Charakterystyka tkaniny technicznej "Panama" w zakresie lepkosprężystym

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.

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.