A Collision Dynamics Model of a Multi-Level Train

In train collisions, multi-level rail passenger vehicles can deform in modes that are different from the behavior of single level cars. The deformation in single level cars usually occurs at the front end during a collision. In one particular incident, a cab car buckled laterally near the back end of the car. The buckling of the car caused both lateral and vertical accelerations, which led to unanticipated injuries to the occupants. A three-dimensional collision dynamics model of a multi-level passenger train has been developed to study the influence of multi-level design parameters and possible train configuration variations on the reactions of a multi-level car in a collision. This model can run multiple scenarios of a train collision. This paper investigates two hypotheses that could account for the unexpected mode of deformation. The first hypothesis emphasizes the non-symmetric resistance of a multi-level car to longitudinal loads. The structure is irregular since the stairwells, supports for tanks, and draglinks vary from side to side and end to end. Since one side is less strong, that side can crush more during a collision. The second hypothesis uses characteristics that are nearly symmetric on each side. Initial imperfections in train geometry induce eccentric loads on the vehicles. For both hypotheses, the deformation modes depend on the closing speed of the collision. When the characteristics are non-symmetric, and the load is applied in-line, two modes of deformation are seen. At low speeds, the couplers crush, and the cars saw-tooth buckle. At high speeds, the front end of the cab car crushes, and the cars remain in-line. If an offset load is applied, the back stairwell of the first coach car crushes unevenly, and the cars saw-tooth buckle. For the second hypothesis, the characteristics are symmetric. At low speeds, the couplers crush, and the cars remain in-line. At higher speeds, the front end crushes, and the cars remain in-line. If an offset load is applied to a car with symmetric characteristics, the cars will saw-tooth buckle.

Eight-Axle Railcar Carbody Roll Performance: Center of Gravity and Track Wavelength Effects

Heavy-duty railcars carry greater than typical payloads by employing additional wheelsets to lessen wheel/rail contact stresses. Rather than the common 4-axle designs, these cars may have up to 16 axles supporting one deck. Traditionally, these car types have not performed as well as desired. As a response, designers have created depressed center body styles to lower the overall center-of-gravity (CG) height. Such designs lead to more complexity and expense. In this investigation, a heavy-duty 8-axle flatcar has been modeled, both with a flat carbody and a depressed body style. Simulations of harmonic roll perturbations were performed using various CG heights, track perturbation wavelengths and operating speeds. Results include comparisons of design versus performance trade-offs.

Train-to-Train Impact Test of Crash Energy Management Passenger Rail Equipment: Structural Results

On March 23, 2006, a full-scale test was conducted on a passenger rail train retrofitted with newly developed cab end and non-cab end crush zone designs. This test was conducted as part of a larger testing program to establish the degree of enhanced performance of alternative design strategies for passenger rail crashworthiness. The alternative design strategy is referred to as crash energy management (CEM), where the collision energy is absorbed in defined unoccupied locations throughout the train in a controlled progressive manner. By controlling the deformations at critical locations the CEM train is able to protect against two dangerous modes of deformation: override and large-scale lateral buckling. The CEM train impacted a standing locomotive-led train of equal mass at 31 mph on tangent track. The interactions at the colliding in Interface and between coupled interfaces performed as expected. Crush was pushed back to subsequent crush zones and the moving passenger train remained in-line and upright on the tracks with minimal vertical and lateral motions. The added complexity associated with this test over previous full-scale tests of the CEM design was the need to control the interactions at the colliding interface. between the two very different engaging geometries. The cab end crush zone performed as intended because the locomotive coupler pushed underneath the cab car buffer beam, and the deformable anti-climber engaged the uneven geometry of the locomotive anti-climber and short hood. Space was preserved for the operator as the cab end crush zone collapsed. The coupled interfaces performed as predicted by the analysis and previous testing. The conventional interlocking anti-climbers engaged after the pushback couplers triggered and absorbed the prescribed amount of energy. Load was transferred through the integrated end frame, and progressive controlled collapsed was contained to the energy absorbers at the roof and floor level. The results of this full-scale test have clearly demonstrated the significant enhancement in safety for passengers and crew members involved in a push mode collision with a standing locomotive train.

Performance of Spent Fuel Transportation Casks in Severe Tunnel Fires

As part of the Nuclear Regulatory Commission's (NRC) overall review of the performance of transportation casks under severe accident conditions, the NRC has undertaken a number of initiatives, including the Package Performance Study (PPS), described in USNRC Package Performance Study Test Protocols, NUREG-1768, which will test full size transportation casks in a severe accident, as well as an examination of the Baltimore tunnel fire of 2001. The final PPS test plan is currently under development by the NRC's Office of Research. The NRC, working with the National Institute of Standards and Technology (NIST), Pacific Northwest National Laboratory (PNNL), and the National Transportation Safety Board (NTSB), performed analyses to predict the response of three different spent fuel transportation cask designs when exposed to a fire similar to that which occurred in the Howard Street railroad tunnel in downtown Baltimore, Maryland on July 18, 2001. NRC Staff evaluated the potential for a release of radioactive material from each of the three transportation casks analyzed for the Baltimore tunnel fire scenario. The results of these analyses are described in detail in Spent Fuel Transportation Package Response to the Baltimore Tunnel Fire Scenario, NUREG/CR-6886, published in draft for comment in November 2005.

Residual Stresses in Passenger Car Wheels

Knowledge of the residual stress state in wheels resulting from manufacturing and subsequent service loading is useful for several practical reasons. The ability to estimate residual stress levels permits the tuning of manufacturing processes to control the magnitude and distribution of these stresses in new wheels in order to achieve safe performance in service. Similarly, understanding the redistribution of residual stresses following application of service loads (wheel/rail contact and thermal stresses) is crucial to avoid operating conditions which may lead to premature wheel failure. Axisymmetric (2-dimensional) analyses are typically performed in order to conduct manufacturing process simulations since these processes affect the entire wheel in a circumferentially uniform sense. Generally, analyses involving service loading have sought to identify the "shakedown state" at which the residual stress distribution stabilizes after some number of loading cycles. In order to properly account for service loads, 3-dimensional models are required since contact and brake shoe thermal loading are not axisymmetric. Since the as-manufactured residual stress distribution must be considered in a service loading simulation, 3-dimensional modeling of this process is required. This paper presents a preliminary comparison of 2- and 3-dimensional modeling of the wheel heat treatment process. Except for the increased computational time required for the 3-dimensional analysis, the results agree favorably. The 3-dimensional model is used to simulate service loads involving wheel-rail contact loading representative of a typical passenger car. The model is exercised with a variety of material models for comparison with previous work. Results are presented for multiple loading scenarios and shakedown stress states are established for a range of applied loads.

Fatigue Testing of Microalloyed AAR Class C Wheel Steel

Railroad wheels guide a freight car along the rails while supporting mechanical loads, and also serve as the brake drum in the air brake system of a freight car. Since a 36-inch diameter freight car wheel experiences approximately 560 revolutions per mile, and since many North American freight cars accrue 100,000 miles per year in service, fatigue properties of steel are very important. Further, elevated tread temperatures resulting from tread braking are known to significantly reduce the yield strength of the wheel steel at the tread surface. This paper describes fatigue testing of AAR rim quenched Class C wheel steel manufactured with microalloy additions. Small amounts of selected alloy elements were purposely added to develop a wheel steel with improved high temperature yield strength. Rotating bending fatigue tests, conducted at a well-known professional testing laboratory, were performed at ambient and elevated temperatures using complete stress reversal (R = -1) cycling. Stress-life (S-N) curves were constructed and the microalloy steel results were compared to existing fatigue data, and to results for typical Class C steel with no microalloy additions. Past research work is briefly reviewed. Test results are discussed with emphasis on the implications for service performance of wheel steel.

Ride Quality of High-Speed Trains Traveling Over the Corrugated Rails

Ride comfort of high-speed trains is studied using Sperling's comfort index. Dynamic model is developed in the frequency domain and the power spectral density (PSD) of the body acceleration is obtained for four classes of tracks. The obtained acceleration PSD is then filtered using Sperling's filter. The effects of the rail roughness and train speed on the comfort indicators are investigated. A parametric study is also carried out to evaluate the effects of the primary and secondary suspension systems on the comfort indicators.

Tracking the Performance of Heavy Axle Load Vehicles in Revenue Service

As market forces drive up the gross weight on rail, railroads continue moving toward increased usage of heavy axle load (HAL) equipment, namely 286,000 lb and 315,000 lb GWR vehicles that provide more competitive and efficient transportation. According to the AAR's Universal Machine Language Equipment Register (UMLER) database, since 1995, at least 70% of vehicles built each year were HAL vehicles. 2005 had 49,923 more HAL vehicles running on the North America railroad system than the previous year. This practice can result in significant overall savings in operating costs. However, HAL equipment can also accelerate wear and damage to the railroad infrastructure and have a greater potential for truck warping and vehicle dynamics problems. Thus, keeping rolling stock and track safe while ramping up the usage of HAL equipment presents a significant challenge. Wheel Impact Load Detector (WILD) SuperSites, developed by Salient Systems Inc. (SSI), provide real time monitoring and alarming on excessive axle loads and vehicle dynamics. SuperSites are important tools in the scientific study of HAL vehicles and the monitoring of heavy haul operations. This paper provides a snapshot of results of studies conducted on Union Pacific (UP) HAL routes and demonstrates how HAL loads affect the rolling stock, the track, and the wheel/rail interaction. The heavier the load, the higher the impact of the defective wheels to the track; therefore, heavily loaded vehicle routes (such as the coal route from the Powder River Basin to Kansas City and the primary intermodal route from Los Angeles to El Paso) need to be monitored more proactively to avoid track structural damage.

An Experimental Investigation of Brake Squeal Suppression of Air Brake Systems for Electric Passenger Trains Using Oil Damper

Recently, the brake noise reduction is one of the most important environmental issues for not only passengers both inside and outside train but also people who live close to railway stations. In this paper, a friction-induced self-excited oscillation and accompanying noise of a tread brake system are experimentally investigated by using a brake dynamometer. The squeal phenomenon occurs in the frequency range over 2000Hz by the test stand and generates high intensity noise up to 120dBA. In order to suppress brake squeal successfully, a simple oil damper attaching to the system is proposed. Since the proposed oil damper is a kind of Houde damper, damping augmentation capability is obtained in broadband of frequencies. The experimental brake test results demonstrate the brake squeal elimination capability of the proposed damper.

Dynamic Simulation of Train Derailments

This paper describes a planar rigid-body model to examine the gross motions of rail cars in a train derailment. The model is implemented using a commercial software package called ADAMS (Automatic Dynamic Analysis of Mechanical Systems). The results of the ADAMS model are compared with results from other engineering models that were developed from explicit derivation of the equations of motion. The ADAMS model was also used to conduct sensitivity studies. Various assumptions and characteristic values were varied to examine their respective effect on the resulting motion. The variations include: the number of cars in the train make-up, on-and off-track coefficients of friction, coupler characteristics, and initial conditions. Results from the simulations suggest that train speed, on- and off-track coefficients of friction, and coupler characteristics have the most significant influence on the gross motions.