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CN-121997470-A - Fatigue life prediction method of riveting joint based on consideration of stress concentration coefficient of dissipation energy

CN121997470ACN 121997470 ACN121997470 ACN 121997470ACN-121997470-A

Abstract

The invention discloses a fatigue life prediction method of a riveting joint based on dissipation energy considering stress concentration coefficient, and belongs to the field of fatigue life assessment of the riveting joint. The method aims to solve the problem of accurate prediction of the fatigue life of the riveting joint under the condition that the material is plastically deformed after the rivet pierces the connected piece. The method comprises the following steps of firstly carrying out numerical simulation under the tensile load action of the riveting joint to determine a stress concentration coefficient, secondly carrying out infrared thermal image amplitude variation and constant-amplitude fatigue experiments of the riveting joint to obtain the material parameters of a dissipative energy damage model, finally constructing a fatigue life prediction model by coupling the stress concentration coefficient, and programming to calculate the fatigue life values of the riveting joint under different cyclic loads. According to the method, the calculation error caused by equivalent nominal stress is corrected through the stress concentration coefficient, the fatigue damage of the riveting joint can be represented through the intrinsic dissipation of reaction fatigue failure, the prediction precision is remarkably improved, and meanwhile, the calculation efficiency is also greatly improved through a mode of combining numerical simulation and fatigue experiments.

Inventors

  • MI CHENGJI
  • ZHANG ZHIYUAN
  • WANG SIRUI
  • Peng xinyang
  • ZHONG HUA
  • WEN CHANGXING

Assignees

  • 湖南工业大学

Dates

Publication Date
20260508
Application Date
20241105

Claims (9)

  1. 1. A method for predicting fatigue life of a riveting joint based on dissipation energy in consideration of stress concentration coefficients is characterized by comprising the following steps of establishing a finite element model of the riveting joint, defining contact conditions among a rivet, a connected piece and the connected piece, applying constraint and tensile load, outputting a maximum stress result of the riveting joint, and determining the stress concentration coefficients, carrying out a parent metal test piece amplitude-variable infrared thermal image fatigue experiment and a constant amplitude infrared thermal image fatigue experiment, recording a temperature change curve in a parent metal fatigue damage evolution process through an infrared thermal imager, determining the thermal physical characteristics of the parent metal, combining the stress concentration coefficients of the riveting joint, and determining material parameters of the dissipation energy fatigue damage model, and establishing a relationship between the stress concentration coefficients, the dissipation energy and the fatigue life, and constructing a fatigue life prediction model of the riveting joint, wherein the relationship is shown in the following formula: (1) In the middle of Is the density of the material; is the specific heat capacity of the material; the frequency of loading for the test; Is the stress ratio; Is a time constant; Is the thermal coefficient; Is a thermal constant; Energy tolerance for material fatigue failure; Is the stress concentration coefficient; The equivalent nominal stress of the test piece is obtained by calculation after the external cyclic load is determined Coefficient of stress concentration And test piece equivalent nominal stress And the fatigue life of the riveting joint under the action of the external cyclic load can be calculated.
  2. 2. The method for predicting fatigue life of a rivet joint based on dissipation energy considering stress concentration coefficient as recited in claim 1, wherein in said step one, said stress concentration coefficient Calculated according to the following formula: (2) Maximum stress of riveted joint The equivalent VonMises stress maximum value obtained by finite element simulation calculation of the riveted joint under the action of tensile load is obtained, and the test piece is equivalent to nominal stress Is the ratio of the tensile load to the cross-sectional area of the joint of the rivet.
  3. 3. The method for predicting fatigue life of a riveted joint based on dissipation energy considering stress concentration coefficients according to claim 1, wherein in the second step, a reference test piece is installed in both of the base material test piece amplitude-variable infrared thermal image fatigue test and the constant amplitude infrared thermal image fatigue test, the material of the reference test piece is consistent with the base material, and the size of the reference test piece is one half of the size of the base material test piece.
  4. 4. The method for predicting fatigue life of a riveted joint based on dissipation energy considering stress concentration coefficient according to claim 1, wherein in the second step, the amplitude of the initial loading stress level of the base metal test piece in the amplitude infrared thermal image fatigue test is equal to 0.7 times of the yield limit of the base metal, and then the initial loading stress level is gradually loaded, wherein the loading increment range is 10MPa to 100MPa, until the riveted joint is completely failed.
  5. 5. The method for predicting fatigue life of a riveted joint based on dissipation energy considering stress concentration coefficients, as recited in claim 4, wherein after 5000 cycles of loading stress levels, the test piece is replaced to the next loading stress level after cooling to room temperature.
  6. 6. The method for predicting fatigue life of a riveted joint based on dissipation energy considering stress concentration coefficient as claimed in claim 1, wherein in the second step, the initial loading stress level of the base metal test piece constant amplitude infrared thermal image fatigue test is equal to 0.7 times of the yield limit of the base metal test piece, the cyclic load is continuously applied until the test piece fails or the cycle number is greater than 10 6 , then the test piece is replaced and loaded step by step, the loading increment range is 10MPa to 100MPa, and the maximum loading stress level does not exceed the tensile strength of the riveted joint.
  7. 7. The method for predicting fatigue life of a rivet joint based on dissipating energy considering stress concentration coefficient as set forth in claim 1, wherein in said step two, said dissipating energy fatigue damage model material parameters include density of said material Specific heat capacity of the material The test loading frequency Said time constant Said thermal coefficient Said thermal constant Said material fatigue failure energy tolerance 。
  8. 8. The rivet joint fatigue life prediction method considering stress concentration coefficient based on dissipation energy as recited in claim 7, wherein said thermal coefficient And the thermal constant Determined by the following formula: (3) In the middle of The temperature rise is asymptotic temperature rise, which is the difference between the temperature of the fatigue test piece corresponding to the first inflection point of the temperature change curve of the base metal test piece under a certain loading stress level of the luffing infrared thermal image fatigue test; The temperature rise is gradually increased by the amplitude of stress and the amplitude of the base metal test piece and the infrared thermal image fatigue test And stress amplitude The thermal coefficient can be determined by least square method data fitting And the thermal constant 。
  9. 9. A method of predicting fatigue life of a riveted joint based on dissipative energy considering stress concentration coefficients as recited in claim 7, wherein the material is fatigue failure energy tolerant Calculated according to the following formula: (4) In the middle of The fatigue life of the fatigue test piece under a certain loading stress level is tested for the constant-amplitude infrared thermal image fatigue of the base metal test piece; And (3) the difference value between the temperature of the fatigue test piece corresponding to the first inflection point of the temperature change curve under the corresponding loading stress level of the constant-amplitude infrared thermal image fatigue test of the base metal test piece and the temperature of the reference test piece is obtained.

Description

Fatigue life prediction method of riveting joint based on consideration of stress concentration coefficient of dissipation energy Technical Field The invention relates to a fatigue life prediction method of a riveting joint based on dissipation energy considering stress concentration coefficient, and belongs to the field of fatigue life prediction of the riveting joint. Background The riveted joint is one of the common connection modes between sheet metal parts. Because of high forming efficiency, good connection performance and low production cost, the modified polypropylene composite material is widely applied to the fields of automobiles, rail transit, aerospace and other equipment. However, the connected parts of the riveted joint are often pierced by rivets, which results in irreversible plastic deformation, and the fatigue properties of the riveted joint are significantly impaired compared to the base material and the rivet material itself. Therefore, accurate calculation of the fatigue life of the riveted joint is a key point for ensuring safe and reliable operation of the riveted structure. With the continuous improvement of quality requirements of high-end equipment such as automobiles, rail transit, aerospace and the like by vast users, many scientific researchers deeply pay attention to the problem of fatigue life prediction of the riveting joint. The university of northwest industry discloses an electromagnetic riveting joint fatigue life prediction method (publication number: CN 103455671B), which is used for coupling residual stress in the forming process of the riveting joint through finite element simulation into a fatigue life analysis model and carrying out the fatigue life prediction of the riveting joint based on a strain fatigue life curve. The method can effectively calculate the fatigue life of the riveted joint in the stage before crack expansion, but fails to consider the fatigue life of the crack expansion stage, and the damage parameter is vector strain, so that the maximum shear strain in a critical plane is difficult to determine for the riveted joint under the action of multiple axes and multiple physical fields. The method carries out fatigue life prediction of the riveting structure based on a Paris formula, acquires a response signal of the riveting structure through an excitation signal, determines fatigue characteristic parameters by combining a neural network model, and can accurately calculate the fatigue life of the riveting structure by utilizing a large amount of data to drive a physical mechanism model. However, the method requires a large amount of experiments to observe the data such as fatigue crack length, mechanical response and the like, and obviously increases the fatigue life prediction time cost of the riveting structure. The Shanghai university of traffic discloses a fatigue failure mode prediction method (publication number: CN 116504334A) of a composite material and metal rivet bonding mixed connection structure, a material parameter prediction model based on water absorption, a chemical structure and environmental temperature is constructed, the maximum strain of the material is obtained, and the service life of the composite material and metal rivet bonding mixed connection structure is predicted by combining a material strain fatigue curve corrected by considering environmental conditions. However, the method is directed to the problem of fatigue life under complex boundary conditions of a composite structure, is very dependent on an accurate material strain fatigue curve, and how to calculate the maximum strain of a material quickly and efficiently is also limited by factors such as structural shape, boundary conditions and the like. Therefore, further research into systems is needed to accurately and efficiently characterize the fatigue damage of the riveted joint. Disclosure of Invention In order to solve the problems of low calculation precision, low efficiency and the like of the traditional method for predicting the fatigue life of the riveting joint and overcome the defects in the background technology, the invention provides a method for predicting the fatigue life of the riveting joint based on the consideration of the stress concentration coefficient of dissipation energy, which comprises the following steps: (1) Establishing a finite element model of the riveting joint, defining contact conditions among the rivet, the connected piece and the connected piece, applying constraint and tensile load, outputting a maximum stress result of the riveting joint, and determining a stress concentration coefficient; (2) Performing a parent metal test piece amplitude-variable infrared thermal image fatigue experiment and a constant amplitude infrared thermal image fatigue experiment, recording a temperature change curve in the parent metal fatigue damage evolution process through an infrared thermal imager, determining the thermophysical characteristics o