High-speed train braking interface friction heat and friction block wear coupling calculation method

Abstract

The invention belongs to the field of high-speed train brake pads, and particularly discloses a high-speed train brake interface friction heat and friction block abrasion coupling calculation method which comprises the following steps: establishing a finite element model of a friction block and a brake disc; finite element software ABAQUS is used for carrying out heat-machine-wear coupling simulation solution; calling a subprogram DFLUX to carry out heat transfer analysis; a subprogram UMESHMOTION is called for abrasion analysis, and the abrasion depth is calculated and recorded; and updating the grid and circularly calculating. According to the high-speed train brake interface friction heat and friction block abrasion coupling calculation method, the temperature characteristic of friction block abrasion is considered, high-temperature abrasion of the friction block is calculated through finite element simulation, and the method has great significance in guiding design and maintenance of the high-speed train brake pad friction block.

Description

Technical Field

[0001] The invention relates to the field of high-speed train brake pads, and in particular to a method for calculating the coupling between friction heat and friction block wear at a high-speed train brake interface. Background Art

[0002] The foundation brake is an important part of the high-speed train braking system, which plays a role in ensuring the smooth operation of the train. The friction block and the brake disc are two key components of the foundation brake device. The friction energy consumption of the friction block and the brake disc can realize the speed regulation and parking of the high-speed train. Under normal circumstances, the foundation brake is used at a low speed, the temperature of the brake interface is not high, and the effect of temperature on the interface wear can be ignored.

[0003] High-speed trains may also need emergency braking, which requires basic braking to slow down the train from high speed to a stop, resulting in high interface temperature and high wear. Under high temperature, the strength, stiffness, hardness, plasticity and other performance indicators of the friction block material will change. At the same time, the friction block absorbs a large amount of heat, which will aggravate wear, leading to high-temperature wear failure of the friction block and reduced braking performance, causing safety issues.

[0004] In recent years, some scholars have used finite element simulation to analyze and predict the wear performance of friction blocks at high temperatures. However, due to the long simulation time and low efficiency in traditional thermal-mechanical coupling simulation, there are few reports on the study of the effect of temperature on wear. Therefore, based on the problems existing in traditional thermal-mechanical coupling simulation, a new method is needed to consider the effect of temperature on wear and improve simulation efficiency. Summary of the invention

[0005] In order to overcome the shortcomings of the prior art, the present invention provides a method for coupling calculation of friction heat and friction block wear at the braking interface of a high-speed train. The method for coupling calculation of friction heat and friction block wear at the braking interface of a high-speed train takes the temperature characteristics of friction block wear into account, and calculates the high-temperature wear of the friction block through finite element simulation, which is of great significance for guiding the design and maintenance of high-speed train brake pad friction blocks.

[0006] The technical solution of the present invention to solve the above technical problems is:

[0007] A coupling calculation method for friction heat and friction block wear of a high-speed train braking interface comprises the following steps:

[0008] Step 1: Establish the finite element model of the friction pad and brake disc;

[0009] Step 2: Use finite element software ABAQUS to perform thermal-mechanical-wear coupling simulation solution;

[0010] Step 3: Update the grid and loop the calculation.

[0011] Preferably, in step 1, the steps of constructing the finite element model are:

[0012] Step 101: Create a three-dimensional model of the friction block and the brake disc, import the created three-dimensional model into finite element software, and assemble it;

[0013] Step 102: assigning material properties, wherein the material properties include but are not limited to density, specific heat capacity, thermal expansion coefficient, Poisson's ratio, and Young's modulus;

[0014] Step 103: Setting up interaction;

[0015] Step 104: Set the load and divide the mesh, using an advanced algorithm to divide the hexahedral mesh.

[0016] Preferably, in step 2, a sequential thermal-mechanical coupling method is used to solve the thermal-mechanical-wear coupling simulation, thereby discretizing the entire simulation process into N incremental steps, and performing a wear calculation in each incremental step.

[0017] Preferably, the sequential thermal-mechanical coupling method first performs heat transfer analysis and then performs wear analysis, and specifically comprises the following steps:

[0018] Step S1: calling subroutine DFLUX to perform heat transfer analysis;

[0019] Step S2: Call the subroutine UMESHMOTION to perform wear analysis, calculate and record the wear depth.

[0020] Preferably, the heat transfer analysis includes heat flux input, heat transfer and heat dissipation.

[0021] Preferably, the heat flux density input is calculated using the friction power method, and the heat flux density is applied to the surfaces of the brake disc and the friction pad, specifically,

[0022] Step S101: Calculate the friction power Q:

[0023] Q=ημFω(t)r p ;

[0024] Where: η is the heat transfer coefficient between kinetic energy and thermal energy; μ is the friction coefficient; F is the contact pressure; ω(t) is the angular velocity of the brake disc; r p is the friction radius;

[0025] Step S102: Calculate the total heat flux density on the brake disc:

[0026]

[0027] Where S is the total contact area between the brake disc and the friction pad; q t is the total heat flux;

[0028] Step S103: The total heat flux q t Assignment to brake discs and friction pads:

[0029] q t =q p +q k ;

[0030] In the formula, q p and q k are the heat flux densities of the brake disc and friction pad respectively;

[0031] Step S104: Calculate the heat flux density of the friction block:

[0032]

[0033] Where: λ is the heat distribution coefficient;

[0034] Step S105: Divide the contact area of ​​the brake disc into N annular zones, and the friction radius is r i The heat flux density of the i-th annular zone is:

[0035]

[0036] In the formula, F i is the total contact pressure on the i-th ring; r i is the average friction radius on the ith ring; S i is the area of ​​the ith ring.

[0037] Preferably, the heat transfer and heat dissipation of the heat flux density is solved by treating the heat conduction process as a flat wall heat conduction process; specifically:

[0038] Step S111: Solve the heat transfer amount q T :

[0039]

[0040] Where: k t is the thermal conductivity of the material; T k and T p are the surface temperatures of the friction pad and brake disc respectively; A is the heat conduction area;

[0041] Step S112: The brake disc and the friction pad are regarded as isotropic materials without internal heat source, and the heat conduction equation is:

[0042]

[0043] Where t is time; T is the solid temperature at time t; x, y, z represent Cartesian coordinates; ρ represents density; c is the specific heat capacity of the material;

[0044] Step S113: Three types of boundary conditions are given for the heat conduction equation, where:

[0045] T = T0;

[0046]

[0047] q c =h c (TT ∞ );

[0048] Where: T0 is the initial temperature; q(x,y,t) is the heat flux density applied to the corresponding friction interface; q c is the heat transfer through convection; T ∞ is the ambient temperature; h c is the convective heat transfer coefficient, and its expression is:

[0049]

[0050] In the formula, k l is the thermal conductivity of air; l is the characteristic length; Nu is the Nusselt number.

[0051] Preferably, in step S2, the wear analysis uses the subroutine UMESHMOTION to perform wear calculations and create a wear information storage path; specifically:

[0052] Step S201: Discretize the entire wear process into N incremental steps, h i-1 is the wear depth before the i-th incremental step, then the cumulative wear depth after the i-th incremental step is:

[0053] h i =h i-1 +k0×p i ×s i ;

[0054] Where: p is the contact stress; k0 is the dimensioned wear coefficient;

[0055] Step S202: Calculate and record the wear depth and record it in the created storage path.

[0056] Preferably, in step 3, the finite element model is updated using ALE adaptive mesh technology, and it is determined whether the calculation time has ended. If the time has not ended, a cyclic thermal-mechanical-wear coupling simulation calculation is performed; if the time has ended, the calculation is completed.

[0057] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0058] The present invention takes into account the influence of temperature on wear and calculates the high-temperature wear of the friction block through finite element simulation, so that the simulation result is closer to reality. The high-temperature wear of the friction block can be predicted, which is of great significance for guiding the design and maintenance of the brake pad friction block of high-speed trains. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 This is a finite element model diagram of the high-speed train brake disc and friction block used in the present invention.

[0060] Figure 2 The present invention is a flow chart of the coupling calculation method of the high-speed train braking interface friction heat and friction block wear.

[0061] Figure 3 Input band position map for the brake disc heat flux.

[0062] Figure 4 This is the graph of friction block temperature changing with time.

[0063] Figure 5 This is the wear distribution diagram of the friction block when temperature is considered.

[0064] In the figure: 1-brake disc; 2-friction block; 3-outer clamp; 4-inner clamp. DETAILED DESCRIPTION

[0065] The present invention is further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0066] The coupling calculation method of friction heat and friction block wear of high-speed train braking interface of the present invention is as follows: Figure 1 As shown, there are brake disc 1, friction block 2, outer clamp 3 and inner clamp 4; wherein the friction block has 4 thicknesses, namely 14mm, 16mm, 18mm and 20mm, and T=20mm, T=18mm, T=16mm and T=14mm are used to replace the friction blocks of these thicknesses. In this embodiment, the 4 thicknesses of friction blocks are used as variables.

[0067] The coupling calculation method of friction heat and friction block wear of high-speed train braking interface of the present invention has the following analysis process: Figure 2 As shown, the following steps are included:

[0068] Step 1: Establish the finite element model of friction pad and brake disc:

[0069] In this embodiment, establishing the finite element model includes establishing a three-dimensional model of the friction block and the brake disc, assigning material properties, setting interactions, setting loads, and dividing the grid, specifically,

[0070] Establish the 3D model of friction block and brake disc: import the established 3D model into finite element software and assemble it;

[0071] Assign material properties: Assign material properties such as density, specific heat capacity, thermal expansion coefficient, Poisson's ratio, and Young's modulus;

[0072] Set up interaction: Since the contact between the brake disc and the friction block is surface-to-surface contact, the contact behavior is tangential friction and normal hard contact, and the COF of the wear simulation is 0.5; therefore, the fixture and the friction block are set as binding constraints;

[0073] Set the load: couple the center point of the inner circle of the brake disc with the inner surface of the brake disc, constrain it, limit the other five degrees of freedom except rotation around the x-axis, and set the rotation speed around the x-axis to 500r / min; similarly couple the center point of the inner ring of the fixture hole, set it to only allow the fixture to move along the x-axis, and apply a braking force of 800N at the coupling point;

[0074] Meshing: Hexahedral meshing is performed using an advanced algorithm.

[0075] Step 2: Use finite element software ABAQUS to perform thermal-mechanical-wear coupling simulation solution;

[0076] In this embodiment, the thermal-mechanical-wear coupling simulation solution adopts a sequential thermal-mechanical coupling method, which mainly performs heat transfer analysis (i.e., step 3) first and then wear analysis (i.e., step 4), wherein the heat transfer analysis uses a heat transfer analysis step with an analysis time of 420s; the wear analysis uses a static general analysis step, adopts an equivalent analysis strategy, sets the wear acceleration factor value to 500, takes an analysis time of 0.84s, and discretizes the entire simulation process into N incremental steps, with a wear calculation performed once in each incremental step.

[0077] Step 3: Call subroutine DFLUX to perform heat transfer analysis;

[0078] In this embodiment, the heat transfer analysis includes heat flux input, heat transfer and heat dissipation.

[0079] For heat flux input, the friction power method is used to calculate the heat flux, and the heat flux is applied to the brake disc and friction pad surface through the subroutine DFLUX.

[0080] The calculation expression of the friction power method is as follows:

[0081] Q=ημFω(t)r p ;

[0082] Where η is the heat transfer coefficient between kinetic energy and thermal energy; μ is the friction coefficient; F is the contact pressure; ω(t) is the angular velocity of the brake disc; r pis the friction radius;

[0083] The total heat flux density on the brake disc is calculated as follows:

[0084]

[0085] Where S is the total contact area between the brake disc and the friction pad; q t is the total heat flux density; the total heat flux density is distributed to the brake disc and the friction pad, and the calculation formula is as follows:

[0086] q t =q p +q k ;

[0087] In the formula, q p and q k are the heat flux densities of the brake disc and friction pad respectively; λ=q k / q p is the heat distribution coefficient between the brake disc and the friction pad;

[0088] The heat flux calculation formulas for the brake disc and friction pad are as follows:

[0089]

[0090]

[0091] The heat flux input calculation formula can be used to calculate the temperature field and thermal stress field, but the heat flux obtained in this way is uniform. Since the contact pressure is unevenly distributed in the contact area between the brake disc and the friction pad, and the friction radius at different positions along the radial direction is also different, the above heat flux calculation formula cannot fully reflect the heat flux distribution of the brake disc and the friction pad.

[0092] In order to solve this problem, the contact area of ​​the brake disc is divided into N annular bands, and the friction radius is r i The calculation formula for the heat flux density of the i-th annular zone is as follows:

[0093]

[0094] In the formula, F i is the total contact pressure on the i-th ring; r i is the average friction radius on the ith ring; S i is the area of ​​the ith ring.

[0095] The annular zone of the brake disc is divided as follows Figure 3 As shown, the number of ring bands 1 is 9, 2 is 8, 3 is 7, 4 is 6, and 5 is 5.

[0096] Table 1 shows the heat flux density of the brake disc and friction pad input (the unit of heat flux density is mW / mm 2 )

[0097]

[0098] As for heat transfer and heat dissipation, due to the temperature difference between the brake disc and the friction block, heat transfer will inevitably occur between the two. The heat conduction process can be solved as a flat wall heat conduction process, satisfying Fourier's law. The calculation formula is as follows:

[0099]

[0100] In the formula, q T Heat transfer capacity; k t is the thermal conductivity of the material; T k and T p are the surface temperatures of the friction pad and brake disc respectively; A is the heat conduction area.

[0101] Due to the uneven temperature distribution during braking, there will be temperature differences between the parts of the brake disc and the friction pad, which will lead to heat exchange between the various positions. The brake disc and the friction pad can be regarded as isotropic materials without internal heat sources, and the heat conduction equation is:

[0102]

[0103] Where t is time; T is the solid temperature at time t; x, y, z represent Cartesian coordinates; ρ represents density; and c is the specific heat capacity of the material.

[0104] In order to make the solution of the heat conduction equation unique, three types of boundary conditions must be given:

[0105] The first type of boundary conditions: given initial temperature T0;

[0106] T = T0;

[0107] The second type of boundary condition: given q(x,y,t), it corresponds to the heat flux density applied by the friction interface;

[0108]

[0109] The third type of boundary conditions: given convection heat transfer conditions;

[0110] q c =h c (TT ∞ );

[0111] Where: q c is the heat transfer through convection; T ∞ is the ambient temperature; h cis the convective heat transfer coefficient, and its expression is:

[0112]

[0113] In the formula, k l is the thermal conductivity of air; l is the characteristic length; Nu is the Nusselt number.

[0114] Step 4: Call the subroutine UMESHMOTION to perform wear analysis, calculate and record the wear depth;

[0115] In this embodiment, the wear analysis is based on Archard theory and uses the ABAQUS subroutine UMESHMOTION to perform wear calculations and create a wear information storage path.

[0116] The wear calculation formula is as follows:

[0117]

[0118] Where V is the wear volume; k is the dimensionless wear coefficient; s is the sliding distance; N and H are the normal load and surface hardness, respectively. When the contact area ΔA increment dt is infinite, equation (1) can be derived into a differential form; assuming that the increment of wear thickness at time dt is dh, then dV = ΔA × dh, then equation (1) can be changed to the following form:

[0119]

[0120] Transforming formula (2), we can get the following form:

[0121]

[0122] In formula (3), N / ΔA is the contact stress p at the contact area ΔA; k / H can be expressed by the dimensioned wear coefficient k0, from which the wear increment is derived as follows:

[0123] dh = k0 × p × ds;

[0124] The entire wear process is discretized into N incremental steps, h i-1 is the wear thickness before the i-th incremental step, then the cumulative wear thickness after the i-th incremental step is:

[0125] h i =h i-1 +k0×p i ×s i ;

[0126] The wear depth is calculated and recorded by using the node number, node coordinates, node temperature, contact pressure, sliding distance and other parameters obtained through the subroutine UMESHMOTION to calculate the wear and record it in the storage path that has been created.

[0127] The calculated wear depth is the wear depth per unit time, and the wear depth is output twice per unit time.

[0128] Step 5: Update the grid and loop the calculation;

[0129] Update the mesh and loop calculation to update the finite element model using ALE adaptive mesh technology and determine whether the calculation time has ended. If the time has not ended, the cyclic thermal-mechanical wear coupling calculation is performed, and the calculation is completed when the time has ended. The wear depth recorded in step 5 is the wear depth per unit time. After loop calculation in step 5, the wear depth of N unit time is obtained. The wear depth needs to be accumulated through a python script to finally obtain the wear depth of the entire simulation time.

[0130] like Figure 4 As shown in Figure 2, the temperature of the friction block changes with time. Figure 4 The wear distribution of the friction block under the influence of temperature is as follows Figure 5 shown.

[0131] The above embodiment uses the coupling calculation method of friction heat and friction block wear of high-speed train brake interface of the present invention, taking temperature characteristics into account, so that the wear depth obtained by simulation is more in line with reality. It is of great significance to guide the design and maintenance of high-speed train brake pad friction blocks.

[0132] The above is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited to the above content. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A coupling calculation method for friction heat and friction block wear of high-speed train braking interface, characterized in that: The steps include: Step 1: Establish the finite element model of the friction pad and brake disc; Step 2: Use finite element software ABAQUS to perform thermal-mechanical-wear coupling simulation solution; Step 3: Update the grid and loop the calculation.

2. The method for coupling calculation of friction heat and friction block wear at the braking interface of a high-speed train according to claim 1 is characterized in that: In step 1, the steps of constructing the finite element model are: Step 101: Create a three-dimensional model of the friction block and the brake disc, import the created three-dimensional model into finite element software, and assemble it; Step 102: assigning material properties, wherein the material properties include but are not limited to density, specific heat capacity, thermal expansion coefficient, Poisson's ratio, and Young's modulus; Step 103: Setting up interaction; Step 104: Set the load and divide the mesh, using an advanced algorithm to divide the hexahedral mesh.

3. The method for coupling calculation of friction heat and friction block wear at the braking interface of a high-speed train according to claim 1 is characterized in that: In step 2, the sequential thermal-mechanical coupling method is used to solve the thermal-mechanical-wear coupling simulation, so that the entire simulation process is discretized into N incremental steps, and a wear calculation is performed in each incremental step.

4. The method for coupling calculation of friction heat and friction block wear at the braking interface of a high-speed train according to claim 3 is characterized in that: The sequential thermal-mechanical coupling method first performs heat transfer analysis and then wear analysis, and specifically includes the following steps: Step S1: calling subroutine DFLUX to perform heat transfer analysis; Step S2: Call the subroutine UMESHMOTION to perform wear analysis, calculate and record the wear depth.

5. The method for coupling calculation of friction heat and friction block wear at the braking interface of a high-speed train according to claim 4 is characterized in that: The heat transfer analysis includes heat flux input, heat transfer and heat dissipation.

6. The method for coupling calculation of friction heat and friction block wear at the braking interface of a high-speed train according to claim 5 is characterized in that: The heat flux density input is calculated using the friction power method and applied to the surfaces of the brake disc and the friction pad. Specifically, Step S101: Calculate the friction power Q: Q=ημFω(t)r p ; Where: η is the heat transfer coefficient between kinetic energy and thermal energy; μ is the friction coefficient; F is the contact pressure; ω(t) is the angular velocity of the brake disc; r p is the friction radius; Step S102: Calculate the total heat flux density on the brake disc: Where S is the total contact area between the brake disc and the friction pad; q t is the total heat flux; Step S103: The total heat flux q t Assignment to brake discs and friction pads: q t =q p +q k ; In the formula, q p and q k are the heat flux densities of the brake disc and friction pad respectively; Step S104: Calculate the heat flux density of the friction block: Where: λ is the heat distribution coefficient; Step S105: Divide the contact area of ​​the brake disc into N annular zones, and the friction radius is r i The heat flux density of the i-th annular zone is: In the formula, F i is the total contact pressure on the i-th ring; r i is the average friction radius on the ith ring; S i is the area of ​​the ith ring.

7. The method for coupling calculation of friction heat and friction block wear at the braking interface of a high-speed train according to claim 5 is characterized in that: The heat transfer and heat dissipation of the heat flux density is to solve the heat conduction process as a flat wall heat conduction process; specifically: Step S111: Solve the heat transfer amount q T : Where: k t is the thermal conductivity of the material; T k and T p are the surface temperatures of the friction pad and brake disc respectively; A is the heat conduction area; Step S112: The brake disc and the friction pad are regarded as isotropic materials without internal heat source, and the heat conduction equation is: Where t is time; T is the solid temperature at time t; x, y, z represent Cartesian coordinates; ρ represents density; c is the specific heat capacity of the material; Step S113: Three types of boundary conditions are given for the heat conduction equation, where: T = T0; q c =h c (T-T ∞ ); Where: T0 is the initial temperature; q(x,y,t) is the heat flux density applied to the corresponding friction interface; q c is the heat transfer through convection; T ∞ is the ambient temperature; h c is the convective heat transfer coefficient, and its expression is: In the formula, k l is the thermal conductivity of air; l is the characteristic length; Nu is the Nusselt number.

8. The method for coupling calculation of friction heat and friction block wear at the braking interface of a high-speed train according to claim 4 is characterized in that: In step S2, the wear analysis uses the subroutine UMESHMOTION to perform wear calculations and create a wear information storage path; specifically: Step S201: Discretize the entire wear process into N incremental steps, h i-1 is the wear depth before the ith incremental step, then the cumulative wear depth after the ith incremental step is: h i =h i-1 +k0×p i ×s i ; Where: p is the contact stress; k0 is the dimensioned wear coefficient; Step S202: Calculate and record the wear depth and record it in the created storage path.

9. The method for coupling calculation of friction heat and friction block wear at the braking interface of a high-speed train according to claim 1 is characterized in that: In step 3, the finite element model is updated using the ALE adaptive mesh technology, and it is determined whether the calculation time has ended. If the time has not ended, a cyclic thermal-mechanical-wear coupling simulation calculation is performed; if the time has ended, the calculation is completed.

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