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The yield calculation will determine the safety factor until the part starts to deform plastically. The ultimate calculation will determine the safety factor until failure. In brittle materials the yield and ultimate strengths are often so close as to be indistinguishable, so it is usually acceptable to only calculate the ultimate safety factor.
The factor can be as high as 10:1 or 10 to 1, if the equipment poses a risk to a person's life. Working Load Limit (WLL) is the maximum working load designed by the manufacturer. This load represents a force that is much less than that required to make the lifting equipment fail or yield. The WLL is calculated by dividing MBL by a safety factor (SF
The "factor" is sometimes called a factor of safety, although this is technically incorrect because the factor includes allowance for matters such as local stresses and manufacturing imperfections that are not specifically calculated; exceeding the allowable values is not considered to be good practice (i.e. is not "safe").
For most practical engineering uses, is multiplied by a factor of safety to obtain a lower value of the offset yield point. High strength steel and aluminum alloys do not exhibit a yield point, so this offset yield point is used on these materials.
Ultimate bearing capacity is the theoretical maximum pressure which can be supported without failure; allowable bearing capacity is the ultimate bearing capacity divided by a factor of safety. Sometimes, on soft soil sites, large settlements may occur under loaded foundations without actual shear failure occurring; in such cases, the allowable ...
The factor of safety on ultimate tensile strength is to prevent sudden fracture and collapse, which would result in greater economic loss and possible loss of life. An aircraft wing might be designed with a factor of safety of 1.25 on the yield strength of the wing and a factor of safety of 1.5 on its ultimate strength.
Margin of Safety is the common method for design criteria. It is defined MS = P u /P − 1. For example, to achieve a factor of safety of 4, the allowable stress in an AISI 1018 steel component can be calculated to be = / = 440/4 = 110 MPa, or = 110×10 6 N/m 2. Such allowable stresses are also known as "design stresses" or "working stresses".
A clear distinction is made between the ultimate state (US) and the ultimate limit state (ULS). The Ultimate State is a physical situation that involves either excessive deformations leading and approaching collapse of the component under consideration or the structure as a whole, as relevant, or deformations exceeding pre-agreed values.