Mechanical design failure models for buckling

This tutorial illustrates design situations where elastic buckling of slender columns and thin plates under compressive loads can result in large deformations, and eventual failure, of the structure. This is a classical example of an overstress failure mechanism, and analytic methods, based on continuum mechanics principles, are presented to design against such failures. Examples illustrate the use of these models in practical design situations in mechanical engineering and electronic packaging applications     

The role of failure analysis in establishing design rules for reliable plastic products

Plastic products can fail in a large variety of modes because of errors in the design, processing and application. The designer must take into account these errors in order to prevent these errors rather than notice them.Without having knowledge of the complex mechanical behaviour of plastics and the structure related properties, adequate design of reliable products is impossible. The designer must also be aware of the specific failure modes, failure causes and failure mechanisms and he can achieve this by failure analysis. Important information from analyses of failed products is the handling of users in ways not foreseen by him. A classification of failed plastic products based on failure causes and failure mechanisms is presented and should be used in carrying out Failure Modes and Effects Analysis.     

Protocol design for scalable and reliable group rekeying

We present the design and specification of a protocol for scalable and reliable group rekeying together with performance evaluation results. The protocol is based upon the use of key trees for secure groups and periodic batch rekeying. At the beginning of each rekey interval, the key server sends a rekey message to all users consisting of encrypted new keys (encryptions, in short) carried in a sequence of packets. We present a scheme for identifying keys, encryptions, and users, and a key assignment algorithm that ensures that the encryptions needed by a user are in the same packet. Our protocol provides reliable delivery of new keys to all users eventually. It also attempts to deliver new keys to all users with a high probability by the end of the rekey interval. For each rekey message, the protocol runs in two steps: a multicast step followed by a unicast step. Proactive forward error correction (FEC) multicast is used to reduce delivery latency. Our experiments show that a small FEC block size can be used to reduce encoding time at the server without increasing server bandwidth overhead. Early transition to unicast, after at most two multicast rounds, further reduces the worst-case delivery latency as well as user bandwidth requirement. The key server adaptively adjusts the proactivity factor based upon past feedback information; our experiments show that the number of NACKs after a multicast round can be effectively controlled around a target number. Throughout the protocol design, we strive to minimize processing and bandwidth requirements for both the key server and users.     

Optimal design of flexible and reliable process systems

In the design and operation of chemical process systems, two categories of uncertainty are important: (1) realization of continuous process parameters (product demands, feedstock qualities, reaction kinetics); and (2) discrete states (typically related to equipment availability). This paper presents a general framework for incorporating both types of uncertainty in process system design. A combined flexibility-reliability index (FRI) is introduced to measure the capability of a process system to cope simultaneously with: (1) (stochastic) parameter variations; and (2) equipment failures, by explicitly accounting for process operational interactions and constraints. A design optimization procedure is then proposed for obtaining flexible, reliable process systems at minimum investment cost and maximum average profit; the potential inclusion of maintenance considerations is briefly discussed     

Ionospheric radio propagation models and predictions--A mini-review

The ionosphere affects radio waves that are propagated within and through it. The magnitude of the effects depends upon the structure of the ionosphere and the frequency of the radio wave. Ionospheric models have been developed over the years to aid in predicting the impact of the ionosphere on ionospheric-dependent telecommunication systems. The status of ionospheric modeling and prediction efforts that are geared toward radio wave propagation system assessment is reviewed.     

On the design of reliable distributed databases

One of the main advantages of distributed databases is their inherent reliability but also associated are problems that must be overcome before it can be achieved. In this paper, we attempt to discuss major design alternatives faced by the designer of a reliable fully replicated distributed database.     

Control plane design for reliable optical networks

The application of an IP-based control plane to optical networks has opened up new opportunities and challenges for network designers. Although much work has been done on standardization of protocols for IP networks, the applicability of these protocols to controlling optical networks and the overall reliability of optical networks needs further investigation. This article provides a detailed discussion of a number of subtle protocol design and implementation issues that were not addressed in early standardization efforts or published papers     

Ignorance, stupidity, and failure [instrumentation design]

This is the first of a series of articles which will present a system's perspective for designing instrumentation and contains heuristics, case studies, and examples. Each article will focus on one part of designing and building electronic devices. I will examine those issues that we often overlook or dismiss when designing instrumentation, and apply a view of the product life cycle. The articles will cover the entire cycle-design, test, manufacture, and service-with such subjects as documentation, the human interface, software, packaging, cooling, and power. In this article I address a few issues common to every design     

First low-cost failure recovery for reliable real-time multimediacommunication

Transmission of multimedia data over a packet-switched network typically requires resource reservation to guarantee an acceptable level of performance (e.g., throughput or delay). In this article we address the problem of how to make such real-time communication reliable. First of all, it is essential to bound the duration of service disruption caused by failures to a reasonably small value. Considering the large volume of multimedia data, minimizing the fault-tolerance overhead is also important. Furthermore, as more applications with different dependability requirements share the same network, the level of dependability for a given application should be “customizable”, depending on the criticality of the application. We first survey the existing approaches, and then present our scheme which is developed in accordance with three design goals: fast failure recovery, low fault-tolerance overhead, and per-connection reliability guarantee. Our scheme provides an integrated solution covering such issues as connection establishment, failure detection, runtime failure recovery, and resource reconfiguration     

Die cracking and reliable die design for flip-chip assemblies

Die cracking during underfill cure or thermal cycling is a cause for concern in flip-chip assemblies. In this work, an integrated process-reliability modeling methodology has been developed to determine the stresses at the backside of the die during underfill cure and subsequent thermal cycling. The predicted die stresses have been compared with experimental data, and excellent agreement is seen between the theoretical predictions and the experimental data. The modeling methodology has been used to understand the effect of material and geometry parameters such as substrate thickness, die thickness, standoff height, interconnect pitch, underfill modulus and coefficient of thermal expansion (CTE), and solder mask CTE on die stresses and thus die cracking. Based on underfill-cure and thermal cycling models for specific cases, the critical flaw size to induce catastrophic die cracking has been calculated using linear-elastic fracture mechanics. Design recommendations, including die thinning and polishing, have been made to reduce the tensile stresses on the backside of the die and thus die cracking     

Computer simulation and analysis techniques for reliable circuit design

The trend toward microelectronics and higher system sophistication requires the development of more advanced simulation and performance prediction techniques. In most large electronic systems the bulk of the total circuitry (60–80 per cent) is made up of multiple usage of relatively few basic standard circuits. The remainder is generally composed of special circuitry unique to that particular system's characteristics. In view of the large quantities of the basic circuits which are used over and over again, it becomes important from the standpoint of reliability, specification setting, and production control to subject these circuits to the most stringent evaluation possible during the design phase. This can be accomplished by supplementing the test and evaluation phase with extensive computer simulation and performance prediction effort. Fortunately, modern high-speed digital computers permit this to be done in an economic manner.North American/Autonetics has designed a number of special computer simulation and performance prediction programmes. This article will discuss two of the more frequently used programmes; namely, a programme implementing the Worst-Case method and another which implements the Monte Carlo method. In addition, a third approach will be described which combines both methods. These programmes require mathematical models for simulation of the electronic components. The models, primarily the diode and transistor mathematical models, will be presented in detail. Special emphasis is given to the non-linear model characteristics required to closely duplicate physical behaviour.     

Applicability of Walfisch-type urban propagation models

The applicability of different propagation models based on the Walfisch-Bertoni or the Walfisch-Ikegami formulations is studied. When this type of model is applied to real urban cells, large areas with errors often appear. The origin of some errors and a proposal to improve the applicability of Walfisch-type models, based on a measurement campaign, are described     

ACTS propagation experiment: experiment design, calibration, anddata preparation and archival

The National Aeronautics and Space Administration Advanced Communications Technology Satellite (ACTS) propagation experiment was designed to obtain slant-path attenuation statistics for locations within the United States and Canada for use in the design of low-margin Ka-band satellite communication systems. Experimenters at seven different locations have collected propagation data for move than two years. The propagation terminals used for the experiment were identical. A single preprocessing program was used by the experimenters to provide for automatic calibration, generation of attenuation histograms, and data archival. In this paper, the calibration procedures are described mid estimates given for measurement accuracy. ACTS provided beacons at 20.2 and 27.5 GHz for use in making attenuation measurements. In addition to the beacon receivers, each ACTS propagation terminal has two total power radiometers with center frequencies at the beacon frequencies. The radiometers are used to establish the beacon signal reference levels needed for calculating beacon attenuation values. For the combined radiometer and beacon measurement system, the attenuation measurement error was less than a maximum of 1.0 dB and was generally less than 0.3 dB. The dynamic range for attenuation measurement varied from site to site depending on location relative to the peak of the satellite beacon antenna pattern. For locations within the continental United States, the dynamic range was better than 20 dB     

Early integration of safety to the mechatronic system design process by the functional failure identification and propagation framework

The research goal of this paper is to introduce a risk analysis methodology that can be applied at the early concept design phase, whose purpose is to identify fault propagation paths that cross disciplinary boundaries, and determine the combined impact of several faults in software-based automation subsystems, electric subsystems and mechanical subsystems. Specifically, the Functional Failure Identification and Propagation (FFIP) analysis framework is proposed to perform a simulation-based analysis of functional failure propagation. The focus is on risk assessment, the earliest activities of the safety process, in which hazards are identified and safety requirements are derived. It is argued that current risk assessment methods are not sufficient for concurrent integration of the safety process to the design process of a complex mechatronic system. In order to facilitate the integration of risk assessment to such systems at the earliest design stages, the design is expressed with syntax and semantics that is able to describe the propagation of failures throughout the system and especially across the boundaries of the mechatronic domains. A boiling water nuclear reactor (limited to the reactor core and steam outlets) is used as a case study. The results demonstrate the capability to handle several fault propagation paths in one scenario for hazard identification at the early, functional, design stage. Specifically, it is shown that FFIP is able to identify fault propagation paths that cross disciplinary boundaries, and which in turn is able to determine the combined impact of several faults in software-based automation subsystems, electric subsystems and mechanical subsystems. The impact is expressed in degradation or loss of safety related functions.     

一种电台中FPGA的可靠初始化逻辑设计

在机载通信领域,由于飞机体积、重量及功耗等要求,往往需要在一个独立电台设备上实现多种通信模式,同时受限于电台的成本、功耗等因素,通常各种通信模式功能依靠FPGA的动态加载来实现。实际工程中发现,当FPGA动态加载时,由于各版本的加载时间、复位管理、时钟管理、接口时序等不一致,非常容易出现偶发的加载后功能异常,此类问题现象随机,极难定位,很容易耗费大量的人力、物力及时间。为解决上述矛盾,提出一种适合在电台中使用的FPGA初始化逻辑设计,保证不同版本的FPGA加载后能稳定工作,提升电台工作的可靠性与稳定性。实践表明,该方法简单、可靠,具有非常强的工程推广意义。     

一种无线代码可靠更新系统的研究与设计

传感节点投入运行后,遇到软件错误或功能升级都需要更新节点的程序,但是传统的现场烧写方式比较繁琐。为了解决该问题,以ARM Cortex M0+内核的MKW01Z128无线射频芯片为基础,设计了一套成本低、实时性好、可靠性高的无线代码更新系统。该系统采用串口和无线射频相结合的通信技术,对片上FLASH进行合理划分,设计了Bootloader对传感节点程序进行代码更新,同时增加了通信帧格式和丢帧重传机制来确保数据传输的可靠性。对更新系统的性能进行了测试,测试结果表明该系统能可靠地实现空旷环境下200 m内的无线代码更新,具有较好的应用前景。