The aim of this thesis is to characterise the mechanical properties of polyamide fiber samples at different levels of torsional loading. It is also necessary to establish a theoretical model to predict the loss of torsional stability and the transition from axial torsional symmetry to helical torsion. In this context, some basic experiments were also carried out to determine realistic values of the critical torsional load. The first part consisted of tensile tests of torsionally loaded specimens at different torsional load levels, while the second part included torsion tests of specimens that were initially unloaded. Using the data obtained from the tests, the material parameters of the polyamide fiber were determined, and our experimental results were compared with theoretical calculations. It was found that the test results and the theoretical predictions were in good agreement.
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