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Tensile strength of fibrous yarns and composites
Rypl, Rostislav ; Šejnoha,, Michal (referee) ; Zeman,, Jan (referee) ; Vořechovský, Miroslav (advisor)
Technical textiles play a highly important role in today's material engineering. In fibrous composites, which are being applied in a number of industrial branches ranging from aviation to civil engineering, technical textiles are used as the reinforcing or toughening constituent. With growing number of production facilities for fibrous materials, the need for standardized and reproducible quality control procedures becomes urgent. The present thesis addresses the issue of tensile strength of high-modulus multifilament yarns both from the theoretical and experimental point of view. In both these aspects, novel approaches are introduced. Regarding the theoretical strength of fibrous yarns, a model for the length dependent tensile strength is formulated, which distinguishes three asymptotes of the mean strength size effect curve. The transition between the model of independent parallel fibers applicable for smaller gauge lengths and the chain-of-bundles model applicable for longer gauge lengths is emphasized in particular. It is found that the transition depends on the stress transfer or anchorage length of filaments and can be identified experimentally by means of standard tensile tests at different gauge lengths. In the experimental part of the thesis, the issue of stress concentration in the clamping has been addressed. High-modulus yarns with brittle filaments are very sensitive to stress concentrations when loaded in tension making the use of traditional tensile test methods difficult. A novel clamp adapter for the Statimat 4U yarn tensile test machine (producer: Textechno GmbH) has been developed and a prototype has been built. A test series comparing yarns strengths tested with the clamp adapter and with commonly used test methods has been performed and the results are discussed. Furthermore, they are compared with theoretical values using the Daniels' statistical fiber-bundle model.
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Tensile strength of fibrous yarns and composites
Rypl, Rostislav ; Šejnoha,, Michal (referee) ; Zeman,, Jan (referee) ; Vořechovský, Miroslav (advisor)
Technical textiles play a highly important role in today's material engineering. In fibrous composites, which are being applied in a number of industrial branches ranging from aviation to civil engineering, technical textiles are used as the reinforcing or toughening constituent. With growing number of production facilities for fibrous materials, the need for standardized and reproducible quality control procedures becomes urgent. The present thesis addresses the issue of tensile strength of high-modulus multifilament yarns both from the theoretical and experimental point of view. In both these aspects, novel approaches are introduced. Regarding the theoretical strength of fibrous yarns, a model for the length dependent tensile strength is formulated, which distinguishes three asymptotes of the mean strength size effect curve. The transition between the model of independent parallel fibers applicable for smaller gauge lengths and the chain-of-bundles model applicable for longer gauge lengths is emphasized in particular. It is found that the transition depends on the stress transfer or anchorage length of filaments and can be identified experimentally by means of standard tensile tests at different gauge lengths. In the experimental part of the thesis, the issue of stress concentration in the clamping has been addressed. High-modulus yarns with brittle filaments are very sensitive to stress concentrations when loaded in tension making the use of traditional tensile test methods difficult. A novel clamp adapter for the Statimat 4U yarn tensile test machine (producer: Textechno GmbH) has been developed and a prototype has been built. A test series comparing yarns strengths tested with the clamp adapter and with commonly used test methods has been performed and the results are discussed. Furthermore, they are compared with theoretical values using the Daniels' statistical fiber-bundle model.
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