Simultaneous Measurement of Young´s Modulus and Damping Dependence on Magnetic Fields by Laser Interferometry

The main objective of this work is to characterize the dependence on applied magnetic field of both Young´s modulus and damping due to aspects relative to magnetostriction and domain theory. The studied samples are ferromagnetic slender rods longitudinally placed inside a straight solenoid with a pair of Helmholtz coils designed to achieve a homogeneous field along all the longitude of the sample. The longitudinal vibration in the sample is induced by a brief impact perpendicular to the base of the cylinder with a pendulum with a quartz sphere, and its vibration velocity is measured by a compact laser vibrometer based on Doppler Effect. The signal acquired is processed by a software developed in Matlab environment obtaining the vibration frequency (related to the Young´s modulus) and the logarithmic decrement. That experimental method has been applied to nickel rods, obtaining maximum variations about 2.5% in Young´s modulus and 156% in logarithmic decrement, and offering important advantages over other methods like lack of interaction with the sample, high accuracy, rapidity, no destruction of the sample after the test and possibility of checking small size specimens such as wires.