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Nonlinear Crest-Cut-Off Method for Reducing the Stress Concentration of Bolt With Many Threads: Application in the Main Bolt of HTGR’s RPV

[+] Author Affiliations
Jiaqing Zhao, Zhengming Zhang

Tsinghua University, Beijing, China

Paper No. ICONE21-16457, pp. V002T03A051; 6 pages
  • 2013 21st International Conference on Nuclear Engineering
  • Volume 2: Plant Systems, Construction, Structures and Components; Next Generation Reactors and Advanced Reactors
  • Chengdu, China, July 29–August 2, 2013
  • Conference Sponsors: Nuclear Engineering Division
  • ISBN: 978-0-7918-5579-9
  • Copyright © 2013 by ASME


For the standard thread, severe stress concentration appears in the root of first several threads which share the major part of bolt load, and this is also an important issue in the design of the main bolt thread in the High Temperature Gas-cooled Reactor’s (HTGR’s) Reactor Pressure Vessel (RPV). The linear crest-cutoff method (LCCOM) linearly cuts down the height of the engaged threads near the bolt head, and it could reduce the stress concentration at the roots of first several threads. However, as revealed in finite element simulation, when there are as many as forty threads in the bolt, even though the axial force shared by the first thread could be decreased by LCCOM, the axial force shared by subsequent threads are still very high, which are often larger than that by the first thread. To settle this problem, a nonlinear crest-cut-off method (NCCOM) is proposed, which employs the curved thread profile of quadratic polynomial function, instead of tapered profile of linear function in LCCOM. The proposed curved thread profile has one additional degree of freedom, and it could also be degenerated to tapered profile. As for the main bolt of forty threads in the HTGR’s RPV, the suitable parameters of curved profile are determined by the intensive numerical simulations. The results show that the proposed NCCOM yields lower axial force of the first several threads, and produces lower stress at the roots of threads in the bolt compared with LCCOM.

Copyright © 2013 by ASME



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