Transactions of Materials and Heat Treatment

Title：Fracture characteristics of bending-torsion composite fatigue for flareless tube joint test piece and stress inversion method of fracture position

Authors： Deng Ying Zheng Yuanbo Zhang Rongxia Wu Wei Zeng Yuansong Li Rongsheng

Unit： AVIC Manufacturing Technology Institute Aeronautical Key Laboratory for Plastic Forming Technologies Beijing Key Laboratory of Digital Plasticity Forming Technology and Equipment

KeyWords： flareless tube joint bending torsion compound fatigue fracture characteristics load calculation

ClassificationCode：TH16

year,vol(issue):pagenumber：2021,46(4):229-234

Abstract：

The fracture characteristics of a certain type of flareless tube joint test piece in fatigue test were analyzed, the macroscopic fracture showed stepped shape, and there were obvious circumferential friction marks on the surface of fracture formation, which was not perpendicular to the tube joint axis in its partial area. Then, at the microscopic scale, there were friction marks on the contact surface of tube and tube sleeve at multiple angles of 0°, 45° and -55° with the tube axis, indicating that the test device had applied an unstable additional torsional load on the test piece and the test piece had fatigue failure under the action of combined bending and torsion loads. Furthermore, the influences of bending-torsion load amplitude and phase difference on friction mark characteristics on the contact surface of tube and tube sleeve were studied by combining finite element method and theoretical analysis. The results show that the relative magnitude of load in the two directions affects the slope of angle between friction direction and tube axis direction, and the phase difference between the loads affects the curvature of friction marks. Based on the above, the amplitude of additional torsional stress at the fracture position of test piece is calculated to be 401.1 MPa.

Funds：

邓瑛（1980-），男，博士，正高级工程师 E-mail：yingdeng@buaa.edu.cn

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