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One of the most useful values from a stress-strain diagram is the Modulus of Elasticity or Young’s modulus.
The modulus of elasticity is the slope of the line that forms the elastic region on a stress-strain diagram. When our data comes from a tension or a compression test, we call this value “Young’s modulus, ” and we give it the symbol E.
Young’ modulus describes how stiff a material is. If we have two identically shaped parts, the one with a higher modulus of elasticity will be stiffer than the other. A steeper slope on the stress-strain diagram indicates a higher modulus of elasticity and a stiffer material. We can use Young’s modulus to calculate how much a part will bend or stretch when a load is applied to it (but only up to the elastic limit).
Let’s have a look at the units of Young’s modulus. Remember that the slope of a line is the rise over the run. On a stress-strain diagram, the rise is the increase in stress, and the corresponding run is the increase in strain. The stress units are force per unit area, and the strain units are length per unit length. Since the strain units cancel themselves out, the units for the slope, or the modulus of elasticity are the same as the units for stress. The values of Young’s modulus for most materials are large numbers. You will likely see values in the millions of pounds per square inch or metric values in the Gigapascals.
It is important to remember that Young’s modulus only applies to the elastic region of the material, and that it measures stiffness, and not the strength of the material. For instance, there are many different alloys of aluminum available. The Young’s modulus values for each of these alloys are nearly identical, but the different aluminum alloys have very different strengths.