Method for repairing damage of foam sandwich structural member

Abstract

The invention belongs to the technical field of manufacturing and repairing of composite material structures, and relates to a repairing method for damage of a foam sandwich structural part. The method comprises the steps that S1, the damage range, type and degree of a damage area are determined, and the damage area is cleaned; s2, micropores are formed in the damaged area, and a channel is provided for subsequent taking-out of the damaged foam core material and injection of the foam material; s3, the foam core material in the damaged area is smashed and cleaned, and a filling space is provided for the foam material; s4, evaluating the size of the damaged area and the use amount of the foaming material; s5, injecting a foaming material in situ; s6, through a gradient curing process, tight combination of the foaming material and the original structure is guaranteed; and S7, after curing, the formed micropores are repaired, and the integrity of the surface of the structure is recovered.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of composite structure manufacturing and repair, and relates to a foam sandwich structure damage repair method. BACKGROUND

[0002] The foam sandwich structure is a composite sandwich structure composed of high-strength face plates and light-weight foam cores. It has the advantages of light weight, high specific strength, excellent sound insulation performance and the like. It is widely used in the fields of aerospace, wind power generation, rail transit and the like. However, the foam sandwich structure is affected by impact external force, fatigue and the like during the manufacturing process or the use process, leading to large-area damage such as debonding of the face plates and the core, cracking of the core and crushing of the core, and is prone to form large-area damage, which seriously affects the load bearing capacity and service life of the structure.

[0003] At present, the damage repair of the foam sandwich structure mainly adopts the following methods: 1. Excavation repair method. The face plates and the core of the damage area are first cut off, then the same or similar materials are used for filling and repairing, and finally surface treatment is performed. 2. Injection repair method. The method uses a syringe to inject adhesive into the damage area to achieve damage repair through the curing of the adhesive. 3. Patch repair method. The method sticks a prepreg or a composite patch on the surface of the damage area to achieve damage repair through pressure curing.

[0004] The above existing repair technologies still have the following disadvantages in the implementation process: 1. Large destruction. The excavation repair method needs to cut off the entire damage area, which usually causes large secondary damage to the structure and reduces the overall performance of the structure. 2. Long repair cycle and low repair efficiency. The injection repair method and the patch repair method require a long curing process, and the repair efficiency is low, which is difficult to meet the demand for rapid repair. 3. Limited application range. The existing technologies are usually more suitable for the repair of flat panels, and it is difficult to repair damage in complex shapes and variable thicknesses. SUMMARY

[0005] In view of the problems of large structural destruction, low foam sandwich structure repair efficiency, great difficulty in repairing complex structures and poor repair effect of large-area damage in the prior art, a high-efficiency and wide-range foam sandwich structure damage repair method based on polyetherimide in-situ foaming is proposed. Through minimally invasive drilling, crushing and cleaning, in-situ foaming and gradient curing, efficient repair and structural performance recovery are realized. The method is based on the polyetherimide in-situ foaming technology, realizes efficient repair and aerodynamic shape recovery of the damage area through minimally invasive drilling, foam crushing and cleaning, in-situ injection of foaming materials and gradient curing process, solves the problems of non-bonding and weak bonding easily caused by glue injection repair, and finally realizes efficient and high-strength repair effect of the foam sandwich structure.

[0006] The technical scheme of the application is: A method for repairing damage to a foam sandwich structure, the specific steps are as follows: Step S1: Determine the damage range, type and extent of the damage area, and clean the damage area; Step S2: Open micro-holes in the damage area to provide a channel for subsequent removal of damaged foam core material and injection of foaming material; Step S3: Crush the foam core material in the damage area and clean it to provide a filling space for the foaming material; Step S4: Evaluate the size of the damage area and the amount of foaming material; Step S5: Inject the foaming material in situ; Step S6: Ensure the close combination of the foaming material and the original structure through the gradient curing process; Step S7: After curing, repair the micro-holes and restore the integrity of the structure surface.

[0007] Further, the S1 specific method includes: Visual inspection, observing the structure surface with the naked eye or magnifying glass to find obvious damage marks such as cracks, depressions, and debonding; Knocking detection: use a knocking tool to knock the structure surface and determine the damage area by sound; Ultrasonic detection: use an ultrasonic flaw detector to scan the structure and determine the location and size of the damage area by reflected wave signals.

[0008] Further, S2 is specifically: grinding the opening area to form a rough surface; the diameter of the micro-holes is set to 5-10mm, and the number of micro-holes is determined according to the size and shape of the damage area.

[0009] Further, every 500cm 2 Open 3-5 micro-holes in the damage area to ensure the removal efficiency of the damaged foam and ensure that the foaming material can be uniformly filled inside and reduce the damage area of the original structure.

[0010] Further, S3 is specifically: Use a rotary cutter or high-pressure air gun to crush the foam core material in the damage area, and use a vacuum cleaner or compressed air to clean the crushed foam debris to ensure that there is no residue inside the damage area, so that the foaming material can be fully filled and tightly combined with the surrounding structure.

[0011] Further, S4 is specifically: Use a laser range finder to measure the length, width and depth of the damage area; calculate the amount of foaming material according to the volume of the damage area to ensure that the foaming amount is not less than 120% of the repair volume.

[0012] Further, S5 is specifically: The foaming material is injected into the damage area, the expansion characteristics of the foaming material are used to fill the damage gap, a polyetherimide prepolymer solution is prepared, a foaming agent and a nano-reinforced filler are added, and the mixed solution is injected into the micro-hole through a syringe needle.

[0013] Further, the S6 gradient curing process is specifically as follows: S7 repairing the opened micro-hole The foam sandwich structure is placed into a blast oven, the first stage foaming is carried out, the temperature is raised to 80-100 DEG C, the temperature is kept for 10-20 min, the foaming ratio is 3-5 times, and the space is filled; the second stage curing is carried out, the temperature is raised to 180-200 DEG C, the temperature is kept for 1-2 h, and the polyetherimide is completely crosslinked; the third stage cooling and shaping is carried out, and the temperature is naturally cooled to below 50 DEG C, and the residual stress is eliminated.

[0014] Further, the S7 repairing the opened micro-hole is specifically as follows: Repairing materials similar to the performance of the panel material are selected, the repairing materials are filled into the micro-hole, and the surface is ensured to be flat; the repairing area is polished and polished, and the surface smoothness is restored.

[0015] The advantages of the present application are: The present application avoids the cutting of the large-area panel and the foam core in the traditional repair method by injecting the foaming material into the micro-hole, significantly reduces the secondary damage to the structure in the repair process, maximizes the integrity of the original structure, avoids the stress concentration problem caused by the large-area cutting in the repair method, replaces the curing method of the traditional repair method by using the complex equipment such as the autoclave, simplifies the curing process, improves the efficiency and reduces the cost, and has strong adaptability to the shape and thickness of the damage area. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The present application is a schematic diagram of the foam sandwich structure after repair.

[0017] The drawing label: 1, outer panel; 2, inner panel; 3, original foam core; 4, repair area foam; 5, hole making position. DETAILED DESCRIPTION

[0018] The present application is further described in detail below in combination with the embodiments and the drawings, but the embodiments of the present application are not limited thereto.

[0019] The present application proposes a repair method for a foam sandwich plate structure based on a polyetherimide in-situ foaming technology, and the specific steps are as follows: Step S1: Damage area assessment and pretreatment. Determine the damage range, type, and extent of the damage area through various technical means. Specific methods include: visual inspection, observing the structure surface with the naked eye or magnifying glass to find obvious damage traces such as cracks, depressions, debonding, etc.; knocking detection: use a knocking tool to knock the structure surface and judge the damage area by sound; ultrasonic detection: use an ultrasonic flaw detector to scan the structure and determine the location and size of the damage area. Remove loose materials, contaminants, and moisture from the damage area.

[0020] Step S2: Open micro-holes in the damage area. Open micro-holes in the damage area to provide channels for subsequent damage foam core removal and foam material injection. Polish the hole area to form a rough surface. The diameter of the micro-holes is set to 5-10mm, and the number is reasonably determined according to the size and shape of the damage area. Generally, 3-5 micro-holes are opened in the damage area to ensure the efficiency of the damage foam removal and ensure that the foam material can be uniformly filled inside and reduce the damage area of the original structure. Use special drilling tools to ensure smooth hole walls and avoid secondary damage to the surrounding structure. 2 Step S2: Open micro-holes in the damage area. Open micro-holes in the damage area to provide channels for subsequent damage foam core removal and foam material injection. Polish the hole area to form a rough surface. The diameter of the micro-holes is set to 5-10mm, and the number is reasonably determined according to the size and shape of the damage area. Generally, 3-5 micro-holes are opened in the damage area to ensure the efficiency of the damage foam removal and ensure that the foam material can be uniformly filled inside and reduce the damage area of the original structure. Use special drilling tools to ensure smooth hole walls and avoid secondary damage to the surrounding structure.

[0021] Step S3: Foam crushing and cleaning. Crush and clean the foam core material in the damage area to provide space for foam material filling. Use a rotary cutter or high-pressure air gun to crush the foam core material in the damage area. Use a vacuum cleaner or compressed air to clean the crushed foam debris to ensure that there is no residue inside the damage area. The cleaning range should be slightly larger than the damage area to ensure that the foam material can be fully filled and tightly combined with the surrounding structure.

[0022] Step S4: Evaluate the size of the damage area and the amount of foam material. Use a laser range finder to measure the length, width, and depth of the damage area. Calculate the amount of foam material according to the volume of the damage area to ensure that the foam volume is not less than 120% of the repair volume. For example, if the volume of the damage area is 100cm 3 , the foam volume should be not less than 150cm 3 . The excess foam material can overflow from the micro-holes, while providing the necessary pressure to ensure the strength of the foam material itself and the tight combination with the surrounding structure.

[0023] Step S5: In-situ injection of foam material. Inject foam material into the damage area to fill the damage gap using its expansion properties. Prepare a polyetherimide prepolymer solution (solid content 40-60%), add a foaming agent (azo dimethylformamide, mass fraction 3-8%) and a nano-enhanced filler (carbon fiber powder or silicon dioxide, mass fraction 5-15%); inject the mixed solution into the cavity through a syringe.

[0024] Step S6: Gradient curing molding. Through the gradient curing process, ensure the close combination of the foamed material with the original structure, and realize efficient repair. First stage foaming, heating to 80-100℃, holding for 10-20min, foaming ratio 3-5 times, filling the cavity; second stage curing, heating to 180-200℃, holding for 1-2h, making the polyetherimide completely cross-linked; third stage cooling and setting, naturally cooling to below 50℃, eliminating residual stress.

[0025] Step S7: Post-processing and detection. After curing, the micro-holes opened are repaired to restore the integrity of the structure surface. Select a repair material similar in performance to the panel material, such as epoxy resin or composite material. Fill the repair material into the micro-holes to ensure the surface is flat. Polish and polish the repaired area to restore the smoothness of the surface. And carry out non-destructive testing to ensure that the repair quality meets the requirements. According to the needs, a protective coating is applied to the repaired area to improve corrosion resistance and aesthetics.

[0026] Example 1: Repair of foam sandwich structure depression of outer hatch door, the specific steps are as follows: Step S1: Damage area evaluation and pretreatment. First, visually inspect the surface of the foam sandwich structure and find a noticeable depression area, which is preliminarily judged as a damage area. Use a knocking tool to knock around the depression area and determine the damage range by sound. Use an ultrasonic flaw detector to scan the damage area and confirm that the damage area size is 200mm-400mm and the depth is 30mm.

[0027] Step S2: Open micro-holes in the damage area. Eight micro-holes with a diameter of 10mm are opened in the outer panel of the damage area to provide a channel for subsequent removal of the damaged foam core and injection of foaming material. The micro-holes are located on the outer panel of the damage area, as shown in Figure 1 , avoiding concentration on one side. Polish the hole opening area to form a rough surface. Ensure the efficiency of removing the damaged foam and ensure that the foaming material can be uniformly filled inside and reduce the damage area of the original structure. Use a special drilling tool to ensure smooth hole walls and avoid secondary damage to the surrounding structure.

[0028] Step S3: Foam crushing and cleaning. Use a rotary cutter to crush the foam core in the damage area. Use a vacuum cleaner to clean the crushed foam debris to ensure that there is no residue inside the damage area. The cleaning range is slightly larger than the damage area to ensure that the foaming material can be fully filled and tightly combined with the surrounding structure.

[0029] Step S4: Estimate the size of the damage area and the amount of foaming material. Use a laser range finder to measure the length, width and depth of the damage area, and calculate the volume of the damage area to be about 2400cm 3, the amount of foaming material is calculated according to the volume of the damage area, and the foaming amount is ensured to be not less than 120% of the repair volume, that is, 2880cm 3 .

[0030] Step S5: in-situ injection of foaming material. A polyetherimide prepolymer solution (solid content 50%) is prepared, a foaming agent (azodicarbonamide, mass fraction 5%) and a nano-enhanced filler (silicon dioxide, mass fraction 10%) are added, and the mixed solution is injected into the cavity of the damage area through a syringe needle.

[0031] Step S6: gradient curing molding. Through the gradient curing process, the foaming material is ensured to be closely combined with the original structure, and efficient repair is achieved. In the first stage of foaming, the temperature is raised to 90 DEG C, and the temperature is kept for 15 min, the foaming ratio is 4.2 times, and the cavity is filled; in the second stage of curing, the temperature is raised to 190 DEG C, and the temperature is kept for 1.5 h, so that the polyetherimide is completely crosslinked; in the third stage of cooling and shaping, it is naturally cooled to 50 DEG C, and the residual stress is eliminated.

[0032] Step S7: post-processing and detection. After curing, the micro-holes opened are repaired, and the integrity of the structure surface is restored. Epoxy resin is selected as the repair material for the surface micro-holes to ensure the surface flatness, and curing is carried out. The repaired area is polished and polished to restore the surface smoothness. And nondestructive testing is carried out to ensure that the repair quality meets the requirements. A protective coating is applied to the repaired area to improve corrosion resistance and aesthetics.

[0033] Example 2: A certain aircraft wing honeycomb sandwich structure is impacted, causing the honeycomb core and the panel to debond, forming a large area of damage. The synchronous repair method provided by the application is used for repair, and the specific steps are as follows: Step S1: damage area evaluation and pretreatment. First, visually inspect the surface of the foam sandwich structure, find a small range of concave areas, and preliminarily judge that it is a damage area. Use a knocking tool to knock around the concave area, and judge the damage range by sound. Use an ultrasonic flaw detector to scan the damage area, and confirm that the size of the damage area is 200mm-150mm, and the depth is 20mm.

[0034] Step S2: opening micro-holes in the damage area. Six micro-holes with a diameter of 8mm are opened in the outer panel of the damage area, and the opening area is polished to form a rough surface. Ensure the efficiency of removing the damaged foam and ensure that the foaming material can be uniformly filled inside and reduce the damage area of the original structure. Use a special drilling tool to ensure that the hole wall is smooth and avoid secondary damage to the surrounding structure.

[0035] Step S3: foam crushing and cleaning. The damage area is a closed area, and the foam core material in the damage area is crushed using a high-pressure air gun. The crushed foam debris is cleaned using a vacuum cleaner and compressed air to ensure that there is no residue inside the damage area.

[0036] Step S4: Estimate the size of the damaged area and the amount of foaming material. Use a laser range finder to measure the length, width and depth of the damaged area, and calculate the volume of the damaged area to be about 600 cm 3 According to the volume of the damaged area, calculate the amount of foaming material, and ensure that the foaming amount is not less than 120% of the repair volume, i.e. 720 cm 3 .

[0037] Step S5: In-situ injection of foaming material. Prepare a polyetherimide prepolymer solution (solid content 60%), add foaming agent (azodicarbonamide, mass fraction 3%) and nano-enhanced filler (silicon dioxide, mass fraction 15%); inject the mixed solution into the cavity of the damaged area through a syringe.

[0038] Step S6: Gradient curing molding. Through the gradient curing process, ensure the close combination of foaming material and original structure, and realize efficient repair. First stage foaming, heat to 90℃, keep warm for 10 min, foaming ratio 3 times, fill the cavity; second stage curing, heat to 180℃, keep warm for 1 h, make polyetherimide completely crosslink; third stage cooling and setting, naturally cool to 50℃, eliminate residual stress.

[0039] Step S7: Post-processing and detection. After curing, repair the micro-holes opened and restore the integrity of the structure surface. Choose epoxy resin as the repair material for the surface micro-holes, ensure the surface flatness, and perform curing. Grind and polish the repaired area to restore the surface smoothness. And carry out non-destructive testing to ensure that the repair quality meets the requirements.

Claims

1. A method for repairing damage to foam sandwich structural components, characterized in that, The specific steps are as follows: Step S1: Determine the extent, type, and degree of damage in the damaged area, and clean the damaged area; Step S2: Create micropores in the damaged area to provide channels for subsequent removal of the damaged foam core material and injection of foaming material; Step S3: Crush and clean the foam core material in the damaged area to provide filling space for the foam material; Step S4: Assess the size of the damaged area and the amount of foaming material used; Step S5: Inject foaming material in situ; Step S6: Ensure a tight bond between the foamed material and the original structure through a gradient curing process; Step S7: After curing, repair the micropores to restore the integrity of the structural surface.

2. The method for repairing damage to a foam sandwich structure according to claim 1, characterized in that, S1 specific methods include: Visual inspection involves examining the surface of the structure with the naked eye or a magnifying glass to look for obvious signs of damage, such as cracks, dents, and delamination. Impact testing: Use a tapping tool to gently tap the surface of the structure and determine the damaged area by the sound. Ultrasonic testing: The structure is scanned using an ultrasonic flaw detector, and the location and size of the damaged area are determined by the reflected wave signal.

3. The method for repairing damage to a foam sandwich structure according to claim 1, characterized in that, S2 specifically involves grinding the opening area to create a rough surface; the diameter of the micropores is set to 5-10 mm, and the number of micropores is determined based on the size and shape of the damaged area.

4. The method for repairing damage to a foam sandwich structure according to claim 3, characterized in that, Every 500cm 2 Three to five micropores are created in the damaged area to ensure efficient removal of the damaged foam and to ensure that the foaming material can be uniformly filled inside, thereby reducing the damaged area of ​​the original structure.

5. The method for repairing damage to a foam sandwich structure according to claim 1, characterized in that, S3 specifically refers to: Use a rotary cutter or high-pressure air gun to crush the foam core material in the damaged area. Clean up the crushed foam debris with a vacuum cleaner or compressed air to ensure that there are no residues inside the damaged area, so that the foam material can fully fill and bond tightly with the surrounding structure.

6. The method for repairing damage to a foam sandwich structure according to claim 1, characterized in that, S4 specifically refers to: Use a laser rangefinder to measure the length, width, and depth of the damaged area; calculate the amount of foam material needed based on the volume of the damaged area, ensuring that the amount of foam is not less than 120% of the repair volume.

7. The method for repairing damage to a foam sandwich structure according to claim 1, characterized in that, S5 specifically refers to: The foaming material is injected into the damaged area to fill the gaps in the damage by utilizing its expansion properties. A polyetherimide prepolymer solution is prepared, and a foaming agent and nano-reinforcing filler are added. The mixed solution is then injected into the micropores through an injection syringe.

8. The method for repairing damage to a foam sandwich structure according to claim 1, characterized in that, The S6 gradient curing process specifically involves: S7 repairing the micropores. The foam sandwich panel structural components are placed in a forced-air drying oven for the first stage of foaming. The temperature is raised to 80-100℃ and held for 10-20 minutes, with a foaming ratio of 3-5 times, to fill the space. The second stage is curing, where the temperature is raised to 180-200℃ and held for 1-2 hours to fully cross-link the polyetherimide. The third stage is cooling and shaping, where the temperature is naturally cooled to below 50℃ to eliminate residual stress.

9. A method for repairing damage to a foam sandwich structure according to claim 1, characterized in that, The S7 repairs the micropores as follows: Select a repair material with properties similar to the panel material, fill the micropores with the repair material to ensure a smooth surface; grind and polish the repaired area to restore surface smoothness.

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