CN115356376A - Composite material damage monitoring method based on embedded distributed electrodes - Google Patents
Composite material damage monitoring method based on embedded distributed electrodes Download PDFInfo
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- CN115356376A CN115356376A CN202210985028.XA CN202210985028A CN115356376A CN 115356376 A CN115356376 A CN 115356376A CN 202210985028 A CN202210985028 A CN 202210985028A CN 115356376 A CN115356376 A CN 115356376A
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- composite material
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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
Abstract
The invention discloses a composite material damage monitoring method based on embedded distributed electrodes, which comprises the following steps: 1) The method comprises the following steps of (1) using aviation foam as a core material of a composite material sandwich structure, and regularly attaching copper foil with a fixed size on the aviation foam to serve as an electrode; 2) Forming a printed circuit board with a customized graphic using a flexible substrate, attaching the printed circuit board to the aerospace foam using an adhesive such that the electrodes extend; 3) Weaving the adhered aviation foam by using a radial weaving machine to enable carbon fibers to wrap the outside of the aviation foam, and filling the aviation foam with resin to form a matrix to form a carbon fiber composite material; 4) And determining a current injection mode and a voltage measurement mode by adopting a snake-shaped excitation mode, reconstructing the real resistance distribution condition by using electrical impedance tomography based on the measured voltage value, further obtaining the damage condition and the damage position, and realizing the nondestructive evaluation and the structural health monitoring of the carbon fiber composite material member.
Description
Technical Field
The invention relates to the technical field of nondestructive testing, in particular to a composite material damage monitoring method based on embedded distributed electrodes.
Background
The superior mechanical properties of carbon fiber composites make them advantageous in many weight-sensitive applications such as the aerospace and automotive industries. However, a key disadvantage is the inability to detect internal or sub-surface damage of these materials at an early stage by simple visual techniques. Due to the presence of multiple damage modes, including fiber breakage, matrix cracking, and delamination, conventional visual inspection and interval or period based inspection methods may not be effective in identifying and tracking these faults. Therefore, structural Health Monitoring (SHM) is a promising approach to continuously track the progress of damage to composite structures for timely intervention and repair. Electrical Impedance Tomography (EIT) has great potential in structural health monitoring. In EIT, lesion detection, localization and visualization in piezoresistive materials (such as CFRP) is achieved by plotting the spatially varying conductivity distribution of a domain through a series of voltage and current measurements collected along the domain boundaries.
Prior work in this area only considered a flat plate with edge mounted electrodes. The geometry of real structures is obviously much more complex and usually does not have well-defined edges. If the edge is provided with an electrode for structural health monitoring, the real situation can not be effectively monitored due to the soft field effect and the inadequacy of the EIT inverse problem; if the surface is provided with the electrode, the method is not suitable for the practical application of composite members, and the structural health monitoring can not be realized in engineering.
Disclosure of Invention
In order to solve the problems, the invention provides a composite material damage monitoring method based on embedded distributed electrodes, which is characterized in that the electrodes are embedded in a carbon fiber composite material member based on the piezoresistive effect of materials, and the real situation is reconstructed by adopting electrical impedance tomography, so that the nondestructive evaluation and the structural health monitoring of the carbon fiber composite material member are realized.
Technical scheme
A composite material damage monitoring method based on embedded distributed electrodes comprises the following process steps:
1) Aviation foam is used as a core material of a sandwich structure of a carbon fiber composite material member, and copper foils with fixed sizes are uniformly attached to the aviation foam at equal intervals to be used as electrodes;
2) Forming a printed circuit board with a customized graphic from a flexible substrate, attaching the printed circuit board to the aerospace foam using an adhesive such that the electrodes extend;
3) Weaving the aviation foam attached with the printed circuit board by using a radial weaving machine to enable carbon fibers to wrap the outside of the aviation foam, and filling the aviation foam with resin to form a carbon fiber composite material member;
4) And a snakelike excitation mode is adopted to carry out current injection and voltage measurement, the real resistance distribution condition is reconstructed by using electrical impedance tomography based on the measured voltage value, and then the damage condition and the damage position are judged, so that the nondestructive evaluation and the structural health monitoring of the carbon fiber composite material component are realized.
Further, the step two of using the flexible substrate to make the printed circuit board with the customized pattern comprises: the flexible substrate is polyimide, a conductive pattern is chemically etched on the surface of the polyimide, the conductive pattern is rolled copper foil, the printed circuit board is a single-layer circuit board, the rolled copper foil is arranged on a single surface of the printed circuit board, and the printed circuit board is further provided with via holes which correspond to the copper foil one to one.
Further, said attaching the printed circuit board to the aviation foam using an adhesive in step two such that the electrodes extend: and the back surfaces of the two printed circuit boards are respectively attached to the two surfaces of the aviation foam through adhesives, and after the two printed circuit boards are attached, the electrodes can extend out from the inside.
Further, in the third step, the aviation foam attached with the printed circuit board is woven by using a radial weaving machine, so that the carbon fibers are wrapped outside the aviation foam, and then filled with resin to serve as a matrix to form a carbon fiber composite material member: customizing a clamp for fixing one end of the aviation foam, installing the clamp on a manipulator, weaving the aviation foam after the attachment is finished by using a radial weaving machine, so that the carbon fibers are wrapped outside the aviation foam, and filling the aviation foam with resin to form a carbon fiber composite material member as a matrix.
Further, the reconstructing a true resistance distribution using electrical impedance tomography based on the measured voltage values in step four: through solving the positive problem and the inverse problem of electrical impedance tomography, the voltage values of two states measured by using differential imaging are used for reconstructing the real conductivity, and the damage condition and the damage position are judged according to the resistance distribution condition.
Further, the positive problem: to reconstruct the internal conductivity distribution, the ill-posed ERT inverse problem needs to be solved, on which a numerical forward model is required to map the internal conductivity to the boundary measurements, for which purpose a Complete Electrode Model (CEM) is used, which is implemented using finite element discretization of the following equations:
wherein
Is the Laplace operator, x represents the Cartesian coordinates in the domain, σ (x) and u (x) represent the conductivity and potential distributions within the object, e l Denotes the L-th electrode, U l Is a measure of the potential at the corresponding electrode, I l Indicating the current injection at the Lth electrode, dS indicating the infinitesimal surface of the domain, z l Representing the contact resistance between the lth electrode and the field.
Further, the inverse problem: the nonlinear ERT inverse problem can be conceptually characterized by a V = U (σ) observation model, where U is a finite element forward model that maps σ to a measured voltage V, and when the measured value and the forward model are matched exactly, the inverse problem (i.e., L) is solved 2 Norm minimization: i V-U (sigma) | non-woven phosphor 2 = 0), but this case is an unrealistic idealization because the measurement noise e is always present, resulting in the noise-corrected observation model being written as V = U (σ) + e, and due to the presence of noise, numerical modeling errors, non-linearity of U (σ), and ill-conditioned nature of the resulting ERT matrix used to solve the inverse optimization problem, the equation has infinite solutions, so in optimizing/solving the non-linear (absolute imaging) inverse problem, advanced regularization is required to reconstruct the difference in conductivity Δ σ based on the difference in boundary voltage measurements Δ V for two different states ( subscripts 1 and 2 representing baseline and damaged states, respectively), using differential imaging, as follows:
ΔV＝V 2 -V 1
Δσ＝σ 2 -σ 1
where J is the calculated Jacobian matrix that linearizes the point, Δ e is the measured noise difference between State 1 and State 2, L R Denoted is a regularizer, W is a diagonal noise weighting matrix.
Compared with the prior art, the invention has the following beneficial effects:
1. the embedded type gets rid of the influence on the appearance performance factor of the real component.
2. The distributed structure can reduce the soft field effect and the ill-posed character of the EIT inverse problem in the reconstruction process, so that more real and effective nondestructive evaluation and structural health monitoring can be obtained.
Drawings
FIG. 1 is a schematic view of a woven structure and an in-line electrode structure;
FIG. 2 is a schematic diagram of a customized graphic printed circuit board;
FIG. 3 is a schematic diagram of a serpentine excitation pattern.
Reference numerals
1-clamp 2-aviation foam 3-guide ring 4-carbon fiber 5-copper foil 6-polyimide 7-rolled copper foil 8-printed circuit board
Detailed Description
For a better illustration of the invention, reference is made to the following description, taken in conjunction with the accompanying drawings and examples:
as shown in fig. 1-3, the invention discloses a composite material damage monitoring method based on embedded distributed electrodes, which comprises the following process steps:
1) The method comprises the following steps of using aviation foam (PMI) 2 as a core material of a carbon fiber composite material member sandwich structure, and uniformly attaching copper foils 5 with fixed sizes on the aviation foam 2 at equal intervals to serve as electrodes;
2) A printed circuit board (FPCB) 8 having a customized pattern is made using a flexible substrate, and the printed circuit board 8 is attached to the aviation foam 2 using an adhesive such that electrodes are extended;
3) Weaving the aviation foam 2 attached with the printed circuit board 8 by using a radial weaving machine to enable the carbon fibers 4 to wrap the aviation foam 2, and filling the aviation foam with resin to form a carbon fiber composite material member;
4) And a snakelike excitation mode is adopted to carry out current injection and voltage measurement, and the real resistance distribution condition is reconstructed by using Electrical Impedance Tomography (EIT) based on the measured voltage value, so that the damage condition and the damage position are judged, and the nondestructive evaluation and the structural health monitoring of the carbon fiber composite material member are realized.
Further, the step two of manufacturing the printed circuit board 8 with the customized pattern by using the flexible substrate comprises: the flexible substrate is polyimide 6, a conductive pattern is chemically etched on the surface of the polyimide 6, the conductive pattern is rolled copper foil 7, the influence of the thickness and the size of the printed circuit board 8 is small enough, the printed circuit board 8 is a single-layer circuit board, the rolled copper foil 7 is arranged on the single surface of the printed circuit board 8, access holes (not shown) are further formed in the printed circuit board 8, and the access holes correspond to the copper foils 5 one to one.
Further, said attaching of the printed circuit board 8 to the aviation foam 2 using an adhesive in step two, so that the electrodes extend: the back surfaces of the two printed circuit boards 8 are respectively attached to the two surfaces of the aviation foam 2 through an adhesive, and after the attachment, the electrodes can extend out from the inside.
Further, in the third step, the aviation foam 2 attached with the printed circuit board 8 is woven by using a radial weaving machine, so that the carbon fibers 4 are wrapped outside the aviation foam 2, and then filled with resin to serve as a matrix to form a carbon fiber composite component: customizing a clamp 1 for fixing one end of the aviation foam 2, installing the clamp 1 on a manipulator, weaving the aviation foam 2 after the attachment is finished by using a radial weaving machine, so that the carbon fibers 4 are wrapped outside the aviation foam 2, and filling the carbon fibers with resin to form a carbon fiber composite material member as a matrix.
Further, the reconstructing a true resistance distribution using Electrical Impedance Tomography (EIT) based on the measured voltage values in step four: through solving the positive problem and the inverse problem of Electrical Impedance Tomography (EIT), the real conductivity is reconstructed by using the voltage values of two states measured by differential image pair, and the damage condition and the damage position are judged according to the resistance distribution condition.
Further, the positive problem: to reconstruct the internal conductivity distribution, the ill-posed ERT inverse problem needs to be solved, on which a numerical forward model is required to map the internal conductivity to the boundary measurements, for which purpose a Complete Electrode Model (CEM) is used, which is implemented using finite element discretization of the following equations:
wherein
Is Laplace operator, x represents Cartesian coordinates in the domain, σ (x) and u (x) represent the conductivity and potential distributions in the object, e l Denotes the L-th electrode, U l Is a measure of the potential at the corresponding electrode, I l Indicating the current injection at the Lth electrode, dS indicating the infinitesimal surface of the domain, z l Representing the contact resistance between the lth electrode and the field.
Further, the inverse problem: the nonlinear ERT problem can be conceptually characterized by a V = U (σ) observation model, where U is a finite element forward model that maps σ to a measured voltage V, and when the measured value and the forward model are exactly matched, the inverse problem (i.e., L) is solved 2 Norm minimization: i V-U (sigma) | non-woven phosphor 2 = 0), but this case is an unrealistic idealization because the measurement noise e is always present, resulting in the noise-corrected observation model being written as V = U (σ) + e, and due to the presence of noise, numerical modeling errors, non-linearity of U (σ), and ill-conditioned nature of the resulting ERT matrix used to solve the inverse optimization problem, there is an infinite solution to the equation, so in optimizing/solving the non-linear (absolute imaging) inverse problem, advanced regularization is required to use differential imaging, with bias priors and physical constraints, aimed at basing the two different states ( subscripts 1 and 2 representing baseline and damaged states, respectively)) The difference in the internal conductivity Δ σ is reconstructed from the difference in the boundary voltage measurements Δ V, as follows:
ΔV＝V 2 -V 1
Δσ＝σ 2 -σ 1
where J is the calculated Jacobian matrix linearizing the point, Δ e is the measured noise difference between State 1 and State 2, L R Denoted is a regularization matrix and W is a diagonal noise weighting matrix.
Specifically, selecting aviation foam 2 with high specific strength and high specific modulus as a core material of a carbon fiber composite material member sandwich structure, cutting a copper foil 5 into 24 squares with the size of 5 multiplied by 5mm, uniformly distributing the squares on the outer surface of the aviation foam 2, and closely attaching the squares on the aviation foam 2 without folds;
the method comprises the following steps of chemically etching a conductive pattern by taking polyimide 6 as a flexible substrate, wherein the conductive pattern is a rolled copper foil 7, selecting a single-layer printed circuit board 8 to ensure that the influence of the thickness and the size of the printed circuit board 8 is small enough, arranging the rolled copper foil 7 on one side of the printed circuit board 8, arranging via holes (not shown) on the printed circuit board 8, enabling the via holes to correspond to the copper foils 5 one by one, respectively attaching the back surfaces of two printed circuit boards 8 to two surfaces of the aviation foam 2 through adhesives, and enabling electrodes to extend out of the inside after attachment;
customizing a clamp 1 for fixing one end of aviation foam 2, installing the clamp 1 on a manipulator, weaving the aviation foam 2 after adhesion by using an annular radial weaving machine, enabling carbon fibers 4 to wrap the aviation foam 2 through a guide ring 3 after weaving, and filling resin to form a carbon fiber composite material serving as a substrate to form a formed blade;
different from the traditional edge-mounted electrode, the embedded uniformly-distributed electrode is adopted, so that the traditional excitation mode of adjacent injection and adjacent measurement is inconvenient to use, a new snake-shaped excitation mode is adopted to determine the current injection and voltage measurement paths, the Electrical Impedance Tomography (EIT) is solved in the positive problem and the inverse problem, the differential image is used for reconstructing the real conductivity of the measured voltage values of two states, the damage condition and the damage position are further judged through the resistance distribution condition, and the nondestructive evaluation and the structural health monitoring of the blade are realized.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the technical solutions of the present invention have been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that the technical solutions described in the foregoing embodiments can be modified or some technical features can be replaced equally; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (5)
1. A composite material damage monitoring method based on embedded distributed electrodes comprises the following process steps:
1) The aviation foam (2) is used as a core material of a carbon fiber composite material member sandwich structure, and copper foils (5) with fixed sizes are uniformly attached to the aviation foam (2) at equal intervals to be used as electrodes;
2) -making a printed circuit board (8) with a customized pattern from a flexible substrate, attaching the printed circuit board (8) to the aerospace foam (2) using an adhesive such that the electrodes extend out;
3) Weaving on the aviation foam (2) attached with the printed circuit board (8) by using a radial weaving machine to enable the carbon fibers (4) to wrap the aviation foam (2), and filling resin to form a carbon fiber composite material member as a matrix;
4) And a snakelike excitation mode is adopted to carry out current injection and voltage measurement, the real resistance distribution condition is reconstructed by using electrical impedance tomography based on the measured voltage value, and then the damage condition and the damage position are judged, so that the nondestructive evaluation and the structural health monitoring of the carbon fiber composite material component are realized.
2. The method for monitoring damage to the composite material based on the embedded distributed electrode as claimed in claim 1, wherein: the step two is to use the flexible base material to manufacture the printed circuit board (8) with the customized graph: the flexible substrate is polyimide (6), a conductive pattern is chemically etched on the surface of the polyimide (6), the conductive pattern is rolled copper foil (7), the printed circuit board (8) is a single-layer circuit board, the single surface of the printed circuit board (8) is provided with the rolled copper foil (7), and the printed circuit board (8) is further provided with via holes which correspond to the copper foil (5) in a one-to-one mode.
3. The method for monitoring damage to the composite material based on the embedded distributed electrode as claimed in claim 2, wherein: said attaching of the printed circuit board (8) to the aeronautical foam (2) using an adhesive in step two, so that the electrodes extend: the back surfaces of the two printed circuit boards (8) are respectively attached to the two surfaces of the aviation foam (2) through adhesives, and after the attachment, the electrodes can extend out from the inside.
4. The method for monitoring damage to the composite material based on the embedded distributed electrode as claimed in claim 3, wherein: weaving on the aviation foam (2) attached with the printed circuit board (8) by using a radial weaving machine in the third step to enable the carbon fibers (4) to wrap the aviation foam (2), and filling resin to form a carbon fiber composite material member serving as a matrix: customizing a clamp (1) for fixing one end of the aviation foam (2), installing the clamp (1) on a mechanical arm, weaving the aviation foam (2) after the attachment is finished by using a radial weaving machine, enabling the carbon fibers (4) to wrap the aviation foam (2), and filling resin to form a matrix to form a carbon fiber composite material member.
5. The method for monitoring damage to the composite material based on the embedded distributed electrode as claimed in claim 4, wherein: the reconstructing of true resistance distribution using electrical impedance tomography based on measured voltage values in step four: through solving the positive problem and the inverse problem of electrical impedance tomography, the voltage values of two states measured by using differential imaging are used for reconstructing the real conductivity, and the damage condition and the damage position are judged according to the resistance distribution condition.
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