Railroad Rails Containing Electrode-Induced Pitting From Pressure Electric Welding

2018 ◽  
Author(s):  
Blain R. Luck ◽  
Gregory N. Vigilante ◽  
Christopher L. Ethier ◽  
Edward J. Troiano ◽  
Brian Marquis ◽  
...  
Keyword(s):  
Rail Steel ◽  
Fatigue Cracks ◽  
Contributing Factors ◽  
Stress Concentrations ◽  
Forensic Evaluations ◽  
Electric Welding ◽  
Welding Head ◽  
As Stress ◽  
Railroad Rails ◽  
The Web

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.

Influence of Microcalcifications on Stress Development Within a Vulnerable Plaque’s Cap

2011 ◽  
Author(s):  
Ze’ev Aronis ◽  
Erez Kanka ◽  
Eyass Massarwa ◽  
Rami Haj-Ali ◽  
Shmuel Einav
Keyword(s):  
Mechanical Characteristics ◽  
Plaque Rupture ◽  
Intraplaque Hemorrhage ◽  
Rapid Progression ◽  
Stress Concentrations ◽  
Coronary Syndrome ◽  
Vulnerable Plaques ◽  
Material Fatigue ◽  
Mechanical Factors ◽  
As Stress

Vulnerable plaques are inflamed, active, and growing lesions which are prone to complications such as rupture, luminal and mural thrombosis, intraplaque hemorrhage, and rapid progression to stenosis. Despite major advances in the prevention and treatment of this disease, it remains the leading cause of morbidity and mortality worldwide, accounting for 30% of all deaths globally [1]. The importance of stress/strain distribution is now well recognized in vascular pathophysiology, specifically in the mechanisms of plaque rupture. Finite element modeling (FEM) and advanced fluid structure interaction (FSI) studies can better characterize coronary stenosis coupling constitutive equations. Mechanical factors such as stress concentrations within a plaque (material fatigue), lesion characteristic (location, size, and composition), and flow patterns are involved in rupture of plaques. Assessment of local mechanical characteristics caused by plaque structure is important for identifying vulnerable plaques and may improve final estimation of the risk for coronary syndrome.

scholarly journals The Influence of Longitudinal Stiffeners on Weld Toe Stress Concentrations in Multi Planar Tubular KK Joints

2007 ◽  
Vol 348-349 ◽  
pp. 409-412
Author(s):  
Charles O. Woghiren ◽  
F.P. Brennan
Keyword(s):  
Stress Concentration ◽  
Hot Spot ◽  
Fatigue Cracks ◽  
Stress Concentrations ◽  
Out Of Plane ◽  
Invaluable Tool ◽  
Weld Toe ◽  
Dimensional Parameters ◽  
Stress Concentration Factors ◽  
Jack Up

This paper reports a parametric stress analysis of various configurations of rack plate stiffened multi-planar welded KK joints using the finite element method. The KK joint finds application in the leg structure of offshore Oil & Gas jack-up platforms. The rack plate is a dual purpose element of the joint because it firstly functions as a stiffener which reduces the stress concentration at the brace/chord intersection. This could be an immense contribution to the increase in fatigue life of the joint but other hot spot sites are introduced to the joint. The rack is also used for raising and lowering of the jack-up hull which gives the jack-up platform its jacking capability. Over 120 models using a combination of shell and solid elements were built and analysed within ABAQUS. Non-dimensional joint geometric parameters; β, γ and . were employed in the study with . being defined as the ratio of rack thickness to chord diameter. Stress Concentration Factors (SCFs) were calculated under applied axial and OPB (out-of-plane-bending) loading. Three critical SCF locations were identified for each load case, with each location becoming the most critical based on the combination of the non-dimensional parameters selected for the joint. This is important as careful design can shift the critical SCF from an area inaccessible to NDT to one that can be easily inspected. The SCF values extracted from the models were used to derive six parametric equations through multiple regression analysis performed using MINITAB. The equations describe the SCF at the different locations as a function of the non-dimensional ratios. The equations not only allow the rapid optimisation of multi-planar joints but also can be used to quickly identify the location of maximum stress concentration and hence the likely position of fatigue cracks. This in itself is an invaluable tool for planning NDT procedures and schedules.

Development of Predictive Models for Fatigue Crack Growth in Rails

2011 ◽  
Vol 488-489 ◽  
pp. 13-16
Author(s):  
Antonio De Iorio ◽  
Marzio Grasso ◽  
George Kotsikos ◽  
F. Penta ◽  
G. P. Pucillo
Keyword(s):  
Crack Growth ◽  
Fatigue Behavior ◽  
Service Condition ◽  
Fatigue Tests ◽  
Analytical Models ◽  
The Finite Element Method ◽  
Stress Concentrations ◽  
Initiation Point ◽  
Fatigue Failures ◽  
The Web

Fatigue failures of rails often occur at the rail foot, since the geometry of this zone gives rise to stress concentrations under service loads or defects during rail manufacture and installation. In this paper, the fatigue behavior of cracks at the web/foot region of a rail is analyzed numerically. Analytical models in the literature for a semi-elliptical surface crack in a finite plate assume that the geometry of the front remains semi-elliptical during the whole propagation phase and the ellipse axes do not undergo translations or rotations. Fatigue tests show that this is not the case for such cracks in rails. A predictive model for crack growth has been developed by assuming an initial small crack at one probable initiation point between the web and foot of the rail in reference to a service condition loading. SIF values have been estimated by means of the finite element method and the plastic radius correction. The results attained were compared with crack growth experimental data.

Growth of Short Fatigue Cracks at Notches in Woven Fiber Glass Reinforced Polymeric Composites

1989 ◽  
Vol 111 (4) ◽  
pp. 363-367 ◽  
Author(s):  
S. B. Biner ◽  
V. C. Yuhas
Keyword(s):  
Composite System ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Polymeric Composites ◽  
Stress Intensity Factor Range ◽  
Stress Concentrations ◽  
Fiber Glass ◽  
Root Radius ◽  
Short Cracks ◽  
Effective Stress Intensity Factor

The fatigue crack initiation and growth characteristics of short cracks emanating from blunt notches with root radius varying from 1.6 to 6.35 mm at various depths in woven fiber-glass reinforced polymeric composites have been investigated. It is demonstrated that the initiation and growth rate of short cracks emanating from blunt notches can be accurately described by an effective stress intensity factor range ΔKeff. The ply orientations studied, did not have any effect on the analysis. The results provide an adequate engineering approach for designing against failure from range of stress concentrations, at least for this composite system.

The formation of martensite during the propagation of fatigue cracks in pearlitic rail steel

2019 ◽  
Vol 747 ◽  
pp. 199-205 ◽  
Author(s):  
J.P. Liu ◽  
Q.Y. Zhou ◽  
Y.H. Zhang ◽  
F.S. Liu ◽  
C.H. Tian ◽  
...  
Keyword(s):  
Rail Steel ◽  
Fatigue Cracks ◽  
Pearlitic Rail Steel

Low-Frequency Sine Webs for Improved Shear Buckling Performance of Plate Girders

2019 ◽  
Author(s):  
Peter Y. Wang ◽  
Maria E. Garlock ◽  
Theodore P. Zoli ◽  
Spencer E. Quiel
Keyword(s):  
Fatigue Cracks ◽  
Low Frequency ◽  
Robotic Welding ◽  
Plate Girders ◽  
Material Efficiency ◽  
Corrugated Webs ◽  
Shear Buckling ◽  
Elastic Shear ◽  
Traditional Strategy ◽  
The Web

<p>Steel plate girders are used extensively in buildings and bridges. Given shear rarely governs, minimizing web thickness is desirable. However, web slenderness can enable shear buckling and fatigue problems. The traditional strategy is to use welded transverse stiffeners; yet transversely-stiffened girders are prone to fatigue cracks and difficult to fabricate at high slenderness ratios. Thus, AASHTO currently limits web slenderness to 150. Alternatively, corrugated web girders overcome these deficiencies but require robotic welding for the web-to-flange weld. Corrugated webs are also limited to small web thicknesses (6mm or less) and girder depths (less than 1.5m) given web forming limits. The authors propose an alternative web geometry, introducing low-frequency sinusoids (LFS) in the web along its length. The LFS web can be welded to the flanges using semi-automatic weld techniques currently employed by bridge fabricators. The reduced web curvature allows for a wider array of web forming techniques with much larger plate thicknesses. In a finite element study, web geometric properties such as sinusoidal frequency and amplitude are varied. Results demonstrate a significant increase in the elastic shear buckling load and ultimate strength using a wavelength equal to the depth of the girder. The results of this study show promise for improved girder durability paired with material efficiency, demonstrating that a web product with constant amplitude and wavelength could work for various girder depths up to 3m and above.</p>

Effect of heat treatment on the growth rate of transverse fatigue cracks in railroad rails

1991 ◽  
Vol 27 (1) ◽  
pp. 67-69
Author(s):  
M. N. Georgier ◽  
K. P. Zamula ◽  
N. Ya. Mezhova ◽  
V. A. Reikhart
Keyword(s):  
Heat Treatment ◽  
Growth Rate ◽  
Fatigue Cracks ◽  
Railroad Rails

Metabolism

2020 ◽  
pp. 363-386
Author(s):  
Anne Craig ◽  
Anthea Hatfield
Keyword(s):  
Nervous System ◽  
Malignant Hyperthermia ◽  
Recovery Room ◽  
Stress Hormones ◽  
The Body ◽  
Thyroid Storm ◽  
Contributing Factors ◽  
Biochemical Reactions ◽  
Acid Base ◽  
As Stress

This chapter tells you how homeostasis in the body is achieved. Contributing factors such as stress, hormones, and the automatic nervous system are integrated into the discussion in a thoughtful way. The problem of cold postoperative patients is thoroughly referenced to modern investigation. Diabetes, how surgery destabilizes diabetics, and how to use insulin is explained. Malignant hyperthermia, thyroid storm, and acid–base disorders are all problems that can occur in the recovery room and guidelines for the management of these patients are outlined. Hydrogen ions affect haemoglobin and biochemical reactions and can cause acidosis and alkalosis—this chapter outlines how to interpret the blood gas results. How to distinguish between respiratory and metabolic causes of acid–base disorders is simply and clearly explained.

Fatigue Behavior of Riblet Structured High Strength Aluminum Alloy Thin Sheets at Very High Cycle Numbers

2015 ◽  
Vol 664 ◽  
pp. 199-208 ◽  
Author(s):  
Sebastian Stille ◽  
Tilmann Beck ◽  
Lorenz Singheiser
Keyword(s):  
Aerodynamic Drag ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Axial Loading ◽  
High Strength ◽  
Threshold Value ◽  
Special Focus ◽  
Stress Concentrations ◽  
Aerospace Applications ◽  
Aa 2024

The VHCF behavior of age hardened 2024 and 7075 aluminum sheets was studied. The experiments were performed at frequencies of ≈ 20 kHz with fully reversed axial loading (R = -1). Special focus was put on the influence of AA 1050 claddings and riblet-like surface structures, which are used in aerospace applications to reduce aerodynamic drag. The fatigue life and fatigue limit of the AA 2024 bare material are – compared to the non-structured case – significantly reduced by the stress concentrations induced by the riblet structure. However, the fatigue behavior of the clad AA 2024 material is less sensitive to the surface structure. In this case, we obtained a sharp transition from HCF failure up to 5x106 cycles to run-outs at ≥ 2x109 cycles. This threshold value for failure differs with cladding thickness as well as with riblet geometry. We attribute this to the modified stress distribution near the interface (cladding/substrate) as well as to a locally reduced thickness of the cladding in the riblet valleys. Fatigue cracks are – even in the case of run-outs – always initiated at the surface of the clad layer and grow easily to the substrate. Samples only fail, if the threshold for further crack growth into the substrate is exceeded. Both Alclad 2024 and 7075 show the same failure mechanism.

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