RESULTS OF EXPERIMENTS ON MEASURING DISPLACEMENTS AND STRESSES IN PRESSURE-GAUGE SPRINGS

G. I. TYZHNOV, V. K. KHRULEV

(Presented by the scientific seminar of the Department of Strength of Materials)

To verify the theories [1, 2, 3] of tubular pressure-gauge springs, experiments were carried out to measure displacements and stresses. The dimensions of the tested springs, their parameters, and the results of the experiments are summarized in the table, where $R$ is the mean radius of the spring, $h$ is the wall thickness, $a$ is the major semiaxis of the section, $b$ is the minor semiaxis, $\gamma$ is the working angle of bending of the spring (the nonworking sections at both ends, $8^\circ$ each, have been discarded [4]), and $\eta$ is the principal parameter of the spring.

Column 11 gives data on the displacement sensitivity of the springs, i.e., the amount of travel per atmosphere. Columns 12 and 13 present the results of calculating this sensitivity by the formula in [3]. Columns 14–25 contain the experimental data on stress measurements and the results of calculations of these stresses [3]. Columns 16, 19, 22, and 25 give the calculated equivalent stresses, computed according to the energy theory of strength:

$$ \sigma_{\mathrm{e}}=\sqrt{\sigma_1^2+\sigma_2^2-\sigma_1\sigma_2}. $$

Stresses were measured only at 2 points located at the ends of the minor axis of the section on the outer surface: at point $A$—on the convex side, and at point $B$—on the concave side of the spring.

The stress $\sigma_1$ is meridional, i.e., directed along the central axis of the spring, while $\sigma_2$ is circumferential, perpendicular to the central axis. To measure the strains $\varepsilon_1$, ordinary gauges with a base of 10 mm were used, and to measure the strains $\varepsilon_2$, specially made gauges with a base of 3 mm were employed.

When measuring strains on thin parts with strain gauges, it is necessary to take into account the influence of the thickness of the gauge.

The springs for a pressure of 100 atm had a modulus of elasticity $E=1.3\cdot10^4\ \text{kgf}/\text{cm}^2$; the remaining springs were made of brass, for which $E=10^4\ \text{kgf}/\text{cm}^2$. Poisson’s ratio was taken to be the same, $\mu=0.3$.

REFERENCES

1. V. I. Feodos’ev. Calculation of thin-walled Bourdon tubes of elliptical section by the energy method. Oborongiz, 1940.

2. V. I. Feodos’ev. Elastic Elements of Precision Instrument Engineering. Oborongiz, 1949.

3. L. E. Andreeva. Elastic Elements of Instruments. Mashgiz, 1962.

4. A. I. Chinarev. Investigation of the deformation of the minor axis and the opening angle of a pressure-gauge tubular spring of flat section. In: Prospects for the Development of Elastic Sensitive Elements. TsINTI, Moscow, 1961.