CN113218858B - Method for evaluating friction coefficient of brake material - Google Patents
Method for evaluating friction coefficient of brake material Download PDFInfo
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Abstract
A friction coefficient testing method for a brake material applies axial load to a test sample when the rotating speed of a main shaft of a testing machine reaches a specified value. The dynamic friction sample with the average friction coefficient, the static friction sample and the dynamic friction sample with the transient friction coefficient are tested at different braking speeds, temperatures and specific pressures, so that the average friction coefficient and the transient friction coefficient are obtained. And (3) carrying out temperature field and vibration simulation on the average friction coefficient and the transient friction coefficient, wherein the goodness of fit of the result and the test is 98%. The invention considers the friction coefficients of the brake material under the conditions of different brake rotating speeds, different temperatures and different specific pressures, provides technical support for simulating the temperature and vibration of the brake wheel by the finite element, obtains a weak area with higher temperature by performing temperature analysis and brake vibration analysis based on the friction coefficients by the finite element, improves the structure of the brake disc before testing and takes corresponding vibration avoidance measures, reduces economic loss caused by test failure, and shortens the period of repeated testing.
Description
Technical Field
The invention relates to the field of performance testing of aircraft brake materials, in particular to a method for measuring the relation between the friction coefficient of a brake material and temperature, specific pressure and brake rotating speed.
Background
The airplane wheel brake is a complex multi-degree-of-freedom dynamic system, the rigor of the working condition of the wheel brake is only second to that of an engine in all equipment of an airplane, and the complexity of the related mechanical problems is almost equal to that of the engine of the airplane. The airplane wheel brake is an important key element for ensuring the safety and reliability of the taking-off and landing process of the airplane, improving the maintainability and economic indexes of the airplane and enhancing the maneuverability and the fighting capacity of the airplane. With the rapid development of aeronautics, the fundamental problem in the thermal protection and brake vibration process has not been solved, i.e. the relationship between the friction material characteristics with temperature, brake speed and specific pressure is not clear.
The existing test conditions at home and abroad can not meet the test requirements of the friction coefficient of the carbon/Tao Chache material on three items of braking rotation speed V, specific pressure P and temperature T, the friction coefficient of the brake material obtained by the test is the comprehensive effect of the average friction coefficient of each point on the friction surface, and the difference of the friction coefficient of each point caused by the structural size of the friction surface, namely the average value, is ignored. And only limited data of diagonal band intervals of low speed, low temperature and high speed and high temperature can be obtained, namely the full view of the friction coefficient characteristic of the carbon/Tao Chache material cannot be reflected, and the transient relation among the friction coefficient of the brake material, the braking rotating speed V, the specific pressure P and the temperature T, namely mu (P) (t) ,V (t) ,T (t) ) In which P is (t) 、V (t) 、T (t) There are various combinations during the use of the brake disc, of which 0<P<21MPa，0<V<60m/s，-55℃<T<70℃。
At present, aeronautics report, 2019, 03 entitled "development of high-precision static friction coefficient measuring device and research on tribological properties of materials" discloses a friction coefficient testing method, the obtained friction coefficient is an average friction coefficient which changes along with braking rotation speed V, specific pressure P and temperature T, and the obtained friction coefficient has less effective data in testing at low speed, low temperature and high speed, and cannot obtain a global transient friction coefficient. In the research on friction coefficient testing method published in 2019, 04, the mechanical engineering journal of China, only the average friction coefficient is obtained in the same way in the friction coefficient testing, and the global transient friction coefficient is difficult to obtain.
Disclosure of Invention
In order to overcome the defect that the friction coefficient value which changes along with the rotating speed V, the specific pressure P and the temperature T in the whole braking process cannot be obtained in the prior art, the invention provides a method for testing the friction coefficient of the brake material.
The specific process of the invention is as follows:
step 1: preparation of friction test pieces to obtain average coefficient of friction:
the friction samples comprise static friction samples and dynamic friction samples. The appearance structure of the static friction sample is the same as that of a static disc in a brake disc. The dynamic friction sample has the same shape and structure as the dynamic disc in the brake disc.
Inner diameter a of the dynamic friction test piece 1 =42 ± 0.2mm, maximum outer diameter b 1 =75 ± 0.2mm, minimum outer diameter c 1 =53 ± 0.2mm. Four key grooves are uniformly distributed on the outer circumference of the dynamic friction sample, and the width d of each key groove 1 ＝15.5±0.2mm。
The static friction sample and the transient static friction coefficient sample have the same structure size and the inner diameter a 2 =42 ± 0.2mm, outer diameter c 2 =75 ± 0.2mm. Four key grooves are uniformly distributed on the inner circumferential surface of the static friction sample, and the width d of each key groove 2 =15.5 ± 0.2mm, radial depth =5.5 ± 0.2mm.
the determined average friction coefficient of the brake material comprises the friction coefficient mu of a dynamic friction sample 1 (P, V, T), average coefficient of Friction of static Friction sample μ 2 (P, V, T) and the average coefficient of friction μ of dynamic friction between dynamic friction sample and static friction sample 3 (P,V,T)。
The specific procedure for determining the mean friction coefficient μ (P, V, T) is:
i determination of the coefficient of friction mu of a dynamic Friction test specimen 1 (P,V,T)
Determination of the average coefficient of friction μ of a dynamic Friction sample 1 (P, V, T), the coefficient of friction μ of the dynamic friction sample was obtained by a friction and wear tester 1 (P,V,T)。
II determination of the coefficient of friction mu of the static Friction test specimens 2 (P,V,T)
Determination of the average coefficient of friction μ of a static Friction test piece 2 (P, V, T), the coefficient of friction μ of the static friction sample was obtained by a friction and wear tester 1 (P,V,T)。
Dynamic friction between III dynamic friction sample and static friction sampleMean coefficient of friction mu 3 (P,V,T)
Determination of the mean coefficient of friction μ of the dynamic friction between the Friction test piece and the static friction test piece 3 (P, V, T), the average friction coefficient mu of the dynamic friction between the dynamic friction sample and the static friction sample is obtained by a friction and wear performance tester 3 (P,V,T)。
Determining the coefficient of friction mu of the dynamic friction sample 1 (P, V, T), coefficient of friction μ of static Friction sample 2 (P, V, T) and the average coefficient of friction μ of dynamic friction between dynamic friction sample and static friction sample 3 And (P, V and T), the technical parameters of the friction and wear performance testing machine are as follows: the brake pressure is 0.2-20 kN; the rotating speed of the main shaft is 2000-10000 r/min during collection; acquiring friction torque required by each friction coefficient: 0 to 300 N.m; the temperature for collecting each friction coefficient is room temperature-1000 ℃.
And step 3: preparing a friction sample for obtaining the transient friction coefficient:
the transient friction coefficient test sample comprises a transient static friction coefficient test sample and a transient dynamic friction coefficient test sample. The appearance structure of the transient static friction coefficient sample is the same as that of a static disc in a brake disc. The transient dynamic friction coefficient sample is in a pin shape, and the material is the same as that of the brake disc.
Height a of big end of the transient dynamic friction coefficient sample 3 =10 ± 0.2mm, diameter b 3 =75 ± 0.2mm, and the groove width in the middle of the large end face is 15.5 ± 0.2mm. The small end of the transient dynamic friction coefficient sample is conical, and the length e of the conical head part 3 Angle f of cone, =10 ± 0.2mm 3 ＝45°。
When the transient dynamic friction coefficient sample and the static friction sample are subjected to a friction test, the contact mode between the transient dynamic friction coefficient sample and the static friction sample is point contact, so that the influence of the friction surface on the friction coefficient is eliminated, and the method is completely consistent with the actual braking process of an airplane.
During the friction test, the transient dynamic friction sample is installed on the friction and wear testing machine and is driven to rotate, so that the transient dynamic friction sample and the static friction sample rotate mutually, and the transient friction coefficient between the transient dynamic friction sample and the static friction sample is obtained.
Step 4, determining the transient friction coefficient mu (P) (t) ,V (t) ,T (t) )：
The transient coefficient of friction mu (P) (t) ,V (t) ,T (t) ) The transient friction coefficient under different specific pressures at constant braking speed and temperature and the transient friction coefficient under different speeds at constant braking specific pressure and temperature are included. The different specific pressures are 0.8MPa, 2.4MPa, 4.0MPa, 6.4MPa and 10.4MPa; the different rotating speeds are 500r/min, 1500r/min, 2500r/min, 3500r/min, 4000r/min and 6500r/min.
And testing the transient friction coefficient of the brake material by using a friction and wear performance testing machine.
The mu (P) (t) ,V (t) ,T (t) ) The method comprises the following steps: p is (t) Specific pressure, V, for rubbing the sample at any time (t) For the rotation speed of the rubbing sample at any moment, T (t) Is the temperature of the rubbing sample at any time.
Determining the μ (P) (t) ,V (t) ,T (t) ) The specific process comprises the following steps:
and I, determining the transient friction coefficient at different specific pressures under constant braking speed and temperature.
Respectively testing the transient friction coefficients of the brake material under the conditions of constant brake rotating speed and temperature under different specific pressures, and processing each test result through MATLAB software to obtain the transient friction coefficients of the contact point of the brake material, the brake rotating speed V and the specific pressure P (t) And temperature T (t) Transient relationship among the three; the transient coefficient of friction mu (P) (t) ,V,T (t) )。
And the constant braking rotating speed and temperature conditions are the shaft rotating speed of the friction and wear performance testing machine obtained in the step 2 and the temperature of each friction coefficient.
And II, determining the transient friction coefficient at different rotating speeds under constant brake specific pressure and temperature.
Respectively testing the transient friction coefficients at different braking rotating speeds when the braking specific pressure and the temperature are constant by taking the braking rotating speed of 5000r/min as a starting point, and using MATLAB softwareThe test results are processed by the device to obtain the instantaneous friction coefficient and the braking rotating speed V of the brake material at different points (t) Specific pressure P and temperature T (t) The transient relation between the three, i.e. the transient friction coefficient mu (P, V) (t) ,T (t) )。
And 5: and (3) verification:
respectively substituting the obtained transient friction coefficients into CAE analysis software to analyze the braking temperature field and the braking vibration of the airplane wheel; specifically, the obtained transient friction coefficient is given to the material property of a brake disc model in the whole wheel brake device through CAE analysis software. And the brake disc endowed with the transient friction coefficient is subjected to temperature field simulation and brake vibration simulation through CAE analysis software. The maximum temperature of a brake disc of a certain model is 700 ℃ and the first-order vibration frequency and the second-order vibration frequency are respectively 200Hz and 365Hz through simulation. The maximum temperature of the brake disc obtained by laboratory tests is 710 ℃, and the first-order vibration frequency and the second-order vibration frequency are 198Hz and 360Hz respectively. The maximum temperature of the brake disc obtained by the external field test is 719 ℃; the first and second order vibration frequencies were 206Hz and 369Hz, respectively.
The test result proves that the laboratory test result and the external field test result are completely consistent with the result of the transient friction coefficient calculation.
And finishing the evaluation of the friction coefficient of the brake material.
The invention considers the friction coefficient of the brake material under the conditions of different brake rotating speeds, different temperatures and different specific pressures, and provides technical support for the problem of finite element simulation of the temperature and the vibration of the brake wheel.
In the invention:
1. friction coefficient test equipment
The friction coefficient testing equipment adopts an MM-3000 type friction and wear performance testing machine, the testing machine is based on GB10006 national standard, and the friction coefficient obtained by using the equipment is mainly used for controlling the development and production quality of brake disc materials and evaluating the performance of the materials.
2. Principle of friction coefficient test
The friction coefficient testing principle is as follows: during testing, the rotating speed of a main shaft of the testing machine provided with the rated rotational inertia flywheel is continuously increased, when the rotating speed reaches a specified value, an axial load is applied to a sample, and an inertia braking (simulated braking) test is carried out. According to the method, three dynamic friction samples, static friction samples and transient friction samples with average friction coefficients are respectively prepared according to the figure 1, the figure 2 and the figure 3 in order to eliminate the influence of the size, and the dynamic friction samples, the static friction samples and the transient friction samples with the average friction coefficients are tested according to different braking speeds, temperatures and specific pressures to obtain the average friction coefficients and the transient friction coefficients.
The average friction coefficient and the transient friction coefficient are respectively substituted into CAE analysis software to carry out temperature field and vibration simulation, the result of the substituted transient friction coefficient simulation calculation and the test goodness of fit are found to reach 98% through comparison, and the goodness of fit of the average friction coefficient simulation calculation is only 60%.
3. Effect of Friction coefficient test
The invention completes the test of the friction performance of the carbon/Tao Chache material according to the industry standard and the characteristics of the brake material, and uses MATLAB software to process the test result to obtain a model of the friction performance of the brake material changing along with the temperature, the specific pressure and the braking rotating speed, and endows the friction coefficient to the material attribute of the whole brake disc model through the CAE script subprogram PYTHON, thereby carrying out the thermal temperature simulation and the brake vibration simulation calculation of the brake material.
Therefore, the method has guiding significance in the design of the wheel, firstly, the temperature analysis and brake vibration analysis based on the friction coefficient can be carried out through the finite element at the initial stage of product design, the weak area with higher temperature can be obtained, the structure of the brake disc is improved and corresponding vibration avoidance measures are taken before the test, and therefore the development period is prolonged; and secondly, result prediction can be carried out before product test, so that economic loss caused by test failure is reduced, and the period of repeated test is shortened.
The friction coefficient obtained by test is adopted to carry out temperature field and brake vibration analysis, the maximum temperature calculated on a certain model is 700 ℃, and the first-order and second-order vibration frequencies are 200Hz and 365Hz respectively; the highest temperature measured by the in-plant and out-plant tests is 710 ℃, and the first-order vibration frequency and the second-order vibration frequency are 198Hz and 360Hz respectively; the results of the in-plant and out-plant tests are completely consistent with the results calculated by the friction coefficient.
Drawings
FIG. 1 is a schematic view of a dynamic friction test piece having an average friction coefficient; wherein fig. 1a is a front view and fig. 1b is a cross-sectional view of fig. 1 a.
FIG. 2 is a schematic structural view of a stiction sample; wherein fig. 2a is a front view and fig. 2b is a cross-sectional view of fig. 2 a.
FIG. 3 is a schematic structural diagram of a dynamic friction test piece with a transient friction coefficient; wherein fig. 3a is a front view and fig. 3b is a side view of fig. 3 a.
FIG. 4 is a graph of the coefficient of friction at constant brake pressure, different speeds and temperatures; the first test point 1 is the influence of the constant specific pressure, speed and temperature change on the transient friction coefficient at a certain point.
FIG. 5 is a graph of friction coefficient at constant initial velocity, brake pressure and temperature; the second test point 2 is the influence of the constant speed, the specific pressure and the temperature change of a certain point on the transient friction coefficient.
Fig. 6 is a flow chart of the present invention.
In the figure: 1. a first test point; 2. a second test point;
Detailed Description
The embodiment is used for obtaining the braking rotating speed V of the braking material with the transient friction coefficient (t) Specific pressure P (t) And temperature T (t) The relationship between the three; therefore, simulation analysis of the temperature field and brake vibration of a certain airplane is carried out.
The specific process of this embodiment is:
step 1: preparation of friction test pieces to obtain average coefficient of friction:
the friction samples comprise static friction samples and dynamic friction samples. The appearance structure of the static friction sample is the same as that of a static disc in a brake disc. The dynamic friction sample has the same shape and structure as the dynamic disc in the brake disc.
The friction contact mode between the static friction sample and the dynamic friction sample is surface contact.
In the present embodiment, the average friction coefficient isInner diameter a of friction sample 1 =42 ± 0.2mm, maximum outer diameter b 1 =75 ± 0.2mm, minimum outer diameter c 1 =53 ± 0.2mm. Four key grooves are uniformly distributed on the outer circumference of the dynamic friction sample, and the width d of each key groove 1 =15.5 ± 0.2mm. Thickness e of the dynamic Friction sample 1 =10 ± 0.2mm. As shown in fig. 1.
In this embodiment, the inner diameter a of the static friction test piece 2 =42 ± 0.2mm, outer diameter c 2 =75 ± 0.2mm. Four key grooves are uniformly distributed on the inner circumferential surface of the static friction sample, and the width d of each key groove 2 =15.5 ± 0.2mm, radial depth =5.5 ± 0.2mm. Thickness e of the static friction test piece 2 =10 ± 0.2mm. As shown in fig. 2.
according to HB5434.7 part 7 of test method of airplane wheel friction material: the friction test method specifies that (P, V, T) is the relationship between the average friction coefficient of the brake material and the brake rotation speed V, the specific pressure P and the temperature T, i.e., the average friction coefficient μ (P, V, T).
The average friction coefficient of the brake material comprises the friction coefficient mu of a dynamic friction sample 1 (P, V, T), average coefficient of Friction of static Friction sample μ 2 (P, V, T) and the average coefficient of friction μ of dynamic friction between dynamic friction sample and static friction sample 3 (P,V,T)。
The specific process for determining the average friction coefficient μ (P, V, T) is:
i determination of the coefficient of friction mu of a dynamic Friction test specimen 1 (P,V,T)
Determination of the average coefficient of friction μ of a dynamic Friction sample 1 (P, V, T). Through an MM-3000 type friction and wear performance tester, according to HB5434.7 part 7 of test method of airplane wheel friction materials: the manner defined in Friction test method. The dynamic friction sample was mounted on a friction and wear tester, and the friction and wear tester was rotated to obtain the coefficient of friction μ of the dynamic friction sample 1 (P, V, T). During collection, the technical parameters of the friction and wear performance testing machine are as follows: the brake pressure is 0.2-20 kN; the rotating speed of the main shaft is 2000-10000 r/m during collectionin; acquiring friction torque required by each friction coefficient: 0 to 300 N.m; the temperature for collecting each friction coefficient is room temperature-1000 ℃. Obtaining the friction coefficient mu of the dynamic friction sample 2 (P,V,T)。
II determination of the coefficient of friction mu of the static Friction test specimens 2 (P,V,T)
Determination of the average coefficient of friction μ of a static Friction test piece 2 (P, V, T). Through an MM-3000 type friction and wear performance tester, according to HB5434.7 part 7 of test method of airplane wheel friction materials: the manner defined in Friction test method. The static friction sample was mounted on a friction and wear tester, and the friction and wear tester was rotated to obtain the friction coefficient μ of the static friction sample 1 (P, V, T). During collection, the technical parameters of the friction and wear performance testing machine are as follows: the brake pressure is 0.2-20 kN; the rotating speed of the main shaft is 2000-10000 r/min during collection; acquiring friction torque required by each friction coefficient: 0 to 300 N.m; the temperature for collecting each friction coefficient is room temperature-1000 ℃. Obtaining the coefficient of friction mu of the static friction sample 2 (P,V,T)。
III average friction coefficient mu of dynamic friction between dynamic friction sample and static friction sample 3 (P,V,T)
Determining the average coefficient of friction mu of the dynamic friction between the dynamic friction sample and the static friction sample 3 (P, V, T). Through an MM-3000 type friction and wear performance tester, according to HB5434.7 part 7 of test method of airplane wheel friction materials: the manner defined in Friction test method. The dynamic friction sample is arranged on a friction and wear testing machine, the friction and wear testing machine is rotated, the dynamic friction sample and the static friction sample are rotated mutually, and the average friction coefficient mu of the dynamic friction between the dynamic friction sample and the static friction sample is obtained 3 (P, V, T). During collection, the technical parameters of the MM-3000 type friction and wear performance testing machine are the same as those of the I type friction and wear performance testing machine.
The friction coefficient obtained by the method is the average friction coefficient mu (P, V, T).
And step 3: preparing a friction sample for obtaining the transient friction coefficient:
the transient friction coefficient test sample comprises a transient static friction coefficient test sample and a transient dynamic friction coefficient test sample. The appearance structure of the transient static friction coefficient sample is the same as that of a static disc in a brake disc. The transient dynamic friction coefficient sample is in a pin shape, and the material is the same as that of the brake disc.
In this embodiment, the inside diameter a of the transient static friction coefficient sample 2 =42 ± 0.2mm, outer diameter c 2 =75 ± 0.2mm. Four key grooves are uniformly distributed on the inner circumferential surface of the transient static friction coefficient sample, and the width d of each key groove 2 =15.5 ± 0.2mm, radial depth =5.5 ± 0.2mm. Thickness e of the transient static friction coefficient sample 2 =10 ± 0.2mm. As shown in fig. 2.
In this embodiment, the height a of the large end of the transient dynamic friction coefficient test piece 3 =10 ± 0.2mm, diameter b 3 =75 ± 0.2mm, and the groove width in the middle of the large end face is 15.5 ± 0.2mm. The small end of the transient dynamic friction coefficient sample is conical, and the length e of the conical head part 3 Angle f of cone, =10 ± 0.2mm 3 =45 °. As shown in fig. 3.
When the transient dynamic friction coefficient sample and the static friction sample obtained in the step 1 are subjected to a friction test, the contact mode between the transient dynamic friction coefficient sample and the static friction sample is point contact, so that the influence of the friction surface on the friction coefficient is eliminated, and the friction coefficient is completely consistent with the actual braking process of an airplane.
The friction test is to install the transient dynamic friction sample on the friction wear testing machine through an MM-3000 type friction wear performance testing machine, and drive the friction wear testing machine to rotate, so that the transient dynamic friction sample and the static friction sample rotate mutually, and the transient friction coefficient between the transient dynamic friction sample and the static friction sample is obtained.
Step 4, determining the transient friction coefficient mu (P) (t) ,V (t) ,T (t) )：
The transient coefficient of friction mu (P) (t) ,V (t) ,T (t) ) The transient friction coefficient under different specific pressures at constant braking speed and temperature and the transient friction coefficient under different speeds at constant braking specific pressure and temperature are included.
And testing the transient friction coefficient of the brake material by adopting an MM-3000 type friction and wear performance testing machine.
The mu (P) (t) ,V (t) ,T (t) ) The method comprises the following steps: p (t) Specific pressure, V, for rubbing the sample at any time (t) Rotational speed, T, of the friction sample at any moment (t) Is the temperature of the rubbed sample at any time.
Determining the μ (P) (t) ,V (t) ,T (t) ) The specific process comprises the following steps:
and I, determining the transient friction coefficients at different specific pressures under the constant braking rotating speed and the constant braking temperature.
Respectively testing the transient friction coefficient of the brake material under the conditions of constant brake rotating speed and temperature under the specific pressure of 0.8MPa, 2.4MPa, 4.0MPa, 6.4MPa and 10.4MPa, and processing each test result by using MATLAB software to obtain the transient friction coefficient of the contact point of the brake material, the brake rotating speed V and the specific pressure P (t) And temperature T (t) Transient relationship among the three; the transient coefficient of friction mu (P) (t) ,V,T (t) )。
And the constant braking rotating speed and temperature conditions are the shaft rotating speed of the friction and wear performance testing machine obtained in the step 2 and the temperature of each friction coefficient.
And II, determining the transient friction coefficient at different rotating speeds under the constant brake specific pressure and the constant brake temperature.
Respectively testing the transient friction coefficients at each speed when the constant brake specific pressure and temperature are measured at 500r/min, 1500r/min, 2500r/min, 3500r/min, 4000r/min and 6500r/min by taking the brake speed of 5000r/min as a reference, and processing each test result by using MATLAB software to obtain the instantaneous friction coefficients at different points of the brake material and the brake speed V (t) Specific pressure P and temperature T (t) The transient relation between the three, i.e. the transient friction coefficient mu (P, V) (t) ,T (t) )。
And (5) performing the following steps: authentication
Respectively substituting the obtained transient friction coefficients into CAE analysis software to analyze the braking temperature field and the braking vibration of the airplane wheel; specifically, the obtained transient friction coefficient is given to the material property of a brake disc model in the whole wheel brake device through CAE analysis software. And the brake disc endowed with the transient friction coefficient is subjected to temperature field simulation and brake vibration simulation through CAE analysis software. The maximum temperature of a brake disc of a certain model is 700 ℃ and the first-order vibration frequency and the second-order vibration frequency are respectively 200Hz and 365Hz through simulation. The maximum temperature of the brake disc obtained by laboratory tests is 710 ℃, and the first-order vibration frequency and the second-order vibration frequency are 198Hz and 360Hz respectively. The maximum temperature of the brake disc obtained by the external field test is 719 ℃; the first and second order vibration frequencies were 206Hz and 369Hz, respectively.
The test results prove that both the laboratory test results and the external field test results are completely consistent with the result of the transient friction coefficient calculation.
Claims (4)
1. A friction coefficient evaluation method for a brake material is characterized by comprising the following specific processes:
step 1: preparation of friction test pieces to obtain average coefficient of friction:
the friction test sample comprises a static friction test sample and a dynamic friction test sample; the static friction sample has the same appearance structure as a static disc in a brake disc; the dynamic friction sample has the same appearance structure as a dynamic disc in a brake disc;
step 2, determining the average friction coefficient μ (P, V, T):
the determined average friction coefficient of the brake material comprises the average friction coefficient mu of a dynamic friction sample 1 (P, V, T), average coefficient of Friction of static Friction sample μ 2 (P, V, T) and the average coefficient of friction μ of dynamic friction between the dynamic friction sample and the static friction sample 3 (P,V,T)；
Determination of the average coefficient of friction μ of a dynamic Friction sample 1 (P, V, T), average coefficient of Friction of static Friction sample μ 2 (P, V, T) and the average coefficient of friction μ of dynamic friction between dynamic friction sample and static friction sample 3 And (P, V, T), the technical parameters of the friction wear tester are as follows: the brake pressure is 0.2 to 20kN; the rotating speed of the main shaft is 2000 to 10000r/min during collection; acquiring friction torque required by each friction coefficient: 0 to 300N · m; collecting the temperature of each friction coefficient to be room temperature-1000 ℃;
and step 3: preparing a friction sample for obtaining the transient friction coefficient:
the transient friction coefficient test sample comprises a transient static friction coefficient test sample and a transient dynamic friction coefficient test sample; the appearance structure of the transient static friction coefficient sample is the same as that of a static disc in a brake disc; the transient dynamic friction coefficient sample is in a pin shape, and the material is the same as that of the brake disc;
step 4, determining the transient friction coefficient mu (P) （t） ,V （t） ,T （t） )：
When the transient dynamic friction coefficient sample and the transient static friction coefficient sample obtained in the step (3) are subjected to a friction test, the transient dynamic friction coefficient sample and the transient static friction coefficient sample are in point contact, so that the influence of a friction surface on the friction coefficient is eliminated, and the friction coefficient is completely consistent with the actual braking process of an airplane;
during the friction test, the transient dynamic friction coefficient sample is installed on a friction and wear testing machine, and the friction and wear testing machine is driven to rotate, so that the transient dynamic friction coefficient sample and the transient static friction coefficient sample rotate mutually, and the transient friction coefficient between the transient dynamic friction coefficient sample and the transient static friction coefficient sample is obtained;
the transient coefficient of friction mu (P) （t） ,V （t） ,T （t） ) The method comprises the transient friction coefficients under the constant braking rotating speed and different specific pressures and temperatures and the transient friction coefficients under the constant braking specific pressure and different rotating speeds and temperatures;
testing the transient friction coefficient of the brake material by adopting a friction and wear testing machine;
the mu (P) （t） ,V （t） ,T （t） ) The method comprises the following steps: p （t） Is the specific pressure, V, of a sample of the friction coefficient at any moment （t） The rotational speed, T, of the friction coefficient sample at any moment （t） The temperature of the friction coefficient sample at any moment;
determining the μ (P) （t） ,V （t） ,T （t） ) The specific process comprises the following steps:
i, determining transient friction coefficients at different specific pressures and temperatures at a constant braking speed;
testing the transient friction coefficient of the brake material under the condition of constant brake speed under different specific pressures and temperatures, and processing each test result through MATLAB software to obtain the transient friction coefficient of the contact point of the brake material, the brake speed V and the specific pressure P （t） And temperature T （t） Transient relationship among the three; the transient coefficient of friction mu (P) （t） ,V,T （t） )；
The conditions of the constant braking rotating speed and the constant braking temperature are the rotating speed of the main shaft of the friction wear testing machine obtained in the step 2 and the temperature range of each friction coefficient;
II, determining the transient friction coefficient under constant brake ratio and at different rotating speeds and temperatures;
respectively testing the transient friction coefficients of the brake material at different braking speeds when the brake specific pressure is constant by taking the braking speed of 5000r/min as a starting point, and processing each test result by using MATLAB software to obtain the transient friction coefficients of different points of the brake material and the braking speed V （t） Specific pressure P and temperature T （t） The transient relation between the three, i.e. the transient friction coefficient mu (P, V) （t） ,T （t） )；
And 5: and (3) verification:
respectively substituting the obtained transient friction coefficients into CAE analysis software to analyze the braking temperature field and the braking vibration of the airplane wheel; specifically, the obtained transient friction coefficient is given to the material attribute of a brake disc model in the whole airplane wheel brake device through CAE analysis software; the brake disc model endowed with the transient friction coefficient is subjected to temperature field simulation and brake vibration simulation through CAE analysis software; the maximum temperature of the brake disc model is 700 ℃ and the first-order vibration frequency and the second-order vibration frequency are respectively 200Hz and 365Hz through simulation; the maximum temperature of the brake disc obtained by laboratory test is 710 ℃, and the first-order vibration frequency and the second-order vibration frequency are 198Hz and 360Hz respectively; the maximum temperature of the brake disc obtained by the external field test is 719 ℃; the first order vibration frequency and the second order vibration frequency are 206Hz and 369Hz respectively;
the test result proves that both the laboratory test result and the external field test result are completely consistent with the result of the transient friction coefficient calculation;
so far, the evaluation of the friction coefficient of the brake material is completed;
inner diameter a of the dynamic friction test piece 1 =42 ± 0.2mm, maximum outer diameter b 1 =75 ± 0.2mm, minimum outer diameter c 1 =53 ± 0.2mm; four key grooves are uniformly distributed on the outer circumference of the dynamic friction sample, and the width d of each key groove 1 =15.5±0.2mm；
The static friction test sample and the transient static friction coefficient test sample have the same structure size and the inner diameter a 2 =42 ± 0.2mm, outer diameter c 2 =75 ± 0.2mm; four key grooves are uniformly distributed on the inner circumferential surface of the static friction sample, and the width d of each key groove 2 =15.5 ± 0.2mm, radial depth =5.5 ± 0.2mm;
height a of big end of the transient dynamic friction coefficient sample 3 =10 ± 0.2mm, diameter b 3 =75 ± 0.2mm, and the groove width in the middle of the end face of the big end is 15.5 ± 0.2mm; the small end of the transient dynamic friction coefficient sample is in a conical shape, and the length e of the conical small end 3 Angle f of cone, =10 ± 0.2mm 3 =45°。
2. The brake material friction coefficient evaluation method according to claim 1, wherein the specific procedure for determining the average friction coefficient μ (P, V, T) is:
i determination of the average coefficient of Friction mu of a dynamic Friction test specimen 1 (P,V,T)
Determination of the average coefficient of friction μ of a dynamic Friction sample 1 (P, V, T), the average friction coefficient μ of the dynamic friction sample was obtained by a friction and wear tester 1 (P,V,T)；
II determination of the average coefficient of friction mu of the static Friction test specimens 2 (P,V,T)
Determination of the average coefficient of friction μ of a static Friction test piece 2 (P, V, T), the average friction coefficient μ of the static friction test piece was obtained by a friction and wear tester 1 (P,V,T)；
III average friction coefficient mu of dynamic friction between dynamic friction sample and static friction sample 3 (P,V,T)
Determining dynamic friction testAverage coefficient of friction mu of dynamic friction between sample and static friction sample 3 (P, V, T), the average friction coefficient mu of the dynamic friction between the dynamic friction sample and the static friction sample was obtained by a friction and wear tester 3 (P,V,T)。
3. The method for evaluating a friction coefficient of a brake material according to claim 1, wherein the differential specific pressures in step 4 are 0.8MPa, 2.4MPa, 4.0MPa, 6.4MPa, and 10.4MPa.
4. The method for evaluating the friction coefficient of a brake material according to claim 1, wherein the different rotation speeds in step 4 are 500r/min, 1500r/min, 2500r/min, 3500r/min, 4000r/min and 6500r/min.
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