Deformation and strength of a cyclically bent threaded connection

Technological sciences, mechanical engineering (09T).

Applying simulations of loads distribution in threads, the disertation investigates the problems of low cycle strength of the threaded joints. More sophisticated high-cycle and low-cycle durability calculation methodologies already quantitatively assess the distribution of axial load among turns what enables a more accurate assessment of the influence of the constructional design particularities. This dissertation thesis aims to create a calculation methodology for the load distribution in the thread, intended for threaded connections cyclically bent too, and to apply this methodology for the calculation of cyclic strength. Created compatibility equation of the displacements of the elements of bent threaded connection enabled to construct the three-segmental and multi-segmental models of the distribution of bending load along turns and to introduce them in the range of the normative methodology for the fatigue calculation.

The dissertation consists of Introduction, 5 chapters, Conclusions, References and lists of published works and presentations in conferences of the author on the topic of dissertation. The introduction reveals the investigated problem, importance of the thesis and the object of research and describes the purpose and tasks of the paper, research methodology, scientific novelty, the practical significance of results examined in the paper and defended statements. The first chapter is dedicated to literature review. It covers the scope of heavily loaded threaded connections and load conditions, a review and analysis of research related to the cycle strength of threaded connections.In the second chapter is preseted the results of the experimental investigation of thread turn pair deformation and previous in the literature not mentioned an unloaded turn pair characteristic analysis. The third chapter presents the deformation scheme of the threaded connection elements, created displacements compatibility equation, differential equations analytical solutions and models for bent threaded connection – three segments and multi-segmental elastic models of bending load distribution calculations. In the fourth chapter the stud’s cycle parameters is established: for the turns load and internal bending moment and for the turns local stress also. Using comparison with experimental results, it was checked the posibility to use data of the bending load distribution in thread for calculation methodology of low-cycle durability of the stud. The fifth chapter presents two methods and mathematical models to increase cycle durability of the threaded connections. There are published 9 articles of the theme of dissertation: three in journals, which are included in Thomson ISI Web of Science list and six of conference materials. The theme of dissertation was represented in 9 reports during lithuanian and foreign conferences and seminars.

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DOI: https://doi.org/10.20334/1969-M