Types Of Imperfections Research Articles

Localization and coalescence of imperfect planar FCC truss lattice metamaterials under multiaxial loadings

This study investigates the effect of stress triaxiality on the failure mechanisms of an-isotropic perfect and imperfect planar FCC (Face Centred Cubic) truss lattice metamaterials. Three types of imperfection have been considered in the numerical modelling, namely, distorted struts, missing struts, and strut diameter variation. In order to maintain constant stress triaxiality during the simulations, a novel numerical framework was developed to overcome computational difficulties within the existing numerical approaches beyond elastic region. Three modes of microscopic localization were observed in perfect and imperfect lattices before failure: crushing band, shear band and void coalescence. A clear separation exists between the three modes of localization depending upon the type and level of defects, as well as the stress triaxiality. Under compressive loading, all lattices fail owing to crushing band; the distorted lattices are prone to shear band localization with increase in distortion, whereas missing lattices majorly fail due to void coalescence at high missing struts defect. Strut diameter variation, within the range of the strut diameters selected, shows no significant influence on the macroscopic mechanical response and strain localization. This work may open the door for predicting failure mechanisms of imperfect lattices under variety of loading conditions.

Buckling of composite cylindrical shells with ovality and thickness variation subjected to hydrostatic pressure

The initial geometric imperfection is one of the primary factors affecting the buckling behaviors of composite cylindrical shells under hydrostatic pressure. In this study, ovality and thickness variations as two representative types of the geometric imperfections are considered. After measuring the geometric imperfections, a typical carbon fiber reinforced polymers (CFRP) cylindrical shell is tested to obtain the buckling pressure. The buckling behaviors of the shell sample are analyzed in combination with the strain responses. By using the nonlinear numerical analysis, the buckling shapes of the CFRP cylinder shells with different combinations of ovality and thickness variation are firstly discussed. The rules of influence of such imperfections on the buckling pressure are then obtained by nonlinear regression method. Finally, an empirical formula is proposed to predict the buckling pressure of the composite cylinder shells, and the calculated results from the formula are in good agreement with the numerical results.

Linear multi-photon storage based on dark modes with frequency tuning

We propose a quantum memory applicable to the optical regime based on a linear system. The system is in a symmetrical star configuration: one central mode is both connected to the input–output channel and uniformly coupled to a number of modes with tunable frequencies. We show that, as long as the number of these tunable modes is double an odd number, such a configuration is just flexible enough to perform the storage and on-demand recall of a number of individual photons. Tuning of the mode frequencies is feasible experimentally by means of adiabatic frequency tuning, and we show the system is scalable and robust against various type of imperfections. Moreover, the linearity of the system is compatible with the use of single-mode continuous-variable error correction code. Our results therefore provide a promising approach to the storage of many photons carrying protected quantum information.

Accelerated curing of glued-in rods: Influence of manufacturing defects

Adhesive bonding is considered a special process, for which very high quality standards exist with regard to manufacturing. These include, amongst other, controlled environmental conditions and avoidance of any contamination of adherend’s surfaces, for which reasons it is performed in dedicated shops by staff specially trained for these tasks. Additionally, because bonding is performed in dedicated environments, a large palette of techniques to accelerate curing can effectively be applied. Totally different is the situation in the construction and building industry, where—excluding prefabrication—significant work has to be performed on site, with all imaginable environmental and contaminational issues critical for adhesive bonding. This paper indicates, for glued-in rods (GiR), a typical joint type of wide use in timber engineering, that it is in principle possible to perform structurally loaded bonded connections on-site, considering all aforedescribed adverse issues. For that, 192 GiR, resulting of the combination of four adhesives, two accelerated curing techniques, and four imperfection types considered relevant, were considered, and their effect on joint capacity evaluated. The results showed that, depending upon the adhesive, a relatively high level of robustness with regard to the adverse conditions prevailing on construction and building sites can be achieved.

Revealing atomic-scale vacancy-solute interaction in nickel

It is widely accepted that the different types of crystalline imperfections, such as vacancies or dislocations, greatly influence a material's physical and mechanical properties. However, imaging individual vacancies in solids and revealing their atomic neighborhood remains one of the frontiers of microscopy and microanalysis. Here, we study a creep-deformed binary Ni-2 at.% Ta alloy. Atom probe tomography reveals a random distribution of Ta. Field ion microscopy, with contrast interpretation supported by density-functional theory and time-of-flight mass spectrometry, evidences a positive correlation of Ta with vacancies, supporting positive solute-vacancy interactions previously predicted by atomistic simulations.

Waves Propagation at an Interface of Two Liquid Saturated Porous Solid Half Spaces

This manuscript is concerned with reflected and refracted elastic waves when transverse waves are incident at the interface between two fluid-saturated porous solid half-spaces. Perfect and imperfect both types of contact of the interfaces are discussed. It has observed that for a specific model the behaviour of different reflected, refracted waves and the ratio of their amplitudes depend on the physical properties of the medium, angle of emergence, the porosity of the fluid, the porosity of fluid drenched incompressible porous medium and stiffness of imperfect boundary. The computer numerically results for this model have been presented graphically by taking a particular case of empty porous solid.

Influence of Imperfections on Behaviour of Thin-walled Steel-concrete Composite Columns

This paper presents experimental and numerical analysis of the composite steel-concrete columns. Three columns are tested experimentally. Overall forty-eight FE models are created. Sixteen different models for every experimental column are analysed to evaluate the influence of the different types of imperfections. It was found that the imperfections reduced the resistance of the composite columns by up to 10 %. Limiting the geometrical imperfection amplitudes to B/200, the steel profile effective cross-sectional area reduction by up to 23 % was observed, while the critical buckling stress was reduced by up to 74 %. Expressions for the calculation of the effective cross-sectional area ratio and critical buckling stress are proposed.

Analysis of SH wave in hollow piezo-composite cylinder with coupled imperfect interface condition

Present study primarily focuses on interpreting the propagation pattern of Shear horizontal (SH) wave in a piezo-composite layered cylinder. The structure consists of three concentric cylinders composed of hollow fiber-reinforced (FR) cylinder enclosed within piezomagnetic (PM) cylinder along the curved surface area which is similarly superimposed by a piezoelectric (PE) cylinder. The overall system is believed to be pre-stressed in a circumferential direction. The common boundary between each of the cylinder is demonstrated as imperfectly bonded. At the interface of PM and PE media, mechanical, electrical, magnetic and inter-coupled types of imperfections are assumed. Dispersion relations have been obtained for both the electrically open magnetically short (EOMS) and electrically short magnetically open (ESMO) circuit condition. Dispersion curves have been plotted to unravel the peculiarities of parameters like the radius of the hollow cylinder, thickness of FR and PM cylinder, thickness ratio of PM and PE cylinder, initial stress parameters, helical angle of the reinforcement. The influence of different interface parameters on the phase velocity of the wave has been studied and marked distinctly. For a detailed study, two successive modes have been plotted. Present study may help in improving the performance of piezo-composite cylindrical surface acoustic wave (SAW) sensors.

Robustness of mode-locking in harmonic cavity nanolasers subjected to potential distortions.

We theoretically analyze the robustness to potential distortion of mode-locking in a harmonic cavity nanolaser sustaining oscillation of Hermite-Gaussian modes. Different types of imperfections of the harmonic potential that create the Hermite-Gaussian modes are considered: the non-parabolicity of the potential and the possible random errors in the shape of the potential. The influence of the different laser parameters, including the Henry factors of the gain medium and the saturable absorber, on the robustness of the mode-locked regime is discussed in detail.

Developing the Conceptual Model of Imperfect Competition Impact on Labour Reproduction and the System of Measures Aimed at its State Regulation

Social and labour relations on today’s home labour market are accompanied by adverse social and economic phenomena, such as poverty of working population, inequality in profit distribution, discrimination in remuneration, shadow forms of employment and pay, illegal and interregional migration, labour exploitation, staff deficit and excess, which results in imperfect nature of competition on home labour market. These adverse phenomena are caused, on the one hand, by imperfect indications of competitive behavior of labour market entities, which shows the imperfect type of social and labour relations where parties’ interests are deprived of mutually beneficial basis of their satisfaction and, on the other hand, by imperfect competitive conditions of labour market entities’ functioning, which is manifested in requirements to labour quality. The article studies the key aspects of imperfect competition on home labour market and shows dynamics of its principles statistics. By analyzing and summarizing the dynamics of competitive situations investigated in the regional aspect the authors gained a conceptual model of imperfect competition taking into account its behavioral and institutional aspects. The key social and economic aspects of imperfect competition impact on labour reproduction were researched. On the basis of the provided conclusions the authors put forward certain measures of state regulation of imperfect competition, which could increase workers’ competitiveness and therefore improve the quality of labour reproduction.

Transition between half-metal and ferromagnetic semiconductor induced by silicon vacancy in bulk non-metallic substrate supported silicene

It should be possible to generate silicene on bulk non-metallic substrates for most applications in electronic components. However, the introduction of different types of imperfections, which significantly change the properties of materials, is inevitable in experimental synthesis. The literature on the defective silicene generated on bulk non-metallic substrates is very limited, perhaps due to the lack of experimental fabrication. Thus, by using first-principles calculations, we systematically study the effect of silicon vacancies on the properties of silicene generated on a N-terminated cubic boron nitride (111) surface. The result shows that the silicon vacancies trigger a transition between the half-metal and the ferromagnetic semiconductor. With small vacancy ratios of 1:36 and 1:24, the ground-state models behave as ferromagnetic semiconductors and the band gaps are about 1.25 and 0.95 eV, respectively. When the vacancy ratio increases up to 1:6, the model turns into a ferromagnetic half-metal with a half-metallic gap of around 0.15 eV. The change of electronic structure is driven by the different electron transfers between the silicon layer and the substrate, i.e. different amounts of electrons are transferred from the silicon layer to the substrate when the vacancy ratio is altered. Our work could extend the applications of silicene in the nanoelectronic field.

Experimental stand for internal pressure testing of pipes

The experimental programs carried out on the stands for the research of mechanical stress behaviour typically target the following objectives: to determine the behaviour of the pipes at internal pressure and / or other mechanical stresses (which may secondary occur as accidental loads during exploitation), to establish the processes and factors of in-service degradation and to determine the load carrying capacity of pipes and other components of pipelines systems with defects of different types and configurations. For this paper an experimental stand was designed and developed for the purpose of determining the behaviour of the pipes with different types of imperfections / defects. The experimental results were verified and validated using the finite element method.

ICA based estimation and compensation of carrier frequency offset for MBOFDM based UWB systems

A carrier frequency offset (CFO) is addressed as a main type of wireless communication system imperfections in this paper. Carrier frequency offset (CFO) severely deteriorates the performance of OFDM receiver. Here an effective time domain CFO estimation and compensation method using symmetric subcarrier allocation (SCA) for multiband orthogonal frequency division multiplexing (MBOFDM) based ultra-wideband system is proposed. A data supported CFO estimation technique, which is robust to a larger offset, is presented as a novel method in compensation of CFO. An effective separation matrix scheme of OFDM signal with CFO is obtained. Subsequently, independent component analysis (ICA) based CFO estimation is stated. On fully exploiting the ECMA-368 preamble symbols, the proposed technique is capable for carrier frequency offset of 100 ppm, and the result is confirmed through simulations.

ЕФЕКТИВНІСТЬ РЕГУЛЮВАННЯ ДЕРЖАВОЮ РИНКУ ОСВІТНІХ ПОСЛУГ У СУЧАСНИХ УМОВАХ

The effectiveness of state regulation of the market of educational services in Ukraine involves several stages. Each of them regulates a certain component of the effectiveness of state regulation. By government regulation we mean an alternative mechanism that compensates for market inefficiency. The basis for government intervention are market gaps, errors. The market and the state are not without flaws: the choice between the market and the state is only a choice between different degrees and types of imperfection. However, in a real mixed economy, state regulation is a typical phenomenon, so there are grounds for its analysis and evaluation. There are the following types of efficiency of state regulation: economic, social, adaptive. Economic efficiency presupposes the conformity of the obtained result to the set socio-economic goal and the methods by which it is achieved. Social efficiency implies a social, or social, succession of political and economic measures taken by the state, as the influence of most instruments of public policy is twofold and contradictory. The adaptive efficiency of state regulation is subject to both static and dynamic analysis. Static analysis considers adaptive efficiency in the narrow sense as a response to developments in the economy, as well as change. Dynamic analysis covers a broader aspect: the subject is the active activities of the state aimed at preventing problems that arise. The effectiveness of the state in the market of educational services depends not only on the increase in budget allocations, especially since public revenues and the public sector always have relative growth limits. The highest form of state regulation is state programming, as it involves the integrated use with a global goal of all elements of state regulation of the economy: political, economic rules and contracts. An example of state programming is the structural reforms that are being carried out in Ukraine today. An important component of structural reforms is education reform. Public administration is carried out through the process of interaction between objects and subjects of public administration. The subjects of public administration are the executive authorities, and the object is the system they govern, in those who are subject to the will of the subjects and their decision.

The B side of imagination: Hume on imperfect ideas

My aim is to look into the representational aspect of ideas, exploring not only to what Hume refers as adequate ideas, but also these cases where for a number of reasons an idea does not reach that standard. It has been suggested that the latter are fictions, but an in-depth examination of Hume texts reveals that there are several types of imperfections, such as incompleteness or imprecision that prevent an idea from being adequate. This leads to an analysis of the status of supposed or pretended ideas, and the possibility of there being terms with no ideas annexed to them.

Identification of 'Defects' in Epoxy Matrix Composites and Carbon Fiber by Ultrasound. Interaction of the Ultrasonic Beam with the Material

Non-Destructive Testing (NDT) methods, and especially, ultrasounds have gone from being a mere laboratory curiosity to an indispensable tool in the industry as a primary means of determining the level of quality achieved in its products (ASM, 1989; Barbero, 1999).
 This study will identify and apply the main physical phenomena of interaction of an ultrasonic wave in a composite material, to see if through this type of waves, you can detect defects of the type of porosity or delaminations in these materials. The percentages of reflected and transmitted waves in real cases of defects in the composite material will also be studied. It will be shown if the frequencies and intensities of the waves are adequate to find this type of defects or imperfections in the material.
 The theoretical study of the ultrasonic wave seeks to help researchers in the development of equipment that uses the methodology of immersion ultrasound for the inspection of materials in the search for 'defects' and to understand the physics of the test.

Optimal Robust Quantum Control by Inverse Geometric Optimization.

We develop an inverse geometric optimization technique that allows the derivation of optimal and robust exact solutions of low-dimension quantum control problems driven by external fields. We determine in the dynamical variable space optimal trajectories constrained to robust solutions by Euler-Lagrange optimization; the control fields are then derived from the obtained robust geodesics and the inverted dynamical equations. We apply this method, referred to as robust inverse optimization (RIO), to design optimal control fields producing a complete or half population transfer and a not quantum gate robust with respect to the pulse inhomogeneities. The method is versatile and can be applied to numerous quantum control problems, e.g., other gates, other types of imperfections, Raman processes, or dynamical decoupling of undesirable effects.

Porosity, mass and geometric imperfection sensitivity in coupled vibration characteristics of CNT-strengthened beams with different boundary conditions

Structures face different types of imperfections and defects during the fabrication process, installation and working environment. In this paper, the imperfection effects in the coupled vibration behaviour of axially functionally graded carbon nanotube (CNT)-strengthened beam structures with different boundary conditions are analysed considering porosity as well as geometric and mass imperfections in the structure. Porosity is modelled using different types of formulations for simple-cell, open-cell and closed-cell porous structures. The porosity is assumed to be either uniform or by varying through the thickness of the hollow beam using different functions. Mass imperfection effect is added to the system by considering a concentrated mass in the system affecting the mass homogeneity of the structure. Geometry imperfection is also considered by having an initial deformation in the structure which could be caused by an improper fabrication process. Coupled axial and transverse equations of motion are obtained using Hamilton’s principle and the von Karman geometrical nonlinearity. Governing equations are solved for different types of boundary conditions using a semi-analytical modal decomposition technique. It is shown that strengthening the base matrix with CNT fibres can improve the vibration behaviour of imperfect structures and the influence of CNT volume fraction and distribution through the length of the beam is discussed. The results provided in this paper may be used as a benchmark to validate future experimental results to prevent imperfection, delamination and stress singularities in the structures.

Effective slenderness ratio approach for thin-walled angle columns connected by the leg

This paper reports results of experimental and numerical investigations on a novel design approach to cold-formed steel angle columns connected by the leg that uses effective slenderness ratios. A FEM model (ANSYS) validated by experimental results obtained at the University of São Paulo enabled the development of a parametric study that involved 170 thin-walled angles connected by the leg by two bolts. An analysis of two types of initial geometric imperfections revealed the imperfection effects can be neglected in the mechanical behavior of the members, in contrast to the existing load eccentricity imposed by the bolted connection on the leg. From the parametric study, a new design approach based on effective slenderness ratio method and with a width/thickness ratio (b/t) is proposed with high accuracy mainly for intermediate angle columns. Although the design formulation was defined for the 20–36 b/t ratio range, the approach can be conservatively applied to angles with up to 50 b/t. Its effectiveness was validated by 3200 structural reliability problems of variable geometrical properties. The results of reliability indexes, with or without the model error, met the requirements of design standards and proved the adequate performance of the proposed design rule for large ranges of b/t and slenderness.

Rarely Occurring Defects on Tinplates

This paper deals with rarely occurring defect on the surface of the tinplates produced in the conditions of U. S. Steel Košice, s.r.o. at the cleaning section of the continuous annealing line (CAL), which was caused by burnt. Random occurrence of such surface imperfections was observed within the short period of time (two months) for various continuous annealed tinplate grades, i.e. TH415, TH435 or TH550 with the thickness of the materials in the interval of 0.172 – 0.240 mm. Surface defects caused by burnt (thermal attack) manifested in different ways. Their appearance on the sheet surface was spot with regular or irregular circle shape, as well as line with the length of up to 2 mm oriented not directly in the rolling direction. By observing of the imperfections in scanning electron microscope (SEM) it was found that the surface of the steel substrate was always compact in the defective areas with clearly visible rolling lines. Foreign material, EDS analysis of which revealed that its chemical composition was on the basis of Fe and Cr, was deposited on the surface of the base material. The appearance of the foreign material shape indicated that it was in the liquid state at the time of incidence on the steel substrate surface. Metallographic analysis from the longitudinal metallographic sections through the defective areas revealed that the substrate under the spot defect with regular circle shape had thermally influenced microstructure. Similar manifestations of the microstructure influence were observed for the line defects. In the case of the spot defect with irregular shape, the microstructure of the material was not influenced, what indicated that the particle of liquid metal was solidified at the time of incidence on the plate surface. After revising technical conditions of the cleaning section of CAL, this type of imperfection was suppressed.