Method for predicting fatigue life of ring groove rivet fastener by considering influence of coating thickness and local plasticity

Abstract

The invention provides a method for predicting the fatigue life of a ring groove rivet fastener by considering the coating thickness influence and the local plasticity influence. According to the method, the coating thickness of a connecting plate and the influence of rivet hole contact local plasticity nonlinear stress are considered. The equivalent method provided by the invention is convenient for engineering application, is simple and practical, considers the equivalent stress of the coating thickness influence and the local plasticity influence, and can avoid the limitations of large calculation amount and difficulty in convergence in elastic-plastic finite element analysis.

Description

Technical Field

[0001] This application relates to a method for predicting the fatigue life of structures, and more particularly to a method for predicting the fatigue life of rivet fasteners. Background Technology

[0002] Ring groove rivets, also known as Hooke rivets, are a type of rivet with a unique ring-shaped groove structure. The key to ring groove rivet connections lies in generating an axial preload that presses the connected parts together through the rivet. Achieving the designed axial force ensures sufficient friction between the contact surfaces of the connected parts to transfer and bear the load. Factors such as plastic deformation losses due to uneven surfaces of the connected parts, surface coating embedding losses, surface coating creep, and fretting wear will all lead to a decrease in the axial force of the ring groove rivet connection. If the initial axial preload generated during tightening is lower than the set target value, it will cause relative slippage and separation of the connected parts, leading to problems such as rivet loosening and fatigue fracture.

[0003] Existing methods for calculating the fatigue life of riveted structures include fracture mechanics, the main SN curve method, and the local stress-strain method. However, existing methods are difficult to consider the influence of the plate coating thickness on the fatigue life of the connectors. Current research lacks an accurate evaluation method for the friction performance between the connectors of riveted structures.

[0004] The fatigue fracture process of grooved rivet joint specimens can be divided into two stages: the slip failure stage under inter-plate frictional bearing and the plastic deformation stage under rivet-plate contact compression bearing. During actual load-bearing, local plastic deformation occurs at the rivet-plate contact point. Considering only the nominal stress under linear elastic conditions will lead to errors in stress identification and life prediction. Therefore, it is necessary to conduct elastoplastic finite element analysis on the riveted specimens. However, elastoplastic finite element analysis has limitations such as large computational load and difficulty in convergence. In engineering, a simple and practical equivalent method is needed to calculate the true local stress of the component. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and to propose an improved method for calculating the fatigue life of riveted joints.

[0006] Therefore, some embodiments of the present invention propose a method for predicting the fatigue life of ring groove rivet fasteners considering the effects of coating thickness and local plasticity, comprising: step S100, performing finite element analysis on the connection structure including the rivet joint; step S300, measuring the coating thickness of the plate; step S400, calculating a coating thickness sensitivity factor based on the measured coating thickness; step S500, calculating a stress concentration factor considering the effect of coating thickness based on the calculated coating thickness sensitivity factor; and step S600, calculating a stress concentration factor K considering the effect of coating thickness. fThe maximum stress at the stress concentration point of the riveted component is equivalent to local plastic stress, and the equivalent stress considering the influence of coating thickness and local plasticity is calculated. Based on the above calculation results, the elastic-plastic strain considering the influence of coating thickness in the stress concentration area of ​​the riveted joint is calculated. In step S700, the calculated elastic-plastic strain considering the influence of coating thickness is substituted into the Manson-Conffin formula to complete the fatigue life prediction.

[0007] In some embodiments, the method further includes determining whether to consider the influence of the coating thickness of the board before step S300; if so, step S300 is executed; otherwise, step S500 is executed.

[0008] In some embodiments, the plate coating thickness is defined as a dimensionless coating thickness without angiographic dimensions.

[0009] In some embodiments, the Manson-Conffin formula is:

[0010] In the formula, σ f ε is the fatigue strength coefficient, b is the fatigue strength index, c is the fatigue ductility index, and ε is the fatigue strength coefficient. f is the fatigue ductility coefficient, and N is the fatigue life.

[0011] In some embodiments, the Manson-Conffin formula is:

[0012]

[0013] In the formula, σ m For the mean stress, σ f ε is the fatigue strength coefficient, b is the fatigue strength index, c is the fatigue ductility index, and ε is the fatigue strength coefficient. f is the fatigue ductility coefficient, and N is the fatigue life.

[0014] The advantages of the method proposed in this application include at least the following: This invention considers the frictional properties between riveted structural connectors, takes into account the influence of coating thickness on axial force loss based on coating thickness measurement data, and calculates the fatigue life of the ring groove rivet fastener accordingly. This invention proposes a simple and practical equivalent method that is easy to apply in engineering. Its equivalent stress, which considers the influence of coating thickness and local plasticity, avoids the limitations of large computational load and difficulty in convergence inherent in elastoplastic finite element analysis. Attached Figure Description

[0015] Figure 1 This is a flowchart of an embodiment of the fatigue life prediction method for ring groove rivet fasteners that takes into account the effects of coating thickness and local plasticity, according to this application.

[0016] Figure 2This is a flowchart of another embodiment of the fatigue life prediction method for ring groove rivet fasteners that takes into account the effects of coating thickness and local plasticity according to this application. Detailed Implementation

[0017] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The advantages of the features of this application will become apparent from the following detailed description.

[0018] It should be understood that although the description of the embodiments uses a numbered approach to represent the steps, the order of the steps is not determined by these numbers, but rather by the principles of the present invention and the specific description. For example, although the steps are numbered S100 and S200 respectively, they can be performed simultaneously, or step S200 can be performed first, followed by step S100.

[0019] This application proposes an equivalent stress method that considers the effects of coating thickness and local plasticity, establishing a novel method for calculating the fatigue life of riveted joints. This method introduces a calculation method for the coating thickness sensitivity factor of ring groove rivet connectors, thus enabling the new method to account for the influence of the connector coating thickness on axial force loss.

[0020] An embodiment of this application proposes... Figure 1 The method shown includes performing finite element analysis on the connection structure including the rivet joint, step S100.

[0021] Measuring the coating thickness t of the sheet metal * Step S300. For ease of description, t can be defined. * For the dimensionless coating thickness without unitization, t * =t / t ref , where t ref =1μm.

[0022] Based on the measured coating thickness t of the plate * The coating thickness sensitivity factor f is calculated using formula (1). c :

[0023] f c =5.969×10 -4 ×t * +1.861×10 -5 ×t *2 Formula (1), i.e. step S400;

[0024] Based on the calculated coating thickness sensitivity factor f c The stress concentration factor K, considering the effect of coating thickness, is calculated using formula (2). f Step S500 In the formula, σmax S represents the maximum stress at the stress concentration point of the riveted component, and S is the nominal stress.

[0025] The stress concentration factor K, calculated to account for the effect of coating thickness, is... f The maximum stress at the stress concentration point of the riveted component is equivalent to local plastic stress. Based on formula (3), the equivalent stress σ considering the influence of coating thickness and local plastic stress is calculated. epf : In the formula, E is the elastic modulus, k` is the cyclic strength coefficient, and n` is the cyclic hardening exponent. Based on the above calculation results, the elastic-plastic strain ε of the stress concentration area of ​​the riveted joint considering the influence of coating thickness is calculated using formulas (3) and (4). epf Step S600

[0026] The calculated elastic-plastic strain ε, which takes into account the effect of coating thickness, is then used. epf Substituting into the Manson-Conffin formula shown in formula (5), fatigue life prediction is completed. Step S700:

[0027] In the formula, σ m For the mean stress, σ f ε is the fatigue strength coefficient, b is the fatigue strength index, c is the fatigue ductility index, and ε is the fatigue strength coefficient. f is the fatigue ductility coefficient, and N is the fatigue life.

[0028] Example 2:

[0029] Another embodiment of this application proposes... Figure 2 The method shown includes performing finite element analysis on the connection structure including the rivet joint, step S100;

[0030] Step S200: Determine whether to consider the influence of the coating thickness on the board. It should be understood that in some embodiments, such as Embodiment 1, this determination step may be omitted, and the coating thickness on the board may be considered directly.

[0031] If the thickness of the coating on the sheet metal is taken into account, then the coating thickness t is measured. * Step S300. For ease of description, t can be defined. * For the dimensionless coating thickness without unitization, t * =t / t ref , where t ref =1μm.

[0032] Based on the measured coating thickness t of the plate * The coating thickness sensitivity factor f is calculated using formula (1). c:

[0033] f c =5.969×10 -4 ×t * +1.861×10 -5 ×t *2 Formula (1), i.e. step S400;

[0034] Based on the calculated coating thickness sensitivity factor f c The stress concentration factor K, considering the effect of coating thickness, is calculated using formula (2). f Step S500:

[0035] In the formula, σ max Let S be the maximum stress at the stress concentration point of the riveted component, and S be the nominal stress. If the thickness of the plate coating is not considered, the stress concentration factor K can be directly calculated based on formula (2). f Calculations and subsequent lifetime prediction.

[0036] The stress concentration factor K, calculated to account for the effect of coating thickness, is... f The maximum stress at the stress concentration point of the riveted component is equivalent to local plastic stress. Based on formula (3), the equivalent stress σ considering the influence of coating thickness and local plastic stress is calculated. epf : In the formula, E is the elastic modulus, k` is the cyclic strength coefficient, and n` is the cyclic hardening exponent.

[0037] Based on the above calculation results, the elastic-plastic strain ε of the stress concentration area of ​​the riveted joint, considering the influence of coating thickness, is calculated using formulas (3) and (4). epf ,

[0038] The calculated elastic-plastic strain ε, which takes into account the effect of coating thickness, is then used. epf Substituting into the Manson-Conffin formula shown in formula (5), fatigue life prediction is completed:

[0039] In the formula, σ f ε is the fatigue strength coefficient, b is the fatigue strength index, c is the fatigue ductility index, and ε is the fatigue strength coefficient. f is the fatigue ductility coefficient, and N is the fatigue life.

[0040] As alternatives to the two embodiments described above, other forms of the Manson-Conffin formula also fit the applicable scenarios of this invention. The Manson-Conffin formula includes different forms, such as the form considering average stress, as shown in formula (6):

[0041]

[0042] In the formula, σ m For the mean stress, σ f ε is the fatigue strength coefficient, b is the fatigue strength index, c is the fatigue ductility index, and ε is the fatigue strength coefficient. f is the fatigue ductility coefficient, and N is the fatigue life.

[0043] In particular, according to embodiments of this disclosure, the processes described in the provided flowcharts can be implemented as computer software programs. For example, embodiments of this disclosure include a computer program product comprising a computer program carried on a computer-readable medium, the computer program containing program code for performing the methods shown in the flowcharts. In such embodiments, the computer program can be downloaded and installed from a network via a communication device, or installed from a storage device, or installed from a ROM. When the computer program is executed by a processing device, it performs the functions defined in the methods of embodiments of this disclosure.

[0044] It should be noted that the computer-readable medium described above in this disclosure can be a computer-readable signal medium or a computer-readable storage medium, or any combination of the two. Computer-readable storage media may include, for example, electrical, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatuses, or devices, or any combination thereof. More specific examples of computer-readable storage media may include, but are not limited to: electrical connections having one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination thereof.

[0045] In embodiments of this disclosure, a computer-readable storage medium can be any tangible medium containing or storing a program that can be used by or in connection with an instruction execution system, apparatus, or device. In embodiments of this disclosure, a computer-readable signal medium can include a data signal propagated in baseband or as part of a carrier wave, carrying computer-readable program code. Such propagated data signals can take various forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof. A computer-readable signal medium can also be any computer-readable medium other than a computer-readable storage medium, which can send, propagate, or transmit a program for use by or in connection with an instruction execution system, apparatus, or device. The program code contained on the computer-readable medium can be transmitted using any suitable medium, including but not limited to: wires, optical cables, radio frequency (RF), etc., or any suitable combination thereof.

[0046] The aforementioned computer-readable medium may be included in the aforementioned server; or it may exist independently and not assembled into the server.

[0047] The aforementioned computer-readable medium carries one or more programs, which, when executed by the server, cause the server to perform the processing method provided in the embodiments of this disclosure.

[0048] Computer program code for performing the operations of this disclosure can be written in one or more programming languages ​​or a combination thereof, including object-oriented programming languages ​​such as Java, Smalltalk, and C++, and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The program code can be executed entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving remote computers, the remote computer can be connected to the user's computer via any type of network, including local area networks (LANs) and wide area networks (WANs), or it can be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0049] The units and / or modules described in the embodiments of this disclosure can be implemented in software or in hardware.

[0050] The preferred embodiments of the present invention have been described above, but the spirit and scope of the present invention are not limited to the specific contents disclosed herein. Those skilled in the art can arbitrarily combine and extend the above embodiments according to the teachings of the present invention to make more implementations and applications within the spirit and scope of the present invention. The spirit and scope of the present invention are not limited by the specific embodiments, but by the claims.

Claims

1. A method for predicting the fatigue life of ring groove rivet fasteners considering the effects of coating thickness and local plasticity, characterized in that... include: Step S100: Perform finite element analysis on the connection structure including the rivet joint; Step S300: Measure the coating thickness t of the plate. * ; Step S400, based on the measured coating thickness t of the plate * The coating thickness sensitivity factor f is calculated using formula (1). c :f c =5.969×10 -4 ×t * +1.861×10 -5 ×t *2 , formula (1); Step S500, based on the calculated coating thickness sensitivity factor f c The stress concentration factor K, considering the effect of coating thickness, is calculated using formula (2). f , In the formula, σ max S represents the maximum stress at the stress concentration point of the riveted component, and S is the nominal stress. Step S600: Based on the calculated stress concentration factor K considering the influence of coating thickness. f The maximum stress at the stress concentration point of the riveted component is equivalent to local plastic stress. Based on formula (3), the equivalent stress σ considering the influence of coating thickness and local plastic stress is calculated. epf : In the formula, E is the elastic modulus, k` is the cyclic strength coefficient, and n` is the cyclic hardening exponent; based on the above calculation results, the elastic-plastic strain ε of the stress concentration area of ​​the riveted joint considering the influence of coating thickness is calculated using formulas (3) and (4). epf , Step S700: The calculated elastic-plastic strain ε considering the effect of coating thickness is then applied. epf Substitute the values ​​into the Manson-Conffin formula to complete the fatigue life prediction.

2. The method for predicting the fatigue life of ring groove rivet fasteners considering the effects of coating thickness and local plasticity according to claim 1, characterized in that, It also includes determining whether to consider the influence of the coating thickness of the board before step S300. If it is considered, step S300 is executed; if it is not considered, step S500 is executed.

3. The method for predicting the fatigue life of ring groove rivet fasteners considering the effects of coating thickness and local plasticity according to claim 1, characterized in that, Define t * For the dimensionless coating thickness without unitization, t * =t / t ref , where t ref =1μm.

4. The method for predicting the fatigue life of ring groove rivet fasteners considering the effects of coating thickness and local plasticity according to claim 1, characterized in that, The Manson-Conffin formula is as follows: ` In the formula, σ f b is the fatigue strength coefficient, c' is the fatigue strength index, and c'' is the fatigue strength coefficient. ε is the fatigue ductility index. f is the fatigue ductility coefficient, and N is the fatigue life.

5. The method for predicting the fatigue life of ring groove rivet fasteners considering the effects of coating thickness and local plasticity according to claim 1, characterized in that, The Manson-Conffin formula is as follows: ` In the formula, σ m For the mean stress, σ f The fatigue strength coefficient, b is the fatigue strength index, c is the fatigue ductility index, and ε is the fatigue strength index. f is the fatigue ductility coefficient, and N is the fatigue life.

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