Composite material impact damage thermal uncovering characterization method

Abstract

The invention discloses a composite material impact damage thermal uncovering characterization method, which comprises the following steps of: leaving traces of impact damage defects on a composite material by dyeing a trace reserving solution, layering the composite material, marking each layer of defect trace, and arranging multiple layers of trace defects according to the sequence of a composite material sample, the method has the advantages of simple operation process, no need of expensive equipment, accurate recording of the damage, realization of low-cost improvement of the recognition precision, efficiency and reliability of the impact damage of the composite material, and provision of reference for the design and service safety of the composite material.

Description

Technical Field

[0001] The present invention relates to the technical field of composite material damage characterization, and particularly relates to a method for characterizing the thermal delamination of composite material impact damage. Background Art

[0002] Due to its excellent properties such as high specific strength and high specific stiffness, composite materials are widely used in the fields of aerospace, transportation, etc. However, the unique laminated structure of composite materials also results in weak impact resistance and complex impact damage modes. During the manufacturing, transportation, use, and maintenance of composite materials, they are inevitably subjected to low-velocity impacts, such as impacts by foreign objects like tool drops, assembly collisions, gravel, and hail, resulting in internal damage such as matrix cracking, fiber fracture, and delamination. Such damage is often difficult to detect on the surface, but it will significantly reduce the compressive strength and fatigue life of the structure, seriously threatening structural safety, and is known as "the most dangerous defect of composite materials". For example, the impact damage of an aircraft skin may evolve into cracks under aerodynamic loads and lead to structural disintegration, while the delamination defect of a wind turbine blade may accelerate fracture during fatigue cycles, causing significant economic losses and even casualties. Therefore, the research on the characterization of composite material impact damage has important reference significance for the design, maintenance, and service life of composite materials, and is one of the key research fields of composite materials at present.

[0003] Current damage detection techniques, such as ultrasonic C-scanning, X-ray, etc., although they can effectively identify impact damage, have disadvantages such as expensive equipment, complex operation procedures, and low signal-to-noise ratio of the results. Moreover, the setting of the scanning threshold of these detection methods mostly relies on manual experience judgment, and the results have large errors caused by human subjective consciousness, making it difficult to achieve accurate and unified evaluation of damage. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for characterizing the thermal delamination of composite material impact damage to solve one or more technical problems existing in the prior art, and at least provide a beneficial choice or create conditions.

[0005] The technical solution adopted to solve the above technical problems, a method for characterizing the thermal delamination of composite material impact damage, includes: Select a composite material specimen to be tested; Perform impact drilling on the surface of the composite material specimen to be tested to obtain a composite material specimen with a through hole; Seal one end of the through hole to form a pit on the surface of the composite material specimen; Drop a dyeing and marking solution into the pit and let it stand for a first preset time; After standing, suck out the dyeing and marking solution in the pit; Pyrolyze the composite material sample according to the preset pyrolysis temperature and preset pyrolysis time; Layer the pyrolyzed composite material sample to obtain multiple composite layers; Replicate the defect traces of the dyeing trace solution near the through holes in each layer of the composite layer onto the replication layer to obtain multiple composite layers; Stack the multiple replication layers together in the arrangement order of the composite material sample to obtain an impact damage map.

[0006] The beneficial effects of the present invention are: The present invention uses a dyeing trace solution to leave traces of impact damage defects on the composite material, then layers the composite material and marks the defect traces of each layer, and then arranges the multiple trace defects in the order of the composite material sample to form a complete impact damage map of the composite material. The operation process is simple, no expensive equipment is required, the damage can be recorded more accurately, the recognition accuracy, efficiency and reliability of the impact damage of the composite material are improved at low cost, and it provides a reference for the design and service safety of the composite material.

[0007] As a further improvement of the above technical solution, impact drilling is performed on the surface of the composite material sample to be tested to obtain a composite material sample with through holes, including: When performing impact drilling, the diameter of the drill bit selected is 1 / 5 to 1 / 4 of the diameter of the impact contact surface of the composite material sample to be tested.

[0008] As a further improvement of the above technical solution, one end of the through hole is blocked to form a pit on the surface of the composite material sample, including: After cleaning the dust, oil stain and dust of the composite material sample with pure water, alcohol and pure water in sequence, dry the composite material sample according to the set temperature and set time and then block it.

[0009] As a further improvement of the above technical solution, pyrolyzing the composite material sample according to the preset pyrolysis process includes: Select the same material as the composite material sample as the test material, pyrolyze the test material, and when the pyrolysis temperature and pyrolysis time make the surface of the test material not loose, not filamentous, each single layer remain intact, and each single layer can be well separated after slightly bending the test material, select the pyrolysis temperature of this pyrolysis as the preset pyrolysis temperature, and select the pyrolysis time of this pyrolysis as the preset pyrolysis time.

[0010] As a further improvement of the above technical solution, dropping the dyeing trace solution into the pit and standing for the first preset time includes: If the surface of the composite material sample is contaminated by the dyeing trace solution, the surface of the composite material sample should be wiped clean with acetone immediately.

[0011] As a further improvement of the above technical solution, the pyrolyzed composite material sample is stratified to obtain multiple composite layers, including: When stratifying the pyrolyzed composite material sample, label paper is attached to each composite layer to mark the corresponding layer number and the direction of the composite layer.

[0012] As a further improvement of the above technical solution, the defect traces of the dyeing and marking solution near the through holes in each composite layer are replicated onto a replication layer to obtain multiple composite layers, including: Trace the outline of the defect traces of the composite layer with a pen and then replicate.

[0013] As a further improvement of the above technical solution, the defect traces of the dyeing and marking solution near the through holes in each composite layer are replicated onto a replication layer to obtain multiple composite layers, including: Replicate by taking photos.

[0014] As a further improvement of the above technical solution, the multiple replication layers are stacked together in the arrangement order of the composite material sample to obtain an impact damage map, including: An impact damage map is obtained through processing with drawing and image editing software.

[0015] As a further improvement of the above technical solution, dropping a dyeing and marking solution into the pit and standing for a first preset time, including: The dyeing and marking solution uses a solution of chloroauric acid tetrahydrate. Description of the Drawings

[0016] The following further describes the present invention in conjunction with the drawings and embodiments; Figure 1 is a flowchart of a method for characterizing impact damage of a composite material by thermal delamination; Figure 2 is a diagram of using a pencil to trace the damage contour in a method for characterizing impact damage of a composite material by thermal delamination; Figure 3 is a diagram of the reconstructed complete laminated plate impact damage in a method for characterizing impact damage of a composite material by thermal delamination. Detailed Embodiments

[0017] This part will describe in detail the specific embodiments of the present invention. The preferred embodiments of the present invention are shown in the drawings. The role of the drawings is to supplement the description in the text part of the specification, enabling people to intuitively and vividly understand each technical feature and the overall technical solution of the present invention, but it should not be construed as a limitation on the protection scope of the present invention.

[0018] In the description of the present invention, it should be understood that for the orientation description, such as the orientation or positional relationship indicated by up, down, front, back, left, right, etc., it is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention.

[0019] In the description of the present invention, if there are descriptions with words such as "several", its meaning is one or more, and the meaning of multiple is more than two. Understandings such as greater than, less than, exceeding, etc. do not include the original number, and understandings such as above, below, within, etc. include the original number.

[0020] In the description of the present invention, unless otherwise clearly defined, words such as setting, installation, connection, etc. should be understood in a broad sense. Those skilled in the art can reasonably determine the specific meanings of the above words in the present invention in combination with the specific content of the technical solution.

[0021] Referring to Figures 1 to 3 , the following embodiments are made for a method for characterizing the thermal delamination of impact damage of a composite material of the present invention: A method for characterizing the thermal delamination of impact damage of a composite material, comprising: Step S100: Select a composite material specimen to be tested; Step S200: Perform impact drilling on the surface of the composite material specimen to be tested to obtain a composite material specimen with a through hole; Step S300: Block one end of the through hole to form a pit on the surface of the composite material specimen; Step S400: Drop a dyeing and marking solution into the pit and let it stand for a first preset time; Step S500: After standing, suck out the dyeing and marking solution in the pit; Step S600: Pyrolyze the composite material specimen according to a preset pyrolysis temperature and a preset pyrolysis time; Step S700: Layer the pyrolyzed composite material specimen to obtain multiple composite layers; Step S800: Replicate the defect traces of the dyeing and marking solution near the through hole in each layer of the composite layer onto a replication layer to obtain multiple composite layers; Step S900: Stack the multiple replication layers together in the arrangement order of the composite material specimen to obtain an impact damage map.

[0022] In the present invention, a staining and marking solution is used to leave traces of impact damage defects on the composite material. Then, the composite material is delaminated and the defect traces of each layer are marked. Subsequently, the multi-layer trace defects are arranged in the order of the composite material specimen to form a complete impact damage map of the composite material. The operation process is simple, no expensive equipment is required, the damage can be recorded more accurately, and the identification accuracy, efficiency and reliability of the impact damage of the composite material can be improved at low cost, providing a reference for the design and service safety of the composite material.

[0023] In step S100, a composite material specimen is selected. The composite material specimen is mostly a flat plate, or can also be a special-shaped plate. In this embodiment, a flat plate is used as the composite material specimen.

[0024] In step S200, impact drilling is performed on the surface of the composite material specimen to be tested to obtain a composite material specimen with a through hole, and the composite material specimen to be tested is impacted to obtain impact damage.

[0025] Step S200 further includes: when performing impact drilling, the diameter of the drill bit selected is 1 / 5 to 1 / 4 of the diameter of the impact contact surface of the composite material specimen to be tested.

[0026] Specifically, after the composite material flat plate to be tested is washed clean, it is fixed on the drilling table. The position of the composite material to be tested is adjusted so that the center of the impact position on its surface is directly opposite to the center of the drill bit of the drilling table. The impact surface diameter is about 15 mm. Subsequently, a 3 mm drill bit is used to drill a through hole at the impact center position on the surface of the composite material flat plate to be tested to obtain a composite material specimen with a through hole. The 3 mm drill bit size is about 1 / 5 of the impact contact surface diameter, ensuring the smallest damage to the composite material specimen while ensuring complete marking of all damage areas. In order to make the advancing direction of the drill bit perpendicular to the impact contact surface of the composite material flat plate, the composite material flat plate to be tested is clamped and fixed through a fixture to improve the stability of the composite material flat plate during the impact process.

[0027] Step S300: Block one end of the through hole to form a pit on the surface of the composite material specimen; Step S300 further includes: sequentially cleaning the dust, oil stain and dust on the composite material specimen with pure water, alcohol and pure water, and then drying the composite material specimen according to the set temperature and set time before blocking.

[0028] Specifically, after the through hole of the composite material flat plate to be tested is drilled, the composite material flat plate is obtained. The dust generated during the drilling process of the composite material flat plate is washed clean with pure water, and then the oil stain on the surface of the composite material flat plate is washed clean with alcohol. Finally, other impurities on the surface of the composite material flat plate are washed clean with pure water. The composite material flat plate is put into an oven at 60 °C and dried for 4 h and then taken out.

[0029] Then, use a tearable sealant to block the lower end of the through-hole of the composite material plate to be tested, so as to seal the through-hole of the composite material plate, making the through-hole of the composite material plate a concave pit with a one-way opening and the ability to hold liquid. In some other embodiments, other materials can be used for blocking, such as elastic rubber sheets.

[0030] Step S400: Drop a dye-trapping solution into the concave pit and let it stand for a first preset time. The step S400 further includes: If the surface of the composite material specimen is contaminated by the dye-trapping solution, the surface of the composite material specimen should be wiped clean immediately with acetone.

[0031] Specifically, the dye-trapping solution is a solution of chloroauric acid tetrahydrate. On the premise that the chloroauric acid tetrahydrate solution does not overflow, use a dropper to suck an appropriate amount of chloroauric acid tetrahydrate solution and drop it into the concave pit of the composite material plate in small amounts and multiple times until the concave pit is filled with chloroauric acid tetrahydrate solution, and then let it stand for 1 h. During the standing process, if the solution in the concave pit decreases, the chloroauric acid tetrahydrate solution should be replenished in time. It should be noted that the chloroauric acid tetrahydrate solution should fill the concave pit in the composite material specimen to be tested, but at the same time, the chloroauric acid tetrahydrate solution cannot overflow, so that the chloroauric acid tetrahydrate solution leaves a trace contour on each layer of impact damage of the composite material plate. And in order to prevent affecting the defect trace, if the surface of the composite material specimen is contaminated by the chloroauric acid tetrahydrate solution, the surface should be wiped clean immediately with acetone.

[0032] Step S500: After standing, suck out the dye-trapping solution in the concave pit. Specifically, after standing, the excess chloroauric acid tetrahydrate solution in the concave pit of the composite material plate can be sucked out and placed in a special container for storage for future use.

[0033] Step S600: Pyrolyze the composite material specimen according to a preset pyrolysis temperature and a preset pyrolysis time. The step S600 further includes: Select the same material as the composite material specimen as the test material and pyrolyze the test material. When the pyrolysis temperature and pyrolysis time make the surface of the test material not loose, not filamentous, each single layer remain intact, and each single layer can be well separated after slightly bending the test material, select the pyrolysis temperature of this pyrolysis as the preset pyrolysis temperature, and select the pyrolysis time of this pyrolysis as the preset pyrolysis time.

[0034] Specifically, composite materials with the same material, thickness, and curing process as the composite material plate to be tested should be selected as test materials. The test materials are placed in a muffle furnace, and a certain temperature and holding time are set to explore the appropriate pyrolysis temperature and holding time process. The specific process depends on the resin type used, the thickness of the component, and the curing process, etc. The evaluation criteria for the finally selected preset pyrolysis temperature and preset pyrolysis time are that after being taken out of the muffle furnace, the surface of the test material does not loosen, does not shed filaments, and each single layer remains intact. After slightly bending the test material, each single layer can be well separated. Among them, the pyrolysis temperature and time required for different composite materials are different. Therefore, each time when exploring the appropriate pyrolysis temperature and holding time process, composite materials with the same material, thickness, and curing process as the composite material plate to be tested should be selected to explore the pyrolysis process, so that the composite material sample can be well delaminated. The selection of the preset pyrolysis time and preset pyrolysis temperature can be carried out simultaneously while soaking the concave pit of the composite material plate in the solution of tetrachloroauric acid tetrahydrate.

[0035] Among them, in the process of exploring and selecting the preset pyrolysis time and preset pyrolysis temperature process, multiple test materials for exploring the appropriate pyrolysis temperature and holding time process need to be prepared. Different pyrolysis temperatures and pyrolysis times are set for each test material. According to the pyrolysis degree of the test material in this test, the pyrolysis temperature and pyrolysis time for the next time are adjusted until the exploration material after pyrolysis in the muffle furnace meets the evaluation criteria, that is, after being taken out of the muffle furnace, the surface of the composite material plate does not loosen, does not shed filaments, and each single layer remains intact. After slightly bending the test material, each single layer can be well separated. Since generally 4 hours at 500 °C can pyrolyze the common epoxy resins on the current market, the initial pyrolysis temperature and holding time can be determined according to this situation. By controlling parameters such as the heating temperature, holding time, and cooling rate of the muffle furnace, the material can achieve a specific heat treatment effect. In some other embodiments, other pyrolysis devices can also be used.

[0036] Specifically, after the solution of tetrachloroauric acid tetrahydrate in the concave pit of the composite material plate is completely sucked out, the bottom sealant is torn off, so that the concave pit of the composite material plate is restored to a through-hole state. The composite material plate is placed in a high-temperature resistant tray, and the tray and the composite material plate as a whole are placed in a muffle furnace. After setting the temperature and holding time of the muffle furnace according to the preset pyrolysis time and preset pyrolysis temperature obtained in step S600, pyrolysis is started. In some other embodiments, the preset pyrolysis time and preset pyrolysis temperature can be selected according to conventional experience.

[0037] Step S700: Delaminate the pyrolyzed composite material sample to obtain multiple composite layers; Step S700 further includes: when delaminating the pyrolyzed composite material sample, label paper is pasted on each composite layer to mark the corresponding layer number and the direction of the composite layer.

[0038] After pyrolysis is completed, take out the composite material plate to be tested. While it is still hot, gently bend it back and forth until the layers of the composite material plate are separated. Place the whole on a draft-free workbench. After sticking the top layer of the composite material plate with a long strip of paper tape, gently separate the top layer of the composite material plate from the lower part with a blade. Then, gently peel off the top layer of the composite material plate with tweezers, stick on a label paper, and mark the layer number and original direction of this layer on the label paper.

[0039] Step S800: Replicate the defect traces of the dye retention solution near the through holes in each of the composite layers onto the replication layer to obtain multiple composite layers. Step S800 further includes: replicating by taking pictures. After uncovering each layer, the defect traces marked by the tetrachloroauric acid tetrahydrate solution can be clearly seen near the through holes, and take pictures and file them.

[0040] Step S800 further includes: replicating after tracing the contour of the defect traces of the composite layer with a pen. To ensure that the traces of the defects marked by the tetrachloroauric acid tetrahydrate solution are clearly visible at all angles, the contour of the traces can be traced with a pencil. In some other embodiments, a pen can also be used for tracing.

[0041] Step S900: Stack the multiple replication layers together in the arrangement order of the composite material specimen to obtain an impact damage diagram.

[0042] Step S900 further includes: obtaining the impact damage diagram through processing by drawing and image editing software.

[0043] Mark and take pictures and file them for each layer of the composite material. Arrange all the archived photos in the order of the composite material plate in a unified direction, and organize the results into a complete impact damage diagram. For the final archived photos, the contour of the defect traces marked by the tetrachloroauric acid tetrahydrate solution can be obtained by using Photoshop, and the layered morphology can be reconstructed by combining with Auto-CAD. Stack the reconstructed layered damages in the order of the thickness direction of the laminate to obtain a complete impact damage diagram of the composite material plate. In some other embodiments, other drawing software can be used to complete it.

[0044] The above has specifically described the preferred embodiments of the present invention, but the present invention is not limited to the embodiments. Those skilled in the art can also make various equivalent variations or substitutions without departing from the spirit of the present invention, and these equivalent variations or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A method for characterizing the thermal debonding of impact damage in a composite material, characterized in that, Including: Select a composite material sample to be tested; Perform impact drilling on the surface of the composite material sample to be tested to obtain a composite material sample with a through hole; Seal one end of the through hole to form a pit on the surface of the composite material sample; Drop a dye retention solution into the pit and let it stand for a first preset time; After standing, suck out the dye retention solution in the pit; Pyrolyze the composite material sample according to a preset pyrolysis temperature and a preset pyrolysis time; Layer the pyrolyzed composite material sample to obtain multiple composite layers; Copy the defect traces of the dye retention solution near the through hole in each composite layer onto a replication layer to obtain multiple composite layers; Stack the multiple replication layers together in the arrangement order of the composite material sample to obtain an impact damage map.

2. The method for characterizing the impact damage of a composite material by thermal delamination according to claim 1, wherein: The performing impact drilling on the surface of the composite material sample to be tested to obtain a composite material sample with a through hole includes: When performing impact drilling, the diameter of the drill bit selected is 1 / 5 to 1 / 4 of the diameter of the impact contact surface of the composite material sample to be tested.

3. The method for characterizing the impact damage of a composite material by thermal delamination according to claim 1, wherein: The sealing one end of the through hole to form a pit on the surface of the composite material sample includes: After successively cleaning the dust, oil stain, and dust of the composite material sample with pure water, alcohol, and pure water, dry the composite material sample according to a set temperature and a set time and then perform the sealing.

4. The method for characterizing the impact damage of a composite material by thermal delamination according to claim 1, wherein: The pyrolyzing the composite material sample according to a preset pyrolysis process includes: Select the same material as the composite material sample as the test material, pyrolyze the test material, and when the pyrolysis temperature and pyrolysis time during pyrolysis make the surface of the test material not loose, not filamentous, each single layer remain intact, and each single layer can be well separated after slightly bending the test material, select the pyrolysis temperature of this pyrolysis as the preset pyrolysis temperature and select the pyrolysis time of this pyrolysis as the preset pyrolysis time.

5. The method for characterizing the impact damage of a composite material by thermal delamination according to claim 1, wherein: The dropping a dye retention solution into the pit and letting it stand for a first preset time includes: If the surface of the composite material sample is contaminated by the dye retention solution, immediately wipe the surface of the composite material sample clean with acetone.

6. The method for characterizing the impact damage of a composite material by thermal delamination according to claim 1, wherein: The layering the pyrolyzed composite material sample to obtain multiple composite layers includes: When layering the pyrolyzed composite material sample, label papers are pasted on each composite layer to mark the corresponding layer number and the direction of the composite layer.

7. The method for characterizing the impact damage of a composite material by thermal delamination according to claim 1, wherein: Replicating the defect traces of the dyeing and marking solution near the through holes in each layer of the composite layer onto the replication layer to obtain a multi-layer composite layer, including: Replicating after tracing the contour of the defect traces of the composite layer with a pen.

8. A method for characterizing the thermal debonding layer of impact damage of a composite material according to claim 1, wherein: Replicating the defect traces of the dyeing and marking solution near the through holes in each layer of the composite layer onto the replication layer to obtain a multi-layer composite layer, further including: Replicating by means of photographing.

9. A method for characterizing the thermal debonding layer of impact damage of a composite material according to claim 1, wherein: Stacking the multiple replication layers together in the arrangement order of the composite material specimen to obtain an impact damage map, including: Obtaining the impact damage map through processing by drawing and image editing software.

10. A method for characterizing the thermal debonding layer of impact damage of a composite material according to claim 1, wherein: Dropping the dyeing and marking solution into the pits and standing for a first preset time, including: The dyeing and marking solution uses a solution of tetrachloroauric acid tetrahydrate.

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