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Influence of structure of the yarn on mechanical characteristics of yarns exposed to dynamic stress

100%

Tumajer P. , Ursíny P. , Bílek M. , Moučková E. , Pokorna M.

tom Vol. 12, no. 2

44--49

This paper is a direct follow-up of the paper [1] describing in detail the VibTex equipment, which facilitates testing of textiles in a wide range of frequencies of their extension, as well as the determination of corresponding dynamic modules and loss angles. This equipment has been employed for testing polyester yarns of concordant fineness manufactured on ring and rotor spinning frames. At the same time, the material concerned has been subjected to a standard strength test. Therefore, the results of experimental measuring published in this paper allow us to assess the effect of the chosen spinning technology upon the mechanical properties of polyester yarns both at their static and dynamic loading. The introductory section of the paper contains a theoretical analysis of the effect of the chosen manner of spinning upon the mechanical characteristics of yarns. The experimental section indicates the results of measurements at static and dynamic loading, and the final section of the paper confronts the obtained pieces of knowledge with theory. This paper is part of a larger group of publications concerned with the behaviour of various linear textiles when exposed to dynamic loading (see [1],[2], [4], [5], [6]).

Statistical damage constitutive model for rocks subjected to cyclic stress and cyclic temperature

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Zhou S. W. , Xia C.-C. , Zhao H. B. , Mei S. H. , Zhou Y.

tom Vol. 65, no. 5

893--906

A constitutive model of rocks subjected to cyclic stress–temperature was proposed. Based on statistical damage theory, the damage constitutive model with Weibull distribution was extended. Influence of model parameters on the stress–strain curve for rock reloading after stress–temperature cycling was then discussed. The proposed model was initially validated by rock tests for cyclic stress–temperature and only cyclic stress. Finally, the total damage evolution induced by stress–temperature cycling and reloading after cycling was explored and discussed. The proposed constitutive model is reasonable and applicable, describing well the stress–strain relationship during stress–temperature cycles and providing a good fit to the test results. Elastic modulus in the reference state and the damage induced by cycling affect the shape of reloading stress–strain curve. Total damage induced by cycling and reloading after cycling exhibits three stages: initial slow increase, mid-term accelerated increase, and final slow increase.

Mechanical Properties Of Traditional And Nanofibre Textiles

80%

Ursíny P. , Bílek M. , Moučková E. , Pokorná M. , Tumajer P. , Wiener J.

tom Vol. 15, no. 3

198--206

This study deals with a comparison of mechanical properties of a conventional yarn and a textile from nanofibres. The conventional yarn represents the textile objects with high degree of orientation of fibres and the textile from nanofibres represents the textile objects with low degree of orientation of fibres. The theoretical section is concerned with the issue of internal structure of plied yarn and resulting differences in the orientation and straightening of fibres and in utilisation of deformation properties of fibres in comparison to the referred nano textile. The experimental section describes the manner of realisation of both static and dynamic tests of conventional yarn and strips of nanofibres. The results show differences in the mechanical properties of conventional yarn and textile strip from nanofibres under static and dynamic loading conditions. The processing technology of conventional yarn has been verified in the long term. But textiles from nanofibres are a relatively new material and mechanical properties of the detected differences point out possible problems with their behaviour during standard technological processes.