CN110887876B - Method for detecting lightning damage of carbon fiber composite laminated plate - Google Patents
Method for detecting lightning damage of carbon fiber composite laminated plate Download PDFInfo
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- CN110887876B CN110887876B CN201911117339.9A CN201911117339A CN110887876B CN 110887876 B CN110887876 B CN 110887876B CN 201911117339 A CN201911117339 A CN 201911117339A CN 110887876 B CN110887876 B CN 110887876B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/20—Investigating the presence of flaws
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/041—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body
Abstract
A method of detecting lightning strike damage to a carbon fiber composite laminate, the method comprising: and measuring the front resistance, the back resistance and the italic resistance of the carbon fiber composite laminated board sample before and after lightning stroke to obtain curves of the front resistance change rate, the back resistance change rate and the italic resistance change rate along with the integral change of a lightning current peak value and a lightning current action, wherein the curves are used as characteristic curves of the lightning stroke damage of the carbon fiber composite laminated board. In the application process, according to the actual front resistance change rate, the back resistance change rate and the italic resistance change rate obtained by measurement, the lightning current type causing the damage and the peak current and action integral at the moment are deduced by utilizing the characteristic curve of the lightning damage. Compared with the existing damage detection method for the carbon fiber composite material laminated plate, the method provided by the invention utilizes the resistance characteristic of the material, does not need an expensive sensor, and can realize quasi-real-time online detection.
Description
Technical Field
The invention belongs to the field of composite material lightning damage detection, and relates to a method for detecting lightning damage of a carbon fiber composite laminated plate.
Background
The carbon fiber composite material has the characteristics of high strength, high modulus, high temperature resistance and the like, and is an ideal structural material. The carbon fiber has good conductivity and resistivity of about 1.2 × 10-5～3×10-5Omega m. The carbon fiber can be used as a sensor due to the high conductivity of the carbon fiber, and the damage condition of the carbon fiber composite material laminated plate can be researched through the change of the resistance of the carbon fiber composite material laminated plate.
Carbon fiber composites are widely used in aircraft and fan blades because of their outstanding properties. These applications are often subject to lightning strikes. Compared with other non-metal materials, the carbon fiber has good electrical conductivity and thermal conductivity, but most of the base materials of the carbon fiber composite materials used in practice are made of high-insulation materials similar to epoxy resin, and the electrical conductivity and the thermal conductivity of the materials are reduced after the two materials are synthesized, and more serious the obvious anisotropy is caused. This low electrical conductivity, low thermal conductivity and anisotropic properties make the carbon fiber composite material more severe damage than the metal material when struck by lightning. At present, the lightning damage of the carbon fiber composite laminated plate is mainly researched by means of ultrasonic scanning, X-ray diffraction, an electron microscope and the like, and the detection methods are expensive and complicated in operation steps and cannot adapt to online quasi-real-time detection. According to the resistance change characteristic of the carbon fiber composite laminated plate, the damage degree of the carbon fiber composite laminated plate after lightning stroke can be judged by using a resistance method. The resistance method is widely applied to mechanical damage detection of carbon fiber composite materials, but the relationship between the resistance change before and after lightning strike of the carbon fiber composite material laminate and the lightning strike damage is not studied in detail in the past, so the lightning strike damage detection of the carbon fiber composite material laminate is not carried out by the resistance method.
After the carbon fiber composite laminated plate is struck by lightning, the resistance of the laminated plate changes. By measuring the resistance change before and after the lightning stroke of the laminated plate, the damage condition of the carbon fiber composite laminated plate can be monitored in real time.
Disclosure of Invention
The invention provides a method for detecting lightning damage of a carbon fiber composite laminate, which is used for realizing the quasi-real-time and nondestructive detection of the lightning damage of the carbon fiber composite laminate.
In order to achieve the above object, the technical solution of the present invention is as follows:
a method for detecting lightning damage of a carbon fiber composite laminated plate is characterized by comprising the following steps: the method comprises the following steps:
1) establishing a characteristic curve of lightning damage of the carbon fiber composite laminated plate:
measuring the front resistance, the back resistance and the italic resistance of the carbon fiber composite laminated plate before and after lightning stroke to obtain curves of the front resistance change rate, the back resistance change rate and the italic resistance change rate along with the integral change of a lightning current peak value and a lightning current action, wherein the curves are used as characteristic curves of lightning stroke damage of the carbon fiber composite laminated plate;
2) according to the front resistance change rate, the back resistance change rate and the italic resistance change rate obtained by actual measurement, the lightning current type causing the damage and the peak current and action integral at the moment are deduced by utilizing the characteristic curve of the lightning damage:
measuring actual front resistance change rate, back resistance change rate and italic resistance change rate of the laminated plate after being damaged by lightning, and calculating total error before inflection point and total error after inflection point of the actual front resistance change rate, the back resistance change rate and the italic resistance change rate of the laminated plate after being damaged by lightning; and comparing the characteristic curve of the lightning damage with the actual front resistance change rate, the actual back resistance change rate and the actual italic resistance change rate of the sample after the lightning damage, and deducing the lightning current type, the corresponding peak current and the corresponding action integral of the lightning damage suffered by the laminated plate according to the principle that the resistance change or damage is caused by the lightning current type with the minimum total error and the corresponding peak current and action integral.
The characteristic curve of the lightning damage is established according to the following steps:
1) pre-embedding electrodes on the front surface and the back surface of the carbon fiber composite material laminated plate to be used as measuring electrodes of resistance before and after lightning stroke, measuring the front resistance by using the front electrode, measuring the back resistance by using the back electrode, and measuring the inclined resistance of the laminated plate between the front electrode and the back electrode;
2) before a lightning stroke test, measuring current (I) and voltage (U) among a front electrode, a back electrode and an inclined electrode by using an adjustable direct-current power supply and two high-precision multimeters, and calculating front resistance, back resistance and inclined resistance before the lightning stroke test according to a resistance law R ═ U/I;
3) carrying out specified peak current and current type lightning stroke tests on the sample;
4) resistance measurement after lightning strike: after the test is finished, measuring according to the measuring method in the step 2) again to obtain the front resistance, the back resistance and the italic resistance of the sample after lightning stroke;
5) the resistance change rate after lightning strike of the carbon fiber composite laminate was expressed as:
in the formula, R0Resistance, R, measured before lightning test1Resistance measured after lightning stroke test;
6) changing the peak current of the lightning current, returning to the step 2) for repeated calculation, and obtaining corresponding data of a plurality of groups of front resistance change rate, back resistance change rate and inclined body resistance change rate and peak current and action integral under a certain type of lightning current;
7) changing the type of lightning current, returning to the step 2), and obtaining corresponding data of a plurality of groups of front resistance change rates, back resistance change rates and inclined resistance change rates under other types of lightning currents and peak currents and action integrals;
8) obtaining curves of the front resistance change rate, the back resistance change rate and the italic resistance change rate about the peak current under different types of lightning currents by using a B spline curve fitting method; curves of front resistance change rate, back resistance change rate and italic resistance change rate under different types of lightning current with respect to action integral, and the curves are used as characteristic curves of lightning damage;
the method for deducing the lightning current type of the lightning strike damage suffered by the laminated plate, the corresponding peak current and the action integral are carried out according to the following steps:
1) before the laminated plate is used, measuring the resistance which is the resistance before lightning stroke, then installing the laminated plate on equipment, and after the laminated plate is struck by lightning, measuring the front resistance, the back resistance and the italic resistance according to the step 2) so as to obtain the front resistance change rate, the back resistance change rate and the italic resistance change rate after the laminated plate is struck by lightning;
2) finding out a corresponding peak current value and action integral value before an inflection point and a corresponding peak current value and action integral value after the inflection point from a front resistance change rate characteristic curve under a certain type of lightning current;
3) finding a peak current value and an action integral value before a corresponding inflection point and a peak current value and an action integral value after the inflection point from a back surface resistance change rate characteristic curve under a certain type of lightning current;
4) finding a peak current value and an action integral value before a corresponding inflection point and a peak current value and an action integral value after the inflection point from an italic resistance change rate characteristic curve under a certain type of lightning current;
5) calculating the following parameters under a certain type of lightning current according to the values obtained in the steps 2) to 4):
a: the average value and the root mean square error of the peak current values before the inflection point corresponding to the three resistance change rates;
b: the average value and the root mean square error of the peak current values after the inflection points corresponding to the three resistance change rates;
c: the average value and the root mean square error of the action integral values before the inflection point corresponding to the three resistance change rates;
d: the average value and the root mean square error of the action integral values after the inflection points corresponding to the three resistance change rates;
6) step 5), the a and the c form a front inflection point group, the b and the d form a rear inflection point group, and the total error before the inflection point under a certain type of lightning current is obtained by utilizing the root mean square error of the current of the front peak value of the inflection point in the a and the integral root mean square error of the front action of the inflection point in the c; obtaining total error after the inflection point under a certain type of lightning current by using the peak current root mean square error after the inflection point in b and the acting integral root mean square error after the inflection point in d;
7) repeating the steps 2) -6), and calculating the total error before the inflection point and the total error after the inflection point under other types of lightning currents;
8) by comparing the total error obtained in 6) and 7), the lightning current type of the lightning damage suffered by the laminate, the corresponding peak current and the action integral are obtained according to the principle that the resistance change or damage should be caused by the lightning current type with the minimum total error and the corresponding peak current and action integral.
The invention has the beneficial effects that:
1. in practical application, the electrodes can be embedded into the laminated plate, the damage condition of the carbon fiber composite material laminated plate can be known through the change of the resistance without damaging the structure of the carbon fiber composite material laminated plate;
2. the method is simple and convenient to operate, the required measuring instrument is a common digital multimeter and an adjustable direct-current power supply, and the test cost and difficulty are greatly reduced;
3. the method can be used for detecting the lightning stroke damage condition of the carbon fiber composite material on site or on line in near real time.
Drawings
FIG. 1 is a layout of a surface measuring electrode of a carbon fiber composite material laminate;
FIG. 2 is a schematic circuit diagram of measuring the resistance of a carbon fiber composite laminate;
FIG. 3 is a graph of the rate of change of resistance and peak current relationship of a carbon fiber composite laminate before and after a lightning strike test;
FIG. 4 is a graph of the rate of change of resistance of a carbon fiber composite laminate before and after a lightning strike test versus the integral of the effect;
table 1 shows the electrode configuration for resistance measurement;
table 2 is the peak current and the effect integral derived from the three rates of resistance change;
Detailed Description
The invention will be further described with reference to the following drawings and examples.
The present embodiment comprises two parts which are,
the first part is: and measuring the front resistance, the back resistance and the italic resistance of the carbon fiber composite laminated board sample before and after lightning stroke to obtain curves of the front resistance change rate, the back resistance change rate and the italic resistance change rate along with the integral change of a lightning current peak value and a lightning current action, wherein the curves are used as characteristic curves of the lightning stroke damage of the carbon fiber composite laminated board.
The second part is as follows: and deducing the lightning current type causing the damage and the peak current and action integral at the moment by utilizing the characteristic curve of the lightning damage according to the front resistance change rate, the back resistance change rate and the italic resistance change rate which are obtained by actual measurement.
In the first part of this example, the carbon fiber composite laminate used had a length of 250mm, a width of 50mm and a thickness of 2mm, the direction of the surface carbon fiber was 0 degrees, and the lay-up was
The method comprises the following steps of obtaining a characteristic curve of lightning damage:
(1) referring to fig. 1, 8 direct current resistance measurement electrodes were fabricated on the front and back sides of a carbon fiber composite laminate using conductive silver paste and copper wires, and 4 electrodes on the front side were a1, a2, A3, a 4; the four electrodes on the back are B1, B2, B3, B4; the electrodes are embedded into the laminated plate;
(2) resistance measurement before lightning strike: when the front resistance is measured, the outer electrodes are A1 and A4, and the inner electrodes are A2 and A3; when the back resistance is measured, the outer electrodes are B1 and B4, and the inner electrodes are B2 and B3; the external electrodes were A1, B4 and the internal electrodes were A2, B3 when the italic resistance was measured. Before a lightning stroke test, the direct current is connected according to a graph 2, an adjustable direct current power supply outputs direct current to be injected into a sample through an outer electrode, a high-precision universal meter 2 measures the current (I) injected into the sample through the outer electrode, and a high-precision universal meter 1 measures the voltage (U) between inner electrodes.
TABLE 1
TABLE 2
Calculating front resistance, back resistance and italic resistance before the lightning stroke test through a resistance law R ═ U/I after measurement;
(3) carrying out lightning stroke test of lightning current type A on the carbon fiber composite material laminated plate;
(4) resistance measurement after lightning strike: after the test is finished, obtaining the front resistance, the back resistance and the inclined resistance of the carbon fiber composite material laminated plate after the lightning stroke according to the measuring method in the step (2);
(5) the resistance change rate after lightning strike of the carbon fiber composite laminate was expressed as:
in the formula, R0Resistance before test, R1Resistance after the test;
(6) changing the peak current of the lightning current type A, repeating the steps (1) to (5), and obtaining corresponding data of a plurality of groups of front resistance change rate, back resistance change rate and italic resistance change rate of the lightning current type A, the peak current and the action integral;
(7) changing the lightning current type A into a lightning current type D, and repeating the steps (1) to (6) to obtain corresponding data of a plurality of groups of front resistance change rates, back resistance change rates and italic resistance change rates of the lightning current type D and peak currents and action integrals;
(8) obtaining curves of the front resistance change rate, the back resistance change rate and the italic resistance change rate relative to the peak current under the lightning current type A and the lightning current type D by using a B spline curve fitting method; the front side resistance change rate, the back side resistance change rate, and the italic resistance change rate for lightning current types a and D are plotted against the integral of action, see fig. 3 and 4.
Curves A-front, A-back and A-oblique in FIG. 3 refer to characteristic curves of the corresponding relationship between the front resistance change rate and the peak current under the lightning current type A, respectively; a characteristic curve of the corresponding relation between the back resistance change rate and the peak current; and the italic resistance change rate and the peak current are in corresponding relation to a characteristic curve. Curves D-front, D-back and D-oblique respectively refer to characteristic curves of corresponding relations between the front resistance change rate and the peak current under the lightning current type D; a characteristic curve of the corresponding relation between the back resistance change rate and the peak current; and the italic resistance change rate and the peak current are in corresponding relation to a characteristic curve.
Curves A-front, A-back and A-oblique in FIG. 4 refer to characteristic curves of the corresponding relationship between the change rate of the front resistance and the action integral under the lightning current type A, respectively; a characteristic curve of the corresponding relation between the back resistance change rate and the action integral; and the italic resistance change rate and the action integral are corresponding to a characteristic curve. Curves D-front, D-back and D-oblique respectively refer to characteristic curves of the corresponding relation between the front resistance change rate and the action integral under the lightning current type D; a characteristic curve of the corresponding relation between the back resistance change rate and the action integral; and the italic resistance change rate and the action integral are corresponding to a characteristic curve.
In the second part of this embodiment, the peak current and the action integral that cause such degree of damage are inferred from the characteristic curve of the lightning damage based on the front surface resistance change rate, the back surface resistance change rate, and the italic resistance change rate obtained by actual measurement, and the type of damage is determined. Taking the cases where the actually detected front surface resistance change rate, back surface resistance change rate, and italic resistance change rate are-13.6%, 7.87%, and-10.31%, respectively, as an example, for the lightning current type a:
(1) when the front resistance change rate is-13.6%, it corresponds to the peak current value I before the inflection point in the curve "A-front" of FIG. 3f,1,A33.07kA, peak current value after inflection point If,2,A38.50 kA; corresponding to the effect integral value AI before the "A-front" curve inflection point of FIG. 4f,1,AIs 56.91X 103A2s, integral value of action AI after inflection pointf,2,AIs 76.85X 103A2s；
(2) When the change rate of the back surface resistance is-7.87%, it corresponds to the peak current value I before the inflection point in the curve "A-back" of FIG. 3b,1,A30.43kA, peak current value after inflection point Ib,2,A40.04 kA; corresponding to the action integral value AI before the inflection point of the curve "A-back" in FIG. 4b,1,AIs 48.25X 103A2s, integral value of action AI after inflection pointb,2,AIs 82.72X 103A2s；
(3) When the rate of change of the italic resistance was-10.31%, it corresponded to the peak current value I before the inflection point in the curve "A-oblique" in FIG. 3o,1,A32.93kA, peak current value I after inflection pointo,2,A40.85 kA; corresponding to the effect integral value AI before the inflection point of the "A-oblique" curve of FIG. 4o,1,AIs 56.47X 103A2s, integral value of action AI after inflection pointo,2,AIs 86.53X 103A2s；
(4) The average value of the peak current before the inflection point of the lightning current type A is as follows:
the root mean square error of the peak current before the inflection point is as follows:
the average value of the peak current after the inflection point is:
the root mean square error of the peak current after the inflection point is as follows:
the pre-inflection point integral mean is:
the pre-inflection point integral root mean square error is:
the post-inflection integral mean value of
Post-inflection integral root mean square error of
(5) Obtaining a total error before the inflection point under the lightning current type A by using the peak current root mean square error before the inflection point and the acting integral root mean square error before the inflection point; obtaining total error after the inflection point under the lightning current type A by utilizing the peak current root mean square error after the inflection point and the action integral root mean square error after the inflection point;
the total error before the inflection point under the lightning current type A is as follows:
the total error after the inflection point under the lightning current type a is:
for lightning current type D:
(6) when the front resistance change rate is-13.6%, it corresponds to the peak current value I before the inflection point in the curve "D-front" of FIG. 3f,1,D40.63kA, peak current value after inflection point If,2,D58.52 kA; corresponding to the effect integration value AI before the "D-front" curve inflection point of FIG. 4f,1,DIs 44.73X 103A2s, integral value of action AI after inflection pointf,2,DIs 94.89X 103A2s；
(7) When the change rate of the back surface resistance is-7.87%, it corresponds to the peak current value I before the inflection point in the curve "D-back" of FIG. 3b,1,D34.40kA, peak current value I after inflection pointb,2,D58.81 kA; corresponding to the action integral value AI before the "D-back" curve inflection point of FIG. 4b,1,DIs 32.12X 103A2s, integral value of action AI after inflection pointb,2,DIs 95.92X 103A2s；
(8) When the rate of change of the italic resistance was-10.31%, it corresponded to the peak current value I before the inflection point in the curve "D-oblique" in FIG. 3o,1,DA peak current value I after the inflection point of 41.51kAo,2,D58.74 kA; corresponding to the action integral value AI before the inflection point of the "D-oblique" curve of FIG. 4o,1,DIs 46.93X 103A2s, integral value of action AI after inflection pointo,2,DIs 96.07 x 103A2s；
(9) Referring to the step (4), calculating to obtain that the average current value of the front peak value of the inflection point under the lightning current type D is 38.85kA, and the root mean square error of the front peak value current of the inflection point is 3.16; the average value of the peak current after the inflection point is 58.69kA, and the root mean square error of the peak current after the inflection point is 0.12; the pre-inflection point integral mean value is 41.26 × 103A2s, the integrated root mean square error before the inflection point is 6.53; the post-inflection integral mean value was 95.63X 103A2s, the post-inflection action integral root mean square error is 0.52;
(10) in the reference step (5), the total error before the inflection point under the lightning current type D is 7.25 by using the peak current root mean square error before the inflection point and the integral root mean square error before the inflection point; obtaining a total error of 0.54 after the inflection point under the lightning current type D by utilizing the peak current root mean square error after the inflection point and the action integral root mean square error after the inflection point;
(11) table 2 shows the results of steps (1) to (10). The resistance change or damage should be caused by the type of lightning current with the smallest total error and the corresponding peak current and contribution integral. For the case where the rates of change of the front resistance, the back resistance and the italic resistance were-13.6%, -7.87% and-10.31%, respectively, the minimum total error value was found to be 0.54 by comparing the four total error values, from which it was concluded that the damage was caused by a peak current of 58.69kA with an integral of 95.63 × 103A2s lightning current type D.
Compared with the existing method for detecting the lightning damage of the carbon fiber composite laminated plate, the method utilizes the resistance characteristic of the material and does not need an expensive sensor, and can realize quasi-real-time online detection.
The invention relates to a carbon fiber composite laminated plate lightning damage detection method based on a resistance method, which can accurately measure the resistance of the carbon fiber composite laminated plate without complex instruments and data processing methods to obtain a change curve of the resistance change rate along with peak current and action integral; and deducing the lightning stroke damage condition of the carbon fiber composite material laminated plate according to the resistance change rate curve.
The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.
Claims (1)
1. A method for detecting lightning damage of a carbon fiber composite laminated plate is characterized by comprising the following steps: the method comprises the following steps:
1) establishing a characteristic curve of lightning damage of the carbon fiber composite laminated plate: measuring the front resistance, the back resistance and the italic resistance of the carbon fiber composite laminated plate before and after lightning stroke to obtain curves of the front resistance change rate, the back resistance change rate and the italic resistance change rate along with the integral change of a lightning current peak value and a lightning current action, wherein the curves are used as characteristic curves of lightning stroke damage of the carbon fiber composite laminated plate;
2) according to the front resistance change rate, the back resistance change rate and the italic resistance change rate obtained by actual measurement, the lightning current type causing the damage and the peak current and action integral at the moment are deduced by utilizing the characteristic curve of the lightning damage:
measuring actual front resistance change rate, back resistance change rate and italic resistance change rate of the laminated plate after being damaged by lightning, and calculating total error before inflection point and total error after inflection point of the actual front resistance change rate, the back resistance change rate and the italic resistance change rate of the laminated plate after being damaged by lightning; comparing the characteristic curve of the lightning damage with the actual front resistance change rate, the actual back resistance change rate and the actual italic resistance change rate of the sample after the lightning damage, and deducing the lightning current type, the corresponding peak current and the corresponding action integral of the lightning damage suffered by the laminated plate according to the principle that the resistance change or damage is caused by the lightning current type with the minimum total error and the corresponding peak current and the action integral;
the characteristic curve of the lightning damage is obtained according to the following steps:
1) pre-embedding electrodes on the front surface and the back surface of the carbon fiber composite material laminated plate to be used as measuring electrodes of resistance before and after lightning stroke, measuring the front resistance by using the front electrode, measuring the back resistance by using the back electrode, and measuring the inclined resistance of the laminated plate between the front electrode and the back electrode;
2) before a lightning stroke test, measuring current (I) and voltage (U) among a front electrode, a back electrode and an inclined electrode by using an adjustable direct-current power supply and two high-precision multimeters, and calculating front resistance, back resistance and inclined resistance before the lightning stroke test according to a resistance law R ═ U/I;
3) carrying out specified peak current and current type lightning stroke tests on the sample;
4) resistance measurement after lightning strike: after the test is finished, measuring according to the measuring method in the step 2) again to obtain the front resistance, the back resistance and the italic resistance of the sample after lightning stroke;
5) the resistance change rate after lightning strike of the carbon fiber composite laminate was expressed as:
in the formula, R0Resistance, R, measured before lightning test1Resistance measured after lightning stroke test;
6) changing the peak current of the lightning current, returning to the step 2) for repeated calculation, and obtaining corresponding data of a plurality of groups of front resistance change rate, back resistance change rate and inclined body resistance change rate and peak current and action integral under a certain type of lightning current;
7) changing the type of lightning current, returning to the step 2), and obtaining corresponding data of a plurality of groups of front resistance change rates, back resistance change rates and inclined resistance change rates under other types of lightning currents and peak currents and action integrals;
8) obtaining curves of the front resistance change rate, the back resistance change rate and the italic resistance change rate about the peak current under different types of lightning currents by using a B spline curve fitting method; curves of front resistance change rate, back resistance change rate and italic resistance change rate under different types of lightning current with respect to action integral, and the curves are used as characteristic curves of lightning damage;
the lightning current type causing the damage and the peak current and action integral at the moment are deduced by utilizing the characteristic curve of the lightning damage according to the front resistance change rate, the back resistance change rate and the italic resistance change rate which are obtained by actual measurement, and the method is carried out according to the following steps:
9) before the laminated plate is used, measuring the resistance which is the resistance before lightning strike, then installing the laminated plate on equipment, and after the laminated plate is struck by lightning, measuring the front resistance, the back resistance and the italic resistance according to the step 2), thereby obtaining the front resistance change rate, the back resistance change rate and the italic resistance change rate after the laminated plate is struck by lightning;
10) finding out a corresponding peak current value and action integral value before an inflection point and a corresponding peak current value and action integral value after the inflection point from a front resistance change rate characteristic curve under a certain type of lightning current;
11) finding a peak current value and an action integral value before a corresponding inflection point and a peak current value and an action integral value after the inflection point from a back surface resistance change rate characteristic curve under a certain type of lightning current;
12) finding a peak current value and an action integral value before a corresponding inflection point and a peak current value and an action integral value after the inflection point from an italic resistance change rate characteristic curve under a certain type of lightning current;
13) calculating the following parameters under a certain type of lightning current according to the values obtained in the steps 10) to 12):
a: the average value and the root mean square error of the peak current values before the inflection point corresponding to the three resistance change rates;
b: the average value and the root mean square error of the peak current values after the inflection points corresponding to the three resistance change rates;
c: the average value and the root mean square error of the action integral values before the inflection point corresponding to the three resistance change rates;
d: the average value and the root mean square error of the action integral values after the inflection points corresponding to the three resistance change rates;
14) step 13) a and c form a front group of inflection points, b and d form a rear group of inflection points, and the total error before the inflection points under a certain type of lightning current is obtained by using the root mean square error of the current of the front peak value of the inflection point in a and the integral root mean square error of the front action of the inflection point in c; obtaining total error after the inflection point under a certain type of lightning current by using the peak current root mean square error after the inflection point in b and the acting integral root mean square error after the inflection point in d;
15) repeating the steps 10) -14), and calculating the total error before the inflection point and the total error after the inflection point under other types of lightning currents;
16) by comparing the total error obtained in 14) and 15), the type of lightning current, the corresponding peak current and the action integral of the lightning strike damage suffered by said laminate is derived, based on the principle that the change or damage in resistance should be caused by the type of lightning current with the minimum total error and the corresponding peak current and action integral.
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| CN1945358B (en) * | 2006-10-19 | 2011-04-27 | 张东来 | High precision measuring method for deep resource based on natural electric field idealization and detecting instrument |
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