Device and method for testing interfacial bonding strength of composite repaired structure

Abstract

The present disclosure provides a test device, a test sample and a test method for testing the interfacial bonding strength of a composite material repair structure. The test device comprises: a pressure chamber comprising a shell having a window formed therein; a clamp arranged on the shell and configured to attach a test sample to be tested on the window; a gas pump in communication with the pressure chamber; and a camera having a lens facing the window, the camera being adapted to obtain deformation information of the test sample generated based on a change in air pressure of the pressure chamber, the deformation information being adapted to calculate a bulging volume, a strain energy and a debonding area of the test sample, and to calculate a fracture energy release rate of interfacial debonding of the test sample accordingly. The test process of the test device provided by the present disclosure is controllable and reproducible for interfacial delamination debonding between the patch layers. The test method proposed by the present disclosure can accurately obtain the interfacial bonding strength of the composite material repair structure.

Description

Technical Field

[0001] This disclosure relates to the field of composite material mechanics, and in particular to a testing device, specimen, and testing method for the interfacial bonding strength of composite material repair structures. Background Technology

[0002] Delamination failure is one of the most common forms of damage and processing defects in composite materials, and it is also the most common form of damage failure in composite material repair structural patches. Delamination failure mainly occurs because the interlayer bonding strength of multilayer composite structures is weaker than the in-plane strength, making them prone to interfacial debonding under alternating loads, external impacts, etc.

[0003] Due to the prevalence of delamination failure, the interfacial bonding strength between composite laminates and between the composite repair structure and the patch is a crucial indicator for composite structural design and strength design. Therefore, accurately characterizing the interfacial bonding strength of composite laminates under different manufacturing processes and material compositions, as well as the interfacial bonding strength between the patch and the substrate under different repair processes, has significant engineering value. Currently, there is no suitable testing device or method that can accurately measure the interfacial bonding strength between the patch and the substrate of a composite repair structure. Summary of the Invention

[0004] In view of the above problems, this disclosure provides a testing device, sample and testing method for the interfacial bonding strength of composite material repair structures.

[0005] According to a first aspect of this disclosure, a testing apparatus for the interfacial bond strength of composite material repair structures is provided, comprising:

[0006] A pressure chamber, including an outer shell, on which a window is provided;

[0007] A clamp is disposed on the housing and is configured to hold the sample to be tested against the window;

[0008] An air pump, connected to the pressure chamber; and

[0009] A camera with its lens facing the window is used to acquire deformation information of the sample based on the pressure change of the pressure chamber. The deformation information is used to calculate the bulging volume and debonding area of ​​the sample, and to calculate the fracture energy release rate of the sample interface debonding.

[0010] According to some embodiments of this disclosure, the camera is a multi-view camera.

[0011] According to some embodiments of this disclosure, the testing apparatus further includes:

[0012] A transmitter is disposed within the pressure chamber, and the transmitter is adapted to acquire the air pressure within the pressure chamber.

[0013] According to some embodiments of this disclosure, the fixture includes a flange ring adapted to engage with a sealing ring to securely fix the sample to the window.

[0014] According to a second aspect of this disclosure, a specimen for testing the interfacial bond strength of composite material repair structures is provided, suitable for the testing apparatus described above, the specimen comprising:

[0015] The main body is a multi-layer composite laminate structure with a through hole in the middle;

[0016] A patch is disposed on the upper surface of the body; and

[0017] An interface adhesive layer is disposed between the body and the patch, and the interface adhesive layer is suitable for bonding the patch to the upper surface of the body;

[0018] The patch is positioned opposite the window.

[0019] According to some embodiments of this disclosure, a groove is provided on the sample near the edge of the patch, so as to guide the sample to delaminate from the groove along the interlayer interface between the patch and the upper surface of the body after the deformation exceeds a preset degree;

[0020] The groove is located around the through hole, where at least one layer of structure is missing, while retaining at least 60% of the body thickness. The width of the groove ranges from 0.5 mm to 3 mm.

[0021] According to some embodiments of this disclosure, the body is provided with a through hole, and the through hole coincides with the center position of the window.

[0022] According to some embodiments of this disclosure, the non-repaired areas of the body and the upper surface of the patch are sprayed with random speckle patterns to facilitate the calculation of the three-dimensional displacement of the sample.

[0023] According to some embodiments of this disclosure, the sample is prepared by a method of co-curing perforated laminates and patches, a method of laminate patching, or a method of removal.

[0024] According to an embodiment of the third aspect of this disclosure, a method for testing the interfacial bonding strength of a composite material repair structure is provided, employing the testing apparatus described above. The testing method includes:

[0025] The sample to be tested is sealed and fixed to the window of the pressure chamber;

[0026] Turn on the air pump and gradually increase the air pressure in the pressure chamber to cause the sample to gradually delaminate and detach along the interlayer interface of the patch.

[0027] Obtain the deformation information of the sample and the pressure change information in the pressure chamber, and calculate the bulging volume of the sample at all times based on the deformation information;

[0028] The work done by the pressure is calculated based on the bulging volume and the pressure change information; the strain energy of the sample is calculated based on the deformation information and the material parameters of the sample; and the change in the debonding area of ​​the sample with the change of air pressure in the pressure chamber is calculated based on the deformation information.

[0029] The binding energy of the debonding interface is calculated using the strain energy and the work done by the pressure; and

[0030] The fracture energy release rate of interfacial debonding is calculated by using the change in debonding area and the binding energy.

[0031] According to some embodiments of this disclosure, obtaining the deformation information of the sample includes:

[0032] A first image set and a second image set of the upper surface of the sample are acquired in real time using a binocular camera;

[0033] The surface data of the upper surface of the sample are reconstructed using the first image set and the second image set; and

[0034] The full-field displacement of the upper surface of the specimen is obtained based on the surface data and the initial position data of the specimen.

[0035] According to some embodiments of this disclosure, calculating the bulge volume of the sample at all times based on the deformation information includes:

[0036]

[0037] Where V(t) represents the bulging volume, W represents the out-of-plane displacement, M and N represent the number of pixels selected to include all the bulging regions in both directions, i and j are pixel coordinates, Δx is the physical length corresponding to a pixel of a single displacement matrix in the x-direction, and Δy is the physical length corresponding to a pixel of a single displacement matrix in the y-direction.

[0038] According to some embodiments of this disclosure, calculating the strain energy of the specimen based on the deformation information and the material parameters of the specimen includes:

[0039] The surface strain is obtained by differential calculation of the full-field displacement of the sample, and the strain in different thickness directions of the sample surface is calculated by combining the plate deflection theory with the surface strain.

[0040] According to some embodiments of this disclosure, calculating the strain energy includes:

[0041] Calculating the strain on the surface of the specimen includes:

[0042]

[0043] in, This represents convolution calculation. This represents the gradient convolution kernel in the x-direction. This represents the gradient convolution kernel in the y-direction. Let represent the normal strain field along the x-direction on the upper surface at time t. This represents the normal strain field along the y-direction on the upper surface at time t. Let U(t) represent the shear strain field on the upper surface at time t, U(t) represent the displacement field along the x direction, V(t) represent the displacement field along the y direction, and W(t) represent the out-of-surface displacement field along the z direction.

[0044] Calculate the curvature at various points on the specimen, including:

[0045]

[0046] in, This represents the curvature along the x-direction calculated using the three-dimensional deformation field of the upper surface. This represents the curvature along the y-direction calculated using the three-dimensional deformation field of the upper surface. and This represents the torsional deformation gradient calculated using the three-dimensional deformation field of the upper surface;

[0047] The distribution of strain components within the specimen is calculated based on the specimen thickness, including:

[0048]

[0049] Where η represents the thickness of the sample surface downwards, and ε x (t, η) represents the normal strain field along the x-direction at each thickness coordinate η calculated from surface deformation and curvature at time t, ε y (t, η) represents the normal strain field along the y-direction at each thickness coordinate η calculated from surface deformation and curvature at time t, γ x (t, η) represents the shear strain field at each thickness coordinate η calculated by surface deformation and curvature at time t;

[0050] Calculate the overall strain energy of the specimen, including:

[0051]

[0052] Where, ε(t)=[ε x(t,i,j,η),ε y (t,i,j,η),γ xy (t,i,j,η)] T Let C(η) represent the strain vector, and let C(η) represent the elastic stress-strain stiffness matrix in the single-layer plate model.

[0053] According to some embodiments of this disclosure, the convolution kernel size for the convolution calculation is 3, including:

[0054]

[0055] Where Δx is the physical length corresponding to a pixel of a single displacement matrix in the x-direction, and Δy is the physical length corresponding to a pixel of a single displacement matrix in the y-direction.

[0056] According to some embodiments of this disclosure, the calculation of pressure work based on the bulge volume and the pressure change information includes:

[0057]

[0058] Where Q(t) represents the work done by pressure, p i Let N(t) represent the pressure at the i-th recording time, and let N(t) represent all recording times up to time t. i This represents the bulge volume at the i-th recording time.

[0059] According to some embodiments of this disclosure, calculating the change in the debonding area of ​​the sample based on the deformation information as the air pressure inside the pressure chamber changes includes:

[0060]

[0061] Where A(t) represents the change in debonding area, and ε0 represents the calculation accuracy of the algorithm for calculating the out-of-plane displacement W.

[0062] According to some embodiments of this disclosure, the calculation of the bonding energy of the debonding interface using the strain energy and the work done by the pressure includes:

[0063] Π(t)=Q(t)-E(t) (9)

[0064] Where Q(t) represents the work done by pressure, and E(t) is the strain energy of the entire sample.

[0065] According to some embodiments of this disclosure, the calculation of the fracture energy release rate of interfacial debonding using the change in debonding area and the binding energy includes:

[0066] The change in debonding area is used as the independent variable, and the binding energy is used as the dependent variable. A straight line segment is obtained by fitting the data using the least squares method. The slope of the straight line segment is used as the fracture energy release rate of the interface debonding.

[0067] According to some embodiments of this disclosure, after the air pump is turned on, the sample debonds from the groove along the interlayer interface between the patch and the upper surface of the body.

[0068] According to the testing device, sample and testing method for the interfacial bonding strength of composite material repair structures provided in this disclosure, the sample is uniformly and controllably pressurized using a pressure chamber and an air pump, and the deformation information of the sample is acquired using a camera. The bulging volume of the sample can be calculated using the deformation information, so as to obtain the fracture energy release rate of the sample interface debonding by calculation. Attached Figure Description

[0069] The foregoing contents, as well as other objects, features, and advantages of this disclosure, will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0070] Figure 1 This schematic diagram illustrates the structure of a testing apparatus for the interfacial bonding strength of composite material repair structures according to an embodiment of the present disclosure;

[0071] Figure 2 A schematic diagram of the structure of a sample according to an embodiment of the present disclosure is shown.

[0072] Figure 3 A flowchart illustrating a method for testing the interfacial bond strength of a composite material repair structure according to an embodiment of the present disclosure is shown schematically.

[0073] Figure 4 A flowchart illustrating the process of obtaining deformation information of a specimen in a test method according to an embodiment of the present disclosure is shown schematically.

[0074] Figure 5 A flowchart illustrating the calculation of strain energy of a specimen in a test method according to an embodiment of the present disclosure is shown.

[0075] The meanings of the reference numerals in the above figures are as follows:

[0076] 1-Outer shell;

[0077] 101 - Window;

[0078] 2-Clamp;

[0079] 3-Sample;

[0080] 301-Ontology;

[0081] 302 - Interface adhesive layer;

[0082] 303 - Patch;

[0083] 304 - Grooved;

[0084] 4-Air pump;

[0085] 5-Camera;

[0086] 6-Transmitter; and

[0087] 7-Sealing ring. Detailed Implementation

[0088] The embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0089] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0090] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0091] When using expressions such as "at least one of A, B, and C", they should generally be interpreted in accordance with the meaning that is commonly understood by a person skilled in the art (e.g., "a system having at least one of A, B, and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B, and C, etc.).

[0092] In the technical solutions disclosed herein, the collection, storage, use, processing, transmission, provision, disclosure, and application of data (including but not limited to user personal information) comply with the provisions of relevant laws and regulations, necessary confidentiality measures have been taken, and they do not violate public order and good morals.

[0093] The embodiments of this disclosure provide a testing device, sample, and testing method for the interfacial bonding strength of composite material repair structures. In these embodiments, a pressure chamber and an air pump are used to uniformly and controllably pressurize the sample. A camera is used to acquire the deformation information of the sample. The bulging volume of the sample can be calculated from the deformation information. The strain energy and pressure work of the sample are calculated based on the bulging volume and pressure change. The change in the debonding area of ​​the sample with pressure change is calculated based on the deformation information. The bonding energy of the debonding interface is calculated using the strain energy and pressure work. Finally, the fracture energy release rate of the interface debonding is calculated using the change in debonding area and bonding energy. The debonding of the interlayer interface of the sample patch is controllable and reproducible, and the interfacial bonding strength of the composite material repair structure can be accurately obtained.

[0094] Figure 1 The schematic diagram illustrates a structural schematic of a test apparatus for testing the interfacial bond strength of composite material repair structures according to an embodiment of the present disclosure.

[0095] According to the first aspect of this disclosure, such as Figure 1 As shown, a testing device for the interfacial bonding strength of composite material repair structures is provided, including a pressure chamber, a clamp 2, an air pump 4, and a camera 5.

[0096] According to some embodiments of this disclosure, the pressure chamber includes an outer shell 1, on which a window 101 is provided.

[0097] In this embodiment, the pressure chamber is a relatively sealed container, wherein the size of the window 101 matches the shape and size of the sample 3 to facilitate the sealed fixation of the sample 3 to the window 101. The pressure chamber is connected to the air pump 4, which changes the gas pressure inside the pressure chamber. As the gas pressure inside the pressure chamber increases, the area on the sample 3 opposite to the window 101 bulges upward under the action of gas pressure. As the gas pressure inside the pressure chamber continues to rise until it exceeds a critical value, the adhesive area between the patch and the main body in the repair area of ​​the sample 3 gradually tears and detaches. The bonding strength of the structure in the repair area of ​​the sample 3 is calculated based on the degree of upward bulging of the sample 3.

[0098] According to some embodiments of this disclosure, a clamp 2 is disposed on the housing 1 and the clamp 2 is configured to attach the sample 3 to be tested to the window 101.

[0099] According to some embodiments of this disclosure, the clamp 2 includes a flange ring, which is adapted to cooperate with the sealing ring 7 to seal the sample 3 onto the window 101. Specifically, the outer shell 1 has a plurality of threaded holes on the periphery of the window 101, and the sample 3 has through holes corresponding to the threaded holes. The flange ring uses a screw to engage with the threaded holes to hold the sample 3 against the outer shell 1.

[0100] According to some alternative embodiments of this disclosure, a wing plate is provided on the periphery of the outer shell 1, and a through hole matching the sample 3 is provided on the wing plate. The flange ring uses bolts to engage the threaded hole to press the sample 3 against the outer shell 1.

[0101] According to some embodiments of this disclosure, the lens of camera 5 is directed toward window 101. Camera 5 is adapted to acquire deformation information of sample 3 based on the pressure change of the pressure chamber. The deformation information is adapted to calculate the bulging volume, strain energy and debonding area of ​​sample 3, and to calculate the fracture energy release rate of debonding at the interface of sample 3.

[0102] According to some embodiments of this disclosure, camera 5 is a multi-view camera. Further optionally, there are two cameras 5, which are arranged side by side in the area above window 101. Alternatively, the two cameras 5 are symmetrically arranged on both sides directly above window 101, with the lenses of the two cameras 5 facing at an angle to the central axis of window 101, so as to aim at the area of ​​window 101 from two different directions.

[0103] According to some embodiments of this disclosure, the testing apparatus further includes a transmitter 6 disposed inside the pressure chamber, the transmitter 6 being adapted to acquire the air pressure inside the pressure chamber.

[0104] Figure 2 A schematic diagram of the structure of a sample according to an embodiment of the present disclosure is shown.

[0105] According to a second aspect of this disclosure, a specimen for testing the interfacial bond strength of composite material repair structures is provided, suitable for the testing apparatus described above, such as... Figure 1 and Figure 2 As shown, the sample includes a body 301, an interface adhesive layer 302, and a patch 303.

[0106] According to some embodiments of this disclosure, the body 301 is a multi-layer composite structure, and the body 301 has a patching and repair area.

[0107] According to some embodiments of this disclosure, patch 303 is disposed on the upper surface of the body in the repair area.

[0108] According to some embodiments of this disclosure, an interface adhesive layer 302 is disposed between the upper surface of the body 301 and the patch 303, and the interface adhesive layer 302 is suitable for bonding the patch 303 to the body 301; wherein, the patch 303 is disposed opposite to the window 101.

[0109] According to some embodiments of this disclosure, a groove 304 is formed on the sample 3 near the edge of the patch 303 to guide the sample 3 to delaminate along the interlayer interface between the patch 303 and the body after the deformation exceeds a preset degree; wherein, the groove 304 lacks at least one layer of structure around the through hole and retains at least 60% of the body thickness of the structure, and the width of the groove 304 includes 0.5mm to 3mm. Optionally, a width of 1mm for the groove 304 is preferred.

[0110] According to some embodiments of this disclosure, a through hole is provided on the body, and the through hole coincides with the center position of the window 101. Optionally, the through hole is to simulate the hole that appears when the composite material is worn in reality. Furthermore, in actual repair, in order to better bond the patch to the body, it is usually necessary to trim the area of ​​the hole. In order to improve its strength, the excess and irregular parts are usually trimmed to form a flat and smooth circular hole.

[0111] According to some embodiments of this disclosure, random speckle patterns are sprayed onto the non-repaired areas of the body 301 and the upper surface of the patch 303 to facilitate the calculation of the three-dimensional displacement of the sample 3. Further, a first image set and a second image set of the sample's upper surface are obtained from two angles using a binocular camera in conjunction with the random speckle pattern. The surface data of the sample's upper surface is reconstructed from the first and second image sets. Based on the surface data and the initial position data of the sample, the full-field displacement of the sample's upper surface is obtained, that is, the three-dimensional displacement of the sample 3 is obtained.

[0112] According to some embodiments of this disclosure, sample 3 is prepared by a method of co-curing perforated laminate and patch, a laminate patching method, or a removal method.

[0113] According to some optional embodiments of this disclosure, the process of preparing sample 3 by co-curing perforated laminate and patch includes: during composite material layup, a prepreg or single-layer plate with holes of the same size removed from layer m, ensuring that the holes overlap in each layer, is stacked together with a complete composite prepreg or single-layer plate from layer n, where m and n are both integers greater than 0. The complete composite prepreg (patch) from layer n is located on top, and the perforated single-layer plate (body) from layer m is located on the bottom. The holes in layer m are filled with polytetrafluoroethylene (PTFE) pads of the same thickness as the stacked single-layer plates from layer m. The entire structure is then placed in a hot press for hot pressing and curing. After curing, a small groove is cut along the inner edge of the hole at the position of layer m to form an initial crack. Finally, a sample matching the size of the clamping flange is cut from the plate-shaped specimen, ensuring that the circular hole is located in the center of the cut sample as much as possible, and holes are drilled at the corresponding positions for screw fastening.

[0114] According to some alternative embodiments of this disclosure, the preparation process of sample 3 by the laminate repair method includes: drilling a hole in the center of the laminate specimen formed by curing m layers of single-layer laminate, cleaning the drilling debris and interface; laying n layers of prepreg at a certain angle above the original m-layer laminate cutout position, filling the lower part of the cutout with polytetrafluoroethylene pads to prevent collapse, placing the patched single-layer laminate in a heat repair instrument to complete the curing; lightly grinding the surface and drilling holes in the corresponding positions for screw fastening.

[0115] According to some alternative embodiments of this disclosure, the process of preparing sample 3 by the excavation method includes: for a complete multilayer composite material plate with m+n layers, m layers of the main body are removed by mechanical drilling, while the remaining n layers of the patch are kept intact. After cleaning up the processing debris, a groove is cut along the inner edge of the hole at the position of the mth layer of the whole to form an initial crack; a sample matching the size of the fixture (flange) is cut from the plate-shaped specimen, ensuring that the round hole is located in the center of the cut sample as much as possible, and holes are drilled in the corresponding positions for screw fastening.

[0116] Figure 3 A flowchart illustrating a method for testing the interfacial bond strength of a composite material repair structure according to an embodiment of the present disclosure is shown.

[0117] According to an embodiment of the third aspect of this disclosure, a method for testing the interfacial bond strength of a composite material repair structure is provided, employing the testing apparatus described above. Figure 3 As shown, the test method includes operations S310 to S360.

[0118] According to some embodiments of this disclosure, operation S310 includes: sealing the sample to be tested onto the window of the pressure chamber.

[0119] According to some embodiments of this disclosure, operation S320 includes: turning on the air pump and gradually increasing the air pressure in the pressure chamber to cause the sample to gradually delaminate and detach along the interlayer interface of the patch.

[0120] According to some embodiments of this disclosure, operation S330 includes: acquiring deformation information of the sample and pressure change information in the pressure chamber, and calculating the bulging volume of the sample at all times based on the deformation information.

[0121] According to some embodiments of this disclosure, operation S340 includes: calculating the work done by pressure based on the bulging volume and pressure change information, calculating the strain energy of the sample based on the deformation information and the material parameters of the sample, and calculating the change in the debonding area of ​​the sample as the air pressure in the pressure chamber changes based on the deformation information.

[0122] According to some embodiments of this disclosure, operation S350 includes: calculating the binding energy of the debonding interface using strain energy and pressure work.

[0123] According to some embodiments of this disclosure, operation S360 includes: calculating the fracture energy release rate of interfacial debonding using the change in debonding area and binding energy.

[0124] Figure 4 A flowchart illustrating the process of obtaining deformation information of a specimen in a test method according to an embodiment of the present disclosure is shown.

[0125] According to some embodiments of this disclosure, in operation S330, such as Figure 4 As shown, obtaining the deformation information of the sample includes sub-operations S331 to S333.

[0126] According to some embodiments of this disclosure, sub-operation S331 includes: acquiring a first image set and a second image set of the upper surface of the sample in real time using a binocular camera.

[0127] According to some embodiments of this disclosure, sub-operation S332 includes: reconstructing surface data of the upper surface of the sample using a first image set and a second image set.

[0128] According to some embodiments of this disclosure, sub-operation S333 includes: obtaining the full-field displacement of the upper surface of the specimen based on the surface data and the initial position data of the specimen.

[0129] According to some embodiments of this disclosure, calculating the bulge volume of the specimen at all times based on deformation information includes:

[0130]

[0131] Where V(t) represents the bulge volume, W represents the out-of-plane displacement, M and N represent the number of pixels selected to include all bulging regions in both directions, i and j are pixel coordinates, Δx is the physical length of a pixel corresponding to a single displacement matrix in the x-direction, and Δy is the physical length of a pixel corresponding to a single displacement matrix in the y-direction.

[0132] According to some optional embodiments of this disclosure, displacement testing of the sample surface is performed using random speckle sprayed onto the sample surface in conjunction with a binocular camera. After detection is initiated, the two cameras synchronously record images of the experimental process. The frame rate is adjusted according to the experimental loading speed, with each camera recording no less than 20 frames throughout the loading process. The pressure p(t) of the transmitter is recorded, and the pressure of the air pump is gradually increased, causing the sample under test to gradually delaminate and debond along the interlayer interface from the pre-fabricated initial crack. All data recorded by the sensors need to be time-aligned to ensure that the pressure p(t) is consistent with the data recorded by the sensors. i The full-field displacement U(t) obtained by calculating images from the left and right cameras. i ), V(t) i ) and W(t i A set of recorded data consisting of )) comes from the same time ti .

[0133] According to some embodiments of this disclosure, calculating the strain energy of a specimen based on deformation information and the material parameters of the specimen includes: performing differential calculations on the full-field displacement of the specimen to obtain the surface strain, and using plate deflection theory in combination with surface strain to calculate the strain in different thickness directions of the specimen surface.

[0134] Figure 5 A flowchart illustrating the calculation of strain energy of a specimen in a test method according to an embodiment of the present disclosure is shown.

[0135] According to some embodiments of this disclosure, in operation S340, such as Figure 5 As shown, the calculation of the strain energy of the specimen includes sub-operations S341 to S344.

[0136] According to some embodiments of this disclosure, sub-operation S341 includes: calculating the strain on the sample surface, including:

[0137]

[0138] in, This represents convolution calculation. This represents the gradient convolution kernel in the x-direction. This represents the gradient convolution kernel in the y-direction. Let represent the normal strain field along the x-direction on the upper surface at time t. This represents the normal strain field along the y-direction on the upper surface at time t. Let U(t) represent the shear strain field on the upper surface at time t, U(t) represent the displacement field along the x-direction, V(t) represent the displacement field along the y-direction, and W(t) represent the out-of-surface displacement field along the z-direction.

[0139] According to some embodiments of this disclosure, sub-operation S342 includes: calculating the curvature at various points on the specimen, including:

[0140]

[0141] in, This represents the curvature along the x-direction calculated using the three-dimensional deformation field of the upper surface. This represents the curvature along the y-direction calculated using the three-dimensional deformation field of the upper surface. and This represents the torsional deformation gradient calculated using the three-dimensional deformation field of the upper surface.

[0142] According to some embodiments of this disclosure, sub-operation S343 includes: calculating the distribution of each strain component within the specimen based on the specimen thickness, including:

[0143]

[0144] Where η represents the thickness of the sample surface downwards, and ε x (t, η) represents the normal strain field along the x-direction at each thickness coordinate η calculated from surface deformation and curvature at time t, ε y (t, η) represents the normal strain field along the y-direction at each thickness coordinate η calculated from surface deformation and curvature at time t, γ x (t, η) represents the shear strain field at each thickness coordinate η calculated from surface deformation and curvature at time t.

[0145] According to some embodiments of this disclosure, sub-operation S344 includes: calculating the strain energy of the entire specimen, including:

[0146]

[0147] Where, ε(t)=[ε x (t,i,j,η),ε y (t,i,j,η),γ xy (t,i,j,η)] T Let C(η) represent the strain vector, and let C(η) represent the elastic stress-strain stiffness matrix in the single-layer plate model.

[0148] According to some optional embodiments of this disclosure, the convolution kernel size for convolution computation is 3, including:

[0149]

[0150] Where Δx is the physical length corresponding to a pixel of a single displacement matrix in the x-direction, and Δy is the physical length corresponding to a pixel of a single displacement matrix in the y-direction.

[0151] According to some embodiments of this disclosure, calculating the work done by pressure based on information about the bulge volume and pressure change includes:

[0152]

[0153] Where Q(t) represents the work done by pressure, p i Let N(t) represent the pressure at the i-th recording time, and let N(t) represent all recording times up to time t. i This represents the bulge volume at the i-th recording time.

[0154] According to some embodiments of this disclosure, calculating the change in the debonding area of ​​the sample based on deformation information as the air pressure inside the pressure chamber changes includes:

[0155]

[0156] Where A(t) represents the change in debonding area, and ε0 represents the calculation accuracy of the algorithm for calculating the out-of-plane displacement W.

[0157] According to some embodiments of this disclosure, calculating the bonding energy of the debonding interface using strain energy and pressure work includes:

[0158] Π(t)=Q(t)-E(t))(9)

[0159] Where Q(t) represents the work done by pressure, and E(t) is the strain energy of the entire sample.

[0160] According to some embodiments of this disclosure, the fracture energy release rate of interfacial debonding is calculated by using the change in debonding area and binding energy. This includes using the change in debonding area as the independent variable and the binding energy as the dependent variable, fitting the data using the least squares method to obtain a straight line segment, and outputting the slope of the straight line segment as the fracture energy release rate of interfacial debonding.

[0161] According to some embodiments of this disclosure, after the air pump is turned on, the sample delaminates from the groove along the interlayer interface between the patch and the body.

[0162] According to some embodiments of this disclosure, the operation also includes: checking the airtightness of the pressure chamber, specifically, turning on the air pump to preload the pressure for a preset duration, and observing the pressure changes inside the pressure chamber through a transmitter.

[0163] Those skilled in the art will understand that the features described in the various embodiments and / or claims of this disclosure can be combined or combined in various ways, even if such combinations or combinations are not explicitly described in this disclosure. In particular, the features described in the various embodiments and / or claims of this disclosure can be combined or combined in various ways without departing from the spirit and teachings of this disclosure. All such combinations and / or combinations fall within the scope of this disclosure.

[0164] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. The scope of this disclosure is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. A testing device for the interfacial bonding strength of composite material repair structures, characterized in that, include: A pressure chamber, including an outer shell, on which a window is provided; A clamp is disposed on the housing and configured to attach a test specimen to the window; wherein the test specimen includes a body and a patch bonded thereto by an interfacial adhesive layer, and the body has a slot for guiding the interfacial delamination and debonding, and the patch faces the window. An air pump, connected to the pressure chamber; and A camera with its lens facing the window is used to acquire deformation information of the specimen based on the pressure change of the pressure chamber. The deformation information is used to calculate the bulging volume, strain energy and debonding area of ​​the specimen, and to calculate the fracture energy release rate of the debonding at the specimen interface.

2. The testing apparatus according to claim 1, characterized in that, The camera is a multi-view camera.

3. The testing apparatus according to claim 1, characterized in that, Also includes: A transmitter is disposed within the pressure chamber, and the transmitter is adapted to acquire the air pressure within the pressure chamber.

4. The testing apparatus according to claim 1, characterized in that, The fixture includes a flange ring, which is adapted to engage with a sealing ring to securely fix the sample to the window.

5. A specimen for testing the interfacial bonding strength of composite material repair structures, characterized in that, Suitable for the testing apparatus as described in any one of claims 1 to 4, the sample comprises: The main body is a multi-layer composite laminate structure with a through hole in the middle; A patch is disposed on the upper surface of the body; and An interface adhesive layer is disposed between the body and the patch, and the interface adhesive layer is suitable for bonding the patch to the upper surface of the body; The patch is positioned opposite to the window; The sample body has a groove near the edge of the patch to guide the sample to delaminate from the groove along the interlayer interface between the patch and the upper surface of the body after the deformation exceeds a preset degree.

6. The sample according to claim 5, characterized in that, The slot is located around the through hole, with at least one layer of structure missing, while retaining at least 60% of the body thickness. The width of the slot ranges from 0.5mm to 3mm.

7. The sample according to claim 5, characterized in that, The main body is provided with a through hole, which coincides with the center position of the window.

8. The sample according to claim 5, characterized in that, The non-repaired areas of the body and the upper surface of the patch are sprayed with random speckle patterns to facilitate the calculation of the three-dimensional displacement of the sample.

9. The sample according to claim 5, characterized in that, The sample was prepared by a method of co-curing perforated laminate and patch, a method of laminate patching, or a method of excavation.

10. A method for testing the interfacial bonding strength of composite material repair structures, characterized in that, The testing method using the testing apparatus as described in any one of claims 1 to 4 includes: The sample to be tested is sealed and fixed to the window of the pressure chamber; Turn on the air pump and gradually increase the air pressure in the pressure chamber to cause the sample to gradually delaminate and detach along the interlayer interface of the patch. Obtain the deformation information of the sample and the pressure change information in the pressure chamber, and calculate the bulging volume of the sample at all times based on the deformation information; The work done by the pressure is calculated based on the bulging volume and the pressure change information; the strain energy of the sample is calculated based on the deformation information and the material parameters of the sample; and the change in the debonding area of ​​the sample is calculated based on the deformation information. The binding energy of the debonding interface is calculated using the strain energy and the work done by the pressure; and The fracture energy release rate of interfacial debonding is calculated by using the change in debonding area and the binding energy.

11. The test method according to claim 10, characterized in that, The process of obtaining the deformation information of the sample includes: A first image set and a second image set of the upper surface of the sample are acquired in real time using a binocular camera; The surface data of the upper surface of the sample are reconstructed using the first image set and the second image set; and The full-field displacement of the upper surface of the specimen is obtained based on the surface data and the initial position data of the specimen.

12. The test method according to claim 11, characterized in that, The calculation of the bulge volume of the sample at all times based on the deformation information includes: （1） Where V(t) represents the bulging volume, W(t, i, j) represents the out-of-plane displacement of the pixel parameter position (i,j) in the z-direction at sampling time t, M and N represent the number of pixels selected that can encompass all bulging regions in both directions, and i and j are pixel coordinates. It is the physical length corresponding to a single pixel of a displacement matrix in the x-direction. It is the physical length corresponding to a pixel of a single displacement matrix in the y-direction.

13. The test method according to claim 11, characterized in that, The calculation of the strain energy of the specimen based on the deformation information and the material parameters of the specimen includes: The surface strain is obtained by differential calculation of the full-field displacement of the sample, and the strain in different thickness directions of the sample surface is calculated by combining the plate deflection theory with the surface strain.

14. The test method according to claim 13, characterized in that, The calculation of strain energy includes: Calculating the strain on the surface of the specimen includes: （2） Where  represents convolution calculation, This represents the gradient convolution kernel in the x-direction. This represents the gradient convolution kernel in the y-direction. Let represent the normal strain field along the x-direction on the upper surface at time t. This represents the normal strain field along the y-direction on the upper surface at time t. Let U(t) represent the shear strain field on the upper surface at time t, U(t) represent the displacement field along the x direction, V(t) represent the displacement field along the y direction, and W(t) represent the out-of-surface displacement field along the z direction. Calculate the curvature at various points on the specimen, including: （3） in, This represents the curvature along the x-direction calculated using the three-dimensional deformation field of the upper surface. This represents the curvature along the y-direction calculated using the three-dimensional deformation field of the upper surface. and This represents the torsional deformation gradient calculated using the three-dimensional deformation field of the upper surface; The distribution of strain components within the specimen is calculated based on the specimen thickness, including: （4） Where η represents the thickness of the sample surface from the top downwards. This represents the normal strain field along the x-direction at each thickness coordinate η calculated from surface deformation and curvature at time t. This represents the normal strain field along the y-direction at each thickness coordinate η calculated from surface deformation and curvature at time t. This represents the shear strain field at each thickness coordinate η calculated using surface deformation and curvature at time t; Calculate the overall strain energy of the specimen, including: （5） Where E(t) represents the strain energy of the entire sample at time t. This represents the strain vector at time t. and These represent the pixel parameter positions at sampling time t. ,thickness At this point, the normal strain in the x-direction and the normal strain in the y-direction, This indicates the pixel parameter position at sampling time t. ,thickness Shear strain at the point, It is the strain vector transpose, Let h(i, j) represent the elastic stress-strain stiffness matrix in the single-layer plate model, and h(i, j) represent the total plate thickness at position (i, j).

15. The test method according to claim 12, characterized in that, The convolution kernel size for the convolution calculation is 3, including: （6） in, It is the physical length corresponding to a single pixel of a displacement matrix in the x-direction. It is the physical length corresponding to a pixel of a single displacement matrix in the y-direction.

16. The test method according to claim 12, characterized in that, The calculation of pressure work based on the bulge volume and the pressure change information includes: （7） Where Q(t) represents the work done by pressure, Let N(t) represent the pressure at the i-th recording time, and let N(t) represent all recording times up to time t. i This represents the bulge volume at the i-th recording time.

17. The test method according to claim 12, characterized in that, The calculation of the change in the debonding area of ​​the sample based on the deformation information as the air pressure inside the pressure chamber changes includes: （8） Where A(t) represents the change in debonding area, The calculation accuracy of the out-of-plane displacement W is indicated by W(t, i, j), which represents the out-of-plane displacement of the pixel parameter position (i, j) in the z direction at the sampling time of frame t.

18. The test method according to claim 10, characterized in that, The calculation of the bonding energy of the debonding interface using the strain energy and the work done by the pressure includes: （9） Where ∏(t) represents the interfacial bonding energy, Q(t) represents the work done by pressure, and E(t) is the strain energy of the entire sample.

19. The test method according to claim 18, characterized in that, The calculation of the fracture energy release rate of interfacial debonding using the change in debonding area and the binding energy includes: The change in debonding area is used as the independent variable, and the binding energy is used as the dependent variable. A straight line segment is obtained by fitting the data using the least squares method. The slope of the straight line segment is used as the fracture energy release rate of the interface debonding.

20. The test method according to claim 10, characterized in that, After the air pump is turned on, the sample debonds from the groove along the interlayer interface between the patch and the body in layers.

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