Wyniki wyszukiwania - BazTech

1

Residual stresses and plastic zones' boundaries in two-dimensional elements

Kozłowska B.

Archive of Mechanical Engineering

|

2009

|

Vol. LVI, nr 4

371-381

EN

In the paper, author presents the analysis of the elastic-plastic residual stresses and the boundaries of plastic zones in two-dimensional model with central circular hole. The experimental testing was carried out by photoelastic coating method. The duralumin model was loaded within the overelastic range by uniformly distributed tensile stresses. For various levels of loading, the photographs of isochromatic pattern were taken. The residual stresses along the axis of symmetry perpendicular to the stretching direction were calculated by the characteristics method, using multisectional schematization of sigma - epsilon relation for the material. The boundaries of plastic zones in the loaded model were obtained on the basis of the Treska-Coulomb yield condition directly from the isochromatic pattern. The analysis and discussion of the test results is presented.

PL

W pracy została przedstawiona analiza naprężeń własnych i granic stref plastycznych na przykładzie płaskiego modelu elementu konstrukcyjnego z otworem kołowym. Model wykonany z duraluminium został obciążony równomiernie rozłożonymi na końcach naprężeniami rozciągającymi wywołującymi częściowe uplastycznienie materiału. Do badań doświadczalnych zastosowano metodę pokryć optycznie czynnych. Na wybranych poziomach obciążenia w zakresie sprężysto-plastycznym zostały zarejestrowane obrazy izochrom, które posłużyły do wyznaczenia granic obszarów uplastycznionych oraz określenia wartości naprężeń własnych na osi symetrii prostopadłej do kierunku rozciągania. Granice obszarów plastycznych zostały wyznaczone metodą izochromy granicznej. Do rozdzielenia odkształceń wykorzystano metodę charakterystyk, a naprężenia zostały wyznaczone na podstawie przyjętego wieloodcinkowego modelu zależności sigma - epsilon dla materiału elementu. W pracy została przeprowadzona dyskusja otrzymanych wyników.

2

Identification of Nonlinear Viscoelastic Properties of the "Panama" Fabric

Komar W., Kłosowski P., Woźnica K.

Machine Dynamics Problems

|

2006

|

Vol. 30, No. 2

63-70

EN

Technical fabric "Panama", manufactured by Sattler Company (Germany), exhibits some nonlinear behaviour including the viscoelastic effects, during the long-term experiments. On the basis of uniaxial creep-recovery laboratory tests, conducted for five different stress levels from 10% to 50% of the ultimate force declared by the producer, an attempt on the nonlinear viscoelastic identification of the fabric properties was made. The Schapery one-integral model of nonlinear viscoelasticity was applied as the constitutive relation, describing material's behaviour in inelastic range. The power law time function was assumed to represent the transient component of the linear creep compliance. For each stress level the same procedure of the parameters identification was conducted, using the least squares method in the Levenberg-Marquardt variant. As the considered material has two thread families, warp and weft, weaved perpendicularly one to another, calculations were carried out for each thread direction individually. Results of the identification were verified and compared to the experiments' data. Good agreement between the nonlinear model representation and the tests' data of the examined technical fabric was obtained. Some remarks upon further research were included.

3

Charakterystyka tkaniny technicznej "Panama" w zakresie lepkosprężystym

Komar W.

Biuletyn Wojskowej Akademii Technicznej

|

2006

|

Vol. 55, nr 4

267-281

PL

Niniejszy artykuł zawiera część prac nad pełnym scharakteryzowaniem tkanin technicznych. Obiektem zainteresowania jest tkanina techniczna "Panama" firmy Sattler. Autor postawił sobie za cel zidentyfikowanie parametrów wybranych lepkosprężystych modeli konstytutywnych materiałów oraz ich weryfikację na podstawie prób jednoosiowego rozciągania ze stałą prędkością odkształcenia. Zaprezentowano dwa wybrane do identyfikacji modele lepkosprężyste, z których jeden jest reprezentowany liniowym równaniem różniczkowym, a drugi - nieliniową zależnością całkową. Dokonano zestawienia otrzymanych wyników z przeprowadzonej już części identyfikacji. Zaproponowano metodę ulepszającą proces identyfikacji parametrów modelu standardowego dla materiałów o charakterystykach nieliniowych. Przedstawiono aktualny stan prac nad identyfikacją kierunki dalszych badań.

EN

Technical fabrics are more often used in different industry interests. Mainly in the civil engineering structures like hanging roofs or pneumatic stores, but also as the road structures reinforcement or transporting belts. The subjected textile, considered in this paper is the technical fabric "Panama", manufactured by Sattler company (Germany). It has two identical polyester thread families: warp and weft of P2/2 weaving with double side PVC coating. Despite the anisotropy of that fabric, it has been assumed that its threads were made of the isotropic material. The research presented here is concerned with the identification of the "Panama" fabric behaviour, for each thread family separately, using the constitutive relations of linear and nonlinear viscoelasticity. The research is based on the laboratory tests of uniaxial tension with the constant strain rate. Tests were conducted for five different strain rate levels from 10⁻⁵ ; till 1.67×10⁻³ ; [1/s]. For linear representation of the examined material, the three-parameter model of viscoelastic solid was applied in a form of the differential equation, and the one-integral relation of the Schapery model was assumed to describe the nonlinear viscoelasticity of examined material. Models selected for further examination were presented more precisely. The identification process based on the linear standard model was conducted using the least squares method in the Marquardt-Levenberg variant. The calculated parameters were subsequently verified and the results were compared to the experiments. As it soon turned out, some problems with parameters determination occurred, and it was necessary to modify the linear viscoelastic model, to make it able to describe the "Panama" behaviour with reference to the tension tests. The proposed modification method was presented in the paper and improved results of material's description were compared to the experiments. Some negative aspects of the identification procedure were finally pointed out, and the next steps in the research schedule were suggested, to tend towards the main aim of this investigation, that is the entire viscoelastic characterization of the "Panama" fabric.