Fixture Measuring the Force Transmitted Due to Dynamic Loading

Courtney Clum

Summary:

The goal of this project was to design and construct a fixture that would measure the force transmitted through a material due to a dynamic loading. With the research of Dr. Veldman, aluminum honeycomb is used as an energy absorbing material to protect the thin aluminum shell that is behind it. Currently there is no method to measure the actual amount of energy that is absorbed so a special device is needed that perform this task.

The different options that were considered to solve this problem were to use either dynamic load cells or stain gages to measure the force. In the exploration of these two methods, several concepts were created that involved different locations of the measuring devices. Inevitably, it was decided that in order to receive the best results a measuring device should be placed in each corner of the fixture. With this setup, any uneven loadings could easily be measured. It was also decided that strain gages would be used to measure the force as they were the cheapest alternative and would be sufficient for the needed task.

The final design is a small, compact fixture that is capable of performing the task. There are four columns that attach to the corners of a base plate and a nest plate. On each of the columns is one strain gage that when connected to instrumentation, measures one quarter of the total strain caused by the applied load. An additional part of the fixture is the clamping device that slides over the testing material and has the capability of being adjusted to snuggly fit over the testing material before being bolted down.

After performing a test using the Instron 4204 to apply a loading, it was found that for a loading of 7500 lbf, the gages read on average 133.7µe while the theoretical strain was 151.5 µe. This led to a percent difference of 11.7%, which is a reasonably small value for the task of measuring transmitted force.