Polymer bolt pretightening force relaxation prediction method and system based on time-temperature equivalence principle

Abstract

This invention relates to the field of reliability evaluation technology for connection structures, specifically a method and system for predicting the relaxation of preload on polymer bolts based on the time-temperature equivalence principle. By establishing a relationship model between temperature, time, initial preload state, nominal bolt diameter, and preload retention rate, the method enables rapid prediction of the preload variation law during long-term service of polymer bolt connection structures. It can be applied to fields such as polymer bolt flange connections, sealing connections, and polymer material fastening structure design and reliability evaluation.

Description

Technical Field

[0001] This invention relates to the field of reliability evaluation and life prediction technology of polymer material connection structures, specifically a method and system for predicting the preload relaxation of polymer bolts based on the time-temperature equivalence principle. Background Technology

[0002] Polymer materials possess excellent corrosion resistance, high and low temperature resistance, and chemical stability, making them widely used in chemical equipment, sealing structures, and special connectors. However, most polymer materials are typical viscoelastic materials, exhibiting significant creep and stress relaxation under long-term loads, leading to a continuous decrease in the preload of bolted connections. When the preload decreases to a certain level, the connection may leak, loosen, or even fail.

[0003] Existing methods for predicting preload mostly employ finite element analysis or single-factor empirical formulas, making it difficult to simultaneously consider the combined effects of factors such as temperature, initial preload, nominal diameter, and time on preload relaxation behavior. Therefore, it is necessary to establish a preload prediction method that can comprehensively consider the influence of temperature, time, preload state, and bolt size, enabling rapid assessment of the long-term service performance of polymer bolted connection structures. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method and system for predicting the preload relaxation of polymer bolts based on the time-temperature equivalence principle.

[0005] The technical solution adopted by this invention to solve its technical problem is:

[0006] A method for predicting the preload relaxation of polymer bolts based on the time-temperature equivalence principle includes the following steps:

[0007] S1. Conduct stress relaxation experiments on polymer material samples under different temperature conditions to obtain relaxation modulus-time curves at each temperature; based on the time-temperature equivalence principle, translate the relaxation modulus-time curves at each temperature to obtain the horizontal displacement of each temperature relative to the reference temperature, and construct the WLF equation based on the relationship between the horizontal displacement and temperature to establish the equivalent time transformation relationship of the material at different temperatures.

[0008] S2. Using polymer bolts of different nominal diameters, conduct a test experiment on the preload decay of the fastening structure under different temperatures and initial preload conditions, and collect experimental data on the change of preload over time.

[0009] S3. Based on the equivalent time conversion relationship, convert the service time corresponding to each acquisition moment in the fastening structure preload decay test experiment into the equivalent time relative to the reference temperature.

[0010] S4. Construct an empirical model of preload relaxation rate that characterizes the exponential functional relationship between preload relaxation rate and equivalent time, initial preload and nominal diameter of polymer bolt;

[0011] S5. Using experimental data, perform nonlinear parameter fitting on the empirical model of preload relaxation rate, determine the undetermined coefficients in the model, and obtain the fitted empirical model.

[0012] S6. For the target working condition, obtain the temperature, service time, initial preload and nominal bolt diameter. Based on the equivalent time conversion relationship, convert the service time into the equivalent time relative to the reference temperature. Substitute the equivalent time, initial preload and nominal bolt diameter under the target working condition into the empirical model to obtain the remaining preload value under the target working condition.

[0013] As a preferred embodiment, a further technical solution of the present invention is:

[0014] Preferably, S1 specifically includes:

[0015] S11. Under different temperature conditions, perform constant-rate tensile tests on polymer material samples, obtain stress-strain curves at each temperature, and determine the strain level within the linear viscoelastic range based on the stress-strain curves.

[0016] S12. Under different temperature conditions, the polymer material sample is stretched to a determined strain level and the strain is kept constant. The stress change data with time during the relaxation process is continuously collected to obtain the relaxation modulus-time curve at each temperature.

[0017] S13, based on reference temperature Using the relaxation modulus-time curve at the specified temperature as a baseline, the relaxation modulus-time curves at the remaining temperatures are horizontally shifted along the logarithmic time axis, causing the curves to overlap and form the master curve. The horizontal displacement corresponding to each temperature is then recorded. ;

[0018] S14. Based on the time-temperature equivalence principle, the horizontal displacement is defined as temperature. Material viscosity and reference temperature Using the commonly used logarithm of the viscosity ratio of the materials, and combining it with the linear thermal expansion relationship of the free volume fraction of polymer materials with temperature, a WLF equation is established to establish the relationship between horizontal displacement and temperature:

[0019] ;

[0020] S15. Calculate the horizontal displacement corresponding to each temperature obtained in S13. Substituting the WLF equations and using a nonlinear regression method for fitting, the material constants are obtained. , as well as The value of .

[0021] Preferably, the equivalent time transformation relationship in S1 is expressed as:

[0022] ;

[0023] in, Indicates equivalent time. This indicates the service time of the polymer bolt at actual temperature or the time of experimental data collection.

[0024] Preferably, S2 specifically includes:

[0025] S21. Select at least two polymer bolts with different nominal diameters, insert the polymer bolts into the rigid connected parts, and install pressure sensors and nuts in sequence at the ends of the polymer bolts to complete the fastening structure assembly. The pressure sensors are installed between the nuts and the rigid connected parts to directly measure the axial preload of the bolts.

[0026] S22. A torque wrench is used as a loading device to obtain multiple sets of different initial preloads by applying different torque values. ;

[0027] S23. Keep the strain of the polymer bolt constant, place the assembled fastening structure in a constant temperature chamber, and conduct experiments at multiple set temperatures to obtain experimental data on the change of preload over time.

[0028] S24. Data acquisition stops when the data collected by the pressure sensor decays to a stable state and reaches the preset experimental duration.

[0029] Preferably, the empirical model for the preload relaxation rate in S4 is expressed as follows:

[0030] ;

[0031] in, Preload relaxation rate This is the material relaxation amplitude coefficient. The initial preload influence index, The nominal diameter influence index. The time decay exponent, This is the initial preload. Nominal diameter, This is the equivalent time.

[0032] Preferably, the nonlinear parameter fitting in S5 includes:

[0033] definition , Indicates the remaining preload;

[0034] The preload force collected at various times in the S2 experiment data With corresponding initial preload The ratio between them is used as the target variable, with the service time t, experimental temperature T, and initial preload at the corresponding time point as the parameters. and nominal diameter As input variables, the following equation is used to identify parameters using the nonlinear least squares method:

[0035] ;

[0036] Thus, the undetermined coefficients are obtained through fitting. , , , .

[0037] Another aspect of this invention provides a polymer bolt preload relaxation prediction system based on the time-temperature equivalence principle, implemented using the above-mentioned method, specifically including:

[0038] The relation construction module is used to conduct material stress relaxation experiments on polymer material samples under different temperature conditions to obtain relaxation modulus-time curves at each temperature. Based on the time-temperature equivalence principle, the relaxation modulus-time curves at each temperature are translated to obtain the horizontal displacement of each temperature relative to the reference temperature. The WLF equation is constructed according to the relationship between the horizontal displacement and temperature, thereby establishing the equivalent time transformation relationship of the material at different temperatures.

[0039] The experimental data acquisition module is used to conduct a test on the preload decay of fastening structures using polymer bolts of different nominal diameters under different temperatures and initial preload conditions, and to collect experimental data on the change of preload over time.

[0040] The time conversion module is used to convert the service time corresponding to each acquisition moment in the fastening structure preload decay test experiment into the equivalent time relative to the reference temperature according to the equivalent time conversion relationship.

[0041] The model building module is used to build an empirical model of preload relaxation rate that characterizes the exponential function relationship between preload relaxation rate and equivalent time, initial preload, and nominal diameter of polymer bolts.

[0042] The model fitting module is used to perform nonlinear parameter fitting on the empirical model of preload relaxation rate using experimental data, determine the undetermined coefficients in the model, and obtain the fitted empirical model.

[0043] The working condition prediction module is used to obtain temperature, service time, initial preload and nominal bolt diameter for a target working condition. Based on the equivalent time conversion relationship, the service time is converted into an equivalent time relative to the reference temperature. The equivalent time, initial preload and nominal bolt diameter under the target working condition are substituted into the empirical model to obtain the remaining preload value under the target working condition.

[0044] In another aspect of the present invention, an electronic device is provided, including a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other through the communication bus.

[0045] Memory is used to store processor-executable instructions;

[0046] When the processor executes the instructions stored in the memory, it implements the above-mentioned method for predicting the preload relaxation of polymer bolts based on the time-temperature equivalence principle.

[0047] The present invention, which adopts the above technical solution, has the following prominent features compared with the prior art:

[0048] By constructing empirical formulas relating temperature, initial preload, nominal diameter, time, and preload relaxation rate, the preload variation of various bolts over different times can be predicted. The model has few parameters, is simple to calculate, and is easy to apply in engineering. Long-term preload prediction can be achieved without complex finite element analysis, enabling rapid prediction of preload variation patterns in polymer bolted connection structures during long-term service. It can be applied to fields such as polymer bolted flange connections, sealing connections, and polymer material fastening structure design and reliability evaluation. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the process for predicting the preload relaxation of polymer bolts based on the time-temperature equivalence principle in an embodiment of the present invention.

[0050] Figure 2 This is a schematic diagram of the bolt connection fastening structure assembly in an embodiment of the present invention, wherein a is a simplified schematic diagram and b is a physical model schematic diagram;

[0051] Figure 3 This is a schematic diagram comparing the predicted results of the present invention with the actual experimental data obtained from M8 bolts at different temperatures in an embodiment of the present invention;

[0052] Figure 4 This is a schematic diagram of the polymer bolt preload relaxation prediction system based on the time-temperature equivalence principle in an embodiment of the present invention;

[0053] Figure 5 This is a schematic diagram of the structure of the electronic device in an embodiment of the present invention. Detailed Implementation

[0054] The present invention will be further illustrated below with reference to specific embodiments. The purpose of this illustration is solely to provide a better understanding of the invention. Therefore, the examples given do not limit the scope of protection of the present invention.

[0055] like Figure 1 As shown in the figure, this embodiment presents a method for predicting the preload relaxation of polymer bolts based on the time-temperature equivalence principle, including the following steps:

[0056] S1. Perform stress relaxation experiments on polymer material samples under different temperature conditions to obtain relaxation modulus-time curves at each temperature; based on the time-temperature equivalence principle, translate the relaxation modulus-time curves at each temperature to obtain the horizontal displacement of each temperature relative to the reference temperature, and construct the WLF equation based on the relationship between the horizontal displacement and temperature to establish the equivalent time transformation relationship of the material at different temperatures.

[0057] Specifically, this includes S11, conducting constant-rate tensile tests on polymer material samples under different temperature conditions, obtaining stress-strain curves at each temperature, and determining the strain level within the linear viscoelastic range based on the stress-strain curves;

[0058] S12. Under different temperature conditions, the polymer material sample is stretched to a determined strain level and the strain is kept constant. The stress change data with time during the relaxation process is continuously collected to obtain the relaxation modulus-time curve at each temperature.

[0059] S13, based on reference temperature Using the relaxation modulus-time curve at the specified temperature as a baseline, the relaxation modulus-time curves at the remaining temperatures are horizontally shifted along the logarithmic time axis so that the curves overlap to form the master curve, and the horizontal displacement corresponding to each temperature is recorded. ;

[0060] S14. Based on the time-temperature equivalence principle, the horizontal displacement is defined as temperature. Material viscosity and reference temperature Using the commonly used logarithm of the viscosity ratio of the materials, and combining it with the linear thermal expansion relationship of the free volume fraction of polymer materials with temperature, a WLF equation is established to establish the relationship between horizontal displacement and temperature:

[0061] ;

[0062] S15. Calculate the horizontal displacement corresponding to each temperature obtained in S13. Substituting the WLF equations and using a nonlinear regression method for fitting, the material constants are obtained. , as well as The value of .

[0063] The equivalent time transformation relationship is expressed as follows:

[0064] ;

[0065] in, Indicates equivalent time. This indicates the service time of the polymer bolt at actual temperature or the time of experimental data collection.

[0066] S2. Using polymer bolts of different nominal diameters, conduct a test experiment on the preload decay of the fastening structure under different temperatures and initial preload conditions, and collect experimental data on the change of preload over time.

[0067] Specifically, S21 involves selecting at least two polymer bolts with different nominal diameters, inserting the polymer bolts into the rigid connected parts, and sequentially installing a pressure sensor and a nut at the end of the polymer bolts to complete the fastening structure assembly. The pressure sensor is installed between the nut and the rigid connected parts to directly measure the axial preload of the bolt.

[0068] S22. A torque wrench is used as a loading device to obtain multiple sets of different initial preloads by applying different torque values. ;

[0069] S23. Keep the strain of the polymer bolt constant, place the assembled fastening structure in a constant temperature chamber, and conduct experiments at multiple set temperatures to obtain experimental data on the change of preload over time.

[0070] S24. Data acquisition stops when the data collected by the pressure sensor decays to a stable state and reaches the preset experimental duration.

[0071] S3. Based on the equivalent time conversion relationship, convert the service time corresponding to each acquisition moment in the fastening structure preload decay test experiment into the equivalent time relative to the reference temperature.

[0072] S4. Construct an empirical model of preload relaxation rate that characterizes the exponential functional relationship between preload relaxation rate and equivalent time, initial preload and nominal diameter of polymer bolt;

[0073] In practice, the empirical model for preload relaxation rate is expressed as follows:

[0074] ;

[0075] in, Preload relaxation rate This is the material relaxation amplitude coefficient. The initial preload influence index, The nominal diameter influence index. The time decay exponent, This is the initial preload. Nominal diameter, This is the equivalent time.

[0076] S5. Using experimental data, perform nonlinear parameter fitting on the empirical model of preload relaxation rate, determine the undetermined coefficients in the model, and obtain the fitted empirical model.

[0077] In practice, nonlinear parameter fitting includes:

[0078] definition , Indicates the remaining preload;

[0079] The preload force collected at various times in the S2 experiment data With corresponding initial preload The ratio between them is used as the target variable, with the service time t, experimental temperature T, and initial preload at the corresponding time point as the parameters. and nominal diameter As input variables, the following equation is used to identify parameters using the nonlinear least squares method:

[0080] ;

[0081] Thus, the undetermined coefficients are obtained through fitting. , , , .

[0082] S6. For the target working condition, obtain the temperature, service time, initial preload and nominal bolt diameter. Based on the equivalent time conversion relationship, convert the service time into the equivalent time relative to the reference temperature. Substitute the equivalent time, initial preload and nominal bolt diameter under the target working condition into the empirical model to obtain the remaining preload value under the target working condition.

[0083] The following uses PTFE bolt fasteners as an example to illustrate the specific implementation process of this invention:

[0084] (1) Material stress relaxation experiment: Analysis of the stress-strain characteristics of materials: A universal testing machine can be used to stretch polymer material samples at different temperatures and sample the tensile force during the relaxation process. The obtained time-tensile force-displacement data can be processed to obtain the stress-strain relationship of the material. However, the isothermal relaxation modulus obtained in this way usually reflects the time-dependent mechanical response of the material at a fixed temperature, and its curve is only applicable to specific temperature conditions. In contrast, the variable-temperature relaxation modulus can characterize the modulus evolution behavior of the material during continuous temperature changes, which is more in line with the multi-condition requirements in actual engineering. Establishing an accurate variable-temperature relaxation modulus curve requires multiple sets of isothermal relaxation experimental data as a basis. Through the time-temperature equivalence principle, the isothermal modulus curves at different temperatures are shifted over time to synthesize a master curve covering a wide temperature range.

[0085] To investigate the stress relaxation behavior of PTFE material within the temperature range of 25℃ to 100℃, an isometric tensile test is required to determine its initial relaxation strain, i.e., a preliminary experiment. First, the specimens are pretreated by placing the clamped specimens and fixtures in an insulated chamber for at least 15 minutes to ensure uniform and stable internal temperature. Extreme temperatures of 25℃ and 100℃ are selected for comparison. The tensile rate is set to 5 mm / min, and the material is stretched until the specimen fractures, with the test repeated. Based on the tensile test results, 1% is selected as the strain level for the relaxation test, at which the stress-strain relationship of PTFE is in the linear stage.

[0086] The actual relaxation modulus test experiment consists of two stages: a constant-rate loading stage and a constant-strain holding stage. In the constant-rate loading stage, the specimen is stretched at a constant rate of 5 mm / min until the strain level reaches 1%. In the strain holding stage, the strain is kept constant for 3 hours (10800 s), and the stress growth and decay data are recorded in both stages.

[0087] (2) Data processing of stress relaxation experiments:

[0088] Considering the significant temperature sensitivity of PTFE material, the WLF (Williams-Landel-Ferry) time-temperature equivalence principle is introduced for temperature correction. The WLF model can be expressed as follows:

[0089] ;

[0090] in, The viscosity of the material, The free volume fraction of the material. and This represents a material constant. Above the glass transition temperature, the free volume fraction of the material satisfies the following relationship (assuming linear thermal expansion of the material):

[0091] ;

[0092] in, The coefficient of thermal expansion is 1 / 3. Indicates reference temperature The free volume fraction of the material. The time-temperature equivalence factor is defined as the ratio of the material viscosity at a given temperature to its viscosity at a reference temperature. The ratio, that is:

[0093] ;

[0094] Based on this, the expression for the WLF time-temperature equivalent model can be derived:

[0095] ;

[0096] The experimental data were processed to obtain the relaxation modulus-time logarithm curve, and the curve was shifted to obtain the offset. By substituting the values ​​into the WLF equation and performing a fit, we can obtain the desired result. , The value of .

[0097] Simultaneously define equivalent time:

[0098] .

[0099] (3) Bolt preload test under different initial conditions:

[0100] The specific experiments used standard PTFE bolts of three sizes: M6, M8, and M10. A high-precision pressure sensor was installed between the nut and the rigid base to directly measure the axial preload. Long-term data acquisition was performed using PC software at a sampling frequency of 1Hz. A torque wrench was used as a loading device to apply the initial preload. In practical applications, PTFE material is significantly affected by temperature; therefore, a constant temperature chamber was selected for the experiments to control the test temperature while also meeting the need to study the effect of temperature on stress relaxation.

[0101] The specific experimental steps are as follows: 1. Specimen installation; see [link to relevant documentation] Figure 2 1. Insert the bolt through the aluminum connector, and install the pressure sensor and nut sequentially at the end. Tighten the nut at the sensor using a torque wrench with the appropriate torque. Record the initial force value as a reference. 2. Data Acquisition: Keep the bolt strain constant (limit deformation with a rigid clamp), place the specimen in a constant temperature chamber, and continuously record the pressure sensor output. 3. Experiment End: Stop data acquisition when the pressure sensor reading decays to a stable state and reaches the preset time, and dismantle the experimental platform.

[0102] (4) Empirical model fitting:

[0103] Based on experimental data analysis, it was found that the preload relaxation rate has an exponential relationship with the initial preload, nominal diameter, and equivalent time. Therefore, the following empirical model is established:

[0104] ;

[0105] The nonlinear least squares fitting method (lsqcurvefit) in MATLAB software was used to identify parameters in the experimental data and obtain... The parameters are as follows:

[0106] ;

[0107] Finally, based on the definition of preload relaxation rate, the following is obtained:

[0108] ;

[0109] The obtained formula can be directly used to predict the preload variation of PTFE bolted connection structures under any temperature and time conditions.

[0110] (5) Error analysis of the empirical model:

[0111] The empirical formulas were compared and analyzed with data obtained from actual experiments on M8 bolts at different temperatures (this data was not used in the least squares fitting). Figure 3 The results showed that the maximum error in stress relaxation rate was no more than 10%, and the average error was no more than 5%, which met the requirements for engineering applications.

[0112] See Figure 4 This invention also provides a polymer bolt preload relaxation prediction system based on the time-temperature equivalence principle, implemented using the above-described method, specifically including:

[0113] The relation construction module is used to conduct material stress relaxation experiments on polymer material samples under different temperature conditions to obtain relaxation modulus-time curves at each temperature. Based on the time-temperature equivalence principle, the relaxation modulus-time curves at each temperature are translated to obtain the horizontal displacement of each temperature relative to the reference temperature. The WLF equation is constructed according to the relationship between the horizontal displacement and temperature, thereby establishing the equivalent time transformation relationship of the material at different temperatures.

[0114] The experimental data acquisition module is used to conduct a test on the preload decay of fastening structures using polymer bolts of different nominal diameters under different temperatures and initial preload conditions, and to collect experimental data on the change of preload over time.

[0115] The time conversion module is used to convert the service time corresponding to each acquisition moment in the fastening structure preload decay test experiment into the equivalent time relative to the reference temperature according to the equivalent time conversion relationship.

[0116] The model building module is used to build an empirical model of preload relaxation rate that characterizes the exponential function relationship between preload relaxation rate and equivalent time, initial preload, and nominal diameter of polymer bolts.

[0117] The model fitting module is used to perform nonlinear parameter fitting on the empirical model of preload relaxation rate using experimental data, determine the undetermined coefficients in the model, and obtain the fitted empirical model.

[0118] The working condition prediction module is used to obtain temperature, service time, initial preload and nominal bolt diameter for a target working condition. Based on the equivalent time conversion relationship, the service time is converted into an equivalent time relative to the reference temperature. The equivalent time, initial preload and nominal bolt diameter under the target working condition are substituted into the empirical model to obtain the remaining preload value under the target working condition.

[0119] The relationship building module is specifically used for...

[0120] Constant-rate tensile tests were conducted on polymer material samples under different temperature conditions to obtain stress-strain curves at each temperature. The strain level within the linear viscoelastic range was determined based on the stress-strain curves.

[0121] Under different temperature conditions, polymer material samples were stretched to a determined strain level and the strain was kept constant. Data on the change of stress over time during the relaxation process were continuously collected to obtain the relaxation modulus-time curves at each temperature.

[0122] Reference temperature Using the relaxation modulus-time curve at the specified temperature as a baseline, the relaxation modulus-time curves at the remaining temperatures are horizontally shifted along the logarithmic time axis so that the curves overlap to form the master curve, and the horizontal displacement corresponding to each temperature is recorded. ;

[0123] Based on the time-temperature equivalence principle, the horizontal displacement is defined as temperature. Material viscosity and reference temperature Using the commonly used logarithm of the viscosity ratio of the materials, and combining it with the linear thermal expansion relationship of the free volume fraction of polymer materials with temperature, a WLF equation is established to establish the relationship between horizontal displacement and temperature:

[0124] ;

[0125] The horizontal displacement corresponding to each temperature is obtained Substituting the WLF equations and using a nonlinear regression method for fitting, the material constants are obtained. , as well as The value of .

[0126] The equivalent time transformation relationship is expressed as follows:

[0127] ;

[0128] in, Indicates equivalent time. This indicates the service time of the polymer bolt at actual temperature or the time of experimental data collection.

[0129] Experimental data acquisition module, specifically used for

[0130] Select at least two polymer bolts with different nominal diameters, insert the polymer bolts into the rigid connected parts, and install pressure sensors and nuts in sequence at the ends of the polymer bolts to complete the fastening structure assembly. The pressure sensors are installed between the nuts and the rigid connected parts to directly measure the axial preload of the bolts.

[0131] Using a torque wrench as a loading device, multiple sets of different initial preloads are obtained by applying different torque values. ;

[0132] To keep the strain of the polymer bolt constant, the assembled fastening structure was placed in a constant temperature chamber, and experiments were conducted at multiple set temperatures to obtain experimental data on the change of preload over time.

[0133] Data acquisition stops when the data collected by the pressure sensor decays to a stable state and reaches the preset experimental duration.

[0134] The empirical model for preload relaxation rate is expressed as follows:

[0135] ;

[0136] in, Preload relaxation rate This is the material relaxation amplitude coefficient. The initial preload influence index, The nominal diameter influence index. The time decay exponent, This is the initial preload. Nominal diameter, This is the equivalent time.

[0137] Nonlinear parameter fitting includes:

[0138] definition , Indicates the remaining preload;

[0139] The preload force collected at various times in the S2 experiment data With corresponding initial preload The ratio between them is used as the target variable, with the service time t, experimental temperature T, and initial preload at the corresponding time point as the parameters. and nominal diameter As input variables, the following equation is used to identify parameters using the nonlinear least squares method:

[0140] ;

[0141] Thus, the undetermined coefficients are obtained through fitting. , , , .

[0142] This invention also provides an electronic device, such as... Figure 5 As shown, it includes a processor 001, a communication interface 002, a memory 003, and a communication bus 004. The processor 001, communication interface 002, and memory 003 communicate with each other via the communication bus 004.

[0143] Memory 003 is used to store computer programs;

[0144] Processor 001, when executing the program stored in memory 003, implements the above-mentioned method for predicting the preload relaxation of polymer bolts based on the time-temperature equivalence principle, including:

[0145] S1. Conduct stress relaxation experiments on polymer material samples under different temperature conditions to obtain relaxation modulus-time curves at each temperature; based on the time-temperature equivalence principle, translate the relaxation modulus-time curves at each temperature to obtain the horizontal displacement of each temperature relative to the reference temperature, and construct the WLF equation based on the relationship between the horizontal displacement and temperature to establish the equivalent time transformation relationship of the material at different temperatures.

[0146] S2. Using polymer bolts of different nominal diameters, conduct a test experiment on the preload decay of the fastening structure under different temperatures and initial preload conditions, and collect experimental data on the change of preload over time.

[0147] S3. Based on the equivalent time conversion relationship, convert the service time corresponding to each acquisition moment in the fastening structure preload decay test experiment into the equivalent time relative to the reference temperature.

[0148] S4. Construct an empirical model of preload relaxation rate that characterizes the exponential functional relationship between preload relaxation rate and equivalent time, initial preload and nominal diameter of polymer bolt;

[0149] S5. Using experimental data, perform nonlinear parameter fitting on the empirical model of preload relaxation rate, determine the undetermined coefficients in the model, and obtain the fitted empirical model.

[0150] S6. For the target working condition, obtain the temperature, service time, initial preload and nominal bolt diameter. Based on the equivalent time conversion relationship, convert the service time into the equivalent time relative to the reference temperature. Substitute the equivalent time, initial preload and nominal bolt diameter under the target working condition into the empirical model to obtain the remaining preload value under the target working condition.

[0151] The solution provided by this invention can predict the preload changes of various bolts over different times by constructing empirical formulas relating temperature, initial preload, nominal diameter, time, and preload relaxation rate. The model has few parameters, is simple to calculate, and is easy to apply in engineering. Long-term preload prediction can be achieved without complex finite element analysis, enabling rapid prediction of preload changes in polymer bolt connection structures during long-term service. It can be applied to fields such as polymer bolt flange connections, sealing connections, and polymer material fastening structure design and reliability evaluation.

[0152] The communication bus mentioned in the above electronic devices can be a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Architecture (EISA) bus, etc. This communication bus can be divided into address bus, data bus, control bus, etc. For ease of illustration, only one thick line is used to represent it in the diagram, but this does not mean that there is only one bus or one type of bus.

[0153] The communication interface is used for communication between the aforementioned electronic devices and other devices.

[0154] The memory may include random access memory (RAM) or non-volatile memory (NVM), such as at least one disk storage device. Optionally, the memory may also be at least one storage device located remotely from the aforementioned processor.

[0155] The processors mentioned above can be general-purpose processors, including central processing units (CPUs), network processors (NPs), etc.; they can also be digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0156] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of the present invention are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium accessible to a computer or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., solid-state disk (SSD)).

[0157] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0158] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system and electronic device embodiments are basically similar to the method embodiments, so the descriptions are relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0159] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for predicting the preload relaxation of polymer bolts based on the time-temperature equivalence principle, characterized in that, Includes the following steps: S1. Conduct stress relaxation experiments on polymer material samples under different temperature conditions to obtain relaxation modulus-time curves at each temperature; based on the time-temperature equivalence principle, translate the relaxation modulus-time curves at each temperature to obtain the horizontal displacement of each temperature relative to the reference temperature, and construct the WLF equation based on the relationship between the horizontal displacement and temperature to establish the equivalent time transformation relationship of the material at different temperatures. S2. Using polymer bolts of different nominal diameters, conduct a test experiment on the preload decay of the fastening structure under different temperatures and initial preload conditions, and collect experimental data on the change of preload over time. S3. Based on the equivalent time conversion relationship, convert the service time corresponding to each acquisition moment in the fastening structure preload decay test experiment into the equivalent time relative to the reference temperature. S4. Construct an empirical model of preload relaxation rate that characterizes the exponential functional relationship between preload relaxation rate and equivalent time, initial preload and nominal diameter of polymer bolt; S5. Using experimental data, perform nonlinear parameter fitting on the empirical model of preload relaxation rate, determine the undetermined coefficients in the model, and obtain the fitted empirical model. S6. For the target working condition, obtain the temperature, service time, initial preload and nominal bolt diameter. Based on the equivalent time conversion relationship, convert the service time into the equivalent time relative to the reference temperature. Substitute the equivalent time, initial preload and nominal bolt diameter under the target working condition into the empirical model to obtain the remaining preload value under the target working condition.

2. The method for predicting the preload relaxation of polymer bolts based on the time-temperature equivalence principle according to claim 1, characterized in that, S1 specifically includes: S11. Under different temperature conditions, perform constant-rate tensile tests on polymer material samples, obtain stress-strain curves at each temperature, and determine the strain level within the linear viscoelastic range based on the stress-strain curves. S12. Under different temperature conditions, the polymer material sample is stretched to a determined strain level and the strain is kept constant. The stress change data with time during the relaxation process is continuously collected to obtain the relaxation modulus-time curve at each temperature. S13, based on reference temperature Using the relaxation modulus-time curve at the specified temperature as a baseline, the relaxation modulus-time curves at the remaining temperatures are horizontally shifted along the logarithmic time axis, causing the curves to overlap and form the master curve. The horizontal displacement corresponding to each temperature is then recorded. ; S14. Based on the time-temperature equivalence principle, the horizontal displacement is defined as temperature. Material viscosity and reference temperature Using the commonly used logarithm of the viscosity ratio of the materials, and combining it with the linear thermal expansion relationship of the free volume fraction of polymer materials with temperature, a WLF equation is established to establish the relationship between horizontal displacement and temperature: ； S15. Calculate the horizontal displacement corresponding to each temperature obtained in S13. Substituting the WLF equations and using a nonlinear regression method for fitting, the material constants are obtained. , as well as The value of .

3. The method for predicting the preload relaxation of polymer bolts based on the time-temperature equivalence principle according to claim 2, characterized in that, The equivalent time transformation relationship in S1 is expressed as: ； in, Indicates equivalent time. This indicates the service time of the polymer bolt at actual temperature or the time of experimental data collection.

4. The method for predicting the preload relaxation of polymer bolts based on the time-temperature equivalence principle according to claim 1, characterized in that, S2 specifically includes: S21. Select at least two polymer bolts with different nominal diameters, insert the polymer bolts into the rigid connected parts, and install pressure sensors and nuts in sequence at the ends of the polymer bolts to complete the fastening structure assembly. The pressure sensors are installed between the nuts and the rigid connected parts to directly measure the axial preload of the bolts. S22. A torque wrench is used as a loading device to obtain multiple sets of different initial preloads by applying different torque values. ; S23. Keep the strain of the polymer bolt constant, place the assembled fastening structure in a constant temperature chamber, and conduct experiments at multiple set temperatures to obtain experimental data on the change of preload over time. S24. Data acquisition stops when the data collected by the pressure sensor decays to a stable state and reaches the preset experimental duration.

5. The method for predicting the preload relaxation of polymer bolts based on the time-temperature equivalence principle according to claim 3, characterized in that, The empirical model for the preload relaxation rate in S4 is expressed as follows: ； in, Preload relaxation rate This is the material relaxation amplitude coefficient. The initial preload influence index, The nominal diameter influence index. The time decay exponent, This is the initial preload. Nominal diameter, This is the equivalent time.

6. The method for predicting the preload relaxation of polymer bolts based on the time-temperature equivalence principle according to claim 5, characterized in that, Nonlinear parameter fitting in S5 includes: definition , Indicates the remaining preload; The preload force collected at various times in the S2 experiment data With corresponding initial preload The ratio between them is used as the target variable, with the service time t, experimental temperature T, and initial preload at the corresponding time point as the parameters. and nominal diameter As input variables, the following equation is used to identify parameters using the nonlinear least squares method: ； Thus, the undetermined coefficients are obtained through fitting. , , , .

7. A polymer bolt preload relaxation prediction system based on the time-temperature equivalence principle, characterized in that, The method described in any one of claims 1 to 6 is used to implement the method, specifically including: The relation construction module is used to conduct material stress relaxation experiments on polymer material samples under different temperature conditions to obtain relaxation modulus-time curves at each temperature. Based on the time-temperature equivalence principle, the relaxation modulus-time curves at each temperature are translated to obtain the horizontal displacement of each temperature relative to the reference temperature. The WLF equation is constructed according to the relationship between the horizontal displacement and temperature, thereby establishing the equivalent time transformation relationship of the material at different temperatures. The experimental data acquisition module is used to conduct a test on the preload decay of fastening structures using polymer bolts of different nominal diameters under different temperatures and initial preload conditions, and to collect experimental data on the change of preload over time. The time conversion module is used to convert the service time corresponding to each acquisition moment in the fastening structure preload decay test experiment into the equivalent time relative to the reference temperature according to the equivalent time conversion relationship. The model building module is used to build an empirical model of preload relaxation rate that characterizes the exponential function relationship between preload relaxation rate and equivalent time, initial preload, and nominal diameter of polymer bolts. The model fitting module is used to perform nonlinear parameter fitting on the empirical model of preload relaxation rate using experimental data, determine the undetermined coefficients in the model, and obtain the fitted empirical model. The working condition prediction module is used to obtain temperature, service time, initial preload and nominal bolt diameter for a target working condition. Based on the equivalent time conversion relationship, the service time is converted into an equivalent time relative to the reference temperature. The equivalent time, initial preload and nominal bolt diameter under the target working condition are substituted into the empirical model to obtain the remaining preload value under the target working condition.

8. The polymer bolt preload relaxation prediction system based on the time-temperature equivalence principle according to claim 7, characterized in that, The relationship building module is specifically used for... Constant-rate tensile tests were conducted on polymer material samples under different temperature conditions to obtain stress-strain curves at each temperature. The strain level within the linear viscoelastic range was determined based on the stress-strain curves. Under different temperature conditions, polymer material samples were stretched to a determined strain level and the strain was kept constant. Data on the change of stress over time during the relaxation process were continuously collected to obtain the relaxation modulus-time curves at each temperature. Reference temperature Using the relaxation modulus-time curve at the specified temperature as a baseline, the relaxation modulus-time curves at the remaining temperatures are horizontally shifted along the logarithmic time axis so that the curves overlap to form the master curve, and the horizontal displacement corresponding to each temperature is recorded. ; Based on the time-temperature equivalence principle, the horizontal displacement is defined as temperature. Material viscosity and reference temperature Using the commonly used logarithm of the viscosity ratio of the materials, and combining it with the linear thermal expansion relationship of the free volume fraction of polymer materials with temperature, a WLF equation is established to establish the relationship between horizontal displacement and temperature: ； The horizontal displacement corresponding to each temperature is obtained Substituting the WLF equations and using a nonlinear regression method for fitting, the material constants are obtained. , as well as The value of .

9. The polymer bolt preload relaxation prediction system based on the time-temperature equivalence principle according to claim 7, characterized in that, Experimental data acquisition module, specifically used for Select at least two polymer bolts with different nominal diameters, insert the polymer bolts into the rigid connected parts, and install pressure sensors and nuts in sequence at the ends of the polymer bolts to complete the fastening structure assembly. The pressure sensors are installed between the nuts and the rigid connected parts to directly measure the axial preload of the bolts. Using a torque wrench as a loading device, multiple sets of different initial preloads are obtained by applying different torque values. ; To keep the strain of the polymer bolt constant, the assembled fastening structure was placed in a constant temperature chamber, and experiments were conducted at multiple set temperatures to obtain experimental data on the change of preload over time. Data acquisition stops when the data collected by the pressure sensor decays to a stable state and reaches the preset experimental duration.

10. An electronic device, characterized in that, It includes a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other through the communication bus; Memory is used to store processor-executable instructions; The processor, when executing instructions stored in the memory, implements the polymer bolt preload relaxation prediction method based on the time-temperature equivalence principle as described in any one of claims 1-6.

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