Numerical modeling of fiber pull-out micromechanics in concrete matrix composites

The presented research work compares numerical results of single fiber pull-out of elastic matrix with the experimental data obtained for single steel fiber pulled out of highstrength concrete matrix. The pull-out process was studied by means of accurate 2D elastic and 3D elasto-plastic finite element models taking into account the nonlinearity. Numerical modeling was performed for straight-shaped fiber embedded into the elastic matrix under variable angle with respect to applied pulling force and at variable depth. Friction between fiber and matrix, matrix shrinkage as well as elastic and plastic deformations in the fiber were taken into account. The objective of numerical modeling was to evaluate significance of different phenomena such as friction between steel fiber and concrete matrix, matrix shrinkage and fiber plasticity in a single fiber pull-out process by taking into consideration experimental findings

Simulation of fatigue crack opening in alloy D16T under constant amplitude loading using finite element method

Створено модель плоского зразка з центральною тріщиною в пружно-пластичній постановці за допомогою методу скінченних елементів. Обґрунтовано вибір розмірів скінченних елементів в околі вістря тріщини. Змодельовано закриття втомної тріщини за регулярного циклічного навантаження з урахуванням залишкових деформацій та напружень в її околі. Отримано задовільне узгодження результатів моделювання та експериментальних даних.The aim of this study was to simulate fatigue crack opening using FE software complex ANSYS and compare it with experimental data. Using the FE simulation software the model of central cracked flat specimen was created. Only half of the specimen with enabled conditions of symmetry was modeled. The true strain diagram of D16T alloy at 20 °C was used for the simulations in order to reproduce the conditions of the experiment. FEM calculations were performed for the plane stress condition. For creation of the accurate computational model the size of finite element mesh in the crack tip was adapted using software experiment. The finite element mesh size for the finite element analysis of the stress strain state of the flat specimen with a central crack under uniaxial tension was found. Fatigue crack closure effect was modeled under constant amplitude cyclic loading considering residual strain and stresses in the crack tip. For software determination of the crack opening a macro that allows to calculate displacement of nodes of the model for a given load step was developed. The node, in which at this moment the crack tip was located, was determined with the help of software and two nodes on both sides of the crack plane at a distance r from its tip and the base b were selected. To maintain constant b and r during each crack growth the points of measurement were upgraded using software. Previous experiments proved that in order to reduce the error of determining opening stress intensity factor the measurement of the crack opening should be performed at the minimum values of b and r. Therefore, according to the experimental data r=0,02 mm and b=0 were used that is, directly on the shore of the crack. The method for determining the moment of crack opening has been chosen. It has been found that the moment of crack opening corresponds to the point of the greatest curvature of diagram efforts – opening of crack tip. For this purpose the derivative approximation by finite differences with a constant increase in stress was used. Results of modeling and experiment were compared

Investigation of Thermodynamic Properties in ZnTe, ZnSe, ZnS Crystals using ab initio Calculations

Using cluster models for cubic sphalerite for stoichiometric ZnX, X = S, Se, Te crystal was spentcalculation of values of thermodynamic parameters under normal conditions, and was defined the analyticalexpressions of temperature dependences of energy ΔE and enthalpy ΔH, Gibbs free energy ΔG, entropy ΔS. Itwas calculated temperature dependences of the Debye temperature ΘD. The correlation beetwenthermodynamic (ΔE, ΔH, ΔG, ΔS), heat (Cv, Cp, ΘD) parameters of ideal crystals ZnTe, ZnSe, ZnS and theirmain fundamental characteristics (band gap Eg, the contribution of ionization δ, electronegativity ΔX, bindingenergy D, comprehensive compression module B) have been find.Keywords: ClusterModels, Thermodynamic Parameters, First Principle Calculations, Debye Temperature

Synthesis and Thermoelectric Properties of PbTe-SnTe Solid Solutions

There are presents X-ray results and measurements of thermoelectric parameters (thermoelectric electromotive force α, specific electrical conductivity σ, and coefficient of thermal conductivity k) for materials on the base of PbTe-SnTe system. The dimensionless thermoelectric figure of merit ZT ≈ 0,3 received for thermoelectric samples p-Pb<sub>0.4</sub>Sn<sub>0.6</sub>Te obtained by cold pressing method in complex with annealing