Wyniki wyszukiwania - BazTech

1

Standard deviation in the simulation of statistical measurements

Przystupa Krzysztof, Kolodiy Zenoviy, Yatsyshyn Svyatoslav, Majewski Jacek, Khoma Yuriy, Petrovska Iryna, Lasarenko Serhiy, Hut Taras

Metrology and Measurement Systems

|

2023

|

Vol. 30, nr 1

17--30

EN

Is this article simulation of statistical measurements is performed on the basis of which the analysis of the standard deviation of the obtained results is carried out. It is shown that the standard deviation is minimum and independent from measurement duration while an object is in the state of equilibrium. For objects in a stationary non-equilibrium state the standard deviation depends on the duration measurements and the parameters of the state. The influence of these factors on the standard deviation is assessed with equation which includes the relaxation time. The value of the relaxation time is determined by approximating the energy spectrum of the studied signals. The analysis of energy spectra showed that the spectrum of white noise is inherent in objects in equilibrium; the flicker component of the spectrum occurs when the state of the object deviates from equilibrium.

2

Use of Tensile Creep Test (TCT) for evaluation of low temperature performance of bituminous mixtures used for bridge pavement

Budziński Bartosz, Mieczkowski Paweł

Archives of Civil Engineering

|

2022

|

Vol. 68, nr 2

679--696

EN

One of the main causes of road pavement distress are low temperatures, and hence the need to thoroughly study the low temperature performance of all bituminous materials used in road construction. The purpose of this study was to determine the performance of alternative and conventional bituminous mixtures in the temperature range between -25°C and -10°C using for this purpose the Tensile Creep Test (TCT). The low-temperature performance data were evaluated using the Burgers model, a tool that is widely used for evaluation of bituminous mixtures. This research focuses on bridge paving mixtures. These included both conventional (mastic asphalt) and alternative (SMA-MA) materials. It was established, based on the test results and their analysis, that low temperature performance of a bituminous mixture is influenced, in the first place, by the characteristics of the asphalt binder it contains. Furthermore, SMA-MA mixtures showed better low temperature performance than conventional, mastic asphalt type mixtures.

PL

Niska temperatura jest jedną z przyczyn powstawania uszkodzeń nawierzchni drogowych, zatem ocena parametrów niskotemperaturowych powinna być przedmiotem pogłębionych badań materiałów asfaltowych stosowanych w drogownictwie. Celem przeprowadzonych badań było określenie parametrów MMA w zakresie temperatur od -25°C do -10°C, z wykorzystaniem badania pełzania przy rozciąganiu (Tensile Creep Test - TCT). Do oceny parametrów niskotemperaturowych wykorzystano szeroko stosowany do oceny mieszanek mineralno-asfaltowych model Burgersa. Analizie poddano mieszanki stosowane na obiektach mostowych. Badania przeprowadzono zarówno na mieszankach klasycznych stosowanych na obiektach (asfalt lany) jak i alternatywnych mieszanek SMA-MA. Na podstawie uzyskanych wyników i przeprowadzonych analiz stwierdzono, że na parametry niskotemperaturowe kluczowy wpływ mają parametry lepiszcza asfaltowego stosowanego w mieszance. Stwierdzono również, że mieszanki w typie SMA-MA cechują się lepszymi parametrami niskotemperaturowymi niż klasyczne mieszanki w typie asfalt lany.

3

Thermal disturbances in twinned orthotropic thermoelastic material

Rani L., Singh V.

International Journal of Applied Mechanics and Engineering

|

2018

|

Vol. 23, no. 4

897--910

EN

This paper deals with deformation in homogeneous, thermally conducting, single-crystal orthotropic twins, bounded symmetrically along a plane containing only one common crystallographic axis. The Fourier transforms technique is applied to basic equations to form a vector matrix differential equation, which is then solved by the eigen value approach. The solution obtained is applied to specific problems of an orthotropic twin crystal subjected to triangular loading. The components of displacement, stresses and temperature distribution so obtained in the physical domain are computed numerically. A numerical inversion technique has been used to obtain the components in the physical domain. Particular cases as quasi-static thermo-elastic and static thermoelastic as well as special cases are also discussed in the context of the problem.

4

Selected aspects of computer modeling of reinforced concrete structures

Szczecina M., Winnicki A.

Archives of Civil Engineering

|

2016

|

Vol. 62, nr 1

51--64

EN

The paper presents some important aspects concerning material constants of concrete and stages of modeling of reinforced concrete structures. The problems taken into account are: a choice of proper material model for concrete, establishing of compressive and tensile behavior of concrete and establishing the values of dilation angle, fracture energy and relaxation time for concrete. Proper values of material constants are fix ed in simple compression and tension tests. The effectiveness and correctness of applied model is checked on the example of reinforced concrete frame corners under opening bending moment. Calculations are performed in Abaqus software using Concrete Damaged Plasticity model of concrete.

PL

W artykule skupiono się na kilku istotnych krokach modelowania konstrukcji żelbetowych przy użyciu oprogramowania w Metodzie Elementów Skończonych. Wszystkie kroki modelowania, które musi wykonać użytkownik programu są zestawione w poniższej liście: - wybór właściwego modelu materiałowego, - ustalenie związków między naprężeniami i odkształceniami dla stali i betonu, - podjęcie decyzji czy zostanie zastosowana regularyzacja, np. przez uwzględnienie lepkich własności betonu, - wybór właściwych stałych materiałowych dla przyjętego modelu, m.in. kąta dylatancji i czasu relaksacji, - definicja geometrii modelu, obciążeń i warunków brzegowych, - definicja współpracy stali z betonem, - wybór rodzaju elementów skończonych oraz stanu analizy (np. płaski stan naprężeń lub płaski stan odkształceń) oraz siatkowanie modelu, - dobór właściwych parametrów MES, np. wielkości przyrostu, kryteriów zbieżności itd., - oraz ostatecznie – obliczenia.

5

Investigation of Dimensional Changes During Garment Production and Suggestions for Solutions

Kalkanci M, Kurumer G.

Fibres & Textiles in Eastern Europe

|

2015

|

Vol. 23, no. 3 (111)

8--13

EN

Dimensional change problems experienced in textile products have always been an important subject and in the focus of attention. Today it is expected that dimensional changes in fabrics, the basic material of textile products, must range within certain limitations. Fabrics processed in the finishing divisions are wound or decatized in various forms according to the fabric structure and the demands of garment manufacturers. However, fabrics may be distorted in these storing processes, which results in undesired dimensional changes under the stress incurred. Nevertheless fabrics are required to be delivered to garment manufacturers at specific tension values. Indeed these values are not acquired as expected; consequently, it is known that they represent a core conflict subject between finishing plants and garment manufacturers. The present study investigated the structures of garment manufacturers and dimensional change problems they experience during fabric layout. The aim was to determine the severity of the problem in terms of the garment manufacturer and fabric types, which cause problems frequently, and to search for solutions to overcome this issue by means of a survey study. Solutions which would increase production efficiency and reduce processing time have been emphasized.

PL

Problem zmiany wymiarów tekstyliów w czasie produkcji odzieży jest bardzo ważnym problemem, a zakres zmian musi być poddany określonym ograniczeniom. Tekstylia obrabiane w procesach wykończalniczych są następnie nawijane i dekatyzowane w określonych warunkach i powinny być dostarczane do wytwórcy pod określonym naprężeniem. Celem artykułu jest zwrócenie uwagi na ważność problemu z punktu widzenia wytwórcy odzieży oraz określenie rozwiązań, które prowadziłyby do zwiększenia wydajności i skrócenia czasu produkcji.

6

Influence of heat sources and relaxation time on temperature distribution in tissues

Sharma S., Sharma K.

International Journal of Applied Mechanics and Engineering

|

2014

|

Vol. 19, no. 2

427--433

EN

In the present study, the temperature fluctuations in tissues based on Penne’s bio-heat transfer equation is investigated by applying the Laplace and Hankel transforms. To get the solution in a physical form, a numerical inversion technique has been applied. The temporal and spatial distribution of temperature is investigated with the effect of relaxation time and is presented graphically.

7

Effects of Mechanical Properties of Fabrics on Clothing Pressure

Chen D., Liu H., Zhang Q., Wang H.

Przegląd Elektrotechniczny

|

2013

|

R. 89, nr 1b

232--235

EN

To investigate how elastic modulus, elongation and relaxation time of fabric influence clothing pressure, the pressure on cylinder model was measured. The fabrics used were cotton spandex and polyester spandex elastic knitted fabric. The fabrics were sewed as 100mm high cylinders. The fabric cylinders with different elongation and with elongation 20% at different relaxation time pressed the cylinder model, and the pressure was measured. By analyzing data, it was found that clothing pressure increases linearly with the increase of fabric elongation basically when fabric elongation was within 60% . The clothing pressure exerted by fabric whose elastic modulus is greater is generally higher than that by fabric whose elastic modulus is lower when elongation was the same. The clothing pressure presents a trend of first order exponential decay with the passage of relaxation time, and the main pressure decrease happens within the first 30 minutes, subsequently, the pressure decreases slowly and tends to be stable ultimately. And the decrease caused by relaxation properties of fabric accounts for a little of total pressure.

PL

W artykule badaniom poddano cylindryczny model, wykonany z różnych rodzajów materiału. Oceniono wpływ współczynnika elastyczności, czas wydłużenia i ściągnięcia na ciśnienie wywierane przez tkaninę. Analiza danych wykazała, że wywierane ciśnienie rośnie liniowo wraz ze wzrostem wydłużenia, zwłaszcza do 60%. Ponadto jego zanik ma charakterystykę wykładniczą pierwszego rzędu a główny spadek następuje w ciągu pierwszych 30 min potem opada wolno.

8

Internal friction in the ferroelectric – ferromagnetic composites

Zachariasz R., Bartkowska J. A., Bochenek D., Niemiec P.

Archives of Metallurgy and Materials

|

2013

|

Vol. 58, iss. 4

1327--1330

EN

In the work, temperature Q-1(T) and amplitude Q-1 (ε) dependences of internal friction for ferroelectric - ferromagnetic composites on the base of the PZT and ferrite were determined. The temperature dependences of internal friction Q-1 reveal the peak in the range of high temperatures. We have investigated the peak associated with the viscous-elastic mobility of ferroelectric domain walls. The internal friction due to the viscous-elastic mobility of ferroelectric domain walls was calculated and compared with the experimental data in the reference to the Wang’s theory. Based on internal friction measurements and theoretical considerations, the peak was described. Additionally the amplitude (isothermal) Q-1 (ε) dependences for the composites were made. This allowed for the interpretation of the maximum observed on the temperature dependences of the internal friction Q-1(T).

PL

W pracy wyznaczano temperaturowe Q-1(T) i amplitudowe Q-1 (ε) zależności tarcia wewnętrznego dla ferroelektryczno - ferromagnetycznych kompozytów powstałych na bazie PZT i ferrytu. Na wykresach temperaturowych zależności tarcia wewnętrznego, uzyskanych dla badanych materiałów, obserwowano występowanie maksimum w zakresie wysokich temperatur. Do opisu maksimum zastosowany został model Wanga, który uwzględnia oddziaływania związane z lepko-sprężystym ruchem ferroelektrycznych ścian domenowych. Model ten bardzo dobrze opisał wyniki doświadczalne zależności tarcia wewnętrznego Q-1 od temperatury. Dobra zgodność pomiędzy modelem, a danymi pomiarowymi sugeruje, że za powstanie maksimum odpowiedzialne są lepko-sprężyste ruchy ścian domenowych. Ponadto przeprowadzono pomiary amplitudowych (izotermicznych) zależności tarcia wewnętrznego Q-1 (ε) dla badanych kompozytów. Pozwoliło to na interpretację maksimum obserwowanego wcześniej na temperaturowych zależnościach tarcia wewnętrznego.

9

Forced vibrations due to mechanical loads in piezothermoelastic half-space

Sharma J. N., Thakur A. D., Sharma Y. D.

International Journal of Applied Mechanics and Engineering

|

2012

|

Vol. 17, no. 2

535-557

EN

The article studies disturbances in a homogeneous, transversely isotropic, generalized piezothermoelastic half-space due to impact/continuous strip mechanical loads acting on a thermally insulated/isothermal and electrically shorted (closed circuit) surface. Combinations of the Laplace transform with respect to time and Fourier transform with respect to a space variable are employed to solve the boundary value problem in the transformed domain, in the context of classical and non-classical theories of thermoelasticity. The systems of equations are solved by using the Gauss elimination process for the unknowns. The values of these unknowns are used in the formal solution which leads to the expressions of displacements, temperature change, electric potential, electric displacement and stresses in the transformed domain. In order to obtain solution in the physical domain the inverse transform integrals are evaluated by using the Romberg integration and Fourier series approximations numerically. Temperature change, stresses and electric displacement so obtained in the physical domain, are computed numerically from the relevant expressions and relations for PZT-5A material. The illustrations and comparisons of the results for classical and non-classical theories of thermoelasticity are presented graphically. This may find applications in buzzers inside pagers and cell phones, shakers inside ultrasonic cleaners and strain sensors inside pressure gages.

10

Transient thermo-elastic disturbances in a visco-elastic semi-space due to a moving internal heat source

Lotfy K.

International Journal of Applied Mechanics and Engineering

|

2011

|

Vol. 16, no 3

747-762

EN

This paper investigates the transient disturbances created by an internal line heat source that suddenly starts moving uniformly inside a visco-elastic half-space. The generalised theory of thermo-elasticity with relaxation time proposed by Lord-Shulman (1967) is applied. The material of the semi-infinite medium is isotropic visco-elastic solid of Kelvin-Voight type. Applying the Fourier and Laplace transform technique, expressions for displacement components in the transformed domain are found out. These expressions prove the existence of three waves - a modified thermal wave, a visco-elastic wave of defused nature and a transverse visco-elastic wave. Surface displacement components are evaluated on the boundary for small time only. Numerical results are given and illustrated graphically to highlight the variations of surface displacement components with distance for different values of time, source depth and velocity of the source.

11

Transient thermo-elastic disturbances in a visco-elastic semi-space due to a moving internal heat source

Lotfy K. H., Fathy R. A.

International Journal of Applied Mechanics and Engineering

|

2010

|

Vol. 15, no 4

1169-1184

EN

This paper investigates the transient disturbances created by an internal line heat source that suddenly starts moving uniformly inside a visco-elastic half-space. The generalised theory of thermo-elasticity with relaxation time proposed by Lord and Shulman (1967) is applied. The material of the semi-infinite medium is an isotropic visco-elastic solid of Kelvin-Voight type. Applying the Fourier and Laplace transform technique, expressions for displacement components in the transformed domain are found. These expressions prove the existence of three waves - a modified thermal wave, a visco-elastic wave of defused nature and a transverse visco-elastic wave. Surface displacement components are evaluated on the boundary for small time only. Numerical results are given and illustrated graphically to highlight the variations of surface displacement components with distance for different values of time, source depth and velocity of the source.

12

Thermoelastic waves at an interface between two solid half-spaces under hydrostatic initial stress

Singh B., Singh J., Ailawalia P.

Archives of Mechanics

|

2010

|

Vol. 62, nr 3

177-193

EN

A model of two semi-infinite half-spaces of different thermoelastic solids is considered in welded contact under hydrostatic initial stress. The appropriate boundary conditions are satisfied at the interface to obtain the reflection and refraction coefficients of various reflected and refracted waves during incidence of the quasi-thermal wave. A particular numerical example is considered to show the effect of hydrostatic initial stress on these coefficients for a certain range of the angle of incidence.

13

Charge relaxation on surfaces of polymeric insulating materials for outdoor applications

Sjöstedt H., Montano R., Serdyuk Y., Gubanski S. M.

Materials Science Poland

|

2009

|

Vol. 27, No. 4/2

1129--1137

EN

The studies have been presented on spatial and temporal distributions of surface charge on samples of ethylene propylene diene monomer (EPDM) and silicon rubber (SIR). The charge was deposited from a positive impulse corona source located at 1 mm above the polymeric surfaces. During the experiments, the number of pulses and their voltage level were varied. It was observed that the spread of the charge over the surface of the samples as well as its magnitude were both increasing with increasing number of impulses applied. EPDM accumulated charge easier and had a longer relaxation time than SIR. A common feature frequently observed in both cases was that the resulting charge distributions had a saddle-like pattern. Performed computer simulations showed that this feature can be attributed to peculiarities of the corona charging in the considered system, which took place in a form of a burst corona, and the dynamics of the deposited charges could be related to burst corona pulses.

14

Interaction due to thermodiffusive and mechanical sources in micropolar elastic medium

Kumar R., Kaushal S., Miglani A.

Journal of Technical Physics

|

2009

|

Vol. 50, no 4

317-342

EN

In this present paper, first the equations of generalized micropolar thermodiffusive medium, based on the theory of Lord and Shulman with one relaxation time are derived and then, deformation in a micropolar thermoelastic diffusive medium has been studied due to various sources. Laplace and Fourier transforms are used to solve the problem. The application of concentrated normal force, thermal point source and chemical potential point source has been considered to show the utility of the solution obtained. The transformed components of stress, temperature distribution and chemical potential are inverted numerically using a numerical inversion technique. The effect of micropolarity and diffusion on these quantities are presented graphically in order to illustrate and compare the analytical results. Some special cases of micropolarity and diffusion are also deduced.

15

Charge relaxation on surfaces of polymeric insulating materials for outdoor applications.

Sjostedt H., Montano R., Serdyuk Y., Gubański M.

Prace Naukowe Instytutu Podstaw Elektrotechniki i Elektrotechnologii Politechniki Wrocławskiej. Konferencje

|

2007

|

Vol. 46, nr 19

17-20

EN

This paper presents studies on spatial and temporal distributions of surface charge on samples of Ethylene Propylene Diene Monomer (EPDM) and Silicon Rubber (SIR). The charge was deposited from a positive impulse corona source at 1 mm above the polymeric surfaces. During the experiments, the number of pulses and their voltage level were varied. It was observed that the spread of the charge over the surface of the samples as well as its magnitude were both increasing with increasing number of impulses applied. EPDM accumulated charge easier and had a longer relaxation time than SIR. A common feature frequently observed in both cases was that the resulting charge distributions had a saddle-like pattern. Performed computer simulations showed that this feature can be attributed to peculiarities of the corona charging proc the considered system, which took place in form of a burst corona, and the dynamics of the deposited charges could be related to burst corona pulses.

16

Conductivity and transmission coefficients of ultra-thin disordered metallic films

Spisak B.J., Paja A.

Materials Science Poland

|

2006

|

Vol. 24, No. 3

605--609

EN

The diffusive motion of quasi-two-dimensional electron gas through an ultra-thin system of disordered potentials is considered. In such system the Fermi sphere splits into a set of independent sheets due to the small thickness of the system. Each sheet can be seen as an electron sub-band. The electron transport goes through these sub-bands independently. The sum of electrical conductivities over these sub-bands determines the total current which is calculated for ultra-thin films of cesium. We also present the relation between our approach and Landauer formalism based on the notation of the transmission coefficient.

17

Viscoelastic model of waterhammer in single pipeline - problems and questions

Weinerowska-Bords K.

Archives of Hydro-Engineering and Environmental Mechanics

|

2006

|

Vol. 53, nr 4

331-351

EN

In the paper, viscoelastic model of waterhammer in a single polymer pipeline is analysed. The theoretical background of viscoelastic behaviour of the structure is shown and the mathematical model of waterhammer in a polymer pipeline is presented. The main problems connected with applying the model are discussed. The main emphasis is on the question of parameter estimation. Important aspects of wave speed calibration are presented. Estimation of a second group of parameters - retardation time and creep compliance values - was analysed. Problems and questions connected with the number of parameters, methods of estimation, potential non-uniqueness of the solution and accuracy of obtained calculations were discussed.

18

The uniqueness and reciprocity theorems for generalized thermo-viscoelasticity with thermal relaxation times

Othman M. I. A.

Mechanics and Mechanical Engineering

|

2004

|

Vol. 7, nr 2

77-87

EN

The equations of generalized thermo-viscoelasticity based on Lord-Shulman (L-S), Green and Lindsay (G-L) and Classical dynamical coupled (CD) theories are given. Using Laplace transforms, a uniqueness theorem for these equations is proved. Also, a reciprocity theorem is obtained.

19

Crystal order and magnetic properties of Fe2.4V0.6Al alloy studied by magnetostatic and Mössbauer methods

Popiel E., Zarek W., Kapuśniak Z., Tuszyński M.

Nukleonika

|

2003

|

Vol. 48,suppl.1

65-70

EN

Performed investigations showed that the magnetic properties of the Fe2.4V0.6Al alloy markedly depend on the degree of atomic order of its cubic structure. The atomically disordered alloy with A2 (bcc) type structure exhibits ferromagnetic properties. Its Mössbauer spectra can be described by the hyperfine field distribution connected with various local environments of Fe atoms. Alloys with B2 (sc) and DO3 (fcc) type structure do not exhibit magnetic transition above 4.2 K. High values of the magnetization and its strongly non-linear variation with magnetic field intensity in a wide temperature range suggest the presence of magnetic iron clusters in these alloys. Superparamagnetic relaxation times of the order of 10-9 s and 5 × 10-8 s correspond to the largest magnetic clusters with a magnetic moment of 4 × 103 žB in B2 and 104 žB in DO3-type structure, respectively. Mössbauer spectra of these alloys confirm lack of the magnetic order and also suggest the presence of the Fe magnetic clusters with those relaxation times. It was shown that the increase of atomic order of the crystal structure causes formation of the Fe magnetic clusters and disappearing of the magnetic order.

20

Elastodynamics of time harmonic sources in a thermally conducing cubic crystal

Kumar R., Rani L.

International Journal of Applied Mechanics and Engineering

|

2003

|

Vol. 8, no 4

637-650

EN

The disturbance due to a time harmonic mechanical, horizontal or vertical and thermal source in a homogeneous, thermally conducting cubic crystal, elastic half-plane is investigated by applying the Fourier transform. The displacements, stresses and temperature distribution so obtained in the physical domain are computed numerically and illustrated graphically. The numerical results of these quantities for magnesium crystal-like material are illustrated to compare the results for different theories of generalized thermoelasticity for insulated boundary and temperature gradient boundary.