The Optimum Preload of a Threaded Joint Against Joint Separation

The strength of a threaded joint loaded by the external load that separates the joint is determined by two main parameters: the joint integrity and the bolt strength. The parts are compressed by the nut tightening force. The bolt is stretched and twisted at the same time by the torque in the thread. In engineering calculations, the stress in the cross section of the bolt is brought to an equivalent stress in which the tangential component is considered as part of the normal stress of the tightening force. To increase the accuracy of the calculation, the equivalent stress is dependent on the coefficient of friction in the thread and the thread size. For this purpose, the equivalent stress factor is used when calculating the bolt load factor. It is proposed to determine the bolt safety load factor depending on the standard proof load. As the preload increases, the bolt safety load factor decreases, while the joint tightness load factor increases. The optimum preload of the threaded joint is calculated, ensuring the equality of both load factors. The range of variation in the preload is determined, within which the bolt safety load factor and the joint tightness load factor do not fall below 1.

References

[1] Ivanov M.N., Finogenov V. A. Detali mashin [Machine parts]. Moscow, Vysshaia shkola publ., 2008. 408 p.

[2] GOST R ISO 898-1–2011. Mekhanicheskie svoistva krepezhnykh izdelii iz uglerodistykh i legirovannykh stalei. Chast’ 1. Bolty, vinty i shpil’ki ustanovlennykh klassov prochnosti s krupnym i melkim shagom rez’by [State Standard 898-1–2011. Mechanical properties of fasteners made of carbon steel and alloy steel. Part 1. Bolts, screws and studs of specified property classes with coarse thread and fine pitch thread]. Moscow, Standartinform publ., 2013. 54 p.

[3] GOST 24705–2004. Osnovnye normy vzaimozameniaemosti. Rez’ba metricheskaia. Osnovnye razmery [State Standard 24705–2004. ISO general-purpose metric screw threads–basic dimensions (MOD)]. Moscow, Standartinform publ., 2005. 20 p.

[4] Syromiatnikov V.S., García J.M., Ortega M.G, Zamora L.A. Raschet momenta i ugla zatiazhki v rez’bovom soedinenii [Calculation of torque and tightening angle of a threaded joint]. Innovatsii i investitsii [Innovation and Investment]. 2013, no. 4, pp. 197–201.

[5] Iosilevich G.B., Lebedev P.A., Streliaev V.S. Prikladnaia mekhanika [Applied mechanics]. Moscow, Mashinostroenie publ., 2013. 576 p.

[6] Solov’ev V.L. Obespechenie nadezhnosti mashin pri ikh remonte v sel’skom khoziaistve putem povysheniia tochnosti i ravnomernosti zatiazhki gruppovykh rez’bovykh soedinenii. Diss. kand. tekhn. nauk [Ensuring reliability of the machines at their repair in agriculture by improving the accuracy and uniformity of the tightening group of threaded connections. Cand. tech. sci. diss.]. Omsk, 2014. 132 p.

[7] Detali mashin [Machine parts]. Ed. Riakhovskii O.A. Moscow, Bauman Press, 2014. 465 p.

[8] Anur’ev V.I. Spravochnik konstruktora-mashinostroitelia [Designer Directory-Machinist]. Vol. 2. Moscow, Mashinostroenie publ., 2006. 860 p.

[9] Budynas R., Nisbett K. Shigley’s mechanical engineering design. McGraw-Hill, 2008. 1059 p.

[10] Valladares D., Carrera M., Castejon L., Martin C. Development of a Numerical Technique for the Static Analysis of Bolted Joints by the FEM. Lecture Notes in Engineering and Computer Science. Proceedings of the World Congress on Engineering 2013 Vol III, WCE 2013, July 3–5, 2013, Imperial College London, London, U.K., 2013, vol. 3, pp. 1791–1796.