Duplex positioning method for increasing the fatigue life of threaded connections under eccentric loading

A new method, duplex positioning method DPM, to increase the fatigue lifetime of the threaded connection under eccentric loading is presented. When DPM is applied, the most damaged stud regions periodically are removed from risky positions by a change of the stud’s and nut’s mutual position in the axial direction alongside with a change of the stud’s position in respect to bending plane. The mathematical model for DPM enables us to predict its efficiency. To simulate the fatigue strength of the stud the following was used: Patterson’s and Kenny’s thread deflection factors, solutions for the distributions of the axial load and bending moment along the threads, Neuber’s method for the stress concentration factors in multiplier notches, Heywood’s formulas for the stress due to the thread flank loading and for the combined stresses, as well as the results of the photoelastic analysis of the araldite models under eccentric loading.

     

Optimization of the fatigue life of threaded connections by the positioning method

The presented paper addresses the problem of optimization of the fatigue life of threaded connections by the positioning method. This method presents a technique operating upon the periodic mutual change of nut and stud positions in order to increase the fatigue life. The modelling of the fatigue life of threaded connections using the positioning method is based on concept of damageability curve. A mathematical model is formulated in terms of mathematical programming taking into account technological and operation constraints. The performance and possibilities of the model are demonstrated by numerical experiments. The influence of weighting and constraints on the fatigue life of threaded connection, the influence of the heights of inter-turnings on threaded connection fatigue life and the influence of a number of positioning periods on threaded connection fatigue life when the height of inter-turnings is constant are presented.