Key Engineering Materials Vol. 627

Abstract: Properties of an interpenetrating metal–ceramic composite with freeze-cast preforms are investigated. For the estimation of elastic properties of the composite numerical homogenization approaches for 2D and 3D finite element models are implemented. The FE models are created based on micro-computed tomography (μCT) images. The results of the numerical 2D and 3D modeling coincide and are in good agreement with available experimental measurements of elastic properties.

Abstract: In November 2013 an experiment was carried out using the testing equipment called stand. During the experiment was loaded steel-fiber reinforced concrete foundation slab model. The stand measures deformation and monitors interaction between stress and deformation. The purpose of this paper is comparison of values measured during the experiment and results of numerical calculations based on FEM. The stress strain analysis of elastic halfspace by means of Gauss numerical integration and Jacobean of transformation is presented here. The objective of this paper is also improving and developing the soil-structure interaction analysis based on the experimental results and FEM.

Abstract: This paper addresses the influence of cold weather on the compressive strength of high performance concrete with silica fume under different curing days. Test variables of this study are weather condition (5°C, -5°C and-15°C) and different curing days (7days and 28 days). In this work, the specimen was designed a water-binder ratio of 0.34. One batches of concrete were prepared for each mixing hour, and the compressive strength of cylindrical concrete specimens was measured after 7 and 28 days. Test results for concrete compressive strength show that the concrete’s best mechanical performance occurred when there was the least difference between ambient temperature and concrete temperature, that is, during the later hours of the day in hot weather conditions.

Abstract: The application of pseudo strain-hardening cement composites (PSH2C) to structural systems depends primarily on the tensile response of the materials, which is a direct function of fiber and matrix characteristics, the fiber content or volume fraction. In general, improved response of material is observed with an increase in the fiber volume fraction, as long as the fiber content does not impede mixing. This paper addresses the direct tensile response of pseudo strain hardening cement composites (PSH2C) reinforced with PET fibers, which belongs to a class of discontinuous short fiber reinforced cement based composites characterized by a strain hardening and multiple cracking responses under direct tensile loading. The variables are different types of fibers (PET, PET+PE, PET+PVA).

Abstract: In this paper a sensitivity formulation using the Boundary Element Method (BEM) is presentedfor analysis of structural reliability problems. The sensitivity formulation is based on implicit differentiation method where the first and second order derivatives of the random variables are obtained directly by differentiation of the discretised boundary integral equation. The structural reliability is assessed using the Monte Carlo Method and FORM with BEM sensitivity parameters. A benchmark example is presented to demonstrate the accuracy and efficiency of the BEM for both Monte Carlo and Sensitivity based FORM approaches.

Abstract: The paper describes results of numerical simulations of experiments on concrete beams loaded in three-point bending. Stochastic lattice-particle model has been applied in which the material was represented by discrete particles of random size and location. Additional spatial variability of material properties was introduced by stationary autocorrelated random field. Three different types of geometrically similar beams were modeled: half-notched, fifth-notched and unnotched, each in four different sizes. The deterministic and stochastic model parameters were identified via automatic procedure based on comparison to a subset of experimental data, so that the adequacy of the model response could be validated by comparison with the remaining experimental data.

Abstract: There are several causes of slip and fall accidents, such as floor and outsole surface characteristics, contaminants, environmental and human factors, and cognition. In relation to controllable causes, floor and outsole surface characteristics have been frequently investigated over the past decades. The characteristics of safety footwear outsoles, such as roughness, hardness, and tread pattern, tend to differ from those of casual shoes on the Korean market. The aim of this study is to investigate the slip resistance of safety footwear on the Korean market and determine the major design factors to improve the slip resistance. All friction tests were performed using the Korean Occupational Safety and Health Agency’s newly developed testing machine. Twenty-eight safety shoes were used in this experiment, and all friction tests were conducted under three different contamination conditions, namely water, detergent, and glycerol. The friction measurement results show that the hardness, material, and patterns of outsoles had a major effect on the slip resistance, but the effects were not statistically significant for some safety footwear. In general, safety footwear that had a number of small extruded blocks shows good slip resistance. Safety footwear patterns that have many small raised blocks on the heel have a higher friction coefficient than the others. A lower outsole hardness also gives a higher coefficient of friction.

Abstract: The formulation developed in this work is based on the coupling of plane elasticity formulation and thin plate formulation for plates (Kirchhoff plates). Both formulations use elastostatic fundamental solutions. Curvature effects are considered as body forces, which generates domain integrals. Domain integrals are transformed into boundary integrals using the radial integration method. Thus, only the boundary is discretized. A radial basis function is used as approximation function in domain integrals. The developed formulation is applied to the dynamic analysis of anisotropic and composite laminate shallow shells under time dependent loads. A computational implementation was performed for the formulation developed and results were compared with results from literature.

Abstract: The paper deals with an estimation of the residual fatigue lifetime of the railway axles. The railway axles can include some cracks either from manufacturing process or from previous loading operation. Because of cyclic loading of the railway axles there is a risk of fatigue failure of the railway axles with unacceptable consequences. Based on this fact, for conservative establishment of the residual fatigue lifetime of the railway axle is necessary to consider an existing crack in the railway axle during design process. The fatigue lifetime estimation of railway axles is very sensitive to used crack propagation rate description (e.g. v-K curve). Typical bending of this curve (knee) can be found in the vicinity of the threshold value in fatigue crack propagation rate dependence (typically v-K curve expressed in log-log coordinates). For accurate estimation of residual fatigue lifetime of the railway axle is necessary to use approximation of v-K curve that takes into account existence of the knee close to the threshold value of the stress intensity factor. The paper shows important differences between different crack propagation rate descriptions on the residual fatigue lifetime estimation of the railway axles. Results obtained can be used for safer design and operation of the railway axles.

Abstract: The generalized model is constructed for jointed rock mass under hydrodynamic pressure. Meanwhile, the influences of crack angle, under hydrodynamic pressure, on the compressive strength is researched. The results show that the flow rate has a significant influence on the compressive strength of jointed rock. When the angle of the crack is 30°, the higher the hydrodynamic pressure is, the larger the decrease of the compressive strength is. While the slopes of the crack are 45° and 60°, the larger the hydrodynamic pressure is, the bigger the increase of the compressive strength is. In the meantime, under the same flow rate, the compressive strength of jointed rock transform regularly with crack angle changed. And the compressive strength of the jointed rock with 45° crack is largest, while the jointed rock with 30° crack is lowest.