4097978003 - ME4214 Design for Product Safety Factor of...

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1 ME4214 Design for Product Safety Factor of Safety The factor of safety also known as Safety Factor, is used to provide a design margin over the theoretical design capacity to allow for uncertainty in the design process. The uncertainities include (but not limited to), 1. Uncertainity regarding exact properties of material. For example, the yield strength can only be specified in between a range. 2. Uncertainity regarding the size. The designer has to use the test data to design parts which are much smaller or larger. It is well known that a small part has more strength than a large one of same material. 3. Unceratinity due to machining processes. 4. Uncertainity due to the effect of assembly operations like riveting, welding etc. 5. Uncertainity due to effect of time on strength. Operating environments may cause a gradual deterioration of strength, leading to premature and unpredictable failure of the part. 6. Uncertainity in the nature and type of load applied. 7. Assumptions and appoximations made in the nature of surface conditions of the machine element. The value of the safety factor is related to the lack of confidence in the design process. The simplest interpretation of the Factor of Safety is FoS = Strength of Component / Load on component If a component needs to withstand a load of 100 Newtons and a FoS of 4 is selected then it is designed with strength to support 400 Newtons. .. The selection of the appropriate factor of safety to be used in design of components is essentially a compromise between the associated additional cost and weight and the benefit of increased safety and/or reliability. Generally an increased factor of safety results from a heavier component or a component made from a more exotic material or / and improved component design The factors of safety listed below are based on the yield strength. Factor of Safety Application 1.25 - 1.5 Material properties known in detail. Operating conditions known in detail Loads and resultant stresses and strains known with with high degree of certainty. Material test certificates, proof loading, regular inspection and maintenance. Low weight is important to design. 1.5 - 2
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This note was uploaded on 04/06/2010 for the course ME ME4214 taught by Professor Dr.yuen during the Spring '10 term at NYU Poly.

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4097978003 - ME4214 Design for Product Safety Factor of...

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