Final answer:
A stress-strain curve for metal demonstrates the linear, elastic behavior followed by plastic deformation, where the material becomes permanently deformed under increasing load. The curve begins with a linear section representing a proportional increase of stress with strain, followed by a nonlinear section where plastic deformation occurs, and the material does not fully recover its original shape when the load is removed.
Step-by-step explanation:
To graph the relationship between stress and strain for a metal, you would plot a stress-strain curve that shows how a metal reacts to forces applied to it. Initially, when the load is gradually increased, the relationship between stress and strain is linear, as indicated by the red line in the diagram. The point where this linearity ends is called the linearity limit (point H). Beyond this point, the curve enters a nonlinear, yet still elastic region up to the elasticity limit (point E), where the material will return to its original shape upon unloading. However, as the stress increases beyond the elasticity limit, the metal will undergo plastic deformation, depicted by the curve bending downwards indicating that the metal gets easier to deform. When the load is eventually removed at any point beyond E, for example at point P, the material will not return to its original shape, and permanent deformation can be observed where the green recovery line intersects the horizontal axis.
The reason for plastic deformation is that microscopic mechanisms within the materials govern its plasticity, which varies from one material to another. This part of the stress-strain curve indicates that the material has been stretched beyond its elastic capabilities. In engineering and construction, such properties of materials are significant for assessing their performance under various loads and conditions. Young's modulus, which represents the stiffness of a material in its linear, elastic region, is an example of an elastic modulus used in industry.