GB1399629A - Method and apparatus for measuring the modulus and the mechanical damping of a material - Google Patents

Abstract

1399629 Measuring torsional modulus electrically DUNLOP Ltd 15 Sept 1972 [15 Sept 1971] 42870/72 Addition to 1331810 Heading G1N Apparatus for measuring the torsional modulus and mechanical damping of a sample of material 12, Fig.1, fixed to a base plate 32, comprises a coil 11 attached to the free end of the sample between two field coils 14 fed with A.C. from a source 13, the voltage induced in coil 11 when the sample is made to oscillate in damped torsional mode being analyzed to measure the frequency and log dec, which are indicative of the torsional modulus and mechanical damping respectively. The induced voltage is demodulated at 47, Fig.2, and fed to trigger circuit 17 which produces a square pulse corresponding to each positive halfcycle, Fig.3, the starts of two consecutive pulses opening and closing a counter 16 for clock pulses from a generator 22, the count being indicative of the periodic time of oscillation and therefore inversely proportional to frequency and indicative of the torsion modulus. Via line 34, the second of the two pulses introduces a two second delay before clearing counter 16 and resets the frequency of generator 22 for the next measurement. The demodulated oscillation signal in coil 11 is also fed to a trigger 27 and two memory stores 23, 24. Trigger 27 produces a square pulse for each positive half-cycle, starting when the oscillation voltage exceeds a threshold level 28 and terminating at the end of that half-cycle. The amplitude A o of the first oscillation positive half cycle is stored in memory 23, and the amplitude of the first half-cycle which does not reach the level 28, e.g. A2 as shown, is stored in memory 24, whilst counter 26 determines how many consecutive pulses have occurred, up to a maximum of four. The difference between voltages A 0 and A2 (as shown) in stores 23, 24 is discharged through an R.C. circuit 40, the time taken for the difference to be eliminated being measured by counter 16 using the clock pulses from generator 22, this time being proportional to log A 0 /A 2 and is proportional to the log dec and mechanical damping. Counter 26 introduces a factor depending on its pulse count.