How Do I Calculate the Ultimate Tensile?

Pull a piece of taffy and it will resist at first. Then, it starts to give, and you'll notice as you continue to pull that it begins to narrow -- because you have surpassed its ultimate tensile strength, formally defined as the maximum load that can be applied to one square inch of cross-sectional material. Whether the surface is a bar of steel or a chunk of taffy, the point of ultimate tensile strength is reached when the substance begins to give way in response to being tugged in opposite directions.

Things You'll Need

• Universal Testing Machine

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Instructions

• 1

  Measure the cross-sectional width of your sample, which will be a bar of uniform width and depth. Typically, test samples have shoulders on either end, enabling a Universal Testing Machine to grasp it more readily. You must know the bar's precise cross-sectional width and depth before you can calculate tensile strength.

• 2

  Set a sample in the Universal Testing Machine, a device designed to test materials under tension or compression. Experts will need to help you with this, as you will only find Universal Testing Machines in colleges or big companies. The machines require trained technicians to operate.

• 3

  Apply increasing strain until the sample fractures. Carefully track the forces that are applied, noting the force that is being applied at the point of fracture.

• 4

  Divide the pounds of force applied at the time of fracture by the sample's cross-sectional area in square inches. The calculation gives you the ultimate tensile strength of your sample, expressed in pounds per square inch.