Modeling of phase interfaces during pre-critical crack growth in concrete

Recent developments in the Rigid-Body-Spring Network (RBSN) modeling of concrete are presented, with candid assessments of research needs for the modeling of pre-critical crack growth under multi-axial stress conditions. Fracture of micro-concrete specimens is investigated through the combined use of such discrete (lattice) models, X-ray tomography, and imaging techniques. The specimens contain small amounts (10–50 wt.% fraction) of spherical glass aggregates. Acid-etching of the glass aggregate surfaces is done to vary the bond properties of the matrix–aggregate interface. Tomographic images of the unloaded specimens provide the initial configurations of the three-dimensional lattice models, which are based on a three-phase representation of the material meso-structure: fine-grained mortar matrix, glass aggregate inclusions, and matrix–aggregate interfaces. The numerical and physical test results agree well with respect to peak loads and the associated crack patterns. Material structure and interface properties affect pre-critical cracking, in accordance with expectations. Dependence of composite strength on aggregate content and arrangement is studied through simulations of large sets of nominally identical models, which differ only in random positioning of the aggregates.     

Automated Modeling of Three-Dimensional Structural Components Using Irregular Lattices

Abstract:   Irregular lattices are used to model three-dimensional (3D) structural components consisting of a bulk material, curvilinear reinforcement, and their interface. Domain discretization is highly automated and involves the semi-random placement of nodal points within the domain, followed by Voronoi tessellation of the nodal point set. A technique is given for the Voronoi partitioning of nonconvex domains. For discretizing nonconvex domains, and for effective gradation of nodal point density, a minimum allowable distance between nodes is maintained and the domain is saturated with nodes. To accelerate this computationally expensive operation, a partitioned domain search is used during the filling process. Reinforcement, and its interface with the bulk material, are discretely modeled and freely positioned in the domain, irrespective of the geometry of the irregular lattice representing the bulk material. This method of discretization facilitates model construction, results interpretation, and possible revisions to the model. While the focus is on automated domain discretization and the modeling of reinforcement, elastic properties of the model are demonstrated through examples involving nodal stress calculations and deflection analyses of prestressed concrete beams.     

Event-based lattice modeling of strain-hardening cementitious composites

Temperature gradient type ESSO test is one of the most popular test methods for evaluating the brittle crack arrest toughness, \(K_{ca}\). However, test conditions which are specimen shape, tab plate shape, applied stress and temperature gradient affect \(K_{ca}\). This document reports effects of specimen geometries that are specimen width, tab plate length, tab plate thickness and tab plate width on \(K_{ca}\) evaluation. In addition, effects of applied stress and temperature gradient have also been investigated. Temperature gradient type ESSO tests are conducted at three different steel mills in Japan. Then, test conditions were varied and test results were compared. In the result, influence range of effect specimen width, tab plate thickness, applied stress and temperature gradient were demonstrated. The applicable range of specimen geometry, applied stress and temperature gradient were clarified and implemented to the brittle crack arrest standard.     

Modeling of fretting wear evolution in rough circular contacts in partial slip

This paper presents a numerical model that maps the evolution of contact pressure and surface profile of Hertzian rough contacting bodies in fretting wear under partial slip conditions. The model was used to determine the sliding distance of the contacting surface asperities for one cycle of tangential load. The contact pressure and sliding distance were used with Archard's wear law to determine local wear at each surface asperity. Subsequently, the contact surface profile was updated due to wear. The approach developed in this study allows for implementation of simulated and/or measured real rough surfaces and study the effects of various statistical surface properties on fretting wear. The results from this investigation indicate that an elastic–perfectly plastic material model is superior to a completely elastic material model. Surface roughness of even small magnitudes is a major factor in wear calculations and cannot be neglected.     

Cellular uptake of gold nanoparticles directly cross-linked with carrier peptides by osteosarcoma cells

Nanoparticles have been extensively used for a variety of biomedical applications and there is a growing need for highly specific and efficient delivery of the nanoparticles into target cells and subcellular location. We attempted to accomplish this goal by modifying gold particles with peptide motif's that are known to deliver a 'cargo' into chosen cellular location specifically, we intended to deliver nanogold particles into cells through chemical cross-linking with different peptides known to carry protein into cells. Our results suggest that specific sequence of such 'carrier peptides' can efficiently deliver gold nanoparticles into cells when chemically cross-linked with the metal particles.     

Thermal instability with radiation by the method of energy

Energy-stability theory is applied to the case of radiation heat transfer in an optically thin, quiescent fluid layer heated from below and bounded by rigid, black, perfectly conducting planes. The radiation term in the energy equation destroys the quadratic character of the energy identity. It is shown, however, that the right-hand side of the energy identity can be bounded by a suitable quadratic term for all physically allowable disturbances. The result is a conditional stability limit dependent upon disturbance amplitude. Results are computed for a variety of cases; these are compared to existing linear and energy stability results.     

Termination for Hybrid Tableaus

This article extends and improves work on tableau-based decisionmethods for hybrid logic by Bolander and Braüner. Theirpaper gives tableau-based decision procedures for basic hybridlogic (with unary modalities) and the basic logic extended withthe global modality. All their proof procedures make use ofloop-checks to ensure termination.  Here we take a closer look at termination for hybrid tableaus.We cover both types of system used in hybrid logic: prefixedtableaus and internalized tableaus. We first treat prefixedtableaus. We prove a termination result for the basic language(with n-ary operators) that does not involve loop-checks. Wethen successively add the global modality and n-ary inversemodalities, show why various different types of loop-check arerequired in these cases, and then re-prove termination. Followingthis we consider internalized tableaus. At first sight, suchsystems seem to be more complex. However, we define a internalizedsystem which terminates without loop-checks. It is simpler thanpreviously known internalized systems (all of which requireloop-checks to terminate) and simpler than our prefix systems(no non-local side conditions on rules are required).