Stress/Strain Apparatus (PASPORT)
Item, Part Number
The Stress Strain apparatus is available in 3 configurations:
Check the User Resources Tab for:
This compact Stress/Strain Apparatus shows the stress and strain during the entire process of stretching and breaking a material. PASCO has scaled-down the typically expensive engineering devices so that this apparatus is able to do all the physics without the high cost of a materials testing machine.
Since the Stress/Strain Apparatus shows the entire stress versus strain curve, it is possible to measure a wide range of material properties including Young's Modulus, the yield strength, tensile strength, ductility and toughness of the material. In addition, the different curve shapes for different materials can be compared.
DataStudio software allows students to determine Young's Modulus by measuring the slope of the initial straight line (the elastic region) and to determine the toughness by integrating under the curve.
Tension is applied to the sample by turning the knob by hand until the sample breaks. The force used to stretch the sample is measured using a Force Sensor connected to a PASPORT Interface. A metal lever provides a five-to-one mechanical advantage, increasing the maximum force that the sensor can read to 250 N.
The stress is calculated using DataStudio by taking the force over the cross-sectional area. No adjustment is made for any change in the cross-sectional area during stretching.
The change in length of the sample is measured using a Rotary Motion Sensor. The resolution is 0.007 mm. The strain is calculated using DataStudio by dividing the change in length by the original length.
At the heart of the Stress/Strain Apparatus is a high quality hand crank that allows the user to generate the force needed to stretch and ultimately break the provided test coupons of different materials.
In order to accurately measure the forces involved a force sensor is used. However, it's limit is 50 N, a number easily surpassed by the forces needed to break some of the materials. That's why the Stress/Strain Apparatus employs a metal bar with a 5:1 mechanical advantage, increasing the maximum force that the sensor can read to 250 N.
A drive belt connects the hand crank to a rotary motion sensor which translates the turn of the crank into the corresponding change in length of the sample. Either PASPORT or Science Workshop sensors may be used with the Stress/Strain Apparatus.
DataStudio automatically calculates stress by dividing the applied force by the cross-sectional area and the strain by dividing the change in length by the original length. Data points are taken continuously creating a graph in real time. A linear curve fit of the initial straight line provides Young's Modulus while integrating under the curve determines the material's toughness.
The Stress/Strain Apparatus is mounted on a rugged aluminum plate.