Flexural-Torsional Buckling of Cantilever Strip Beam-Columns with Linearly Varying Depth

In this paper, one investigates the elastic flexural-torsional buckling of linearly tapered cantilever strip beam-columns acted by axial and transversal point loads applied at the tip. For prismatic and wedge-shaped members, the governing differential equation is integrated in closed form by means of confluent hypergeometric functions. For general tapered members (0<(hmax?hmin)/hmax<1), the solution to the boundary value problem is obtained in the form of a Frobenius’ series, which is shown to converge in the interior of the domain and at the boundary if and only if 0<(hmax?hmin)/hmax<1/2. Therefore, for 1/2?(hmax?hmin)/hmax<1 the Frobenius’ series solution cannot be used to establish the characteristic equation for the cantilever beam-columns; the problem is then solved numerically by means of a collocation procedure. Some of the analytical solutions (buckling loads) were compared with the results of shell finite-element analyses and an excellent agreement was found in all cases, thus validating the mathematical model and confirming the correctness of the analytical results. The paper closes with a discussion on the convexity of the stability domain (in the load parameter space) and the accuracy of approximations based on Dunkerley-type theorems.     

Synthesis and characterization of hafnium carbide fine powders

Hafnium carbide powder was synthesized by sol–gel polycondensation of hafnium chloride with citric acid. The starting materials were dissolved in water and mixed homogeneously on a hot plate until precursor gel was formed. Pyrolysis of this gel resulted in monoclinic hafnia which after subsequent heat treatment transformed into hafnium carbide. The obtained materials were analyzed by means of X-ray diffraction and scanning electron microscopy. The results showed that the obtained carbide powders were composed of nearly equiaxed particles with narrow size distribution. Characterization by nitrogen adsorption showed that the obtained powders were micro- and mesoporous materials with high specific surface area.     

Advanced Visualization and Accessibility to Heterogeneous Monitoring Data

Structural health monitoring (SHM) is a promising tool for better management of infrastructure. However, failure to manage large amounts of SHM data properly is a big barrier for its widespread application. Data management is especially challenging when heterogeneous data are involved and combined with camera images. Various sensors based on different technologies can measure many parameters such as strain, tilt, weather, etc., whereas live cameras can visualize traffic response. In addition, all the data streams can be registered both statically and dynamically. Data management is even more complex if multiple users access the data and have diverse backgrounds and interests (e.g., the owner/manager of the structure, operator, responsible engineer, and academic). In this article, general principles for SHM data management are researched, established, and proposed by the authors, and an original solution for data management based on these principles is presented. For validation purposes, the proposed principles were implemented in novel data management software and applied to a signature bridge. Feedback from interested groups including the managers, operators, engineers of record, and academics is used for validation. Thus, this article details the researched and proposed accessibility and visualization principles, and conceptual development of novel solution for data management, which combines computer science, internet omnipresence, and structural engineering.     

Inhibition of hydrogen oxidation by HBr and Br2

The high-temperature bromine chemistry was updated and the inhibition mechanisms involving HBr and Br₂ were re-examined. The thermochemistry of the bromine species was obtained using the Active Thermochemical Tables (ATcT) approach, resulting in improved data for, among others, Br, HBr, HOBr and BrO. Ab initio calculations were used to obtain rate coefficients for selected reactions of HBr and HOBr, and the hydrogen/bromine/oxygen reaction mechanism was updated. The resulting model was validated against selected experimental data from the literature and used to analyze the effect of HBr and Br₂ on laminar, premixed hydrogen flames. Our work shows that hydrogen bromide and molecular bromine act differently as inhibitors in flames. For HBr, the reaction HBr + H ? H₂ + Br (R2) is rapidly equilibrated, depleting HBr in favor of atomic Br, which is the major bromine species throughout the reaction zone. The chain-breaking steps are then H + Br + M → HBr + M (R1), Br + HO₂ → HBr + O₂ (R7), and Br + Br + M → Br₂ + M (R8). In Br₂-doped flames, the reaction Br₂ + H ? HBr + Br (R9) is far from equilibration and serves to deplete H in the reaction zone by competing with H + O₂ → O + OH. The inhibition is augmented by recombination of Br (R8). If the inlet Br₂ mole fraction exceeds about 20%, reactions (R8), (R2) are both reversed, now acting to promote chain branching and increase the flame speed. According to the present model, cycles involving HOBr are not important for generation or removal of chain carriers in these flames.     

WDX-PIXE analysis of low energy X-rays using a microbeam

A high-energy resolution PIXE system developed at a heavy ion microbeam line was used to analyze low energy X-rays below 1 keV. The system is equipped with a plane crystal spectrometer with a gas flow position sensitive proportional counter (PSPC), which enables high-energy resolution PIXE analysis using a microbeam. In order to improve the detection efficiency for the low energy X-rays, the X-ray entrance window of the PSPC was replaced with a thin polymer film supported by a metal grid. As the result, the detectable energy range was extended to carbon K X-rays and chemical effect in Fe and Cu L X-rays could be detected. A preliminary result of high-energy resolution PIXE mapping of Cu mesh (#500) showed that it is possible to obtain the Cu L mapping image using a 2 MeV proton microbeam with the size of 20 × 20 μm.     

Distributed measurement and control system based on microcontrollers with automatic program generation

The paper describes an open architecture microcontroller based distributed measurement and control system with automatic generation of application program. Interpretation of functions and generation of program for control of the newly added distributed unit or distributed unit of a new type connected to the system performs automatically, without user assistance. The elements of the system are interconnected by means of a serial common bus according to the reduced OSI protocol. The proposed concept was tested in a system developed by using 8-bit Atmel microcontrollers of 89S and 89C series. Apart from the central unit, intelligent distributed units were developed for the control of a stepper motor, programmable linear movement, control of halogen lamps, acquisition and generation of analogue, digital and timing pulses and a real time clock (RTC).     

Empirical Equation for Limit of Hygroscopicity

ABSTRACT

In this paper we are promoting the properties related to wood anatomy and chemical composition as the factor of influence to limit of hygroscopicity of wood (LH).

The wood samples of the most important domestic Hood species: oak Ouercus robur, beech Fogus sylvatica, fir Abies alba and spruce Picea abies were selected for this investigation.

For determining LH in our investigations we have applied the method of compression strength parallel to grain.

The results of experimental measurements were statistically analyzed and the empirical equation for LH dependance upon the significant (influential) factors: temperature. cellullse content and wood density in oven dry state is defined.     

Designing monotonic low-pass filters—comparison of some methods and criteria

A New Approach Has Been Presented To Find Characteristic Functions Of A Certain Class Of Monotonic Low-Pass Filters Of Non-Maximally Flat Type. The Well-Known Legendre Filters, And The More Recently Introduced Class H Filters, Both Belonging To This Class, Are Derived As Special Cases Of The Application Of Least-Squares Approximation Technique By Optimizing The Asymptotic Loss. It Is Shown That Class H Filters Provide Higher Stopband Attenuation Than The Legendre Filters But Have Less Favourable Passband Magnitude Response. On The Other Hand, If The Minimization Of The Passband Loss Is At A Premium Then The Unconstrained Least-Squares Monotonic Approximants, Referred To As Lsm Filters, Yield The Best Results. Therefore, Among All Filters With Monotonic Magnitude Response, The Legendre Filters Have Neither Optimum Passband, Nor Optimum Stopband Performance, Though They Are Suitable For Some Applications.     

Towards understanding the influence of porosity on mechanical and fracture behaviour of quasi-brittle materials: experiments and modelling

In this work, porosity-property relationships of quasi-brittle materials are explored through a combined experimental and numerical approach. In the experimental part, hemihyrate gypsum plaster powder (\(\hbox {CaSO}_{4}\cdot 1/2\hbox {H}_{2}\hbox {O}\)) and expanded spherical polystyrene beads (1.5–2.0 mm dia.) have been mixed to form a model material with controlled additions of porosity. The expanded polystyrene beads represent pores within the bulk due to their light weight and low strength compared with plaster. Varying the addition of infill allows the production of a material with different percentages of porosity: 0, 10, 20, 30 and 31 vol%. The size and location of these pores have been characterised by 3D X-ray computed tomography. Beams of the size of \(20 \times 20 \times 150\) mm were cast and loaded under four-point bending to obtain the mechanical characteristics of each porosity level. The elastic modulus and flexural strength are found to decrease with increased porosity. Fractography studies have been undertaken to identify the role of the pores on the fracture path. Based on the known porosity, a 3D model of each microstructure has been built and the deformation and fracture was computed using a lattice-based multi-scale finite element model. This model predicted similar trends as the experimental results and was able to quantify the fractured sites. The results from this model material experimental data and the lattice model predictions are discussed with respect to the role of porosity on the deformation and fracture of quasi-brittle materials.