ANALYTICAL MODELING OF SELF-LOOSENING OF BOLTED JOINTS

Self-loosening of bolted joints is a common issue in Pressure Vessel and Piping equipment. This phenomenon can not only cause the industry a lot of losses due to maintenance but can result in catastrophic incidents leading to environment and health issues. This paper presents several improvements and innovations that are brought to the subject of self-loosening of bolted joints through a study involving analytical, numerical and experimental work. A new model to prevent self-loosening of bolted joints is developed. Particular focus is put on the effect of the clamping plate thickness on the self-loosening of the joint. A fully instrumented experimental set-up, in conjunction with an M121.75 bolt, is deployed to track the bolt tension decrease with the application of an imposed cyclic transversal displacement. In addition to the measurement of the transverse relative displacement between the two clamping parts, the clamping and transverse loads are also recorded. Finally, the relative rotation between the bolt and the nut is measured by means of a rotation sensor directly installed on the nut. The results show that there is a good agreement between the analytical, numerical and experimental results. The new model is compared with FEM and experimentation for different plate thickness configurations.