Calculation of Yield Shear Load for the AA2017-T3 Internal Thread with Various Assumptions

The aim of this paper is the selection of a formula to calculate the yield shear load of internal thread. Two stress states introduced into the internal thread were studied by considering two ways of tightening such as screw torquing and screw tensioning methods. Different expressions of yield shear load were developed based on various assumptions regarding the location of the maximum shear stress, stress distribution and way of yield shear strength determination. Threaded assembly joining the AA2017-T3 aluminum internal thread and steel screw of grade 8.8 was considered as an example to select the adequate assumptions. The quality of the screw was chosen so that its thread has a higher resistance than the internal thread. Two devices were used to determine experimentally the yield shear load of internal thread for each tightening method: torquing and tensioning. The comparison between the experimental results showed that the yield shear load for torquing is only three-fifths of load reached with tensioning method. The comparison of experimental and calculated values of yield shear load allowed to justify the improvement obtained in tensioning method. For the two ways of tightening, this comparison also led to identify the adequate assumptions for which the analytical expressions predict accurately the yield shear loads.