Experimental and analytical investigation of loosening and shakedown of the threaded joints

Abstract

In a tight threaded joint subjected to cyclic bending the regularities of crack formation and propagation possess specific faetures compared to joints subjected to the cyclic tension. The investigation results of tightening dependence on the number of cycles of threaded joints made of various steels show that a fatigue crack forms and propagates, plastic deformations develop or a structure element adapts oneself to a cyclic effect. In threaded joints subjected to tension and cyclic bending there is a link established between loosening and the fracturing process parameters such as the configuration and depth of crack. Due to such non-elastic deformation dangerous states may occur leading to deterioration of bolts. One of such states is characterised by a progressing accumulation of deformations resulting in the changes in the geometry of constructive elements. The approximate kinematic theorem has been used for the estimation of the bolt shakedown parameters in case of tension and bending.