CN-116542033-B - Bolt axial force attenuation prediction method considering bolt creep

CN116542033BCN 116542033 BCN116542033 BCN 116542033BCN-116542033-B

Abstract

The invention discloses a bolt shaft force attenuation prediction method considering bolt creep, which is characterized by comprising the following steps of 1) obtaining a creep curve of a standard bolt for connection at a use temperature, 2) determining a functional relation between rigidity of a bolt model in bolt connection and time according to the creep curve, and 3) calculating a residual shaft force at a selected time according to the functional relation between rigidity of the bolt model and time and the functional relation between the residual shaft force and time, so as to predict the shaft force attenuation of the bolt. According to the invention, through the establishment of the equivalent model, the relation between the change rule of the internal stress and strain of the bolt and the external load is researched, so that the change rule of the pretightening force of the bolt in a screwed state due to the creep effect in a medium-high temperature environment is summarized, a mathematical function model of the pretightening force of the bolt along with the change of time is established, and the residual axial force and the loosening life of the bolt are predicted.

Inventors

WANG DECHENG
LI WENBO
DING BAOPING
CHENG PENG
SHAO CHENXI
LIU LINGXIAO

Assignees

中机生产力促进中心有限公司

Dates

Publication Date: 20260508
Application Date: 20230425

Claims (2)

1. A method for predicting the attenuation of the axial force of a bolt by considering the creep of the bolt is characterized by comprising the following steps: 1) Obtaining a creep curve of a standard bolt for connection at a use temperature; 2) Determining the functional relation between the rigidity of the bolt model in the bolt connection and time according to the creep curve; 3) According to the functional relation between the rigidity of the bolt model and time and the functional relation between the residual axial force and time, calculating the residual axial force at the selected time, and realizing the prediction of the coupling bolt axial force attenuation; Wherein the residual axial force is a function of time, F (t) is the residual axial force at time t, F (0) is the pretightening force of the bolt connection, J B (t) is the compliance of the bolt model at time t, J B (0) is the compliance of the bolt model at time t=0, J U is the compliance of the upper clamped piece, and J D is the compliance of the lower clamped piece; The bolt model is equivalent to three units connected in series, wherein the first unit is a spring with the rigidity of K 1 and represents a pure elastic part, the second unit is an elastic-damping part which is formed by connecting a spring with the rigidity of K 2 and a damper with the damping rate of C 2 in parallel, the third unit is a damper with the damping rate of C 1 and represents a pure damping part, the function relation of the rigidity of the bolt model and time is that, Wherein K (t) is the inverse of the stiffness, i.e. the compliance, of the bolt model at time t; Determining the function relation between the rigidity of the bolt model and time in the bolt connection according to the creep curve, namely selecting t 0 、t 1 、t 2 、t 3 points in the creep curve, wherein t 0 is a point with time 0, substituting the points into an equation of the function relation between the rigidity of the bolt model and time to solve the points that K 1 ;t 1 and t 2 are far more than 0, substituting the points into an equation of the function relation between the rigidity of the bolt model and time to solve the points that K 2 and C 1 ;t 3 are close to 0 after solving K 1 , substituting the points into an equation of the function relation between the rigidity of the bolt model and time to solve C 2 after solving K 1 、K 2 and C 1 , and finally determining the equation of the function relation between the rigidity of the bolt model and time; The strain rate of the creep curves at t 1 and t 2 is less than 5×10 -4 /hr, and t 3 is less than or equal to 20 hr; Wherein, the 、、 Wherein L is the effective clamping length of each element, E is the elastic modulus of each element at the use temperature, and A is the effective stress cross-sectional area of each element.
2. A method of predicting bolt shaft force attenuation taking into account bolt creep according to claim 1, wherein the finally determined curve of the functional relation of the rigidity of the bolt model with time is compared with the creep test result, and when the deviation between the fitted curve and the creep test result is greater than the expected value, the selection of t 1 、t 2 、t 3 points is further adjusted to recalculate and fit until the deviation between the fitted curve and the creep test result is less than the expected value.

Description

Bolt axial force attenuation prediction method considering bolt creep Technical Field The invention relates to the technical field of testing and predicting of bolt connection, in particular to a bolt shaft force attenuation prediction method considering bolt creep. Background The main function of the bolt is to ensure a reliable transfer of force (or movement) between the coupled structures. When the coupled piece is a pressure vessel or a pipeline, the threaded coupling structure is also required to ensure that the assembly body has good tightness. Whether fastening, sealing or transmission is achieved, it is premised on a sufficiently large clamping force between the coupled structures. Intensity analysis and life analysis of this component have been a concern. Bolt looseness is ubiquitous and difficult to avoid, and a bolt axial force attenuation process needs to be predicted before the bolt is used, so that guidance is provided for the use, maintenance and the like of the bolt. However, the axial force attenuation process of the bolt connection structure is extremely complex, the influence factors are more, and the bolt connection looseness degree and a plurality of influence factors have complex nonlinear relations. In the related technology, the influence rules of partial influence factors are qualitatively summarized through a large amount of test data, but no model with simple form and accurate prediction precision can be used for predicting the residual axial force of the bolt connection structure under different working conditions and reflecting the axial force attenuation degree of the bolt, so that the reliability and attenuation characteristic of the bolt connection structure cannot be ensured. In particular, the effect of temperature on the attenuation of the bolt shaft force is very significant, whereas existing prediction methods, such as patent applications CN202111375331.X and CN201810578081.1, which, while also providing a method for predicting bolt life or bolt preload, do not take into account temperature as a major factor, and therefore have significant application limitations and accuracy problems. Disclosure of Invention In view of the above, the invention provides a method for predicting the loosening life of a bolt at medium and high temperature based on the self loosening phenomenon caused by the stress relaxation of the bolt due to the creep effect in the high temperature working environment, and the expression of the bolt pre-tightening force changing with time is established in the form of a mathematical model, so that the influence of temperature, pre-tightening force, bolt size and the like on the bolt shaft force attenuation and the bolt life is fully considered. In order to achieve the above purpose, the present invention adopts the following technical scheme: a method for predicting the attenuation of the axial force of a bolt by considering the creep of the bolt is characterized by comprising the following steps: 1) Obtaining a creep curve of a standard bolt for connection at a use temperature; 2) Determining the functional relation between the rigidity of the bolt model in the bolt connection and time according to the creep curve; 3) According to the functional relation between the rigidity of the bolt model and time and the functional relation between the residual axial force and time, calculating the residual axial force at the selected time, and realizing the prediction of the coupling bolt axial force attenuation; Wherein the residual axial force is a function of time, F (t) is the residual axial force at time t, F (0) is the pretightening force of the bolt connection, J B (t) is the compliance of the bolt model at time t, J B (0) is the compliance of the bolt model at time t=0, J U is the compliance of the upper clamped piece, and J D is the compliance of the lower clamped piece. It is further preferred that the bolt model is equivalent to three units in series, wherein the first unit is a spring with a stiffness of K 1 representing a pure elastic part, the second unit is a spring-damped part composed of a spring with a stiffness of K 2 and a damper with a damping rate of C 2 in parallel, the third unit is a damper with a damping rate of C 1 representing a pure damped part, the stiffness of the bolt model as a function of time,Wherein K (t) is the inverse of J B (t) which is the rigidity of the bolt model at time t. Further preferably, the functional relation between the rigidity and time of the bolt model in the bolt connection is determined according to the creep curve, t 0、t1、t2、t3 points are selected in the creep curve, wherein t 0 is a point with time 0, the point with time 0 is substituted into an equation of the functional relation between the rigidity and time of the bolt model to solve the point that K 1;t1 and t 2 are far more than 0, the point with time 0 is substituted into an equation of the functional relation between the rigidity and time of the bolt