GB1431111A - Method of and apparatus for measuring dynamic characteristics of materials - Google Patents

Abstract

1431111 Measuring properties of materials TSENTRAL KONSTRUKT BJURO UNIKAL PRIBOROSTROEN 28 Aug 1973 40540/73 Heading G1A The dynamic properties of materials at very low frequencies (1Hz to 10<SP>-6</SP> Hz) are determined by oscillating a specimen at a pre-set amplitude and frequency using means comparing the motion of one end of the sample with that of a reference member driven at the desired amplitude and frequency and generating an error signal which is used to control the motion of the sample. As shown, Fig. 1, the specimen 2 is oscillated by a driving coil 9 placed in a uniform magnetic field in which is also placed a galvanometer coil 12 which is energized from a low frequency oscillator 24 via an attenuator 27 which determines the amplitude of the oscillation. Mirrors 10 and 13 are connected to the coils 9 and 12 and a photo-electric system is utilized to produce an error signal which is applied to coil 9 to cause it to follow the motion of coil 12. The real and imaginary components of the error signal are also analyzed to enable the properties of the sample 2 to be determined. The accuracy of the measurement is increased by adding two restoring signals to the error signal to form the driving current by means of attenuators 28 and 29 supplied with quadrature signals from oscillator 24. The amplitudes of the restoring signals are adjusted to be commensurate with the corresponding components of the required driving current so that the error signal produced by the photoelectric system comprises the small differences between the components of the driving current and the restoring currents. The photo-electric arrangement comprises a laser 14 and a modulator 15 the resulting beam being reflected from mirror 10 to mirror 13, back to mirror 10 and then to a critical angle prism 16. When the beam strikes the prism symmetrically it is totally reflected back towards mirror 10 this condition being achieved when both mirrors are deflected by equal amounts. Any difference in deflection of the mirrors causes a displacement of the beam which passes to one of photo-cells 17, 18 which are connected differentially to a common load 19. The resulting difference signal is applied via an A.C.amplifier 20 to a demodulator 21 and hence to a D.C. amplifier 22 the output of which is the error signal which is applied to the component analyzer 23 and also via a buffer amplifier 25 to a summing amplifier 26 where it is combined with the output of attenuators 28 and 29 to produce the driving current. The sample 2 is enclosed in a thermocryostatic chamber 1 controlled by a temperature programmer 5. Solid samples may be in the form of plates or cylinders, liquid samples may be introduced between a pair of cylinders or cones and high elastic polymers may be introduced between a pair of cylinders or moulded into cylinders.