Wyniki wyszukiwania - Biblioteka Nauki

1

Niektóre aspekty wyznaczania sztywności elastomerów

100%

Nadolny K. , Jurkowski B.

Archiwum Technologii Maszyn i Automatyzacji

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2006

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tom Vol. 26, nr 1

201-210

PL

Naprężenia przy wydłużeniach 100%, 200% i 300%, zwane modułami, są powszechnie stosowane do oceny sztywności elastomerów. Pokazano, że sztywność gumy zależna jest w dużym stopniu od wydłużenia, niezależnie od użytej metody jej wyznaczenia. Sztywność początkowa jest największa, po czyrn ze wzrostem wydłużenia stopniowo zmniejsza się, dochodząc do minimum (punkt przegięcia) i znów zaczyna rosnąć. Z powodu nieliniowej zależności moduły standardowe nie charakteryzują sztywności elastomeru w warunkach pracy większości wyrobów (wydłużenia 5-10%). Dlatego zaproponowano dwa sposoby obliczenia modułu stycznego za pomocą różniczkowania krzywej rozciągania. Algorytm postępowania zostaf zaprogramowany. Uwzględniono w nim automatyczną poprawę początku krzywej, wygładzanie przez usunięcie powtarzających się wartości oraz zmianę liczby punktów doświadczalnych branych do obliczeń.

EN

Stresses at 100%, 200%, and 300% eiongation are usually used to evaluate the elastic modulus of elastomers. It was shown that modulus of rubber to a high degree depends on elongation, independently on the method used for its evaluation. The initial modulus is the highest; next, is lower till minimal value reaches the knee point of the stress-strain curve, and starts to increase as strain increases. Due to nonlinear dependence of the curve, standard moduli do not characterize stiffness at usage conditions of most of rubber goods (strain 5-10%). Because of this, there were proposed two methods for calculation of tangent modulus by differentiation of the strain-stress curve. The elaborated software was based on the algorithm of actions needed to be performed. There a correction of the beginning of the stress-strain curve was taken into account. In addition, the curve was smoothens by extraction of the replicated values and changes in a number of experimental points taken for calculation.

2

Approximate Study on a Tensile Model of Wool/spandex Core - spun Yarn

84%

Dang M. , Wang S.

Fibres & Textiles in Eastern Europe

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2007

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tom Vol. 15, no. 4 (63)

59--62

EN

An approximate approach is presented to calculate and predict the specific stress of wool/spandex core-spun yarn, based on an idealised yarn structure model and Hearle’s yarn theory. The approximate model covers some major parameters from wool fiber, spandex and core-spun yarn. Comparing with experimental tensile (stress-strain) curves of core-spun yarn, we can see that the theoretical model can basically reflect the shape of wool/spandex core-spun yarn’s tensile curve and the model is useful for predicting the stress-strain behaviour of wool/spandex core-spun yarn at small extension.

PL

Przedstawiono próbę obliczania i przewidywania wytrzymałości właściwej przędz rdzeniowych wełna-elastomer. Metoda oparta jest na modelu unikalnej struktury włókna i teorii włókna Heorlego. W modelu uwzględniono podstawowe parametry przędzy wełnianej, elastomerowej i połączonej przędzy rdzeniowej. Porównując wyniki obliczeń z krzywymi eksperymentalnymi przędz rdzeniowych, widzimy że model teoretyczny może odzwierciedlać kształt krzywej siła-wydłużenie i musi służyć do przewidywania właściwości wytrzymałościowo-sprężystych przędz rdzeniowych wełna-elastomer przy małych wydłużeniach.

3

Modelling the Stress - strain Curve of Textile Products. Part 2, Simulation of Real Stress - strain Curves

84%

Serwatka A. , Bruniaux P. , Frydrych I.

Fibres & Textiles in Eastern Europe

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2007

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tom Vol. 15, no. 3 (62)

60--62

EN

This paper presents the second part of our study describing the modelling of the yarn stretching phenomena recently published in F&T in EE [1]. The continuation of this app-roach involves the identification of unknown parameters in the model, as well as proper stress-strain curve division, in order to avoid problems of identification. In order to avoid the effects of parametric compensation, which has been very often observed, when the number of model parameters becomes significant we use a new strategy of identification. The division of the model into submodels contributes to the correct operation of the identification, because we use a method which partially identifies with submodels which have a small number of parameters. The parameters of the proposed model were identified using MATLAB software. Various types of yarns were tested according to whether their origin was natural and man-made. Finally, the superposition of the practical and simulated curves was carried out, with the aim of verifying the correctness of the proposed model. The results show that the model was adapted perfectly in almost all types of the yarns used.

PL

Pierwsza część tej pracy [1] dotyczyła omówienia nowego modelu, opracowanego w GEMTEX, Francja, wyróżniającego się podziałem krzywej rozciągania na trzy strefy. Kontynuacja tej pracy obejmuje identyfikację nieznanych parametrów modelu oraz prawidłowego podziału krzywych rozciągania celem uniknięcia problemów z identyfikacją. Dla zapobieżenia powstawaniu efektu kompensacji parametrów, często obserwowanemu jeżeli liczba parametrów modelu jest zmienna, zastosowano nową strukturę identyfikacji. Podział modelu na podmodele przyczynia się do prawidłowego postępowania przy identyfikacji, gdyż identyfikuje się modele o prostszej strukturze i mniejszej liczbie parametrów. Identyfikację przeprowadzono za pomocą programu komputerowego MATLAB. Testowano przędze wytworzone z włókien o różnym pochodzeniu, a co za tym idzie różnej charakterystyce. Jako surowce wykorzystano włókna pochodzenia naturalnego (bawełnę) oraz włókna chemiczne z polimeru naturalnego (Tencel) i syntetycznego (poliester). Stwierdzono dużą zgodność pomiędzy krzywymi wykonanymi doświadczalnie i za pomocą symulacji.

4

Hardness prediction of a cold rolled Nimonic 80A exhaust valve spindle

84%

Kang S. W. , Heo S. J. , Yoo J. H. , Kang J. H.

Journal of Achievements in Materials and Manufacturing Engineering

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2019

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tom Vol. 94, nr 1-2

13--21

EN

Purpose: of this paper is to predict the hardness of cold rolled exhausts valve spindle fabricated of Nimonic 80A via axisymmetric finite element analysis, compression testing, and hardness inspection. Design/methodology/approach: The stress-strain relationship of Nimonic 80A was obtained via compression testing with deformation ratios of 10%, 20%, and 30%. Hardness changes caused by the strain hardening effect were measured in cut specimens in both the axial and circumferential directions following compression testing. The effective strain at the measurement position was calculated via finite element analysis. The regression equation for hardness changes caused by work hardening was derived from analysed strain and inspected hardness. The cold-rolling deformation of an exhaust valve spindle was analysed using axisymmetric finite element analysis. Findings: The stress-strain relationship calculated from compression testing was well expressed using the Holloman equation and the strain-hardness relationship by strain hardening was successfully regressed using the shifted power law model for Nimonic 80A, Nickel-Chromium based super alloy. Research limitations/implications: This research focused hardness prediction of spindle after ring rolling operation for generating beneficial compressive surface residual stresses for enhancing fatigue life. Further research to quantify compressive residual stress after rolling shall be followed to increase fatigue life. Practical implications: The cold rolling process is a typical incremental forming method and should be analysed under three-dimensional conditions. However, it takes lots of time to solve incremental forming analysis. To predict hardness distribution after rolling in the manufacturing field, FE analysis was performed under two-dimensional axisymmetric conditions based on the assumption of no friction generated by the rolling tool. The deformed shapes and hardness distribution from the inspection quality standard and two-dimensional FE analysis showed very similar results. Simplified finite element analysis method for ring rolling process for local area could be very effective method in the industrial field. Originality/value: The stress-strain relationship and the hardness and strain relationship were derived by compression test and hardness measurement for compressed specimen for Nimonic 80A, Nickel-Chromium based super alloy. And simplified finite element analysis method was suggested to predict deformed shape and hardness distribution of locally cold rolled region and achieved similar result between FE analysis result and Quality standard. Suggested method would be very effective method to engine spindle manufacture to predict hardness of different size of product.

5

Long-term effect of different particle size distributions of waste glass powder on the mechanical properties of concrete

84%

Omer B. , Saeed J.

Architecture Civil Engineering Environment

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2020

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tom Vol. 13, no. 4

61--75

EN

In this paper, a comprehensive experimental investigation was conducted into the effect of the particle size distributions (PSDs) and percentages of waste powdered glass as a partial replacement of cement on the long-term mechanical behavior of concrete produced at two different cement levels. For this purpose, two different mixtures of concrete were used as reference mixtures; the first has a relatively low cement content (331 kg/m3), and the second has a relatively high cement content (490 kg/m3). Two different PSDs of glass powder (GP) labeled GP-A and GP-B ((55 μmGP-B) were used, and the considered GP content for the low cement content mixture (LCCM) and the high cement content mixture (HCCM) were (0%, 5%, and 10%) and (0%, 5%, 10%, and 15%) by weight of cement, respectively. The mechanical performance of all concrete mixtures at 180 days was investigated and evaluated in related tests as compressive strength and toughness, splitting and flexural tensile strength, elastic modulus, and compressive stress-strain behavior. The experimental results generally indicated that the compressive strength of GP-modified concrete improved significantly over the long-term age (180-days) compared to the early age (28-days). The contribution of PSDs of GP to enhancing the mechanical properties of concrete is insignificant compared to its replacement amount. Finally, independent of the PSDs, the incorporation of 10% GP for LCCM and 15% of GP for HCCM has a positive effect on the long-term mechanical properties of concrete, indicating that GP can be used as a replacement for cement.

6

The application of Zurek’s rheological model for description of mechanical behaviour of textiles subjected to different state of loads

84%

Żurek W. , Chrzanowski M. , Sybilska W. , Jałmużna I.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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tom Vol. 43, nr 2

702--710

EN

Purpose: In order to describe the rheological properties of textile products there have been used various models but none of them delivers the complementary solution for textiles subjected to different fields of loads. Therefore the idea presented by Hasley in 1945 was an inspiration for us to propose the new rheological model based on theory of plastic-elastic solids. Design/methodology/approach: It was assumed that the modified rheological model would consist of two parallel parts: I - Hooke’s spring with rigidity C1 and II - Hooke’s spring with rigidity C2, connected in series with a frictional element with a constant resistance, T and additional force Kε22, and a piston with a weight m displacing in a liquid with a viscosity η, where ε22 is a shift of the piston from its initial position. Findings: The proposed model represents adequately stress – strain relationships of polypropylene monofilaments subjected to tensile test. The results indicate that for each investigated type of nonwovens there is no significant difference between the shape of the theoretical and experimental elastic recovery curve during the recovery test. Research limitations/implications: The application of presented model was used for illustration of the description of relaxation of polypropylene monofilament subjected to tensile load and rheological properties of non-woven fabrics made also from polypropylene fibres subjected to the compression loads. Originality/value: The new rheological model was proposed. It can be universal for description of mechanical behaviour of textiles subjected to the tension or compression loads.

7

The modelling of temperature-dependent stress-strain curves for weldable steels

84%

Winczek J. , Mičian M. , Ivanov V.

Journal of Applied Mathematics and Computational Mechanics

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2018

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tom Vol. 17, nr 3

111--117

EN

The calculation of stresses in the steel elements subjected to the thermomechanical loads requires taking into account the influence of temperature on mechanical properties of a material, including the stress-strain curve. The simplified and extended computational models of temperature-dependent tensile curves have been discussed. The methodology of the stress-strain curve construction in the entire temperature range of the solid state of the material has been proposed. The considerations are illustrated by the examples of calculated stress-strain curves in different temperatures for S235 and S355 welding steels.

8

New Approach to Modeling the Stress - Strain Curve of Linear Textile Products. Part 1, Theoretical Considerations

67%

Serwatka A. , Bruniaux P. , Frydrych I.

Fibres & Textiles in Eastern Europe

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2006

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tom Vol. 14, no. 1 (55)

30--35

EN

The first part of this paper presents a modelling of the stretching phenomena of linear textile products, specifically yarns. The stretching phenomena are described by a model of the yarn stress-strain curve which was developed by a team from the GEMTEX laboratory. This analysis of the yarn stress-strain curve is an attempt to interpret this curve in the form of a set of various models. This differentiation is due to the change of the yarn’s state at the time of its stretching. The model differs very clearly from the other models presented in literature. In order to compare our research with that described in literature, the sensitivity of the parameters of various models was studied. Dividing the model into sub-models is crucial, because this enables the identification of vector parameter as a whole, by assembling parameters of sub-models. The second part of this approach to modelling the stress-strain curve is concerned with modelling the stress-strain curves of real natural and synthetic yarns.

PL

Pierwsza część tego opracowania poświęcona jest modelowaniu krzywej naprężenie-odkształcenie dla liniowych produktach włókienniczych. Model, opracowany w GEMTEX (Francja) odróżnia się od dotychczas proponowanych modeli, podziałem krzywej na trzy strefy. W artykule przedstawiono analizę porównawczą proponowanego przez autorów modelu z modelami dotychczasowymi przedstawiając m. in. przebiegi odzwierciedlające charakter i intensywność oddziaływania poszczególnych parametrów równań. Podział modelu na submodele jest istotny, ponieważ pozwala na identyfikację parametrów całego układu poprzez prezentację parametrów submodeli. W części drugiej artykułu omówione będzie modelowanie krzywych naprężenie-odkształcenie dla rzeczywistych liniowych produktów włókienniczych.

9

Stress-strain model for confined fiber-reinforced concrete under axial compression

67%

Sabariman B. , Soehardjono A. , Wisnumurti , Wibowo A. , Tavio

Archives of Civil Engineering

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2020

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tom Vol. 66, nr 2

119--133

EN

Confinement in concrete can improve the descending branch of the stress-strain relationship of concrete. The addition of steel fiber in concrete can also improve the descending branch of the stress-strain relationship of concrete. The combination of the use of both can double the impact significantly on the post-peak response. It can be seen from the trend of the post-peak response that the values of both 0.85fccf and 0.5fccf can be well predicted. The study involved an experimental investigation on the effect of confinement on square column specimens reinforced with steel fiber. From the experimental program, it is proven that the use of combination of confining steel and steel fiber works very well which is indicated by the better improvement on the post-peak response. The proposed equations can predict the actual stress-strain curves quite accurately which include the effects of confinement parameters (Zm) and steel fiber volumetric parameter (Vf).

10

Model konstytutywny skrępowanego ściskania fibrobetonu

67%

Zaborski A.

Cement Wapno Beton

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2016

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tom R. 21/83, nr 1

46--52

PL

Beton zbrojony włóknami wykazuje szereg korzystnych właściwości mechanicznych. Zarówno jego wytrzymałość jak i odkształcalność znacznie wzrastają, w przypadku stosowania tego kompozytu wraz z dodatkowym, krępującym zbrojeniem obwodowym. W artykule przedstawiono analityczny model uogólnionego związku naprężenie-odkształcenie, opartego na dostępnych w literaturze badaniach doświadczalnych. Zaproponowane równanie pozwala na oszacowanie zależności krzywizny pręta zbrojącego od momentu zginającego, w warunkach skrępowanej pracy elementu betonowego.

EN

Fiber reinforced concrete offers several mechanical benefits. The material strength and deformability are highly increased when the material is used with restricting passive confinement. In this paper, an analytical model for general stress-strain behavior in compression is presented, based on available in literature experimental data. Postulated formula is further used to predict bending moment-curvature relationship for confined fiber reinforced concrete.