The plastic moment for a given section will always be larger than the yield moment (the bending moment at which the first part of the sections reaches the yield stress). The plastic moment for a rectangular section can be calculated with the following formula: This is of little significance in structural mechanics as the deflection prior to this occurring is considered to be an earlier failure point in the member. In practice most materials are work-hardened resulting in increased stiffness and moment resistance until the material fails. This is theoretically the maximum bending moment that the section can resist - when this point is reached a plastic hinge is formed and any load beyond this point will result in theoretically infinite plastic deformation. It is defined as the moment at which the entire cross section has reached its yield stress. In structural engineering, the plastic moment (M p) is a property of a structural section. The factor of safety, FS, is calculated as: where actual is the calculated stress in the structure, and limit is a maximum stress limit, typically a material strength such as the yield strength (S ty). JSTOR ( December 2009) ( Learn how and when to remove this template message) The yield strength of the material is commonly chosen as the strength limit to which the calculated stresses are compared.Unsourced material may be challenged and removed. Please help improve this article by adding citations to reliable sources.
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