Proportional Limit  
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The graph plots stress in p s i versus the strain in inch per inch. The vertical axis ranges from 0 to 80,000 p s i and the horizontal axis ranges from 0 to 0.25. The graph starts from the bottom left of the viewing window at the origin, goes up and to the right with very high steepness till the point (0.01, 60,000). The graph then goes up and to the right with constant steepness till (0.125, 74,000). The graph then goes down and to the right with approximately constant steepness till (0.24, 68,000). All values estimated.

We will initially focus our attention on the straight-line portion of the stress-strain curve.