RU2082082C1 - Device measuring deformations of flexible envelopes of flying vehicles - Google Patents

Abstract

FIELD: measurement technology, measurement of deformations of flexible envelopes of structures of flying vehicles, for instance, balloons filled with air heated by gas burners. SUBSTANCE: proposed device is composed of case-base made of plastic material, restoring member, units for attachment to tested structure, limiter of travel of restoring member. Restoring member is fabricated in the form of cylindrical ring on which surface resistance strain gauges are mounted. Restoring member is so mounted in case that its walls are oriented perpendicular to surface of base and tested structure. Device is attached to tested structure by means of attachment units or adhesive. Limiter of travel is provided in proposed device to protected restoring member against overloads when surface of structure is deformed above measurement range of device or with sudden destruction of material of structure. EFFECT: expanded range of measurement of deformations of soft envelopes of structure of flying vehicles, increased precision of measurement within range of operational temperatures of structure, reduced expenses for preparation and performance of measurements. 2 cl, 4 dwg

Description

 The invention relates to measuring technique, in particular to means for measuring the deformation of flexible shells of aircraft structures. Scope aircraft manufacturing, shipbuilding, mechanical engineering, etc.

One of the important tasks, on the solution of which the further development of aircraft with flexible shells depends to a large extent: balloons, airships, parachutes, airborne rescue equipment, inflatable boats, large building structures such as multilayer inflatable vehicles, etc. is the creation of tools deformations of these structures during their testing for strength in laboratory conditions until fracture or control of deviations of their forms during operation. The most difficult of these tasks is to provide measurements of the deformations of flexible shells of balloons with air heating by gas burners. For the manufacture of such shells, materials are used based on lavsan or kapron with acrylosilicone and other impregnations, the elongation of which, respectively, reaches δ during operation $\genfrac{}{}{0ex}{}{\text{P}}{\text{ek.}}$ = 3-5% or 30,000 50,000 μm / m and δ $\genfrac{}{}{0ex}{}{\text{r}}{\text{ek}}$ = 5-10% or 50,000 100,000 μm / m and when tested to failure δ $\genfrac{}{}{0ex}{}{\text{g}}{\text{bit}}$ = 15-20% or 150,000 200,000 μm / m and δ $\genfrac{}{}{0ex}{}{\text{r}}{\text{bit}}$ = 20-28% or 200,000 to 280,000 microns / m. The operating temperature range is from -50 to +170 ^o C. The intrinsic rigidity of the measuring device should be minimal and cause an additional error of no more than half of the main measurement error.

 Specific and rather stringent requirements are imposed on measuring devices of this type in terms of the strain measurement range, temperature range, variation in resistance in a batch, measurement error, self-creep, temperature compensation of resistance, reproducibility of characteristics, etc. Analysis showed that known strain gages and measuring devices indicate the indicated requirements do not answer, therefore, the creation and implementation of the proposed device is an urgent task and will be widely applied ie when testing soft shells aircraft structures.

Known glued heat-resistant strain gauges containing a dielectric substrate, a sensitive lattice and output wires [1]
A disadvantage of the known heat-resistant strain gages are: a limited range of strain measurements up to ± 2000 • 10 ^-6 Rel. units the absence of circuit compensation for the temperature increment of resistance, the presence of significant measurement errors during electromagnetic interference, the use of an indirect calibration method to determine the sensitivity, a sample from a batch of strain gages is graduated and the characteristics of the entire batch are assigned, etc.

Known high temperature strain gauge type NMT-450, adopted as a prototype for measuring structural deformations in the temperature range of 20-450 ^o C [2]
The basis of the elastic element of the strain gage is made in the form of a flat plate of steel foil, attached to the structure in the zone of measurement by spot welding. On the external surface of the housing base, before mounting the device, one sensitive grating is glued to the structure, which is then coated with cement and heat treated.

The disadvantages of the device are: a limited range of strain measurements up to ± 2000 • 10 ^-6 rel. units a large value of the temperature increment of the resistance, the value of the temperature characteristic at 450 ^o C reaches 14000 • 10 ^-6 Rel. units high intrinsic rigidity of the tensile compression device; great importance of measurement errors under the influence of electromagnetic interference.

 The objective of the invention is to increase the range of strain measurements in the operating temperature range of flexible shells of aircraft structures, increase the accuracy of strain measurements, provide the ability to measure strains under unsteady thermal conditions, reduce operating costs for the preparation and conduct of tests and measurements.

 The technical result is achieved by a wide range of measured strains, high accuracy and reliability of measurements in the operating temperature range of the aircraft.

 The technical result is achieved by the fact that in the known device a flat metal base, which is simultaneously an elastic element, and one sensitive lattice of a heat-resistant strain gauge are replaced by a base of non-metallic plastic material equipped with a thin-walled ring elastic element with low tensile strength with fastening assemblies easily removable from the tested structure, in where the wall of the elastic element with 2-4 heat-resistant strain gauges glued on it is oriented perpendicularly to xnosti of the device body and the tested design, and the attachment points are equipped with a flexible protective limiter of the course of the elastic element.

 In FIG. 1 and 2 show the design of the measuring device; in FIG. 3 shows an electrical diagram of a device and its connection to a multi-channel measuring system; in FIG. 4 shows the calibration characteristic of the device when working with the SIIT-3 measuring system.

 The device consists of a housing 1, a thin-walled annular elastic element 2 and attachment points 3. On the surface of the elastic element 2 there are two or four heat-resistant strain gages 4, the connected wires of which are connected to the mounting block 5. In the holes of the attachment points 3, a flexible travel limiter 6 of the elastic element is installed 2. The device is attached to the studied flexible shell of the structure 8 using an easily removable lining 7, attachment points or with glue. Temperature sensors 9 are installed on the body and the elastic element.

 The case is made of an elastic material, for example, from kapron or lavsan with acrylosilicate impregnation, serves to set the base of measurement B. The body stiffness should be selected so that the additional error from its interaction with the shell does not exceed half of the basic error in the measurement of deformations . As glue for mounting the device, cold curing glue is used, for example, PIR-2 glue.

 The elastic element is made in the form of a cylindrical ring of low tensile stiffness compression made of tool steel. The wall of the elastic element is installed perpendicular to the surface of the device body and the structure under study in order to reduce errors arising from bending deformations.

 Strain gages are glued on the surface of the elastic element in stretched and compressible zones, connected according to the scheme of the measuring half-bridge or bridge, which provides an increase in the output signal by 2 or 4 times, respectively, temperature compensation, reduction of measurement errors due to electromagnetic interference, etc.

 The limiter 6 is made of kapron fishing line or steel cable with stops at the ends.

 The travel stop 6 is fixed in the holes of the attachment points. The length of the stroke limiter is determined depending on the measurement base and the regulated range of its change.

 The low-inertia thermocouples consisting of chromel and alumel thermoelectrics with a diameter of 0.05 mm glued on a dielectric substrate are used as a temperature sensor in the device.

 The present invention works as follows.

 The device is strengthened on the surface of the structure in the studied area by overlays of attachment points or cold-cured adhesive and is connected to measuring equipment.

When testing or preparing for the flight of an aircraft, the flexible shell is filled with gas under pressure or with air heated by gas burners, the construction material is stretched, which leads to a change in the measurement base of device “B”, see FIG. 1. When the measurement base of the distance between the attachment points changes, the elastic element 2 deforms, which deforms the sensitive lattice of the strain gauges 4 glued to the surface of the elastic element. In this case, the initial resistance R of the shoulder of the measuring bridge changes, for example, the resistance of the strain gages R ₁ and R ₃ increases by ΔR ₁ and ΔR ₃ and the strain gages R ₂ and R ₄ decreases by ΔR ₂ and ΔR _4, respectively, which leads to the appearance in the measuring diagonal the bridge of the electric signal ΔU, proportional to the magnitude of the deformation of the surface of the structure, which is recorded by the apparatus 10 and processed by the computing device 11 taking into account the calibration characteristics previously obtained by oschi calibration tool to test A = Φ [ε] or A = Φ (f)
A _{0-i the} output signal of the measuring equipment at specified values of deformation ε _oi or given values of displacements f _0-i .

 If during testing the magnitude of the deformation of the structure in a given zone exceeds the maximum permissible range for a given size of the measuring device, which corresponds to the length of the traction limiter 6 set when manufacturing the device, the stop end supports of the limiter will abut against the walls of the attachment points 3 of the elastic elements, will limit further deformation elastic element and strain gages.

где U напряжение питания измерительного моста;
R номинальное сопротивление каждого плеча тензорезистора измерительного моста;
ΔR приращение сопротивления при деформировании тензорезистора;
при R₁=R₂=R₃=R₄=R и ΔR₁=ΔR₂=ΔR₃=ΔR₄=ΔR
т.е. выходной сигнал увеличивается в 4 раза по сравнению с одним рабочим тензорезистором.The value of the output signal ΔU of the measuring bridge with four working strain gages is equal to:

where U is the supply voltage of the measuring bridge;
R is the nominal resistance of each arm of the strain gauge of the measuring bridge;
ΔR resistance increment during strain gauge deformation;
when R ₁ = R ₂ = R ₃ = R ₄ = R and ΔR ₁ = ΔR ₂ = ΔR ₃ = ΔR ₄ = ΔR
those. the output signal is increased 4 times in comparison with one working strain gauge.

S чувствительность тензорезистора;
ε средняя деформация чувствительной решетки тензорезистора;
l₂-l₁ Б база измерения тензорезистора;
e_уi деформация поверхности упругого элемента;
δ толщина упругого элемента;
d_n толщина диэлектрической основы тензорезистора;
d_п диаметр проволоки чувствительной решетки.Formula 1 can be represented as:

S sensitivity of the strain gauge;
ε average strain of the sensitive grating of the strain gauge;
l ₂ -l ₁ B base of the strain gauge measurement;
e _уi deformation of the surface of the elastic element;
δ thickness of the elastic element;
d _{n the} thickness of the dielectric base of the strain gauge;
d _p wire diameter of the sensitive array.

The deformation of the elastic element ε _{y is} determined by the nonlinear theory of bending of rods at large displacements. The calibration characteristic is determined by the dependence of the output signal of equipment A on the specified strain value ε or displacement fA = Φ (ε) or A = Φ (f) of the device together with the equipment using a calibration strain gauge installation or an optical measuring microscope.

 As an example in FIG. Figure 3 shows the dependence A = Φ (f) for prototype devices with measurement bases B equal to 15 and 20 mm for elastic elements with two working strain gauges connected according to the measuring half-bridge circuit and connected to the SIIT-3 system.

 The use of the device provides the ability to measure the deformation of soft shells and structures in the range of operating temperatures, expand the range of measurement of deformations by 50-100 times, increases the accuracy of measurements and reduces 1.5-2 times the operating costs of preparing and conducting measurements during structural testing.

Claims (2)

 1. A device for measuring the deformation of the flexible shells of aircraft, containing a flat substrate, a heat-resistant strain gauge and measuring equipment, characterized in that it is equipped with attachment points with holes installed in the attachment points, a thin-walled annular elastic element, the walls of which are perpendicular to the surface of the substrate, flexible a stroke limiter of the elastic element installed in the holes of the attachment points, heat-resistant strain gauges located on the walls of the annular elastic th element, and the substrate is made of a non-metallic plastic material.  2. The device according to claim 1, characterized in that the substrate is made of lavsan or kapron with acrylosilicone impregnation.

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