Thermal Crack Development and Wheel Useful Life

2002 ◽  
Author(s):  
Radovan Sarunac
Keyword(s):  
Crack Development ◽  
Surface Zone ◽  
Thermal Crack ◽  
Brake Application ◽  
Higher Temperature ◽  
Alternative Approaches ◽  
Useful Life ◽  
Braking Control ◽  
Equipment Configuration ◽  
The Impact

The impact of thermal crack development on the wheel useful life was investigated. The actual data from the “Railroad” has been actively and intensely reviewed. Initial efforts were concentrated on the wheel metallurgy, thermal crack development mechanism and maximum allowable operating speeds on each line. Recent efforts have concentrated on the braking control and associated equipment configuration. The effect of worn wheel and repetitive braking was also investigated. However, it is difficult to postulate alternative approaches to managing wheel useful life without completely identifying existing operating policies and maintenance procedures, and without establishing measurable results of such policies/procedures. It is also crucial to understand the physical process involved. This process will be repeated with every brake application in combination with the residual compressive stress (due to rolling and battering of the wheel on the rail and by rim-quenching) causing the cyclic stressing of the material due to thermal expansion, i.e., “thermal fatigue”. Higher brake rate and higher tread to disc brake ratio lead to higher temperature gradient and higher compression stresses (higher portion of stress in plastic range). In addition, the microstructure change in the surface zone material involves additional uncertainty, i.e., the existence of material of unknown physical properties (perlite transformation in to spheroidite). The presence of spheroidite is a good indication that a wheel tread has been subjected to direct thermal damage. It is a common conclusion based on two completely independent research projects that the combination of heat and compression increases hardness and yield strength. The maximum wheel temperature has a major impact on microstructure changes of the wheel surface layer. Also a smaller wheel diameter yields to higher maximum tread temperature. Various studies relating new and worn wheel clearly show the impact.

Расчетные методы оценки ударной вязкости сварных элементов с трещинами

2020 ◽  
Vol 44 (3) ◽  
pp. 22-36
Author(s):  
Keyword(s):  
Stress Intensity ◽  
Impact Strength ◽  
Welded Joints ◽  
Development Process ◽  
Welded Joint ◽  
Operating Temperature ◽  
Crack Development ◽  
Heterogeneous Structure ◽  
Critical Crack Length ◽  
The Impact

Практика показывает, что для сварных конструкций, эксплуатируемых в условиях Крайнего Севера необходимо уделять внимание работоспособности сварных соединений при низких температурах. Металл сварных соединений в процессе воздействия обработки изменяет свои свойства, снижается ударная вязкость, образуется гетерогенная структура с большой степенью разнозернистости. Чтобы оценивать и иметь возможность правильно контролировать термическое воздействие и последствия сварочного процесса, требуется решить задачу аналитического определения ударной вязкости для всех зон сварного соединения. В настоящей статье представлен инженерный метод оценки ударной вязкости, применимый для любой зоны сварного соединения, в которой имеется острый или особый концентратор напряжений – трещина. Разработанный аналитический метод расчета ударной вязкости отражает качественную и количественную картину взаимосвязи структурно-механических характеристик и работы развития трещины в диапазоне температур 77…300 К. Предложенная схематизация зависимости критического коэффициента интенсивности напряжений от температуры позволила найти коэффициенты, характеризующие свойства материала, и выполнить расчеты изменения предела текучести и предела прочности от температуры эксплуатации. Построены графики зависимости работы развития трещины от температуры эксплуатации для сталей 15ГС и 17ГС, сравнение которых с экспериментальными данными показывает удовлетворительное согласование. Найдено, что при напряжениях предела выносливости отношение работы развития трещины к критической длине трещины постоянно, не зависит от температуры и для сталей 15ГС и 17ГС равно около 10. Ключевые слова: ударная вязкость, работа разрушения, коэффициент интенсивности напряжений, трещина, феррито-перлитная сталь, зона термического влияния. For welded structures under operation in the Far North, attention must be paid to the performance of welded joints at low temperatures. The properties of metal of welded joints are changed in the process of treatment, its toughness decreases, and a heterogeneous structure with a large range of different grain sizes is formed. In order to evaluate and be able to correctly control the thermal effect and the consequences of the welding process, it is necessary to solve the problem of analytical determination of impact strength for all zones of the welded joint. The paper presents an engineering method for evaluation of the impact strength applicable to any area of the welded joint in which there is a sharp or super sharp stress concentrator – a crack. The developed analytical method for calculating the impact strength reflects a qualitative and quantitative codependency of structural and mechanical characteristics and the process of crack development in the temperature range of 77–300 K. The proposed schematization of dependence of the critical coefficient of stress intensity on the temperature made it possible to find coefficients characterizing the properties of the material and to perform calculations of changes in yield strength and tensile strength on operating temperature. Graphs of the crack development process dependency on the operating temperature for 15ГС and 17ГС steels were constructed, and their comparison with experimental data displays satisfactory agreement. It was found that at endurance limit stresses, the ratio of the crack development process to the critical crack length is constant, non-dependent on temperature, and is equal to 10 for 15ГС and 17ГС steels. Keywords: impact strength, fracture work, stress intensity factor, crack, ferrite-pearlite steel, heat affected zone, steel tempering.

scholarly journals Impact of temperature and relative humidity on the transmission of COVID-19: a modelling study in China and the United States

BMJ Open ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. e043863
Author(s):  
Jingyuan Wang ◽  
Ke Tang ◽  
Kai Feng ◽  
Xin Lin ◽  
Weifeng Lv ◽  
...  
Keyword(s):  
Regression Analysis ◽  
Relative Humidity ◽  
Human Mobility ◽  
The United States ◽  
Reproductive Number ◽  
Cross Sectional ◽  
The Usa ◽  
Higher Temperature ◽  
Potential Impact ◽  
The Impact

ObjectivesWe aim to assess the impact of temperature and relative humidity on the transmission of COVID-19 across communities after accounting for community-level factors such as demographics, socioeconomic status and human mobility status.DesignA retrospective cross-sectional regression analysis via the Fama-MacBeth procedure is adopted.SettingWe use the data for COVID-19 daily symptom-onset cases for 100 Chinese cities and COVID-19 daily confirmed cases for 1005 US counties.ParticipantsA total of 69 498 cases in China and 740 843 cases in the USA are used for calculating the effective reproductive numbers.Primary outcome measuresRegression analysis of the impact of temperature and relative humidity on the effective reproductive number (R value).ResultsStatistically significant negative correlations are found between temperature/relative humidity and the effective reproductive number (R value) in both China and the USA.ConclusionsHigher temperature and higher relative humidity potentially suppress the transmission of COVID-19. Specifically, an increase in temperature by 1°C is associated with a reduction in the R value of COVID-19 by 0.026 (95% CI (−0.0395 to −0.0125)) in China and by 0.020 (95% CI (−0.0311 to −0.0096)) in the USA; an increase in relative humidity by 1% is associated with a reduction in the R value by 0.0076 (95% CI (−0.0108 to −0.0045)) in China and by 0.0080 (95% CI (−0.0150 to −0.0010)) in the USA. Therefore, the potential impact of temperature/relative humidity on the effective reproductive number alone is not strong enough to stop the pandemic.

Managing uncertainty in a general insurance company

1990 ◽  
Vol 117 (2) ◽  
pp. 173-277 ◽  
Author(s):  
C. D. Daykin ◽  
G. B. Hey
Keyword(s):  
Computer Model ◽  
Flow Model ◽  
Insurance Companies ◽  
Simulation Methods ◽  
Insurance Company ◽  
Practical Applications ◽  
General Insurance ◽  
Alternative Approaches ◽  
The Impact

AbstractA cash flow model is proposed as a way of analysing uncertainty in the future development of a general insurance company. The company is modelled alongside the market in aggregate so that the impact of changes in premium rates relative to the market can be assessed. An extensive computer model is developed along these lines, intended for use in practical applications by actuaries advising the management of genera1 insurance companies. Simulation methods are used to explore the consequences of uncertainty, particularly in regard to inflation and investments. Some comments are made on the role of actuaries in general insurance. Alternative approaches to describing the behaviour of an insurance firm in the market are considered.

Effect of Tensile Strain on Performance Parameters of Different Structures of MoS2 Monolayer

2021 ◽  
Author(s):  
Priya kaushal ◽  
Tarun Chaudhary ◽  
Gargi Khanna
Keyword(s):  
Tensile Strain ◽  
Computational Study ◽  
Level Structure ◽  
Charge Carriers ◽  
Performance Parameters ◽  
Mos2 Monolayer ◽  
Higher Temperature ◽  
Silicon Doped ◽  
The Impact ◽  
Biaxial Tensile Strain

Abstract The present work is based on the computational study of MoS2 monolayer and effect of tensile strain on its atomic level structure. The bandgap for MoS2 monolayer, defected MoS2 monolayer and Silicon-doped monolayer are 1.82 eV (direct bandgap), 0.04 (indirect bandgap) and 1.25eV (indirect bandgap), respectively. The impact of tensile strain (0-0.7%) on the bandgap and effective mass of charge carriers of these three MoS2 structure has been investigated. The bandgap decrease of 5.76%, 31.86% and 6.03% has been observed in the three structures for biaxial strain while the impact of uniaxial strain is quite low. The impact of higher temperature on the bandgap under biaxial tensile strain has been also analyzed in this paper. These observations are extremely important for 2D material-based research for electronic applications.

Prognostics Health Management Model for LED Package Failure Under Contaminated Environment

2015 ◽  
Author(s):  
Pradeep Lall ◽  
Hao Zhang ◽  
Lynn Davis
Keyword(s):  
Health Management ◽  
Luminous Flux ◽  
The State ◽  
Remaining Useful Life ◽  
Integrating Sphere ◽  
State Estimator ◽  
Acceptable Error ◽  
Color Shift ◽  
Useful Life ◽  
The Impact

The reliability consideration of LED products includes both luminous flux drop and color shift. Previous research either talks about luminous maintenance or color shift, because luminous flux degradation usually takes very long time to observe. In this paper, the impact of a VOC (volatile organic compound) contaminated luminous flux and color stability are examined. As a result, both luminous degradation and color shift had been recorded in a short time. Test samples are white, phosphor-converted, high-power LED packages. Absolute radiant flux is measured with integrating sphere system to calculate the luminous flux. Luminous flux degradation and color shift distance were plotted versus aging time to show the degradation pattern. A prognostic health management (PHM) method based on the state variables and state estimator have been proposed in this paper. In this PHM framework, unscented kalman filter (UKF) was deployed as the carrier of all states. During the estimation process, third order dynamic transfer function was used to implement the PHM framework. Both of the luminous flux and color shift distance have been used as the state variable with the same PHM framework to exam the robustness of the method. Predicted remaining useful life is calculated at every measurement point to compare with the tested remaining useful life. The result shows that state estimator can be used as the method for the PHM of LED degradation with respect to both luminous flux and color shift distance. The prediction of remaining useful life of LED package, made by the states estimator and data driven approach, falls in the acceptable error-bounds (20%) after a short training of the estimator.

The Second Great Debate Revisited: Exploring the Impact of the Qualitative-Quantitative Divide in International Relations

2018 ◽  
Vol 21 (3) ◽  
pp. 447-476
Author(s):  
Quan Li
Keyword(s):  
International Relations ◽  
Political Science ◽  
Quantitative Research ◽  
Recent Decade ◽  
Journal Articles ◽  
Academic Communities ◽  
Great Debate ◽  
Alternative Approaches ◽  
The Impact ◽  
Political Science Journals

Abstract Half a century after the “Second Great Debate” in international relations (IR) started, scholars still perceive the qualitative versus quantitative division as their principal divide, and yet we do not have a good grasp of the impact of this divide. My research explores how the divide shaped the incentives and behaviors of scholars and influenced the organization of our academic communities and knowledge production. The impact of the divide expressed itself in the distribution of research among methodologies in terms of relative quantity and impact. Less obviously, and yet more importantly, the divide influenced the distribution of quantitative research among different institution types, across fields and journals, and with respect to policy engagement. Using the TRIP database of 7,792 IR articles in twelve top journals from 1980 to 2014, I classify journal articles into three categories—quantitative-only, qualitative-only, and mixed-methods—and categorize author institutions into similar types—publishing quantitative research only, producing nonquantitative work only, and publishing various proportions of quantitative research. Notably, qualitative and quantitative works switched positions over time in terms of relative quantity and impact, with quantitative research more likely published but only slightly more cited in the recent decade. More importantly, the divide produced other less obvious but more serious outcomes. Among 1,111 institutions that ever published IR research in twelve top journals over thirty-five years, two-thirds published nonquantitative research only; fifty-three institutions published more than half of all quantitative articles; institutions publishing quantitative-only or nonquantitative-only research constituted two modal categories. Political science journals published more quantitative research, persistently and with growing convergence; IR journals also evolved toward publishing more quantitative research though with persistent divergence and forming two clusters. Quantitative articles and political science journals were significantly less engaged in providing policy prescriptions than qualitative articles and IR journals. To overcome this lasting and self-perpetuating divide, we must better understand its impact, learn to appreciate alternative approaches, and change the way we train future scholars.

scholarly journals The effect of temperature on differentSalmonellaserotypes during warm seasons in a Mediterranean climate city, Adelaide, Australia

2015 ◽  
Vol 144 (6) ◽  
pp. 1231-1240 ◽  
Author(s):  
A. MILAZZO ◽  
L. C. GILES ◽  
Y. ZHANG ◽  
A. P. KOEHLER ◽  
J. E. HILLER ◽  
...  
Keyword(s):  
Phage Type ◽  
Warm Season ◽  
Substantial Effect ◽  
Effect Of Temperature ◽  
Temperature Sensitive ◽  
Ambient Temperatures ◽  
Policy Interventions ◽  
Long Term Trends ◽  
Higher Temperature ◽  
The Impact

SUMMARYChanging trends in foodborne disease are influenced by many factors, including temperature. Globally and in Australia, warmer ambient temperatures are projected to rise if climate change continues.Salmonellaspp. are a temperature-sensitive pathogen and rising temperature can have a substantial effect on disease burden affecting human health. We examined the relationship between temperature andSalmonellaspp. and serotype notifications in Adelaide, Australia. Time-series Poisson regression models were fit to estimate the effect of temperature during warmer months onSalmonellaspp. and serotype cases notified from 1990 to 2012. Long-term trends, seasonality, autocorrelation and lagged effects were included in the statistical models. DailySalmonellaspp. counts increased by 1·3% [incidence rate ratio (IRR) 1·013, 95% confidence interval (CI) 1·008–1·019] per 1 °C rise in temperature in the warm season with greater increases observed in specific serotype and phage-type cases ranging from 3·4% (IRR 1·034, 95% CI 1·008–1·061) to 4·4% (IRR 1·044, 95% CI 1·024–1·064). We observed increased cases ofS. Typhimurium PT9 andS. Typhimurium PT108 notifications above a threshold of 39 °C. This study has identified the impact of warm season temperature on differentSalmonellaspp. strains and confirms higher temperature has a greater effect on phage-type notifications. The findings will contribute targeted information for public health policy interventions, including food safety programmes during warmer weather.

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