Photoelastic element

FIELD: instrumentation.

SUBSTANCE: photoelastic element in plan view has a crosswise shape the frontal surfaces of which, parallel to the direction of applied efforts, are optically flat, and lateral surfaces of the photoelastic element have the constant and/or variable curvature radius.

EFFECT: increase of voltages in the central part of the photoelastic element, improvement of sensitivity of piezoelectric sensors due to the use of these photoelastic elements.

3 dwg

 

Area of technology

The invention relates to test and measurement technology, in particular to measure the deformation (strain) in various designs by means of polarization-optical converters, and can be used in construction, transportation, industrial production, control and measuring equipment.

The level of technology

Photoelasticity effect (piezooptical effect) is used for precision measurement of strain (or stress). Anisotropic mechanical stresses in the material lead to anisotropic change of refractive index (birefringence). This changes the angle of polarization of the light passing through the material. There are devices called piezooptical converters, which convert the amount of change in polarization angle in the magnitude of an electrical signal proportional to the amount of deformation or strain. It is known that the strain sensors, based on piezoelectric converters, have the greatest sensitivity compared with others, such as sensors based on piezoresistive transducers (Slesinger I. Piezooptical transducers. Measurement technology, 1985, No. 11, pp. 45-48) [1]).

Piezooptical Converter is �W led optically coupled, polarizer, phase plate, a photoelastic element analyzer and a photodetector. The form of photoelastic element can be different: box, cylinder, truncated cone.

The closest in technical essence to the proposed photoelastic element is a photoelastic element proposed in the patent of Russian Federation №2422786 dated 23.04.2010 and No. 2454642 from 29.03.2011 [2, 3]. In these patents the photoelastic element is in the form of either a cylinder or a truncated cone. Photoelastic element is initially clamped in two mutually perpendicular directions, which makes it work, as in compression and in tension.

The disadvantage of these designs photoelastic element (PE) is that, as shown by calculations and experiments, the voltage in PV is concentrated near the areas of its contact with the load element piezo-optical strain sensor, which fixed the Feh, and fall to the center of the PV, while the light beam of the sensor passes through the Central portion of the FE, i.e. in the region of minimum stress. This leads to a reduction of the sensor sensitivity.

At the same time as a load element, which is fixed Feh, greatly exceeding the dimensions of PV, it is not possible to reduce the dimensions of the piezo-optical strain gauge and make it miniature.

Disclosure of the Fig�"

The task of the invention is to provide such a form of photoelastic element, which will provide the increase of stresses in the Central (working) part of the photoelastic element.

The technical result - improving the sensitivity of PV to the load.

In addition, the use of the proposed PV in piezooptical the strain gauges will improve the sensitivity and accuracy of measurements and reduce their dimensions.

The task is solved due to the fact that known photoelastic element according to the invention has in terms of cruciform shape, the front surface of which is parallel to the direction of the efforts, are optically flat, and the lateral surface of the photoelastic element have a constant and/or variable radius of curvature.

Description of photoelastic element and justification of new signs

Description of the proposed photoelastic element is illustrated by Fig.1, 2, 3.

Fig.1 shows an example of a photoelastic element (PE), which has a cruciform shape, the side surfaces of which have a constant radius of curvature. To determine the effectiveness of this form Feh carried out numerical simulation of elastic stresses arising in the Feh volume of work effort. Originally Feh was elastically compressed in the direction of axes X and Y by the efforts of the Px=Py=87.9 MPa. R�Boxee force was applied along the Y-axis and equal to ΔP y=19.5 MPa. In the simulation varied the value of the "tie" d (see Fig.1) 0 mm, for a circular element with a diameter of 12 mm, to 3.5 mm.

Fig.2(a, b, C, d, e) shows the simulation results for different forms of FE, with the same work force. In the figures 2A-2D shows contours of the magnitude of the voltage difference of Δσ=σxy, the magnitude of which is proportional to the electric signal output piezooptical Converter. Numerical values of Δσ are indicated on the figure numbers in MPa. The value of the "frame" in Fig.2A, 2B, 2C, 2G, 2D to 0 mm, 1.13 mm, 1.84 mm, 2.55 mm, 3.26 mm, respectively.

Fig.3 shows the dependence of Δσ on the depth "tie-d. From the figures it is seen that as the "tie-in" voltage (with the same working force) shifted from the periphery of the PE to its center, i.e. in the area where the light beam piezooptical Converter. For example, to form Feh, shown in Fig.2G (depth "tie" is 2.55 mm, the radius of a "tie" is 5 mm, the diameter of the whole PV 12 mm) increase in Δσ compared to round Feh is 32%. Thus confirmed the increase in voltage, and hence the output signal piezooptical Converter with cross Feh. The obtained simulation results are in good agreement with experimental data.

Maximum depth and forms� "frame" is determined by the strength characteristics of the material of photoelastic element.

When placing a Phillips Feh in piezooptical the Converter, the attachment elements can be placed in the spaces between the side surfaces of FE, not exceeding the dimensions of the outer diameter of the PE (the shaded region in Fig.1). Thus, the transverse dimension of the transducer will not exceed the diameter of the PE.

As the material of photoelastic element can be used, for example, fused quartz, having a high damage threshold in compression, which provides high dynamic range measurements of deformations and reliability. In addition, the technology of processing of fused quartz is well developed, which reduces the design strain of the Converter.

Description of the device

Photoelastic element operates as follows.

When the measured load to the photoelastic element along one of its axes, there is additional stress Δσxand Δσyin the Central part of the Feh. As a result there is an additional phase difference of ±Δ between orthogonal polarization components of the beam passed through the photoelastic element. The phase difference caused by birefringence loaded Feh. Phase change of the polarization leads to a change of an electrical signal at the output of the photodetector. In the case of NB�topicscape Converter, it is recorded and processed by the processing unit of the signal. The magnitude of the transducer output signal is proportional to the value of Δσ=Δσx-Δσythat is proportional to the magnitude of the measured voltage (deformation).

Photoelastic element, characterized in that it has in terms of cruciform shape, the front surface of which is parallel to the direction of the efforts, are optically flat, and the lateral surface of the photoelastic element have a constant and/or variable radius of curvature.



 

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