Elastic properties of isotropic discrete systems with skew contact normals

The macroscopic elastic properties of discrete assemblies are fundamental characteristics of such systems. The contribution uses homogenization procedure based on equivalence of virtual work between the isotropic elastic continuum and the discrete system to develop analytical formulas for estimation of macroscopic elastic modulus and Poisson’s ratio. Such homogenization was recently used to derive formulas for discrete assemblies where (i) there is no vacant space between the discrete units, (ii) the orientation of contacts is uniformly distributed and (iii) the contact normals are parallel to contact vectors (directions connecting centers of discrete units). The third assumption is now removed, three dimensional systems with arbitrary relation between contact vectors and contact normals are studied here. It is shown that the limits of Poisson’s ratio of such system depends on the relation between contact normal and contact vector. The widest limits are however obtained when these two vectors are parallel. This means that arbitrary manipulations with discrete geometry cannot extend Poisson’s ratio of the system outside the known boundaries

Adaptive refinement technique for discrete static models of fracture

The discrete static models are advantageneously used for fracture simulations in heterogeneous materails. These simulations are often extremely computationally demanding. The contribution aims to reduction of computationa cost via adaptivity in construction of the discrete model geometry. The simulation starts with coarse discretiza- tion that provides correct elastic behavior; the discretization is adaptively refined during the simulation in regions that suffer high stresses

DEM simulation of railway ballast using polyhedral elemental shapes

Modelling of railway ballast response using Discrete Element Method with polyhedral shape of grains is presented. The convex polyhedrons are generated pseudorandomly via Voronoi tessellation. Inter-particle contact is based on calculation of intersecting (polyhedral) volume. Large oedometric test is simulated using this model and results are compared to an experimental data from literature

Mechanical behavior of boundary layer in discrete models based on Voronoi tessellation

The contribution introduces 2D and 3D discrete static model of concrete based on Voronoi tessellation. Attention is focused on the boundary region where, due to presence of boundaries, the orientation of contacts exhibits strong bias. The bias has consequences in mechanical behavior of the boundary region in both elastic and inelastic regimes. The boundary layer is typically weaker and more brittle compared to the interior and also stiffer or more compliant depending on macroscopic Poisson’s ratio and straining directio

Representation of bulk and surface crushing phenomenon in DEM model of railway ballast

To simulate ballast behaviour in railway track using Discrete Element Models (DEM), it is reasonable to take into account the crushing and the abrasion of grains. Nowadays, two approaches have been used in discrete modelling. The first approach represents each grain as an assembly of smaller particles with cohesive contacts between them. The crushing is represented by rupturing of contacts between particles. Such approach is universal, but demands very high computational resources. Therefore, the second approach is utilized here. At the beginning every ballast grain is modelled as one rigid body and may be replaced by several smaller particles later. Both crushing and abrasion is considered. Crushing is studied on model of oedometric test of railway ballast

Fracturing in concrete via lattice-particle model

Numerical simulation is used to explore the behavior of concrete beams of different sizes and different notch lengths, loaded in three-point bending. The entire range of notch depth is studied. One limit case is type 1 fracture, which occurs when the notch depth is zero and the crack initiates from a smooth surface (this is the case of the modulus of rupture test). Another limit is type 2 fracture, which occurs for deep enough notches. Both cases exhibit very different size effects. The fracture is simulated numerically with a robust mesolevel lattice-particle model. The results shed light on the transitional behavior in which the notch depth is non-zero but not deep enough for developing the the type 2 size effect dominated by energy release from the structure. In agreement with experimental observations and theoretical predictions, the numerical results show evidence of a decreasing macroscopic fracture energy as the ligament gets very short

Magyar Siketnéma Oktatás 17 (1915) 06-10

A Siketnéma-Intézeti Tanárok Országos Egyesületének hivatalos lapja 17. évfolyam, 6-10. szám Budapest, 1915. június-október hó. Előzménye a "Szemle a siketnémák, vakok, hülyék, gyengeelméjűek, dadogók és hebegők oktatásával foglalkozók szakközlönye". A lap a 26. évfolyam 7. számától (1924) "Siketnémák és vakok oktatásügye a Siketnémák és Vakok Tanárai Országos Egyesületének hivatalos lapja" cím alatt jelent meg

An Interdisciplinary Approach to Optimize the Care of Transitioning Adolescents and Young Adults with CKD

Adolescents and young adults (AYAs) with CKD or end-stage kidney disease (ESKD) have unique medical, dental, psychosocial, neurocognitive, and academic needs and require close interdisciplinary collaboration to optimize their care. The etiology of CKD in AYAs is diverse compared to older adults. With their continuously improved survival, AYAs must start preparation for health-care transition (HCT) from pediatric- to adult-focused health care in the pediatric setting and it must continue at the adult-focused setting, given that their brain maturation and self-management skill acquisition occur until their mid-20s. While the growth and physical maturation of most visible body parts occur before 18 years of age, the prefrontal cortex of the brain, where reasoning, impulse control, and other higher executive functions reside, matures around 25 years of age. The HCT process must be monitored using patient- and caregiver-measuring tools to guide interventions. The HCT process becomes more complex when patients and/or caregivers have a language barrier, different cultural beliefs, or lower literacy levels. In this article, we discuss the unique comorbidities of pediatric-onset CKD/ESKD, provide information for a planned HCT preparation, and suggest interdisciplinary coordination as well as cultural and literacy-appropriate activities to achieve optimal patient outcomes

DEM simulation of railway ballast using polyhedral elemental shapes

Modelling of railway ballast response using Discrete Element Method with polyhedral shape of grains is presented. The convex polyhedrons are generated pseudorandomly via Voronoi tessellation. Inter-particle contact is based on calculation of intersecting (polyhedral) volume. Large oedometric test is simulated using this model and results are compared to an experimental data from literature

Mechanical behavior of boundary layer in discrete models based on Voronoi tessellation

The contribution introduces 2D and 3D discrete static model of concrete based on Voronoi tessellation. Attention is focused on the boundary region where, due to presence of boundaries, the orientation of contacts exhibits strong bias. The bias has consequences in mechanical behavior of the boundary region in both elastic and inelastic regimes. The boundary layer is typically weaker and more brittle compared to the interior and also stiffer or more compliant depending on macroscopic Poisson’s ratio and straining directio