Semi-probabilistic method for residual lifetime of aluminothermic welded rails with foot cracks

One of the most frequent and dangerous failure modes in continuous welded rails is fatigue crack propagation terminated by brittle fracture. Due to the brittleness of the weld material and HAZ and the scatter in its mechanical properties, a statistical approach is necessary. The paper deals with surface cracks at the foot base of aluminothermic welded rails, developing a probabilistic methodology for determining the day by day prospective failure probability. The investigations presented here comprise weld material characterization, simulation of fatigue crack propagation and finally the determination of the failure probability using the Monte Carlo method. The effect of various parameters, such as axle weight, initial crack size, residual stresses, fatigue crack propagation threshold and date of inspection were analyzed. The results show that, independent of the date of the last inspection, almost any failure event happens in wintertime. This is in accordance with practical experience. However, from the proposed analysis it is evident that the main parameter controlling rail fracture is not only the minimum local temperature, but the temperature range over the whole year. Finally, the results are compared to the standard rail classification method

Modeling the Afferent Dynamics of the Baroreflex Control System

In this study we develop a modeling framework for predicting baroreceptor firing rate as a function of blood pressure. We test models within this framework both quantitatively and qualitatively using data from rats. The models describe three components: arterial wall deformation, stimulation of mechanoreceptors located in the BR nerve-endings, and modulation of the action potential frequency. The three sub-systems are modeled individually following well-established biological principles. The first submodel, predicting arterial wall deformation, uses blood pressure as an input and outputs circumferential strain. The mechanoreceptor stimulation model, uses circumferential strain as an input, predicting receptor deformation as an output. Finally, the neural model takes receptor deformation as an input predicting the BR firing rate as an output. Our results show that nonlinear dependence of firing rate on pressure can be accounted for by taking into account the nonlinear elastic properties of the artery wall. This was observed when testing the models using multiple experiments with a single set of parameters. We find that to model the response to a square pressure stimulus, giving rise to post-excitatory depression, it is necessary to include an integrate-and-fire model, which allows the firing rate to cease when the stimulus falls below a given threshold. We show that our modeling framework in combination with sensitivity analysis and parameter estimation can be used to test and compare models. Finally, we demonstrate that our preferred model can exhibit all known dynamics and that it is advantageous to combine qualitative and quantitative analysis methods

Trimethylamine and Trimethylamine N-Oxide, a Flavin-Containing Monooxygenase 3 (FMO3)-Mediated Host-Microbiome Metabolic Axis Implicated in Health and Disease

Flavin-containing monooxygenase 3 (FMO3) is known primarily as an enzyme involved in the metabolism of therapeutic drugs. However, on a daily basis we are exposed to one of the most abundant substrates of the enzyme, trimethylamine, which is released from various dietary components by the action of gut bacteria. FMO3 converts the odorous trimethylamine to non-odorous trimethylamine N-oxide, which is excreted in urine. Impaired FMO3 activity gives rise to the inherited disorder primary trimethylaminuria. Affected individuals cannot produce trimethylamine N-oxide and, consequently, excrete large amounts of trimethylamine. A dysbiosis in gut bacteria can give rise to secondary trimethylaminuria. Recently, there has been much interest in FMO3 and its catalytic product trimethylamine N-oxide. This is because trimethylamine N-oxide has been implicated in various conditions affecting health, including cardiovascular disease, reverse cholesterol transport and glucose and lipid homeostasis. In this review, we consider the dietary components that can give rise to trimethylamine, the gut bacteria involved in the production of trimethylamine from dietary precursors, the metabolic reactions by which bacteria produce and utilize trimethylamine and the enzymes that catalyze the reactions. Also included is information on bacteria that produce trimethylamine in the oral cavity and vagina, two key microbiome niches that can influence health. Finally, we discuss the importance of the trimethylamine/trimethylamine N-oxide microbiome-host axis in health and disease, considering factors that affect bacterial production and host metabolism of trimethylamine, the involvement of trimethylamine N-oxide and FMO3 in disease and the implications of the host-microbiome axis for management of trimethylaminuria

Fracture in Natural and Engineered Systems

IASS-IACM 2008 Session: Fracture in Natural and Engineered Systems -- Session Organizers: Robert HABER (UIUC), Anthony INGRAFFEA (Cornell Univ.) -- Keynote Lecture: "Assessment of stiffened shell structures using advanced fracture and damage mechanics methods" by Karl-Heinz SCHWALBE , Wolfgang BROCKS, Alfred CORNEC, Wernfried Schonfeld, Ingo SCHEIDER, Uwe ZERBST (GKSS Research Centre) -- "Residual strength characterization of integrally-stiffened structures utilizing novel manufacturing technologies" by B. R. SESHADRI, S. W. SMITH , W. M. JOHNSTON, JR. (NASA Langley Research Center) -- "Towards modeling of fragmentation and dynamic delamination interactions in CFRP composites" by Jean-Mathieu GUIMARD , Oliver ALLIX (ENS Cachan), Nicolas PECHNIK (AIRBUS France), Pascal THEVENET (EADS France) -- "A damage-based cohesive model in an adaptive spacetime discontinuous Galerkin method" by Reza ABEDI, Robert B. HABER (University of Illinois at Urbana-Champaign) -- "A unified potential-based cohesive model of mixed-mode fracture" by Glaucio H. PAULINO , Kyoungsoo PARK, Jeffrey ROESLER (The University of Illinois at Urbana-Champaign) -- "Surface and embedded cracks in offshore pipelines subjected to plastic strains" by Espen BERG , Bjorn SKALLERUD, Kjell HOLTHE (Norwegian University of Science and Technology) -- "Automated finite element based predictions of simultaneous crack growth and delamination growth in multi-layers in advanced metallic hybrid stiffened panels using the Alcoa ASPAN-FP tool" by Henry SKLYUT , Michael KULAK, Marcus HEINIMANN, Mark JAMES (Alcoa Technical Center), Olexander V. GONDLIAKH, Roman PASHINSKIJ (KPI, Kiev, Ukraine) -- "Crack trajectory prediction in thin shells using finite element analysis" by Jake D. HOCHHALTER , Ashley D. SPEAR, Anthony R. INGRAFFEA (Cornell University) -- "Analysis of localized failure in metal beams and plates" by Jaka DUJC, Bostjan BRANK (University of Ljubljana), Adnan IBRAHIMBEGOVIC (ENS Cachan

An analytical fracture mechanics model for estimation of S–N curves of metallic alloys containing large second phase particles

An analytical fracture mechanics model for predicting the finite life fatigue strength of components is presented which combines a number of well established and newly developed approaches such as Murakami's and McEvily's approach for describing the transient behaviour of crack closure of short cracks, the analytical (long) crack closure function of Newman which became part of the widely used NASGRO approach, the R6 procedure, a method for improving the ligament yielding correction f(Lr ) of R6 proposed by the authors of the present paper and other elements. Basic assumption is the preexistence of initial flaws such that the crack initiation or nucleation stage is small and can be neglected. The application of the model is demonstrated for small tension plates of aluminium Al 5380 H321 with artificial initial defects generated by FIB technology, the size of which was fixed on the basis of fractographic investigations on broken, smooth specimens

Semi-probabilistic method for residual lifetime of aluminothermic welded rails with foot cracks

One of the most frequent and dangerous failure modes in continuous welded rails is fatigue crack Propagation terminated by brittle fracture. Due to the brittleness of the weld material and HAZ and the scatter in its mechanical properties, a statistical approach is necessary. The paper deals with surface cracks at the foot base of aluminothermic welded rails, developing a probabilistic methodology for determining the day by day prospective failure probability. The investigations presented here comprise weld material characterization, simulation of fatigue crack propagation and finally the determination of the failure probability using the Monte Carlo method. The effect of various parameters, such as axle weight, Initial crack size, residual stresses, fatigue crack propagation threshold and date of inspection were analyzed. The results show that, independent of the date of the last inspection, almost any failure event happens in wintertime. This is in accordance with practical experience. However, from the proposed analysis it is evident that the main parameter controlling rail fracture is not only the minimum local temperature, but the temperature range over the whole year. Finally, the results are compared to the standard rail classification method