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Establishment of Prediction Technology of Fatigue Strength in Roots of Internal Thread for Crankcase Assembly and Application in Product Development

Article of Honda R&D Technical Review Vol.22 No.2


Aluminum alloy crankcases are generally used in motorcycle engines. Fatigue fractures sometimes occur in the roots of the internal threads of the cylinder head fastening bolts and the crankshaft main bearing fastening bolts in durability tests in the prototype stage. Conventionally, theoretical evaluation of absolute values of fatigue strength in the roots of the internal threads was a challenge, so evaluation of fatigue strength had to rely on durability tests using actual engines.
This study developed technology that uses FEM analysis to theoretically evaluate the fatigue strength of the entire crankcase, including the internal thread portions of the main bolts. This technology performs parallel calculation processing on a large-scale FEM model that takes into account the forms and contact characteristics of the external and internal threads, and was found to be practical in terms of both calculation accuracy and calculation time. Examples of applying this new method to product design showed that fatigue strength in the roots of the internal threads for crankcase assembly can be enhanced without increasing the weight, by modifying the form around the bolt fastening area and the form of the bolt tip.


(1) Fukuoka, T., Yamasaki, N., Kitagawa, H., Hamada, M.: Stress Concentration at the Root of a Screw Thread (Efficient of Root Radius and Friction Coefficient), Transactions of the Japan Society of Mechanical Engineers, A, 52 (481), p. 2201-2208 (1986)
(2) Fukuoka, T., Nomura, M., Morimoto, Y.: Proposition of Helical Thread Modeling with Accurate Geometry and Finite Element Analysis, Transactions of the Japan Society of Mechanical Engineers, A, 72 (723), p. 1639-1645 (2006)
(3) Momii, H., Ikeda, S., Tanoue, M., Ushijima, K., Takahashi, N.: Stress Analysis Method for Bolt Thread under Operating Condition of Automotive Engine, 2009 JSAE Annual Congress Proceedings, No. 99-09, p. 13-16 (2009)
(4) Niino, T., Iwamoto, T., Ueda, S.: Development of simulation technology for dynamic behavior of crankshaft systems in motorcycle engines, JSAE Review, Vol. 23, p. 127-131 (2002)

Author (organization or company)

Hiroshi KURIBARA(Motorcycle R&D Center)、Junya SAITO(Motorcycle R&D Center)、Hideki SAITO(Motorcycle R&D Center)、Daisuke SEKIYA(Motorcycle R&D Center)

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