Abstract
In this study, Kachanov–Rabotnov model and stress relaxation damage constitutive equations deduced from Kachanov–Rabotnov model were applied to analyze the creep damage and to predict life for threaded connection structure at high temperature with finite element method. The parameters of Kachanov–Rabotnov model were obtained by fitting the results of creep experiments for titanium alloy at 650°C. Based on the experimental and finite element analysis results for standard specimen, a creep failure criterion was established. Then the influences of the external tensile load on the creep damage and life, as well as the stress relaxation on the initial preload, were studied. The analysis of stress relaxation for bolt shows that the stress relaxation has a remarkable effect on the bolt preload. The preloads decrease to a determined value with creep time and remain almost unchanged later. When the determined value is less than the required preload acting on the bolt, the structure will fail due to insufficient preload caused by stress relaxation.
Highlights
Bolted connection is an important fastening member widely used in gas turbine, steam pipes, boilers, and other high temperature systems
The previous study was mostly focused on the analysis of creep damage for bolt materials, while little attention was given to creep damage and stress relaxation of threaded connection structures at high temperature
Uniaxial creep test for titanium alloy was conducted at 650°C under different stress, and the results are listed in Table 1.15 The elastic modulus and Poisson ratio of titanium alloy at 650°C are 89.5 GPa and 0.3, respectively, and the yield strength is 450 MPa, and the creep parameters in equation (1), derived from experimental results listed in Table 1, were shown in Table 2.15 On the other hand, we take a = 0 based on the comparison between creep experimental and finite element method (FEM)
Summary
Bolted connection is an important fastening member widely used in gas turbine, steam pipes, boilers, and other high temperature systems. The previous study was mostly focused on the analysis of creep damage for bolt materials, while little attention was given to creep damage and stress relaxation of threaded connection structures at high temperature. The creep damage and life prediction of bolt under constant axial tensile load at high temperature were analyzed using FEM.
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