Academic literature on the topic 'Instantaneous Failure Rate'
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Journal articles on the topic "Instantaneous Failure Rate"
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Mercier, Sophie, and Michel Roussignol. "Asymptotic failure rate of a Markov deteriorating system with preventive maintenance." Journal of Applied Probability 40, no. 1 (2003): 1–19. http://dx.doi.org/10.1239/jap/1044476824.
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We consider a system with a finite state space subject to continuous-time Markovian deterioration while running that leads to failure. Failures are instantaneously detected. This system is submitted to sequential checking and preventive maintenance: up states are divided into ‘good’ and ‘degraded’ ones and the system is sequentially checked through perfect and instantaneous inspections until it is found in a degraded up state and stopped to allow maintenance (or until it fails). Time between inspections is random and is chosen at each inspection according to the current degradation degree of the system. Markov renewal equations fulfilled by the reliability of the maintained system are given and an exponential equivalent is derived for the reliability. We prove the existence of an asymptotic failure rate for the maintained system, which we are able to compute. Sufficient conditions are given for the preventive maintenance policy to improve the reliability and the asymptotic failure rate of the system. A numerical example illustrates our study.
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Mercier, Sophie, and Michel Roussignol. "Asymptotic failure rate of a Markov deteriorating system with preventive maintenance." Journal of Applied Probability 40, no. 01 (2003): 1–19. http://dx.doi.org/10.1017/s0021900200022233.
Full textAbstract:
We consider a system with a finite state space subject to continuous-time Markovian deterioration while running that leads to failure. Failures are instantaneously detected. This system is submitted to sequential checking and preventive maintenance: up states are divided into ‘good’ and ‘degraded’ ones and the system is sequentially checked through perfect and instantaneous inspections until it is found in a degraded up state and stopped to allow maintenance (or until it fails). Time between inspections is random and is chosen at each inspection according to the current degradation degree of the system. Markov renewal equations fulfilled by the reliability of the maintained system are given and an exponential equivalent is derived for the reliability. We prove the existence of an asymptotic failure rate for the maintained system, which we are able to compute. Sufficient conditions are given for the preventive maintenance policy to improve the reliability and the asymptotic failure rate of the system. A numerical example illustrates our study.
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Yi, Yang, Ren Si Chao, Fan Guimei, and Kang Rui. "NUMERICAL SIMULATION ON THE EXISTENCE OF FLUCTUATION OF INSTANTANEOUS AVAILABILITY." Transactions of the Canadian Society for Mechanical Engineering 40, no. 5 (2016): 703–13. http://dx.doi.org/10.1139/tcsme-2016-0057.
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This paper considers the fluctuation of the instantaneous availability by numerical methods for a one-unit repairable system. The choices of the failure rate and repair rate are linear or cubic increasing functions. For the equation of instantaneous availability composing of two convolutions, the following numerical methods are used: the composite Simpson formula and the trapezoidal formula. That is to say, the simulated curves of instantaneous availability under any condition are obtained. Through the simulated results, when the failure rate and repair rate are selected as increasing functions, the extremum of simulated curve exists so fluctuation exists. On the other hand, if parameters of increasing functions become smaller, the fluctuation weakens.
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Yue, Shaofei, Kai Wang, Xiaoqiang Zhang, Tianhe Kang, Jianbing Yan, and Yulong Jiang. "Creep and Hardening Characteristics of Anthracite under Graded Static–Dynamic Coupled Loading." Applied Sciences 13, no. 19 (2023): 10648. http://dx.doi.org/10.3390/app131910648.
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Remaining coal pillars in remining areas exhibit clear creep characteristics, and dynamic pressure accelerates their instability and failure. The creep and hardening characteristics of coal under dynamic pressure are of great engineering significance for the stability of remaining coal pillars in remining areas and their control. To investigate the creep and hardening characteristics of anthracite under static–dynamic coupled loading, graded loading creep tests with different loading rates were conducted. In this research, the creep strain, instantaneous elastic modulus, and creep rate of anthracite were studied under different graded loading rates. The results showed that the hardening effect of the samples manifested as an increasing instantaneous elastic modulus at the loading stage and a decreasing strain rate at the creep stage. When the graded loading rate increases from 0.01 to 0.1 mm/s, the instantaneous elastic modulus increases by 0.16–2.32 times. The sudden increase in the instantaneous elastic modulus at the failure stress level explains the instantaneous failure of the samples well. The actual yield levels corresponding to the peak instantaneous elastic modulus of the samples linearly decreased with increasing graded loading rate. The functional relationship between the graded loading rate and the elastic modulus hardening coefficient, the actual yield stress, and the strain rate decay coefficient were established, which could quantitatively describe the influence of different graded loading rates on the creep and hardening characteristics of anthracite and predict its creep damage.
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Moriya, K., J. T. Pearson, W. W. Burggren, A. Ar, and H. Tazawa. "Continuous measurements of instantaneous heart rate and its fluctuations before and after hatching in chickens." Journal of Experimental Biology 203, no. 5 (2000): 895–903. http://dx.doi.org/10.1242/jeb.203.5.895.
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There has been considerable interest in heart rate (fh) fluctuations in relation to cardiovascular control systems and foetal conditions during pregnancy in mammals. Prominent fluctuations in fh also occur in avian embryos, which are an important experimental model for studying developmental physiology. The present study determined the instantaneous fh of seven chick embryos continuously from the last stage of prenatal development (day 18), throughout the pipping (perinatal) period (days 19–21) until hatching and, subsequently, of newly hatched chicks (up to day 2). The distinctive patterns of instantaneous fh fluctuations took the form of specific changes within a broad mean fh baseline. Cyclic oscillations (ultradian rhythm) occurred until an early stage of the perinatal period, when the fh baseline started rising. Subsequently, the baseline dropped and respiratory arrhythmia began to appear concomitant with external pipping. During the final stage of external pipping, when the fh baseline rose again prior to hatching, three unique patterns of instantaneous fh fluctuations were evident: relatively long-lasting cyclic small accelerations, irregular intermittent large accelerations and short-term repeated large accelerations. Furthermore, repeated alternate occurrences of the latter two types of acceleration formed an additional oscillating pattern with a period of 10–15 min. During the early period after hatching, when the fh baseline reached its maximum, instantaneous fh changed relatively slowly accompanied by transient rapid decelerations, probably due to augmented vagal tone. Subsequently, the mean fh baseline dropped to its minimum, and a circadian rhythm and three types of previously reported fh fluctuations (types I-III) appeared. Developmental patterns of mean fh and the appearance of distinctive patterns of instantaneous fluctuations in fh and circadian rhythms were not influenced by an ultimate failure of hatching after a normal development. The demonstration of complex, repeatable patterns of fh fluctuation that change during development suggests that the avian embryo model should be useful in studying the phenomenon of fh fluctuation and its underlying causes.
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Yan, Jianbing, Xiaoqiang Zhang, Kai Wang, Xuanmin Song, Shaofei Yue, and Jian Hou. "Experimental Study on Creep Characteristics and Long–Term Strength of Anthracite." Processes 11, no. 3 (2023): 947. http://dx.doi.org/10.3390/pr11030947.
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Coal pillars from old mines undergo creep, a type of time−dependent deformation. Research on underground engineering stability of coal mines has increasingly focused on long−term strength as an important mechanical index of the creep characteristics of coal pillars. This study performed conventional triaxial compression and triaxial creep tests of anthracite under different confining pressures. The creep law of anthracite and the long−term strength of anthracite was studied according to the test results. The test results demonstrated the following: (1) The conventional elastic modulus and peak strain of anthracite increased exponentially with the confining pressure. (2) Under low stress levels, anthracite exhibited only instantaneous deformation and attenuation creep. In contrast, anthracite exhibited instantaneous deformation, attenuation creep, and steady creep under high stress levels; accelerated creep occurred until failure when the stress reached a particular value. (3) By fitting the steady−state creep rate of anthracite under high stress levels, the functional relationship between axial stress and steady−state creep rate was established, and the threshold of the steady−state creep rate in high−stress−level areas was suggested as the optimum long−term strength of anthracite. (4) The ratio of the long−term strength to instantaneous strength under various confining pressure grades ranged from 70% to 91%.
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Burde, Gila, Ahron Rosenfeld, and Zachary Sheaffer. "Prediction of Financial Vulnerability to Funding Instability." Nonprofit and Voluntary Sector Quarterly 46, no. 2 (2016): 280–304. http://dx.doi.org/10.1177/0899764016655618.
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Financial vulnerability of nonprofit organizations arising from governmental funding instability is examined using hazard analysis. Funding instability is characterized by time-at-risk, and vulnerability is expressed by hazard rate measuring the speed of nonprofit organizations closure. The analysis provides estimation of instantaneous probability of a nonprofit organization failure at a given point in time. Drawing on 2,660 Israeli nonprofit organizations, we found that the relationship between hazard rate and time-at-risk has an inverted U–shape curve; hazard rate increases with time-at-risk, reaches a maximum then descends.
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Sarig, Erez, Michael Evzelman, and Mor Mordechai Peretz. "Analog Frontend for Big Data Compression and Instantaneous Failure Prediction in Power Management Systems." Electronics 14, no. 3 (2025): 641. https://doi.org/10.3390/electronics14030641.
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An innovative analog frontend for big data collection and intelligent compression as part of an instantaneous failure prediction platform is presented. Failure prediction in power management systems is crucial for increasing uptime and preventing massive failure. Accurate failure prediction, with real-time decision-making, requires data collection from many wide-bandwidth signals within a system, as low-bandwidth information such as DC output voltage is of limited value for decision-making and failure prediction. Analog compression, data profiling, and anomaly detection methods enabled by the unique analog frontend are presented. The system significantly reduces the demand for high computational power, fast communication, and large storage space required for the task. A real-time compression ratio exceeding 100:1 was achieved by the experimental analog frontend, digitizing the analog signal at a rate of 135 MS/s with a 10-bit resolution. The motivation, existing solutions, performance metrics, and advantages of the analog frontend are demonstrated, along with the details of the circuit operation principle. The process of data collection, its intelligent processing using the analog frontend, and anomaly detection are simulated to validate the theoretical hypotheses. For experimental validation, a laboratory setup that includes a dedicated analog frontend prototype and step-down DC-DC converter was built and evaluated to demonstrate the robust performance in sampling and monitoring wide-bandwidth signals and smart data processing using analog frontend for quick decision-making.
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Kulkarni, Abhaya V., James M. Drake, John R. W. Kestle, Conor L. Mallucci, Spyros Sgouros, and Shlomi Constantini. "Predicting who will benefit from endoscopic third ventriculostomy compared with shunt insertion in childhood hydrocephalus using the ETV Success Score." Journal of Neurosurgery: Pediatrics 6, no. 4 (2010): 310–15. http://dx.doi.org/10.3171/2010.8.peds103.
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Object The authors recently developed and internally validated the ETV Success Score (ETVSS)—a simplified means of predicting the 6-month success rate of endoscopic third ventriculostomy (ETV) for a child with hydrocephalus, based on age, etiology of hydrocephalus, and presence of a previous shunt. A high ETVSS predicts a high chance of early ETV success. In this paper, they assess the clinical utility of the ETVSS by determining whether long-term survival outcomes for ETV versus shunt insertion are different within strata of ETVSS (low, moderate, and high scores). Methods A multicenter, international cohort of children (≤ 19 years old) with newly diagnosed hydrocephalus treated with either ETV (489 patients) or shunt insertion (720 patients) was analyzed. The ETVSS was calculated for all patients. Survival analyses with time-dependent modeling of the hazard ratios were performed. Results For the High-ETVSS Group (255 ETV-treated patients, 117 shunt-treated patients), ETV appeared to have a lower risk of failure right from the early postoperative phase and became more favorable with time. For the Moderate-ETVSS Group (172 ETV-treated patients, 245 shunt-treated patients), ETV appeared to have a higher initial failure rate, but after about 3 months the instantaneous risk of ETV failure became slightly lower than shunt failure (that is, the hazard ratio became < 1). For the Low-ETVSS Group (62 ETV-treated patients, 358 shunt-treated patients), the early risk of ETV failure was much higher than the risk of shunt failure, but the instantaneous risk of ETV failure became lower than the risk of shunt failure at about 6 months following surgery (the hazard ratio became < 1). Conclusions Across all ETVSS strata, the risk of ETV failure becomes progressively lower compared with the risk of shunt failure with increasing time from the surgery. In the best ETV candidates (ETVSS ≥ 80), however, the risk of ETV failure is lower than the risk of shunt failure very soon after surgery, while for less-than-ideal ETV candidates (ETVSS ≤ 70), the risk of ETV failure is initially higher than the risk of shunt failure and only becomes lower after 3–6 months from surgery. These results need to be confirmed by larger, prospective, and preferably randomized studies.
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Buono, Francesco, and Maria Kateri. "Aging Intensity for Step-Stress Accelerated Life Testing Experiments." Entropy 26, no. 5 (2024): 417. http://dx.doi.org/10.3390/e26050417.
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The aging intensity (AI), defined as the ratio of the instantaneous hazard rate and a baseline hazard rate, is a useful tool for the describing reliability properties of a random variable corresponding to a lifetime. In this work, the concept of AI is introduced in step-stress accelerated life testing (SSALT) experiments, providing new insights to the model and enabling the further clarification of the differences between the two commonly employed cumulative exposure (CE) and tampered failure rate (TFR) models. New AI-based estimators for the parameters of a SSALT model are proposed and compared to the MLEs in terms of examples and a simulation study.
Dissertations / Theses on the topic "Instantaneous Failure Rate"
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Chen, Jou-yen, and 陳柔諺. "The Application of Grey System Theory to Forecast the Aircrafts Reliability Instantaneous Failure Rate." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/00660450220661496402.
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碩士<br>朝陽科技大學<br>企業管理系碩士班<br>98<br>For modern air fighters, the reliability of weapon systems is a useful reference for improvement and modification of logistics managements, such as engineering modification,maintenance quality control, maintenance capability, inspection intervals, maintenance schemes,adjustment of technical training program, prediction of equipment and material requirement,and operation mission support. By using Grey Theroy GM(1,1)model, the study can predict the instantaneous failure of fighter reliability. The results are as follows,
The accuracy of GM(1,1) model is all over 90 %, verifying that GM(1,1) can indeed be used for reliability prediction of fighters, which is with less figure data and non normal distribution.
With prediction, the instantaneous failure value on three models of fighters is decreasing, mean that the mean time between failures(MTBF) value is increasing.It indicates that after receiving aircrafts, the maintenance ability of technicians and the reliability of equipment and materials are in a stable state.
Book chapters on the topic "Instantaneous Failure Rate"
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Hojjati-Emami, Khashayar, Balbir S. Dhillon, and Kouroush Jenab. "The HRA-Based Road Crash Data." In Human Performance Technology. IGI Global, 2019. http://dx.doi.org/10.4018/978-1-5225-8356-1.ch027.
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Human error has played a critical role in the events precipitating the road accidents. Such accidents can be predicted and prevented by risk assessment, in particular assessing the human contribution to risk. As part of the Human Reliability Assessment (HRA) process, it is usually necessary not only to define what human errors can occur, but how often they will occur. Lack of understanding of the failure distribution characteristics of drivers on roads at any given time is a factor impeding the development of human reliability assessment and prediction of road accidents in order to take best proactive measures. The authors developed the complete investigation methodology for crash data collection. Furthermore, they have experimentally tested the proposed predictive behavioral characteristics of drivers in light of their instantaneous error rate over the course of driving period to assist processing and analysis of data collection as part of risk assessment. The findings of this research can assist road safety authorities to collect the necessary data, to better understand the behavioral characteristics of drivers on roads, to make more accurate risk assessments and finally to come up with right preventive measures.
Conference papers on the topic "Instantaneous Failure Rate"
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Frail, Paul R., Reza Sharghi-Moshtaghin, Gilad Zorn, and Martin M. Morra. "Elucidating the Differences between Weight Loss and Instantaneous Corrosion Rates for Azole Films on Copper Metallurgy." In CORROSION 2015. NACE International, 2015. https://doi.org/10.5006/c2015-05924.
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Abstract Water systems with mixed metallurgies require proper low carbon steel and copper alloy metal corrosion control. Improper copper corrosion control can lead to failure of copper alloys, such as admiralty brass metal within the system and cause galvanic corrosion on less noble metal, like carbon steel and cast iron. Azoles, benzotriazole (BZT) and tolyltriazole (TTA), are generally used to control copper corrosion in heat exchangers that are employed in open recirculation cooling tower systems, via a film forming mechanism on the metal surface. Monitoring of corrosion control can be done by using metal coupons or corrosion rate meter (CRM) utilizing linear polarization methods. Often there is a discrepancy between coupon and a CRM probe corrosion rates due to each technique acquiring corrosion rate values by different means: mechanical (weight loss) and electrochemical, respectively. CRM data suggests a steady state in admiralty brass (ADM) corrosion rate is reached anywhere from 2 to 6 hours with an azole inhibitor present in typical cooling water chemistry. Surface analysis revealed coupons to achieve maximum azole coverage in 30-60 min. This report utilizes electrochemical techniques and surface analysis to identify early passivation mechanism differences between TTA treated ADM coupon and CRM probes. Various water matrix conditions will be used to determine drivers for changes in surface chemistry.
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Olesen, Andreas Junker, Frank Fontenay, Lars Vendelbo Nielsen, and Lisbeth Hilbert. "Atmospheric Corrosion Monitoring Using Electrical Resistance Probes." In CONFERENCE 2023. AMPP, 2023. https://doi.org/10.5006/c2023-19271.
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Abstract Many sensors or electrodes for corrosion and condition monitoring produce an indirect measure of the condition of the structure. This can be in the form of electrical signals or spectrums that need subsequent analysis. Electrical resistance (ER) probes, however, can be used to realistically represent the structure and will provide an accurate measure of corrosion in any environment, with or without an electrolyte. The probe surface can even be treated with a representative corrosion protection system, such as thermal spray or organic coatings or cathodic protection for that matter. Furthermore, they will capture not only the semi-instantaneous corrosion rate at any given time, but also the accumulated corrosion loss in the event of a power or logger failure. This paper presents some currently available sensors particularly applicable also for atmospheric and splash-zone monitoring in marine environments through examples of installations and gathered data.
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Onsrud, Gisle, and Terje Søntvedt. "Recording of Local Flow Disturbances behind Obstacles Where Mesa Attack Have Occurred." In CORROSION 1998. NACE International, 1998. https://doi.org/10.5006/c1998-98040.
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Abstract Laboratory investigations have demonstrated that flow induced limits for the application of C-steel exist. Flow limits have been found for all types of C-steels investigated. Obstacles in pipes constitute exposed areas for destruction of the carbonate film and determine the maximum allowable production rate rather than the smooth pipe sections. The purpose with our ongoing research project is to connect the strength of carbonate films with stress caused by fluid flow. Flow-induced wall shear stress fluctuations on smooth pipe sections and behind obstacles have been systematically mapped. Mean wall shear stress and shear stress amplitudes have been recorded downstream obstacles in a 69 mm diameter stainless steel pipe with single phase oil flow. The influence from obstacle location, its height and flow velocity on mean shear stress, shear stress amplitudes and dominant frequencies have been studied. The fast K-tubes allowed recording of the instantaneous shear also when the stress cycled to negative values. Relationships for the wall shear stress amplitudes, frequencies and mean values have been developed. The paper shows why weld like obstacles constitute exposed areas. A model has been developed which describes the time to failure of the corrosion product when delaminated from the base metal. This model connects the residual strength of the corrosion product with the fluctuating wall shear from the liquid, its dominant frequency and the mean shear. The model allows transformation of observed flow limits in the laboratory to completely different flow conditions. Simple limits to production rate in the form of wall shear have been found for smooth pipes and pipes with weld like obstacles.
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Alves, Andre L. R., and Theodoro A. Netto. "Instantaneous Probability of Uncontrolled External Leakage During the Production Phase of a Subsea Well." In ASME 2013 32nd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/omae2013-10558.
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This work develops a methodology for evaluating the uncontrolled external leakage probability of a subsea well during the production phase. Based on a barrier diagram, an algorithm for possible leak paths identification is proposed, considering different operation modes: gas lift operation, free flowing or well closed at the subsea Xmas Tree. Considering the equivalency between these paths and the minimum cut sets from a fault tree modeling, the uncontrolled external leakage probability is calculated using the upper bound approximation. The effect of common cause failures is considered for the failure mode fail-to-close-valve. The instantaneous availability function of each component is modeled to represent the maintenance strategy applied. Non repairable, repairable and periodically tested items are used. For the latter, a nomenclature to distinguish two subtypes is introduced: the PT-R and PT-NR models, respectively Periodically Tested Repairable, and Periodically Tested Non Repairable. Probability distributions parameters are roughly estimated in order to make a case study. The failure rate functions determined are used as input for the proposed model, regarding the following failure modes: fail-to-close, external-leakage, and internal-leakage at the closed position. The objective of this section is to adjust a Weibull distribution, eliminate the usual assumption of constant failure rate and account for eventual wear-out effects. Finally, instantaneous probability results and sensitivity analysis are demonstrated for a base case study. Parameters like time between tests, inspections, and component reliability are varied in order to identify the impact on the uncontrolled external leakage probability. Therefore, the main objective is to propose a model that could support decision making on the well integrity management system during the production phase of a subsea well. To make this possible, reliable input data should be further considered.
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Birnbaum, Andrew J., John C. Steuben, Athanasios P. Iliopoulos, and John G. Michopoulos. "Simulating Hypervelocity Impact and Material Failure in Glass." In ASME 2018 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/detc2018-85948.
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Simulating hypervelocity impact introduces a host of complexities due to inherent strain, pressure and strain rate sensitivities. Brittle materials, and glasses in particular, exhibit significant deviations from their respective quasi-static responses, displaying permanent densification, gradual softening, and significant variation in response depending on the degree of material damage. This work seeks to examine the evolution of material failure due to hypervelocity impact of a spherical steel projectile in to a soda-lime target plate over a range of impact velocities via the utilization of a scalable, explicit finite element code, Velodyne, and a high strain rate, brittle material model. It is shown that, by analyzing both the evolutionary instantaneous and accumulated failure behaviors, the resulting performance is profoundly effected by target/projectile geometries, as well as the complex behaviors observed with respect to shock propagation, reflection and interference.
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Duan, Xinjian, Arnaud Weck, David S. Wilkinson, and Don R. Metzger. "Plastic Limit Analysis of Perforated Material Under Finite Deformation." In ASME 2005 Pressure Vessels and Piping Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/pvp2005-71646.
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In this paper, the fracture pattern of a perforated aluminum sheet is studied experimentally and numerically using finite element models on two different length scales: a full-scale structural and a local cell models based on the large deformation theory. Through appropriate application of boundary conditions, the more efficient local cell model is shown to produce almost the same results as the full structural model. It is also found that the failure path is significantly affected by the loading conditions (uniaxial vs. biaxial) and the hole distribution pattern. By plotting the instantaneous contour of plastic strain rate, the fracture path could clearly be distinguished by the time that the overall engineering strain had reached 3%.
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Halfmann, Eric B., and C. Steve Suh. "High Speed Non-Linear Micro-Milling Dynamics." In ASME 2012 International Manufacturing Science and Engineering Conference collocated with the 40th North American Manufacturing Research Conference and in participation with the International Conference on Tribology Materials and Processing. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/msec2012-7287.
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The efficiency of the milling process is limited due to excessive vibrations that negatively impact the tool and work-piece quality. This becomes even more of a concern in micro-milling where sudden tool breakage occurs before the operator can adjust cutting parameters. Due to different chip formation mechanisms in micro-milling, an increased tool-radius to feed-rate ratio, and higher spindle speeds, micro-milling is a highly non-linear process which can produce multiple and broadband frequencies which increase the probability of tool failure. This paper investigates micro-milling through the development and analysis of a 3-D nonlinear micro-milling dynamic model. A lumped mass, spring, damper system is assumed for modeling the dynamic properties of the tool. The force mechanism utilized is a slip-line field model that provides the advantages of being highly dynamic by accounting for the constantly changing effective rake angle and slip-line variables. Accurate prediction of the chip thickness is important in correctly predicting the dynamics of the system since the force mechanism and its variables are a function of the chip thickness. A novel approach for calculating the instantaneous chip thickness which accounts for the tool jumping out of the cut and elastic recovery of the work-piece is presented. The derivation for the effective rake angle is given and the helical angle is accounted for resulting in a 3-D micro-milling model. The results of simulating the model demonstrate its capability of producing the high frequency force components that are seen in experimental data available in literature. The advantages of using this approach over the constant empirical force coefficient approach when studying micro-milling dynamics is discussed and the instability of the system is investigated utilizing instantaneous frequency.
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Alkharabsheh, Sami A., Bahgat Sammakia, Saurabh Shrivastava, Michael Ellsworth, Milnes David, and Roger Schmidt. "A Numerical Steady State and Dynamic Study in a Data Center Using Calibrated Fan Curves for CRACs and Servers." In ASME 2013 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/ipack2013-73217.
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This study presents the results of a detailed parametric study for a data center that is air cooled using a set of four CRAC units in a cold/hot aisle raised floor configuration. The fans of the CRAC units and the servers are calibrated using their practical characteristics fan curves. A commercial CFD code is utilized for this purpose in which the buoyancy forces are taken into account. The k-epsilon model and the Boussinesq approximation are used to model the turbulent airflow and the buoyancy effect, respectively. A dynamic model is developed to take into account the changes in flow rates and power dissipation in the data center environment. The current dynamic model does not take into account the thermal mass of the CRAC units or the servers. The effect of the CRAC fan speed, instantaneous change in power dissipation, tiles perforation ratio, and servers fan speeds on the total flow rate in the room and the inlet temperatures of the racks are investigated. In the transient model, we investigate the effect of different CRAC failure scenarios on the time history of the temperatures and the flow pattern in the data center. Time constants and safe time are estimated from this study. A fundamental understanding of the effect of different data center entities on the flow and the temperatures is developed. Interesting flow patterns are observed in the case of different CRAC failures that could be used to recommend general design guidelines.
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Doleiden, Daniel, Wyatt Culler, Ankit Tyagi, Stephen Peluso, and Jacqueline O’Connor. "Flame Edge Dynamics and Interaction in a Multi-Nozzle Can Combustor With Fuel Staging." In ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-91656.
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Abstract The characterization and mitigation of thermoacoustic combustion instabilities in gas turbine engines is necessary to reduce pollutant emissions, premature wear, and component failure associated with unstable flames. Fuel staging, a technique in which the fuel flow to a multi-nozzle combustor is unevenly distributed between the nozzles, has been shown to mitigate the intensity of self-excited combustion instabilities in multiple nozzle combustors. In our previous work, we hypothesized that staging suppresses instability through a phase-cancellation effect in which the heat release rate from the staged nozzle oscillates out of phase with that of the other nozzles, leading to destructive interference that suppresses the instability. This previous theory, however, was based on chemiluminescence imaging, which is a line-of-sight integrated technique. In this work, we use high-speed laser-induced fluorescence to further investigate instability suppression in two staging configurations: center-nozzle and outer-nozzle staging. An edge-tracking algorithm is used to compute local flame edge displacement as a function of time, allowing instability-driven edge oscillation phase coherence and other instantaneous flame dynamics to be spectrally and spatially resolved. Analysis of flame edge oscillations shows the presence of convecting coherent fluctuations of the flame edge caused by periodic vortex shedding. When the system is unstable, these two flame edges oscillate together as a result of high-intensity longitudinal-mode acoustic oscillations in the combustor that drive periodic vortex shedding at each of the nozzle exits. In the stable cases, however, the phase between the oscillations of the center and outer flame edges is greater than 90 degrees (∼114 degrees), suggesting that the phase-cancellation hypothesis may be valid. This analysis allows a better understanding of the instantaneous flame dynamics behind flame edge oscillation phase offset and fuel staging-based instability suppression.
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Halfmann, Eric B., and C. Steve Suh. "Impact of Spindle Speed on Micro-Milling Stability." In ASME 2012 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/imece2012-88071.
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Milling efficiency is hampered by excessive tool vibrations that negatively impact the work-piece quality. This is more of a concern in micro-milling where sudden tool breakage occurs before the operator can adjust cutting parameters. Due to different chip formation mechanisms in micro-milling, an increased tool-radius to feed-rate ratio, and higher spindle speeds, micro-milling is a highly non-linear process which can produce multiple and broadband frequencies which increase the probability of tool failure. Micro-milling is studied through the development and analysis of a 3-D nonlinear micro-milling dynamic model. A lumped mass, spring, damper system is assumed for modeling the dynamic properties of the tool. The force mechanism utilized is a slip-line field model that provides the advantages of being highly dynamic by accounting for the constantly changing effective rake angle and slip-line variables. Accurate prediction of the chip thickness is important in correctly predicting the dynamics of the system since the force mechanism and its variables are a function of the chip thickness. A novel approach for calculating the instantaneous chip thickness which accounts for the tool jumping out of the cut and elastic recovery of the work-piece is presented. The effective rake angle and helical angle is accounted for resulting in a 3-D micro-milling model. The model is shown to resolve the high frequency force components that are seen in experimental data available in literature. Also, exciting the system at various spindle speeds results in dynamic states of motion that negatively impact the process through increased vibration amplitude and a broad frequency bandwidth.
Reports on the topic "Instantaneous Failure Rate"
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Bubenik and Nestleroth. L51619 Effects of Loading on the Growth Rates in Deep Stress-Corrosion Cracks. Pipeline Research Council International, Inc. (PRCI), 1990. http://dx.doi.org/10.55274/r0010094.
Full textAbstract:
With the development of improved techniques for detection of stress corrosion cracks in existing pipelines, the pipeline industry is faced with the problem of estimating the growth rates of these cracks. Current efforts in model development are addressing the problem but, in order to verify these models, accurate average crack velocity data are needed (average crack velocity being defined as the average rate of crack growth with time, crack velocity is the instantaneous rate of crack tip dissolution.) Currently available data are limited and are based primarily on either slow-strain rate tests or tapered tensile tests. The loading conditions in the former are unrepresentative of actual operating conditions while the crack depths in the latter are much shallower than those observed in service. Some fracture mechanics data also are available for this system but the specimen and crack geometry used in these tests are not similar to the geometry of the field failures*. In addition, results of recent PRCI research suggest that the stress intensity parameter, K, which is used to relate different cracking geometries, is a poor crack driving force parameter for SCC in line pipe steels. The overall objective of this work is to obtain accurate average crack velocity data as a function of crack depth and loading conditions. The program is divided into two tasks: Task 1 - Effect of Crack Depth and Cyclic Loading Conditions on Crack Growth and Task 2 - Inhibition of Crack Growth.