... engineering stress and the extension is converted to engineering strain. These can be defined as, Engineering Stress = ..........equation 01 Engineering Strain = ..........equation 02 Where, F - Force applied - Original cross sectional area l - Length of the specimen after a force F is applied - Original length of the specimen The slope of the stress - strain curve in the elastic region is defined as the Young's modulus (E). And, ..........equation 03 The stress at the point on a stress - strain curve where the plastic deformation becomes noticeable is called the Yield Stress. But some materials do not show a well-defined Yield point. Hence a the term "Proof stress" is used, which is defined as the nominal stress that is just sufficient to produce a non-proportional extension, equal to a specified percentage (usually 0.1% is used) of the original gauge length. (Please refer to figure 03) 0.1% proof stress = The stress obtained at the highest applied force is called the tensile ...

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