Component external failure modes

Component external failure modes This is where a component may physically fail in such a way to have negative impact on its surrounding. Examples include leakage, overheat, burst, etc. These data may be obtained from the FMEA (see Chapter 5). 

ID Component in zone External failure mode(s) Intrinsic hazards Systemic vulnerabilities Effect on the aircraft Corrective/preventative action and/or mitigations... 

This report provides an aging assessment of electric motors and was conducted under the auspices of the USNRC NPAR. Pertinent failure-related information was derived from LERs, IPRDS, NPRDS, and NPE including failure modes, mechanisms, and causes for motor problems. In addition, motor design and materials of construction were reviewed to identify age-sensitive components. The study included consideration of the seismic susceptibility of age-degraded motor components to externally-induced vibrational effects. 

A systems hazards analysis (SHA) is a systematic and comprehensive search for and evaluation of all significant failure modes of facility systems components that can be identified by an experienced team. The hazards assessment often includes failure modes and effects analysis, fault tree analysis, event tree analysis, and hazards and operability studies. Generally, the SHA does not include external factors (e.g., natural disasters) or an integrated assessment of systems interactions. However, the tools of SHA are valuable for examining the causes and the effects of chemical events. They provide the basis for the integrated analysis known as quantitative risk assessment. For an example SHA see the TOCDF Functional Analysis Workbook (U.S. Army, 1993-1995). 

The bonded repair can take the form of either an external patch, internal patch or a flush scarf or stepped repair as described in M1L-HDBK-17-3F 3. The internal patch usually is not an option due to accessibility. For simplicity the external lap is commonly used on internal component repairs such as bulkheads and inner skins. To maintain aerodynamic cleanliness and to minimise moment-induced failure modes, however, the flush scarf repair is preferred [1]. Furthermore, on composite control surfaces (flaps, ailerons etc.) which have critical mass balance limitations, the lighter weight flush scarf repair is often the only acceptable means of repair, but a high skill level and longer time is required to prepare the damaged area for repair. 

Essentially, the problem of adiabatic leak is mitigated by the presence of constraints, whether in the form of steric hindrance, external forces, or in reduction of dimensionality (for example, simulations in torsion space). In simulations of proposed nanomachines, for example, rigid body dynamics is sometimes applied to components or substructures in order to make the entire nanostructure more rigid. All of this suggests that the prediction of failure modes in some nanomachine designs due strictly to vibrational motion is overly pessimistic. However, this does not by any means minimize concerns such as the difficulty of building desired nanostructures, chemical reactivity. 

The Primary Secondary-Command (P-S-C) concept is to concentrate the analyst on specific causal factors. This concept is based on components having three ways of failing, the primary failure mode (inherent failure), secondary failure mode (external influence) or a command path fault (function provided when not required). All of these failure modes should he considered to ensure nothing is overlooked. 

It should be noted that in system safety and FTA, a secondary failure is typically a dependent failure mode. A secondary failure occurs when the failure of an item is caused by an external source or force, such as radio frequency (RF) energy and heat. For example, when excessive heat on a transistor from an external source causes the transistor to fail, this is referred to as a secondary type failure of the transistor (vs. a primary inherent failure mode). Conditional probability should be used on secondary failures because it is dependency situation however, in FTA, the conditional aspect is often ignored and the failure event is simply treated as an independent failure and is assigned an appropriate failure that considers both the component failure and the external event failure rate. The mathematical error produced by this approach is typically minimal. 

A component failure is an independent failure is when the failure is solely due to an inherent failure mode of the component, and is not caused by the failure of a different component or an external event. In probability theory, events are independent when the outcome of one event does not influence the... 

The analysis is dedicated to software components. The postulated failures of these components are supposed to be caused by software faults present in the components, triggered by external conditions. In the example, the status of the input boards (hardware ok or non-ok) is one of these conditions. Other possible conditions may be sensors input values, operator interfaces, operating modes. 

In order to use the PRISM probabilistic model checker, we have to precisely define the state of a component as a finite state model note that FPTC abstracts away from internal state and represents failures as observable external behaviour. The state of a component can be formally defined by the modes of its input and output ports because they can be observed and measured directly. 

One method of preventing the catastrophic failure of components by chloride SCO would be the use of austenitic stainless steel as an internal cladding. The highly branched mode of any cracking would effectively prevent the development of stress raisers. Carbon or low alloy steel base metal would not be susceptible to cracking in chloride solutions, but some localized corrosion may occur. This type of construction would also provide resistance to cracking when chlorides are hable to contact the outside of the components, as in external insulation, for example. 

---