2D-2 Ultrasonic Methods in Determining Elastic Material Properties of Fibres in Suspension

The presented study concerns the application of the pulse-echo ultrasound measurement technique in determining the elastic properties of fibres suspended in water. The two kinds of fibre materials are investigated, nylon 6/6 fibres and softwood pulp fibres. The fibre mass fraction was 0.5 % for nylon and ranges from 0 % up to 1 % for softwood pulp. The ultrasonic measurements are performed in the frequency range of 2 -11 MHz. It is shown that the velocity dispersion of the ultrasound is small for each suspension sample. In obtaining the fibres longitudinal Young´s modulus two methods are used, one based on phase velocity and one based on acoustic attenuation. It is found that both methods gives reasonable estimates of the longitudinal Young´s modulus for nylon 6/6. For pulp fibres the determined Young´s modulus is overestimated in comparison with earlier findings.