CN108562609B - Method for predicting influence of thermal cycle on thermal expansion coefficient of polymer matrix composite based on free radical content - Google Patents
Method for predicting influence of thermal cycle on thermal expansion coefficient of polymer matrix composite based on free radical content Download PDFInfo
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Abstract
The invention discloses a method for predicting the influence of thermal cycling on the thermal expansion coefficient of a polymer-based composite material based on the content of free radicals, belongs to the technical field of evaluation of dimensional stability of the composite material, and solves the problems that the time required for measuring the thermal expansion coefficient of the polymer-based composite material with a complex structure is longer and the measurement difficulty is higher due to the limitation of experimental conditions and equipment conditions during the in-orbit operation of a spacecraft. According to the invention, under the condition that the vacuum degree is less than 1Pa, the thermal cycle experiment is carried out on the polymer matrix composite material of which the thermal expansion coefficient needs to be determined, so that the change rule of the free radical content of the polymer matrix composite material along with the thermal cycle times is consistent with the change rule of the thermal expansion coefficient along with the thermal cycle times, therefore, during the on-track operation period, the thermal expansion coefficient of the polymer matrix composite material can be predicted by only measuring the free radical content. The method can be applied to the technical field of evaluation of the dimensional stability of the composite material.
Description
Technical Field
The invention belongs to the technical field of evaluation of dimensional stability of composite materials, and particularly relates to a method for predicting influence of thermal cycling on thermal expansion coefficient of a polymer matrix composite material based on free radical content.
Background
In the aerospace field, the polymer-based composite material is mainly applied to structures such as a main bearing cylinder, a solar cell array substrate, an optical remote sensor, a parabolic antenna and the like. As the spacecraft needs to repeatedly enter and exit the earth shadow region during the in-orbit operation, the external environment temperature of the spacecraft is alternately changed within the range of minus 160 ℃ to 120 ℃. The American space agency, the European space agency and China clearly stipulate vacuum thermal cycle experimental specifications when the spacecraft and components thereof are tested, and therefore, the research on the behavior of the polymer-based composite material under the vacuum thermal cycle condition is significant for ensuring the on-orbit safe operation of the spacecraft, improving the service reliability and prolonging the service life.
Because the thermal expansion coefficients of the polymer matrix composite and the reinforcing fiber are different by one order of magnitude, the polymer matrix composite generates thermal stress in the material under the action of an alternating temperature field, microcracks are generated in the material along with the accumulation of the thermal stress, and the mechanical property and the dimensional stability of the material are finally reduced, so that the prediction of the thermal expansion coefficient of the polymer matrix composite has important significance for researching the structure of the polymer matrix complex material. However, during the in-orbit operation of the spacecraft, due to the limitation of the current experimental conditions and equipment conditions, the measurement time for directly measuring the thermal expansion coefficient of many polymer matrix composite materials with complex structures is long, and the measurement difficulty is high because the measurement of the thermal expansion coefficient is carried out only by manufacturing the polymer matrix composite materials into standard parts.
Disclosure of Invention
The invention aims to solve the problems that the measurement of the thermal expansion coefficient of a polymer matrix composite material with a complex structure needs longer time and has higher measurement difficulty due to the limitation of experimental conditions and equipment conditions during the on-orbit operation of a spacecraft.
The technical scheme adopted by the invention for solving the technical problems is as follows:
selecting a polymer matrix composite material as an experimental sample, and carrying out a thermal cycle test on the selected experimental sample under the condition that the vacuum degree is less than 1 Pa; setting the thermal cycle times of each group of thermal cycle tests to be not less than 200 times, and setting the number of the groups of the thermal cycle tests to be not less than 3 groups;
step two, taking out an experimental sample after each thermal cycle, and testing the thermal expansion coefficient of the taken out experimental sample; respectively recording the thermal expansion coefficients of each group of thermal cycle tests under different thermal cycle times; calculating the average value of the thermal expansion coefficients corresponding to the same thermal cycle times of each group of thermal cycle tests to obtain the thermal expansion coefficient change rule under different thermal cycle times;
step three, carrying out free radical content test on the experimental sample taken out each time in the step two, calculating the average value of the free radical content corresponding to the same thermal cycle times of each group of thermal cycle tests, and obtaining the change rule of the free radical content under different thermal cycle times;
step four, comparing the change curve of the thermal expansion coefficient along with the thermal cycle times in the step two with the change curve of the free radical content along with the thermal cycle times in the step three to obtain that the free radical content and the thermal expansion coefficient are both reduced along with the increase of the thermal cycle times, and the change rule of the free radical content along with the thermal cycle times is consistent with the change rule of the thermal expansion coefficient along with the thermal cycle times;
step five, for a certain polymer matrix composite material needing to measure the thermal expansion coefficient, obtaining the change rule of the thermal expansion coefficient of the polymer matrix composite material along with the change rule of the thermal cycle times and the change rule of the free radical content along with the thermal cycle times according to the methods from the step one to the step three; during the on-track operation, the free radical content of the polymer matrix composite material only needs to be measured according to the method of the step three;
and step six, according to the content of the free radicals obtained by measurement in the step five, predicting the thermal expansion coefficient of the polymer-based composite material by checking the change rule of the thermal expansion coefficient of the polymer-based composite material along with the thermal cycle times and the change rule of the content of the free radicals along with the thermal cycle times.
The invention has the beneficial effects that: the invention provides a method for predicting the influence of thermal cycling on the thermal expansion coefficient of a polymer matrix composite based on the content of free radicals, which selects a carbon fiber cyanate ester resin composite or a carbon fiber epoxy resin composite as an experimental sample, carries out thermal cycling tests on the experimental sample under the condition that the vacuum degree is less than 1Pa, the thermal cycling frequency of each group of thermal cycling tests is not less than 200 times, the experimental sample is taken out after each thermal cycling, the content of the free radicals and the thermal expansion coefficient of the taken out experimental sample are tested, and the change rule of the content of the free radicals along with the thermal cycling frequency is consistent with the change rule of the thermal expansion coefficient along with the thermal cycling frequency; therefore, for a certain polymer matrix composite material needing to measure the thermal expansion coefficient, the change rule of the thermal expansion coefficient and the free radical content of the polymer matrix composite material along with the thermal cycle number can be obtained by simulating the space condition during the in-orbit operation, and the thermal expansion coefficient of the polymer matrix composite material can be predicted by checking the measured change rule of the thermal expansion coefficient and the free radical content of the polymer matrix composite material along with the thermal cycle number.
The method of the invention is adopted to predict the thermal expansion coefficient of the polymer matrix composite after thermal cycle, which can save 80% of the measurement time of the thermal expansion coefficient, and the invention predicts the thermal expansion coefficient according to the content of free radicals, namely the polymer matrix composite with complex structure is not required to be made into a standard component, which can realize the measurement of the thermal expansion coefficient, greatly simplifies the measurement process and reduces the measurement difficulty.
The method can be applied to the research of the composite material in the aerospace field.
Drawings
FIG. 1 is a flow chart of a method of the present invention for predicting the effect of thermal cycling on the coefficient of thermal expansion of a polymer-based composite based on free radical content;
FIG. 2 is a graph showing characteristic peaks of free radicals at different thermal cycle times when the temperature rise and decrease rate of the thermal cycle test of the carbon fiber cyanate ester resin composite material of the experimental sample of the present invention is 1.5 ℃/min;
FIG. 3 is a graph showing the variation of the free radical content with the number of thermal cycles when the temperature rise and decrease rate of the thermal cycle test of the carbon fiber cyanate ester resin composite material of the experimental sample of the present invention is 1.5 ℃/min;
FIG. 4 is a graph showing the variation of the thermal expansion coefficient with the number of thermal cycles when the temperature rising and lowering rate of the thermal cycle test of the carbon fiber cyanate ester resin composite material of the experimental sample of the present invention is 1.5 ℃/min;
FIG. 5 is a graph showing characteristic peaks of free radicals at different thermal cycle times when the temperature rise and decrease rate of a thermal cycle test of a carbon fiber epoxy resin composite material is 1.5 ℃/min;
FIG. 6 is a graph showing the variation of the free radical content with the number of thermal cycles when the temperature rise and decrease rate of the thermal cycle test of the carbon fiber epoxy resin composite material of the experimental sample of the present invention is 1.5 ℃/min;
FIG. 7 is a graph showing the thermal expansion coefficient variation with the number of thermal cycles of a thermal cycle test in which the experimental sample is a carbon fiber-epoxy resin composite material, when the temperature rising and lowering rate is 1.5 ℃/min;
FIG. 8 is a graph showing characteristic peaks of free radicals at different thermal cycle times when the temperature increase and decrease rate of the thermal cycle test of the carbon fiber cyanate ester resin composite material of the experimental sample of the present invention is 2.5 ℃/min;
FIG. 9 is a graph showing the variation of the free radical content with the number of thermal cycles when the temperature rise and decrease rates of the thermal cycle test of the carbon fiber cyanate ester resin composite material of the experimental sample of the present invention are both 2.5 ℃/min;
FIG. 10 is a graph showing the variation of the thermal expansion coefficient with the number of thermal cycles when the temperature rise and decrease rates of the thermal cycle test of the carbon fiber cyanate ester resin composite material of the experimental sample of the present invention are both 2.5 ℃/min;
FIG. 11 is a graph showing characteristic peaks of free radicals at different thermal cycle times when the temperature rise and decrease rates of a thermal cycle test of a carbon fiber epoxy resin composite material according to the present invention are both 2.5 ℃/min;
FIG. 12 is a graph showing the variation of the free radical content with the number of thermal cycles when the temperature rise and decrease rates of the thermal cycle test of the carbon fiber epoxy resin composite material of the experimental sample of the present invention are both 2.5 ℃/min;
FIG. 13 is a graph showing the thermal expansion coefficient variation with the number of thermal cycles of a thermal cycle test in which the experimental sample is a carbon fiber-epoxy resin composite material, when the temperature rise and decrease rates are both 2.5 ℃/min;
Detailed Description
The technical solution of the present invention is further described below with reference to the accompanying drawings, but not limited thereto, and any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention shall be covered by the protection scope of the present invention.
The first embodiment is as follows: this embodiment will be described with reference to fig. 1. The method for predicting the influence of thermal cycling on the thermal expansion coefficient of the polymer matrix composite based on the content of the free radicals in the embodiment comprises the following specific steps:
selecting a polymer matrix composite material as an experimental sample, and carrying out a thermal cycle test on the selected experimental sample under the condition that the vacuum degree is less than 1 Pa; setting the thermal cycle times of each group of thermal cycle tests to be not less than 200 times, and setting the number of the groups of the thermal cycle tests to be not less than 3 groups;
step two, taking out an experimental sample after each thermal cycle, and testing the thermal expansion coefficient of the taken out experimental sample; respectively recording the thermal expansion coefficients of each group of thermal cycle tests under different thermal cycle times; calculating the average value of the thermal expansion coefficients corresponding to the same thermal cycle times of each group of thermal cycle tests to obtain the thermal expansion coefficient change rule under different thermal cycle times;
step three, carrying out free radical content test on the experimental sample taken out each time in the step two, calculating the average value of the free radical content corresponding to the same thermal cycle times of each group of thermal cycle tests, and obtaining the change rule of the free radical content under different thermal cycle times;
step four, comparing the change curve of the thermal expansion coefficient along with the thermal cycle times in the step two with the change curve of the free radical content along with the thermal cycle times in the step three to obtain that the free radical content and the thermal expansion coefficient are both reduced along with the increase of the thermal cycle times, and the change rule of the free radical content along with the thermal cycle times is consistent with the change rule of the thermal expansion coefficient along with the thermal cycle times;
step five, for a certain polymer matrix composite material needing to measure the thermal expansion coefficient, obtaining the change rule of the thermal expansion coefficient of the polymer matrix composite material along with the change rule of the thermal cycle times and the change rule of the free radical content along with the thermal cycle times according to the methods from the step one to the step three; during the on-track operation, the free radical content of the polymer matrix composite material only needs to be measured according to the method of the step three;
and step six, according to the content of the free radicals obtained by measurement in the step five, predicting the thermal expansion coefficient of the polymer-based composite material by checking the change rule of the thermal expansion coefficient of the polymer-based composite material along with the thermal cycle times and the change rule of the content of the free radicals along with the thermal cycle times.
In the embodiment, the number of groups of thermal cycle tests is not less than 3, the thermal cycle times of each group of thermal cycle tests are not less than 200, and the test samples are taken out to test the thermal expansion coefficient and the free radical content after each thermal cycle, so that the mean value of the thermal expansion coefficients and the mean value of the free radical content of each group at each thermal cycle time point can be respectively calculated, the mean value of the thermal expansion coefficients and the mean value of the free radical content are respectively used as the thermal expansion coefficient and the free radical content of each thermal cycle time point, and a change curve of the thermal expansion coefficients along with the thermal cycle times and a change curve of the free radical content along with the thermal cycle times are drawn. The comparison shows that the change rule of the thermal expansion coefficient along with the thermal cycle is consistent with the change rule of the free radical content along with the thermal cycle.
Therefore, for a certain polymer matrix composite material needing to measure the thermal expansion coefficient, during the in-orbit operation, the content of free radicals is only required to be measured, and then the thermal expansion coefficient of the polymer matrix composite material can be obtained by checking the thermal expansion coefficient of the polymer matrix composite material and the change rule curve of the content of the free radicals along with the number of thermal cycles under experimental conditions.
The number of groups of the thermal cycle test is set to be not less than 3 groups, so that the thermal expansion coefficient and the free radical content corresponding to each thermal cycle number are averaged, and the accuracy of data is improved.
The second embodiment is as follows: this embodiment further defines the method for estimating the influence of the thermal cycle on the thermal expansion coefficient of the polymer matrix composite based on the content of the free radicals in the first embodiment, wherein the dimensions of the experimental sample in the first step in this embodiment are as follows: the length is 20 mm-25 mm, the width is 5 mm-6 mm, and the thickness is 1 mm-3 mm; setting the temperature range of each thermal cycle to be-150 ℃;
setting the ambient temperature around the experimental sample to be gradually reduced from 150 ℃ to-150 ℃, wherein the temperature reduction rate is x, 0.2 is more than or equal to x >0, and the unit is ℃/min, and then gradually increasing the ambient temperature from-150 ℃ to 150 ℃ at the temperature increase rate x; when the ambient temperature around the experimental sample is from 150 ℃ to-150 ℃, and then the process from-150 ℃ to 150 ℃ is a thermal cycle;
in the embodiment, the temperature range of each thermal cycle is set to be-150 ℃ so as to ensure that the test temperature of the experimental sample is matched with the external environment temperature in the actual on-orbit running period.
The third concrete implementation mode: the present embodiment further defines the method for estimating the influence of the thermal cycle on the thermal expansion coefficient of the polymer matrix composite based on the content of the free radicals in the second embodiment, wherein the polymer matrix composite is a carbon fiber composite.
The fourth concrete implementation mode: the method for estimating the influence of the thermal cycle on the thermal expansion coefficient of the polymer matrix composite based on the content of the free radicals in the third embodiment is further limited in the present embodiment, and the process of testing the thermal expansion coefficient of the experimental sample taken out after each thermal cycle in the second embodiment needs to be performed under the protection of nitrogen or argon with the flow rate of 50 ml/min; respectively recording the thermal expansion coefficients of each group of thermal cycle tests under different thermal cycle times;
in order to prevent the experimental sample from being oxidized in the process of testing the thermal expansion coefficient, nitrogen or argon is used for protection during testing, and the flow rate of the nitrogen or argon is 50 ml/min.
And calculating the average value of the thermal expansion coefficients corresponding to the same thermal cycle times of each group of thermal cycle tests, and processing and analyzing the measured thermal expansion coefficients to obtain the thermal expansion coefficient change rule of the thermal cycle tests under different thermal cycle times.
The fifth concrete implementation mode: the embodiment further defines the method for estimating the influence of the thermal cycle on the thermal expansion coefficient of the polymer matrix composite based on the content of the free radicals in the fourth embodiment, and the step in the fourth embodiment is to adjust the frequency, the magnetic field and the gain of the device to test the content of the free radicals of the taken experimental sample;
and calculating the average value of the free radical content corresponding to the same thermal cycle times of each group of thermal cycle tests, and processing and analyzing the measured free radical content to obtain the change rule of the free radical content under different thermal cycle times of the thermal cycle tests.
Examples
Example 1
The invention discloses a method for estimating the influence of thermal cycle on the thermal expansion coefficient of a polymer matrix composite based on the content of free radicals, which comprises the following steps:
step one, selecting a carbon fiber cyanate ester resin composite material as an experimental sample, wherein the size of the experimental sample is as follows: the length is 25mm, the width is 5mm, and the thickness is 2 mm; performing a thermal cycle experiment on a selected experimental sample under the condition that the vacuum degree is less than 1Pa, setting the temperature range of the thermal cycle experiment to be-150 ℃ and the heating rate and the cooling rate to be 1.5 ℃/min according to the on-orbit task time requirement of the spacecraft and the on-orbit working time;
and step two, taking out the experimental sample after each thermal cycle according to the experimental requirements, testing the thermal expansion coefficient of the taken out experimental sample, and respectively calculating the average value of the thermal expansion coefficients corresponding to the same thermal cycle times of each group of thermal cycle tests. In order to ensure uniform temperature and prevent oxidation in the test process, argon gas protection is adopted during the test, the flow rate is 50ml/min, and the change rule of the thermal expansion coefficient of the thermal cycle test along with the thermal cycle times is drawn according to the average value of the thermal expansion coefficients corresponding to the thermal cycles of 0 time, 50 times, 100 times and 200 times, as shown in fig. 4.
And step three, carrying out free radical content test on the experimental sample taken out in the step two each time, wherein the frequency, the magnetic field and the gain of equipment need to be adjusted during the test, and the change curve of the characteristic peak of the free radical under different thermal cycle times is shown in fig. 2.
The change rule of the free radical content along with the thermal cycle number of the thermal cycle test is drawn according to the average value of the free radical content corresponding to the thermal cycles of 0 time, 50 times, 100 times and 200 times, as shown in fig. 3.
Step four, utilizing the curve of the content of the free radicals of the thermal cycle test obtained in the step two and the curve of the thermal expansion coefficient of the thermal cycle test along with the change of the thermal cycle times; obtaining that the content of free radicals and the thermal expansion coefficient are both reduced along with the increase of the thermal cycle times, and the change rule of the content of the free radicals along with the thermal cycle times is consistent with the change rule of the thermal expansion coefficient along with the thermal cycle times;
step five, for a certain polymer matrix composite material needing to measure the thermal expansion coefficient, the environmental conditions of the polymer matrix composite material during on-orbit operation can be simulated, and the change rule of the thermal expansion coefficient of the polymer matrix composite material along with the thermal cycle times and the change rule of the free radical content along with the thermal cycle times are obtained according to the method from the step one to the step three; therefore, during the operation of the rail, the free radical content of the polymer matrix composite material only needs to be measured according to the method of the step three; the thermal expansion coefficient of the polymer-based composite material can be predicted by checking the change rule of the thermal expansion coefficient of the polymer-based composite material along with the change rule of the thermal cycle number and the change rule of the free radical content along with the thermal cycle number.
The method of the invention is adopted to predict the thermal expansion coefficient of the polymer matrix composite after thermal cycle, which can save 80% of the measurement time of the thermal expansion coefficient, and the invention predicts the thermal expansion coefficient according to the content of free radicals, namely the polymer matrix composite with complex structure is not required to be made into a standard component, which can realize the measurement of the thermal expansion coefficient, greatly simplifies the measurement process and reduces the measurement difficulty.
Example 2
The invention discloses a method for estimating the influence of thermal cycle on the thermal expansion coefficient of a polymer matrix composite based on the content of free radicals, which comprises the following steps:
step one, selecting a carbon fiber epoxy resin composite material as an experimental sample, wherein the size of the experimental sample is as follows: the length is 25mm, the width is 5mm, and the thickness is 2 mm; performing a thermal cycle experiment on a selected experimental sample under the condition that the vacuum degree is less than 1Pa, setting the temperature range of the thermal cycle experiment to be-150 ℃ and the heating rate and the cooling rate to be 1.5 ℃/min according to the on-orbit task time requirement of the spacecraft and the on-orbit working time;
and step two, taking out the experimental sample after each thermal cycle according to the experimental requirements, testing the thermal expansion coefficient of the taken out experimental sample, and respectively calculating the average value of the thermal expansion coefficients corresponding to the same thermal cycle times of each group of thermal cycle tests. In order to ensure uniform temperature and prevent oxidation in the test process, argon gas protection is adopted during the test, the flow rate is 50ml/min, and the change rule of the thermal expansion coefficient of the thermal cycle test along with the thermal cycle times is drawn according to the average value of the thermal expansion coefficients corresponding to the thermal cycles of 0 time, 50 times, 100 times and 200 times, as shown in fig. 7.
And step three, carrying out free radical content test on the experimental sample taken out in the step two each time, wherein the frequency, the magnetic field and the gain of equipment need to be adjusted during the test, and as shown in fig. 5, the change curve of the characteristic peak of the free radical under different thermal cycle times is shown.
The change rule of the free radical content along with the thermal cycle number in the thermal cycle test is plotted according to the average value of the free radical content corresponding to the thermal cycles of 0, 50, 100 and 200, as shown in fig. 6.
Step four, utilizing the curve of the content of the free radicals of the thermal cycle test obtained in the step two and the curve of the thermal expansion coefficient of the thermal cycle test along with the change of the thermal cycle times; obtaining that the change rule of the content of the free radicals along with the number of thermal cycles is consistent with the change rule of the thermal expansion coefficient along with the number of thermal cycles.
Example 3
The invention discloses a method for estimating the influence of thermal cycle on the thermal expansion coefficient of a polymer matrix composite based on the content of free radicals, which comprises the following steps:
step one, selecting a carbon fiber cyanate ester resin composite material as an experimental sample, wherein the size of the experimental sample is as follows: the length is 25mm, the width is 5mm, and the thickness is 2 mm; performing a thermal cycle experiment on a selected experimental sample under the condition that the vacuum degree is less than 1Pa, setting the temperature range of the thermal cycle experiment to be-150 ℃ and the heating rate and the cooling rate to be 2.5 ℃/min according to the on-orbit task time requirement of the spacecraft and the on-orbit working time;
and step two, taking out the experimental sample after each thermal cycle according to the experimental requirements, testing the thermal expansion coefficient of the taken out experimental sample, and respectively calculating the average value of the thermal expansion coefficients corresponding to the same thermal cycle times of each group of thermal cycle tests. In order to ensure uniform temperature and prevent oxidation during the test, argon gas is adopted for protection during the test, the flow rate is 50ml/min, and the change rule of the thermal expansion coefficient of the thermal cycle test along with the thermal cycle times is drawn according to the average value of the thermal expansion coefficients corresponding to the thermal cycles of 0 time, 50 times, 100 times, 200 times and 2000 times, as shown in fig. 10.
And step three, carrying out free radical content test on the experimental sample taken out in the step two each time, wherein the frequency, the magnetic field and the gain of equipment need to be adjusted during the test, and as shown in fig. 8, the change curve of the characteristic peak of the free radical under different thermal cycle times is shown.
The change rule of the radical content with the thermal cycle number in the thermal cycle test is plotted according to the average value of the radical content corresponding to the thermal cycles of 0, 50, 100, 200 and 2000, as shown in fig. 9.
Step four, utilizing the curve of the content of the free radicals of the thermal cycle test obtained in the step two and the curve of the thermal expansion coefficient of the thermal cycle test along with the change of the thermal cycle times; obtaining that the change rule of the content of the free radicals along with the number of thermal cycles is consistent with the change rule of the thermal expansion coefficient along with the number of thermal cycles.
Example 4
The invention discloses a method for estimating the influence of thermal cycle on the thermal expansion coefficient of a polymer matrix composite based on the content of free radicals, which comprises the following steps:
step one, selecting a carbon fiber epoxy resin composite material as an experimental sample, wherein the size of the experimental sample is as follows: the length is 25mm, the width is 5mm, and the thickness is 2 mm; performing a thermal cycle experiment on a selected experimental sample under the condition that the vacuum degree is less than 1Pa, setting the temperature range of the thermal cycle experiment to be-150 ℃ and the heating rate and the cooling rate to be 2.5 ℃/min according to the on-orbit task time requirement of the spacecraft and the on-orbit working time;
and step two, taking out the experimental sample after each thermal cycle according to the experimental requirements, testing the thermal expansion coefficient of the taken out experimental sample, and respectively calculating the average value of the thermal expansion coefficients corresponding to the same thermal cycle times of each group of thermal cycle tests. In order to ensure uniform temperature and prevent oxidation during the test, argon gas is adopted for protection during the test, the flow rate is 50ml/min, and the change rule of the thermal expansion coefficient of the thermal cycle test along with the thermal cycle times is drawn according to the average value of the thermal expansion coefficients corresponding to the thermal cycles of 0 time, 50 times, 100 times, 200 times and 2000 times, as shown in fig. 13.
And step three, carrying out free radical content test on the experimental sample taken out in the step two each time, wherein the frequency, the magnetic field and the gain of equipment need to be adjusted during the test, and as shown in fig. 11, the change curve of the characteristic peak of the free radical under different thermal cycle times is shown.
The change rule of the radical content with the thermal cycle number in the thermal cycle test is plotted according to the average value of the radical content corresponding to the thermal cycles of 0, 50, 100, 200 and 2000, as shown in fig. 12.
Step four, utilizing the curve of the content of the free radicals of the thermal cycle test obtained in the step two and the curve of the thermal expansion coefficient of the thermal cycle test along with the change of the thermal cycle times; obtaining that the change rule of the content of the free radicals along with the number of thermal cycles is consistent with the change rule of the thermal expansion coefficient along with the number of thermal cycles.
Claims (3)
1. A method for predicting the influence of thermal cycling on the thermal expansion coefficient of a polymer matrix composite based on the content of free radicals is characterized by comprising the following specific steps:
selecting a polymer matrix composite material as an experimental sample, and carrying out a thermal cycle test on the selected experimental sample under the condition that the vacuum degree is less than 1 Pa; setting the thermal cycle times of each group of thermal cycle tests to be not less than 200 times, and setting the number of the groups of the thermal cycle tests to be not less than 3 groups;
the sizes of the experimental samples in the first step are as follows: the length is 20 mm-25 mm, the width is 5 mm-6 mm, and the thickness is 1 mm-3 mm; setting the temperature range of each thermal cycle to be-150 ℃;
setting the ambient temperature around the experimental sample to be gradually reduced from 150 ℃ to-150 ℃, wherein the temperature reduction rate is x, x is more than 0.2 and the unit is ℃/min, and then gradually increasing the ambient temperature from-150 ℃ to 150 ℃ at the temperature increase rate x; when the ambient temperature around the experimental sample is from 150 ℃ to-150 ℃, and then the process from-150 ℃ to 150 ℃ is a thermal cycle;
the polymer matrix composite material is a carbon fiber composite material; the carbon fiber composite material is a carbon fiber cyanate ester resin composite material or a carbon fiber epoxy resin composite material;
step two, taking out an experimental sample after each thermal cycle, and testing the thermal expansion coefficient of the taken out experimental sample; respectively recording the thermal expansion coefficients of each group of thermal cycle tests under different thermal cycle times; calculating the average value of the thermal expansion coefficients corresponding to the same thermal cycle times of each group of thermal cycle tests to obtain the thermal expansion coefficient change rule under different thermal cycle times;
step three, carrying out free radical content test on the experimental sample taken out each time in the step two, calculating the average value of the free radical content corresponding to the same thermal cycle times of each group of thermal cycle tests, and obtaining the change rule of the free radical content under different thermal cycle times;
step four, comparing the change curve of the thermal expansion coefficient along with the thermal cycle times in the step two with the change curve of the free radical content along with the thermal cycle times in the step three to obtain that the free radical content and the thermal expansion coefficient are both reduced along with the increase of the thermal cycle times, and the change rule of the free radical content along with the thermal cycle times is consistent with the change rule of the thermal expansion coefficient along with the thermal cycle times;
step five, for a certain polymer matrix composite material needing to measure the thermal expansion coefficient, obtaining the change rule of the thermal expansion coefficient of the polymer matrix composite material along with the change rule of the thermal cycle times and the change rule of the free radical content along with the thermal cycle times according to the methods from the step one to the step three; during the on-track operation, the free radical content of the polymer matrix composite material only needs to be measured according to the method of the step three;
and step six, according to the content of the free radicals obtained by measurement in the step five, predicting the thermal expansion coefficient of the polymer-based composite material by checking the change rule of the thermal expansion coefficient of the polymer-based composite material along with the thermal cycle times and the change rule of the content of the free radicals along with the thermal cycle times.
2. The method for predicting the influence of thermal cycling on the thermal expansion coefficient of the polymer matrix composite material based on the content of free radicals in claim 1, wherein the process of testing the thermal expansion coefficient of the experimental sample taken out after each thermal cycling in the second step is carried out under the protection of nitrogen or argon with the flow rate of 50 ml/min; respectively recording the thermal expansion coefficients of each group of thermal cycle tests under different thermal cycle times;
and calculating the average value of the thermal expansion coefficients corresponding to the same thermal cycle times of each group of thermal cycle tests, and processing and analyzing the measured thermal expansion coefficients to obtain the thermal expansion coefficient change rule of the thermal cycle tests under different thermal cycle times.
3. The method for predicting the influence of thermal cycling on the thermal expansion coefficient of the polymer-matrix composite material based on the free radical content as claimed in claim 2, wherein the third step is to test the free radical content of the taken experimental sample by adjusting the frequency, the magnetic field and the gain of the device;
and calculating the average value of the free radical content corresponding to the same thermal cycle times of each group of thermal cycle tests, and processing and analyzing the measured free radical content to obtain the change rule of the free radical content under different thermal cycle times of the thermal cycle tests.
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