FailSafe and SafeLife Designs And Factor of （失效保护和SafeLife设计和因子）.pdfVIP

Fail-Safe and Safe-Life Designs And Factor of Safety Factors of Safety (a.k.a. Safety Factor) The factor of safety is usually expressed as a ratio of the “load carrying capability” of the structure to the expected loading. Loading may be static, impact, fatigue, wear, et cetera. The purpose of using a safety factor is to assure that the design does not fail in the event of unexpectedly high loads or the presence of material/design defects. Factors of safety are applied to decrease the probability of failure, or in more positive terms, they increase the probability of success. They are applied in part due to inherent ignorance present in all designs. Ignorance stems from natural variability in materials and manufacturing processes, maintenance, and what the design really experiences in its lifetime. Lower factors of safety may be required if the following are true, larger ones are justified if these are less true: High quality and consistency of materials, manufacturing, maintenance and inspection Good control or knowledge of the actual loads and environment Highly reliable analysis and/or experimental data The commercial airplane business has extremely rigorous control over airplane structures and systems from fabrication and assembly through inspection and maintenance. The environmental effects and maximum loads airplanes experience are also well understood. Extensive fatigue and static testing is conducted on components and systems. Therefore, relatively low factors of safety are applied (around 1.3) even though safety is at stake. The degree of ignorance is not the only element that the engineer should use to determine appropriate factors of safety. The potential harm that failure can produce is also important. If failure would result in a mere inconvenience, then a small factor of safety ma