Offset yield stress

i. When a material such as aluminum does not have an obvious yield point and yet undergoes large strains after the proportional limit is exceeded

ii. Offset Method - A straight line is drawn on the stress-strain diagram parallel to the initial linear part of the curve (Fig. 1-14) but offset by some standard strain, such as 0.002 (or 0.2%). The intersection of the offset line and the stress-strain curve (point A in the figure) defines the yield stress.

b. Rubber maintains a linear relationship between stress and strain up to relatively large strains

i. Although rubber exhibits very large strains, it is not a ductile material because the strains are not permanent. It is called elastic material