A New Method for Measuring the Dynamic Rigidity Modulus of a Bar of Rectangular Cross Section

Abstract

A new method for measuring torsional resonance frequencies or rigidity moduli of specimens in the shape of a bar of rectangular cross section is described. The measuring system is based on the principle of the vibrator-controlled oscillator using an electrostatic pickup and driving system . The new system, in the original form, was already developed by the authors for measuring the flexural resonance frequency or Young’s modulus of elasticity for specimens in the same shape as used in the present investigation. To obtain the torsional mode of vibrations, a new arrangement of a pickup and driving electrode system was adopted.
The modulus of rigidity was determined at room temperature for specimens (8∼10 mm in width, 1.5∼2.5 mm in thickness, and 112∼150 mm in length) of electrolytic iron, electrolytic copper, silver and coelinvar alloy, with a view to testing the performance of this experimental apparatus. The Poisson’s ratios and the compressibilities were also computed by using the rigidity moduli from the torsional resonance frequencies and the Young’s moduli from the flexural resonance frequencies.
Furthermore, the temperature dependence of torsional resonance frequency of a specimen of the coelinvar alloy was investigated in the temperature range of about 15° to 80°C.