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Technical Data

Metallurgical Terms


An increase of strain without increase in stress. In soft steel yielding takes place suddenly giving upper and lower yield stresses. Upper yield stress is the stress at which yield begins and lower yield stress is the lowest stress at which yield proceeds. The onset of yielding may be indicated by measuring with dividers or by hesitation in the progress of the pointer indicating the load. Some materials do not show clearly defined yielding; for such materials the proof stress should be measured.

Young’s Modulus.

(Modulus of Elasticity). The ratio, within the limits of elasticity, of the stress to the corresponding strain, i.e., the stress divided by the resulting strain. Assuming a material to be perfectly elastic, the modulus of elasticity would be the stress applied to extend the test piece to double its length. For steel, Young’s Modulus is of the order of 200kN/mm2 (13,000 tons per square inch), and is only very slightly affected by composition and heat treatment.