Simulation evaluation method for thermal fatigue crack thermal stress of subway train axle-mounted brake disc

Abstract

The invention relates to the technical field of thermal stress, in particular to a subway train axle-mounted brake disc thermal fatigue crack thermal stress simulation evaluation method which comprises the following steps: simulating interaction between a brake disc and a friction plate by adopting a uniform contact model; properly simplifying the structure of the brake disc, and establishing a finite element model; based on actual data, an emergency braking mode with a constant friction coefficient is selected; the surface conditions of the brake disc under different crack conditions are listed, and the change of a thermal stress field under continuous two times of constant-pressure emergency braking is studied; through comparison with the actual thermal fatigue damage condition of the brake disc, the accuracy and reliability of the simulation model are verified; and improvement suggestions including brake disc design, material selection and brake system optimization are provided. The method has the effects that the thermal-mechanical coupling performance of the braking system during emergency braking is improved, and the maximum temperature and thermal stress of the brake disc under continuous braking are effectively reduced.

Description

Technical Field

[0001] The present application relates to the field of thermal stress technology, and in particular to a method for simulating and evaluating thermal stress of thermal fatigue cracks of axle-mounted brake discs of subway trains. Background Art

[0002] As an indispensable part of the modern transportation system, rail vehicles are widely used in urban rail transit, high-speed railways and other fields. Due to the increase in transportation demand, the design speed level of subway trains has reached 120km / h, 140km / h and even 160km / h. The increase in train operating speed has also put forward higher requirements on its braking performance. Subway trains brake frequently between stations, and a large amount of heat energy generated by the friction between the brake disc and the friction plate is mainly absorbed by the brake disc, which will cause the brake disc temperature to rise rapidly, and then induce thermal deformation of the structure. Once the thermal stress change exceeds the material strength, the brake disc surface is prone to thermal fatigue damage such as thermal cracks and hot spots, which will affect the braking performance and even cause serious operational accidents. Therefore, improvements are needed. Summary of the invention

[0003] In order to solve the above problems, the present application provides a method for simulating and evaluating thermal fatigue cracks and thermal stresses of axle-mounted brake discs of subway trains.

[0004] The first invention objective of this application is achieved through the following technical solutions:

[0005] A method for simulating and evaluating thermal fatigue cracks and thermal stresses of a subway train axle-mounted brake disc, comprising the steps of:

[0006] A uniform contact model is used to simulate the interaction between the brake disc and the friction pad;

[0007] The brake disc structure is appropriately simplified and a finite element model is established;

[0008] Based on actual data, select the emergency braking mode with constant friction coefficient;

[0009] The surface conditions of the brake disc under different crack conditions are listed, and the changes in the thermal stress field under two consecutive constant-pressure emergency braking are studied;

[0010] By comparing the thermal fatigue damage of the actual brake disc, the accuracy and reliability of the simulation model are verified;

[0011] Provide suggestions for improvements including brake disc design, material selection and brake system optimization.

[0012] In a preferred embodiment, the step of listing the surface conditions of the brake disc under different crack conditions and studying the changes in the thermal stress field under two consecutive constant-pressure emergency brakings includes the following steps:

[0013] Single cracks and double cracks are provided on the surface of the brake disc;

[0014] Construct two types of crack models: rectangular and elliptical;

[0015] Based on the indirect thermal-mechanical coupling method, the thermal field and mechanical field are solved respectively, and the temperature field and stress field distribution of the brake disc during emergency braking are analyzed;

[0016] Based on the friction power method, the work done by friction and the heat flux density of the disk are calculated;

[0017] Based on the transient heat transfer model, the transient temperature field of the brake disc is solved;

[0018] Solve the transient temperature field based on the backward difference method and derive the solution formula of the temperature field;

[0019] Determine the airflow type based on the Reynolds number and calculate the convective heat transfer coefficient at different speeds;

[0020] Probes are placed near the cracks, and temperature and stress cloud maps are obtained through simulation to analyze the influence of crack morphology and distribution on the thermal stress distribution and hot spot formation of the brake disc.

[0021] In a preferred embodiment, the step of calculating the work done by the friction force and the heat flux density of the disk surface based on the friction power method comprises the steps of:

[0022] Based on the preset formula W = ηFv(r, t) = ηp(r)μv(r, t) and η represents the energy distribution coefficient, p(r) represents the friction plate pressure, μ represents the friction coefficient, r represents the friction radius, S represents the area swept by the friction surface, S = 0.2670m 2 , R and Represent the inner diameter and outer diameter of the friction plate respectively, v0 represents the initial braking velocity, a represents the braking deceleration, D represents the wheel diameter, and the work W done by the friction force during braking and the heat flux density q(r,t) of the disc surface are calculated.

[0023] In a preferred embodiment, the step of solving the transient temperature field of the brake disc based on the transient heat transfer model comprises the steps of:

[0024] Based on preset formula Solve the transient temperature field, K, D represent the thermal conductivity matrix and temperature change matrix respectively, T, They represent the node temperature vector and the derivative vector of the node temperature with respect to time, respectively, and F represents the generalized node heat flux vector;

[0025] Based on preset formula C ij =∫∫∫ΩρcN i N jdxdydz, F i =∫∫∫ΩQN i dxdydz-∫∫S(q-αT f )N i ds, solve the thermal conductivity matrix K of each unit ij , temperature matrix C ij 、Node heat flow vector F i .

[0026] In a preferred embodiment, the step of solving the transient temperature field based on the backward difference method and deriving the solution formula of the temperature field includes the steps of:

[0027] Based on the preset formula T n+1 =T n +T n+1 Δt, derive the solution formula for transient temperature field in

[0028] In a preferred embodiment, the step of determining the airflow type based on the Reynolds number and calculating the convective heat transfer coefficient at different speeds comprises the steps of:

[0029] Setting braking condition parameters, including vehicle speed, wheel diameter, initial braking speed, braking time, braking pressure, friction factor and acceleration;

[0030] Determine the type of airflow based on the Reynolds number, where the airflow type includes laminar flow and turbulent flow;

[0031] When Re≤2.4×10 5 When the airflow type is laminar flow, the empirical formula is K a represents the thermal conductivity of air, which is 0.0276W / (m·K), D represents the outer diameter of the brake disc, in m, and R e Reynolds number, Re = (ωR)ρ a D / μ a , ω represents the angular velocity of the brake disc, R represents the rolling radius of the wheel, R = 0.42m, ρ a represents the density of air, ρ a =1.13kg / m 3 , μ a represents the dynamic viscosity of air, which is 1.91×10 -5 Pa·s;

[0032] When Re>2.4×10 5 When the airflow type is turbulent, the empirical formula is

[0033] Calculate the convective heat transfer coefficient for different airflow types and speeds;

[0034] Based on the friction power method, the heat flux input time function table under braking conditions is output.

[0035] In a preferred embodiment, the step of arranging a probe near the crack, obtaining a temperature and stress cloud map by simulation, and analyzing the influence of the crack morphology and distribution on the thermal stress distribution and hot spot formation of the brake disc comprises the following steps:

[0036] Arrange the probe near the crack;

[0037] Conduct temperature field simulation, simulate continuous emergency braking conditions, obtain temperature cloud maps, and analyze temperature distribution and causes of hot spots;

[0038] Conduct stress field simulation, obtain equivalent stress cloud diagram, and analyze the impact of cracks on stress distribution;

[0039] Analyze the simulation results of a single crack brake disc, compare the temperature and stress changes under different crack shapes, and analyze the impact of cracks on temperature and stress;

[0040] Analyze the simulation results of the double-crack brake disc, study the interaction mechanism between multiple cracks, and compare the temperature and stress differences between the double-crack and no-crack cases;

[0041] By comparing probe data, the effects of crack shape, location and number on brake disc temperature and stress, as well as the stress concentration phenomenon caused by cracks, are analyzed.

[0042] The above-mentioned second objective of the present application is achieved through the following technical solutions:

[0043] A computer device comprises a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above-mentioned method for simulating and evaluating thermal fatigue cracks and thermal stresses of axle-mounted brake discs of subway trains when executing the computer program.

[0044] The third objective of the present application is achieved through the following technical solutions:

[0045] A computer-readable storage medium stores a computer program, wherein the computer program, when executed by a processor, implements the steps of the above-mentioned method for simulating and evaluating thermal fatigue cracks and thermal stresses of axle-mounted brake discs of subway trains.

[0046] In summary, the present application includes at least one of the following beneficial technical effects:

[0047] The interaction between the brake disc and the friction pad is simulated using a uniform contact model. This means that the pressure between the two contacting surfaces is assumed to be uniformly distributed, and the actual contact spots or pressure concentrations are not considered, which simplifies the calculations. The brake disc is the main component in the vehicle braking system, while the friction pad is part of the braking system, and the interaction between them includes the generation of friction and the exchange of heat. The structure of the brake disc is necessary to simplify in order to reduce the complexity of the calculation while maintaining the validity of the model. Then, a finite element model is used, which is a numerical analysis method that analyzes a continuum by splitting it into many small, interconnected elements to predict the stress, deformation, etc. of the structure. The emergency braking method is selected using actual data collected through experiments, tests, or real-world observations. It is assumed that the friction coefficient remains constant during braking, although in reality the friction coefficient may change due to factors such as temperature and speed. The emergency braking method is a fast and forced braking method used to quickly slow down or stop the vehicle in an emergency. Different possible crack conditions on the surface of the brake disc are listed, and the changes in the thermal stress field of the brake disc in the emergency braking situation with the same pressure applied twice in succession are studied. The cracking condition may affect the performance and life of the brake disc, while the thermal stress field is the stress distribution generated inside the material due to temperature changes. The thermal stress field predicted by the simulation model is compared with the thermal fatigue damage experienced by the actual brake disc. Thermal fatigue damage refers to the damage that may occur to the material after repeated thermal cycles. Through this comparison, the accuracy and reliability of the simulation model are verified, that is, the consistency and trustworthiness of the model prediction results with the actual observation results. Based on the previous research results, improvement suggestions are proposed. These suggestions may involve the structural and shape design of the brake disc, material selection, and overall optimization of the brake system. The purpose is to improve the performance, efficiency, safety or reliability of the brake system, which may include measures such as improving braking force, reducing wear, and increasing heat capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a flow chart of an implementation of a method for simulating and evaluating thermal fatigue cracks and thermal stresses of axle-mounted brake discs of subway trains according to the present application;

[0049] Figure 2 This is a flowchart for implementing step S40 in an embodiment of a method for simulating and evaluating thermal fatigue cracks and thermal stresses of axle-mounted brake discs of subway trains of the present application;

[0050] Figure 3 This is a flowchart for implementing step S404 in an embodiment of a method for simulating and evaluating thermal fatigue cracks and thermal stresses of axle-mounted brake discs of subway trains of the present application;

[0051] Figure 4This is a flowchart for implementing step S405 in an embodiment of a method for simulating and evaluating thermal fatigue cracks and thermal stresses of axle-mounted brake discs of subway trains of the present application;

[0052] Figure 5 This is a flowchart for implementing step S406 in an embodiment of a method for simulating and evaluating thermal fatigue cracks and thermal stresses of axle-mounted brake discs of subway trains of the present application;

[0053] Figure 6 This is a flowchart for implementing step S407 in an embodiment of a method for simulating and evaluating thermal fatigue cracks of axle-mounted brake discs of subway trains of the present application;

[0054] Figure 7 This is a flowchart for implementing step S408 in an embodiment of a method for simulating and evaluating thermal fatigue cracks and thermal stresses of axle-mounted brake discs of subway trains of the present application;

[0055] Figure 8 This is a principle block diagram of a computer device of the present application. DETAILED DESCRIPTION

[0056] The following is combined with Figure 1-8 This application is described in further detail.

[0057] In one embodiment, if Figure 1 As shown, the present application discloses a method for simulating and evaluating thermal fatigue cracks of axle-mounted brake discs of subway trains, which specifically includes the following steps:

[0058] S10: Use uniform contact model to simulate the interaction between brake disc and friction pad;

[0059] In this embodiment, uniform contact model: This is a theoretical model that assumes that the contact pressure between the two contact surfaces is uniformly distributed. In this model, the actual contact spots or pressure concentrations on the contact surface are not considered, but it is simplified to have the same pressure on the entire contact surface; brake disc: refers to a major component in the vehicle braking system, usually a rotating metal disc. When the brake is applied, the friction pad is pressed against the brake disc, slowing down or stopping the rotation of the wheel through friction; friction pad: It is part of the braking system, usually made of a special friction material, used to contact the brake disc and generate friction, thereby achieving the braking effect; interaction: Here refers to the physical contact and interaction between the brake disc and the friction pad, including the generation of friction and the exchange of heat.

[0060] Specifically, in this step, the uniform contact model is used to simulate the interaction between the brake disc and the friction pad. This means that the pressure between the two contact surfaces is assumed to be uniformly distributed, and the actual contact spots or pressure concentrations are not considered, thereby simplifying the calculation. The brake disc is the main component in the vehicle braking system, and the friction pad is part of the braking system. The interaction between them includes the generation of friction and the exchange of heat.

[0061] S20: appropriately simplify the brake disc structure and establish a finite element model;

[0062] In this embodiment, appropriate simplification refers to the necessary simplification of the structure or characteristics of the actual object in order to reduce the complexity of calculation while maintaining the validity of the model when establishing the model; the finite element model is a numerical analysis method that analyzes the continuum by dividing it into many small, interconnected elements (usually polygons or tetrahedrons). This method can be used to predict the stress, deformation, etc. of the structure.

[0063] Specifically, in this step, the structure of the brake disc is simplified as necessary to reduce the complexity of the calculation while maintaining the validity of the model. Then, the finite element model is used, which is a numerical analysis method that analyzes by dividing a continuum into many small, interconnected elements to predict the stress, deformation, etc. of the structure.

[0064] S30: Based on actual data, select an emergency braking mode with a constant friction coefficient;

[0065] In this embodiment, actual data refers to information collected through experiments, tests, or real-world observations. These data are used to verify the accuracy and reliability of the model; constant friction coefficient refers to the fact that the friction coefficient remains unchanged during braking. This is a theoretical assumption. In fact, the friction coefficient may change due to factors such as temperature and speed; emergency braking method refers to a fast and forced braking method used to quickly slow down or stop the vehicle in an emergency.

[0066] Specifically, in this step, the emergency braking method is selected using actual data collected through experiments, tests, or real-world observations. It is assumed that the friction coefficient remains constant during braking, although in reality the friction coefficient may change due to factors such as temperature and speed. The emergency braking method is a fast, forced braking method used to quickly slow down or stop the vehicle in an emergency.

[0067] S40: List the surface conditions of the brake disc under different crack conditions and study the changes in the thermal stress field under two consecutive constant-pressure emergency braking;

[0068] In this embodiment, crack condition: refers to cracks or defects that may exist on the surface of the brake disc. Cracks may affect the performance and life of the brake disc; thermal stress field: stress distribution generated inside the material due to temperature changes. During the braking process, the brake disc will experience changes in thermal stress due to the heat generated by friction; two consecutive constant pressure emergency brakes: refers to the situation where two emergency brakes are performed consecutively in a short period of time, and the same pressure is applied each time. This situation will generate thermal stress on the brake disc.

[0069] Specifically, in this step, different possible crack conditions on the surface of the brake disc are listed, and the changes in the thermal stress field of the brake disc under emergency braking conditions with the same pressure applied twice in a row are studied. The crack condition may affect the performance and life of the brake disc, and the thermal stress field is the stress distribution generated inside the material due to temperature changes.

[0070] S50: Verify the accuracy and reliability of the simulation model by comparing it with the thermal fatigue damage of the actual brake disc;

[0071] In this embodiment, thermal fatigue damage refers to the damage that may occur to a material after repeated thermal cycles (heating and cooling), which may cause the material performance to deteriorate; simulation model is a computer program used to simulate and analyze the behavior of an actual system. A simulation model can be used to predict the response of a system under different conditions; accuracy and reliability are terms that describe the consistency and trustworthiness of the simulation model's predictions with actual observations. Accuracy refers to the precision of the model's predictions, and reliability refers to the stability of the model under different conditions and time points.

[0072] Specifically, in this step, the thermal stress field predicted by the simulation model is compared with the thermal fatigue damage experienced by the actual brake disc. Thermal fatigue damage refers to the damage that may occur to the material after repeated thermal cycles. Through this comparison, the accuracy and reliability of the simulation model are verified, that is, the consistency and trustworthiness of the model prediction results and the actual observation results.

[0073] S60: Provide suggestions for improvements, including brake disc design, material selection and brake system optimization.

[0074] In this embodiment, improvement suggestions: improvement measures for existing systems, designs or processes proposed based on research results. The purpose is to improve performance, efficiency, safety or reliability; brake disc design: refers to the structural and shape design of the brake disc, including its size, shape, thickness and material, etc.; material selection: refers to the selection of suitable materials for brake discs and friction pads during the manufacturing process. The choice of materials is crucial to braking performance and durability; brake system optimization: refers to improvements to the design, operation or components of the brake system to improve its overall performance and efficiency. This may include improving braking force, reducing wear, increasing heat capacity, etc.

[0075] Specifically, in this step, improvement suggestions are proposed based on the previous research results. These suggestions may involve the structure and shape design of the brake disc, material selection, and overall optimization of the brake system. The purpose is to improve the performance, efficiency, safety or reliability of the brake system, which may include measures such as improving braking force, reducing wear, and increasing heat capacity.

[0076] Figure 2 , step S40, comprising the steps of:

[0077] S401: setting a single crack and a double crack on the surface of the brake disc;

[0078] S402: construct two types of crack models: rectangular and elliptical;

[0079] S403: Solving the thermal field and mechanical field respectively based on the indirect thermal-mechanical coupling method, and analyzing the temperature field and stress field distribution of the brake disc during emergency braking;

[0080] S404: Calculate the work done by the friction force and the heat flux density of the disk surface based on the friction power method;

[0081] S405: solving the transient temperature field of the brake disc based on the transient heat transfer model;

[0082] S406: Solving the transient temperature field based on the backward difference method, and deriving a solution formula for the temperature field;

[0083] S407: Determine the airflow type based on the Reynolds number, and calculate the convective heat transfer coefficient at different speeds;

[0084] S408: Arrange probes near the cracks, obtain temperature and stress cloud maps through simulation, and analyze the influence of crack morphology and distribution on the thermal stress distribution and hot spot formation of the brake disc.

[0085] In this embodiment, in step S401, single cracks and double cracks are simulated on the surface of the brake disc to explore the effect of cracks on braking performance. Then, in step S402, two crack models, rectangular and elliptical, are constructed to provide different crack geometries for subsequent simulation analysis. Step S403 uses the indirect thermal-mechanical coupling method to solve the thermal field and mechanical field of the brake disc during emergency braking, respectively, so as to analyze the distribution of the temperature field and stress field. In step S404, the work done by the friction force and the heat flux density of the disc surface are calculated by the friction power method, which is crucial to understanding the heat generation and distribution of the brake disc. Step S405 uses the transient heat transfer model to solve the transient temperature field of the brake disc to capture the change of temperature over time. In order to solve the transient temperature field more accurately, step S406 uses the backward difference method and derives the solution formula for the temperature field. In step S407, the Reynolds number is calculated to determine the type of airflow, and the convective heat transfer coefficient at different speeds is calculated, which is critical for analyzing the heat dissipation performance of the brake disc. Finally, in step S408, probes are arranged near the cracks, and temperature and stress cloud maps are obtained through simulation, analyzing the influence of crack morphology and distribution on the thermal stress distribution and hot spot formation of the brake disc, providing an important basis for the design optimization of the brake disc.

[0086] Figure 3 , step S404, comprising the steps of:

[0087] SB1: Based on the preset formula W = ηFv(r, t) = ηp(r)μv(r, t) and η represents the energy distribution coefficient, p(r) represents the friction plate pressure, μ represents the friction coefficient, r represents the friction radius, S represents the area swept by the friction surface, S = 0.2670m 2 , R and Represent the inner diameter and outer diameter of the friction plate respectively, v0 represents the initial braking velocity, a represents the braking deceleration, D represents the wheel diameter, and the work W done by the friction force during braking and the heat flux density q(r,t) of the disc surface are calculated.

[0088] In this embodiment, in step SB1, a series of calculations are performed to determine the work W done by the friction force during braking and the heat flux density q(r, t) on the disc surface. This calculation is based on a series of preset formulas, which involve the definition and calculation of multiple physical quantities. First, the energy distribution coefficient η is a dimensionless parameter that describes how the heat generated by friction during braking is distributed between the friction pad and the brake disc. The friction pad pressure p(r) refers to the vertical pressure acting on the friction pad, usually expressed in Pascals (Pa). The friction coefficient μ is a dimensionless parameter that describes the friction characteristics between two contact surfaces. The friction radius r refers to the distance from the center of the brake disc to the contact point of the friction pad, usually expressed in meters (m). The area swept by the friction surface S refers to the area covered by the friction pad when it moves relative to the brake disc during braking, usually expressed in square meters (m 2 ) is the unit. In the formula, R and Represents the inner diameter and outer diameter of the friction plate, respectively. These parameters are used to calculate the actual contact area of ​​the friction plate. The initial braking speed v0 refers to the speed of the wheel when braking begins, usually in meters per second (m / s). The braking deceleration a refers to the rate at which the wheel decelerates during braking, usually in meters per square second (m / s 2 ) as the unit. The wheel diameter D refers to the diameter of the wheel, usually in meters (m). By putting these parameters into the preset formula W = ηFv(r,t) = ηp(r)μv(r,t), the work W done by the friction force during braking can be calculated. This is the negative work done by the friction force on the wheel during braking, usually in joules (J). At the same time, putting these parameters into the preset formula The heat flux density q(r,t) of the disk is also calculated, which is the heat flow rate per unit area, usually expressed in watts per square meter (W / m 2 These calculations are critical to understanding and analyzing the thermodynamic behavior of brake systems, especially when considering thermal management and braking effectiveness when designing brake systems.

[0089] Figure 4 , step S405, comprising the steps of:

[0090] SD1: Based on preset formula Solve the transient temperature field, K, D represent the thermal conductivity matrix and temperature change matrix respectively, T, They represent the node temperature vector and the derivative vector of the node temperature with respect to time, respectively, and F represents the generalized node heat flux vector;

[0091] SD2: Based on preset formula C ij =∫∫∫ΩρcN i N j dxdydz, F i =∫∫∫ΩQNi dxdydz-∫∫S(q-αT f )N i ds, solve the thermal conductivity matrix K of each unit ij , temperature matrix C ij 、Node heat flow vector F i .

[0092] In this embodiment, in steps SD1 and SD2, a numerical method is used to solve the transient temperature field of the brake disc during the braking process, in order to simulate and analyze the temperature change of the brake disc when it is subjected to repeated thermal loads. In step SD1, based on the preset formula Solve the transient temperature field. Here, the thermal conductivity matrix K contains the heat conduction characteristics between each node in the system, which is usually related to the thermal conductivity and geometry of the material. The temperature change matrix D contains the relationship between the node temperature change and the heat capacity. The node temperature vector T is a set of values ​​representing the temperature of each node, and the node temperature derivative vector with respect to time is It represents the rate of change of the temperature of these nodes over time. The generalized nodal heat flux vector F represents the heat flux acting on each node, including the heat flux generated by friction and the heat transferred by conduction, convection and radiation. In the SD2 step, the solution process is further refined, based on the preset formula C ij =∫∫∫ΩρcN i N j dxdydz, F i =∫∫∫ΩQN i dxdydz-∫∫S(q-αT f )N i ds solves the thermal conductivity matrix K of each unit ij , temperature matrix C ij and the node heat flux vector F i The unit here refers to the small area or element into which the brake disc is divided. Each unit has its own thermal conductivity characteristics. By solving the thermal conductivity matrix K of each unit ij , temperature matrix C ij and the node heat flux vector F i , which can more accurately simulate the temperature distribution and heat flow dynamics inside the brake disc.

[0093] Figure 5 , step S406, comprising the steps of:

[0094] SE1: Based on the preset formula T n+1 =T n +T n+1 Δt, derive the solution formula for transient temperature field in

[0095] In this embodiment, step SE1 involves deriving a formula for solving the transient temperature field based on the basic heat transfer principle. n+1 =T n +T n+1 Δt, the solution formula for the transient temperature field will be derived in

[0096] Figure 6 , step S407, comprising the steps of:

[0097] SF1: Setting braking condition parameters, including vehicle speed, wheel diameter, initial braking speed, braking time, braking pressure, friction factor and acceleration;

[0098] SF2: judging the airflow type based on the Reynolds number, wherein the airflow type includes laminar flow and turbulent flow;

[0099] SF3: When Re≤2.4×10 5 When the airflow type is laminar flow, the empirical formula is K a represents the thermal conductivity of air, which is 0.0276W / (m·K), D represents the outer diameter of the brake disc, in m, and R e Reynolds number, Re = (ωR)ρ a D / μ a , ω represents the angular velocity of the brake disc, R represents the rolling radius of the wheel, R = 0.42m, ρ a represents the density of air, ρ a =1.13kg / m 3 , μ a represents the dynamic viscosity of air, which is 1.91×10 -5 Pa·s;

[0100] SF4: When Re>2.4×10 5 When the airflow type is turbulent, the empirical formula is

[0101] SF5: Calculate the convective heat transfer coefficient for different airflow types and speeds;

[0102] SF6: Based on the friction power method, output the heat flux input time function table under braking conditions.

[0103] In this embodiment, during the simulation and thermodynamic analysis of the braking system, the following steps SF1 to SF6 describe in detail how to set the braking condition parameters, determine the airflow type, calculate the convection heat transfer coefficient, and output the heat flux density input time function table: SF1: Set the braking condition parameters, which include vehicle speed, wheel diameter, initial braking speed, braking time, braking pressure, friction factor and acceleration. These parameters are the basis for the performance analysis of the braking system, and they will directly affect the heat generated during the braking process and the braking effect. SF2: By calculating the Reynolds number R e To determine the type of airflow, the Reynolds number is a dimensionless parameter used to distinguish between two different fluid flow states: laminar flow and turbulent flow. Laminar flow refers to the flow of fluid in the form of ordered layers, while turbulent flow refers to the chaotic flow of fluid. SF3: When Re≤2.4×10 5 When , the airflow type is judged as laminar flow. At this time, the empirical formula is used To calculate the convection heat transfer coefficient, the formula includes parameters such as air thermal conductivity, brake disc outer diameter, Reynolds number, brake disc angular velocity, wheel rolling radius, air density and aerodynamic viscosity. SF4: When Re>2.4×10 5 When , the airflow type is judged as turbulent. For turbulent flow, the empirical formula is also used to calculate the convective heat transfer coefficient, but the parameters in the formula are different from those in the laminar flow case to accommodate the more complex heat transfer characteristics under turbulent conditions. SF5: Calculate the convective heat transfer coefficient under different airflow types and different speeds. This step is to determine the heat exchange efficiency between the brake disc and the surrounding air under different braking conditions, which is critical to understanding the heat dissipation performance of the brake disc. SF6: Based on the friction power method, output the heat flux input time function table under braking conditions. The friction power method is a method for calculating the heat generated by friction during braking. In this way, a time-varying heat flux function can be obtained, which reflects the changes in heat flux at different time points during braking, which is critical for predicting and analyzing the temperature distribution and thermal stress of the brake disc.

[0104] Figure 7 , step S408, comprising the steps of:

[0105] SG1: Place probes near the crack;

[0106] SG2: Perform temperature field simulation, simulate continuous emergency braking conditions, obtain temperature cloud maps, and analyze temperature distribution and causes of hot spots;

[0107] SG3: Perform stress field simulation, obtain equivalent stress cloud diagram, and analyze the impact of cracks on stress distribution;

[0108] SG4: Analyze the simulation results of a single crack brake disc, compare the temperature and stress changes under different crack shapes, and analyze the impact of cracks on temperature and stress;

[0109] SG5: Analyze the simulation results of the double-crack brake disc, study the interaction mechanism between multiple cracks, and compare the temperature and stress differences between the double-crack and no-crack cases;

[0110] SG6: By comparing probe data, analyze the impact of crack shape, location and number on brake disc temperature and stress, as well as the stress concentration phenomenon caused by cracks.

[0111] In this embodiment, in the study of the crack effect on the brake disc, the following steps elaborate on how to evaluate the effect of cracks on the performance of the brake disc through simulation and data analysis: In step SG1, probes are arranged near the cracks in the simulation model. These probes are used to monitor the temperature and stress changes in the crack area in real time, providing key information for subsequent data analysis. In step SG2, temperature field simulation is performed to simulate the situation of continuous emergency braking. Through the generated temperature cloud map, the temperature distribution on the surface of the brake disc and the reasons for the formation of hot spots can be analyzed, which is crucial for understanding the thermal behavior and thermal fatigue life of the brake disc at high temperatures. Step SG3 involves stress field simulation. Through the equivalent stress cloud map obtained, the effect of cracks on the stress distribution of the brake disc can be analyzed to understand how cracks change the size and distribution pattern of stress. Step SG4 analyzes the simulation results of the single-crack brake disc, compares the temperature and stress changes under different crack forms, and thus evaluates the specific effects of cracks on the thermal and mechanical properties of the brake disc. In step SG5, the simulation results of the double-crack brake disc were analyzed, the interaction mechanism between multiple cracks was studied, and the difference in the impact of double cracks on temperature and stress distribution was revealed by comparison with the crack-free case, which is of great significance for understanding the behavior of complex crack systems. Finally, step SG6 analyzed the impact of the shape, location and number of cracks on the temperature and stress distribution of the brake disc, as well as the stress concentration phenomenon caused by cracks by comparing probe data. This analysis helps to reveal the relationship between crack characteristics and brake disc performance, and provides an important scientific basis for brake disc design optimization, material selection and failure prevention. These steps together constitute a comprehensive analysis framework for evaluating and improving the structural integrity and safety of cracked brake discs.

[0112] In one embodiment, a computer device is provided. The computer device may be a server, and its internal structure diagram may be as follows: Figure 8As shown. The computer device includes a processor, a memory, a network interface and a database connected through a system bus. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store temperature cloud maps and equivalent stress cloud maps. The network interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, a method for simulating and evaluating thermal fatigue cracks and thermal stresses of axle-mounted brake discs of subway trains is implemented.

[0113] In one embodiment, a computer device is provided, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, a method for simulating and evaluating thermal fatigue cracks and thermal stresses of axle-mounted brake discs of subway trains is implemented.

[0114] In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, a method for simulating and evaluating thermal fatigue cracks and thermal stresses of axle-mounted brake discs of subway trains is provided.

[0115] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. As an illustration and not limitation, RAM is available in many forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).

[0116] Those skilled in the art can clearly understand that for the convenience and simplicity of description, only the division of the above-mentioned functional units and modules is used as an example. In actual applications, the above-mentioned functions can be distributed and completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above.

Claims

1. A method for simulating and evaluating thermal fatigue cracks and thermal stresses of axle-mounted brake discs of subway trains, characterized in that: Includes steps: A uniform contact model is used to simulate the interaction between the brake disc and the friction pad; The brake disc structure is appropriately simplified and a finite element model is established; Based on actual data, select the emergency braking mode with constant friction coefficient; The surface conditions of the brake disc under different crack conditions are listed, and the changes in the thermal stress field under two consecutive constant-pressure emergency braking are studied; By comparing the thermal fatigue damage of the actual brake disc, the accuracy and reliability of the simulation model are verified; Provide suggestions for improvements including brake disc design, material selection and brake system optimization.

2. The method for simulating and evaluating thermal fatigue cracks and thermal stresses of axle-mounted brake discs of subway trains according to claim 1 is characterized in that: The steps of listing the surface conditions of the brake disc under different crack conditions and studying the changes in the thermal stress field under two consecutive constant-pressure emergency brakings include the following steps: Single cracks and double cracks are provided on the surface of the brake disc; Construct two types of crack models: rectangular and elliptical; Based on the indirect thermal-mechanical coupling method, the thermal field and mechanical field are solved respectively, and the temperature field and stress field distribution of the brake disc during emergency braking are analyzed; Based on the friction power method, the work done by friction and the heat flux density of the disk are calculated; Based on the transient heat transfer model, the transient temperature field of the brake disc is solved; Solve the transient temperature field based on the backward difference method and derive the solution formula of the temperature field; Determine the airflow type based on the Reynolds number and calculate the convective heat transfer coefficient at different speeds; Probes are placed near the cracks, and temperature and stress cloud maps are obtained through simulation to analyze the influence of crack morphology and distribution on the thermal stress distribution and hot spot formation of the brake disc.

3. The method for simulating and evaluating thermal fatigue cracks and thermal stresses of axle-mounted brake discs of subway trains according to claim 2 is characterized in that: The step of calculating the work done by the friction force and the heat flux density of the disk surface based on the friction power method comprises the following steps: Based on the preset formula W = ηFv(r, t) = ηp(r)μv(r, t) and η represents the energy distribution coefficient, p(r) represents the friction plate pressure, μ represents the friction coefficient, r represents the friction radius, S represents the area swept by the friction surface, S = 0.2670m 2 , R and Represent the inner diameter and outer diameter of the friction plate respectively, v0 represents the initial braking velocity, a represents the braking deceleration, D represents the wheel diameter, and the work W done by the friction force during braking and the heat flux density q(r,t) of the disc surface are calculated.

4. The method for simulating and evaluating thermal fatigue cracks and thermal stresses of axle-mounted brake discs of subway trains according to claim 2 is characterized in that: The step of solving the transient temperature field of the brake disc based on the transient heat transfer model comprises the following steps: Based on preset formula Solve the transient temperature field, K, D represent the thermal conductivity matrix and temperature change matrix respectively, T, They represent the node temperature vector and the derivative vector of the node temperature with respect to time, respectively, and F represents the generalized node heat flux vector; Based on preset formula C ij =∫∫∫ΩρcN i N j dxdydz, F i =∫∫∫ΩQN i dxdydz-∫∫S(q-αT f )N i ds, solve the thermal conductivity matrix K of each unit ij , temperature matrix C ij 、Node heat flow vector F i .

5. The method for simulating and evaluating thermal fatigue cracks and thermal stresses of axle-mounted brake discs of subway trains according to claim 2 is characterized in that: The step of solving the transient temperature field based on the backward difference method and deriving the solution formula of the temperature field comprises the steps of: Based on the preset formula T n+1 =T n +T n+1 Δt, derive the solution formula for transient temperature field in 6. The method for simulating and evaluating thermal fatigue cracks and thermal stresses of axle-mounted brake discs of subway trains according to claim 2 is characterized in that: The step of determining the airflow type based on the Reynolds number and calculating the convective heat transfer coefficient at different speeds comprises the following steps: Setting braking condition parameters, including vehicle speed, wheel diameter, initial braking speed, braking time, braking pressure, friction factor and acceleration; Determine the type of airflow based on the Reynolds number, where the airflow type includes laminar flow and turbulent flow; When Re≤2.4×10 5 When the airflow type is laminar flow, the empirical formula is K a represents the thermal conductivity of air, which is 0.0276W / (m·K), D represents the outer diameter of the brake disc, in m, and R e Reynolds number, Re = (ωR)ρ a D / μ a , ω represents the angular velocity of the brake disc, R represents the rolling radius of the wheel, R = 0.42m, ρ a represents the density of air, ρ a =1.13kg / m 3 , μ a represents the dynamic viscosity of air, which is 1.91×10 -5 Pa·s; When Re>2.4×10 5 When the airflow type is turbulent, the empirical formula is Calculate the convective heat transfer coefficient for different airflow types and speeds; Based on the friction power method, the heat flux input time function table under braking conditions is output.

7. The method for simulating and evaluating thermal fatigue cracks and thermal stresses of axle-mounted brake discs of subway trains according to claim 2 is characterized in that: The step of arranging a probe near the crack, obtaining a temperature and stress cloud map by simulation, and analyzing the influence of the crack morphology and distribution on the thermal stress distribution and hot spot formation of the brake disc comprises the following steps: Arrange the probe near the crack; Conduct temperature field simulation, simulate continuous emergency braking conditions, obtain temperature cloud maps, and analyze temperature distribution and causes of hot spots; Conduct stress field simulation, obtain equivalent stress cloud diagram, and analyze the impact of cracks on stress distribution; Analyze the simulation results of a single crack brake disc, compare the temperature and stress changes under different crack shapes, and analyze the impact of cracks on temperature and stress; Analyze the simulation results of the double-crack brake disc, study the interaction mechanism between multiple cracks, and compare the temperature and stress differences between the double-crack and no-crack cases; By comparing probe data, the effects of crack shape, location and number on brake disc temperature and stress, as well as the stress concentration phenomenon caused by cracks, are analyzed.

8. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method for simulating and evaluating thermal fatigue cracks and thermal stresses of axle-mounted brake discs of subway trains as described in any one of claims 1 to 7 are implemented.

9. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of a method for simulating and evaluating thermal fatigue cracks and thermal stresses of axle-mounted brake discs of subway trains as described in any one of claims 1 to 7 are implemented.

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