A method for predicting the micro fatigue life of a petal-shaped fuel rod using a simplified spring support

Abstract

The present application provides a kind of petal-shaped fuel rod fretting fatigue life prediction method using simplified spring support.The present application simplifies the non-key support area of petal-shaped fuel rod by equivalent spring unit, concentrates calculation resources on the key area of petal support wear, realizes creep and dynamic gap evolution.The present application couples vibration load, thermal-mechanical response, contact friction problem, considers the nonlinear characteristics of friction coefficient with temperature, slip speed and normal contact pressure, makes the contact state, temperature field and local stress-strain response of petal support contact area more close to actual service conditions.The present application includes reverse movement stage into wear time accumulation process, and combines vibration excitation cycle and cycle jump number to carry out cross-time scale equivalent processing, which can reduce the calculation cost caused by small fretting wear single increment and large number of cycles, and reduce the life prediction deviation caused by wear contribution omission in reverse movement stage.

Description

Technical Field

[0001] This invention relates to the field of novel fuel element fretting fatigue life prediction technology, and in particular to a method for predicting the fretting fatigue life of a petal-shaped fuel rod using simplified spring support. Background Technology

[0002] Currently, fuel assemblies face high standards in terms of design safety margin and long-term service performance. Their contact state, vibration response, wear behavior, and fatigue damage evolution during service directly affect the safe operation of the fuel assembly. Petal-shaped fuel rods, with their self-supporting petal structure design, eliminate the need for traditional positioning grid clamps, offering higher power output and enhanced heat transfer capabilities, and have become a hot research topic in the field of advanced nuclear fuel development.

[0003] The petal support points of four-petal fuel rods are key areas for wear fatigue. Currently, simulation methods exist for fretting wear, creep, and gap evolution between circular fuel rods and the positioning grid, used to describe gap relaxation and contact evolution in circular fuel rod-grid contact systems. However, petal-shaped fuel rods do not rely on traditional positioning grid clamping, and their contact support methods, load transfer paths, and local flow-induced vibration characteristics differ significantly from those of traditional circular fuel rods. The self-supporting petal structure alters the contact stiffness and gap evolution between the rod bundles, and the turbulent disturbances caused by coolant flow subject the petal contact area to more complex vibration load excitations, leading to more complex contact states, stress-strain distributions, wear morphology changes, and fatigue damage evolution processes.

[0004] Therefore, how to reasonably simplify the non-critical support area while ensuring the accuracy of fretting wear and fatigue damage calculation in the petal contact area, establish an equivalent support model that can reflect creep, swelling and contact gap evolution, and further realize the coupled analysis of flow-induced vibration, frictional heat generation, wear morphology update and fatigue life prediction is an urgent technical problem to be solved in the fretting fatigue simulation and structural life assessment of petal-shaped fuel rods. Summary of the Invention

[0005] The purpose of this invention is to address the problems in existing technologies by proposing a method for predicting the fretting fatigue life of petal-shaped fuel rods using simplified spring supports. This method can rapidly predict fretting fatigue failure in the contact area of ​​petal-shaped fuel rods, providing theoretical support for structural optimization and life prediction of petal-shaped fuel rods.

[0006] This invention is achieved through the following technical solution: This invention proposes a method for predicting the fretting fatigue life of a petal-shaped fuel rod using simplified spring support, the method comprising: Step S1: Establish a simplified three-dimensional finite element model of the petal-shaped fuel rod, and use equivalent spring elements for support and constraint in non-critical structural areas; Step S2: Establish a constitutive model of the fuel rod based on the fuel material performance data. The constitutive model of the fuel rod includes the creep, elastic-plastic and irradiation swelling behavior of the cladding and core materials, and realizes the material constitutive calculation through the subroutines UMAT and CREEP. Step S3: Construct a spring support model that evolves with fuel consumption and time, simulate irradiation and stress relaxation behavior through dynamic stiffness, and describe the evolution of contact gap caused by creep and swelling through gap function; Step S4: Under the condition of thermo-mechanical coupling, the contact friction heat generation effect is considered, and the boundary conditions of heat conduction and convection heat transfer are updated through the subroutines UMATHT and FILM. At the same time, the friction coefficient is changed with temperature, slip velocity and contact stress through the subroutines FRIC. Step S5: Based on the energy dissipation wear model, and combined with the subroutine UMESHMOTION and ALE adaptive meshing technology, update the contact surface morphology caused by wear. Step S6: Apply a fluid excitation load to the petal-shaped fuel rod to simulate the fretting wear process under vibration, and include the reverse movement stage of the fuel rod in the wear time accumulation process; Step S7: Import the stress-strain results calculated by ABAQUS into Fe-safe, and use the multiaxial fatigue analysis method to predict the fatigue life of the petal-shaped contact area. Step S8: Analyze the effects of cyclic load, number of cycles, tilt angle, shell thickness and friction coefficient on fretting fatigue life using orthogonal experimental design method, and establish a regression prediction model.

[0007] Furthermore, the equivalent spring unit is used to simulate the structural support of non-critical structural areas of the petal-shaped fuel rod, and its dynamic stiffness decreases with time, fuel consumption and temperature.

[0008] Furthermore, creep and swelling deformation work together to influence the contact geometry evolution, and the gap function is used to characterize the combined effect of creep and swelling on the contact gap.

[0009] Furthermore, the dynamic stiffness k eff Using an exponential decay-saturation model:

[0010] In the formula, t For time, B For burn depth, k 0 represents the initial stiffness. R ∞ It is a saturation relaxation factor. λ Let be the relaxation rate constant. TThis refers to the cladding temperature. f ( T ) represents the influence coefficient of temperature on the material.

[0011] Furthermore, the frictional heat generation is fed back to the temperature field solution as a transient heat conduction boundary condition, and the friction coefficient is defined by the subroutine FRIC so that it is dynamically adjusted with changes in temperature, relative sliding velocity and normal contact pressure.

[0012] Furthermore, incorporating the reverse movement phase into the wear time accumulation process includes: capturing the reverse movement time period in the displacement load spectrum, treating the reverse movement time period as part of the wear accumulation time, and performing cross-timescale equivalent processing by combining the vibration excitation cycle and the number of load cycle jumps.

[0013] Furthermore, the fatigue life prediction is calculated using the Fe-safe Brown-Miller multiaxial fatigue criterion and the equivalent amplitude value is obtained by combining the critical plane method; the fatigue life prediction is further combined with the O'Donnell-Langer zirconium alloy fatigue curve and the load cycle spectrum is processed by the rainflow counting method.

[0014] Furthermore, the orthogonal experimental design was implemented using Design-Expert software, and a quantitative relationship between fatigue life and vibration load, wear, and structural parameters was established through multi-factor regression analysis.

[0015] The present invention also proposes an electronic device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of the method for predicting the fretting fatigue life of a petal-shaped fuel rod with simplified spring support.

[0016] The present invention also proposes a computer-readable storage medium for storing computer instructions, which, when executed by a processor, implement the steps of the method for predicting the fretting fatigue life of a petal-shaped fuel rod with simplified spring support.

[0017] The beneficial effects of this invention are: 1. This invention simplifies the non-critical support area of ​​the petal-shaped fuel rod by using an equivalent spring unit, and concentrates computational resources on the critical area of ​​petal support wear, thereby realizing creep and dynamic gap evolution.

[0018] 2. This invention couples vibration load, thermo-mechanical response, and contact friction problems, and considers the nonlinear characteristics of the friction coefficient as a function of temperature, slip velocity, and normal contact pressure, so that the contact state, temperature field, and local stress-strain response of the petal support contact area are closer to the actual service conditions.

[0019] 3. This invention incorporates the reverse movement stage into the wear time accumulation process and combines the vibration excitation cycle and the number of cycle jumps for cross-time scale equivalent processing. This can reduce the calculation cost caused by the small single-step increment of fretting wear and the large number of cycles, while reducing the life prediction deviation caused by the omission of wear contribution in the reverse movement stage.

[0020] 4. This invention combines finite element calculation, multiaxial fatigue life prediction, and orthogonal experimental design to systematically analyze the influence of multiple factors on fatigue life, providing a basis for optimizing the structural parameters of petal-shaped fuel rods and assessing their life margin.

[0021] 5. The theoretical system of this invention is rigorous and can be widely promoted and applied in the nuclear industry. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0023] Figure 1 This is a flowchart of the fretting fatigue simulation for petal-shaped fuel rods.

[0024] Figure 2 This is a schematic diagram of a 5×5 petal-shaped fuel assembly with a length of 600mm.

[0025] Figure 3 A simplified schematic diagram of the spring support structure.

[0026] Figure 4 This is a schematic diagram of the structural model for fretting fatigue simulation.

[0027] Figure 5 This is a schematic diagram illustrating the effect of spring support.

[0028] Figure 6 This is a schematic diagram of the excitation load for flow-induced vibration.

[0029] Figure 7 This is a schematic diagram of the micro-motion operation state.

[0030] Figure 8 This is a schematic diagram of the fatigue analysis curve.

[0031] Figure 9 This is a schematic diagram of a multi-factor orthogonal experimental design. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Combination Figures 1-9 This invention proposes a method for predicting the fretting fatigue life of a petal-shaped fuel rod using simplified spring support. The method includes: Step S1: Establish a simplified three-dimensional finite element model of the petal-shaped fuel rod, and use equivalent spring elements for support and constraint in non-critical structural areas; Step S2: Establish a constitutive model of the fuel rod based on the fuel material performance data. The constitutive model of the fuel rod includes the creep, elastic-plastic and irradiation swelling behavior of the cladding and core materials, and realizes the material constitutive calculation through the subroutines UMAT and CREEP. Step S3: Construct a spring support model that evolves with fuel consumption and time, simulate irradiation and stress relaxation behavior through dynamic stiffness, and describe the evolution of contact gap caused by creep and swelling through gap function; Step S4: Under the condition of thermo-mechanical coupling, the contact friction heat generation effect is considered, and the boundary conditions of heat conduction and convection heat transfer are updated through the subroutines UMATHT and FILM. At the same time, the friction coefficient is changed with temperature, slip velocity and contact stress through the subroutines FRIC. Step S5: Based on the energy dissipation wear model, and combined with the subroutine UMESHMOTION and ALE adaptive meshing technology, update the contact surface morphology caused by wear. Step S6: Apply a fluid excitation load to the petal-shaped fuel rod to simulate the fretting wear process under vibration, and include the reverse movement stage of the fuel rod in the wear time accumulation process; Step S7: Import the stress-strain results calculated by ABAQUS into Fe-safe, and use the multiaxial fatigue analysis method to predict the fatigue life of the petal-shaped contact area. Step S8: Analyze the effects of cyclic load, number of cycles, tilt angle, shell thickness and friction coefficient on fretting fatigue life using orthogonal experimental design method, and establish a regression prediction model.

[0034] Furthermore, the equivalent spring unit is used to simulate the structural support of non-critical structural areas of the petal-shaped fuel rod, and its dynamic stiffness decreases with time, fuel consumption and temperature.

[0035] Furthermore, creep and swelling deformation work together to influence the contact geometry evolution, and the gap function is used to characterize the combined effect of creep and swelling on the contact gap.

[0036] Furthermore, the dynamic stiffness k eff Using an exponential decay-saturation model:

[0037] In the formula, t For time, B For burn depth, k 0 represents the initial stiffness. R ∞ It is a saturation relaxation factor. λ Let be the relaxation rate constant. T This refers to the cladding temperature. f ( T ) represents the influence coefficient of temperature on the material.

[0038] Furthermore, the frictional heat generation is fed back to the temperature field solution as a transient heat conduction boundary condition, and the friction coefficient is defined by the subroutine FRIC so that it is dynamically adjusted with changes in temperature, relative sliding velocity and normal contact pressure.

[0039] Furthermore, the wear update process employs the subroutine UMESHMOTION combined with ALE adaptive mesh technology to achieve contact node position updates and wear morphology evolution.

[0040] Furthermore, incorporating the reverse movement phase into the wear time accumulation process includes: capturing the reverse movement time period in the displacement load spectrum, treating the reverse movement time period as part of the wear accumulation time, and performing cross-timescale equivalent processing by combining the vibration excitation cycle and the number of load cycle jumps.

[0041] Furthermore, the fatigue life prediction is calculated using the Fe-safe Brown-Miller multiaxial fatigue criterion and the equivalent amplitude value is obtained by combining the critical plane method; the fatigue life prediction is further combined with the O'Donnell-Langer zirconium alloy fatigue curve and the load cycle spectrum is processed by the rainflow counting method.

[0042] Furthermore, the orthogonal experimental design was implemented using Design-Expert software, and a quantitative relationship between fatigue life and parameters such as vibration and wear was established through multi-factor regression analysis.

[0043] Example 1 This invention proposes a method for predicting the fretting fatigue life of a petal-shaped fuel rod using simplified spring support. The method includes the following steps: Step S1: To improve computational efficiency, a simplified geometric model of the petal-shaped fuel rod contact is established, and the non-critical areas supported by the fuel rod petals are constrained by equivalent springs. Step S2: Further, establish a mechanical performance analysis model for petal-shaped fuel rods based on the fuel performance manual, specifically including calculation models for creep, elasticity and plasticity of the cladding and fuel pellets, and develop model code in conjunction with subroutines UMAT and CREEP. Step S3: Spring constraints provide time-varying constraint forces, while the core provides compressive forces caused by thermal expansion due to increased fuel consumption and irradiation swelling. Furthermore, the stress relaxation and mechanical properties of the boundary support under long-term irradiation conditions are dynamically simulated using spring stiffness. The stress relaxation and mechanical properties of the spring model are manifested as dynamic stiffness. k eff attenuation and gap g The evolution of the dynamic stiffness adopts an exponential decay-saturation model:

[0044] In the formula, t For time, B For burn depth, k 0 represents the initial stiffness. R ∞ It is a saturation relaxation factor. λ Let be the relaxation rate constant. T This refers to the cladding temperature. f ( T ) represents the influence coefficient of temperature on the material.

[0045] Step S4: Further, the relationship between irradiation creep and swelling changes is simulated using a dynamic gap:

[0046] In the formula, For the initial gap, subscript swell and creep These represent the changes in gap caused by irradiation swelling and creep, respectively. σ For stress.

[0047] Step S5: Further, in the ABAQUS finite element simulation software, the fuel rod is divided into structured elements, the wear area is locally focused and densified, and relevant parameters are set; Step S6: The friction coefficient of the cladding alloy changes with ambient temperature and local temperature fluctuations caused by frictional heat generation. Further, considering the frictional heat generation problem, subroutines UMATHT and FILM are developed to realize the variation of the heat transfer boundary conditions of the fuel rods:

[0048] In the formula, ρ For density, c p ( T ( ) is the specific heat capacity at constant pressure. Temperature as a function of time k ( T ) represents thermal conductivity. For temperature gradient, η For heat-to-work conversion rate, τ For tangential friction, For slip velocity, h ( T () represents the convective heat transfer coefficient. T 0 represents the fluid temperature.

[0049] Step S7: Further, the transient temperature field is solved using the heat flow parameters as boundary conditions, and the updated temperature field is passed to the material model and contact boundary conditions. The friction coefficient is varied with slip, temperature, and contact stress using the subroutine FRIC.

[0050] In the formula, μ Given the current coefficient of friction, μ 0 is the initial coefficient of friction. C s As a static friction enhancing factor, d v Let be the velocity decay constant. This is the temperature influence coefficient. p c For normal contact pressure, p 0 represents the initial contact pressure. n This is a stress index.

[0051] Step S8: Further, the morphology of the contact area continuously changes with the accumulation of wear depth, directly affecting the contact pressure distribution, friction behavior, and local stress field, further influencing the prediction of fretting fatigue life. A subroutine, UMESHMOTION, was developed based on an energy dissipation model, and ALE adaptive meshing technology was used to update the wear node coordinates. The corrected wear equation is:

[0052] In the formula, h ( x ) is the location x Wear depth at Δ N To accelerate the number of load cycle jumps, α The wear coefficient is... δ This represents the sliding distance.

[0053] Step S9: Further, the displacement load spectrum obtained from CFD calculation is applied to Rod1 as a boundary condition to simulate the fluid excitation effect and realize the fuel rod wear simulation. Under long-term burnup, the fuel rod will undergo significant expansion and swelling during the reverse movement process under vibration excitation. At this time, failure to calculate wear will lead to an underestimation of the predicted value. Therefore, it is proposed to add the reverse movement process time to the wear process for analysis. Step S10: Further, the fuel rod fatigue analysis is performed using Fe-safe software, employing the Brown-Miller multiaxial fatigue algorithm based on the critical plane method.

[0054] In the formula, Δ γ max This represents the maximum shear strain amplitude. K Let Δ be the influence function of strain amplitude. ε n This represents the critical surface strain amplitude. A , B and C The fatigue constant of the material; The fatigue strength coefficient, σ m For average stress, E For elastic modulus, The fatigue ductility coefficient, N f This is the stress cycle coefficient.

[0055] Step S11: Further, based on strain fatigue theory, fatigue life prediction is performed using the O'Donnell-Langer zirconium alloy fatigue curve with stress amplitude as the reference. The fatigue stress response of the fuel rod under different load conditions is obtained by combining the rainflow counting method, thus yielding the structural fatigue life. The life prediction formula is:

[0056] In the formula, S For allowable stress, RA Reduction of area S e This represents the fatigue limit value.

[0057] Step S12: Further, based on orthogonal design experiments, fretting fatigue analysis under the influence of multiple factors is completed using Design-Expert to explore the effects of amplitude, frequency, shell thickness, friction coefficient, etc. on fretting fatigue life.

[0058] Example 2 This invention proposes a method for predicting the fretting fatigue life of a petal-shaped fuel rod using simplified spring support. The method includes the following steps: Step S1: Establish using 3D modeling software Figure 4 The typical petal-shaped fuel rod analysis model is shown, and the model is imported into the ABAQUS finite element software.

[0059] Step S2: Further, in the software interaction module, the critical wear area of ​​the petal is set as a nonlinear contact pair between the rod bundles to define the friction behavior, and the non-wear self-supporting area of ​​the petal is set as a spring constraint.

[0060] Step S3: Further, based on the fuel performance manual, establish constitutive models of petal-shaped fuel rods for irradiation swelling, creep, and elastoplastic deformation, and develop subroutines UMAT and CREEP to achieve the interconnected solution of different models.

[0061] Step S4: Creep and relaxation of the petal-shaped fuel rod are processes of permanent deformation and stress decay of the material over time under stress and irradiation, which are represented as dynamic stiffness in the spring model. k eff attenuation and gap g The evolution of dynamic stiffness simulation of radiation stress relaxation is further described using an exponential decay-saturation model:

[0062] In the formula, t For time, B For burn depth, k 0 represents the initial stiffness. R ∞ It is a saturation relaxation factor. λ Let be the relaxation rate constant. T This refers to the cladding temperature. f ( T ) represents the influence coefficient of temperature on the material.

[0063] Step S5: Further, the relationship between irradiation creep and swelling changes is simulated using a dynamic gap:

[0064] In the formula, For the initial gap, subscript swell and creep These represent the changes in gap caused by irradiation swelling and creep, respectively. σ For stress.

[0065] Step S6: Further, in ABAQUS, set the material properties, adaptive time step, heat transfer boundary conditions, thermal power and pressure parameters for the core and shell in the material properties, analysis step, interaction, load and mesh modules, and specify the power distribution form and its history over time. Local element refinement is performed in the petal wear area.

[0066] Step S7: The friction coefficients at different temperatures can characterize the contact state and mechanical properties of the material surface. Furthermore, by developing subroutines UMATHT and FILM, the thermal conductivity and specific heat capacity of the material at high temperatures are defined, thereby realizing the change of the heat transfer boundary conditions of the fuel rod.

[0067] In the formula, ρ For density, c p ( T ( ) is the specific heat capacity at constant pressure. Temperature as a function of time k ( T ) represents thermal conductivity, ▽ T For temperature gradient, η For heat-to-work conversion rate, τ For tangential friction, For slip velocity, h ( T () represents the convective heat transfer coefficient. T 0 represents the fluid temperature.

[0068] Step S8: The friction of the rod bundles is converted into heat energy, altering the local material properties of the contact area, which is a key issue that must be considered in the fretting wear process. Furthermore, for the friction coefficient of the cladding alloy, the variation of the friction coefficient with slip, temperature, and contact stress is achieved through the subroutine FRIC.

[0069]

[0070] In the formula, μ Given the current coefficient of friction, μ 0 is the initial coefficient of friction. C s As a static friction enhancing factor, d v Let be the velocity decay constant. This is the temperature influence coefficient. p c For normal contact pressure, p 0 represents the initial contact pressure. n This is a stress index.

[0071] Step S9: Further, the petal wear region morphology is updated based on the subroutine UMESHMOTION and ALE adaptive meshing technology. The corrected wear equation based on energy dissipation is as follows:

[0072] In the formula, h ( x ) is the locationx Wear depth at Δ N To accelerate the number of load cycle jumps, α The wear coefficient is... δ This represents the sliding distance.

[0073] Step S10: Further, determine the master-slave surface relationship and select... Figure 4 The Rod1 petal contact area is the main surface, and Rod2 is the slave surface. The main surface uses sparser elements to reduce computation, while the slave surface uses denser elements. An adaptive node set and adaptive region are set on the slave surface to capture the wear morphology.

[0074] Step S11: Further, fluid excitation is applied as a boundary condition to both sides of Rod1, and the movement of the two end faces is controlled by the subroutine DISP. Figure 6 The vibration displacement is shown. By capturing the time variation through DISP, a method is proposed to gradually increase the wear time variation during the reverse movement process into the wear process calculation, and to achieve wear analysis across time scales by combining the vibration excitation period and cycle number control.

[0075] Step S12: Unlike force loading, displacement loading requires capturing the forces between fuel rods. Furthermore, combined with displacement motion, a system is established... Figure 7 As shown F - D The curve relationship is used to determine the partial and full slip states in order to analyze the effects of creep and wear at different stages.

[0076] Step S13: Further, based on the fatigue damage constitutive relation, the aforementioned petal wear morphology change is introduced, and the odb result file obtained by ABAQUS solution is imported into Fe-safe to assign fatigue characteristic parameters to the material.

[0077] Step S14: Further, based on the Brown-Miller multiaxial fatigue algorithm, the complex stress-strain state of the petal wear region is processed, and the equivalent strain amplitude of the wear region is calculated. The Brown-Miller criterion is:

[0078] In the formula, Δ γ max This represents the maximum shear strain amplitude. K Let Δ be the influence function of strain amplitude. ε n This represents the critical surface strain amplitude. A , B and C The fatigue constant of the material; The fatigue strength coefficient, σ mFor average stress, E For elastic modulus, The fatigue ductility coefficient, N f This is the stress cycle coefficient.

[0079] Step S15: Further, based on strain fatigue theory, the fatigue life of the O'Donnell-Langer zirconium alloy is calculated using the stress amplitude as a reference:

[0080] In the formula, S For allowable stress, RA Reduction of area S e This represents the fatigue limit.

[0081] Step S16: Further, based on orthogonal design experiments, data statistical analysis is performed using Design-Expert to establish a regression equation for the degree of influence on fatigue life, and to explore the significant influence and quantitative relationship between cyclic load, number of cycles, tilt angle, and shell thickness on fretting fatigue life.

[0082] The present invention also proposes an electronic device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of the method for predicting the fretting fatigue life of a petal-shaped fuel rod with simplified spring support.

[0083] The present invention also proposes a computer-readable storage medium for storing computer instructions, which, when executed by a processor, implement the steps of the method for predicting the fretting fatigue life of a petal-shaped fuel rod with simplified spring support.

[0084] The memory in this application embodiment can be volatile memory or non-volatile memory, or it can include both volatile and non-volatile memory. The non-volatile memory can be read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), or flash memory. The volatile memory can be random access memory (RAM), which is used as an external cache. By way of example, but not limitation, many forms of RAM are available, such as static random access memory (SRAM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), double data rate synchronous dynamic random access memory (DDRSDRAM), enhanced synchronous dynamic random access memory (ESDRAM), synchronous linked dynamic random access memory (SLDRAM), and direct rambus RAM (DR RAM). It should be noted that the memory used in the methods described in this invention is intended to include, but is not limited to, these and any other suitable types of memory.

[0085] 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 instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this application 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 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 media may be magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g., high-density digital video discs (DVDs)), or semiconductor media (e.g., solid-state disks (SSDs)).

[0086] In implementation, each step of the above method can be completed by integrated logic circuits in the processor's hardware or by instructions in software. The steps of the method disclosed in the embodiments of this application can be directly implemented by a hardware processor, or by a combination of hardware and software modules in the processor. The software modules can reside in random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, registers, or other mature storage media in the art. This storage medium is located in memory, and the processor reads information from the memory and, in conjunction with its hardware, completes the steps of the above method. To avoid repetition, detailed descriptions are omitted here.

[0087] It should be noted that the processor in the embodiments of this application can be an integrated circuit chip with signal processing capabilities. During implementation, each step of the above method embodiments can be completed by the integrated logic circuitry in the processor's hardware or by instructions in software form. The processor can be a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components. It can implement or execute the methods, steps, and logic block diagrams disclosed in the embodiments of this application. The general-purpose processor can be a microprocessor or any conventional processor. The steps of the methods disclosed in the embodiments of this application can be directly embodied as execution by a hardware decoding processor, or as a combination of hardware and software modules in the decoding processor. The software modules can be located in random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, registers, or other mature storage media in the art. This storage medium is located in memory, and the processor reads the information in the memory and, in conjunction with its hardware, completes the steps of the above methods.

[0088] The above provides a detailed description of the fretting fatigue life prediction method for petal-shaped fuel rods using simplified spring support proposed in this invention. Specific examples have been used to illustrate the principle and implementation of this invention. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for predicting the fretting fatigue life of a petal-shaped fuel rod using simplified spring support, characterized in that, The method includes: Step S1: Establish a simplified three-dimensional finite element model of the petal-shaped fuel rod, and use equivalent spring elements for support and constraint in non-critical structural areas; Step S2: Establish a constitutive model of the fuel rod based on the fuel material performance data. The constitutive model of the fuel rod includes the creep, elastic-plastic and irradiation swelling behavior of the cladding and core materials, and realizes the material constitutive calculation through the subroutines UMAT and CREEP. Step S3: Construct a spring support model that evolves with fuel consumption and time, simulate irradiation and stress relaxation behavior through dynamic stiffness, and describe the evolution of contact gap caused by creep and swelling through gap function; Step S4: Under the condition of thermo-mechanical coupling, the contact friction heat generation effect is considered, and the boundary conditions of heat conduction and convection heat transfer are updated through the subroutines UMATHT and FILM. At the same time, the friction coefficient is changed with temperature, slip velocity and contact stress through the subroutines FRIC. Step S5: Based on the energy dissipation wear model, and combined with the subroutine UMESHMOTION and ALE adaptive meshing technology, update the contact surface morphology caused by wear. Step S6: Apply a fluid excitation load to the petal-shaped fuel rod to simulate the fretting wear process under vibration, and include the reverse movement stage of the fuel rod in the wear time accumulation process; Step S7: Import the stress-strain results calculated by ABAQUS into Fe-safe, and use the multiaxial fatigue analysis method to predict the fatigue life of the petal-shaped contact area. Step S8: Analyze the effects of cyclic load, number of cycles, tilt angle, shell thickness and friction coefficient on fretting fatigue life using orthogonal experimental design method, and establish a regression prediction model.

2. The method according to claim 1, characterized in that, The equivalent spring unit is used to simulate the structural support of non-critical structural areas of the petal-shaped fuel rod, and its dynamic stiffness decreases with time, fuel consumption and temperature.

3. The method according to claim 1, characterized in that, Creep and swelling deformation work together to influence the evolution of contact geometry, and the gap function is used to characterize the combined effect of creep and swelling on the contact gap.

4. The method according to claim 1, characterized in that, The dynamic stiffness k eff Using an exponential decay-saturation model: In the formula, t For time, B For burn depth, k 0 represents the initial stiffness. R ∞ It is a saturation relaxation factor. λ Let be the relaxation rate constant. T This refers to the cladding temperature. f ( T ) represents the influence coefficient of temperature on the material.

5. The method according to claim 1, characterized in that, The frictional heat generation is fed back to the temperature field solution as a transient heat conduction boundary condition. The friction coefficient is defined by the subroutine FRIC, which dynamically adjusts with changes in temperature, relative slip velocity, and normal contact pressure.

6. The method according to claim 1, characterized in that, Including the reverse movement phase in the wear time accumulation process includes: capturing the reverse movement time period in the displacement load spectrum, taking the reverse movement time period as part of the wear accumulation time, and performing cross-timescale equivalent processing by combining the vibration excitation cycle and the number of load cycle jumps.

7. The method according to claim 1, characterized in that, The fatigue life prediction is calculated using the Fe-safe Brown-Miller multiaxial fatigue criterion and combined with the critical plane method to obtain the equivalent amplitude value; the fatigue life prediction is further combined with the O'Donnell-Langer zirconium alloy fatigue curve and the rainflow counting method is used to process the load cycle spectrum.

8. The method according to claim 1, characterized in that, The orthogonal experimental design was implemented using Design-Expert software, and a quantitative relationship between fatigue life and vibration load, wear and structural parameters was established through multi-factor regression analysis.

9. An electronic device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1-8.

10. A computer-readable storage medium for storing computer instructions, characterized in that, When the computer instructions are executed by the processor, they implement the steps of the method according to any one of claims 1-8.

Images