Determination of yield Strength

Hello Everyone,

  In the previous articles, I told what is yield strength is? Now how to determine it is always a problem. Many a ductile materials get deformed (elastic and plastic). But the boundaries of deformation cannot be strictly defined due to hell lot of reasons. 

   So the Americans devised a plan to find out the yield strength. They define the same as the stress at which a predetermined amount of permanent deformation occurs. To find yield strength, the predetermined amount of permanent strain is set along the strain axis of the graph, to the right of the origin (zero). It is indicated in Figure as Point (D).

 

A straight line is drawn through Point (D) at the same slope as the initial portion of the stress-strain curve. The point of intersection of the new line and the stress-strain curve is projected to the stress axis. The stress value, in pounds per square inch, is the yield strength. It is indicated in Figure 5 as Point 3. This method of plotting is done for the purpose of subtracting the elastic strain from the total strain, leaving the predetermined "permanent offset" as a remainder. When yield strength is reported, the amount of offset used in the determination should be stated. For example, "Yield Strength (at 0.2% offset) = 51,200 psi."

 Notes for the above article is taken from www.engineersedge.com. Please do refer to them for more info

Don't forget to grab a copy of Material Science and Engineering book, which is essential for preparing for AMIE, Material Science.

with warm regards
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