The application of encapsulation material stability data to photovoltaic module life assessment

For any piece of hardware that degrades when subject to environmental and application stresses, the route or sequence that describes the degradation process may be summarized in terms of six key words: LOADS, RESPONSE, CHANGE, DAMAGE, FAILURE, and PENALTY. Applied to photovoltaic modules, these six factors form the core outline of an expanded failure analysis matrix for unifying and integrating relevant material degradation data and analyses. An important feature of this approach is the deliberate differentiation between factors such as CHANGE, DAMAGE, and FAILURE. The application of this outline to materials degradation research facilitates the distinction between quantifying material property changes and quantifying module damage or power loss with their economic consequences. The approach recommended for relating material stability data to photovoltaic module life is to use the degree of DAMAGE to (1) optical coupling, (2) encapsulant package integrity, (3) PV circuit integrity or (4) electrical isolation as the quantitative criterion for assessing module potential service life rather than simply using module power loss

NASA pyrotechnically actuated systems program

The Office of Safety and Mission Quality initiated a Pyrotechnically Actuated Systems (PAS) Program in FY-92 to address problems experienced with pyrotechnically actuated systems and devices used both on the ground and in flight. The PAS Program will provide the technical basis for NASA's projects to incorporate new technological developments in operational systems. The program will accomplish that objective by developing/testing current and new hardware designs for flight applications and by providing a pyrotechnic data base. This marks the first applied pyrotechnic technology program funded by NASA to address pyrotechnic issues. The PAS Program has been structured to address the results of a survey of pyrotechnic device and system problems with the goal of alleviating or minimizing their risks. Major program initiatives include the development of a Laser Initiated Ordnance System, a pyrotechnic systems data base, NASA Standard Initiator model, a NASA Standard Linear Separation System and a NASA Standard Gas Generator. The PAS Program sponsors annual aerospace pyrotechnic systems workshops

Analysis of Software Aging in a Web Server

A number of recent studies have reported the phenomenon of “software aging”, characterized by progressive performance degradation and/or an increased occurrence rate of hang/crash failures of a software system due to the exhaustion of operating system resources or the accumulation of errors. To counteract this phenomenon, a proactive technique called 'software rejuvenation' has been proposed. It essentially involves stopping the running software, cleaning its internal state and/or its environment and then restarting it. Software rejuvenation, being preventive in nature, begs the question as to when to schedule it. Periodic rejuvenation, while straightforward to implement, may not yield the best results, because the rate at which software ages is not constant, but it depends on the time-varying system workload. Software rejuvenation should therefore be planned and initiated in the face of the actual system behavior. This requires the measurement, analysis and prediction of system resource usage. In this paper, we study the development of resource usage in a web server while subjecting it to an artificial workload. We first collect data on several system resource usage and activity parameters. Non-parametric statistical methods are then applied for detecting and estimating trends in the data sets. Finally, we fit time series models to the data collected. Unlike the models used previously in the research on software aging, these time series models allow for seasonal patterns, and we show how the exploitation of the seasonal variation can help in adequately predicting the future resource usage. Based on the models employed here, proactive management techniques like software rejuvenation triggered by actual measurements can be built. --Software aging,software rejuvenation,Linux,Apache,web server,performance monitoring,prediction of resource utilization,non-parametric trend analysis,time series analysis

17. Issues for Nuclear Power Plants Steam Generators

Open Access Boo

Electricity from photovoltaic solar cells: Flat-Plate Solar Array Project final report. Volume VI: Engineering sciences and reliability

The Flat-Plate Solar Array (FSA) Project, funded by the U.S. Government and managed by the Jet Propulsion Laboratory, was formed in 1975 to develop the module/array technology needed to attain widespread terrestrial use of photovoltaics by 1985. To accomplish this, the FSA Project established and managed an Industry, University, and Federal Government Team to perform the needed research and development. This volume of the series of final reports documenting the FSA Project deals with the Project's activities directed at developing the engineering technology base required to achieve modules that meet the functional, safety and reliability requirements of large-scale terrestrial photovoltaic systems applications. These activities included: (1) development of functional, safety, and reliability requirements for such applications; (2) development of the engineering analytical approaches, test techniques, and design solutions required to meet the requirements; (3) synthesis and procurement of candidate designs for test and evaluation; and (4) performance of extensive testing, evaluation, and failure analysis to define design shortfalls and, thus, areas requiring additional research and development. During the life of the FSA Project, these activities were known by and included a variety of evolving organizational titles: Design and Test, Large-Scale Procurements, Engineering, Engineering Sciences, Operations, Module Performance and Failure Analysis, and at the end of the Project, Reliability and Engineering Sciences. This volume provides both a summary of the approach and technical outcome of these activities and provides a complete Bibliography (Appendix A) of the published documentation covering the detailed accomplishments and technologies developed

Time-Dependent Reliability Framework for Durability Design of FRP Composites

The life-cycle performance, durability, and aging characteristics of Fiber Reinforced Polymer (FRP or Structural Composites) have been of keen interest to the engineers engaged in the FRP design, construction, and manufacturing. Unlike conventional construction materials such as steel and concrete, the design guidelines to account for the aging of FRP are somewhat scattered or not available in an approved or consistent format. Loss of strength over time or aging of any structural material should be of concern to engineers as the in-service lifespan of many engineering structures is expected to exceed 100 years. Use of durability strength-reduction factors or factors of safety (aka knock-down factors) is a common way to account for the anticipated in-situ site conditions during the FRP design phase; however, the considerations for FRP service life is often ignored or smeared into knock-down or safety factors. The individual or combined effect of these factors can be arbitrary and can lead to the system’s premature failure (or overdesigns), rendering FRP commercial application unreliable (or cost-prohibitive). Reliability or risk-based approach to the development of strength reduction factors has been successfully applied in modern Load, and Resistance Factor Design codes (e.g., highway bridge design specifications), and an original design framework (i.e., a set of ideas, tools or techniques that forms the basis for filling in the final details) incorporating the time-dependent behavior of FRP composites (e.g., decrease of mechanical strengths with an increase of variability with aging) is proposed. The research presented herein utilizes available natural and accelerated aged test databases to develop a relationship between the probability of failures (using reliability index and confidence intervals to measure reliability) and the desired service life of FRP members. The proposed framework illustrates how to use time-dependent reliability techniques to account for environmental and physical effects. For environmental effects, developing a direct relationship of reliability index with time-dependent durability works better, and for physical effects, indirect inclusion of probability in projecting the time (or cycles) to failure is more effective. The techniques presented in this research, along with three real-life design examples and a case study (i.e., the basis of design), can be readily used by design professionals to ascertain an adequate life cycle performance of FRP while maintaining a consistent component or system-level reliability. The intent is to allow others to refine this knowledge bank and to further the professional FRP design practice in a consistent, rational manner leading to the adaptation of formal codes and specifications. Although the presented data and associated findings primarily refer to pultruded glass fiber reinforced polymers (GFRP) in Vinylester resin, the presented framework can be easily extended to other structural composites. The report entails thorough documentation of published analytical and experimental formulations for various modes of FRP failures due to the typical aging process (e.g., moisture, temperature, alkalinity, and sustained loading, and a combination thereof) along with an associated sampling of durability strength reduction factors. Critical reviews of deterministic and stochastic methods are conducted, and gaps in the current approach to determining durability factors for FRP systems have been identified. A Basis of Design (BOD) for vinylester/polyester-based GFRP in a submerged marine condition using an accelerated test database with illustrative design examples has also been included for a better understanding of the proposed time-dependent reliability-durability concept. Understanding how an FRP system’s reliability changes over its life-span, designers will be able to confidentially choose the most suitable durability strength reduction factors, or factors of safety, that will meet their design’s target service life-span without exceeding strength or service limit states. Since absolute safety is not possible, all FRP members must be designed for a specific acceptable risk of failure. The research illustrates a unique set of techniques for determining FRP composites\u27 durability strength reduction factors, or threshold design values, by integrating durability characteristics developed in the laboratory tests with desired service lives and commonly acceptable risks of failure. Due to the limited availability of complete durability datasets, vast applications, varieties of FRP composites, and the enormity of calibration efforts required, this research proposes additional work to determine the final durability recommendations for the general use of FRP composites. However, this unique research forms a rational tool for designing specific FRP composites that are consistent with other modern design codes, takes into account their target service lives (e.g., 10, 50, 100 years), and bridges the gap between traditional deterministic FRP design methods and state of the art risked-based design philosophies