Theoretical and practical studies of this phenomenon indicate that the top face of the nut contracts in a radial direction while its bearing surface expands. The net effect of this dilation is to reduce the shear area of both the internal and external thread. The stripping strength of an assembly can be improved by increasing the width across flats of the nut, or boss diameter, up to about 1.9 times the nominal thread diameter. This increases the stiffness locally around the internal thread and reduces radial expansion. Bending The tensile force present in the fastener during the tightening process results in a degree of thread bending between internal and external threads.
Thread bending reduces the shear area of both internal and external threads.
A dominating factor controlling the degree of thread bending is the ratio between the strength of internal and external threads. The strength ratio is the ratio between the force necessary to cause the nut thread to strip, divided by the force required to cause the bolt thread to strip. To assist the Engineer in overcoming the problems associated with the use of threaded fasteners and bolted joints, Bolt Science has developed a number of computer programs . These programs are designed to be easy to use so that an engineer without detailed knowledge in this field can solve problems related to this subject. All Trademarks are acknowledged.