Critical load determination for preventing rotational loosening in bolted joints under dynamic transverse loads

To ensure the reliability of bolted joints, it is essential to accurately determine the critical load that prevents rotational loosening of the nuts. In this paper, the mechanical behavior of bolted joints during tightening, after tightening, and under transverse loading was analyzed. The contact status of two mating surfaces, including the thread and nut bearing surfaces, and their ability to withstand transverse loads were calculated. Based on the conditions leading to rotational loosening, defined by the occurrence of sliding across both sets of contact surfaces, the critical condition for transverse force that precipitates rotational loosening in bolted joints has been established. Furthermore, a systematic procedure for determining this critical state of rotational loosening in bolted joint assemblies has been developed. Finite element simulations on bolted joints subjected to dynamic transverse loads, using various combinations of friction coefficients, showed results in good agreement with theoretical predictions. Finally, experimental measurements of the critical rotational loosening loads were conducted. The experimental results highlight that the decrease in clamping force due to non-rotational factors has a significant impact on the critical loads. Considering this influence and adjusting the preload accordingly, the calculated results for the critical loads are in good agreement with the experimental data.