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Tensile Stress Strain Curve
Plotting tensile stress-strain curves depicts the entire behavior of a sample as it is loaded in tension from the onset of the load to the final failure of the sample.
The sample stress (psi, MPa) is equal to the load divided by the surface area to which the load is applied; sample strain is equal to the change in the sample’s length divided by the original length. Initially the loading of the sample takes place in the linear elastic region of the curve in which the sample behaves according to Hooke’s law where the ratio of stress to strain remains constant. In this region of loading the information needed to determine both the modulus of elasticity and rigidity as well as Poisson’s ratio is contained. Once the material reaches its yield point, at which the yield limit and strength may be determined, it will no longer return to its original shape when unloaded and switches from the elastic deformation region to the plastic deformation region of loading. This region contains the information needed to determine the ultimate tensile strength of the material. After this the material quickly enters the region of necking, where the gage length begins to narrow, and then finally fractures at which the test is ended.
Depending on the whether or not the material behaves in a brittle or ductile manner the fracturing may occur very quickly without much necking or a relatively long period of time in which noticeable necking occurs.
