Abstrakt
Under certain, comparatively general assumptions it is possible to derive the relation between the Young's modulus in tension and in shear E = 2G (1+ σ), where in case of an uncompressible sample G = 1/3 E, approximately. We have decided to verify this relation and for this purpose we have constructed a device where it is possible to determine both modules on the same sample.
In both cases the measuring is non-destructive; the samples are measured by optical methods. In both cases the fiber is deformed less than 1% which brings us to the Hook's area of a deformation curve.
In case of measuring the Young's modulus in tension, the horizontally positioned hair with a known weight in the middle of it is slightly taut. The hair deflection caused by the potential weight is photographed and the photograph is computer-analyzed subsequently.
The sample is verticalized after this measuring and the weight, provided with a mirror surface, is swung torsionally. A laser beam is sent to the weight and its reflection is scanned by a couple of photo-transistors, whose status is recorded by a fast AD converter.
The attenuation coefficient and the oscillation period are determined from the moment o the beam passage and the Young's modulus in shear and dynamic viscosity is determined from them. A slight discrepancy between the theoretical assumption of the Young's modules dependence and the measured series of samples has appeared; we attribute it to the manner of keratin location in the hair cuticle.