The Security factor ( FoS ), also known as (and used interchangeably) security factor ( SF ), is a term that describes the load carrying capacity of a system beyond the expected or actual charge. Basically, the security factor is how strong the system is than it takes for the intended load. Security factors are often calculated using detailed analysis because comprehensive testing is impractical on many projects, such as bridges and buildings, but the ability of the structure to carry the load should be determined with reasonable accuracy.
Many systems are deliberately made much more powerful than required for normal use to allow for emergency situations, unexpected loads, misuse, or degradation (reliability).
Video Factor of safety
Definisi
There are two definitions for the safety factor: One as the ratio of absolute strength (structural capacity) to the actual applied load, this is a measure of the reliability of a particular design. Another use of FoS is the constant value established by law, standard, specification, contract or custom which must be confirmed or exceeded by the structure.
The first usage (calculated value) is commonly referred to as the security factor or, to explicitly, the realized realization factor realized . Second use (required value) as design factor , safety design factor or required security factor . The realized safety factor must be greater than the required safety design factor . However, among the various industries and the use of technical groups are inconsistent and confusing, it is important to know what definitions are being used. The cause of much of the confusion is that various reference books and standard institutions use different definitions of security and terms. Design codes and textbooks of structural and mechanical engineering often use "Factor of Safety" to mean the total fraction of structural capability than is required and aware of safety factors (first use). Many Power Material books use the "Factor of Safety" as a constant value that is intended as a minimum target for design (second use).
Maps Factor of safety
Calculation
There are several ways to compare the security factor for the structure. All the different calculations basically measure the same thing: how much extra load beyond what the intended structure would actually take (or needed to hold). The difference between methods is the way in which values ​​are calculated and compared. The value of a security factor can be considered as a standard way to compare strength and reliability between systems.
The use of security factors does not mean that the goods, structures, or designs are "safe". A lot of quality assurance, engineering design, manufacturing, installation, and end-use factors can influence whether something is safe or not in certain situations.
Design factor and security factor
The difference between the security factor and the design factor (design safety factor) is as follows: The security factor is how much the part is designed to actually survive (first "use" from above). The design factor is what items need to survive ("second" use). Design factors are defined for applications (generally provided in advance and often governed by regulatory or policy codes) and not actual calculations, the security factor is the maximum power ratio for the load intended for the actual item being designed.
- Design loads become the maximum load that the service has to look at.
With this definition, the structure with the exact FOS 1 will only support the design load and nothing more. Any additional load will cause the structure to fail. The structure with FOS 2 will fail at twice the design load.
Margin of safety
Many government and industry agencies (such as aerospace) require the use of margin of safety (MoS or MS ) to illustrate the ratio of structural strength to requirements. There are two separate definitions for the safety margin so it is necessary to be careful to determine which one is used for the given application. One use of M.S. is as a measure of capacity as FoS. Other uses of M.S. is as a satisfactory measure of design requirements (verification requirements). Margin of safety can be conceptualized (together with the backup factor described below) to represent how much total capacity the structure is held "in reserve" during loading.
M.S. as a measure of structural capacity: The definition of safety margins commonly seen in textbooks basically says that if the piece is loaded to the maximum load that should have been seen in the service, how much more the same power can do it survive before it fails. Consequently, this is a measure of excess capacity. If the margin is 0, the section will not take additional load before it fails, otherwise the negative part will fail before it reaches its design load in the service. If the margin is 1, it can withstand one additional load of the same power with the maximum load designed to support (ie twice the design load).
M.S. as a measure of requirements verification: Many agencies and organizations such as NASA and AIAA set safety limits including design factors; in other words, safety margins are calculated after applying design factors. In the case of margin 0, the part is exactly on the mandatory power (the security factor will be the same as the design factor). If there is a part with the required design factor 3 and margin 1, that part will have a security factor of 6 (capable of supporting two loads equal to design factor 3, supporting six times the design load before failure). Margin 0 means the passage will pass by a security factor 3. If the margin is less than 0 in this definition, even though that part may not necessarily fail, the design requirement has not been met. Convenience of this usage is that for all applications, the margin 0 or higher passes, one does not need to know the details of the application or compare with the requirements, just glance at the margin calculation telling whether the design passed or not. This is useful for monitoring and reviewing projects with various integrated components, since different components may have different design factors involved and margin calculations help prevent confusion.
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For successful designs, the Reflected Safety Factor must always be the same or exceed the Safety Design Factor so that the Safety Limit is greater than or equal to zero. The Margin of Safety is sometimes, but rarely, used as a percentage, ie 0.50 M.S equivalent to 50% M.S. When a design meets the test it is said to have a "positive margin," and, conversely, a "negative margin" when it is not.
In the field of Nuclear Safety (as applied to US government-owned facilities), the Margin of Safety has been defined as an irreducible quantity without inspection by the controlling government office. The US Department of Energy issues DOE G 424.1-1, "Implementation Guide for Use in Handling Unwanted Security Questions Requirements" as a guide to determine how to identify and determine whether the safety margin will be reduced by the proposed changes. This guide develops and implements the concept of qualitative safety margins that may not be explicit or quantifiable, but may be conceptually evaluated to determine whether an increase or decrease will occur with the proposed changes. This approach becomes important when examining designs with large or undefined margins (historic) and that rely on 'soft' controls such as program boundaries or requirements. The US nuclear industry used the same concept in evaluating planned changes until 2001, when 10 CFR 50.59 was revised to capture and apply information available in risk-specific analysis of facilities and other quantitative risk management tools.
Backup factor
The most commonly used strength measure in Europe is the Backup Factor (RF) . With applied strengths and loads expressed in the same unit, the Backup Factor is defined as:
RF = Strength of Evidence/Load of Evidence RF = Ultimate Strength/Main Load
The load applied has any factor, including the security factor applied.
Results and end calculations
For ductile materials (eg most metals), it is often necessary that safety factors be checked for final results and strengths. The calculation of the results will determine the safety factor until the part begins to change shape in plastic. The final calculation will determine the safety factor until the failure. On fragile material, these values ​​are often so close that they can not be distinguished, so it is usually acceptable to only count the final security factor.
Select design factor
Appropriate design factors are based on a number of considerations, such as prediction accuracy on forced loads, strength, wear and tear, and environmental impacts to which products will be exposed in service; consequence of failure of technique; and excessive engineering component costs to achieve that security factor. For example, a failed component can result in substantial financial loss, serious injury, or death can use four or more security factors (often ten). Non-critical components generally may have two design factors. Risk analysis, failure modes and effects analysis, and other tools are commonly used. Design factors for specific applications are often mandated by law, policy, or industry standards.
Buildings typically use a security factor of 2.0 for each structural member. The value for the building is relatively low because the load is well understood and most of the structure is excessive. Pressure vessels use 3.5 to 4.0, cars use 3.0, and airplanes and spacecraft use 1.2 to 3.0 depending on applications and materials. Ductile, metallic materials tend to use lower values ​​while fragile materials use higher values. The aerospace engineering field generally uses a lower design factor due to the costs associated with high structural weight (ie a plane with an overall safety factor of 5 might be too heavy to get off the ground). This low design factor is why aerospace components and materials are subject to very stringent quality control and strict preventive maintenance schedules to help ensure reliability. The normally applied Safety factor is 1.5, but for the pressurized aircraft it is 2.0, and for the main landing structure is often 1.25.
In some cases it is impractical or impossible for parts to meet "standard" design factors. Penalties (mass or otherwise) to meet the requirements will prevent the system from becoming feasible (as in the case of aircraft or spacecraft). In this case, it is sometimes specified to allow components to meet lower than normal security factors, often referred to as "exempt" requirements. Doing this is often accompanied by additional detailed analysis or verification of quality control to ensure that the part will function as intended, as it will be loaded closer to its limit.
For cyclical, repetitive, or fluctuating loading, it is important to consider the possibility of metal fatigue when choosing a safety factor. Cyclic loads below the yield strength of the material can cause failure if repeated through an adequate cycle.
See also
- Restrict country design
- Redundancy (total quality management)
- Probabilistic design
- Sacrifice section
- Statistical interference
- Verification and validation
Note
Further reading
- Lalanne, C., Development Specs - Ed 2. , ISTE-Wiley, 2009
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Source of the article : Wikipedia
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