CN114184082A - Device and method for measuring gun barrel strain - Google Patents

Abstract

The invention discloses a device for measuring the strain of a gun barrel, which mainly comprises an input end coupler, an output end coupler and a single-mode optical fiber connected between the input end coupler and the output end coupler, wherein the single-mode optical fiber is repeatedly wound and tightly attached to the outer wall of the gun barrel to be measured to form an annular cavity which is used as a ring-down cavity; the input end coupler and the output end coupler are one-to-two couplers and comprise 99% ports and 1% ports; the 99% port of the input end coupler is directly connected with the 99% port of the output end coupler, and the 1% port of the output end coupler is sequentially connected with the photoelectric detector and the oscilloscope. The invention adopts the optical fiber annular cavity ring-down technology, which not only can improve the sensitivity, but also has strong applicability.

Description

Device and method for measuring gun barrel strain

Technical Field

The invention belongs to the technical field of gun barrels, and particularly relates to a device and a method for measuring gun barrel strain.

Background

The artillery is a heavy barrel weapon which takes gunpowder as a transmitting energy source to transmit a bullet, and the strength design of the structure is very important content in the design work of the artillery. During the firing process, the transient strain measurement of the barrel is a verification of the design and processing. The common method is that the strain is measured by using the change of the optical fiber interference fringes, namely, the length of two paths of optical fibers is changed due to the expansion of a gun barrel, so that the phase change is influenced, and the method is not high in sensitivity; the second most commonly used is fiber grating, which is a spatially periodic refractive index profile established in an optical fiber that is reflective or transmissive only to light of a particular wavelength, thereby allowing the behavior of the light at that wavelength to be altered and controlled. Since the peak wavelength thereof changes with changes in physical quantities such as temperature and strain, it is susceptible to various factors, resulting in poor environmental suitability.

Disclosure of Invention

In view of the above, the invention provides a device and a method for measuring gun barrel strain, and the device and the method adopt an optical fiber annular cavity ring-down technology, so that not only can the sensitivity be improved, but also the applicability is very strong. The specific technical scheme is as follows:

a device for measuring the strain of a gun barrel mainly comprises an input end coupler, an output end coupler and a single mode fiber connected between the input end coupler and the output end coupler, wherein the single mode fiber is repeatedly wound and tightly attached to the outer wall of the gun barrel to be measured to form an annular cavity which is used as a ring-down cavity; the input end coupler and the output end coupler are one-to-two couplers and comprise 99% ports and 1% ports; the 99% port of the input end coupler is directly connected with the 99% port of the output end coupler, and the 1% port of the output end coupler is sequentially connected with the photoelectric detector and the oscilloscope.

The length of the annular cavity is such that the width of the input light pulse is less than the time required for the light to move one circle in the annular cavity.

The loss of the single-mode optical fiber is 0.2dB/km

The device also comprises piezoelectric ceramics, and the piezoelectric ceramics are arranged on the single-mode optical fiber at the annular cavity section.

The invention also provides a method for measuring the strain of the gun barrel, which comprises the following steps:

(1) will have a length L₀The single mode fiber is wound on the outer wall of the gun barrel to be tested to form an annular cavity, the input end coupler and the output end coupler are connected to two ends of the single mode fiber, wherein 1% of ports of the input end coupler are connected with 99% of ports of the output end coupler;

(2) connecting the output end coupler to an oscilloscope through a photoelectric detector;

(3) transmitting the input pulsed light into the annular cavity;

(4) collecting and recording the ring-down time tau of input pulse light in the annular cavity by an oscilloscope₀；

(5) Calculating ring cavity ring-down factor B, B ═ tau₀/L₀Wherein, τ₀For the ring-down time, L, of the input pulsed light in the ring-shaped cavity₀The initial length of the annular cavity;

(6) applying external force to the gun barrel to deform the gun barrel, reading ring-down time tau recorded by an oscilloscope, and calculating the length L of the deformed annular cavity: l ═ τ/B;

(7) calculating the length variation of the annular cavity:

ΔL＝L-L₀

(8) calculating the strain delta epsilon of the gun barrel:

Δ ε is Δ L/N, where N is the number of fiber windings that make up the ring cavity.

Drawings

FIG. 1 is a view of the apparatus for measuring strain in a gun barrel according to the present invention;

FIG. 2 is a graph showing the exponential decrease of light intensity with time observed on an oscilloscope at the output end;

in the figure, 1, apulse laser 2, aninput end coupler 3, anoutput end coupler 4, anannular cavity 5, a gun barrel to be tested 6, aphotoelectric detector 7 and an oscilloscope are arranged.

Detailed Description

The invention is explained in further detail below with reference to the drawings.

As shown in fig. 1, the device for measuring the strain of the gun barrel mainly comprises aninput end coupler 2, anoutput end coupler 3 and a single-mode fiber connected between the input end coupler and the output end coupler, wherein the single-mode fiber is repeatedly wound and tightly attached to the outer wall of agun barrel 5 to be measured to form anannular cavity 4, and theannular cavity 4 is used as a ring-down cavity; the input end coupler and the output end coupler are one-to-two couplers and comprise 99% ports and 1% ports; wherein, 99% port of the input end coupler is directly connected with 99% port of the output end coupler; and 1% of ports of the output end coupler are sequentially connected with aphotoelectric detector 6 and anoscilloscope 7.

When pulse light emitted by thepulse laser 1 enters the annular cavity through 1% of ports of the input end coupler and is transmitted to the output end coupler, most of the pulse light returns to 99% of ports of the input end coupler through 99% of ports of the output end coupler and continuously circulates in the annular cavity repeatedly in an anticlockwise direction; a small portion of the signal light is transmitted to thephotodetector 6 and theoscilloscope 7 through the 1% port of the output end coupler. Most of the pulsed light was circulated within the toroidal cavity for several weeks until the intensity decay to 0 was observed in the oscilloscope and the decay time was recorded.

Further, if the incident light is a narrow pulse laser, the length of the annular cavity (i.e. the circumference of the annular cavity) should be such that the pulse width of the input light is less than the time required for the light to move in the annular cavity for one revolution (the length of the annular cavity is L)₀The time of one cycle of movement is L₀C, c is the speed of light in vacuum), at which time it will be observed on an oscilloscope at the outputTo a phenomenon in which the light intensity decreases exponentially with time, as shown in fig. 2. When stable, ring down time τ₀Is a constant.

The change in the length of the fiber ring cavity results in a change in the ring down time due to the external pressure.

And on the premise that the length of the annular cavity is required to meet the condition that the input light pulse width is less than the time required by one circle of light moving in the annular cavity, the optical fiber is wound on the outer wall of the gun barrel in a surrounding manner, so that the winding number N of the optical fiber can be increased for increasing the sensitivity. When strain is induced in the barrel, such as by radial expansion, the length of the fiber increases, which in turn affects the length of the annular cavity of the fiber, and the ring-down time changes, thereby measuring the barrel strain.

Furthermore, the technology has the advantages that the measuring result is not influenced by the fluctuation of the incident light intensity, the smaller the cavity loss is, the higher the precision is (the loss of the single-mode optical fiber is 0.2dB/km, the common length is several meters, the loss is small), the optical fiber annular cavity is directly fixed on the outer wall of the gun barrel, the deformation effect of the gun barrel can be amplified by winding the optical fiber annular cavity for several circles, and the sensitivity is increased.

Furthermore, the device also comprises piezoelectric ceramics, and the piezoelectric ceramics are arranged on the single-mode optical fiber at the annular cavity section so as to change the length of the annular cavity. If continuous laser is used, the sensitivity is higher. The continuous wave ring-down cavity spectrum forms standing waves in the cavity, the output light intensity is improved by utilizing high spectral resolution, the detection signal-to-noise ratio is increased, and the measurement sensitivity is improved. When continuous laser is injected into a ring-down cavity (optical fiber ring cavity), the length of the cavity is controlled by using piezoelectric ceramics (PZT), when a certain mode in the cavity is matched with a continuous laser mode, the energy in the cavity is rapidly accumulated, and incident light is cut off by setting a threshold value in the cavity. At the moment, the optical signal in the optical cavity is attenuated exponentially, and the measurement of the micro strain of the gun barrel is realized by using a method for calculating the ring-down time.

The invention also provides a method for measuring the strain of the gun barrel based on the device, which comprises the following steps:

(1) will have a length L₀The single mode fiber is wound on the outer wall of the gun barrel to form an annular cavity, and the input end coupler is connected withThe output end coupler is connected to two ends of the single-mode optical fiber, wherein 1% of ports of the input end coupler are connected with 99% of the output end coupler;

(2) connecting the output end coupler to an oscilloscope through a photoelectric detector;

(3) transmitting the input pulsed light into the annular cavity;

(4) collecting and recording ring-down time tau by oscilloscope₀Said ring-down time τ₀The light intensity of the input pulse is attenuated to I₀1/e, e is ring down time, I₀The initial light intensity when the pulsed light enters the ring cavity.

(5) Calculating a ring-down factor B, wherein the ring-down factor B is equal to tau₀/L₀Wherein, τ₀Ring down time of the ring cavity, L₀The initial length of the annular cavity; the derivation process of the formula is as follows:

ring-down time of the ring cavity is:

τ₀＝nL/cA

where n is the refractive index of the optical fiber, L is the length of the ring cavity, c is the speed of light in vacuum, and a is the loss of one round of transmission of the optical pulse in the ring cavity, including the absorption loss of the optical fiber, the insertion loss of the optical fiber coupler, the connection loss of the optical fiber connector, and the scattering loss of the optical fiber. When the ring cavity is fixed, a is constant. Therefore, the ring-down time of the ring-cavity is proportional to the length of the ring-cavity, and this proportionality coefficient is defined as the ring-down factor B, i.e. the

B＝τ₀/L₀

(6) Applying external force to the gun barrel to deform the gun barrel, reading ring-down time tau recorded by an oscilloscope, and calculating the length L of the deformed annular cavity according to the following formula: l ═ τ/a;

(7) calculating the length variation of the annular cavity:

ΔL＝L-L₀

(8) the strain delta epsilon of the gun barrel is calculated according to the following formula

And delta epsilon is delta L/N, and N is the winding number of the optical fiber in the ring cavity.

Claims (5)

1. The device for measuring the strain of the gun barrel is characterized by mainly comprising an input end coupler (2), an output end coupler (3) and a single-mode optical fiber connected between the input end coupler and the output end coupler, wherein the single-mode optical fiber is repeatedly wound and tightly attached to the outer wall of the gun barrel (5) to be measured to form an annular cavity (4), and the annular cavity is used as a ring-down cavity; the input end coupler and the output end coupler are one-to-two couplers and comprise 99% ports and 1% ports; wherein, the 99% port of the input end coupler is directly connected with the 99% port of the output end coupler, and the 1% port of the output end coupler is sequentially connected with the photoelectric detector (6) and the oscilloscope (7).

2. The apparatus of claim 1 wherein the length of the toroidal cavity is such that the width of the input light pulse is less than the time required for one revolution of the light within the toroidal cavity.

3. The apparatus of claim 1, wherein the single mode fiber has a loss of 0.2 dB/km.

4. The device of claim 1, further comprising a piezoelectric ceramic disposed on the single mode fiber at the ring cavity section.

5. A method of measuring strain in a barrel, the method comprising the steps of:

(1) will have a length L₀The single mode fiber is wound on the outer wall of the gun barrel to be tested to form an annular cavity, the input end coupler and the output end coupler are connected to two ends of the single mode fiber, wherein 1% of ports of the input end coupler are connected with 99% of ports of the output end coupler;

(2) connecting the output end coupler to an oscilloscope through a photoelectric detector;

(3) transmitting the input pulsed light into the annular cavity;

(4) collecting and recording the ring-down time tau of input pulse light in the annular cavity by an oscilloscope₀；

(5) Calculating ring cavity ring-down factor B，B＝τ₀/L₀Wherein, τ₀For the ring-down time, L, of the input pulsed light in the ring-shaped cavity₀The initial length of the annular cavity;

(6) applying external force to the gun barrel to deform the gun barrel, reading ring-down time tau recorded by an oscilloscope, and calculating the length L of the deformed annular cavity: l ═ τ/B;

(7) calculating the length variation of the annular cavity: Δ L ═ L-L₀；

(8) Calculating the strain delta epsilon of the gun barrel: Δ ε is Δ L/N, where N is the number of fiber windings that make up the ring cavity.

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