Unload/Reload Behavior  
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The figure on the right shows a test specimen fixed between upper and lower grips. The knife edges of an extensometer contact the specimen at two points. The specimen is shown fractured in the middle when the load is 13,620 pounds and the elongation reaches 0.4764 inches. A graph is shown on the left and a caption above the graph reads: The unload reload behavior seen here is a very useful characteristic particularly for metals. One technique for increasing the strength of a material is a process of stretching and relaxing called work hardening. The vertical axis ranges from 0 to 16,000 pounds and the horizontal axis ranges from 0 to 0.5 inches. The graph starts from the bottom left at the origin, goes up and to the right with very high steepness till the point (0.025, 12,000). The graph then goes up and to the right with constant steepness till (0.25, 14,200). The graph then goes down and to the right with approximately constant steepness till (0.4764, 13,620). A straight line is drawn between the points (0.0799, 0) and (0.0911, 11,860).