Summary of Test
ASTM E132 describes the determination of Poisson’s ratio from tension tests. This method is limited to specimens with rectangular section and with stresses at which creep is negligible compared to the strain produced immediately upon loading.
When uniaxial force is applied to a solid, it deforms in the direction of the applied force, but also deflects in the transverse or the axial direction depending on whether the force is tensile or compressive. If the solid is homogeneous and isotropic, then the material remains elastic under the applied force and the lateral strain bears a constant relationship to the axial strain. This constant is called Poisson’s ratio and is used for design of structures where all dimensional changes resulting from application of force need to be taken into account.
For ASTM E132, forces need to be applied using a tensile machine calibrated in accordance with Practices E4. The deflectometer to measure the transverse strain must be class B-1 or better. Please note that the accuracy of Poisson’s ratio measurements depends on the accuracy of the transverse strain measurements, which can be quantified by the accuracy of the calibration of the deflectometer. It is recommended to calculate the longitudinal (axial) strain as well as the transverse strain. In order to calculate the longitudinal (axial) strain; an extensometer, class B-1 or better, should be used.
Before conducting ASTM E132, it is important to read the entire specification in the relevant ASTM publication.
Recommended Equipment
Testing Procedure
- Measure and record the width and thickness. Calculate the average cross-sectional area of the specimen gauge section.
- Place the specimen in the grip. Attach the deflectometer and the optional extensometer to the gauge section of the sample. The two measurement devices should be placed on the specimen with a free distance of at least one specimen width between any extensometer and the nearest fillet, and at least two specimen widths between any extensometer and the nearest grip.
- Apply the load. The speed of testing should be low enough to make the thermal effects of adiabatic expansion or contraction negligible. The precision of the value of Poisson’s ratio obtained will depend on the number of data pair of longitudinal (axial) and transverse strain taken.
- For ductile materials, continue the test until the yield strength or yield point, and sometimes the strength at a strain greater than the yield strain, can be determined. For brittle materials, remove extensometer and continue test until failure.
- Plot the average longitudinal (axial) strain and the average transverse strain, against the applied force.
Just Ask!
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