Failure modes, definition

Fig. 6. A fault tree for the pumped storage example of Figure 5. For a real system the tank and pump failures would be more precisely defined, or set as intermediate events having further definition by subsequent basic events and more detailed failure modes.

Before setting about the task of developing such a model, the product development process requires definition along with an indication of its key stages, this is so the appropriate tools and techniques can be applied (Booker et al., 1997). In the approach presented here in Figure 5.11, the product development phases are activities generally defined in the automotive industry (Clark and Fujimoto, 1991). QFD Phase 1 is used to understand and quantify the importance of customer needs and requirements, and to support the definition of product and process requirements. The FMEA process is used to explore any potential failure modes, their likely Occurrence, Severity and Detectability. DFA/DFM techniques are used to minimize part count, facilitate ease of assembly and project component manufacturing and assembly costs, and are primarily aimed at cost reduction. 

A uniform definition of a failure and a method of classifying failures is essential if data from different sources are to be compared. The anatomy of a failure includes the initiating or root cause of a failure that is propagated by contributory causes and results in a failure mode—the effect by which a failure occurs or is observed. Modes include failure to operate, no output, failure to alarm on demand. The end result of a failure sequence is the failure effect, such as no fluid is pumped to the absorber, or a tank overflows. As discussed in Appendix A of IEEE Std. 500-1984, only the equipment failure mode is relevant for data that are needed in a CPQRA. The failure model used in this book is based upon those in the IEEE publication and IPRDS. ... 

Opening segments of the IP2 PRA data analysis section describe the definitions of terms and concepts employed, the assumptions made, and limitations recognized during the data base construction. A set of 39 plant-specific component failure mode summaries established the basis for component service hour determinations, the number of failures, and the test data source for each failure mode given for each component. Generic data from WASH-1400, IEEE Std 500, and the LER data summaries on valves, pumps, and diesels were combined with plant-specific failure data to produce "updated" failure information. All the IP2 specialized component hardware failure data, both generic and updated, are contained in Table 1.5.1-4 (IP3 1.6.1-4). This table contains (by system, component, and failure mode) plant-specific data on the number of failures and service hours or demands. For some components, it was determined that specifications of the system was warranted because of its impact on the data values. 

Due to such subtleties, the need to develop well-defined basic events, failure modes, and equipment boundaries prior to data encoding cannot be overemphasized. Familiarity with failure definitions and failure severities will be extremely helpful to the analyst. Figures 2.1 and 2.2, reprinted from IEEE Std. 500-19845, list a large number of failure modes by failure severity and may help encode failures. IPRDS also contains helpful information on failure encoding. Information on some equipment boundaries may be found in the Data Tables in Section 5.5. 

Process step definition Functional performance criteria Functional failure mode analysis Failure mode recovery requirements Informational requirements Information structures Legacy system interfaces Data entry range Data retention requirements Human/machine interface requirements Screen specifications Data entry modes Refresh rates Data migration... 

Developing an FMEA is a DFSS team effort. The numerical ratings for severity, detectability and frequency must be agreed on by the team, so that everyone agrees on the definitions. Otherwise one team member may consider the effect to be mild, another moderate, and yet another severe. As with QFD, the numbers here are semi quantitative, and round table team discussions help to achieve a more accurate picture of the true risks associated with the specific failure modes. If possible, the team should formalize the rating system as much as possible. A sample of such a formalized scale is given in Fig. 14. 

Strain-controlled applications. In these applications, a definite strain is applied. The failure mode for the part may be fracture from exceeding the maximum elongation for the material, permanent deformation from exceeding the yield point, or fracture over time from strain close to the maximum elongation and subsequent creep rupture. 

FYom the multitude of intricate corrosion processes in the presence of mechanical action (friction, erosion, vibration, cavitation, fretting and so on) it is justified to touch upon corrosion types joined under a single failure mode induced by mechanical stresses. These are the stresses that govern the corrosion wear rate of metals during friction. Such processes are usually called corrosion stress-induced cracking in the case that the mechanical action is effective only in one definite direction, or otherwise termed corrosion fatigue in the case that compressive and tensile stresses alternate within cycles. In spite of the differences between the appearance of these corrosion types, they have much in common, e.g. fundamental mechanisms, the causes, and they overlap to a certain degree [19]. 

Definitions of software failure modes in the context of SPINLINE3 software... 

In this paper, we have presented this software FMEA experienee including adaptation of the principles of FMEA to analyze a software program choice of a block of instmction (BI) approach to identify the components to analyze definition of the software failure modes associated with the Bis examples of the analyses performed on the SPINLINE3 Operational System Software feedback of experience... 

Another common technique for showing probability combinations is called a fault tree. This technique begins with the definition of an "undesirable event," usually a system failure of some type. The analyst continues by identifying all events and combinations of events that result in the identified imdesirable event. The fault tree is therefore quite useful when modeling failures in a specific failure mode. These different failure... 

There are a range of failure modes which affect large ranges of valve designs due to shared features. Care must be taken in the analysis of these failure modes. This limits the definition of a particular design as the "best" SIS valve. The dangerous failure modes can be simplified to two basic... 

Fig. 3.4 is not definitive, bnt shows how some of the assessment tools (in SAE ARP4761 and the remaining chapters of this book) interrelate. For instance, an item-level Failnre Modes and Effects Analysis (FMEA) is performed and is summarized into the Failure Modes and Effects Snmmary (FMES) to support the failure rates of the failure modes considered in the item FTA. The system FMEA is summarized into the system FMES to snpport the failnre rates of the failure modes considered in the system FTA. The system is reviewed via FTA to identify the failure modes and probabilities nsed in the aircraft FTA. The aircraft FTA is used to establish compliance with the aircraft-level failnre conditions and probabilities described by the aircraft FHA. 

Evaluate the effect of the failure mode on the system level under consideration. This process is facilitated by the definition of the function of the component. 

Complex system A system is complex when its operation, failure modes or failure effects are difficult to comprehend without the aid of analytical methods or structured assessment methods. FMEA and ETA are examples of such structured assessment methods. Increased system complexity is often caused by such items as sophisticated components and multiple interrelationships. For example, for these types of systems, a portion of the comphance may be shown by the use of DALs such as by processes in RTCA/ DO-178B or RTCA/DO-254 or equivalent. See the definitions for conventional and simple for more information. 

The learning process of the net has followed several steps. The first one was the definition of the system variables it meant to decide which variables described the system behavior from the diagnostic and prognostic point of view. So some field measures have been excluded from the model while only the sensors measures that can be considered the effects of a failure modes has been introduced. Moreover, the model has been enriched by a set of variables with prognostic and diagnostic issues. So the variables failure modes and system prognosis have been modeled by some nodes that represent the support elements for the condition based maintenance. 

According to EC, 2009, a safety-related system is regarded as low complexity if the failure modes of each individual component are well defined, and the behaviour of the system under fault conditions can be completely determined. This paper focuses on SIS to which this definition does not apply. 

As a more abstract use case one might consider to model only the launch use case that includes by definition programming, launch and initiation. This is also implemented in some systems. But this abstract view does not allow modelling the failure modes of non initiation and unintended initiation. Therefore such an abstract use case view, which only takes the intended... 

Definition of failure mode non-achievement of the Objective / ( worst case )... 

The second analysis is the FMEA, this is the bottom-up analysis. First, the failure modes of all the transmitter blocks are defined. Each of these modes is related to one or more effects on the transmitter functionality. Once the modes and effects are listed, the last step is the definition of the solution to mitigate the effect of the possible failures. These conclusions can result in changes in the transceiver design or changes in other components of the system, as DPU. Table 1 shows the summary of the results of the process where the most significant cases are presented. 

Definition of Failure Modes Mechanisms of Bond Failure... 

The first three chapters discuss definitions, adhesion theories, surface characterization and analysis, surface energy measurement methods, adhesion mechanism, failure modes, and surface treatment of materials. 

Step 5 is concerned with developing a list of crihcal items. The list is prepared to facilitate the communication of important analysis results, generally to the management personnel, and it contains information on areas such as item identification, concise statement of failure mode, criticality classification, and degree of loss effect. Finally, Step 6 is concerned with documenting the analysis. This step is equivalent in importance to all the previous steps (i.e., Step 1 to Step 5) because poor documentation can result in ineffectiveness of the FMEA process. The FMEA report includes items such as system description, ground rules, system definition, failure modes and their effects, and critical items list. 

DEFINITION— Failure Mode and Effects Analysis or other accepted analytic methodology to increase prospectively the safety of high-risk procedures. 

The often used FPL etdi of an aluminum-lithium alloy bonded with polysulfone leads to interfacial (at the metal oxide/polymer interface) failure (38) which is a surprisingly uncommon type of failure. The results leading to this assignment are shown as XPS C Is and O Is narrow scan spectra in Figure 15. This definitive assignment of failure mode is based on the fact that one failure surfece has an oi gen photopeak similar to the pretreated adherend before bonding and the other failure surfece has an 0 gen photopeak similar to the adhesive. 

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