The Reduction of Stress Concentration by Tapering Threads

• Published in: Nihon Kikai Gakkai ronbunshū. A Vol. 74; no. 746; pp. 1305 - 1313
• Main Authors: KUHARA, Masahiro, XIAO, Yang, NODA, Nao-Aki
• Format: Journal Article
• Language: English; Japanese
• Published: The Japan Society of Mechanical Engineers 2008
• Subjects: Finite Element Method; Fixing Element; Machine Element; Stress Concentration
• ISSN: 0387-5008; 1884-8338
• DOI: 10.1299/kikaia.74.1305

In a bolted joint, it is known that failures usually happen at the root of the first bolt thread where the maximum stress concentration occurs. Previously several methods were proposed to reduce the stress concentration through improving bolts and nuts profile. Among those methods, tapering threads have been widely used in mechanical structures. Those types of threads are called CD bolts, which were proposed by Nishida as an effective method for stress reduction. Several experimental studies indicated that CD bolts have higher fatigue strength although little FEM analyses is available. In this study, therefore, the bolted joint with tapered threads is analyzed with the finite element method, and stress reduction effect of CD bolts is discussed with varying geometrical conditions. The reduction of the stress concentration is realized by tapering bolt thread. Then, it is found that the stress reduction is notable when the height of bolt threads is reduced significantly near the bolt heat and the nut is closer to the bolt head. According to those results, optimum conditions for stress reduction are discussed. Then, it is shown that the maximum stress can be decreased by 20% compared with the cases of standard bolts and nuts.