Poisson's Ratio Testing With A Biaxial Extensometer

Poisson’s Ratio has proven to be a challenging calculation for obtaining both repeatable and accurate results. To improve repeatability, we typically recommend grips that provide consistent clamping pressure, such as pneumatic side acting grips. In addition, alignment devices can be mounted on these grips to ensure that specimens are identically aligned for each test. An extensometer with appropriate accuracy is critical for achieving reliable results. For both ASTM D638-10 and ISO 527, the extensometer must be capable of measuring the change in strains with an accuracy of 1% of the relevant value or better. For Poisson’s Ratio testing, we recommend using a biaxial extensometer. When testing with the biaxial extensometer, it is important to ensure that the top of the device is parallel to the grips and the device body is perpendicular to the grips. Essentially, it is critical to have the extensometer positioned straight when attaching to the test specimen. We also recommend carefully draping the extensometer’s wires and cords to remove any effect of additional weight hanging off of the extensometer.