Effect of Thread Shape on Screw Stress Concentration by Photoelastic Measurements

[+] Author and Article Information
E. Dragoni

Department of Mechanics, University of Bologna, Viale Risorgimento, 2, 40136 Bologna, Italy

J. Offshore Mech. Arct. Eng 116(4), 228-232 (Nov 01, 1994) (5 pages) doi:10.1115/1.2920156 History: Received January 01, 1993; Revised May 02, 1994; Online June 12, 2008


The screw stress concentration for six nut-bolt connections embodying three different thread profiles and two nut shapes is measured photoelastically. Buttress (nearly zero flank angle), trapezoidal (15-deg flank angle), and triangular (30-deg flank angle) thread forms are examined in combination with standard and lip-type nuts. The effect of the thread profile on the screw stress concentration appears to be dependent upon the kind of nut considered. If the fastening incorporates a standard nut, the buttress thread is stronger than the triangular one, which, in turn, behaves better than the trapezoidal contour. The improvement is roughly a 20-percent reduction in the stress concentration factor from the trapezoidal to the buttress thread. In the case of lip nut, conversely, this tendency is somewhat reversed, with the trapezoidal thread performing slightly (but not decidedly) better than the other two shapes. Finally, averaged over all three thread forms, the lip nut exhibits a stress concentration factor which is about 50 percent lower than that of the standard nut.

Copyright © 1994 by The American Society of Mechanical Engineers
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