Background
The coefficient of thermal expansion (CTE) is one of the most important characteristics when testing materials in order to understand their behavior when it comes to temperature change. The CTE is the rate at which a material expands with an increase in temperature. It is determined at a constant pressure without a phase change within the material. In general, the CTE depends on the bond strength between the atoms that make up the material. Covalent materials, such as diamond and crystals, have strong bonds between the atoms resulting in low CTEs.
When a resistance strain gage is installed on a stress-free specimen and its temperature is changed, the output of the gage changes correspondingly. This is referred to as temperature induced apparent strain or thermal output. A dilatometer is a tool that can be used to measure the coefficient of expansion and contraction by measuring volume changes. While this is highly effective, this is restricted to materials that are fluid. Materials that are viscous and elastic (viscoelastic) or polymers currently do not have any test procedures to measure their thermal expansion/contraction coefficient.
Invention Description
Researchers at Arizona State University have developed a new method for testing material properties that improves upon the accuracy of measurements. This method requires two strain gages, where one is bonded to the test specimen and the other to a material of known coefficient. The resistivity of the grid alloy of the gage will change with the change in temperature. With this change, the grid is mechanically strained by an amount equal to the difference in expansion coefficients. Since the gage grid is made from a strain sensitive alloy, it produces a resistance change proportional to the thermally induced strain.
Potential Applications:
- Asphalt-based materials
- Roofing shingles
- Polymer surface coatings
Benefits and Advantages:
- Testing can occur at a large testing temperature range, possibly mimicking field paving conditions in both hot and cold climatic conditions
- Cheaper than available methods
- Easy to replicate and highly reliable