CN114526851B - Method for measuring thermal stress of metal-composite material mixed structure for airplane - Google Patents

Method for measuring thermal stress of metal-composite material mixed structure for airplane Download PDF

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CN114526851B
CN114526851B CN202210436691.4A CN202210436691A CN114526851B CN 114526851 B CN114526851 B CN 114526851B CN 202210436691 A CN202210436691 A CN 202210436691A CN 114526851 B CN114526851 B CN 114526851B
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strain
temperature
strain gauge
resistor
test piece
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CN114526851A (en
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刘海燕
李闯勤
李红贤
白泽瑞
任战鹏
杜文辉
吴敬涛
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AVIC Aircraft Strength Research Institute
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/20—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
    • G01L1/22—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress using resistance strain gauges
    • G01L1/225—Measuring circuits therefor
    • G01L1/2262—Measuring circuits therefor involving simple electrical bridges
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/16—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring the deformation in a solid, e.g. by resistance strain gauge
    • G01B7/18—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring the deformation in a solid, e.g. by resistance strain gauge using change in resistance

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Abstract

The invention discloses a method for measuring the thermal stress of a metal-composite material mixed structure for an airplane, which comprises the following steps: firstly, obtaining a test piece and a standard test piece according to a metal-composite material mixed structure for an airplane; secondly, calibrating the sensitivity coefficient of the strain gauge; thirdly, carrying out heat output measurement on the standard test piece; fourthly, measuring the total strain of the test piece; and fifthly, acquiring the thermal stress of the metal-composite material mixed structure for the airplane. The method has simple steps and reasonable design, obtains the thermal strain at the test point in the test specimen at the measurement temperature by correcting the total strain at the test point in the test specimen at the measurement temperature, and further obtains the thermal stress at the test point, so as to improve the measurement accuracy of the thermal stress of the metal-composite material mixed structure for the airplane.

Description

Method for measuring thermal stress of metal-composite material mixed structure for airplane
Technical Field
The invention belongs to the technical field of thermal stress testing of airplane structures, and particularly relates to a method for measuring thermal stress of a metal-composite material mixed structure for an airplane.
Background
Composite materials have higher specific strength and specific stiffness than metal materials, and are widely applied to aircrafts such as airplanes, and the proportion of composite materials in airplane structures is on an increasing trend. Nevertheless, composite materials are limited by strength and stiffness and cannot be completely substituted for metal materials. Therefore, in the design of an aircraft structure, in order to meet the requirements of structural strength and weight reduction, a metal-composite material mixed structure which takes a metal material as a main load-bearing structure and takes a composite material as a secondary load-bearing structure and a functional structure is generally adopted. For example, the thermal expansion coefficient of the metal material is not in the same order as that of the carbon fiber composite material, for example, the thermal expansion coefficient of aluminum is 23.21 × 10-6/K, and the thermal expansion coefficient of the T300 carbon fiber is-0.74 × 10-6/K, so that when the temperature of the metal-composite material hybrid structure composed of aluminum and the T300 carbon fiber changes, although the hybrid structure reaches a self-balancing state based on deformation coordination, the new self-balancing state already generates structural internal stress, which is not subjected to mechanical load, and the structural internal stress caused only by the temperature change is called thermal stress.
Typically, structural strength on an aircraft is ensured by structural strength design and strength verification tests. The thermal stress is usually determined by simulation analysis during structural strength design, and due to the complexity of the structure and the heat transfer, the simulation analysis result is often not accurate enough and can only be used as reference data. The strength verification test of the structure includes a static strength test and a fatigue test, and in these tests, the thermal stress is generally considered in a manner of amplifying the mechanical load by 1.15 to 1.30 times. The processing mode of the thermal stress inevitably causes great deviation between the structural strength verification test result and the actual use condition, the structural weight is unnecessarily increased under the conservative condition, and the safety risk is brought under the dangerous condition. In recent years, as safety accidents caused by the thermal stress of the metal-composite material mixed structure increase, the requirement for accurate test of the thermal stress of the metal-composite material mixed structure is extremely urgent.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide a method for measuring thermal stress of a metal-composite material mixed structure for an aircraft, which has simple steps and reasonable design, and obtains thermal strain at a test point in a test specimen at a measurement temperature by correcting total strain at the test point in the test specimen at the measurement temperature, thereby obtaining thermal stress at the test point, and improving the accuracy of measuring thermal stress of the metal-composite material mixed structure for the aircraft.
In order to solve the technical problems, the invention adopts the technical scheme that: a method of measuring thermal stress of a metal-composite hybrid structure for an aircraft, the method comprising the steps of:
step one, obtaining a test piece and a standard test piece according to a metal-composite material mixed structure for an airplane:
step 101, taking a part to be tested on an airplane as a test piece; wherein, the test piece is a metal-composite material mixed structure;
step 102, presetting a plurality of test points on the surface of a test specimen;
103, manufacturing a 200mm multiplied by 200mm square test piece as a standard test piece; wherein, the standard test piece and the test piece are made of the same material at the test point;
step two, calibrating the sensitivity coefficient of the strain gauge:
calibrating the strain gauge by using an equal-strength beam experimental device to obtain a sensitivity coefficient of the calibrated strain gauge at each temperature;
step three, carrying out heat output measurement on the standard test piece:
placing the standard test piece in the step 103 in an environmental laboratory, pasting a first strain gauge on the standard test piece, connecting the first strain gauge with a resistor R2, a resistor R3 and a resistor R4 to form a first Wheatstone bridge circuit, and obtaining a second Wheatstone bridge circuit through the first Wheatstone bridge circuit
Figure 833108DEST_PATH_IMAGE001
Heat output at a measured temperature
Figure 433854DEST_PATH_IMAGE002
(ii) a Wherein the content of the first and second substances,
Figure 897196DEST_PATH_IMAGE001
is a positive integer;
step four, carrying out total strain measurement on the test specimen:
placing a test piece in an environmental laboratory, pasting a second strain gauge at the test point of the test piece, connecting the second strain gauge with a resistor R2 ', a resistor R3 ' and a resistor R4 ' to form a second Wheatstone bridge circuit, and obtaining a second Wheatstone bridge circuit through the second Wheatstone bridge circuit
Figure 241590DEST_PATH_IMAGE001
Total strain at test point in test specimen at individual measurement temperature
Figure 801884DEST_PATH_IMAGE003
；
Step five, obtaining the thermal stress of the metal-composite material mixed structure for the airplane:
step 501, according to the formula
Figure 307952DEST_PATH_IMAGE004
To obtain the first
Figure 524170DEST_PATH_IMAGE005
Measuring thermal strain at a test point in a metal-composite hybrid structure for an aircraft at a temperature
Figure 406675DEST_PATH_IMAGE006
；
502, according to a formula
Figure 759159DEST_PATH_IMAGE007
To obtain the first
Figure 249177DEST_PATH_IMAGE008
Thermal stress at a test point in a metal-composite hybrid structure for an aircraft at a measured temperature
Figure 687112DEST_PATH_IMAGE009
(ii) a Wherein the content of the first and second substances,
Figure 373308DEST_PATH_IMAGE010
is shown as
Figure 580298DEST_PATH_IMAGE011
The test piece was tested for stiffness of the material at the test point at each measurement temperature.
The method for measuring the thermal stress of the metal-composite material mixed structure for the airplane is characterized by comprising the following steps of: when the material at the test point on the test specimen is a metal material, the standard specimen is a metal material standard specimen;
and when the material at the test point on the test specimen is the composite material, the standard specimen is the composite material standard specimen.
The method for measuring the thermal stress of the metal-composite material mixed structure for the airplane is characterized by comprising the following steps of: and step two, calibrating the strain gauge by using an equal-strength beam experimental device to obtain the calibrated sensitivity coefficient of the strain gauge at each temperature, wherein the specific process is as follows:
step 201, symmetrically sticking a plurality of strain gauges and a plurality of temperature sensors at the set positions on the upper surface and the lower surface of a constant-strength beam in an experimental device of the constant-strength beam; the strain gauges and the temperature sensors are arranged close to the fixed end of the constant-strength beam, the strain gauges are arranged at equal intervals, and the constant-strength beam is horizontally arranged in an environmental laboratory;
step 202, recording a plurality of strain gauges and a plurality of temperature sensors on the upper surface of the equal-strength beam as a plurality of upper strain gauges and a plurality of upper temperature sensors, respectively, and recording the plurality of upper strain gauges as a 1 st upper strain gauge in sequence
Figure 693748DEST_PATH_IMAGE012
One strain gauge, the first
Figure 618979DEST_PATH_IMAGE013
An upper strain gauge, which sequentially marks the upper temperature sensors as the 1 st upper temperature sensor
Figure 905603DEST_PATH_IMAGE012
On the temperature sensor, the first
Figure 232680DEST_PATH_IMAGE013
An upper temperature sensor; wherein the content of the first and second substances,
Figure 517030DEST_PATH_IMAGE012
and
Figure 663978DEST_PATH_IMAGE014
are all positive integers, and
Figure 691977DEST_PATH_IMAGE015
of 1 at
Figure 683679DEST_PATH_IMAGE016
The upper temperature sensor is close to
Figure 138931DEST_PATH_IMAGE012
The upper strain gauges are adhered, and the number of the upper strain gauges is the same as that of the upper temperature sensors, and the upper strain gauges correspond to the upper temperature sensors one by one;
step 203, respectively recording a plurality of strain gauges and a plurality of temperature sensors on the lower surface of the equal-strength beam as a plurality of lower strain gauges and a plurality of lower temperature sensors, and sequentially recording a plurality of lower strain gauges as a 1 st lower strain gauge
Figure 38754DEST_PATH_IMAGE017
A lower strain gage, the first
Figure 604865DEST_PATH_IMAGE018
A lower strain gauge, which sequentially marks the lower temperature sensors as the 1 st lower temperature sensor
Figure 640954DEST_PATH_IMAGE017
A lower temperature sensor, a
Figure 267107DEST_PATH_IMAGE018
A lower temperature sensor; wherein the content of the first and second substances,
Figure 450964DEST_PATH_IMAGE017
and
Figure 820765DEST_PATH_IMAGE018
are all positive integers, and
Figure 976940DEST_PATH_IMAGE019
first, of
Figure 773995DEST_PATH_IMAGE017
A lower temperature sensor is close to
Figure 382831DEST_PATH_IMAGE017
The lower strain gauges are adhered, the number of the lower strain gauges is the same as that of the lower temperature sensors, the lower strain gauges correspond to that of the lower temperature sensors one by one, and the upper strain gauges and the lower strain gauges are arranged in an up-down symmetrical mode relative to the equal-strength beam;
step 204, adjusting the temperature in the environmental laboratory until
Figure 290744DEST_PATH_IMAGE020
Average sum of temperatures detected by individual temperature sensors
Figure 114474DEST_PATH_IMAGE021
The average value of the temperatures detected by the lower temperature sensors all meet the 1 st temperature
Figure 82430DEST_PATH_IMAGE022
；
Step 205, keeping the temperature in the environment laboratory at the 1 st temperature
Figure 178562DEST_PATH_IMAGE022
After 15-20 min, applying 30N load to the end of the constant-strength beam through a weight, and acquiring the second time by adopting a strain acquisition instrument
Figure 890167DEST_PATH_IMAGE023
First strain value and second strain value of upper strain gauge
Figure 20934DEST_PATH_IMAGE024
A first strain value of the next lower strain gage;
step 206, unloading the weights to enable the end of the equal-strength beam to apply zero load, and acquiring the second strength by using the strain acquisition instrument
Figure 159791DEST_PATH_IMAGE023
Second strain value and second strain value of upper strain gage
Figure 539957DEST_PATH_IMAGE024
A second strain value of the lower strain gage;
step 207, according to
Figure 55252DEST_PATH_IMAGE023
First strain value and second strain value of upper strain gauge
Figure 40525DEST_PATH_IMAGE023
The second strain value of the upper strain gauge is obtained
Figure 350284DEST_PATH_IMAGE023
Difference in strain of individual strain gauges
Figure 155429DEST_PATH_IMAGE025
(ii) a According to the first
Figure 208835DEST_PATH_IMAGE024
First strain value and second strain value of each lower strain gauge
Figure 861665DEST_PATH_IMAGE024
The second strain value of the lower strain gauge is obtained
Figure 342325DEST_PATH_IMAGE024
Difference of strain of lower strain gauge
Figure 900345DEST_PATH_IMAGE026
；
Step 208, according to the formula
Figure 491863DEST_PATH_IMAGE027
Obtaining a first average value of the strain difference
Figure 451729DEST_PATH_IMAGE028
；
Step 209, repeating step 205 to step 208 twice to respectively obtain a second average value of the strain difference
Figure 103290DEST_PATH_IMAGE029
And third mean value of strain difference
Figure 945344DEST_PATH_IMAGE030
；
Step 20A, according to the formula
Figure 340554DEST_PATH_IMAGE031
Obtaining the average value of the strain difference values at the 1 st temperature
Figure 154926DEST_PATH_IMAGE032
；
Step 20B, according to the formula
Figure 977388DEST_PATH_IMAGE033
Obtaining the sensitivity coefficient of the calibrated strain gauge at the 1 st temperature
Figure 244422DEST_PATH_IMAGE034
(ii) a Wherein, the first and the second end of the pipe are connected with each other,
Figure 256371DEST_PATH_IMAGE035
the sensitivity coefficient of the strain gauge at normal temperature;
Figure 925250DEST_PATH_IMAGE036
represents the standard strain of the constant strength beam under the load of 30N and at normal temperature;
step 20C, repeating the step 204 to the step 20B for multiple times, and adjusting the temperature in the environmental laboratory until the temperature is adjusted
Figure 918614DEST_PATH_IMAGE037
Average sum of temperatures detected by temperature sensors on each
Figure 672943DEST_PATH_IMAGE038
The average value of the temperatures detected by the lower temperature sensors satisfies the second
Figure 675534DEST_PATH_IMAGE039
A temperature
Figure 198919DEST_PATH_IMAGE040
And get the first
Figure 363184DEST_PATH_IMAGE041
Sensitivity coefficient of calibrated strain gauge at individual temperature
Figure 667127DEST_PATH_IMAGE042
；
Step 20D, repeating step 20C for multiple times until the first step is obtained
Figure 207829DEST_PATH_IMAGE043
A temperature
Figure 585721DEST_PATH_IMAGE044
Sensitivity coefficient of lower strain gauge after calibration
Figure 186467DEST_PATH_IMAGE045
(ii) a Wherein the content of the first and second substances,
Figure 649809DEST_PATH_IMAGE046
when it comes to
Figure 994203DEST_PATH_IMAGE047
When the content of the carbon dioxide is greater than or equal to 2,
Figure 36721DEST_PATH_IMAGE048
，
Figure 808368DEST_PATH_IMAGE049
it is indicated that the value of the temperature increase,
Figure 759006DEST_PATH_IMAGE050
is shown as
Figure 641511DEST_PATH_IMAGE051
The temperature;
and 20E, drawing the obtained temperature by taking the sensitivity coefficient calibrated by the strain gauge as a vertical coordinate and the temperature as a horizontal coordinate
Figure 993995DEST_PATH_IMAGE052
，...，
Figure 936544DEST_PATH_IMAGE053
，...，
Figure 436795DEST_PATH_IMAGE054
Sensitivity coefficient calibrated with strain gauge corresponding to each temperature
Figure 122991DEST_PATH_IMAGE055
，...，
Figure 329982DEST_PATH_IMAGE056
，...，
Figure 443431DEST_PATH_IMAGE057
And fitting to obtain a relation curve between the temperature and the calibrated sensitivity coefficient of the strain gauge, thereby obtaining the calibrated sensitivity coefficient of the strain gauge at each temperature.
The method for measuring the thermal stress of the metal-composite material mixed structure for the airplane is characterized by comprising the following steps of: in step 202
Figure 368662DEST_PATH_IMAGE058
The distances between the upper strain gauges and the fixed end faces of the equal-strength beams are the same,
Figure 592970DEST_PATH_IMAGE058
the distance between the upper strain gauge and the loading end of the equal-strength beam is greater than 1/2 of the length of the equal-strength beam;
the value of the 1 st temperature in the step 20D is-55 DEG C
Figure 733095DEST_PATH_IMAGE059
The temperature is 90 deg.C, and the temperature increase value
Figure 751867DEST_PATH_IMAGE060
The value of (A) is 1-2 ℃.
The metal-composite material mixture for the airplaneThe method for measuring the thermal stress of the structure is characterized by comprising the following steps: in the third step, the standard test piece in the step 103 is placed in an environmental laboratory, the first strain gauge is pasted on the standard test piece, the first strain gauge is connected with the resistor R2, the resistor R3 and the resistor R4 to form a first Wheatstone bridge circuit, and the first Wheatstone bridge circuit is used for obtaining a first Wheatstone bridge circuit
Figure 164394DEST_PATH_IMAGE061
Heat output at a measured temperature
Figure 192393DEST_PATH_IMAGE062
The specific process is as follows:
step 301, placing the standard test piece in the step 103 in an environmental laboratory, pasting a first strain gauge on the standard test piece, and connecting the first strain gauge with a resistor R2, a resistor R3 and a resistor R4 to form a first wheatstone bridge circuit; the initial resistance value of the first strain gauge is set as R1, the junction of R1 and R2 is set as point A, the junction of R2 and R3 is set as point C, the junction of R3 and R4 is set as point B, the junction of R4 and R1 is set as point D, and the resistance values of R1, R2, R3 and R4 are the same;
step 302, adjusting the temperature of the laboratory in which the standard test piece is located to the second temperature
Figure 373975DEST_PATH_IMAGE061
A measured temperature
Figure 829227DEST_PATH_IMAGE063
And preserving heat;
step 303, applying an excitation voltage between the points C and D
Figure 525788DEST_PATH_IMAGE064
And obtaining an output voltage between the points A and B
Figure 91898DEST_PATH_IMAGE065
；
Step 304, according to the formula
Figure 393567DEST_PATH_IMAGE066
To obtain the first
Figure 19720DEST_PATH_IMAGE067
Heat output at a measured temperature
Figure 141260DEST_PATH_IMAGE068
(ii) a Wherein;
Figure 511061DEST_PATH_IMAGE069
is shown as
Figure 480286DEST_PATH_IMAGE070
A measured temperature
Figure 277340DEST_PATH_IMAGE071
And (5) calibrating the sensitivity coefficient of the lower strain gauge.
The method for measuring the thermal stress of the metal-composite material mixed structure for the airplane is characterized by comprising the following steps: in the fourth step, the test specimen is placed in an environmental laboratory, a second strain gauge is pasted at the test point of the test specimen, the second strain gauge is connected with the resistor R2 ', the resistor R3 ' and the resistor R4 ' to form a second Wheatstone bridge circuit, and the second Wheatstone bridge circuit is used for obtaining a second Wheatstone bridge circuit
Figure 886176DEST_PATH_IMAGE072
Total strain at test point in test specimen at individual measurement temperature
Figure 794089DEST_PATH_IMAGE073
The specific process is as follows:
step 401, placing a test specimen in an environmental laboratory, adhering a second strain gauge to a test point of the test specimen, and connecting the second strain gauge with a resistor R2 ', a resistor R3 ' and a resistor R4 ' to form a second Wheatstone bridge circuit; wherein, the initial resistance value of the second strain gauge is set as R1 ', the junction of R1' and R2 'is marked as A', the junction of R2 'and R3' is marked as C ', the junction of R3' and R4 'is marked as B', the junction of R4 'and R1' is marked as D, and the resistance values of R1 ', R2', R3 'and R4' as well as R1, R2, R3 and R4 are all the same;
step 402, adjusting the temperature of the laboratory in which the test specimen is located to be the second temperature
Figure 804771DEST_PATH_IMAGE074
A measured temperature
Figure 772727DEST_PATH_IMAGE075
And preserving heat;
step 403, applying an excitation voltage between the points C' and D
Figure 931176DEST_PATH_IMAGE076
And obtaining an output voltage between the A 'point and the B' point
Figure 642780DEST_PATH_IMAGE077
；
404, according to the formula
Figure 507967DEST_PATH_IMAGE078
To obtain the first
Figure 646825DEST_PATH_IMAGE079
Total strain at test point in test specimen at individual measurement temperature
Figure 230253DEST_PATH_IMAGE080
。
Compared with the prior art, the invention has the following advantages:
1. the method for measuring the thermal stress of the metal-composite material mixed structure for the airplane has the advantages of simple steps, convenient realization and simple and convenient operation, considers the thermal output at the measurement temperature of the standard test piece, and improves the accuracy of obtaining the thermal strain at the test point in the test piece at the measurement temperature, thereby improving the measurement accuracy of the thermal stress of the metal-composite material mixed structure for the airplane.
2. The measuring method of the thermal stress of the metal-composite material mixed structure for the airplane is simple and convenient to measure and good in measuring effect, and firstly, a test piece and a standard test piece are obtained according to the metal-composite material mixed structure for the airplane; secondly, calibrating the sensitivity coefficient of the strain gauge; then, carrying out heat output measurement on the standard test piece; then, measuring the total strain of the test piece; and finally, acquiring the thermal stress of the metal-composite material mixed structure for the airplane.
3. The invention calibrates the sensitivity coefficient of the strain gauge so that the calibrated sensitivity coefficient of the strain gauge participates in the heat output measurement of a subsequent standard test piece and the total strain measurement of a test piece, thereby reducing the strain error caused by temperature change.
4. The Wheatstone bridge circuit of 1/4 bridge is adopted in the heat output measurement of the standard test piece and the total strain measurement of the test piece, so that the test resource requirement is greatly reduced, and the measurement cost and the measurement time are saved.
In conclusion, the method provided by the invention has the advantages of simple steps and reasonable design, and the thermal strain at the test point in the test specimen at the measurement temperature is obtained by correcting the total strain at the test point in the test specimen at the measurement temperature, so that the thermal stress at the test point is further obtained, and the accuracy of measuring the thermal stress of the metal-composite material mixed structure for the airplane is improved.
The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.
Drawings
FIG. 1 is a schematic structural view of an isobeam, strain gage and temperature sensor of the present invention.
FIG. 2 is a circuit diagram of a first Wheatstone bridge according to the present invention.
FIG. 3 is a circuit diagram of a second Wheatstone bridge according to the invention.
FIG. 4 is a block diagram of a method flow of the present invention.
Description of the reference numerals:
1-beam of equal strength; 2-upper strain gauges; 3-upper temperature sensor.
Detailed Description
A method for measuring thermal stress of a metal-composite hybrid structure for an aircraft as shown in fig. 1 to 4, the method comprising the steps of:
the method comprises the following steps:
step one, obtaining a test piece and a standard test piece according to a metal-composite material mixed structure for an airplane:
step 101, taking a part to be tested on an airplane as a test piece; wherein, the test piece is a metal-composite material mixed structure;
step 102, presetting a plurality of test points on the surface of a test specimen;
103, manufacturing a 200mm multiplied by 200mm square test piece as a standard test piece; wherein, the standard test piece and the test piece are made of the same material at the test point;
step two, calibrating the sensitivity coefficient of the strain gauge:
calibrating the strain gauge by using an equal-strength beam experimental device to obtain a sensitivity coefficient of the calibrated strain gauge at each temperature;
step three, carrying out heat output measurement on the standard test piece:
placing the standard test piece in the step 103 in an environmental laboratory, pasting a first strain gauge on the standard test piece, connecting the first strain gauge with a resistor R2, a resistor R3 and a resistor R4 to form a first Wheatstone bridge circuit, and obtaining a second Wheatstone bridge circuit through the first Wheatstone bridge circuit
Figure 558597DEST_PATH_IMAGE001
Heat output at a measured temperature
Figure 278291DEST_PATH_IMAGE002
(ii) a Wherein the content of the first and second substances,
Figure 588050DEST_PATH_IMAGE001
is a positive integer;
step four, carrying out total strain measurement on the test specimen:
placing a test piece in an environmental laboratory, pasting a second strain gauge at the test point of the test piece, connecting the second strain gauge with a resistor R2 ', a resistor R3 ' and a resistor R4 ' to form a second Wheatstone bridge circuit, and obtaining a second Wheatstone bridge circuit through the second Wheatstone bridge circuit
Figure 658774DEST_PATH_IMAGE001
Total strain at test point in test piece at individual measurement temperature
Figure 712181DEST_PATH_IMAGE003
；
Step five, obtaining the thermal stress of the metal-composite material mixed structure for the airplane:
step 501, according to the formula
Figure 551961DEST_PATH_IMAGE004
To obtain the first
Figure 94938DEST_PATH_IMAGE005
Thermal strain at a test point in a metal-composite hybrid structure for an aircraft at a measured temperature
Figure 652958DEST_PATH_IMAGE006
；
502, according to a formula
Figure 244476DEST_PATH_IMAGE007
To obtain the first
Figure 938763DEST_PATH_IMAGE008
Thermal stress at a test point in a metal-composite hybrid structure for an aircraft at a measured temperature
Figure 855903DEST_PATH_IMAGE009
(ii) a Wherein the content of the first and second substances,
Figure 445760DEST_PATH_IMAGE010
denotes the first
Figure 840969DEST_PATH_IMAGE011
The test piece was tested for stiffness of the material at the test point at each measurement temperature.
In the embodiment, when the material at the test point on the test specimen is a metal material, the standard specimen is a metal material standard specimen;
and when the material at the test point on the test specimen is the composite material, the standard specimen is the composite material standard specimen.
In this embodiment, in the second step, the strain gauge is calibrated by using the equal-strength beam experimental apparatus, so as to obtain the calibrated sensitivity coefficient of the strain gauge at each temperature, and the specific process is as follows:
step 201, symmetrically sticking a plurality of strain gauges and a plurality of temperature sensors at the set positions on the upper surface and the lower surface of a medium-strength beam 1 in a medium-strength beam experimental device; the constant-strength beam comprises a constant-strength beam 1, a plurality of strain gauges, a plurality of temperature sensors, a plurality of strain gauges and a plurality of temperature sensors, wherein the plurality of strain gauges and the plurality of temperature sensors are arranged close to the fixed end of the constant-strength beam 1, the plurality of strain gauges are arranged at equal intervals, and the constant-strength beam 1 is horizontally arranged in an environmental laboratory;
step 202, recording a plurality of strain gauges and a plurality of temperature sensors on the upper surface of the equal-strength beam 1 as a plurality of upper strain gauges 2 and a plurality of upper temperature sensors 3, respectively, and recording the plurality of upper strain gauges as a 1 st upper strain gauge in sequence
Figure 655342DEST_PATH_IMAGE012
An upper strain gage, the first
Figure 477804DEST_PATH_IMAGE081
A plurality of upper strain gauges, which are sequentially recorded as the 1 st upper temperature sensor
Figure 744837DEST_PATH_IMAGE012
An upper temperature sensor, the first
Figure 943738DEST_PATH_IMAGE081
An upper temperature sensor; wherein, the first and the second end of the pipe are connected with each other,
Figure 674933DEST_PATH_IMAGE012
and
Figure 668297DEST_PATH_IMAGE082
are all positive integers, an
Figure 422626DEST_PATH_IMAGE015
First, of
Figure 159638DEST_PATH_IMAGE016
The upper temperature sensor is close to
Figure 683023DEST_PATH_IMAGE012
The upper strain gauges 2 and the upper temperature sensors 3 are same in number and correspond to each other one by one;
step 203, recording a plurality of strain gauges and a plurality of temperature sensors on the lower surface of the equal-strength beam 1 as a plurality of lower strain gauges and a plurality of lower temperature sensors, respectively, and recording the plurality of lower strain gauges as a 1 st lower strain gauge in sequence
Figure 112868DEST_PATH_IMAGE017
A lower strain gage, the first
Figure 167543DEST_PATH_IMAGE018
A lower strain gage, wherein the plurality of lower temperature sensors are sequentially recorded as the 1 st lower temperature sensor
Figure 442666DEST_PATH_IMAGE017
A lower temperature sensor, the first
Figure 86137DEST_PATH_IMAGE018
A lower temperature sensor; wherein the content of the first and second substances,
Figure 421303DEST_PATH_IMAGE017
and
Figure 150225DEST_PATH_IMAGE018
are all positive integers, and
Figure 229039DEST_PATH_IMAGE019
of 1 at
Figure 789334DEST_PATH_IMAGE017
A lower temperature sensor is close to
Figure 560981DEST_PATH_IMAGE017
The lower strain gauges are adhered, the number of the lower strain gauges is the same as that of the lower temperature sensors, the lower strain gauges correspond to that of the lower temperature sensors one by one, and the upper strain gauges 2 and the lower strain gauges are symmetrically arranged up and down relative to the equal-strength beam 1;
step 204, adjusting the temperature in the environmental laboratory until
Figure 511619DEST_PATH_IMAGE020
Average sum of temperatures detected by individual temperature sensors
Figure 394125DEST_PATH_IMAGE021
The average value of the temperatures detected by the lower temperature sensors all meet the 1 st temperature
Figure 746608DEST_PATH_IMAGE022
；
Step 205, keeping the temperature in the environment laboratory at the 1 st temperature
Figure 689157DEST_PATH_IMAGE022
After 15-20 min, applying 30N load to the end of the constant-strength beam 1 through a weight, and acquiring the first time by adopting a strain acquisition instrument
Figure 940141DEST_PATH_IMAGE023
First strain value and second strain value of upper strain gauge
Figure 360758DEST_PATH_IMAGE024
A first strain value of the next lower strain gage;
step 206, unloading the weights to enable the end part of the equal-strength beam 1 to apply zero load, and acquiring the second strength by adopting a strain acquisition instrument
Figure 833327DEST_PATH_IMAGE023
Second strain value and second strain value of upper strain gage
Figure 946777DEST_PATH_IMAGE024
A second strain value of the lower strain gage;
step 207, according to
Figure 872007DEST_PATH_IMAGE023
First strain value and second strain value of upper strain gauge
Figure 96315DEST_PATH_IMAGE023
Obtaining a second strain value of the upper strain gage
Figure 220129DEST_PATH_IMAGE023
Difference of strain of upper strain gauge
Figure 504480DEST_PATH_IMAGE025
(ii) a According to the first
Figure 917007DEST_PATH_IMAGE024
First strain value and second strain value of each lower strain gauge
Figure 945006DEST_PATH_IMAGE024
The second strain value of the lower strain gage obtains the first strain value
Figure 126588DEST_PATH_IMAGE024
Difference of strain of lower strain gauge
Figure 316261DEST_PATH_IMAGE026
；
Step 208, according to the formula
Figure 29133DEST_PATH_IMAGE027
Obtaining the first average value of the strain difference
Figure 595244DEST_PATH_IMAGE028
；
Step 209, repeating step 205 to step 208 twice to respectively obtain a second average value of the strain difference
Figure 896912DEST_PATH_IMAGE029
And third mean value of strain difference
Figure 257486DEST_PATH_IMAGE030
；
Step 20A, according to the formula
Figure 644605DEST_PATH_IMAGE031
Obtaining the average value of the strain difference values at the 1 st temperature
Figure 14407DEST_PATH_IMAGE032
；
Step 20B, according to the formula
Figure 967319DEST_PATH_IMAGE033
Obtaining the sensitivity coefficient of the calibrated strain gauge at the 1 st temperature
Figure 764374DEST_PATH_IMAGE034
(ii) a Wherein, the first and the second end of the pipe are connected with each other,
Figure 373210DEST_PATH_IMAGE035
the sensitivity coefficient of the strain gauge at normal temperature;
Figure 546702DEST_PATH_IMAGE036
the standard strain of the equal-strength beam 1 under a load of 30N and at normal temperature is shown;
step 20C, repeating the step 204 to the step 20B for multiple times, and adjusting the temperature in the environmental laboratory until the temperature is adjusted
Figure 557384DEST_PATH_IMAGE083
Average sum of temperatures detected by temperature sensors on each
Figure 525340DEST_PATH_IMAGE038
The average value of the temperatures detected by the lower temperature sensors satisfies the second
Figure 455029DEST_PATH_IMAGE039
A temperature
Figure 166633DEST_PATH_IMAGE040
And get the first
Figure 31821DEST_PATH_IMAGE041
Sensitivity coefficient of calibrated strain gauge at individual temperature
Figure 170678DEST_PATH_IMAGE042
；
Step 20D, repeating step 20C for multiple times until the first step is obtained
Figure 754106DEST_PATH_IMAGE043
A temperature
Figure 3822DEST_PATH_IMAGE044
Sensitivity coefficient of lower strain gauge after calibration
Figure 51412DEST_PATH_IMAGE045
(ii) a Wherein, the first and the second end of the pipe are connected with each other,
Figure 361171DEST_PATH_IMAGE046
when it comes to
Figure 431895DEST_PATH_IMAGE047
When the content of the carbon dioxide is greater than or equal to 2,
Figure 485302DEST_PATH_IMAGE048
，
Figure 325082DEST_PATH_IMAGE049
it indicates the increase in the temperature of the material,
Figure 618791DEST_PATH_IMAGE050
denotes the first
Figure 911232DEST_PATH_IMAGE051
The temperature;
and 20E, drawing the obtained temperature by taking the sensitivity coefficient after the strain gauge calibration as a vertical coordinate and the temperature as a horizontal coordinate
Figure 768330DEST_PATH_IMAGE052
，...，
Figure 462616DEST_PATH_IMAGE053
，...，
Figure 114177DEST_PATH_IMAGE054
The sensitivity coefficient after the calibration of the strain gauge corresponding to each temperature
Figure 159494DEST_PATH_IMAGE055
，...，
Figure 617020DEST_PATH_IMAGE056
，...，
Figure 165813DEST_PATH_IMAGE057
And fitting to obtain a relation curve between the temperature and the calibrated sensitivity coefficient of the strain gauge, thereby obtaining the calibrated sensitivity coefficient of the strain gauge at each temperature.
In this embodiment, in step 202
Figure 253855DEST_PATH_IMAGE058
The distances between the upper strain gauges and the fixed end faces of the equal-strength beams 1 are the same,
Figure 520888DEST_PATH_IMAGE058
the distance between each upper strain gage and the loading end of the equal-strength beam 1 is greater than 1/2 of the length of the equal-strength beam 1;
the value of the 1 st temperature in the step 20D is-55 DEG C
Figure 719788DEST_PATH_IMAGE059
The temperature is 90 deg.C, and the temperature increase value
Figure 123088DEST_PATH_IMAGE060
The value of (A) is 1-2 ℃.
In this embodiment, in the third step, the standard test piece in step 103 is placed in an environmental laboratory, the first strain gauge is pasted on the standard test piece, the first strain gauge is connected with the resistor R2, the resistor R3, and the resistor R4 to form a first wheatstone bridge circuit, and a first wheatstone bridge circuit is obtained through the first wheatstone bridge circuit
Figure 195080DEST_PATH_IMAGE061
Heat output at a measured temperature
Figure 949409DEST_PATH_IMAGE002
The specific process is as follows:
step 301, placing the standard test piece in the step 103 in an environmental laboratory, pasting a first strain gauge on the standard test piece, and connecting the first strain gauge with a resistor R2, a resistor R3 and a resistor R4 to form a first Wheatstone bridge circuit; the initial resistance value of the first strain gauge is set as R1, the junction of R1 and R2 is set as point A, the junction of R2 and R3 is set as point C, the junction of R3 and R4 is set as point B, the junction of R4 and R1 is set as point D, and the resistance values of R1, R2, R3 and R4 are the same;
step 302, adjusting the temperature of the laboratory in which the standard test piece is located to the second temperature
Figure 686421DEST_PATH_IMAGE061
A measured temperature
Figure 209806DEST_PATH_IMAGE063
And preserving heat;
step 303, applying an excitation voltage between the points C and D
Figure 639651DEST_PATH_IMAGE064
And obtaining an output voltage between the points A and B
Figure 615697DEST_PATH_IMAGE065
；
Step 304, according to the formula
Figure 218717DEST_PATH_IMAGE066
To obtain the first
Figure 862188DEST_PATH_IMAGE067
Heat output at a measured temperature
Figure 197354DEST_PATH_IMAGE068
(ii) a Wherein;
Figure 926276DEST_PATH_IMAGE069
is shown as
Figure 5090DEST_PATH_IMAGE070
A measured temperature
Figure 503067DEST_PATH_IMAGE071
And (5) calibrating the sensitivity coefficient of the lower strain gauge.
In this embodiment, in the fourth step, the test specimen is placed in an environmental laboratory, the second strain gauge is adhered to the test point of the test specimen, the second strain gauge is connected with the resistor R2 ', the resistor R3 ' and the resistor R4 ' to form a second wheatstone bridge circuit, and a second wheatstone bridge circuit is obtained through the second wheatstone bridge circuit
Figure 822184DEST_PATH_IMAGE072
Total strain at test point in test piece at individual measurement temperature
Figure 38402DEST_PATH_IMAGE073
The specific process is as follows:
step 401, placing a test specimen in an environmental laboratory, adhering a second strain gauge to a test point of the test specimen, and connecting the second strain gauge with a resistor R2 ', a resistor R3 ' and a resistor R4 ' to form a second Wheatstone bridge circuit; wherein, the initial resistance value of the second strain gauge is set as R1 ', the junction of R1' and R2 'is marked as A', the junction of R2 'and R3' is marked as C ', the junction of R3' and R4 'is marked as B', the junction of R4 'and R1' is marked as D, and the resistance values of R1 ', R2', R3 'and R4' as well as R1, R2, R3 and R4 are all the same;
step 402, adjusting the temperature of the laboratory in which the test specimen is located to be the second temperature
Figure 920907DEST_PATH_IMAGE074
A measured temperature
Figure 273391DEST_PATH_IMAGE075
And preserving heat;
step 403, applying an excitation voltage between the point C' and the point D
Figure 215940DEST_PATH_IMAGE076
And obtaining an output voltage between the A 'point and the B' point
Figure 653874DEST_PATH_IMAGE077
；
Step 404, according to the formula
Figure 136808DEST_PATH_IMAGE078
To obtain the first
Figure 609378DEST_PATH_IMAGE079
Total strain at test point in test piece at individual measurement temperature
Figure 457248DEST_PATH_IMAGE080
。
In this embodiment, the first
Figure 382479DEST_PATH_IMAGE074
A measured temperature
Figure 606787DEST_PATH_IMAGE075
Is positioned in the range of-55 ℃ to-90 ℃,
Figure 933863DEST_PATH_IMAGE084
and obtaining the sensitivity coefficient after the strain gauge calibration at each temperature in the second step.
In practical use, the part to be tested on the airplane can be the airplane wing or the part to be tested.
In this embodiment, in actual use, the thickness of the standard test piece is the same as that of the test piece.
In this embodiment, the normal temperature is 20 to 25 ℃.
In this embodiment, in actual use, step 202
Figure 28333DEST_PATH_IMAGE085
The set value of the distance between the upper strain gauge and the fixed end face of the equal-strength beam 1 is 10 cm.
In this embodiment, in actual use, the composite material is a carbon fiber composite material.
In the embodiment, when in actual use,
Figure 440860DEST_PATH_IMAGE086
and
Figure 203280DEST_PATH_IMAGE087
is 3.
In this embodiment, in actual use, the axis direction of the second strain gauge is the same as the measurement direction of the test point on the test specimen, and the axis direction of the first strain gauge is the same as the measurement direction of the test point on the test specimen in the pasting direction of the standard specimen.
In the embodiment, when in actual use,
Figure 384862DEST_PATH_IMAGE088
is 2.0.
In this embodiment, in actual use, when the measurement direction at the test point on the test specimen is unidirectional, the strain gauge adopted is a uniaxial strain gauge;
when the measuring direction of the test point on the test specimen is triaxial 45 degrees, the adopted strain gauge is triaxial 45 degree strain gauge.
In this embodiment, in actual use, when a triaxial 45 ° strain rosette is used, total strain in three directions and heat output in three directions are obtained, and thermal strain in three directions and thermal stress in three directions are obtained according to a difference between the total strain in three directions and the heat output in three directions.
In the embodiment, when the material at the test point on the test specimen is a metal material in practical use, a BAB350-3AA250-X-QT (23) uniaxial strain gage and a BAB350-3CA250-X-QT (23) strain gage can be adopted; when the material at the test point on the test specimen is a composite material, a BAB350-3AA250-X-QT (11) uniaxial strain gage and a BAB350-3CA250-X-QT (11) strain gage can be used to bring the coefficient of linear expansion of the strain gage sensitive grid material close to the coefficient of thermal expansion of the material at the test point on the test specimen.
In this embodiment, in actual use, the first strain gauge is used as one arm of the first wheatstone bridge circuit, the resistor R2, the resistor R3 and the resistor R4 are respectively used as three arms of the first wheatstone bridge circuit, and the resistances of the resistor R2, the resistor R3 and the resistor R4 are all the same as the initial resistor R1 of the first strain gauge.
In this embodiment, in actual use, the second strain gauge is used as one arm of the second wheatstone bridge circuit, the resistor R2 ', the resistor R3 ' and the resistor R4 ' are used as three arms of the second wheatstone bridge circuit, and the resistances of the resistor R2 ', the resistor R3 ' and the resistor R4 ' are all the same as the initial resistor R1 ' of the second strain gauge.
In this embodiment, in actual use, the first strain gauge and the second strain gauge both adopt the strain gauge calibrated in step two, and then R1 is the same as R1'.
In this embodiment, the excitation voltage is applied in actual use
Figure 840114DEST_PATH_IMAGE089
Is 1.8V.
In conclusion, the method provided by the invention has the advantages that the steps are simple, the design is reasonable, the thermal strain at the test point in the test specimen at the measurement temperature is obtained by correcting the total strain at the test point in the test specimen at the measurement temperature, and the thermal stress at the test point is further obtained, so that the measurement accuracy of the thermal stress of the metal-composite material mixed structure for the airplane is improved.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and any simple modifications, changes and equivalent structural changes made to the above embodiment according to the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims (5)

1. A method for measuring thermal stress of a metal-composite hybrid structure for an aircraft, the method comprising the steps of:
step one, obtaining a test piece and a standard test piece according to a metal-composite material mixed structure for an airplane:
step 101, taking a part to be tested on an airplane as a test piece; wherein, the test piece is of a metal-composite material mixed structure;
step 102, presetting a plurality of test points on the surface of a test specimen;
103, manufacturing a 200mm multiplied by 200mm square test piece as a standard test piece; wherein, the standard test piece and the test piece are made of the same material at the test point;
step two, calibrating the sensitivity coefficient of the strain gauge:
calibrating the strain gauge by adopting an equal-strength beam experimental device to obtain the calibrated sensitivity coefficient of the strain gauge at each temperature;
step three, carrying out heat output measurement on the standard test piece:
placing the standard test piece in the step 103 in an environmental laboratory, pasting a first strain gauge on the standard test piece, connecting the first strain gauge with a resistor R2, a resistor R3 and a resistor R4 to form a first Wheatstone bridge circuit, and obtaining a second Wheatstone bridge circuit through the first Wheatstone bridge circuit
Figure 434423DEST_PATH_IMAGE001
Heat output at a measured temperature
Figure 769589DEST_PATH_IMAGE002
(ii) a Wherein, the first and the second end of the pipe are connected with each other,
Figure 498511DEST_PATH_IMAGE001
is a positive integer;
step four, carrying out total strain measurement on the test piece:
placing a test piece in an environmental laboratory, pasting a second strain gauge at the test point of the test piece, connecting the second strain gauge with a resistor R2 ', a resistor R3' and a resistor R4 'to form a second Wheatstone bridge circuit, and connecting the second strain gauge with the resistor R2', the resistor R3 'and the resistor R4' through the second Wheatstone bridge circuitTo obtain the first
Figure 577325DEST_PATH_IMAGE001
A measured temperature
Figure 75303DEST_PATH_IMAGE003
Total strain at test point in lower test specimen
Figure 768321DEST_PATH_IMAGE004
；
Step five, obtaining the thermal stress of the metal-composite material mixed structure for the airplane:
step 501, according to the formula
Figure 984539DEST_PATH_IMAGE005
To obtain the first
Figure 867044DEST_PATH_IMAGE006
Measuring thermal strain at a test point in a metal-composite hybrid structure for an aircraft at a temperature
Figure 219528DEST_PATH_IMAGE007
；
502, according to a formula
Figure 162076DEST_PATH_IMAGE008
To obtain the first
Figure 600011DEST_PATH_IMAGE009
Thermal stress at a test point in a metal-composite hybrid structure for an aircraft at a measured temperature
Figure 958311DEST_PATH_IMAGE010
(ii) a Wherein the content of the first and second substances,
Figure 430880DEST_PATH_IMAGE011
is shown as
Figure 278751DEST_PATH_IMAGE012
Testing the rigidity of the material at the test point in the test piece at the measurement temperature;
and step two, calibrating the strain gauge by using an equal-strength beam experimental device to obtain the calibrated sensitivity coefficient of the strain gauge at each temperature, wherein the specific process is as follows:
step 201, symmetrically sticking a plurality of strain gauges and a plurality of temperature sensors on the upper and lower surface set positions of an equal-strength beam in an equal-strength beam experimental device; the constant-strength beam is horizontally arranged in an environmental laboratory;
step 202, recording a plurality of strain gauges and a plurality of temperature sensors on the upper surface of the equal-strength beam as a plurality of upper strain gauges and a plurality of upper temperature sensors, respectively, and recording the plurality of upper strain gauges as a 1 st upper strain gauge in sequence
Figure 203981DEST_PATH_IMAGE013
One strain gauge, the first
Figure 428289DEST_PATH_IMAGE014
A plurality of upper strain gauges, which are sequentially recorded as the 1 st upper temperature sensor
Figure 464289DEST_PATH_IMAGE013
On the temperature sensor, the first
Figure 748640DEST_PATH_IMAGE014
An upper temperature sensor; wherein, the first and the second end of the pipe are connected with each other,
Figure 161166DEST_PATH_IMAGE013
and
Figure 923586DEST_PATH_IMAGE015
are all positive integers, an
Figure 105169DEST_PATH_IMAGE016
First, of
Figure 498104DEST_PATH_IMAGE017
The upper temperature sensor is close to
Figure 397927DEST_PATH_IMAGE013
The upper strain gauges are adhered, and the number of the upper strain gauges is the same as that of the upper temperature sensors, and the upper strain gauges correspond to the upper temperature sensors one by one;
step 203, respectively recording a plurality of strain gauges and a plurality of temperature sensors on the lower surface of the equal-strength beam as a plurality of lower strain gauges and a plurality of lower temperature sensors, and sequentially recording a plurality of lower strain gauges as a 1 st lower strain gauge
Figure 964037DEST_PATH_IMAGE018
A lower strain gage, a
Figure 127DEST_PATH_IMAGE019
A lower strain gage, wherein the plurality of lower temperature sensors are sequentially recorded as the 1 st lower temperature sensor
Figure 626280DEST_PATH_IMAGE018
A lower temperature sensor, a
Figure 13399DEST_PATH_IMAGE019
A lower temperature sensor; wherein the content of the first and second substances,
Figure 304572DEST_PATH_IMAGE018
and
Figure 460747DEST_PATH_IMAGE019
are all positive integers, an
Figure 257801DEST_PATH_IMAGE020
First, of
Figure 866637DEST_PATH_IMAGE018
A lower temperature sensor is close to
Figure 40130DEST_PATH_IMAGE018
The lower strain gauges are adhered, the number of the lower strain gauges is the same as that of the lower temperature sensors, the lower strain gauges correspond to that of the lower temperature sensors one by one, and the upper strain gauges and the lower strain gauges are arranged in an up-down symmetrical mode relative to the equal-strength beam;
step 204, adjusting the temperature in the environmental laboratory until
Figure 50811DEST_PATH_IMAGE021
Average sum of temperatures detected by individual temperature sensors
Figure 956450DEST_PATH_IMAGE022
The average value of the temperatures detected by the lower temperature sensors all meet the 1 st temperature
Figure 52582DEST_PATH_IMAGE023
；
Step 205, keeping the temperature in the environment laboratory at the 1 st temperature
Figure 498607DEST_PATH_IMAGE023
After 15-20 min, applying 30N load to the end of the constant-strength beam through a weight, and acquiring the second time by adopting a strain acquisition instrument
Figure 629374DEST_PATH_IMAGE024
First strain value and second strain value of upper strain gauge
Figure 768231DEST_PATH_IMAGE025
A first strain value of the next lower strain gage;
and step 206, unloading the weights to enable the end part of the constant-strength beam to apply zero load, and acquiring the second signal by adopting a strain acquisition instrument
Figure 40075DEST_PATH_IMAGE024
On oneSecond strain value and second strain value of strain gauge
Figure 289791DEST_PATH_IMAGE025
A second strain value of the lower strain gage;
step 207, according to
Figure 275064DEST_PATH_IMAGE024
First strain value and second strain value of upper strain gauge
Figure 584823DEST_PATH_IMAGE024
Obtaining a second strain value of the upper strain gage
Figure 655547DEST_PATH_IMAGE024
Difference in strain of individual strain gauges
Figure 708954DEST_PATH_IMAGE026
(ii) a According to the first
Figure 486417DEST_PATH_IMAGE025
First strain value and second strain value of lower strain gauge
Figure 967077DEST_PATH_IMAGE025
The second strain value of the lower strain gage obtains the first strain value
Figure 259518DEST_PATH_IMAGE025
Difference of strain of lower strain gauge
Figure 116615DEST_PATH_IMAGE027
；
Step 208, according to the formula
Figure 810902DEST_PATH_IMAGE028
Obtaining the first average value of the strain difference
Figure 462463DEST_PATH_IMAGE029
；
Step 209, repeating step 205 to step 208 twice to respectively obtain a second average value of the strain difference
Figure 694730DEST_PATH_IMAGE030
And third mean value of strain difference
Figure 89939DEST_PATH_IMAGE031
；
Step 20A, according to the formula
Figure 638732DEST_PATH_IMAGE032
Obtaining the average value of the strain difference values at the 1 st temperature
Figure 726774DEST_PATH_IMAGE033
；
Step 20B, according to the formula
Figure 993807DEST_PATH_IMAGE034
Obtaining the sensitivity coefficient of the strain gauge calibrated at the 1 st temperature
Figure 927128DEST_PATH_IMAGE035
(ii) a Wherein the content of the first and second substances,
Figure 533690DEST_PATH_IMAGE036
the sensitivity coefficient of the strain gauge at normal temperature;
Figure 792633DEST_PATH_IMAGE037
represents the standard strain of the constant strength beam under the load of 30N and at normal temperature;
step 20C, repeating the step 204 to the step 20B for multiple times, and adjusting the temperature in the environmental laboratory until the temperature is adjusted
Figure 281383DEST_PATH_IMAGE038
Average sum of temperatures detected by temperature sensors on each
Figure 283974DEST_PATH_IMAGE039
The average value of the temperatures detected by the lower temperature sensors satisfies the second
Figure 807360DEST_PATH_IMAGE040
A temperature
Figure 657111DEST_PATH_IMAGE041
And get the first
Figure 898736DEST_PATH_IMAGE042
Sensitivity coefficient of calibrated strain gauge at individual temperature
Figure 439439DEST_PATH_IMAGE043
；
Step 20D, repeating step 20C for multiple times until the first step is obtained
Figure 817331DEST_PATH_IMAGE044
A temperature
Figure 418076DEST_PATH_IMAGE045
Sensitivity coefficient of lower strain gauge after calibration
Figure 881419DEST_PATH_IMAGE046
(ii) a Wherein the content of the first and second substances,
Figure 163495DEST_PATH_IMAGE047
when it comes to
Figure 661473DEST_PATH_IMAGE048
When the content is greater than or equal to 2,
Figure 167540DEST_PATH_IMAGE049
，
Figure 383758DEST_PATH_IMAGE050
indicating an increase in temperatureThe value of the added value is added,
Figure 266263DEST_PATH_IMAGE051
is shown as
Figure 618747DEST_PATH_IMAGE052
The temperature;
and 20E, drawing the obtained temperature by taking the sensitivity coefficient calibrated by the strain gauge as a vertical coordinate and the temperature as a horizontal coordinate
Figure 482667DEST_PATH_IMAGE053
，...，
Figure 920602DEST_PATH_IMAGE054
，...，
Figure 606798DEST_PATH_IMAGE055
The sensitivity coefficient after the calibration of the strain gauge corresponding to each temperature
Figure 813788DEST_PATH_IMAGE056
，...，
Figure 927238DEST_PATH_IMAGE057
，...，
Figure 790152DEST_PATH_IMAGE058
And fitting to obtain a relation curve between the temperature and the calibrated sensitivity coefficient of the strain gauge, thereby obtaining the calibrated sensitivity coefficient of the strain gauge at each temperature.
2. A method of measuring thermal stress of a metal-composite hybrid structure for an aircraft according to claim 1, wherein: when the material at the test point on the test specimen is a metal material, the standard specimen is a metal material standard specimen;
and when the material at the test point on the test specimen is the composite material, the standard specimen is the composite material standard specimen.
3. A method of measuring thermal stress of a metal-composite hybrid structure for an aircraft according to claim 1, wherein: in step 202
Figure 14460DEST_PATH_IMAGE059
The distances between the upper strain gauges and the fixed end faces of the equal-strength beams are the same,
Figure 341536DEST_PATH_IMAGE059
the distance between the upper strain gauge and the loading end of the equal-strength beam is greater than 1/2 of the length of the equal-strength beam;
the value of the 1 st temperature in the step 20D is-55 DEG C
Figure 625887DEST_PATH_IMAGE060
The temperature is 90 deg.C, and the temperature increase value
Figure 772834DEST_PATH_IMAGE061
The value of (a) is 1-2 ℃.
4. A method of measuring thermal stress of a metal-composite hybrid structure for an aircraft according to claim 1, wherein: in the third step, the standard test piece in the step 103 is placed in an environmental laboratory, the first strain gauge is pasted on the standard test piece, the first strain gauge is connected with the resistor R2, the resistor R3 and the resistor R4 to form a first Wheatstone bridge circuit, and the first Wheatstone bridge circuit is used for obtaining a first Wheatstone bridge circuit
Figure 800833DEST_PATH_IMAGE062
Heat output at a measured temperature
Figure 982416DEST_PATH_IMAGE002
The specific process is as follows:
step 301, placing the standard test piece in the step 103 in an environmental laboratory, pasting a first strain gauge on the standard test piece, and connecting the first strain gauge with a resistor R2, a resistor R3 and a resistor R4 to form a first Wheatstone bridge circuit; the initial resistance value of the first strain gauge is set as R1, the joint of R1 and R2 is set as point A, the joint of R2 and R3 is set as point C, the joint of R3 and R4 is set as point B, the joint of R4 and R1 is set as point D, and the resistance values of R1, R2, R3 and R4 are the same;
step 302, adjusting the temperature of the laboratory in which the standard test piece is located to the second temperature
Figure 126083DEST_PATH_IMAGE062
A measured temperature
Figure 25906DEST_PATH_IMAGE063
And preserving heat;
step 303, applying an excitation voltage between the points C and D
Figure 592017DEST_PATH_IMAGE064
And obtaining an output voltage between the points A and B
Figure 628106DEST_PATH_IMAGE065
；
Step 304, according to the formula
Figure 254259DEST_PATH_IMAGE066
To obtain the first
Figure 313482DEST_PATH_IMAGE067
Heat output at a measured temperature
Figure 683284DEST_PATH_IMAGE068
(ii) a Wherein;
Figure 839458DEST_PATH_IMAGE069
is shown as
Figure 636513DEST_PATH_IMAGE070
A measured temperature
Figure 245349DEST_PATH_IMAGE071
And (5) calibrating the sensitivity coefficient of the lower strain gauge.
5. A method of measuring thermal stress of a metal-composite hybrid structure for an aircraft according to claim 1, wherein: in the fourth step, the test specimen is placed in an environmental laboratory, a second strain gauge is pasted at the test point of the test specimen, the second strain gauge is connected with the resistor R2 ', the resistor R3 ' and the resistor R4 ' to form a second Wheatstone bridge circuit, and the second Wheatstone bridge circuit is used for obtaining a second Wheatstone bridge circuit
Figure 153262DEST_PATH_IMAGE072
A measured temperature
Figure 350894DEST_PATH_IMAGE003
Total strain at test point in lower test specimen
Figure 318850DEST_PATH_IMAGE073
The specific process is as follows:
step 401, placing a test specimen in an environmental laboratory, adhering a second strain gauge to a test point of the test specimen, and connecting the second strain gauge with a resistor R2 ', a resistor R3 ' and a resistor R4 ' to form a second Wheatstone bridge circuit; wherein, the initial resistance value of the second strain gauge is set as R1 ', the junction of R1' and R2 'is marked as A', the junction of R2 'and R3' is marked as C ', the junction of R3' and R4 'is marked as B', the junction of R4 'and R1' is marked as D, and the resistance values of R1 ', R2', R3 'and R4' as well as R1, R2, R3 and R4 are all the same;
step 402, adjusting the temperature of the laboratory in which the test specimen is located to be the second temperature
Figure 414982DEST_PATH_IMAGE074
A measured temperature
Figure 126586DEST_PATH_IMAGE003
And preserving heat;
step 403, applying an excitation voltage between the point C' and the point D
Figure 257353DEST_PATH_IMAGE075
And obtaining an output voltage between the A 'point and the B' point
Figure 396211DEST_PATH_IMAGE076
；
404, according to the formula
Figure 651743DEST_PATH_IMAGE077
To obtain the first
Figure 167037DEST_PATH_IMAGE078
A measured temperature
Figure 152311DEST_PATH_IMAGE003
Total strain at test point in lower test specimen
Figure 462070DEST_PATH_IMAGE079
。
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