Development of high speed rail-wheel contact simulator

Development of high speed rail-wheel contact simulator J.Y. Choi 1), I.Y. Choi 1), J.S. Lee 1), T.W. Kim 1), D.H. LEE 1), J.W. Seo 1) 1) Korea Railroad Research Institute, Uiwang, S.Korea 1. Introduction In recently, rail deteriorations such as rolling contact fatigue and wear are arising as hot issue of track maintenance. Excessive defect or profile changing of wheel and rail might have effect on running safety and riding comfort of vehicle. In case of subway or metro line, a severe wear on a sharp curve has caused operational problem such as limitation of running speed and excessive noise as well as maintenance problem including reducing period of rail renewal. For high speed line, rolling contact fatigue is anticipated as a critical issue in maintenance of railway, particularly, in case of concrete track, maintenance of rail would be the most important issue. To solve these problems, many researches are performing in the way of analytically and experimentally. Especially, for the experimental study, some simulator or test machine were developed in the world. 1),2),3),4) As a part of those efforts, the wheel-rail contact simulator was developed in KRRI. The developed high speed railwheel contact simulator was designed to achieve the maximum designed speed up to 445km/h in case of wheel diameter of 100 in preparation for speed increasing more than 400km/h. It was also designed to investigate deterioration phenomena between wheel and rail under various contact angles, attack angle, environmental condition, and radial and thrust load condition. The wheel-rail rolling contact fatigue test, wheel-rail wear test, and wheel-rail adhesion coefficient measuring test are available with the high speed rail-wheel contact simulator. From those tests, we are able to enhance the contact characteristics; to achieve profile renovation; to predict the fatigue life of rail and wheel; to identify the characteristics of wear, adhesion, and friction between wheel and rail. 2. Features of the developed simulator 2.1 General feature The developed system is organized by the main frame, wheel & rail disk specimen, wheel & rail driving motor, radial & thrust load actuator, contact angle & attack angle adjuster, environmental chamber, main control system, safety and measuring devices, and etc. In addition, the system has environmental simulation equipment of water, oil, wind, sand insertion with temperature control. The feature of the system is shown in Fig.1 and Fig.2. And the target performance of the system is summarized in Table1. Fig.1. Concept Drawing of the Rail-Wheel Contact Simulator

Fig.2. Rail-Wheel Contact Simulator in Situ Table 1. Target Performance of the System Performance Specification Specimen Test Speed Radial Force Thrust Force Wheel & Rail : Φ30 to Φ100 0~2470 rpm @100(diameter), Max. 445km/h Max. 180kN, ±2.5mm@20Hz Max. 100kN, ±7.5mm@20Hz Slip rate -10~+100% Torque Control Contact Angle Attack Angle Environment Control System Safety Device 1% of F.S. 0~3º (1% of F.S.) -3º~+3º (1% of F.S.) Dry, Wet, Oil, Sand, Temperature, Humidity Controller Manual RPM, Radial & thrust force, Slip rate, HSM, Environment, Laser scan Contact & Attack angle, Test space adjustment Safety shield, EMG(motor current, acceleration, BRG temp.) CCD camera The maximum test speed is 445km/h with 100 of the wheel diameter. The size of the specimen is adoptable from 30 to 100 in diameter. The maximum radial and thrust load were decided as 180kN and 100kN in each by considering real wheel load including dynamic effect. The slip phenomenon between wheel and rail is also possible to simulate from -10 to 100% with 0.2% accuracy at 2470rpm. And also to consider the situation in curved track, the contact and attack angle is adjustable 0~3º and -3º~+3º in each. For tests in various environmental circumstances, environmental chamber was established having function of temperature & humidity control and injection of dry, wet, water, oil and sand. The detail specifications and performances of each part are as following. 2.2 Wheel Driving Module The wheel driving module contains the 355kW AC servo motor for rotating the wheel specimen and the high performance hydraulic servo actuators (100kN and 180kN) for the radial & thrust load at the contact point between the wheel and rail. Those are around the wheel specimen in the shape of T.

Fig.3. Wheel Driving Module In order to rotate specimens under slip condition, a tangential force which excesses a friction force between wheel and rail surface is required. The required minimum tangential force is determined from the amount of the radial load and the friction coefficient between wheel and rail surface, and it can be converted to the torque required, which is also concerned to the specimen size. If specimen diameter becomes larger, higher torque is required. The relationship between torque and speed of adopted motor is shown in Fig. 4(a), and also, Fig. 4(b) shows available radial loads according to maximum specimen size in case of slip rate 100% and surface friction coefficient 0.1. If there is no slip, the motor can run maximum speed 2470rpm regardless amount of radial load because there is no friction force. (a) Motor Speed vs. Torque (b) Allowable Specimen Size Fig.4. Performance Curve of the Motor The driving power from electric motor is transferred to the spindle through the CV-joint. The spindle which is linked to a specimen is designed having high rigidity to resist the radial & thrust load and high speed rotation. Each component of the rig is designed for easy setting and detaching with enough rigidity. In addition, there is a brake system to stop the wheel specimen in an emergency situation. For applying the radial and thrust load, hydrostatic actuators were adopted. Performance is shown in table 2. Table 2. Performance of Radial & Thrust Loader Specification Radial Loader Thrust Loader Type Servo hydraulic system Control mode Force, Displacement Loading type Static, Cycle, Random Capacity 180kN 100kN Stroke ±75mm ±75mm Dynamic performance ±2.85mm@20Hz ±7.55mm@20Hz Accumulator Included Included LVDT linearity 0.1% of full scale 0.1% of full scale

2.2 Rail Driving Module The rail driving module is comprised of 355kW AC servo motor and spindle, and a sensor for measuring the friction torque between the motor and spindle. The torque sensor is including a noncontact type telemetry. The rail driving module is set at the high rigidity fixture (horizontal direction) for the adjustment of attack angle. Fig.5. Rail Driving Module 2.3 Contact and Attack angle adjust The contact & attack angle of the specimen can be adjusted by the mechanical structure. The contact angle adjuster is equipped to simulate the real contacting condition between the wheel and rail. From the Fig. 5, this equipment can rotate the wheel driving module (clock wise 0 ~+3 ) around the wheel specimen. The user can control the angle by the electric motor through the sensor. The attack angle adjuster can rotate the rail driving module (-3 ~+3 of the rail specimen) to simulate train s curving movement. The user can control the rotation angle through the sensor at the electric motor. (a) Contact Angle Adjuster (b) Attack Angle Adjuster Fig.6. Contact & Attack Angle Adjuster

2.4 Environmental Control System There are three modules of the environmental control system such as the main chamber for the temperature and humidity control, sub chamber for the temperature control around the specimen by using the air from the main chamber, and the equipment with nozzle system for simulating second environment such as water, oil, and sand. Capacity of the environmental chamber is shown in Table. 3. Table 3. Capacity of Environmental Chamber Temperature range -30 ~ +80 Humidity range Oil injection system Water injection system Sand injection system 30% - 98% (absolute humidity) max. 5 lpm max. 5 lpm max. 5kg/min In order to prevent high temperature in specimen, the surface cooling devices are attached on each side of the specimens. And also, the high pressure air nozzle is installed on the contact point of two specimens to blow away particles. It reduces friction between wheel and rail specimen. The feature and concept drawing of environmental chamber are shown in Fig.7, and the sub chamber and nozzles in the sub chamber are shown in Fig. 8. AIR Tem perat ure Co nt rol ler Injection System Tem perat ure Co nt roll er Feedb ack Con tro l Feed back Co nt rol Su rf ace Coo lin g Device Su rface Coo lin g Device Infrared Temperature Sensor Inf rared Tem perat ure Sen so r Fig.7. Feature and Concept Drawing of Environmental Chamber Fig.8. Sub Chamber and Injection Nozzles 2.5 Safety Cover The disk type specimens are operated in high speed. So, if some fatal damage happens at specimen, splinter from the specimen can be scattered with high speed during the test, then it occurs very dangerous situation. For protecting from those undesirable situations, the system has multiple safety covers. The sub camber (sec. 2.4) is the first safety cover, and the second safety cover made

up of steel plate and beam is covering over sub chamber. The third safety cover is the main cover of the system; it is made by 5 layered composite material and steel plate. Fig.9. Safety Covers 2.6 Measuring Devices For detection a flaw on the surface of specimen during operating, non-contact eddy current type flaw detection device is adopted. And in order to measuring the changing of section shape by wear or flaw on surface of specimen, 2D laser scanning device is also equipped. These devices are installed at 3 axis robot which attached on sub chamber as shown in Fig. 10, which make possible to measure by moving from wheel side to rail side continuously without interrupting test. 2.7 Specimens Fig.10. Measuring Devices The adoptable size of specimen for the developed simulator is from Φ30 to Φ100. The axle distance between wheel disk and rail disk is minimum 30 to maximum 100 but minimum and maximum disk size is limited Φ17 and Φ100 in each. The wheel and rail specimen is made of steel plate having same metallic property as real wheel and rail. It is also possible to use the real wheel from wheel set of a vehicle. In Fig. 11, it is shown specimens are installed for a test. Fig.11. Installed Specimens

2.8 Control System The configuration of the control system is shown in Fig. 12. The master controller is comprised with the server PC for operating and monitoring testing status, the main controller for control actuators and motors according to the command from server PC, and several sensors for monitoring temperature and acceleration of spindle. The server PC and the main controller are communicated by Ethernet; and the main controller is communicated with actuators and sensors by analog data signal. Fig. 13 is a picture of window of the Main control S/W. Fig.12. Configuration of Control System Fig.13. Window of the Main Control S/W 3. Tests for Performance Verification 3.1 Main System The simulator is developed to test for investigating various contact mechanism between wheel and rail, especially rolling contact fatigue, wear and adhesion property of wheel and rail surface. To verify capabilities for performing those tests, many experimental tests were carried out. At first, tests to examine full performance each component in separated operation conditions were conducted, and then overall performance tests under the various conditions were executed. Test results on the each component in separate are shown in Table 4. From the results on the table, it is known that the components have very good performance since the control accuracy of each component is below 0.1% of full performance.

Table 4. Test Results of Each Component Module Control Object Full Performance Max. Error Error rate Wheel Drive Speed 3300rpm 2.66 rpm 0.08% Rail Drive Speed 3300rpm 3.13 rpm 0.09% Radial Displacement ±75mm(15) 0.07 mm 0.05% Actuator Load 250kN 0.52 kn 0.02% Thrust Actuator Displacement ±75mm(15) 0.06 mm 0.04% Load 125kN 0.2 kn 0.02% The overall performance tests under the complex conditions are shown in Table 5, and among the tests, some typical test results are summarized. Even though the test condition is very complex and the poor surface state of the specimen due to repeated test, the results is below 1% error ratio for full scale, and this leads the developed simulator has good control performance even under the complex and coarse test circumstance. Table 5. Tests for Performance Verification wheel slip wheel rail radial load size rate speed speed Φ300 (mm) Φ860 (mm) 0% 10% 0% 2470 1040 2470 10kN (1100MPa)* 8kN+/-2kN @ 1Hz 8kN+/-2kN @ 10Hz 10kN (1100MPa) 8kN+/-2kN @ 1Hz 10kN (1100MPa) 35kN+/-10kN @ 1Hz 45kN (1200MPa) 40kN+/-5kN @ 1Hz 40kN+/-5kN @ 10Hz thrust load 3kN+/-2kN @ 1Hz 4kN+/-1kN @ 1Hz 4kN+/-1kN @ 10Hz 3kN+/-2kN @ 1Hz 4kN+/-1kN @ 1Hz 4kN+/-1kN @ 10Hz 20kN+/-2.5kN @ 1Hz 20kN+/-2.5kN @ 10Hz 17.5kN+/-5kN @ 1Hz 20kN+/-2.5kN @ 1Hz 20kN+/-2.5kN @ 1Hz 20kN+/-2.5kN @ 1Hz contact angle attack angle 3 0 3 0

10% 1040 22kN 17kN+/-5kN @ 1Hz 17kN+/-5kN @ 10Hz 8kN+/-3kN @ 1Hz 8kN+/-3kN @ 1Hz 8kN+/-3kN @ 1Hz * Hertzian Contact Pressure from reference 5. 1) Test result 1 Test Condition Size of Wheel and Rail Specimen : Φ 860 mm Radial Load : -40 +/- 5kN, 10Hz(Force Control) Thrust Displacement : +/-1mm, 10Hz (Displacement Control) Running Speed of Wheel & Rail Disk : 2470rpm (Non Slip Condition) Contact angle : 3 Attack angle : 0 Test Result Radial Load Thrust Disp. Wheel Speed Rail Speed Target Measure Difference Error Ratio 1) Error Ratio for F.S. 2) Max. -35.0 kn -36.80 kn 1.80 kn 4.90 % 0.72 % Min. -45.0 kn -43.62 kn 1.38 kn 3.16 % 0.55 % Max. +1.0 mm +1.10 mm 0.10 mm 8.94 % 0.07 % Min. -1.0 mm -1.13 mm 0.13 mm 11.16 % 0.09 % Max. 2470.0 rpm 2469.64 rpm 0.36 rpm 0.01 % 0.01 % Min. 2470.0 rpm 2468.21 rpm 1.79 rpm 0.08 % 0.05 % Max. 2470.0 rpm 2470.98 rpm 0.98 rpm 0.04 % 0.03 % Min. 2470.0 rpm 2467.34 rpm 2.66 rpm 0.11 % 0.08 % 1) Error Ratio = Difference / Target (%) 2) Error Ratio for Full Scale = Difference / Full Performance of Each Component (%) 2) Test result 2 Test Condition Size of Wheel and Rail Specimen : Φ 860 mm Radial Load : -17 +/- 5kN, 10Hz(Force Control) Thrust Load : -8 +/- 3kN, 1Hz(Force Control)

Running Speed of Wheel & Rail Disk : rpm & 1040 rpm ( 10% Slip Condition) Contact angle : 3 Attack angle : 0 Test Result Radial Load Thrust Disp. Wheel Speed Rail Speed Target Measure Difference Error Ratio 1) Error Ratio for F.S. 2) Max. -12.0 kn -13.92 kn 1.92 kn 13.82 % 0.77 % Min. -22.0 kn -20.32 kn -1.68 kn 8.29 % 0.67 % Max. -5.0 kn -4.58 kn -0.42 kn 9.09 % 0.33 % Min. -11.0 kn -11.24 kn 0.24 kn 2.14 % 0.19 % Max..0 rpm 1154.59 rpm -4.59 rpm 0.40 % 0.14 % Min..0 rpm 1145.33 rpm 4.67 rpm 0.41 % 0.14 % Max. 1040.0 rpm 1041.85 rpm 1.85 rpm 0.18 % 0.06 % Min. 1040.0 rpm 1036.21 rpm 3.79 rpm 0.37 % 0.11 % Slip Max. 10.0 % 10.11 % 0.11 % - - Ratio 1) Min. 10.0 % 9.72 % 0.28 % - - 1) Slip Ratio = (V wheel V rail ) / ((V wheel + V rail )/2) Where, V wheel : speed of wheel specimen V rail : speed of rail specimen 4. Conclusion and Further Study The high speed rail-wheel contact simulator was developed to investigate various rail-wheel contact phenomena. The developed high speed rail-wheel contact simulator was designed to operate more than 400km/h and perform test under the various contact angles, attack angle, environmental condition, and axial and thrust load condition. The performance of the developed simulator was proved through tests to examine full performance each component in separated operation conditions, and overall performance tests under the various conditions. Using the developed machine, some case of trial tests for the wheel-rail rolling contact fatigue (RCF) test, wheel-rail wear test, and wheel-rail adhesion coefficient measuring test was conducted. In recently, tests to establish standard process for each test item using the developed machine are carrying out. And also, the parametric studies to investigate mechanism and phenomena of wheel rail contact will be progress successively. Based on outcome of such tests, the simulator is expected to provide information of improved profile and material for wheel and rail; to reduce maintenance cost. Besides, implementation of laboratory test of rail fatigue and wear at high speed range including parametric test of various influence factors would be able to identify inherent wheel-rail contact problems that may be occurred during operation of high speed train at early stage. References 1. M. Ishida and Y. Satoh, "Development of Rail/Wheel High Speed Contact Fatigue Testing Machine and Experimental Results," RTRI Report Vol2, No, 5, pp. 2-7, 1988. 2. M. Takikawa and Y. Iriya, "Laboratory Simlulations with Twin-Disk Machine on Head Check," CM2006 conference paper, pp. 431-437, 2006 3. D.I. Fletcher and J.H. Beynon, "Development of a Machine for Closely Contralled Rolling Contact

Fatigue and Wear Testing," J. Testing and Evaluation, JTEVA, Vol.28, No.4, pp. 267-275, 2000 4. W. Wang, J. Gou, Q. Liu and Z. Zhou, "Experimental Study on Wear and Spalling Behavior of Railway Wheel," CM2006 conference paper, pp. 629-637, 2006 5. H.L. Whittemore, S.N. Petrenko, Tech. Paper Bureau Standards, No.201, 1921