SU1281930A1 - Method of measuring bending moment applied in span of supporting beam - Google Patents

Abstract

The invention relates to a measurement technique and makes it possible to increase the measurement accuracy by eliminating the influence of immeasurable cantilever loads of transverse and longitudinal forces and unmeasurable bending moments. In sections of beam 1 with constant stiffness, cross sections are chosen at specific distances between the supports and the zone of application of immeasurable transverse forces and moments. The R-R strain gauges are arranged one at a time in the first, second, fifth, and sixth sections in the bend plane, and the strain gauges are in the same two planes diametrically opposite in the third and fourth sections. The strain gages are included in the measuring circuit so that the strain from the measured moment in the first and sixth sections is opposite to the sign of the strain in the other sections. 2 or ..

Description

1

The invention relates to a measurement technique, in particular to the measurement of bending moments arising in spans of double-support shafts and beams, and can be used in the process of testing machine parts and building structures ..

The aim of the invention is to increase the measurement accuracy by eliminating the effect of immeasurable cantilever loads, transverse and longitudinal forces, and unmeasurable bending moments acting on the beam.

Figure 1 shows the layout of the strain gauges on the beam; Fig. 2 is an electrical circuit for including strain gages in the measuring circuit.

To implement the method, beam 1 is used, which is mounted on supports 2 and 3.

In the span of the beam outside the zones of concentration and stress gradients, in sections of the beam with constant rigidity, cross sections are chosen to accommodate the strain gauges at a distance P, E, and E from the left support and at a distance j, 5, and g from the right support.

The strain gages R, R, R ,,, R are placed on the part one by one in the first, second, fifth and sixth sections in the plane of the bend, and the strain gages R, Rg, R, Rg in the same plane by two, diametrically opposite to the third and fourth sections.

The deformations of the external fibers of the beam in diametrically opposite points of sections 3 and 4 from the action of the measured bending moment M will be of the same sign, and from the action of cantilever loads

ruka

and P ,, unmeasurable transverse P, and unmeasurable bending moments M, M, M - the opposite. With the inclusion of two tensor

where t. G, 1 5

five

0

.% 0

five

0

cash from the longitudinal force will be compensated.

In order to compensate for signals from cantilever loads, immeasurable transverse forces and moments, the location coordinates of the resistance strain gages are chosen from the following relation 1:

f, -i. (2w, / w,). (f, -f3);

, (2W3 / W,). (, - f, -e,), f is the distance from the left support to the immeasurable transverse force, m;

the distances from the first, second, fifth, and sixth strain gauges, respectively, to the left support, m; the distances from the seventh and eighth, third and fourth strain gauges, respectively, to the right support, m; distance from the left support to the immeasurable transverse force, m; distance between supports, MJ

the moment of resistance of the beam in the zone of placement of the first and second strain gauges, m j the moment of resistance of the beam in the zone of placement of the fifth and sixth, seventh and eighth strain gauges, the moment of resistance of the beam in the zone of placement of the third and fourth strain gauges, m

Resistance strain gages included in the measurement, J

W. W. W.

resistors located in a diametrically-45 circuit so that the deformation

from the measured moment in the first and sixth sections h; was one sign, and in the rest of the opposite. With

but the opposite points of sections 3 and 4 in one arm of the measuring bridge, and the remaining points in the other, the signals of these strain gauges are summed from the measured bending moment, and from the cantilever loads, immeasurable transverse forces and moments, are subtracted from each other with doubled difference. The deformation of the outer fibers of a beam of section 3 or 4 due to the influence of a longitudinal force N will be of the same sign and of the same size. When you turn on a pair of strain gauges located in section 3 or 4 in the adjacent shoulders of the bridge, the strain gauges position (figure 1) 50, this condition is satisfied if the strain resistors R-, R, K, R are included in one shoulder, and strain gauges R, , K, R, R to another. Since the strain gauges and Rj, R are placed in pairs 55 in sections of the beam in cross sections with the same stiffness and included in the opposite shoulders of the bridge, they compensate for the signal from the immeasurable longitudinal force.

the location of the strain gauges (Fig. 1), this condition is satisfied if the strain resistors R-, R, K, R are included in one arm, and the strain gauges R ,, K, R, R in the other. Since the strain gages and Rj, R are arranged in pairs on sections of the beam in cross sections with the same rigidity and included in the opposite shoulders of the bridge, they compensate for the signal from the immeasurable longitudinal force.

The operation of the circuit is not disturbed if the strain gauges R, K пом swap places in the shoulders of the bridge and place diametrically opposite to the strain gauges Rj.R on the beam or if the R and R strain gauges are interchanged in the arms of the bridge and placed on the beam diametrically opposite the strain gauge Rj, R respectively.

If a full bridge is used in the measurements, the strain gauges include two in each arm. For example, the resistance strain gauges R ,,, R3 include in one R ,, R, - in another, Rj, in the remaining.

bridge shoulder, k, r third,

.

...

Rf - in

When the distance between the supports or to one of the supports changes, the operation of the circuit is not disturbed, since the reduced relations do not change.

If the plane of action of the measured bending moment is unknown and a shaft in bearing bearings is used as a beam 1, then the readings of the strain gage device made according to the proposed method are multiplied by cos H (shaft rotation angle). Under constant conditions, the sensitivity of the device to the

mats in one revolution of the beam changes

from zero to maximum taking into account the sign of deformation. To measure the bending moment on stationary beams with unknown planes of action of forces, two devices are used, made according to this method and installed in two mutually perpendicular planes relative to the beam. The use of the invention in the study of machine parts and building structures allows us to find the accuracy and performance of measurements by automatically eliminating the influence of cantilever loads, unmeasurable bending moments, transverse and longitudinal forces, and rigidity of supports, and simplifies the mathematical processing of test results.

Claims (1)

Invention Formula A method for measuring a bending moment applied in a span of a two-support beam, which consists in measuring the beam deformation with the help of eight strain gauges connected in an electrical circuit and placed in a longitudinal section of the span of the beam, -:five - ten f5 25 20 YAP 35 0 characterized in that, in order to increase accuracy by eliminating the effect of immeasurable cantilever loads, transverse and longitudinal bending moments, the first, second, fifth and sixth strain gauges are placed between the left support and the area of application of immeasurable transverse forces, and moments the third, fourth, seventh and eighth strain gauges are located between the right support and the zone of application of immeasurable transverse forces and the measured bending moment, while the fifth and sixth, seventh and eighth strain gauges are arranged in pairs of different The lengths of the corresponding beam sections, and the location coordinates of the strain gauges are chosen from the following ratios: t, -f, (2W, / W,) - (l, -E,); t, -, (2W, / W,). (, - P,), where ,, l, l the distance from the first, second, fifth and sixth strain gauges, respectively, to the left support, MJ Е, f, t - distances from the seventh and eighth, third and fourth strain gages, respectively, to the right support, m ;. f is the distance from the left support to unmeasurable transverse force, m; I, - distance between opoi ramie beams, m; W - the moment of resistance of the beam in the area of the first and second strain gauges, W is the moment of resistance of the beam in the zone of placement of the fifth and sixth, seventh and eighth strain gauges, W is the moment of resistance of the beam in the area of placement of the third and fourth strain gauges, m f then the signals of odd resistance strain gages are summed up and the sum of the signals of even resistance strain gages is subtracted from the result, and the difference is judged on the measured bending moment. / R3 R5 K7 R2, / f 4-, R6, ffS. FIG. 2