The quantity and length of optical fibers required for the Hobby-Eberly Telescope Dark Energy eXperiment (HETDEX) create unique fiber handling challenges. More than 33,000 optical fibers will enable the Hobby-Eberly Telescope (HET) to collect data on at least one million galaxies that are 9 billion to 11 billion light-years away, yielding the largest map of the universe ever produced [1,2]. The design advantages made possible by optical fibers also forms challenges to prevent damage to the fragile fibers that can lead to Focal Ratio Degradation (FRD) [3]. Therefore, a life cycle test must be conducted to study fiber behavior and measure FRD as a function of time. This thesis describes the design and design methodology of an electro-mechanical test apparatus for accelerated life testing of optical fiber assemblies. The design methodology summarizes the development of functional requirements and constraints that drove the design. The test apparatus design utilizes six linear actuators to replicate the movement of the fiber system deployed on HETDEX for over 65,000 accelerated cycles, simulating five years of actual operation. The electro-mechanical test apparatus will provide insight into the effects of load history on the performance of optical fibers which published data has thus far been lacking. Performance of the electro-mechanical test apparatus will be demonstrated through simulation, modeling and calculations. The test results that will be generated from the accelerated life test will be of great interest to designers of robotic fiber handling systems for major telescopes. / text

Since new product designs have little field data available a correlation between field and accelerated test life cannot be made. However, a step partially accelerated life test approach where samples are tested under normal conditions for a time and then run to failure on an accelerated test can be used to estimate the statistical model parameters. This thesis developed the maximum likelihood parameter estimates for a step partially accelerated life test based on a Weibull distribution model for a hypothetical automotive component. Using a Monte Carlo approach with type-II censoring, the effect of sample size and length of sampling period used on the variability of the estimated parameters was examined. A smaller sampling period and small sizes lead to significant variability, which decreased as the sampling period and sample size increased. Use of a partitioned sample did not lead to an improvement in the variability of the estimates. / Department of Mathematical Sciences

Thesis (M.S.)--West Virginia University, 1998. / Title from document title page. "December 1998." Document formatted into pages; contains xviii, 153 p. : ill. (some col.) Includes abstract. Includes bibliographical references (p. 101-105).

Thesis (Ph.D)--Aerospace Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Schrage, Daniel; Committee Member: Loewy, Robert; Committee Member: O'Neill, Gary; Committee Member: Saleh, Joseph; Committee Member: Volovoi, Vitali. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Accelerated Life Testing (ALT) is an effective method of demonstrating and improving product reliability in applications where the products are expected to perform for a long period of time. ALT accelerates a given failure mode by testing at amplified stress level(s) in excess of operational limits. Statistical analysis (parameter estimation) is then performed on the data, based on an acceleration model to make life predictions at use level. The acceleration model thus forms the basis of accelerated life testing methodology. Well established accelerated models such as the Arrhenius model and the Inverse Power Law (IPL) model exist for key stresses such as temperature and voltage. But there are other stresses like subsea pressure, where there is no clear model of choice. This research proposes a pressure-life (acceleration) model for the first time for life prediction under subsea pressure for key mechanical/physical failure mechanisms. Three independent accelerated tests were conducted and their results analyzed to identify the best model for the pressure-life relationship. The testing included material tests in standard coupons to investigate the effect of subsea pressure on key physical, mechanical, and electrical properties. Tests were also conducted at the component level on critical components that function as a pressure barrier. By comparing the likelihood values of multiple reasonable candidate models for the individual tests, the exponential model was identified as a good model for the pressure-life relationship. In addition to consistently providing good fit among the three tests, the exponential model was also consistent with field data (validation with over 10 years of field data) and demonstrated several characteristics that enable robust life predictions in a variety iv of scenarios. In addition the research also used the process of Bayesian analysis to incorporate prior information from field and test data to bolster the results and increase the confidence in the predictions from the proposed model.

In this thesis, we develop several novel degradation models based on techniques from functional data analysis. These models are suitable for characterizing different types of sensor-based degradation signals, whether they are censored at a certain fixed time point or truncated at the failure threshold. Our proposed models can also be easily extended to accommodate for the effects of environmental conditions on degradation processes. Unlike many existing degradation models that rely on the existence of a historical sample of complete degradation signals, our modeling framework is well-suited for modeling complete as well as incomplete (sparse and fragmented) degradation signals. We utilize these models to predict and continuously update, in real time, the residual life distributions of partially degraded components. We assess and compare the performance of our proposed models and existing benchmark models by using simulated signals and real world data sets. The results indicate that our models can provide a better characterization of the degradation signals and a more accurate prediction of a system's lifetime under different signal scenarios. Another major advantage of our models is their robustness to the model mis-specification, which is especially important for applications with incomplete degradation signals (sparse or fragmented).

Thesis (MEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Accelerated pavement testing (APT) is the application of a wheel loading, to a prototype or actual layered, structural pavement system to determine pavement response and performance under controlled, accelerated accumulation of damage in a compressed time period. It is a tool used for the evaluation of performance of new pavement materials, distress mechanisms, pavement distress, and selection of rehabilitation strategies. In this study, the research work that was done in Jacksboro, Texas (USA) with the third-scale Model Mobile Load Simulator (MMLS3) as part of the APT programme of the Texas Department of Transportation (TxDOT) is presented. The primary objective was to evaluate the performance ofthe different asphalt concrete (AC) materials (Dustrol and Remixer) used on highway US 281, in terms of rutting and distress due to wet trafficking. The other objective was to investigate the difference in rutting between the MMLS3 and the full-scale Texas Mobile Load Simulator (TxMLS). The scope of the study included fieldwork, laboratory work and theoretical analysis. On average, the performance of the layer from the Dustrol process was found to be poorer than that of the Remixer process. The Dustrol process was more susceptible to moisture damage and less resistant to permanent deformation compared to the Remixer process. The MMLS3 and TxMLS permanent deformations in the upper 90 mm surface layers correlated well in terms of the respective vertical stresses imposed by the two APT devices, after allowing for the difference in environmental conditions during trafficking. Overall, the study demonstrated that the MMLS3, used in conjunction with nondestructive field and laboratory testing, is a significant cost-effective APT device that can be used for evaluating the response and performance of the (surface) layers of full-scale, in-service pavements. / AFRIKAANSE OPSOMMING: Versnelde Plaveisel Toetsing bestaan uit die gebruik van 'n wiellas op 'n prototipe of 'n bestaande gelaagde plaveiselstruktuur om die plaveiselgedrag onder beheerde en versnelde toename in skade in 'n verkorte periode te bepaal. Dit word gebruik om die gedrag van nuwe plaveiselmateriale, swigtingsmeganismes, plaveiselswigting en die keuse van rehabilitasie strategieë te evalueer. Die navorsingswerk met die derde skaal Model Mobile Load Simulator (MMLS3) wat onderneem is in Jacksboro, Texas (VSA), en deel uitmaak van die Versnelde Plaveisel Toetsingsprojek van die Texas Departement van Vervoer (TxDOT), word uiteengesit. Die hoofdoel van die studie was om die gedrag van twee verskillende asfaltmateriale, naamlik Dustrol en Remixer, wat gebruik is op die US 281-snelweg, in terme van sporing en swigting as gevolg van nat belastingstoestande te evalueer. 'n Verdere doelstelling was om die verskil in die gemete sporing tussen die MMLS3 en die volskaal Texas Mobile Load Simulator (TxMLS) te ondersoek. Die studie het veld- en laboratoriumtoetse en teoretiese analise behels. Die gedrag van die Dustrol laag is oor die algemeen swakker as die Remixer lae. Die Dustrol laag, in vergelyking met die Remixer lae, is meer vatbaar vir vogskade en spoor makliker. Nadat die invloed van verskillende omgewingstoestande gedurende asbelasting inaggeneem is, korreleer die sporing vir die MMLS3 en die TxMLS in die lae van die boonste 90mm van die plaveisel goed in terme van die vertikale spannings soos opgewek deur die twee toetstoestelle. In die geheel word bewys dat die MMLS3 tesame met nie-destruktiewe veld- en laboratoriumtoetse 'n belangrike koste-effektiewe versnelde plaveisel toetstoestel is, wat aangewend kan word in die evaluasieproses van die gedrag van (oppervlak) lae van volskaalse plaveisels in gebruik.

A thesis submitted in fulfillment of the requirements for the Degree of Doctor of Philosophy, School of Statistics and Actuarial Science, Faculty of Science University of Witwatersrand, Johannesburg. February 2017. / The work done in this thesis on finite planning horizon inspection models has demonstrated that with the advent of powerful computers these days it is possible to easily find an optimal inspection schedule when the lifetime distribution is known. For the case of system time to failure following a uniform distribution, a result for the maximum number of inspections for the finite planning models has been derived. If the time to failure follows an exponential distribution, it has been noted that periodically carrying out inspections may not result in maximization of expected profit. For the Weibull distributions family (of which the exponential distribution is a special case), evenly spreading the inspections over a given finite planning horizon may not lead to any serious prejudice in profit. The case of inspection models where inspections are of non-negligible duration has also been explored. The conditions necessary for inspections that are evenly spread over the entire planning horizon to be near-optimal when system time to failure either follows a uniform distribution or exponential distribution have been explored. Finite and infinite planning horizon models where inspections are imperfect have been researched on. Interesting observations on the impact of Type I and Type II errors in inspection have been made. These observations are listed on page 174. A clear and easy to implement road map on how to get an optimal inspection permutation in problems first discussed by Zuckerman (1989) and later reviewed by Qiu (1991) for both the undiscounted and discounted cases has been given. The only challenge envisaged when a system has a large number of components is that of computer memory requirements - which nowadays is fast being overcome. In particular, it has been clearly demonstrated that the impact of repair times and per unit of time repair costs on the optimal inspection permutation cannot be ignored. The ideas and procedures of determining optimal inspection permutations which have been developed in this thesis will no doubt lead to huge cost savings especially for systems where the cost of inspecting components is huge. / XL2018

To meet increasing competition, get products to market in the shortest possible time, and satisfy heightened customer expectations, products must be made more robust and fewer failures must be observed in a short development period. In this circumstance, assessing product reliability based on degradation data at high stress levels becomes necessary. This assessment is accomplished through accelerated degradation tests (ADT). These tests involve over stress testing in which instead of life product performance is measured as it degrades over time. Due to the role these tests play in determining proper reliability estimates for the product, it is necessary to scientifically design these test plans so as to save time and expense and provide more accurate estimates of reliability for a given number of test units and test time. In ADTs, several decision variables such as inspection frequency,the sample size, and the termination time at each stress level are important. In this research, an optimal plan is developed for the design of accelerated degradation test with a reciprocal Weibull degradation data using the mean time to failure (MTTF) as the minimizing criteria. A non linear integer programming problem is developed under the constraint that the total experimental cost does not exceed a pre-determined budget. The optimal combination of sample size, inspection frequency and the termination time at each stress level is found. A case example based on Light Emitting Diode (LED) example is used to illustrate the proposed method. Sensitivity analyses on the cost parameters and the parameters of the underlying probability distribution are performed to assess the robustness of the proposed method.

Because of the needs for producing highly reliable products and reducing product development time, Accelerated Life Testing (ALT) has been widely used in new product development as an alternative to traditional testing methods. The basic idea of ALT is to expose a limited number of test units of a product to harsher-than-normal operating conditions to expedite failures. Based on the failure time data collected in a short time period, an ALT model incorporating the underlying failure time distribution and life-stress relationship can be developed to predict the product reliability under the normal operating condition. However, ALT experiments often consume significant amount of energy due to the harsher-than-normal operating conditions created and controlled by the test equipment used in the experiments. This challenge may obstruct successful implementations of ALT in practice. In this dissertation, a new ALT design methodology is developed to improve the reliability estimation precision and the efficiency of energy utilization in ALT. This methodology involves two types of ALT design procedures - the sequential optimization approach and the simultaneous optimization alternative with a fully integrated double-loop design architecture. Using the sequential optimum ALT design procedure, the statistical estimation precision of the ALT experiment will be improved first followed by energy minimization through the optimum design of controller for the test equipment. On the other hand, we can optimize the statistical estimation precision and energy consumption of an ALT plan simultaneously by solving a multi-objective optimization problem using a controlled elitist genetic algorithm. When implementing either of the methods, the resulting statistically and energy efficient ALT plan depends not only on the reliability of the product to be evaluated but also on the physical characteristics of the test equipment and its controller. Particularly, the statistical efficiency of each candidate ALT plan needs to be evaluated and the corresponding controller capable of providing the required stress loadings must be designed and simulated in order to evaluate the total energy consumption of the ALT plan. Moreover, the realistic physical constraints and tracking performance of the test equipment are also addressed in the proposed methods for improving the accuracy of test environment. In this dissertation, mathematical formulations, computational algorithms and simulation tools are provided to handle such complex experimental design problems. To the best of our knowledge, this is the first methodological investigation on experimental design of statistically precise and energy efficient ALT. The new experimental design methodology is different from most of the previous work on planning ALT in that (1) the energy consumption of an ALT experiment, depending on both the designed stress loadings and controllers, cannot be expressed as a simple function of the related decision variables; (2) the associated optimum experimental design procedure involves tuning the parameters of the controller and evaluating the objective function via computer experiment (simulation). Our numerical examples demonstrate the effectiveness of the proposed methodology in improving the reliability estimation precision while minimizing the total energy consumption in ALT. The robustness of the sequential optimization method is also verified through sensitivity analysis.