 ## Analyzing a Stress-Strain Curve

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• 2022 College Interns
• Tensile strength is an important physical measurement that represents the maximum amount of force a specific material can undergo before fracturing/ breakage. Tensile strain is another important measurement that represents how ductile a material is, or how much a material can be stretched. Although there is typically just one graph generated, there are many different components to these graphs to keep in mind that tell us more about the structural integrity of the material itself.

The beginning portion of the graph represents the elastic deformation region. From its linear characteristic, we can see that the amount of force being applied is increasing at a constant rate. This relationship between stress and strain gives us a good indication of the material’s elasticity. Think of the material as a rubber band during this phase: it can only be stretched to a certain point (% strain) and still able to return to its initial state. The slope of this linear curve represents the materials modulus. The Modulus value is a measurement of the overall stiffness of a material and how easily it can be returned to its initial state (in the elastic region). A higher modulus correlates to a higher elasticity rating.

The top of the elastic region represents the yield strength, which is essentially the maximum amount of stress a material can be under and still return to its initial state. Past this point is the region of plastic deformation. In this section, the material is permanently damaged and can never go back to how it was.

The peak of the graph represents the maximum tensile strength of the material – the maximum amount of stress the material can undergo until it begins to fracture. Once this point is reached, you can visually see the sample begin to deform as the graph shows a decreasing slope. This is the "necking" region where the weakest point in the sample begins to get narrower the longer stress is applied. Getting thinner and thinner, the sample eventually breaks into two parts. At the exact moment when the sample fractures, the test is done and that is the point at which ductility (strain) is measured.

Tensile testing has been a large part of my project throughout this summer and the materials science industry as a whole. These tests can tell us a lot of information about how a certain material will perform under different conditions. These measurements can be important baselines when one is incorporating these materials into real-world uses such as automobiles and mobile devices.