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B-1 APPENDIX B: Investigation of Wheel Flange Climb Derailment Criteria for Transit Vehicles (Phase I Report)

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INVESTIGATION OF WHEEL FLANGE CLIMB DERAILMENT CRITERIA FOR TRANSIT VEHICLES (PHASE I REPORT) SUMMARY This research investigated wheelset flange climb derailment with the intent of develop- ing limiting criteria for single-wheel L/V ratios and distance to climb for transit vehicles. The investigations used simulations of single wheelsets and representative transit vehicles. Based on the single wheelset simulation results, preliminary L/V ratio and climb-distance criteria for transit vehicle wheelsets are proposed. The proposed criteria are further val- idated through simulation of three types of transit vehicles. This research has been based on the methods previously used by the research team to develop flange climb derailment criteria for the North American freight railroads. The following conclusions are drawn from single wheelset and vehicle simulations: New single wheel L/V distance criteria have been proposed for transit vehicles with specified wheel profiles: Wheel 1 profile: 5 L/V Distance (feet) < , if AOA < 10 mrad 0.13 * AOA + 1 L/V Distance (feet) = 2.2, if AOA 10 mrad Wheel 2 profile: 4.1 L/V Distance (feet) < , if AOA < 10 mrad 0.16 * AOA + 1 L/V Distance (feet) = 1.6, if AOA 10 mrad Wheel 3 profile: 4.2 L/V Distance (feet) < , if AOA < 10 mrad 0.136 * AOA + 1 L/V Distance (feet) = 1.8, if AOA 10 mrad

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B-4 Wheel 4/5 profile: 28 L/V Distance (feet) < , if AOA < 10 mrad 2 * AOA + 1.5 L/V Distance (feet) = 1.3, if AOA 10 mrad Wheel 6 profile: 49 L/V Distance (feet) < , if AOA < 10 mrad 2 * AOA + 2.2 L/V Distance (feet) = 2.2, if AOA 10 mrad where AOA is in mrad. In situations where AOA is not known and cannot be mea- sured, the equivalent AOA (AOAe) calculated from curve curvature and truck geometry should be used in the above criteria. In situations where AOA is known and can be measured, more accurate new single wheel L/V ratio criteria based on AOA have also been proposed (see correspond- ing equation in Chapter 2 of this appendix). Simulation results for transit vehicles assembled with different types of wheel pro- files confirm the validity of the proposed criteria. An incipient derailment occurs for most conditions when the climb distance exceeds the proposed criteria value. The proposed climb distance criteria are conservative for most conditions. Under many conditions, variations of AOA act to reduce the likelihood of flange climb. The single wheel L/V ratio required for flange climb derailment is determined by the wheel maximum flange angle, friction coefficient, and wheelset AOA. The L/V ratio required for flange climb converges to Nadal's value at higher AOA (above 10 mrad). For the lower wheelset AOA, the wheel L/V ratio necessary for flange climb becomes progressively higher than Nadal's value. The distance required for flange climb derailment is determined by the L/V ratio, wheel maximum flange angle, wheel flange length, and wheelset AOA. The flange climb distance converges to a limiting value at higher AOAs and higher L/V ratios. This limiting value is highly correlated with wheel flange length. The longer the flange length, the longer the climb distance. For the lower wheelset AOA, when the L/V ratio is high enough for the wheel to climb, the wheel-climb distance for derailment becomes progressively longer than the proposed flange-climb-distance limit. The wheel-climb distance at lower wheelset AOA is mainly determined by the maximum flange angle and L/V ratio. Besides the flange contact angle, flange length also plays an important role in pre- venting derailment. The climb distance can be increased through use of higher wheel maximum flange angles and longer flange length. The flanging wheel friction coefficient significantly affects the wheel L/V ratio required for flange climb. The lower the friction coefficient, the higher the single wheel L/V ratio required. For conventional solid wheelsets, a low nonflanging wheel friction coefficient has a tendency to cause flange climb at a lower flanging wheel L/V ratio, and flange climb occurs over a shorter distance for the same flanging wheel L/V ratio. The proposed L/V ratio and flange-climb-distance criteria are conservative because they are based on an assumption of a low nonflanging wheel friction coefficient.

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B-5 For independent rotating wheelsets, the effect of the nonflanging wheel friction coefficient is negligible because the longitudinal creep force vanishes. The proposed L/V ratio and flange-climb-distance criteria are less conservative for independent rotating wheels because independent rotating wheels do not generate significant longitudinal creep forces. For the range of track lateral stiffness normally present in actual track, the wheel- climb distance is not likely to be significantly affected by variations in the track lateral stiffness. The effect of inertial parameters on the wheel-climb distance is negligible at low speed. At high speed, the climb distance increases with increasing wheelset rotating inertia. However, the effect of inertial parameters is not significant at a low nonflanging wheel friction coefficient. Increasing vehicle speed increases the distance to climb. Phase I of this project proposed specific L/V ratio and flange-climb-distance criteria for several specific wheel/rail profile combinations. Preliminary validation of these cri- teria was made using derailment simulations of several different passenger vehicles. To provide further validation of the criteria, the main task in Phase II of this project was to perform comparisons with results from full-scale transit vehicle tests. The conditions and limitations for the application of the criteria were also proposed. Since the climb distance limit is highly correlated with the flange parameters (flange angle, length, and height), a general climb distance criterion that depends on both the AOA and flange parameters was further investigated in Phase II.

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B-6 CHAPTER 1 INTRODUCTION The research team conducted a full-scale wheel-climb Correspondingly, the L/V distance criterion was proposed as: derailment test with its TLV during 1994 and 1995 (1). The primary objective of the test was to reexamine the current (1) With onboard AOA measurement system, flange climb criteria used in the Chapter XI track worthiness 16 tests described in M-1001, AAR Manual of Standards and (a) L/V Distance (ft) < AOA (mrad) + 1.5 Recommended Practices, 1993. In 1999, the research team conducted extensive mathe- {for AOA > -2 mrad} matical modeling of a single wheelset flange using its (b) L/V Distance (ft) = {for AOA < -2 mrad} dynamic modeling software (2). The objective of this work was to gain a detailed understanding of the mechanisms of flange climb. This research resulted in the proposal of a new single-wheel L/V ratio criterion and a new flange-climb- distance criterion for freight cars. Subsequently, some revi- sions were made to the proposed criteria (3). Both of these projects were jointly funded by the FRA and the AAR. The proposed L/V and distance-to-climb criteria were developed for freight cars with an AAR1B wheelset with a 75-degree flange angle. These were developed based on fit- ting L/V and distance-to-climb curves to numerous simula- tions of flange climb derailment. These were verified by comparison to the single wheel flange climb test results. Because the test and simulation results showed considerable sensitivity to axle AOA, the criteria were proposed in two Figure B-1. Proposed single wheel L/V criterion with forms. The first is for use when evaluating test results where wheelset AOA measurement. the AOA is being measured, and the second, which is more conservative, is for use when the AOA is unknown or cannot be measured. The following are the proposed criteria. Because mea- 14 surement of AOA is usually quite difficult, the second forms 12 are most likely to be used. The criteria are shown graphically L/V distance limit (ft). 10 in Figures B-1 and B-2. 8 (1) With capability to measure AOA during the test: 6 50 msec duration at 50 mph L 4 (a) Wheel V 5 mrad} 50 msec duration at 25 mph 2 (b) Wheel L < 12 0 V AOA (mrad) + 7 2 0 2 4 6 8 10 12 {for AOA < 5 mrad} Angle of attack (mrad) (2) Without ability to measure AOA, Figure B-2. Proposed L/V distance limit with wheelset L AOA measurement. (Dots represent results; line represents Wheel < 1.0 V the proposed distance limit.)

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B-7 (2) Without onboard AOA measurement system, the condition may be temporary, with wheel and rail returning to L/V distance criterion is proposed relating to the normal contact, or it may result in the wheel climbing fully track curvature: over the rail. Researchers have been investigating the wheel 16 flange climb derailment phenomena since the early 20th cen- L/V Distance (ft) < Curve (degree) + 3.5 tury. As a result of these studies, six flange climb criteria have been proposed. These criteria have been used by railroad engi- The research to develop these criteria was based primarily neers as guidelines for safety certification testing of railway on tests and simulations of wheel and rail profiles and load- vehicles. Briefly, they are the following: ing conditions typical for the North American freight rail- roads. Analyses were also limited to 50 mph. The research Nadal Single-Wheel L/V Limit Criterion team is conducting further research to finalize these proposed Japanese National Railways (JNR) L/V Time Duration criteria for adoption by the AAR. Criterion Currently, no consistent flange climb safety criteria exist General Motors' Electromotive Division (EMD) L/V for the North American transit industry. Wheel and rail pro- Time Duration Criterion file standards and loading conditions vary widely for differ- Weinstock Axle-Sum L/V Limit Criterion ent transit systems and for different types of vehicles used in FRA High-Speed Passenger Distance Limit (5 ft) light rail and rapid transit services. Therefore, the proposed AAR Chapter XI 50-millisecond (ms) Time Limit flange climb criteria developed by the research team for freight cars may not be directly applicable to any particular The Nadal single-wheel L/V limit criterion, proposed by transit system. The purpose of this project was to use similar Nadal in 1908 for the French Railways, has been used through- analytical methods to develop flange climb derailment safety out the railroad community. Nadal established the original for- criteria, specifically for different types of transit systems and mulation for limiting the L/V ratio in order to minimize the transit vehicles. risk of derailment. He assumed that the wheel was initially in The research team undertook a program of developing two-point contact with the flange point leading the tread. He wheel/rail profile optimization technology and flange climb concluded that the wheel material at the flange contact point criteria at the request of the NCHRP. This program included was moving downwards relative to the rail material, due to the two phases, as listed Table B-1. wheel rolling about the tread contact. Nadal further theorized This report describes the methodology and results derived that wheel climb occurs when the downward motion ceases from the work performed in Task 2 of Phase I of this program. with the friction saturated at the contact point. Based on his Wheel and rail profile data, and vehicle and track system data assumptions and a simple equilibrium of the forces between a gathered as a part of Phase I, Task 1, were used to develop the wheel and rail at the single point of flange contact, Nadal pro- inputs to the simulations of flange climb derailment. posed a limiting criterion as a ratio of L/V forces: L tan( ) - 1.1 BACKGROUND = V 1 + tan( ) Wheel-flange-climb derailments occur when the forward motion of the axle is combined with an excessive ratio of L/V The expression for the L/V criterion is dependent on the wheel/rail contact forces. This usually occurs under conditions flange angle and friction coefficient . Figure B-3 shows of reduced vertical force and increased lateral force that causes the solution of this expression for a range of values, appro- the wheel flange to roll onto the top of the rail head. The climb priate to normal railroad operations. The AAR developed its TABLE B-1 Wheel/rail profile optimization and flange climb criteria development tasks Program: Development of Wheel/Rail Profile Optimization Technology and Flange Climb Criteria Survey the transit industry and define common problems and Task 1 concerns related to wheel/rail profiles in transit operation Phase I Propose preliminary flange climb derailment criteria for application to Task 2 transit operation Develop a general methodology of wheel/rail profile assessment Task 1 applicable to transit system operation Phase II Task 2 Propose final flange climb derailment criteria validated by test data

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B-8 1.5 A review of recent flange climb and wheel/rail interaction 1.4 literature has been conducted as part of the work (shown in 1.3 the Appendix B-1). Although several other teams are cur- 1.2 Nadal L/V Value 1.1 rently active in the field of flange climb research, no signifi- 1 cant new flange climb criteria have been reported. 0.9 0.8 Therefore, it was concluded that the development of new cri- 0.7 teria for the transit industry would be based on applying the 0.6 research and analytical methods used in the research team's 0.5 0.4 previous flange climb research. To develop wheel-climb derail- 0.3 ment criteria for transit vehicles, some parameters--such as 50 55 60 65 70 75 80 85 forward speed, inertial parameters of wheelsets, and wheel and Flange Angle (Degree) rail profiles used in the transit industry--would need to be fur- ther investigated. The criteria also need to be further validated 0.1 0.2 0.3 0.4 0.5 0.6 through simulations and tests of representative transit vehicles. Previous research has also shown that flange climb is Figure B-3. Nadal criterion values. strongly influenced by wheelset AOA. Transit vehicles are likely to experience considerably different conditions of AOA than freight vehicles. Further, AOA is very difficult to Chapter XI single-wheel L/V ratio criterion based on Nadal's measure. Thus, the proposed flange climb criteria are based theory using a friction coefficient of 0.5. on conservative expectations for AOA in different ranges of Following a large number of laboratory experiments and track curvature. observations of actual values of L/V ratios greater than the Nadal criterion at incipient derailment, researchers at JNR proposed a modification to Nadal's criterion (4). For time 1.2 OBJECTIVE durations of less than 0.05 s, such as might be expected dur- ing flange impacts due to hunting, an increase was given to The objectives of Phase I of this project were the following: the value of the Nadal L/V criterion. However, small-scale tests conducted at Princeton University indicated that the To further investigate wheel/rail flange climb mecha- JNR criterion was unable to predict incipient wheel-climb nisms for transit vehicles. derailment under a number of test conditions. To evaluate and propose wheelset flange climb derail- A less conservative adaptation of the JNR criterion was ment criteria for transit systems using simulations of used by General Motors EMD in its locomotive research (5). single wheelsets. More recently, Weinstock, of the United States Volpe To validate the criteria through simulations of represen- National Transportation Systems Center, observed that this tative transit vehicles. balance of forces does not depend on the flanging wheel alone (6). Therefore, he proposed a limit criterion that utilizes the 1.3 METHODOLOGY sum of the absolute value of the L/V ratios seen by two wheels of an axle, known as the "Axle Sum L/V" ratio. He proposed 1.3.1 Single Wheelset Flange Climb Derailment that this sum be limited by the sum of the Nadal limit (for the Simulations flanging wheel) and the coefficient of friction (at the non- flanging wheel). Weinstock's criterion was argued to be not The effects of different parameters on derailment were inves- as overly conservative as Nadal's at small or negative AOA tigated through single-wheelset simulation. Based on these sim- and less sensitive to variations in the coefficient of friction. ulation results, the L/V ratio and climb distance criteria for six Based on the JNR and EMD research, and considerable different kinds of transit wheelsets were proposed. experience in on-track testing of freight cars, a 0.05-s (50-ms) To minimize the number of variables and focus on time duration was adopted by the AAR for the Chapter XI cer- wheel/rail interaction, a computer simulation model of a sin- tification testing of new freight cars. This time duration has gle wheelset was used. The wheel and rail profiles, inertia since been widely adopted by test engineers throughout North parameters, and vertical wheel loads were adopted from America for both freight and passenger vehicles. actual transit vehicle drawings and documents. Much of this A flange-climb-distance limit of 5 ft was adopted by the data had been gathered as a part of the surveys being con- FRA for their Class 6 high speed track standards (7). This dis- ducted for Phase I, Task 1 of this TCRP research project (8). tance limit appears to have been based partly on the results of The same basic simulation methods used in the research the joint AAR/FRA flange climb research conducted by the team's previous flange climb studies were adopted here. To research team and also on experience gained during the test- perform the flange climb derailment simulations, the ing of various commuter rail and long distance passenger cars. wheelset AOA was set at a fixed value. A large yaw stiffness

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B-9 between the axle and ground ensured that the AOA remained approximately constant throughout the flange climb process. 10000 Applied Lateral Force (lb) A vertical wheel load that corresponded to the particular 9000 8000 A vehicle axle load was applied to the wheelset to obtain the 7000 appropriate loading at the wheel/rail contact points. 6000 The magnitude of the external lateral force and the 5000 wheelset AOA controls the flanging wheel L/V ratio. To 4000 make the wheel climb the rail and derail, an external lateral 3000 2000 force was applied, acting towards the field side of the derail- 1000 ing wheel at the level of the rail head. Figure B-4 shows a 0 typical lateral force history. During a constant speed move- 0 5 10 15 20 25 30 35 40 ment, an initial lateral force was applied at either 50 percent Distance (feet) or 80 percent of the expected L/V ratio for steady-state climb (based on Nadal's theory). This initial load level was held for 5 ft of travel to ensure equilibrium. The lateral force was then Figure B-4. Lateral force step input. increased to the final desired L/V ratio (starting from A in Figure B-4). This high load was held until the end of the sim- modeled. The vehicle models included typical passenger car ulation. From this point, the wheel either climbed on top of components, such as air bag suspensions, primary rubber the rail or it traveled a distance of 40 ft without flange climb; suspensions, and articulation joints. the latter was considered as no occurrence of derailment. To generate the large AOA, a large lateral force and Flange climb results from each of the six different vertical wheel unloading typical of actual flange climb con- wheelsets were analyzed to develop and propose limiting ditions were used. The track input to the models used a mea- flange climb L/V criteria and distance-to-climb criteria for sured track file, with variations in curvature, superelevation, the different types of transit systems. gage, cross level, and alignment perturbations along the track. 1.3.2 Vehicle Derailment Simulations The wheelset L/V ratio and climb distance for vehicles assembled with different wheelsets were obtained through As a preliminary validation of the proposed flange climb vehicle simulations at different running speeds. The pro- derailment criteria, three hypothetical passenger vehicles posed flange climb derailment criteria were then evaluated representing heavy rail and light rail transit vehicles were by applying them to the vehicle simulation results.

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B-10 CHAPTER 2 SINGLE WHEELSET FLANGE CLIMB DERAILMENT SIMULATIONS The dynamic behavior of six different transit wheelsets used for all profiles, only a synopsis of results is provided for were investigated through simulations of single wheelsets. the other five wheel profiles. The wheel profiles were taken from the transit system survey conducted as part of Phase I, Task 1 of this TCRP project. The basic parameters of these six wheelsets are listed in 2.1 TRANSIT VEHICLE WHEELSET 1 Table B-2. Vehicle derailment usually occurs because of a combina- Besides the wheel profiles, other parameters in the tion of circumstances. Correspondingly, the indexes for the models--such as wheelset mass, inertia and axle loads-- evaluation of derailment, the wheel L/V ratio, and climb dis- were adopted from drawings or corresponding documents tance are also affected by many factors. To evaluate the to represent the real vehicle conditions in the particular effects of these factors, case studies are presented for each of transit systems. them in this section. For Wheels 1 through 5 (light rail and heavy rail) the sim- ulations used a new AREMA 115 lb/yd rail section. For Wheel 6 (commuter rail) the AREMA 136 RE rail profile 2.1.1 Definition of Flange Climb Distance was used. Flange climb results and the corresponding proposed lim- An important output parameter from the simulations is iting flange climb criteria are presented in the following sec- flange climb distance. The climb distance here is defined as the tions for each of the six wheel profiles. A very detailed dis- distance traveled from the final step in lateral force (point "A" cussion is provided for Wheel 1. Since the same method was in Figure B-4) to the point of derailment. For the purposes of TABLE B-2 Wheel profile parameters Parameter Wheel 1 Wheel 2 Wheel 3 Wheel 4 Wheel 5 Wheel 6 Maximum Flange Angle (degree) 63.361 63.243 60.483 75.068 75.068 75.125 Nominal Wheel Diameter (in.) 28 27 27 26 26 36 Nadal Value 0.748 0.745 0.671 1.130 1.130 1.132 Flange Height (mm) 26.194 17.272 20.599 19.177 19.177 28.042 (in.) 1.031 0.680 0.811 0.755 0.755 1.104 Flange Length (mm) 19.149 11.853 17.232 10.038 10.038 15.687 (in.) 0.754 0.467 0.678 0.395 0.395 0.618 SEPTA- SEPTA- Source WMATA NJ-Solid NJ-IRW AAR-1B GRN 101 Light rail, Commuter Type of Service Heavy rail Light rail Light rail Light rail independent cars rotating wheels

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B-11 these studies, the point of derailment was determined by the contact angle on the flange tip decreasing to 26.6 degrees after 30 passing the maximum contact angle of 63.3 degrees for 25 Climb Distances(feet) Wheelset 1. 20 The 26.6-degree contact angle corresponds to the minimum contact angle for a friction coefficient of 0.5. Figure B-5 15 shows the wheel flange tip in contact with the rail at a 10 26.6-degree angle. Between the maximum contact angle (point Q) and the 26.6-degree flange tip angle (point O), the 5 wheelset can slip back down the gage face of the rail due to 0 its own vertical axle load if the external lateral force is sud- 0.5 1 1.5 2 2.5 denly reduced to zero. In this condition, the lateral creep force Flanging Wheel L/V Ratio F (due to AOA) by itself is not large enough to cause the wheel to derail. 0mrad 2.5mrad 5mrad When the wheel climbs past the 26.6-degree contact angle 10mrad 20mrad Nadal (point O) on the flange tip, the wheelset cannot slip back down the gage face of the rail due to its own vertical axle Figure B-6. Effect of wheelset AOA on distance to climb, load: the lateral creep force F generated by the wheelset u = 0.5 (Wheel 1). AOA is large enough to resist the fall of the wheel and force the flange tip to climb on top of the rail. As shown in Figure B-5, the flange length is defined as the 2.1.3 Effect of Flanging Wheel Friction sum of the maximum flange angle arc length QP and flange Coefficient tip arc length PO. As indicated by Nadal's criterion (Figure B-3), the L/V ratio required for quasi-steady derailment is higher for a 2.1.2 Effect of Wheelset AOA lower flanging wheel friction coefficient. Figure B-7 shows the effect on distance-to-climb of reducing the friction coef- Figure B-6 shows the effect of AOA on wheel flange climb ficient from 0.5 to 0.3. Compared with Figure B-6, the for Wheel 1 for a range of wheel L/V ratios. A friction coef- asymptotic L/V ratio for flanging wheel friction coefficient ficient of 0.5 was used on the flange and the tread of the 0.3 in Figure B-7 is higher. However, as with the 0.5 coeffi- derailing wheel. cient of friction cases, for AOAs greater than 10 mrad flange Figure B-6 indicates that wheel climb will not occur for an climb still occurs in less than 5 ft for L/V ratios that are L/V ratio less than the asymptotic value for each AOA. This slightly greater than the Nadal value. asymptotic L/V value corresponds to the quasi-steady derail- Figure B-8 compares the simulation results with Nadal's val- ment value for this AOA. For L/V values higher than this, ues for coefficients of friction of 0.1, 0.3, and 0.5 for a 5-mrad derailment occurs at progressively shorter distances. As wheelset AOA. The dashed lines represent Nadal's values. The AOA is decreased, the wheel quasi-steady derailment L/V value increases and the distance to climb also increases. This result clearly indicates that the Nadal criterion is con- 30 servative for small AOAs, while for AOAs greater than 10 mrad flange climb occurs in distances less than 5 ft for 25 Climb Distance (feet) L/V ratios that are slightly greater than the Nadal value. 20 15 10 5 0 0.5 1 1.5 2 2.5 Flanging Wheel L/V Ratio 0mrad 2.5mrad 5mrad 10mrad 20mrad Nadal Figure B-5. Wheel/rail interaction and contact forces on Figure B-7. Effect of wheelset AOA on distance to climb, flange tip. u = 0.3 (Wheel 1).

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B-12 30 When the nonflanging wheel friction coefficients are increased, the lateral creep forces on the nonflanging wheel 25 side and the longitudinal creep forces on both sides become Climb Distance (feet) 20 mu=0.3 higher. As the longitudinal creep forces increase, the lateral creep force on the flanging wheel decreases with the satura- 15 mu=0.1 tion of resultant creep force. As a result, the quasi-steady wheel L/V ratio required for derailment increases, as shown 10 mu=0.5 in Figure B-9. However, if the L/V ratio is large enough to 5 cause derailment (above 1.4 in Figure B-9), the climb distance is not affected by the nonflanging wheel friction coefficient. 0 0.5 1 1.5 2 2.5 3 This result indicates that a low nonflanging wheel friction Flanging Wheel L/V Ratio coefficient has a tendency to cause flange climb at a lower flanging-wheel L/V ratio and climbs in a shorter distance mu=0.1 mu=0.3 mu=0.5 than a wheelset with the same friction coefficient on both wheels. Low friction on the nonflanging wheel therefore rep- Figure B-8. Effect of coefficient of friction, 5 mrad AOA resents the worst-case condition resulting in the shortest dis- (Wheel 1). tances for flange climb. Thus, to produce conservative results, most of the single wheelset derailment simulations discussed in this report were performed with a very low non- asymptotic value increases with decreasing friction coefficient. flanging wheel friction coefficient (0.001). A lower flange friction coefficient significantly increases the quasi-steady L/V ratio required for derailment but has almost 2.1.5 Effect of Track Lateral Stiffness no effect on the L/V distance limit if this L/V ratio is much exceeded. Figure B-10 shows the effect of lateral track stiffness on the wheel flange climb at 5 mrad wheelset AOA. The difference of lateral track stiffness of 105 lb/in. and 106 lb/in. are negli- 2.1.4 Effect of Nonflanging Wheel Friction Coefficient gible. As the lateral track stiffness decreases to 104 lb/in., the climb distance increases by 9 ft compared to the other two Figure B-9 shows the effect of the nonflanging wheel fric- stiffness values. With stiffness of regular track normally in the tion coefficient nf with a flanging wheel friction coefficient range of 105 to 106 lb/in., the flange-climb distance is not of 0.5 and a 5-mrad wheelset AOA. At a very low nf, the non- likely to be significantly affected by the track lateral stiffness. flanging wheel lateral and longitudinal creep forces were neg- Note that the simulations do not allow the rail to roll. ligible; the initial high flanging wheel longitudinal creep force Therefore, the effect of reducing the track stiffness is to allow quickly decreased to the same small amplitude but in the only increased lateral motion of the rails. In actual conditions reverse direction as the nonflanging longitudinal creep force. of reduced lateral track stiffness it is common to have reduced 30 30 25 25 C l i m b D i st a n c e ( f e e t ) C lim b D is ta n c e (fe e t) 20 20 15 15 10 10 5 5 0 0 0.5 1 1.5 2 0.5 1 1.5 2 2.5 Flanging Wheel L/V Ratio Flanging Wheel L/V Ratio mu-nf=0.001 mu-nf=0.3 mu-nf=0.5 1.0E4 1.0E5 1.0E6 Figure B-9. Effect of nonflanging wheel friction Figure B-10. Effect of track lateral stiffness, 5 mrad AOA coefficient, 5 mrad AOA (Wheel 1). (Wheel 1).

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B-30 TABLE B-7 Third axle wheel-climb distance (ft) (Light Rail Vehicle 1, IRW Wheel 3) Speed (mph) Start Climbing Point End Climbing Point Climb Distance 7 580.1 581.9 1.8 10 580.2 583.5 3.3 11 580.2 581.5 1.3,Derail This result gives a better demonstration of the high risk for is 0.66. The curvature at this location is 1.95 degrees and the vehicles to run when the climb distance is over the limiting climb distance limit is 3.3 ft according to Equation B-15. value. The simulation results also confirm the validation of When the vehicle travels at speed lower than 10 mph, the the proposed climb distance criteria discussed in Chapter 2. climb distance is less than or equal to the limiting value. The wheel climbs onto maximum flange angle and the contact angle stays at 60 degrees, as seen in Figure B-58. 3.2.2.2 Low Floor Light Rail Vehicles Assembled However, when the vehicle travels at a speed of 10 mph, with Solid and IRW Wheelset 3 the climb distance equals the limiting value. Although the wheel still stays at the maximum flange angle, it has climbed The second set of simulations of the light rail vehicle farther up the flange than at 7 mph, as shown by the RRD in Model 1 were conducted with Wheelset 3 on the end trucks Figure B-59. and Wheelset 3 modified with independent rotating wheels When the running speed is increased a little more to 11 on the center truck under the articulation unit. Simulation mph, the wheel climbs above the maximum flange angle, results show the following: over the flange tip, and ultimately derails. In contrast to Wheel 5 discussed in the previous section, the IRW Wheel 3 The third axle begins to climb at the location of 580 ft is unacceptable for this kind of light rail vehicle. When distance (distance referred to the third axle). derailment occurred, the climb distance was very rapid and The climb distance becomes longer with increasing much shorter than the proposed limiting value, which is to be speed before derailment occurs, as shown in Table B-7 expected. and Figure B-57. Compared to Wheel 5, the RRD for IRW Wheel 3 in Fig- The third wheelset (independent rotating wheels) derails ure B-59 increases significantly even when the wheel is still at a speed of 11 mph. climbing on the maximum flange angle. This is an impor- tant characteristic for low maximum flange angle profile For the Wheel 3 profile, the Nadal value is 0.67. Accord- wheels. In other words, the very low maximum flange angle ing to Equation B-14, the proposed L/V ratio limiting value makes it easy for the wheelset to climb up on the flange tip, 60 0.06 Contact Angle (Degree) 50 0.04 0.14 40 Whee L/V Ratio 0.24 30 0.34 20 0.44 0.54 10 0.64 0 0.74 579 581 583 585 587 589 591 Travel Distance (feet) Travel Distance (feet) 7mph 10mph 11mph Nadal Value 7mph 10mph 11mph Figure B-57. Wheel L/V ratio at different speeds (Light Figure B-58. Wheel contact angle at different speeds Rail Vehicle 1, Wheel 3). (Light Rail Vehicle 1, Wheel 3).

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B-31 ficient is 0.5. The track input model is the same as described 0.90 Rolling Radius Difference (inch) in Section 3.1.2. 0.80 0.70 0.60 3.3.2 High Floor Light Rail Vehicle (Model 2) 0.50 Simulation Results 0.40 0.30 Simulations for the high floor articulated light rail vehicle 0.20 0.10 ratio (Model 2) were made for two different wheel profiles to 0.00 validate the corresponding proposed L/V ratio and distance- 579 581 583 585 587 589 591 to-climb criteria. Travel Distance (feet) The first wheel/rail profile combination used was Wheel 2 7mph 10mph 11mph on standard AREMA 115 10-lb/yd rail. This combination is the same as that used for the Wheel 2 single wheelset simu- lations discussed in Section 2.2. The rail/wheel friction coef- Figure B-59. Wheel RRD at different speeds (Light Rail ficient is 0.5. The flange angle is 63 degrees. Vehicle 1, Wheel 3). The second wheel/rail profile combination used was Wheel 3 on standard AREMA 115 10-lb/yd rail. This is the same as that used for the Wheel 3 single wheelset simulations even though there may be a longer maximum flange angle discussed in Section 2.3. The rail/wheel friction coefficient length. is 0.5. The flange angle is 60 degrees. The simulation results for light rail vehicles assembled The simulations were conducted for a range of speeds to with Wheel 5 and Wheel 3 IRW profile wheelsets also con- generate a range of flange climbing conditions: firm the methodology and criteria proposed for them in Chapter 2. Contact with maximum flange angle, but not flange The significant difference in the simulation results for climbing. these two wheel profiles shows that optimization of wheel Flange beginning to climb up the rail, but not derailing profiles are extremely important in the design of a particular (incipient derailment). vehicle. Flange climbing that terminated in derailment. This range of conditions represents what happens to actual vehicles when they encounter severe track perturbations. The 3.3 ARTICULATED HIGH FLOOR LIGHT RAIL VEHICLE (MODEL 2) proposed criteria were evaluated by comparing them to the results for these different flange climb conditions. 3.3.1 The Vehicle Model The articulated high floor light rail vehicle Model 2, com- 3.3.2.1 High Floor Light Rail Vehicle (Model 2) posed of two car bodies and three trucks, represents another Assembled with Wheelset 2 typical type of articulated transit system vehicle. The two car bodies articulate on the middle truck, with all three Simulation results show the following: trucks having solid wheelsets. The principal dimensions of the vehicle are as follows: (1) rigid wheel base 75 in., (2) The first axle begins to climb near the location of 555 ft wheel diameter 26 in., and (3) truck centers 275.5 in. Over- distance (distance referred to the third axle). all, a total of 18 bodies and 85 connections were used to The climb distance becomes progressively longer with assemble the simulation model. The rail/wheel friction coef- increasing speed, as shown in Table B-8 and Figure B-60. TABLE B-8 Third axle wheel-climb distance (ft) (Light Rail Vehicle 2, Wheel 2) Speed (mph) Start Climbing Point End Climbing Point Climb Distance 20 555.2 558.5 3.2 30 555.1 559 3.9 40 555 560 5

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B-32 Rolling Radius Difference (inch) 0.10 0.60 0.10 0.50 0.30 W hee l L/ V R a t io 0.40 0.50 0.70 0.30 0.90 0.20 1.10 0.10 1.30 1.50 0.00 554 556 558 560 562 564 566 554 556 558 560 562 564 566 Travel Distance (feet) Travel Distance (feet) 20mph 30mph 40mph Nadal Value 20mph 30mph 40mph Figure B-60. Wheel L/V ratio at different speeds (Light Figure B-62. Wheel RRD at different speeds (Light Rail Rail Vehicle 2, Wheel 2). Vehicle 2, Wheel 2). The Nadal value and proposed criterion for Wheel 2 have flange angle and onto the flange tip between the distances been listed in Section 3.1.3.2. The proposed L/V ratio limit- of 557.2 and 557.9 ft. The contact angle reduces from 63 ing value is 0.74, and the proposed flange-climb-distance degrees to 59.5 degrees, with a significant drop in the L/V limit is 3.1 ft. ratio. At the same time, the RRD (shown in Figure B-62) When the vehicle travels at speeds lower than 30 mph, the increases significantly when the wheel contacts the rail climb distance is longer than the limiting value. The wheel on the flange tip. The vehicle is running unsafely in this climbs to the maximum flange angle face, and the contact condition. angle stays at 63 degrees, as seen in Figure B-61. The pro- The simulation results of light rail vehicles (Model 2) posed criterion for Wheel 2 is conservative for this situation assembled with Wheel 2 show that the criterion proposed for (the same conclusion has been found in 3.1.3.2). Wheel 2 in Section 2 is conservative at low speed, which is However, when the running speed is increased to consistent with the conclusion in Section 3.1.1.2 for heavy 40 mph, the climb distance is 5 ft--much higher than the rail vehicles assembled with the same profile wheelsets. limiting value. The wheel climbs above the maximum However, the proposed criterion is still valid when the climb distance is much higher than the limit. 3.3.2.2 High Floor Light Rail Vehicle (Model 2) 60 Assembled with Wheelset 3 Contact Angle (degree) 50 The Nadal value and proposed criterion for Wheel 3 have 40 been listed in Section 3.2.2.2. The proposed L/V ratio limit value is 0.66, the proposed climb distance limit is 3.3 ft. 30 The simulation results for light rail vehicles (Model 2) 20 assembled with Wheel 3 are shown in Table B-9 and Figures B-63 through B-65. In general the results are simi- 10 lar to those of Wheel 2. 0 The simulation results also show that the proposed climb 554 556 558 560 562 564 566 distance criterion for Wheel 3 is valid when the climb Travel Distance (feet) distance is very much over the limit value, although it is con- servative for low speed situations. 20mph 30mph 40mph In contrast to Wheel 2, Wheel 3 takes more distance to climb at the same speed even though it has a smaller flange Figure B-61. Wheel contact angle at different speeds angle. This is because Wheel 3 has a longer flange length, (Light Rail Vehicle 2, Wheel 2). which allows the wheel to climb in a longer distance.

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B-33 TABLE B-9 Third axle wheel-climb distance (ft) (Light Rail Vehicle 2, Wheel 3) Speed (mph) Start Climbing Point End Climbing Point Climb Distance 15 555.5 559 3.5 20 555.3 559.3 4.0 35 555.1 560.7 5.6 0.1 Rolling Radius Difference (inch) 0.60 -0.1 0.50 Wheel L/V Ratio -0.3 0.40 -0.5 0.30 -0.7 0.20 -0.9 0.10 -1.1 0.00 554 556 558 560 562 564 566 568 570 -1.3 Travel Distance (feet) 554 556 558 560 562 564 566 568 570 Travel Distance (feet) 15mph 20mph 35mph 15mph 20mph 35mph Nadal Value Figure B-65. Wheel RRD at different speeds (Light Figure B-63. Wheel L/V ratio at different speeds (Light Rail Vehicle 2, Wheel 3). Rail Vehicle 2, Wheel 3). proposed in Chapter 2. The incipient derailment can be pre- 60 dicted by applying these criteria in vehicle dynamics simula- tion analysis. 50 Contact Angle (Degree) The simulation results also show that the proposed climb 40 distance criteria for low-maximum-flange-angle wheelsets 30 are conservative at low speeds. For the simulations shown, once the flange climb reached the maximum flange angle the 20 AOA began to reduce for two reasons: 10 0 Increased rolling radius causes the wheelset to start 554 556 558 560 562 564 566 568 570 steering back (this does not happen for the IRW). Travel Distance (feet) The track perturbation geometry changes, reducing the 15mph 20mph 35mph AOA. Figure B-64. Wheel contact angle at different speeds This reduction in AOA increases the effective L/V ratio (Light Rail Vehicle 2, Wheel 3). limit and lengthens the effective flange-climb-distance limit. This has the effect, in general, of making the proposed crite- 3.4 VEHICLE SIMULATION SUMMARY ria conservative. Because the L/V ratios and climb distance are sensitive to In general, the simulation results for these three types of the wheelset AOA, the effects of AOA variation during transit vehicles assembled with five different types of wheel climb need to be further investigated both by single profiles confirm the validity of the methodology and criteria wheelsets and vehicles simulations.

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B-34 CHAPTER 4 CONCLUSIONS AND DISCUSSIONS 4.1 CONCLUSIONS where AOA is in mrad. In situations where AOA is not known and cannot be measured, the equivalent AOA Based on the single wheelset and vehicle simulation (AOAe) calculated from curve curvature and truck results, the following conclusions are drawn: geometry should be used in the above criteria. If AOA is known and can be measured, more accurate New single wheel L/V distance criteria have been pro- new single wheel L/V ratio criteria based on AOA have posed for transit vehicles with specified wheel profiles: also been proposed (see corresponding equation in Wheel 1 profile: Chapter 2). The simulation results for transit vehicles assembled 5 L/V Distance (feet) < , with different types of wheel profiles confirm the valid- 0.13 * AOA + 1 ity of the proposed criteria. if AOA < 10 mrad For most conditions, an incipient derailment occurs when the climb distance exceeds the proposed criterion value. L/V Distance (feet) = 2.2, if AOA 10 mrad The proposed climb distance criteria are conservative for most conditions. Under many conditions, variations Wheel 2 profile: of AOA act to reduce the likelihood of flange climb. The single wheel L/V ratio required for flange climb 4.1 L/V Distance (feet) < , derailment is determined by the wheel maximum flange 0.16 * AOA + 1 angle, friction coefficient, and wheelset AOA. if AOA < 10 mrad The L/V ratio required for flange climb converges to Nadal's value at higher AOAs (above 10 mrad). For lower L/V Distance (feet) = 1.6, if AOA 10 mrad wheelset AOAs, the wheel L/V ratio necessary for flange climb becomes progressively higher than Nadal's value. Wheel 3 profile: The distance required for flange climb derailment is determined by the L/V ratio, wheel maximum flange 4.2 L/V Distance (feet) < , angle, wheel flange length, and wheelset AOA. 0.136 * AOA + 1 The flange-climb distance converges to a limiting value if AOA < 10 mrad at higher AOAs and higher L/V ratios. This limiting value is highly correlated with wheel flange length. The L/V Distance (feet) = 1.8, if AOA 10 mrad longer the flange length, the longer the climb distance. For lower wheelset AOAs, when the L/V ratio is high Wheel 4/5 profile: enough for the wheel to climb, the wheel-climb distance for derailment becomes progressively longer than the 28 L/V Distance (feet) < , proposed flange-climb-distance limit. The wheel-climb 2 * AOA + 1.5 distance at lower wheelset AOA is mainly determined if AOA < 10 mrad by the maximum flange angle and L/V ratio. Besides the flange contact angle, flange length also L/V Distance (feet) = 1.3, if AOA 10 mrad plays an important role in preventing derailment. The climb distance can be increased through use of higher Wheel 6 profile: wheel maximum flange angles and longer flange length. The flanging wheel friction coefficient significantly 49 L/V Distance (feet) < , affects the wheel L/V ratio required for flange climb; the 2 * AOA + 2.2 lower the friction coefficient, the higher the single if AOA < 10 mrad wheel L/V ratio required. For conventional solid wheelsets, a low nonflanging L/V Distance (feet) = 2.2, if AOA 10 mrad wheel friction coefficient has a tendency to cause flange

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B-35 climb at a lower flanging wheel L/V ratio, and flange capabilities. The more conservative criteria will provide a climb occurs over a shorter distance for the same flang- greater margin of safety for the better performing vehicles ing wheel L/V ratio. and ensure that the poor performing trucks are captured. The proposed L/V ratio and flange-climb-distance crite- Based on the single wheelset and complete car simulation ria are conservative because they are based on an assump- results, both the L/V ratio and climb distance converge to cor- tion of a low nonflanging wheel friction coefficient. responding limit values when the wheelset AOA is over For independent rotating wheelsets, the effect of the 10 mrad. Therefore, the 10-mrad AOA situation represents the nonflanging wheel friction coefficient is negligible most conservative case for wheelset climb derailment, which because the longitudinal creep force vanishes. could be used as an alternative criterion for both tangent and The proposed L/V ratio and flange-climb-distance crite- curved track line cases together with the proposed criterion in ria are less conservative for independently rotating this report. This has the significant advantage of proposing wheels because they do not generate significant longi- only one L/V criterion and one distance-to-climb criterion for tudinal creep forces. a particular wheel/rail profile combination and they are not For the range of track lateral stiffness normally present dependent on knowing AOA, curvature, truck design, or track in actual track, the wheel-climb distance is not likely to perturbation conditions. The resulting criteria for Wheelset 1 be significantly affected by variations in the track lateral using the AOA of 10 mrad would be: stiffness. The effect of inertial parameters on the wheel-climb dis- L tance is negligible at low speeds. < 0.74, if AOA 10 mrad V At high speeds, the climb distance increases with increasing wheelset rotating inertia. However, the effect L/V Distance (feet) < 2.2, if AOA 10 mrad of inertial parameters is not significant at low nonflang- ing wheel friction coefficients. Although onboard AOA measurement is not available in Increasing vehicle speed increases the distance to climb. practice, the wheelset AOA at a specific location can be mea- sured by a wayside measurement system. This system makes the 10-mrad criteria operational in practical running and 4.2 DISCUSSION tests. The 10-mrad criteria need further investigation and An AOA measurement is not usually available in practice. evaluation in comparison to the criteria proposed thus far. Therefore, the proposed climb distance criteria based on A significant concern with the proposed criteria is that they curvature will normally be used. For the situation of a vehi- are specific to the particular wheel/rail profile combinations cle running on tangent track, the equivalent AOAe is zero that were analyzed. The criteria appear to be dependent on because the tangent line curvature is zero. However, under details of the particular wheel and rail profile shapes. certain track perturbations and running speeds, the wheelset Although similar analyses could be performed to develop AOA could in practice be very large for some poor-steering new criteria for a specific wheel and rail profile pair, it is rec- trucks, such as typical freight car trucks, very worn passen- ognized that the transit industry would prefer to have some ger trucks, trucks with axle misalignments, and trucks with general formulas for calculating flange climb safety criteria large turning resistance. Although certain types of trucks for any conditions. (H-frame passenger car trucks, trucks with soft primary sus- Another concern is that the proposed criteria have been pension) could have small AOAs due to a better steering abil- developed based on some simple assumptions of likely ity, the criteria must be conservative enough to identify wheelset AOA in curved and straight track. Uncertainties potential bad performance. For the cases on tangent lines, the regarding differences in the axle steering characteristics of criteria based on a zero AOAe may not be conservative different vehicles and the likelihood of encountering track enough to capture bad trucks. geometry deviations that can cause local increases in wheelset Most passenger rail cars (including transit and intercity AOA require that conservative assumptions be made, result- cars) have truck designs that control axle yaw angles better ing in proposed criteria that may be too conservative. than standard freight cars; and, in some instances, passenger The friction coefficient varies with the rail and wheel sur- cars have softer primary suspensions that provide for better face conditions and has important effects on derailment. A axle steering, resulting in lower AOAs and longer flange climb distance criterion taking the variation of friction coef- climb distances. Therefore, the proposed criteria for transit ficients into account will provide more valuable information cars are made less conservative than freight cars. However, for wheel/rail interaction mechanisms and rail vehicle there is no guarantee that all rail passenger cars have better safety. truck designs, and the criteria must be made sufficiently con- Under the conditions of flange climb, large lateral forces servative to capture poor performance either from poor track are likely to be present that may cause the rail to roll--espe- quality or from poor axle steering. Rail passenger cars with cially if the track structure is weak. Rail roll will change the good truck designs and good axle steering will meet the wheel/rail contact conditions and may result in lower effec- more conservative criteria because of their better steering tive contact angles and shorter effective maximum flange

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B-36 angle lengths, with consequent reductions in L/V limits and Because the L/V ratios and the climb distance are sen- flange climb distances. sitive to the wheelset AOA, further investigate the effect The following are specific recommendations for work in of variations of AOA during flange climb using simula- the future to complete the validation efforts and to address tions of both single wheelsets and full vehicles. some of these concerns: Further develop flange-climb-distance criteria to account for the effects of carrying friction coefficient. Perform comparisons with results from full-scale tests to Perform additional single wheel simulations to investi- further validate the criteria proposed for transit vehicles. gate the effects of rail rotation. Since the climb distance limit is highly correlated with the flange parameters (flange angle, length, height), fur- Because of the complexity of derailments and due to lim- ther investigate and propose a general climb distance ited funding, only a few of these tasks can be accomplished criterion that depends on both the AOA and flange in Phase II. The rest of the recommended work may need parameters. continuing efforts in the future.

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B-37 APPENDIX B-1: LITERATURE REVIEW B1.1 INTRODUCTION The expression for the L/V ratio criterion is dependent on the flange angle and friction coefficient . Figure B1-1 The research work performed for this project was based on shows the solution of this expression for a range of values methods developed by the research team during tests and appropriate to normal railroad operations. The AAR has analyses performed from 1994 to 1999 (1, 2). In recent years, based its Chapter XI single-wheel L/V ratio criterion on other organizations have also been performing flange climb Nadal's theory using a friction coefficient of 0.5. derailment research. A literature review was conducted to Following several laboratory experiments and observations ensure their findings were understood prior to performing of actual values of L/V ratios greater than the Nadal criterion this research project. at incipient derailment, researchers at the Japanese National Railways (JNR) proposed a modification to Nadal's criterion (4). For time durations of less than 0.05 s, such as might be B1.2 BLADER (9) expected during flange impacts due to hunting, an increase was given to the value of the Nadal L/V criterion. However, F. B. Blader (9) has given a clear description and discus- small-scale tests conducted at Princeton University indicated sion of wheel-climb research and safety criteria that had been that the JNR criterion was unable to predict incipient wheel- examined or adopted by railroad operators and railroad test climb derailment under a number of test conditions. facilities as guidelines for safety certification testing of rail- A less conservative adaptation of the JNR criterion was way vehicles. Briefly, they are the following: used by the Electromotive Division of General Motors (EMD) in its locomotive research (5). Nadal's Single-Wheel L/V Limit Criterion. More recently, Weinstock of the United States Volpe Japanese National Railways' (JNR) L/V Time Duration National Transportation Systems Center observed that this Criterion. balance of forces does not depend on the flanging wheel GM Electromotive Division's (EMD) L/V Time Dura- alone (6). Therefore, he proposed a limit criterion that uti- tion Criterion. lizes the sum of the absolute value of the L/V ratios seen by Weinstock's Axle-Sum L/V Limit Criterion. two wheels of an axle, known as the "Axle Sum L/V" ratio. The Nadal single-wheel L/V limit criterion, proposed by Nadal in 1908 for the French Railways, has been used throughout the railroad community. Nadal established the 1.5 original formulation for limiting the L/V ratio in order to 1.4 1.3 minimize the risk of derailment. He assumed that the wheel 1.2 Nadal L/V Value was initially in two-point contact with the flange contact 1.1 point leading the tread, and he concluded that the wheel 1 0.9 material at the flange contact point was moving downwards 0.8 relative to the rail material, due to the wheel rolling about the 0.7 tread contact point. Nadal further theorized that wheel climb 0.6 0.5 occurs when the downward motion ceases with the friction 0.4 saturated at the contact point. Based on his assumption and a 0.3 simple equilibrium of the forces between a wheel and rail at 50 55 60 65 70 75 80 85 the single point of flange contact, Nadal proposed a limiting Flange Angle (Degree) criterion as a ratio of L/V forces: 0.1 0.2 0.3 0.4 0.5 0.6 L tan( ) - = V 1 + tan( ) Figure B1-1. Nadal criterion values.

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B-38 He proposed that this sum be limited by the sum of the Nadal Nadal's original formulation assumes the worst sce- limit (for the flanging wheel) and the coefficient of friction nario--that of a zero longitudinal creepage between wheel (at the nonflanging wheel). Weinstock's criterion was argued and rail. Shust et al. (1) propose a modified formulation using to be not as overly conservative as Nadal's at small or nega- the effective coefficient of friction to replace the friction tive AOA and less sensitive to variations in the coefficient of coefficient in Nadal's formulation. The modified formulation friction. is considered less conservative as it accounts for the presence The Weinstock criterion retains the advantage of simplic- of longitudinal creep forces that tend to provide a stabilizing ity. It can be measured with an instrumented wheelset, which effect to the wheel climb. measures the values of L/V ratio on both wheels. It is not Following the extensive tests of Reference 1, TTCI per- only more accurate than Nadal's criterion, it also has the formed theoretical simulations of flange climb using the merit of being less sensitive to errors or variations in the NUCARS model. This resulted in proposing a new maximum coefficient of friction. L/V ratio limit and flange-climb-distance limit (2). These were subsequently revised and presented in Reference 3. B1.3 50-MS DISTANCE CRITERION Based on the JNR and EMD research, and considerable B1.6 DYNAMIC SAFETY (DYSAF) RESEARCH (10, 11) experience in on-track testing of freight vehicles, a 0.05-s (50-ms) time duration was adopted by the AAR for the Chap- Kik et al.'s "Comparison of Result of Calculations and ter XI certification testing of new freight vehicles. This time Measurements of DYSAF-tests" (10) compares results of duration has since been widely adopted by test engineers calculations and measurements from this research project: throughout North America for both freight and passenger DYSAF (assessment of vehicle-track interaction with special vehicles. reference to DYnamic SAFety in operating conditions). A test running gear was developed to test derailment of a wheelset in guiding and unloaded conditions. The aim of this B1.4 FRA TRACK SAFETY STANDARDS (7) project was to investigate safety limits of derailment at high A flange-climb-distance limit of 5 ft was adopted by the speed. The test was carried out in Velim, Czech Republic, in FRA for their Class 6 high speed track standards (7). This August 2000 to analyze derailment conditions at higher distance limit appears to have been based partly on the results speeds up to 160 km/h. The test was performed in quasi- of the joint AAR/FRA flange climb research conducted by stationary conditions on a small circuit at low speeds (from 20 TTCI and also on experience gained during the testing of var- to 75 km/h) and dynamic conditions on a great circuit at high ious commuter rail and long distance passenger vehicles. speed (from 80 to 160 km/h). The influence of AOA L/V ratio and duration of L/V were investigated in different test series. An extension to the existing Nadal's formula was B1.5 PREVIOUS TTCI RESEARCH (13 ) developed, but parameter identification in this formula has not been done yet. The results of wheel climb (also called flange climb) The lateral, vertical, and roll movement of rails and lateral derailment testing and mathematical simulations performed movement of sleepers were included in the simulation model with the TLV at the TTCI are summarized in Reference 1. of 21 rigid bodies with 93 degrees of freedom (DOF). Mea- The important conclusions are the following: sured track irregularities, including gage as well as lateral and vertical alignment of left and right rail, were also stud- Large flanging rail friction and nonflanging friction dur- ied in the simulation. Special effort was made in the identifi- ing the test resulted in axle sum L/V ratios at wheel cation of simulation parameters such as friction coefficients. climb that were lower than the Chapter XI limit of 1.5. The authors reached the following conclusions: All L/V force ratios found in the tests and with NUCARS simulations converged to the Nadal and For the higher velocity, the L/V ratio is much more Weinstock values at higher AOAs (10 to 15 mrad). At dominated by higher frequency dynamics and it can no lower and negative AOAs, the predicated and measured longer be neglected. Measurement of track irregularities L/V ratios exceeded Nadal and Weinstock values. should be improved to include the smaller wavelength The wheel/rail coefficient of friction, the maximum defects. wheel/rail contact angle, and the wheelset AOA have a A reasonable threshold of L/V ratio as a derailment cri- major influence on the potential for wheel climb. terion or a general multicriterion based on L/V ratio Vertical load unbalance does not affect the critical L/V could not be derived until now. Simulation might be values as computed by the Weinstock and Nadal equa- the best solution for safety investigations of railway tions and the L/V ratios measured experimentally. vehicles.

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B-39 Results of single wheelset derailment simulations, con- The second case study concerned the derailment by flange ducted as a part of the DYSAF research project, are presented climbing of a loaded steel coil-carrying car fitted with Y25 by Parena et al. in "Derailment Simulation, Parametric bogies. Dynamic simulations showed that unequal dips in the Study" (11). The simulation cases were based on a wheelset two rails caused a pitching and swaying response of the model forced to derail by a lateral force on the level of track wagon, which unloaded the leading outer wheel just as it ran with and without excitations in vertical and roll direction, into a lateral misalignment giving rise to a very high L/V ratio and excitations in the lateral direction. The influence of and subsequent flange climbing. An additional contributory rail/wheel geometric and friction parameters, vertical load- factor was a fault in the vehicle suspension giving rise to an ing, and lateral loading duration was investigated. The fol- unequal static load distribution across the leading wheelset, lowing conclusions were reached: combined with offset loading of the steel coil above the lead- ing bogie. Simulations were carried out at 40, 45, and 50 mph Without influence of lateral sliding, a revised Nadal for- with three different load conditions. For nominal vehicles, the mula with 3/4 friction coefficient is quite useful to com- L/V ratio increased and was sustained for a longer distance. pute maximum L/V ratio. As the speed increased, the flange climbed to 3 mm and then Maximum L/V ratio occurs higher up the flange than the dropped back. For the asymmetric vehicle, the flange climbed maximum angle of the flange, seemingly due to the lat- 22 mm to the flange tip and then derailed. eral sliding of the wheel on the rail. Nonsymmetric, low frequency vertical loading or lat- eral force excitation of longer duration reduces the B1.8 CHEN AND JIN (13 ) maximum lateral force that the wheelset resists until In "On a New Method for Evaluation of Wheel Climb derailment. Derailment," Chen and Jin (13) propose a derailment index In any case, bounce and the lower sway of a vehicle for evaluation of the wheel-climb derailment with the mea- should have different Eigen frequencies. If they are surement of primary suspension forces. The purpose of the excited with nearly the same frequency, only very low adoption of primary suspension forces was to replace the lateral force might let the vehicle derail. quasi-steady wheel/rail contact forces with dynamic suspen- sion forces for the calculation of derailment index. The derailment index was dependent on the wheelset AOA and B1.7 CLEMENTSON AND EVANS (12 ) vertical unloading ratio. Two real derailment incidents were investigated by Clementson and Evans (12). The first case study concerned B1.9 LITERATURE REVIEW SUMMARY the derailment of a loaded train of two-axle coal hopper cars on straight track. This derailment was caused by a combina- Although considerable research into flange climb is under- tion of cyclic twist and lateral and vertical alignment in the way, there were no new criteria proposed. The only new cri- rails causing rocking of the cars. Dynamic simulations teria, single wheel L/V ratio criterion and L/V distance crite- showed the build up of a swaying motion in the vehicle and rion for freight cars, were proposed by Wu and Elkins (2) and the wheels lifting substantially off the rails at the point of revised by Elkins and Wu (3). These were developed through derailment. The body roll and wheel loads confirmed a wheel/rail interaction analysis and extensive NUCARS sim- rolling response to the track geometry that resulted in the ulations. The criteria are strongly dependent on AOA. If cyclic unloading of the wheels. At the derailment speed, it AOA cannot be measured, a reduced limit depending on cur- was found that the wheelsets were hunting. vature is recommended.

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