Using a Radio Interferometer for Measurement of the Dynamic Poisson’s Ratio of Wood

We proposed a new method for measuring the dynamic Poisson’s ratio of both isotropic and anisotropic materials. The specimen was loaded with a compressive pulsed load generated by gas gun and a split Hopkinson bar. The longitudinal compression deformation of the specimen was determined from the signals recorded with the use of small-base strain gauges glued to the measuring pressure bars. To measure the temporal progress of the radial components of the specimen deformation, a millimeter-wave radio interferometer was used. To assess the possible asymmetry of the radial expansion, measurements were carried out using two independent channels irradiating diametrically opposite zones of the lateral surface of the specimen. The tests were carried out on a pine specimen with air humidity in the form of a cylinder 54 mm in diameter and 30 mm in height. A compressive pulsed load was applied along the fibers by using the split Hopkinson pressure bar (SHPB). The separate movement of the lateral surfaces of the sample was recorded both along and across the annual layers by using the two-channel radio interferometer. It was determined that the opposite displacements of the regions of the lateral surface of the specimen during its expansion along the annual layers are quite close; while during expansion across the annual layers, they are very different. The relative transverse deformation of the sample in both cases was determined as the sum of lateral opposite displacements relative to the specimen’s diameter. As a result, two components of the dynamic Poisson’s ratio were obtained, which amounted to ~0.2 (in the direction along the annual layers) and ~0.24 (in the direction across the annual layers).