For a given material and set of test conditions, fatigue crack propagation behavior can be described by the relationship between cyclic crack-growth rate, da/dN and the fluctuation of stress intensity factor, △K. Such test data are... more
For a given material and set of test conditions, fatigue crack propagation behavior can be described by the relationship between cyclic crack-growth rate, da/dN and the fluctuation of stress intensity factor, △K. Such test data are usually displayed in a log-log plot. At intermediate values of △K, fatigue crack-growth data fall along a straight line such that a power-law equation may be used as a curve-fit to the data. Various numerical techniques are applied in order to (1) derive the crack-growth rate and (2) determine the parameters for the power-law equation. Using data from laboratory tests conducted on rail steels, this paper explores the various numerical methods used to characterize fatigue crack-growth behavior. Tests were conducted using two different fracture-mechanics specimens (a standard compact tension specimen and a non-standard single edge notch specimen). Three different numerical techniques were applied to determine the fatigue crack-growth rate, da/dN from test d...
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This report is the second in a series focusing on methods to determine the puncture velocity of railroad tank car shells. In this context, puncture velocity refers to the impact velocity at which a coupler will completely pierce the shell... more
This report is the second in a series focusing on methods to determine the puncture velocity of railroad tank car shells. In this context, puncture velocity refers to the impact velocity at which a coupler will completely pierce the shell and puncture the tank. In the first report in this series, a set of semi-empirical equations was evaluated by comparing calculated puncture velocities with data from tank car impact tests. These equations were originally developed by the RPA-AAR Tank Car Safety Committee and later modified by the industry to account for head shield protection and jacket insulation. The semi-empirical equations generally produced reasonable and conservative estimates of puncture velocity when compared with the experimental data. However, differences between the calculated and observed results become more widespread when the tank is pressurized or when shield protection is present. Moreover, alternative methods to determine puncture velocity may be observed by the industry to avoid overdesign. In this report, methods to predict puncture velocity based only on engineering mechanics principles (i.e., no empiricism) are developed and described. Results from the semi-empirical approach are compared with results from the engineering methods. These methods rely on both analytical and computational tools to examine the structural behavior of tanks with ellipsoidal shapes. These tools include finite element and dynamic lumped mass models.
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Elber's crack closure model is studied in relation to the results of laboratory spectrum crack growth tests on compact tension specimens (CTS) fabricated from rail effected by mean of an analysis of a center cracked panel (CCP)... more
Elber's crack closure model is studied in relation to the results of laboratory spectrum crack growth tests on compact tension specimens (CTS) fabricated from rail effected by mean of an analysis of a center cracked panel (CCP) subjected to an equivalent stress spectrum. (The model cannot be directly applied to the CTS because it is numerically unstable when supplied with finite element approximations for the elastic displacement field at the plastic zone boundary.) The trends of the model predictions and test results agree as to the effect of changing cycle order in the spectrum, but the actual effect on crack growth life in the laboratory tests is found to be much stronger than the effect predicted by Elber's model.
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A series of tests, aimed at assessing the structural integrity of joint bars under differing service conditions, were conducted to address concerns regarding joint bar failures in the revenue service environment. Data collected through... more
A series of tests, aimed at assessing the structural integrity of joint bars under differing service conditions, were conducted to address concerns regarding joint bar failures in the revenue service environment. Data collected through the course of this study revealed that bending stress invoked by normal track surfacing operations is not a likely cause for cracks that initiate at the top center of joint bars. Instead, cracking at this location is probably the result of fatigue at the top center of the joint bar due to rail-joint contact. Surface hardening at the area of rail-joint contact was largely ineffective, resulting in metal flow developing adjacent to the easement at the top of the joint bar. Additional data gathered in this study suggests little correlation between the surface hardness of the joint bar and the depth of metal flow. Bending stresses and wheel/rail forces were also measured on joint bars used in rail end gaps and rail height mismatches, which revealed minimal effects on overall joint bar performance for the installation conditions and range of speeds evaluated.
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This paper reviews the main failure modes of concrete ties observed in the U.S. railroads, including chemical degradation, prestress cracks, flexural cracks, rail seat deterioration, freeze-thaw cracks, and shoulder/fastener wear or... more
This paper reviews the main failure modes of concrete ties observed in the U.S. railroads, including chemical degradation, prestress cracks, flexural cracks, rail seat deterioration, freeze-thaw cracks, and shoulder/fastener wear or fatigue. The observed characteristics, probable causes and detrimental effects of each failure mode are described. A finite element analysis framework aimed at achieving a better understanding of the basic failure mechanisms of concrete ties is presented. The ability of the modeling approach to simulate and predict critical failure modes of concrete ties is demonstrated. To meet the new challenges and demands placed on the U.S. rail infrastructure by increased high speed and heavy haul applications, concrete tie performance issues need to be addressed at both material and structural levels. Continued research needs to quantitatively characterize concrete tie failure under realistic track load and support conditions and to improve existing test and inspection standards are further discussed.
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Terminating action is a remedial repair which entails the replacement of shear head countersunk rivets with universal head rivets which have a larger shank diameter. The procedure was developed to eliminate the risk of widespread fatigue... more
Terminating action is a remedial repair which entails the replacement of shear head countersunk rivets with universal head rivets which have a larger shank diameter. The procedure was developed to eliminate the risk of widespread fatigue damage (WFD) in the upper rivet row of a ...
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PDFTech ReportCorrelation analysisDefectsFailureFracture mechanicsField testsLaboratory testsRail (Railroads)Risk analysisWearUnited StatesInternational Union of RailwaysJeong, David Y.John A. Volpe National Transportation Systems Center... more
PDFTech ReportCorrelation analysisDefectsFailureFracture mechanicsField testsLaboratory testsRail (Railroads)Risk analysisWearUnited StatesInternational Union of RailwaysJeong, David Y.John A. Volpe National Transportation Systems Center (U.S.)NTL-RAIL TRANSPORTATION-RAIL TRANSPORTATIONNTL-RAIL TRANSPORTATION-Rail SafetyNTL-SAFETY AND SECURITY-Rail SafetyVolpe National Transportation Systems Center, Technical Reference CenterThis report is the first in a three-part series describing the technical contributions of theFederal Railroad Administration (FRA) and the Volpe National Transportation SystemsCenter (Volpe Center) to the UIC/WEC (International Union of Railways/World ExecutiveCouncil) joint research project on Rail Defect Management. Specifically, this reportdescribes engineering analyses that are used to examine the growth of internal rail defectsthat were tested under laboratory conditions. The second report in this series describessimilar engineering analyses that were conducted to examine the growth of internal raildefects tested under field conditions. The third report discusses applications of the raildefect modelling efforts
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This paper is the second in a two-part series describing research sponsored by the Federal Railroad Administration (FRA) to study the structural integrity of joint bars. In Part I, observations from field surveys of joint bar inspections... more
This paper is the second in a two-part series describing research sponsored by the Federal Railroad Administration (FRA) to study the structural integrity of joint bars. In Part I, observations from field surveys of joint bar inspections conducted on revenue service track were presented [1]. In this paper, finite element analyses are described to examine the structural performance of rail joints under various loading and tie-ballast support conditions. The primary purpose of these analyses is to help interpret and understand the observations from the field surveys. Moreover, the finite element analyses described in this paper are applied to conduct comparative studies and to assess the relative effect of various factors on the structural response of jointed rail to applied loads. Such factors include: discrete tie support (i.e. supported joint versus suspended joint with varying spans between effective ties), bolt pattern (four versus six bolts), initial bolt tension, and easement. In addition, results are shown for 90 lb rail joined with long-toe angle bars compared to 136 lb rail joined with standard short-toe joint bars.
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The Federal Railroad Administration (FRA) routinely conducts investigations of railroad accidents to determine causation and any contributing factors to help the railroad industry implement corrective measures that may prevent similar... more
The Federal Railroad Administration (FRA) routinely conducts investigations of railroad accidents to determine causation and any contributing factors to help the railroad industry implement corrective measures that may prevent similar incidents in the future. Over the past decade, FRA has investigated multiple broken rail accidents in which fractures in the rail web were identified. The common features observed in the recovered rail fragments from these accidents included welds and spots or burn marks on the web, indicating that the rails were joined together by pressure electric welding. Pressure electric welding uses a welding head that clamps around two opposing rail ends, pressing an electrode on each rail, then hydraulically pulling the rail ends together while arcing current through the electrodes into the rails, causing them to essentially melt together to form a continuous rail. Based on the similarities observed in the web fractures, FRA rail integrity specialists hypothesized that stray (i.e. inadvertent and unwanted) arcing during pressure electric welding can result in the formation of burns or pits on the rail where it makes contact with the electrodes. Moreover, these electrode-induced pits behave as stress raisers (also referred to as stress concentrations). Fatigue cracks often develop at locations of stress concentration. Once a fatigue crack initiates, the localized stress encourages the growth of the crack, which may potentially lead to rail failure. This paper describes the forensic evaluations of three railroad rails containing electrode-induced pitting. These evaluations include: magnetic particle inspection to nondestructively detect cracks emanating from the pitting; fractography to study the fracture surfaces of the cracks; metallography to study the microstructure; analysis of chemical composition; and measurements of tensile mechanical properties and fracture toughness of rail steel. Moreover, the results of these evaluations confirm the hypothesis postulated by FRA that stray arcing during pressure electric welding can cause electrode-induced pitting.
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ABSTRACT In support of the Federal Aviation Administration Technical Center's (FMTC) National Aging Aircraft Research Program (NAARP), Sandia National Laboratories and the John A. Volpe National Transportation Systems Center... more
ABSTRACT In support of the Federal Aviation Administration Technical Center's (FMTC) National Aging Aircraft Research Program (NAARP), Sandia National Laboratories and the John A. Volpe National Transportation Systems Center (Volpe Center) are conducting research to determine if current rules for design, inspection, and maintenance are sufficient to ensure the safe operation of the aging fleet. Particular emphasis has been given to a phenomenon of multiple cracking that appears to be an attribute of airplanes that have been in service for some time. This phenomenon is commonly referred to as Widespread Fatigue Damage (WFD). Several experimental and analytical studies have been initiated by FAATC to understand the phenomenon of WFD. Some of these research activities include: collection of strain gage data from a Boeing 737 airplane conducted by the Aging Aircraft Nondestructive Inspection Validation Center (AANC); laboratory testing of full-scale curved panels conducted by Foster-Miller, Inc. (FMI); and modeling of fuselage lap splices by the Votpe Center. This report documents the strain gage testing of the Boeing 737 airplane acquired by the AANC. Additionally, correlations among the three research activities mentioned above have been performed, and are described in this report. (AN)
Research Interests: Engineering, Materials Science, Aviation, Finite Element Analysis, Nondestructive testing, and 14 moreStress analysis, Correlation, Data acquisition, Mathematical Models, Structural mechanics, Aeronautics, Aircraft Maintenance, Repetitive Strain Injury, Airplane, Stress Analysis, Bending Stress, Crew, Fuselage, and Strain Gauge
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Research addressing rail failures in the United States has been an ongoing effort by the government and industry. Particular attention has been given to defects known as detail fractures because of their tendency to comprise the most... more
Research addressing rail failures in the United States has been an ongoing effort by the government and industry. Particular attention has been given to defects known as detail fractures because of their tendency to comprise the most commonly found defects. Attempts have been made to simulate the actual service conditions of detail fractures by using standard laboratory specimens [[4.1]]1.
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ABSTRACT The coalescence or linkup of multiple cracks is considered in this paper. Moreover, two criteria for multiple crack linkup are proposed which are based on linear elastic models. Analytical predictions of multiple crack linkup are... more
ABSTRACT The coalescence or linkup of multiple cracks is considered in this paper. Moreover, two criteria for multiple crack linkup are proposed which are based on linear elastic models. Analytical predictions of multiple crack linkup are compared with experimental results from flat panel tests. The effect of stable tearing has been included in these predictions. The agreement between analysis and experiment is shown to be reasonable. 8 refs.
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Abstract An effective stress intensity factor crack closure model is studied in relation to results of laboratory spectrum crack growth tests on compact tension specimens (CTS) fabricated from rail steel. Comparison of model predictions... more
Abstract An effective stress intensity factor crack closure model is studied in relation to results of laboratory spectrum crack growth tests on compact tension specimens (CTS) fabricated from rail steel. Comparison of model predictions with test results for crack growth life is effected by means of an analysis of a center-cracked tension panel (CCT) subjected to an equivalent stress spectrum. The trends of the model predictions and test results agree as to the effect of changing cycle order in the spectrum, but the actual effect on crack growth life in the laboratory tests is found to be much stronger than the effect predicted by the crack closure model using the effective stress intensity factor.
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The problems associated with fatigue were brought to the forefront of research by the structural failure of a transport category aircraft in 1988. This failure was attributed to the occurrence of multiple cracking which has since been... more
The problems associated with fatigue were brought to the forefront of research by the structural failure of a transport category aircraft in 1988. This failure was attributed to the occurrence of multiple cracking which has since been termed “Widespread Fatigue Damage” (WFD). Figure 1 is a photograph of the multiple cracking that occurred in the upper rivet row of a lap splice joint located in the vicinity of the fuselage crown. Apparently, the fatigue cracks propagate at an inclined angle rather than purely horizontal. The inclined angle of the cracks implies that the fuselage lap joint is subjected to mixed mode loading. The source of the mixed mode loading in the fuselage is assumed to be biaxial stress due to cabin pressurization combined with transverse shear due to body bending. In this paper, a methodology to perform mixed mode fatigue crack growth calculations is proposed to predict the growth of inclined cracks emanating from an open hole in an infinite medium subjected to remote stress. This methodology is based on an engineering approximation of a curved crack modelled as a straight crack of equal stress intensity. Two different criteria are considered to determine the crack trajectory or angle of crack propagation. Also, different crack growth rate models are assumed for each criterion. In particular, the maximum principal stress criterion [1] is used in conjunction with an effective Paris-Walker type equation, and the strain energy density criterion [2] is used with a corresponding crack growth model.
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Research Interests: Mechanical Engineering, Civil Engineering, Applied Mathematics, Materials Science, Structural Engineering, and 10 moreFracture Mechanics, Fatigue crack growth, Crack propagation, Mixed Mode, Stress Intensity Factor, Crack Closure, Growth rate, Strain Energy Density, Strain Energy Release Rate, and Crack growth
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This final volume of the Crash Padding Research report summarizes the application of the laboratory material model developed in Volumes I and II to the prediction of impact behavior. This involved embedding the material model in a... more
This final volume of the Crash Padding Research report summarizes the application of the laboratory material model developed in Volumes I and II to the prediction of impact behavior. This involved embedding the material model in a simplified dynamic simulation of the occupant-vehicle impact. The simulation is a computer program predicting force, acceleration, etc., versus time, based on fundamental inputs of the occupant's initial speed, mass, and geometry, the vehicle's structural stiffness, and the laboratory model for padding. By comparing simulation predictions with impact test results, the computer simulation has been validated for impact scenarios involving metal structures similar to an automobile dashboard.
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This final volume of the Crash Padding Research report summarizes the application of the laboratory material model developed in Volumes I and II to the prediction of impact behavior. This involved embedding the material model in a... more
This final volume of the Crash Padding Research report summarizes the application of the laboratory material model developed in Volumes I and II to the prediction of impact behavior. This involved embedding the material model in a simplified dynamic simulation of the occupant-vehicle impact. The simulation is a computer program predicting force, acceleration, etc., versus time, based on fundamental inputs of the occupant's initial speed, mass, and geometry, the vehicle's structural stiffness, and the laboratory model for padding. By comparing simulation predictions with impact test results, the computer simulation has been validated for impact scenarios involving metal structures similar to an automobile dashboard.
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Elber's crack closure model is studied in relation to the results of laboratory spectrum crack growth tests on compact tension specimens (CTS) fabricated from rail effected by mean of an analysis of a center cracked panel (CCP)... more
Elber's crack closure model is studied in relation to the results of laboratory spectrum crack growth tests on compact tension specimens (CTS) fabricated from rail effected by mean of an analysis of a center cracked panel (CCP) subjected to an equivalent stress spectrum. (The model cannot be directly applied to the CTS because it is numerically unstable when supplied with finite element approximations for the elastic displacement field at the plastic zone boundary.) The trends of the model predictions and test results agree as to the effect of changing cycle order in the spectrum, but the actual effect on crack growth life in the laboratory tests is found to be much stronger than the effect predicted by Elber's model.
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Thermal buckling of railroad tracks in the lateral plane is an important problem in the design and maintenance of continuous welded rail (CWR) track. The severity of the problem is manifested through the increasing number of derailments... more
Thermal buckling of railroad tracks in the lateral plane is an important problem in the design and maintenance of continuous welded rail (CWR) track. The severity of the problem is manifested through the increasing number of derailments which are attributable to track buckling, indicating a need for developing better control on the allowable safe temperature increase for CWR track. The work reported here is a part of a major investigation conducted by the Transportation Systems Center for the Federal Railroad Administration on the thermal buckling of CWR tracks in the lateral plane. In this report, the influence of vehicles on the stability of CWR track subjected to temperature rise is examined. The changes in lateral resistance distribution due to vehicle loads are theoretically computed and the buckling response of tracks due to temperature increase is determined for various length cars. It is found that the dynamic buckling temperature for tangent tracks under long cars can be significantly lower than the static buckling temperature, whereas the safe temperature increase values do not appreciably differ. Curved tracks with low lateral resistance can buckle progressively in the presence of long cars, whereas statically (without-vehicle), they may exhibit safe temperature and buckling temperature values.