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allowable stress – Or permissible stress. typically the average stress level experienced during operation. Equal to the allowable load divided by the area.
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alternating stress – Is a stress that behaves according to a cyclic loading state.
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clearance fit – One having limits of size so prescribed that a clearance always results when mating parts are assembled. A fit in which there is clearance in the assembly for all tolerance conditions.
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factor of safety – Same as safety factor.
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interference fit – Limits are so prescribed that interference always results on assembly. A fit in which there is interference for all tolerance conditions.
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loss-of-function parameter – Say a load at 1000lb is causing failure. but that load is known within 10%. Therefore, the load causing failure can actually range from 900lb to 1100lb. So to be safe, the highest possible load is taken into account, which would be 1100lb. But the loss-of-function parameter is actually 1 over 1 minus the variance, where the variance is 10%. Which would then be 1/(1 – 0.1) = 1.11111. The loss-of-function parameter is used in conjunction with the maximum allowable parameter to get the design factor. The parameter part of the loss-of-function parameter can be a number of things, such as load or torque. Then loss-of-function load or loss-of-function torque would be obtained.
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maximum allowable parameter – Say a load at 1000lb is causing failure and the maximum load on the structure is known with an uncertainty of 15%. The maximum allowable parameter is actually 1 over 1 plus the variance, where the variance is 15%. Which would then be 1/(1 + 0.15) = 0.8696. The maximum allowable parameter is used in conjunction with the loss-of-function parameter to get the design factor. The parameter part of the maximum allowable parameter can be a number of things, such as load or torque. Then maximum allowable load or maximum allowable torque would be obtained.
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proof load – The maximum load that a bolt can withstand without acquiring a permanent set.
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proof strength – The proof strength is the quotient of the proof load and the tensile-stress area. With respect to the offset yield method, proof strength is the nominal stress corresponding to an offset of 0.01 percent. Stated another way, the proof strength corresponds to 0.0001 in permanent set in the fastener (first measurable deviation from elastic behavior). This value is very close to the proportional limit.
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resilience - The ability of a material to absorb energy in the elastic range. Also see: Modulus of Resilience.
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rigidity - The property of a material which indicates its rigidity is its modulus of elasticity.
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toughness - The ability of a material to absorb energy prior to fracture. The capacity of a material to absorb energy without failing. The toughness of a material is related to its ductility as well as to its ultimate strength. The capacity of a structure to withstand an impact load depends upon the toughness of the material used. Toughness is usually characterized by a combination of strength and ductility in the material. A material with good toughness implies good yield strength, good impact strength, good tear strength, and good puncture resistance. Also see: Modulus of Toughness.
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transition fit - A fit for applications where accuracy of location is important, but a small amount of either clearance or interference is permissible.
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ultimate stress - Same as ultimate strength.
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