Wyniki wyszukiwania - BazTech

1

Quantitative approaches to concrete repair compatibility

Bissonnette B., Garbacz A., Modjabi-Sangnier F., Courard L., Vaysburd A. M.

Materiały Budowlane

|

2017

|

nr 6

58--61

EN

The compatibility concept, which started developing in the early nineties, is now widely considered as a fundamental basis of the concrete repair design process. The main challenges to be faced in view of fully implementing the approach in engineering practice lies in evaluating quantitatively the various compatibility requirements. In this paper, analytical and modeling tools are considered for the evaluation of dimensional compatibility. The ability of these tools to take into account the combination of variables such as the exposure conditions is shown through a few examples.

PL

Koncepcja kompatybilności została sformułowana w latach 90. i jest powszechnie uważana za podstawową zasadę napraw betonu. Jednym z największych wyzwań dotyczących pełnego wdrożenia tego podejścia do praktyki inżynierskiej jest możliwość ilościowej oceny różnych typów kompatybilności. W artykule zaprezentowano dwa podejścia do ilościowego charakteryzowania kompatybilności napraw. Na kilku przykładach przedstawiono możliwość ich wykorzystania w analizie wpływu kombinacji różnych warunków podczas stosowania wyrobów i użytkowania obiektu na kompatybilność.

2

Friction evaluation of laser textured tool steel surfaces

Šugárová J., Šugár P., Frnčík M.

Acta Mechanica et Automatica

|

2017

|

Vol. 11, no. 2

129--134

EN

Surface textures can be defined as a regularly arranged micro-depressions or grooves with defined shape and dimensions. These textures, if they are manufactured by laser ablation process, contribute to a significant improvement of the tribological, optical or various biological properties. The aim of this paper is to analyze the influence of the surface textures prepared by laser surface texturing (LST) at the friction coefficient value measured on the tool (90MnCrV8 steel) – workpiece (S235JRG1 steel) interface. Planar frontal surfaces of compression platens have been covered by parabolic dimple-like depressions with different dimensions. The morphological analysis of such manufactured depressions has been performed by laser scanning microscopy. Influence of such created textures on the tribological properties of the contact pair has been analyzed by the ring compression test method in the terms of hydrodynamic lubrication regime. The experimental research shown that by applying of surface textures with defined shape and dimensions and using an appropriate liquid lubricant at the same time, the coefficient of contact friction can be reduced nearly to the half of its original value.

3

A multi-layered ring under parabolic pressure

Markides Ch. F., Pasiou E. D., Kourkoulis S. K.

Engineering Transactions

|

2016

|

Vol. 64, iss. 4

433--440

EN

The stress- and displacement-fields developed in a circular ring consisting of a finite number of linearly elastic homogeneous and isotropic concentric layers are determined. The composite ring is subjected to a distribution of radial stresses (acting along two finite arcs of its periphery) varying according to a parabolic law. The problem is solved analytically adopting Savin’s approach for an infinite plate with a hole strengthened by rings. Taking advantage of the analytic solution, a numerical model is properly calibrated and validated by considering the case of a three-layered ring. It is concluded that the constructed model simulates reality in an excellent manner and therefore it can be safely used for a thorough parametric analysis of the numerous factors influencing the stress- and displacement-fields.

4

Effect of temperature and strain rate on friction factor during hot deformation of Al-Mn and Al-Cu-Mg Al-alloys

Petrov P., Gnevashev D., Dubinchin A., Petrov M., Solotych V., Eiesland J. W.

Computer Methods in Materials Science

|

2009

|

Vol. 9, No. 1

55-60

EN

Massive hot forging of any aluminium alloy can be performed with the help of several types of metal-forming machines, namely hydraulic press, mechanical press, screw press etc. Applying one of these machines allows production of either typical forgings or near net shape forgings. Anyway, there is a technological parameter which has a strong influence the quality of a forging made of Al-alloy. This is the composition of lubricant. The choice of a lubricant for forging is major task, especially in case of aluminium alloys deformation. The efficiency of any lubricant can be estimated by at least three criteria: 1) the lubricant should have good tribological properties; 2) the lubricant should have good heat-shielding properties; 3) the lubricant should produce little or no smoke. The paper is linked to the investigation of the effect of temperature as well as strain rate on lubricants for massive hot forging. Friction factor was chosen as one of the criteria for the estimation of the effects mentioned. Wide range of temperatures was observed. The research on friction has been done for Al-Mn and Al-Cu-Mg aluminium alloys. In this connection, physical and numerical investigation of friction performed. The condition of experimental investigation corresponded to the forging process of Al-alloys with the help of the hydraulic and screw press as well. The ring upsetting technique with combination of FE-simulation was chosen for investigation of the effect of temperature and strain rate on friction factor value. The regressions for the relationship between friction factor and temperature as well as strain rate for all lubricant under study have been obtained. Some practical recommendations were given.

PL

Tematem artykułu są badania wpływu temperatury oraz prędkości odkształcenia na własności smarów w procesie kucia matrycowego na gorąco. Wspólczynnik tarcia został wybrany jako jedno z kryteriów estymacji analizowanego efektu. Badania tarcia wykonano dla stopów aluminium Al-Mg oraz Al-Cu-Mg w podwyższonej temperaturze. Zachowanie się smarów analizowano w zakresie temperatur 200-470°C. Przeprowadzono fizyczne oraz numeryczne symulacje. Badania doświadczalne wykonane zostały dla procesu kucia stopów aluminium na prasach hydraulicznej i śrubowej. Natomiast do analizy numerycznej wpływu temperatury i prędkości odkształcenia na współczynnik tarcia wybrano proces spęczania pierścieni symulowany przy użyciu metody elementów skończonych. Ostatecznie otrzymano zależności regresyjne pomiędzy analizowanymi parametrami, które zostały przedstawione w artykule wraz z pewnymi praktycznymi wskazówkami.

5

Modelowanie tarcia w próbie spęczania pierścieni ze stopu Ti6Al4V

Lacki P.

Tribologia

|

2008

|

nr 3

347-355

PL

W pracy przedstawiono wyniki badań doświadczalnych z próby spęczania na zimno pierścieni wykonanych ze stopu Ti6Al4V. Uwzględniono wpływ mikrogeometrii powierzchni na charakter współpracy pary trącej. Wyniki badań eksperymentalnych porównano z wynikami symulacji numerycznej. Do obliczeń numerycznych wykorzystano program ADINA System, bazujący na metodzie elementów skończonych. W modelu numerycznym założono sprężyste właściwości materiału matryc oraz sprężysto-plastyczne właściwości odkształcanego materiału. Ze względu na symetrię osiową procesu przyjęto dwuwymiarowy model osiowo-symetryczny. W pracy przedstawiono wyniki obliczeń numerycznych pokazujące zmianę płynięcia materiału na skutek różnych warunków tarcia.

EN

Friction has a large influence on the course of the metal forming process. Many authors point to the complexity of the frictional processes occurring between the deformed material (especially titanium alloys) and the tools (steel). It results from the physical and chemical properties of titanium alloys and the particular conditions occurring in the metal forming processes. Complexity of the phenomena occurring in the contact zone causes that frictional hypotheses do not meet reflection in tests. It can be stated that the agreement between frictional hypotheses and real conditions worsens with increasingly difficult frictional conditions. The present-day knowledge does not allow for defining one universal hypothesis describing frictional conditions in relation to the metal working processes. The research mainly concentrates on the determination of the influence of the individual parameters on the frictional state of the specific frictional pair. Some tests show that the microgeometry of the contact surface affects the kind and character of the contact phenomena significantly. Numerical simulation is the only method allowing for the determination of the plastic strains in the deformed material. It is very difficult, or even impossible, to obtain such information by other methods. In most cases of the numerical simulations, the surface roughness is neglected because of a large number of the finished elements needed for modelling the process. Generally, such a simplification is justified and does not affect the calculation results significantly. In the paper, an influence of the contact microgeometry (surface roughness) on the deformation process was analysed. The numerical simulation of the upset forging of the titanium rings was carried out with the ADINA System v. 8.3, based on the finite element method. In the numerical model, the elastic properties of the die material and the elastic-plastic ones of the deformed material were assumed. According to the axial symmetry of the process, a 2-D model with axial symmetry was applied. The numerical model geometry of the upper and lower surface of the ring was varied in order to show a difference between a smooth and rough surface. The surface topography of the sample and dies was imaged. Imaging was produced of the surface roughness aimed at analysing the influence of the contact microgeometry on the course of the deformation process in the top layer of the deformed ring. The calculation results showing some changes in material flow resulting from different frictional conditions were compared with the test results. The "ring test" for Ti6Al4V alloy rings was carried out. Additionally, metallographic specimens of the deformed rings were obtained and analysed. It is observed that, with worsening frictional conditions, the rate of plastic deformation in the top layer increases. The local values of the plastic strains occurring at the unevenness tops can exceed limit values, and material decohesion appears. It is especially dangerous in the case of titanium deformation because the fractures, which are invisible at the beginning, develop suddenly after the end of the forging process.

6

An influence of the frictional conditions on the forging process of Ti6A14V alloy

Lacki P.

Advances in Materials Science

|

2007

|

Vol. 7, nr 4(14)

68-74

EN

In the paper some experimental results of the "ring test" are given. The tests were done for Ti6A14V alloy. An influence of the contact microgeometry on the deformation process was analysed. The test results were compared with the results of the numerical simulation carried out for the upset forging of the titanium rings. The simulation was carried out with the ADINA System based on the finite element method. In the numerical model the elastic properties of the die material and the elastic-plastic ones of the deformed material were assumed. According to the axial symmetry of the process 2-D model with axial symmetry was applied. In the paper the calculation results showing some changes in material flow resulting from different frictional conditions were given.

7

Simulation of friction in upsetting process

Lacki P.

International Journal of Applied Mechanics and Engineering

|

2004

|

Vol. 9, no spec.

247-253

EN

In the paper both numerical simulation of the upsetting process and experimental verification have been presented. Some test results of the surface roughness for the contact surfaces and geometrical parameters of the forging have been given. Three frictional models had been applied in the numerical model of the upsetting process and then the obtained results have been compared. Simulation of the frictional pair has been made with the "User-supplied friction models" of the ADINA System v.8.1. Probability of the appearance of the different friction coefficients depending on lubrication, surface roughness and relative velocity of the contact surfaces have been taken into consideration in the frictional models.