Tensile strength is a measure of the stress needed to break a material by stretching. Stress is the force applied divided by the cross-sectional area of the material. Tensile strength is also referred to as ultimate tensile strength. Tensile strength is measured using tensile test rigs and samples of particular materials. Tensile tests can also be used to identify the yield point, which is the stress needed to permanently deform the material. It is easy to make a simple tensile test rig and use it to test the tensile strength of common metals.

Attach the laboratory clamp to the laboratory stand. Place the stand on a flat, stable surface.

Attach the 16-gauge metal wire sample to the clamp. Use the hole punch to create two holes in the sides of the plastic cup. Thread a piece of string through these holes and tie the ends of the string to the lower end of the wire sample.

## Sciencing Video Vault

Place the meter stick alongside the wire sample. Make a note of the initial length of the wire.

Add the masses of a defined weight one at a time. After adding each mass make a note of the length of the wire. Use the calipers to measure the thickness of the wire after each mass addition. Create a table showing the cumulative mass in the cup, the corresponding length of wire and the thickness of the wire. Continue adding masses until the wire breaks.

Divide the thickness values as measured by the calipers by two. Square the result and multiply by pi. This produces the cross-sectional area of the wire at each point in the experiment. Make a note of these values.

Multiply the cumulative mass in the cup at each step in the experiment by the gravitational field strength of the Earth. These values represent the tensile force on the wire. Make a note of these values.

Divide the tensile force as measured just before the wire broke by the cross sectional area of the wire just before the wire broke. This value represents the ultimate tensile strength of the material you are testing.

#### Tip

Ensure you use a consistent set of units throughout when performing your calculations. For example if you measure the length of the wire in inches, be sure to use pounds for the masses.

Pi is approximately 3.1415.

The gravitational field strength of the Earth is 32.2 feet per second squared or 9.81 meters per second squared, depending on which unit of measurement you are using.

#### Warning

Be sure to stand clear of the apparatus after adding each of the masses. To ensure the laboratory stand is stable place the clamp pointing in the same direction as the base of the stand.