RU2200309C2 - Gear testing fiber-optical light guides for mechanical fatigue - Google Patents

Abstract

FIELD: measurement of parameters of mechanical fatigue of fiber-optical light guides. SUBSTANCE: gear testing fiber-optical light guides for mechanical fatigue has vertical base, unit with fixed upper clamp, unit with fixed lower clamp, upper and lower cramps. Gear includes drive of precision controllable rotation of unit with upper clamp with reference to vertical axis, inductor destroying specimen of fiber-optical light guide located in upper part of vertical base of gear, guides ensuring free movement of unit of lower clamp in vertical direction and preventing its rotation relative to vertical axis. Units of upper and lower clamps are provided with guides which axes are perpendicular to rotation axis of light guide and are intended for free thrust of corresponding clamps on them. Upper and lower clamps has first guides to align units of upper and lower clamps with guides. Clamps are fitted with two or more pressure screws to fix specimen. Upper and lower clamps have second guides to match axis of specimen of fiber-optical light guide with rotation axis of upper clamp. Weight W_car of unit of lower clamp is so chosen that it complies with condition 0,09 krc≤W_car≤3,23 kgf. Center of gravity of upper clamp is displaced with regard to its rotation axis towards side of clamp thrust. EFFECT: reduced cost of test of fiber-optical light guides, raised productivity of operators in process of operation of gear. 5 dwg

Description

 The invention relates to devices for measuring process parameters of mechanical fatigue of optical fibers.

 A device-analogue is known, which makes it possible to measure the parameters of the process of fatigue fracture of optical fibers — this is a universal explosive machine [1]. From the point of view of fatigue tests, a fundamentally important quality of a tensile testing machine is the ability to test samples at various constant values of the loading speed (i.e., the rate of increase of the normal tensile stress). Typically, tensile testing machines are equipped with climate chambers that allow testing samples and measuring mechanical fatigue under various environmental conditions, in particular at 100% humidity. However, explosive machines are expensive devices. The process of fatigue tests using a tensile testing machine is also expensive because of the inefficient use of the length of the samples during these tests. For example, during the tests, the results of which are given below, the length of each sample tested on a tensile testing machine was ~ 1 m, with a loading length of ~ 0.15 m. The ends of the samples ~ 0.85 m long were necessary for fixing the samples on the drum clamps of the tensile testing machine [1] .

 A known prototype device for mechanical testing of samples of glass fibers by simultaneously exposing them to stresses of dynamic torsion and dynamic axial tension [2]. The device was created by modifying a universal explosive machine. The modification consisted in the fact that on the lower part of the base of the tensile testing machine the base of a specially designed table is fixedly fixed, having a movable platform, which is rotated relative to the vertical axis by a DC motor and on which the clip is fixedly fixed to fix the lower end of the glass fiber sample.

The prototype device has:
vertical base;
a node with a fixed upper clamp (for fixing the upper end of the test sample);
a node with a fixed lower clamp (for fixing the lower end of the sample);
upper and lower clamp type clamps for fixing the ends of the sample;
a drive for precision controlled movement of the upper clamp assembly in a vertical direction;
a drive for precision controlled rotation of the lower clamp assembly relative to the vertical axis;
a tensile force meter applied to the test sample;
measuring angle of rotation of the lower clamp assembly relative to the vertical axis.

 The advantage of this device is the efficient use of sample lengths. Due to the possibility of using clamps in this case, the total length of the samples for the prototype device was slightly different from the loaded length.

 The measured values in the prototype device are the breaking force W, recorded by the tensile force sensor, and the angle of rotation φ of the table area with the lower clamp, at which the sample is destroyed.

где l - нагружаемая длина образца,

R_of - радиус стеклянного волокна, E и v - соответственно модуль Юнга и коэффициент Пуассона материала образца. Для кварцевых стекол Е ~ 7200 кгс/мм², v≈ 0.1682.As a measure of the mechanical strength of glass fibers, the value of the normal breaking stress σ _N , which is calculated by the well-known formula [3], is used.

where l is the loaded length of the sample,

R _of is the radius of the glass fiber, E and v are Young's modulus and Poisson's ratio of the sample material, respectively. For quartz glasses, E ~ 7200 kgf / mm ² , v≈ 0.1682.

 When carrying out fatigue tests of optical fibers, it is important to ensure a constant loading rate [1]. Measurements of the values of the median strength at various constant loading rates make it possible to determine the parameters of the process of fatigue failure of a fiber waveguide and, therefore, to construct a scientifically based forecast for its durability. In the case when the test stress is created due to the combined effects of dynamic torsion stresses and dynamic axial tension, the loading speed is constant only at constant (non-zero) speeds and axial tension and dynamic torsion.

The prototype device has the following disadvantages:
it is expensive;
allows you to test samples only in a laboratory environment;
the design of the clamps for samples does not provide high productivity for the operator of the device and does not allow testing of modern fiber optic fibers coated with protective polymer shells.

 The high cost of the device is caused by the presence of two precision loading mechanisms: the longitudinal tension of the samples and their axial twisting, and, accordingly, the presence of two meters: tensile strength and the angle of rotation of the table with the lower clamp. The prototype device does not allow to study the properties of samples in environments other than laboratory, because due to the presence of a rotary table, the standard climatic chamber of the tensile testing machine cannot be used. The process of installing test specimens using a prototype device is lengthy and inconvenient. High accuracy of sample installation is required: it is necessary to combine its axis with the axis of rotation of the lower clamp with an error not exceeding the value of the diameter of the sample. Due to the fact that the upper and lower clamps are rigidly fixed in the corresponding nodes of the prototype device and it does not have any devices to simplify and speed up the refueling process, the productivity of the device operator is low - a lot of time is spent on special sample preparation.

A prototype device was developed and used to test glass fibers without a protective polymer coating. In the clamps of the prototype device, the glass ends of the fiber were fixed, protected from the action of the hard clamping lips of the clamp clamps by cardboard overlays. Modern fiber optic fibers are multilayer structures: the glass light guide part is coated on the outside with several protective layers of polymers. Typically, the primary polymer coating applied directly to the glass is made of soft polymer, and the outer one is made of hard. An attempt to use clamps with one clamping screw (as in the prototype) when testing such fiber optic fibers revealed the following difficulties. For effective fixation of the ends of the sample, it is necessary to deform the hard outer coating so that the soft primary coating cannot play the role of a “lubricant” between the outer coating and the glass light guide. If the clamp is insufficient, then the torque is not transmitted from the clamp to the glass part of the fiber, and the sample cannot be tested. If the clamp turns out to be too strong, then the sample may break at the clamps and the measured strength values are underestimated in comparison with the test results of the same fiber waveguide on a tensile testing machine with drum clamps. This is illustrated in FIG. Here are the results of measuring the strength of a single-mode fiber with a two-layer polymer coating. On the graph, the abscissa axis shows the values of tensile forces equivalent to the measured values of normal tensile stresses, and the ordinates show the probabilities P of fracture of the samples. Equivalent breaking forces F _unit calculated by the formula F _unit = σ _N • π • R $\genfrac{}{}{0ex}{}{\text{2}}{\text{of}}$ . The diameter of the glass part of the fiber was 0.125 mm, and the outer diameter of the fiber in the coating was 0.255 mm. The primary coating used was DeSolite 950-106 polymer, the coating thickness was 0.04 mm. The material of the secondary coating is DeSolite 950-108 polymer, the coating thickness is 0.025 mm. The experimental points marked with an “o” are obtained when using clamping clamps with one clamping screw in the proposed device. The experimental points marked with an "x" are obtained on a tensile testing machine with drum clamps.

The aim of the invention is
cheaper device for measuring the parameters of the process of fatigue fracture of optical fibers (including in conditions other than laboratory);
increasing the productivity of the device operator.

The circuit is achieved due to the fact that the proposed device for testing samples of optical fibers for mechanical fatigue has
vertical base;
a node with a fixed upper clamp (for fixing the upper end of the test sample);
a node with a fixed lower clamp (for fixing the lower end of the sample);
upper and lower clamp type clamps for fixing the ends of the sample;
according to the invention
the device has a drive for precision controlled rotation of the upper clamp assembly relative to the vertical axis;
the device has an indicator of destruction of the fiber sample, located in the upper part of the vertical base of the device;
the device has guides that provide free movement of the lower clamp assembly in the vertical direction and prevent its rotation relative to the vertical axis;
the nodes of the upper and lower clamps are provided with guides, the axes of which are perpendicular to the axis of rotation of the fiber, for the free movement of the respective clamps along them;
the upper and lower clamps have first guides for aligning with the guides of the nodes of the upper and lower clamps;
the clamps are provided with two or more clamping screws for fixing the sample;
the upper and lower clamps have second guides for aligning the axis of the sample of the fiber with the axis of rotation of the upper clamp;
the weight of the lower clamp assembly W _{car is} chosen so that the conditions are met
0.090 kgf ≤ W _car ≤ 3.23 kgf; (3)
the center of gravity of the upper clamp is offset relative to the axis of rotation in the direction of the clamp's sliding.

 The invention is illustrated by drawings.

 FIG. 1. Comparison of the distribution of the tensile strength of a fiber waveguide, measured using a lnstron-1122 universal tensile machine, and the torsional strength, measured using a device for testing optical fibers for mechanical fatigue by simultaneously applying torsional and axial tensile stresses to them. During torsion tests, clamp clamps with one clamping screw were used.

 FIG. 2 Schematic diagram of a device for testing samples of optical fibers for mechanical fatigue by simultaneously acting on them with dynamic torsion stresses and static axial tension.

 Figure 3 Schematic diagram of an implemented device for testing samples of optical fibers for mechanical fatigue by simultaneously exposing them to stresses of dynamic torsion and static axial tension.

 FIG. 4. Comparison of the distribution of the tensile strength of a fiber waveguide, measured using a lnstron-1122 universal tensile machine, and the torsional strength, measured using a device for testing fiber optic fibers for mechanical fatigue by simultaneously applying dynamic torsional stresses and static axial tensile stresses to them. During torsion tests, clamp clamps with two clamping screws were used.

 Figure 5 Schematic diagram of a clamp clamp with two clamping screws for fixing samples of optical fibers in a device for testing mechanical fatigue by simultaneously affecting the samples with stresses of dynamic torsion and static axial tension.

 A schematic diagram of the proposed device for testing samples of optical fibers for mechanical fatigue is presented in figure 2.

 The device contains a vertical base 1, on which all the nodes of the device are fixed. The node 2 with the upper clamp fixed on it is located in the upper part of the vertical base. Precise controlled rotation of the node 2 relative to the vertical axis is carried out using the drive 4, consisting of a stepper motor (SM) and gearbox. Using a stepper motor allows you to do without a meter for the angle of rotation of the upper clamp unit, since for a high-precision determination of the angle value it is enough to count the number of steps performed by the stepper motor. At the bottom of the vertical base is a node 3 with a fixed lower clamp. The node can freely move in the vertical direction along the guides 6, which at the same time prevent rotation of the node relative to the vertical axis. Due to this, the dynamic twisting of the fiber sample 9 is carried out by means of the drive of the upper clamp assembly. During the test, the lower clamp assembly hangs freely on the fiber under test, carrying out its static tension. When the sample is destroyed, the node 3 falls along the guides 6 and changes the state of the indicator 5 of the destruction of the sample of the optical fiber. The electrical part of the indicator 5, as well as the actuator 4, are located in the upper part of the vertical base 1. The indicator of the destruction of the fiber sample is a necessary node of the proposed device. In the prototype device, a sign of fracture was a sharp drop in tensile force, recorded by a tensile force meter during the destruction of a glass fiber sample. The tensile force meter is an expensive high-precision element of the test device, and its presence is not necessary to ensure fracture fixation. For this purpose, an indicator is enough, which has two states: “the sample is intact”, “the sample is destroyed”.

 The low weight and compactness of the device as a whole make it possible, in contrast to the prototype device, to use the proposed device for testing samples in various environments, for example, in water. The weight of the proposed device does not exceed 4 kgf and it is arranged so that the electric drive for the controlled rotation of the upper clamp assembly, as well as the electrical part of the destruction indicator of the fiber sample, are located in the upper part of the vertical base of the device. Due to this, when the device is immersed in a container of water (an aquarium), the drive and the electrical part of the indicator are higher than the water level, which allows testing the samples in conditions of 100% humidity.

 The prototype device is based on a universal explosive machine, the price of which, together with the climate chamber, is ~ $ 20,000. The proposed device costs ~ $ 3000. This price difference is due to the following reasons. In the prototype device, the axial tension of the specimen is created due to the precision controlled vertical movement of the upper clamp assembly using a powerful drive of a universal tensile testing machine. In the proposed device, the static axial tension of the sample is created due to the weight of the lower clamp assembly, which during the test freely hangs on the sample of the optical fiber. The weight of this node is known, therefore, the axial tensile force sensor of the sample is not needed, which is necessary when using the prototype device.

 The normal stresses in the samples of optical fibers during mechanical tests by the torsion method can be calculated by measuring either the values of the torque applied to the sample or the values of deformation. The values of the moment during the destruction of fiber fibers do not exceed 0.1 kgf • mm. To measure such small values of the moment of force, there are no standards. The use of deformation for calculating the breaking stress can lead to large errors caused by the fact that the part of the sample located between the clamps and the ends of the sample on the clamps are deformed differently. The deformation of the fiber can be described by introducing the effective length [4] of the sample, which differs from the distance between the clamps (that is, the loaded length of the sample) the greater, the greater the deformable length of the fiber at the clips. The difficulty is that the length at which the deformation of the sample at the clamps decreases to zero depends on its maximum value. In developing the design of clamps for testing fiber optic fibers by dynamic torsion, special attention was paid to minimize the difference between the loaded and effective lengths of the samples. The successful solution of this problem made it possible to use the values of sample deformation for calculating destructive normal stresses.

 The prototype device uses clamp type clamps with one clamping screw. When using such clamps, there is a high probability of damage to the surface of the fiber waveguide on the clamp. As a result, the distribution of strength, measured on a torsion machine with such clamping clamps, is shifted to the region of low strengths compared with the distribution of strength obtained by testing samples of the same fiber waveguide on a tensile testing machine with drum clamps (see figure 1). Figure 4 presents a comparison of the distribution of strength of the same fiber, measured on a twisting machine equipped with clamping clamps with two clamping screws (as with the proposed device), and using a tensile testing machine equipped with drum clamps. It is seen that when using clamps with two clamping screws, the distribution of torsional strength coincides with the distribution of tensile strength. This is due to the fact that when using such clamps, damage and destruction of samples on the clamps does not occur.

 At the same time, such clamps also belong to the class of clamping clamps, since, according to TSB (second edition, vol. 41, p. 147), the clamp is a rectangular frame through which one or several clamping screws are passed through one of the long bars.

 For the convenience of refueling, increasing the accuracy of the installation of samples and increasing the productivity of the operator of the test device, the nodes of the upper and lower clamps have guides compatible with the first guides on the upper and lower clamps. The axes of those and other guides are perpendicular to the axis of rotation of the sample. Due to this, the clamps are easily removed and installed in nodes. This allows samples to be inserted into the clamps outside the device and then to freely slide the clamps along the guides located on the nodes of the upper and lower clamps.

 To ensure high accuracy of alignment of the axis of the sample of the fiber with the axis of rotation of the upper clamp, the upper and lower clamps are equipped with second guides that allow you to combine the axis of rotation of the clamp with the axis of the fiber with an error not exceeding 0.1 mm, i.e. less than the radius of the sample.

 The proposed device for testing samples of optical fibers for mechanical fatigue operates as follows. The operator removes the clamps from the nodes and, using the second guides, inserts the ends of the pre-cut sample of the optical fiber into the clamps. Then the ends of the sample are fixed by tightening the clamping screws of the clamps and the clamps with the sample fixed in them are pushed along the guides in nodes 2 and 3. The node 3 is kept from moving in the vertical direction due to the elasticity of the sample 9. The indicator of destruction of the sample is in the state “sample intact” .

 After this, the actuator motor drive 4 is turned on and the sample is twisted relative to the vertical axis. In order that during rotation the upper clamp does not fly off the guide of unit 2, its center of gravity is shifted relative to the axis of rotation in the direction of the clamp's sliding. Thus, during rotation, the clamp is pressed against the supporting surface by centrifugal force. The fiber optic cable experiences the simultaneous effect of static axial tension due to the weight of the assembly 3 with the lower clamp and the dynamic torsion stress generated by the precision drive 4. After the stress reaches the breaking value and the specimen breaks, the assembly 3 falls along the guides 6, changing the state of the specimen destruction indicator 5 fiber optic fiber to the "sample is destroyed." In this case, the value of the angle of rotation of the stepper motor made from the moment the test begins is recorded. The breaking stress value is calculated using relations (6) (see below) or (1), in which the angle φ is equal to the angle of rotation of the upper clamp assembly relative to the axis of the specimen made by the actuator 4, and the value of W is equal to the weight of the assembly 3 with the lower clamp. When conducting tests in an aquarium, the weight of node 3 decreases by Archimedean force.

при напряжениях, значения которых превышают 80% значения напряжения разрушения [1] . Здесь и ниже точка сверху означает дифференцирование по времени. Если вес узла с нижним зажимом удовлетворяет условию
W_car≤3,6•10^-2•E•π•R $\genfrac{}{}{0ex}{}{\text{2}}{\text{of}}$ , (5)
то значение нормального напряжения (1) в указанном диапазоне значений нормальных напряжений с точностью до единиц процентов определяется выражением

так что скорость нагружения при закручивании образца составляет

Таким образом, скорость нагружения

оказывается постоянной (в указанном диапазоне значений нормальных напряжений) при постоянной скорости закручивания образца

Условия (4) и (5) являются необходимыми и достаточными для того, чтобы при испытаниях образцов волоконных световодов путем одновременного воздействия на них напряжениями динамического кручения и статического осевого растяжения не происходило потери устойчивости образцов и скорость их нагружения была постоянной (в указанном диапазоне значений нормальных напряжений) при постоянной скорости вращения электродвигателя привода 4. Объединение условий (4) и (5) дает условие
10^-3•E•π•R $\genfrac{}{}{0ex}{}{\text{2}}{\text{of}}$ ≤W_car≤3,6•10^-2•E•π•R $\genfrac{}{}{0ex}{}{\text{2}}{\text{of}}$ . (7)
Для стандартных кварцевых волоконных световодов диаметром 125 мкм условия (7) принимают вид
0.090 кгс ≤ W_car ≤ 3.23 кгс. (8)
Таким образом, предлагаемое устройство характеризуется новой совокупностью признаков, которая позволяет достичь нового технического свойства, не являющегося суммарным эффектом: выполнить испытания образцов волоконных световодов на механическую усталость путем одновременного воздействия на них напряжениями динамического кручения и статического осевого растяжения. Благодаря указанным выше существенным признакам устройство позволяет проводить испытания образцов волоконных световодов в различных средах, в частности в условиях 100% влажности, обеспечивает высокую точность получаемых результатов (не уступающую точности результатов при испытании образцов на разрывной машине) и постоянство скорости нагружения (в указанном диапазоне напряжений), необходимое для получения характеристик механической усталости.The weight of the lower clamp assembly is chosen such (3) to ensure mechanical stability and constant loading speed of the tested samples. Due to this, the device is used to measure the parameters of the process of mechanical fatigue of optical fibers. Torsion of the fiber during testing can lead to loss of mechanical stability, while the axis of the sample forms a complex spatial curve, and the voltage acting on it is very complex. In this case, the interpretation of the test results is difficult. In order to prevent stability loss, it is enough to apply an additional tensile σ _t to the sample that exceeds some critical value of σ _zer :
σ _zer ≤σ _t .
Tests show that for fiber fibers σ _zer ≈ 10 ^-3 • E, so that when tested with the proposed device, the loss of stability of the samples can be avoided if the weight of unit 3 with the lower clamp satisfies the condition
10 ^-3 • E • π • R $\genfrac{}{}{0ex}{}{\text{2}}{\text{of}}$ ≤W _car .
In the case when the test stress in the sample is created due to the combined action of dynamic torsion stresses and static axial tension, it is impossible to ensure a constant loading rate over the entire range of normal stress values. When performing tests to determine the parameters of mechanical fatigue of optical fibers, it is important to ensure a constant rate of increase in normal voltage

at stresses whose values exceed 80% of the value of the fracture stress [1]. Here and below, the dot above means differentiation in time. If the weight of the unit with the lower clamp satisfies the condition
W _car ≤3.6 • 10 ^-2 • E • π • R $\genfrac{}{}{0ex}{}{\text{2}}{\text{of}}$ , (5)
then the value of the normal voltage (1) in the specified range of values of normal stresses with an accuracy of units of percent is determined by the expression

so that the loading speed when twisting the sample is

Thus, the loading rate

turns out to be constant (in the indicated range of normal stresses) at a constant swirling speed of the sample

Conditions (4) and (5) are necessary and sufficient so that when testing samples of optical fibers by simultaneously applying dynamic torsion and static axial tensile stresses to them, there is no loss of stability of the samples and their loading speed is constant (in the indicated range of normal voltage) at a constant speed of rotation of the electric motor of the drive 4. The combination of conditions (4) and (5) gives the condition
10 ^-3 • E • π • R $\genfrac{}{}{0ex}{}{\text{2}}{\text{of}}$ ≤W _car ≤3.6 • 10 ^-2 • E • π • R $\genfrac{}{}{0ex}{}{\text{2}}{\text{of}}$ . (7)
For standard quartz fiber optical fibers with a diameter of 125 μm, conditions (7) take the form
0.090 kgf ≤ W _car ≤ 3.23 kgf. (8)
Thus, the proposed device is characterized by a new set of features, which allows to achieve a new technical property, which is not the total effect: to test samples of fiber optical fibers for mechanical fatigue by simultaneously influencing them with dynamic torsional stresses and static axial tension. Due to the above mentioned essential features, the device allows testing fiber fiber samples in various environments, in particular in conditions of 100% humidity, provides high accuracy of the results obtained (not inferior to the accuracy of the results when testing samples on a tensile testing machine) and constant loading speed (in the specified voltage range ) necessary to obtain the characteristics of mechanical fatigue.

 In terms of simplicity and low cost, the proposed device is superior to all known devices for performing fatigue tests of optical fibers [1], and in terms of accuracy and applicability for predicting the durability of optical fibers under various operating conditions, it is not inferior to tensile testing machines.

EXAMPLE OF IMPLEMENTATION
The proposed device for testing samples of optical fibers for mechanical fatigue is implemented (see figure 3) and tested. The cost of design work, work on the implementation of the device in metal and the development of software for controlling the device using a personal computer amounted to about $ 3000.

 On the upper part of the vertical base 1 of the device is a node 2 with a fixed upper clamp. The nodes 2 and 3 of the upper and lower clamps have guides, the axes of which are perpendicular to the axis of rotation of the fiber, for alignment with the first guides of the respective clamps. Guides such as "dovetail" and "sleeve-guide rod" were implemented. The node 2 is driven into rotation relative to the vertical axis by means of a drive 4 based on the stepper motor DSHI-200-3. The node 3 with the fixed lower clamp is a carriage 7, which freely moves in the vertical direction along two guides. The vertical base 1 of the device is used as one guide. The second guide 6 also performs the function of traction indicator 5 destruction of the sample of the fiber.

For the convenience of the operator, the test device has a latch that restricts the vertical movement of the node 3. The latch is used when installing clamps with a sample fixed in them. Before starting the test, the operator using the clamp sets the node 3 in such a position that the distance between the upper and lower clamps is slightly less than the length of the tested samples. When installing the sample, the upper clamp is first pushed along the guides of the assembly 2. Then, along the guides of the fixed assembly 3, the lower clamp is pushed. Moreover, the sample does not limit the necessary movement of the clamps and does not interfere with these operations. Before turning on the loading engine, the operator releases the lock and the lower clamp assembly 3 hangs on the specimen, creating a static tensile stress σ _t in the latter.
The electrical part of the destruction indicator of the fiber sample is located on the upper part of the vertical base of the device and is a pair: LED - photodiode. The luminous flux from the LED to the photodiode is blocked by an opaque petal mounted on the upper part of the guide 6, which can be moved in the vertical direction. The lower and upper ends of the guide are attached to leaf springs 8 located on the lower and upper parts of the installation. Under the action of the springs, the guide takes a position in which the petal blocks the luminous flux from the LED to the photodiode. After the destruction of sample 9, the carriage with the lower clamp falls down, bends the springs and shifts the guide 6 so that the light diode from the LED begins to arrive on the photodiode. The rotation of the assembly with the lower clamp relative to the vertical axis is blocked due to the presence of the two guides indicated above. At the same time, the guides do not interfere with the vertical movement of this node.

 The device has clamp clamps for securing the ends of the test samples. Figure 5 presents a schematic diagram of the upper clamp and part 10 of the node of the upper clamp with the guide 12 for the free sliding of the clamp. Structurally, the upper and lower clamps are the same. The dimensions of the clamps were selected so that their center of gravity was shifted relative to the axis of rotation of the upper clamp in the direction of sliding onto the guides of the upper clamp assembly. Each clamp has a housing 11, a first guide 13 (compatible with the guide 12 of the upper or lower clamp assembly) for quick installation of the clamp on the test device, clamping screws 14. The second guides 15 and 16, fixing the end of the sample 9 at two points: at the entrance to the clamp and when exiting, the clamp is made of a material that does not damage the sample (for example, caprolon). Due to this, the axis of the fiber optic being tested is aligned with the axis of rotation of the upper clamp with an error not exceeding 0.1 mm, i.e., less than the radius of the sample (in figure 5 two clamping screws are shown; their number can be increased if necessary).

 The operator controls the device and receives the test results using a personal computer.

 The implemented design options for the nodes of the device do not exhaust all possible structural options for constructing the device. For example, the vertical base of the device can be made in the form of a pipe with cutouts for clamps, an indicator of the destruction of a fiber sample can be implemented using reed switches, the device does not have to be controlled using a personal computer, etc.

 To assess the accuracy of the test results, a comparison was made of the results of measuring the distribution of strength of optical fibers on an Instron-1122 universal tensile testing machine and on a device for testing samples of optical fibers for mechanical fatigue by the simultaneous action of dynamic torsional stresses and static axial tension on them. Two randomized ensembles of samples were cut from the same single-mode fiber with a two-layer polymer coating and tested on two devices. The diameter of the glass part of the fiber was 0.125 mm, and the outer diameter in the coating was 0.255 mm. The primary coating used was DeSolite 950-106 polymer, the coating thickness was 0.04 mm. The material of the secondary coating is DeSolite 950-108 polymer, the coating thickness is 0.025 mm. During the tests, a set of additional weights was used, which were hung on the carriage 7 with the lower clamp. A set of additional weights allowed us to cover the entire range of static tensile values (8). In order to provide the possibility of testing in water and other aggressive environments, as well as to realize an additional tensile force of ~ 0.1 kgf, special clamp clamp type clamps with two clamping screws each were made of titanium.

 The test results for all additional weights are brought together and presented in FIG. 4 (experimental points marked with an o). Here, for comparison, the test results of the second ensemble of samples on a tensile testing machine with drum clamps are shown (experimental points marked with an x). On the graph, the abscissa axis shows the values of tensile forces equivalent to the measured values of normal tensile stresses, and the ordinates show the probabilities P of fracture of the samples.

 From the graphs in figure 4 it is seen that the measured distribution of strength coincide. This means that the accuracy of the measurement of the fatigue characteristics of the optical fibers on a universal tensile machine and using the proposed device are the same in the entire range of values of the static tension of the samples indicated above. Using the proposed device were also measured the distribution of the strength of the optical fibers in conditions of 100% humidity at various loading speeds. These measurements made it possible to obtain the values of the mechanical fatigue parameters of optical fibers under various environmental conditions and to make a prediction of their durability. The prototype device does not allow to obtain such results.

Literature
1. International Electrotechnical Commission. Draft International Standard 86A / 302 / DIS, Project number 86A / 793-1-3 / Ed. 1.

 2. William J. Kroenke. "Torsional testing techniques applied to fine diameter glass fibers." The Glass Industry, v. 47, 5, p.p. 262-266, 282-284, 1966.

 3.S.P. Tymoshenko, J. Goodyear. Theory of elasticity, Moscow: Nauka, 1975.

 4. I.V. Aleksandrov, M.E. Zhabotinsky, S.Ya. Feld, O.E. Shushpanov. "Optimization of drum clamps in static and dynamic tests of optical fibers." - Journal of Technical Physics, vol. 61, 11, pp. 140-150 (1991).

Claims (1)

A device for testing samples of fiber optical fibers for mechanical fatigue, containing a vertical base, a node with a fixed upper clamp (for fixing the upper end of the test sample), a node with a fixed lower clamp (for fixing the lower end of the sample), the upper and lower clamp type clamps for fixing the ends of the sample, characterized in that the device has a drive for precision controlled rotation of the node of the upper clamp relative to the vertical axis, the indicator of destruction of the image fiber optic cable located in the upper part of the vertical base of the device, guides that provide free movement of the lower clamp assembly in the vertical direction and prevent its rotation relative to the vertical axis, the nodes of the upper and lower clamps are equipped with guides, the axes of which are perpendicular to the axis of rotation of the optical fiber, for free pushing the corresponding clamps along them, the upper and lower clamps have first guides for aligning with the guides of the upper and lower nodes about the clamps, the clamps are equipped with two or more clamping screws for fixing the sample, the upper and lower clamps have second guides to align the axis of the sample of the fiber with the axis of rotation of the upper clamp, the weight of the lower clamp assembly W _{car is} selected so that the condition 0,090 kgf ≤ W _car ≤ 3.23 kgf, the center of gravity of the upper clamp is offset relative to the axis of its rotation in the direction of the clamp's sliding.

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