How to Calculate Ductility

How to Calculate Ductility
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Ductility is a mechanical property of materials that refers to the degree of plastic deformation a material can sustain prior to fracture. If little or no plastic deformation can occur, the material is brittle. You can express ductility in terms of either a percent elongation or a percent reduction in an area. However, the values for percent elongation and percent reduction in area are not necessarily the same for the same material.

Calculating Percent Elongation

    Measure the original gauge length (Lo) of the material around the point of intended fracture. This value is commonly 2 inches or 50 millimeters.

    Apply a tensile force to the material slowly until fracture occurs.

    Fit the broken parts back together and measure the fracture length (Lf), using the same endpoints on the material as the initially measured gauge length.

    Calculate the percent elongation using the equation 100 x (Lf-Lo) ÷ Lo.

Calculating Percent Reduction in an Area

    Measure the diameter of the solid cylindrical material to be tested (d).

    Calculate the original cross-sectional area (Ao) of the rod by inserting the diameter into the equation pi x (d ÷ 2)^2.

    Apply a tensile force to the material slowly until fracture occurs.

    Measure the diameter of the cylinder at the point of fracture (df) then calculate the cross-sectional area at the point of fracture (Af), using the same equation.

    Calculate the percent reduction in area using the equation 100 x (Ao-Af) ÷ Ao.

    Tips

    • The magnitude of percent elongation depends on specimen gauge length and therefore it is customary to specify the initial gauge length when reporting the percent elongation.

    Warnings

    • Metals tend to become more brittle in lower temperatures and more ductile in higher temperatures.

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