (e.g. stiffness, friction, cohesion) on the macroscopic response (e.g. elastic moduli, attenuation). The research methodology combines experiments, numerical simulations, theory.
One goal is to extract the macroscopic material properties from the microscopic interactions among the individual constituent particles; for simple enough systems this can often be done using techniques from mechanics and statistical physics. While these simplified models can not capture all aspects of technically relevant realistic grains the fundamental physical phase transitions can be studied with these model systems.
Complex mixtures with more than one particle species can exhibit enhanced mechanical properties, better than each of the ingredients. The interplay of soft with stiff particles is one reason for this, but requires a more accurate formation of the interaction of deformable spheres. A new multicontact approach is pro posed which shows a better agreement between experiments and simulations in comparison to the conventional pair interactions.
The study of wave propagation in granular materials allows inferring many fundamental properties of particulate systems such as effective elastic and dissipative mechanisms as well as their dispersive interplay. Measurements of both phase velocities and attenuation provide complementary information about intrinsic material properties. Softstiff mixtures, with the same particle size, tested in the geomechanical laboratory, using a triaxial cell equipped with wave transducers, display a discontinuous dependence of wave speed with composition.
The diffusive characteristic of energy propagation (scattering) and its frequency dependence (attenuation) are past into a reduced order model, a master equation devised and utilized for analytically predicting the transfer of energy across a few different wavenumber ranges, in a onedimensional chain.
The focus of this work is the investigation of elastic and dissipative behavior of isotropic, dense assemblies. In particular, the attention is devoted on the effect of microscopic parameters (e.g. stiffness, friction, cohesion) on the macroscopic response (e.g. elastic moduli, attenuation). The research methodology combines experiments, numerical simulations, theory.
One goal is to extract the macroscopic material properties from the microscopic interactions among the individual constituent particles; for simple enough systems this can often be done using techniques from mechanics and statistical physics. While these simplified models can not capture all aspects of technically relevant realistic grains the fundamental physical phase transitions can be studied with these model systems.
Complex mixtures with more than one particle species can exhibit enhanced mechanical properties, better than each of the ingredients. The interplay of soft with stiff particles is one reason for this, but requires a more accurate formation of the interaction of deformable spheres. A new multicontact approach is pro posed which shows a better agreement between experiments and simulations in comparison to the conventional pair interactions.
The study of wave propagation in granular materials allows inferring many fundamental properties of particulate systems such as effective elastic and dissipative mechanisms as well as their dispersive interplay. Measurements of both phase velocities and attenuation provide complementary information about intrinsic material properties. Softstiff mixtures, with the same particle size, tested in the geomechanical laboratory, using a triaxial cell equipped with wave transducers, display a discontinuous dependence of wave speed with composition.
The diffusive characteristic of energy propagation (scattering) and its frequency dependence (attenuation) are past into a reduced order model, a master equation devised and utilized for analytically predicting the transfer of energy across a few different wavenumber ranges, in a onedimensional chain.
Original language  English 

Qualification  Doctor of Philosophy 
Awarding Institution 

Supervisors/Advisors 

Award date  26 Sep 2019 
Place of Publication  Enschede 
Publisher  
Print ISBNs  9789036548601 
DOIs  
Publication status  Published  24 Sep 2019 
Keywords
 Granular Materials
 Wave propagation
 Elasticity
 Granular Mixture
 Discrete element modeling
 Particle simulation
 Continuum Modeling