A fiber metal laminate with an added microcapsule self-repair layer and a method of making the same

Abstract

The application discloses a kind of fiber metal laminates with microcapsule self-repairing layer and its preparation method, including metal matrix layer, interface reinforcement film layer and fiber prepreg layer, the fiber metal laminates also include microcapsule coating, and the layer plate adopts the structure of metal matrix layer / interface reinforcement film layer / microcapsule coating / fiber prepreg layer / microcapsule coating / interface reinforcement film layer / metal matrix layer for alternative lay-up.It is proposed that the new lay-up structure of fiber metal laminates is coated with a layer of microcapsule coating containing microcapsules between the interface reinforcement layer and the fiber prepreg.The microcapsule coating contains a suitable mass fraction of microcapsules, wherein the microcapsules are well mixed in the microcapsule coating and do not penetrate into adjacent layers, can produce self-healing effect, realize self-repairing function, and improve the shear strength and interlaminar adhesion of the fiber metal laminates.

Description

A fiber-metal laminate with added microcapsule self-healing layer and its preparation method Technical Field

[0001] This invention relates to the field of fiber metal laminate technology, and in particular to a fiber metal laminate with added microcapsule self-healing layer and its preparation method, which enhances the interlayer toughening effect of the fiber metal laminate and gives it high toughness and fatigue life. Background Technology

[0002] Aerospace materials are currently developing towards lower density, higher specific strength, and better fatigue resistance. However, alloy materials have poor fatigue strength, and composite materials, due to their different layup methods, exhibit anisotropy, making them less sensitive to fatigue damage but with poor impact resistance. Fiber-coated metal laminates combine the advantages of metal materials and fiber composites, exhibiting excellent impact resistance and fatigue resistance.

[0003] Since fiber-metal laminates are essentially a hyperhybrid composite material, under insufficient interfacial bonding or external shear stress, the metal matrix layer and fiber layer may debond. Separation of the metal matrix layer from the fiber prepreg layer is one of the main failure modes of fiber-metal laminates. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the technical problem this invention aims to solve is to provide a method for preparing a fiber-metal laminate with an added microcapsule self-healing layer, thereby improving the interlayer adhesion between the metal matrix layer and the fiber layer by adding microcapsules.

[0005] The technical solution adopted by the present invention to solve the aforementioned technical problem is to provide a fiber metal laminate with an added microcapsule self-healing layer, comprising a metal substrate layer, an interface reinforcement film layer, and a fiber prepreg layer. The fiber metal laminate further comprises a microcapsule coating, and the laminate is constructed by alternating layers of a structure consisting of a metal substrate layer, an interface reinforcement film layer, a microcapsule coating, a fiber prepreg layer, a microcapsule coating, an interface reinforcement film layer, and a metal substrate layer.

[0006] The fiber layup angles in the fiber-metal laminate are 0°, 90°, and ±45°.

[0007] The metal substrate layer is at least one of aluminum alloy, magnesium alloy, and titanium alloy, and its thickness is no more than 0.5 mm;

[0008] The fiber prepreg layer is composed of fibers and resin, wherein the fibers are at least one of glass fibers, carbon fibers, and aramid fibers; and the resin is a thermosetting epoxy resin.

[0009] The interface-enhancing thin film layer is made of a malleable material, including polymer films or polymer-based composite materials;

[0010] The microcapsule coating 3 is uniformly applied to the front and back surfaces of the fiber prepreg layer 4 by spraying or coating. The microcapsule coating is formed by dispersing micron-sized microcapsules in an epoxy resin-based varnish by stirring or ultrasonication and then spraying or coating. The micron-sized microcapsules are spherical and have a core-shell structure.

[0011] The average diameter of the micron-sized microcapsules is 2-5 μm. The micron-sized microcapsules do not agglomerate in epoxy resin-based varnish and can be uniformly dispersed on the fiber prepreg layer.

[0012] The microcapsules encapsulate isocyanate (IPDI), and the capsule shell is made of polyurethane. The micron-sized microcapsules account for 1-5 wt% of the epoxy resin-based varnish, preferably 1.5 wt%. The microcapsule coating is tens of micrometers thick. When the interface layer cracks under external stress, the microcapsules rupture, releasing the self-healing substance—isocyanate (IPDI). The isocyanate (NCO) groups in the IPDI react with the epoxy groups in the epoxy resin of the microcapsule coating to form urea bonds or uryl bonds. When the isocyanate comes into contact with the epoxy resin, the NCO groups in the isocyanate react with the epoxy groups in the epoxy resin to form chemical bonds. After the reaction, the isocyanate and epoxy resin chemically combine to form a new cross-linked network, thereby repairing the epoxy resin matrix. At the same time, the broken microcapsule shell can also promote the interlocking effect in the longitudinal direction when the structure is bent.

[0013] When the laminate is subjected to shear, tensile, or compressive loads, the added microcapsule coating provides additional adhesive protection. The microcapsules open upon mechanical stimulation, and the encapsulated repair agent is released into the microcapsule coating or the interface between adjacent layers. This process inhibits crack propagation by filling cracks and forming a mortise-and-tenon-like structure. Furthermore, it promotes crack adhesion by forming a new adhesive layer at the interface, thus resisting delamination caused by external mechanical loads.

[0014] This invention also protects a method for preparing a fiber-metal laminate with an added microcapsule self-healing layer, the method comprising the following steps:

[0015] 1) Treatment of the metal substrate: Degrease the metal substrate, and then polish it with fine and coarse sandpaper to increase the surface roughness of the metal substrate and increase the bonding area.

[0016] 2) Selection of fiber prepreg layer: Epoxy resin-based fiber prepreg is selected, and polyimide film with good thermal and chemical stability is selected for the interface reinforcement film layer;

[0017] 3) Preparation of microcapsules: Polyurethane microcapsules were prepared using a microemulsion system combined with interfacial polymerization, including:

[0018] Prepolymer preparation: Prepare p-toluene diisocyanate, cyclohexanone, and butanediol in a mass ratio of 1:6.5:0.2. Dissolve p-toluene diisocyanate in cyclohexanone. While slowly pouring in butanediol, heat and stir the solution at 60-80°C. After the reaction is complete, distill to obtain the prepolymer.

[0019] Isophorone diisocyanate (IPDI) was dissolved in ethyl acetate at a ratio of 3.5:1 as the core material and prepolymer to form an oil phase, and the mixture was stirred thoroughly.

[0020] Mix deionized water and emulsifier and stir thoroughly to form an emulsion;

[0021] The oil phase is added to the emulsion to form an oil-in-water (O / W) emulsion system;

[0022] Then, butylene glycol was slowly added, the entire system was heated to 60°C and stirred at 1500 rpm for 1.5 hours to obtain a microcapsule suspension;

[0023] After washing, filtration and vacuum drying, microcapsule samples with a diameter of 2 to 5 μm were obtained.

[0024] 4) Preparation of microcapsule coating: The microcapsule sample was mixed with epoxy resin-based varnish, wherein the mass fraction of the microcapsule sample was 1.5 wt%. After mixing, the mixture was coated onto the fiber prepreg layer and dried.

[0025] 5) Shaping and curing: The fiber prepreg layer containing the microcapsule coating, polyimide film and metal substrate are placed in a vacuum bag and hot-pressed and cured until the desired shape is formed, to obtain a fiber metal laminate with added microcapsule self-healing layer.

[0026] The hot-press curing temperature is 130-140℃, and the applied pressure will not cause the microcapsule shell to rupture or the IPDI core material to leak.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] This invention creatively proposes a novel layup structure for fiber-metal laminates, in which a microcapsule coating containing microcapsules is applied between the interface reinforcement layer and the fiber prepreg. The microcapsule coating contains a suitable mass fraction (1.5% wt in this embodiment) of microcapsules, which are thoroughly mixed within the coating and do not penetrate into adjacent layers. This creates a self-healing effect, achieving self-repair function and improving the shear strength and interlayer adhesion of the fiber-metal laminate.

[0029] This invention provides a method for preparing a fiber-metal laminate with a microcapsule self-healing layer. By coating a layer containing microcapsules between the interface reinforcement film layer and the fiber prepreg layer, the bonding performance between the metal matrix layer and the fiber prepreg layer is effectively improved, thereby enhancing the interlayer toughening effect of the fiber-metal laminate.

[0030] This invention presents a novel fiber-metal laminate structure, providing ideas and methods for developing higher-performance composite materials. This invention is specifically designed to repair cracks in the interlayer bonding between the fiber prepreg layer and the microcapsule coating, thereby improving interlayer adhesion. Attached Figure Description

[0031] Figure 1 is a schematic diagram of the layup structure of the fiber metal laminate of the present invention.

[0032] Figure 2 is a schematic diagram of the self-repair of microcapsules.

[0033] In the figure, 1—metal substrate layer; 2—interface reinforcement film layer; 3—microcapsule coating; 4—fiber prepreg layer. Detailed Implementation

[0034] The present invention will be further explained below with reference to the embodiments and accompanying drawings, but this is not intended to limit the scope of protection of this application.

[0035] The fiber-metal laminate of the present invention with added microcapsule self-healing layer (see Figure 1) includes a metal substrate layer 1, an interface reinforcement film layer 2, a microcapsule coating 3, and a fiber prepreg layer 4. The laminate adopts an alternating layup structure of metal substrate layer / interface reinforcement film layer / microcapsule coating 3 / fiber prepreg layer 4 / microcapsule coating 3 / interface reinforcement film layer / metal substrate layer. The fiber layup angle is 0°, 90°, ±45°, etc. The specific layup angle is determined according to the type of load borne by the laminate part and the service environment. After layup, it is bonded together by pressure thermosetting.

[0036] The metal substrate layer can be made of aluminum alloy, magnesium alloy, or titanium alloy, and its thickness is generally less than 0.5 mm.

[0037] Fiber prepreg layer 4: The fiber prepreg is composed of fibers and resin. The fibers can be high-performance fiber materials such as glass fiber, carbon fiber, and aramid fiber; the resin is thermosetting epoxy resin.

[0038] Interface-reinforced film layer 2: The interface-reinforced layer embedded in the fiber-metal laminate is made of a plastic material, such as a polymer film or a polymer-based composite material, to enhance the bonding performance between the metal matrix layer and the fiber prepreg layer.

[0039] The microcapsule coating 3 is uniformly applied to both sides of the fiber prepreg layer 4 by spraying or coating. The microcapsule coating is formed by dispersing micron-sized microcapsules in epoxy resin through stirring or ultrasonication followed by spraying or coating. The micron-sized microcapsules are spherical with a core-shell structure. The shell layer of the core-shell structure is uniform in texture and relatively wrinkle-free. The average diameter of the micron-sized microcapsules is controlled at 2-5 μm, exhibiting uniform particle size. The micron-sized microcapsules do not agglomerate in the epoxy resin-based varnish and can be uniformly dispersed on the fiber prepreg layer.

[0040] The microcapsule coating 3 is in contact with the fiber prepreg layer 4 and the interface reinforcement film layer 2 on both sides, respectively. In this invention, the size of the microcapsules is as small as possible to avoid occupying too much resin space while ensuring sufficient repair agent coverage. The ratio of the microcapsule wall to the core material should be selected according to the matrix to achieve the best repair effect and reduce microcapsule aggregation.

[0041] This invention exhibits enhanced resistance to external loads such as shear failure. When the laminate is subjected to shear, tensile, or compressive loads, the added microcapsule coating provides additional adhesive protection. The microcapsules open upon mechanical stimulation, releasing the encapsulated repair agent into the microcapsule coating or at the interface between adjacent layers. This process fills cracks, forming a mortise-and-tenon-like structure to inhibit crack propagation and promotes crack adhesion by forming a new adhesive layer at the interface, thus resisting delamination caused by external mechanical load damage.

[0042] The microcapsules encapsulate isocyanate (IPDI) because it is highly reactive with active hydrogen (H) groups such as OH groups, which are present in the epoxy resin matrix, and the microcapsules are contained within the epoxy resin. The function of the microcapsules in this invention is to provide an additional self-healing interface layer on the CFRP (carbon fiber reinforced polymer) interface, thereby improving the adhesion between the metal and the fiber prepreg and reducing the likelihood of delamination and separation. When the interface layer cracks under external stress, the microcapsules rupture, releasing the self-healing substance—IPDI. The isocyanate (NCO) groups in the IPDI react with the epoxy groups in the epoxy resin of the microcapsule coating, forming urea bonds or carbamate bonds. This reaction occurs in the presence of compounds containing active hydrogen, with the epoxy groups in the epoxy resin being a typical source of active hydrogen. When the isocyanate comes into contact with the epoxy resin, the NCO groups in the isocyanate react with the epoxy groups in the epoxy resin to form chemical bonds. After the reaction, the isocyanate chemically bonds with the epoxy resin to form a new cross-linked network, thereby repairing the epoxy resin matrix. Simultaneously, the broken microcapsule shells (made of polyurethane) can promote a longitudinal interlocking effect during structural bending. These self-healing properties are mainly affected by the morphology, size, and dosage of the microcapsules. In this invention, the dosage of microcapsules is 1.0-5.0 wt%, preferably 1.5 wt%. Excessive dosage can easily lead to agglomeration. The dosage range of this invention ensures that adding microcapsules does not excessively compress the space that would otherwise belong to the epoxy resin matrix. On the contrary, appropriately sized microcapsules fill and reduce porosity, enabling repair of every crack, achieving comprehensive repair, and improving overall density.

[0043] The microcapsule repair process described in this application is similar to a mortise and tenon structure rather than a building block stacking method. It can penetrate each other, enhance density, and effectively prevent cracks from expanding.

[0044] Microcapsule encapsulation: The microcapsule coating in the figure, which is closely attached to the fiber prepreg layer, is composed of epoxy resin containing 1.5 wt% microcapsules. The thickness of the microcapsule coating is about tens of micrometers, and the microcapsules are evenly distributed in it.

[0045] Damage Occurrence: When the laminate is damaged, such as by impact, the anisotropy of the materials in each layer usually leads to peeling and debonding between the fiber prepreg layer and the metal layer. This damage typically first causes micro-cracks or defects between the layers. When cracks occur between the layers, the microcapsules located between the two layers and closely attached to the fiber prepreg layer will rupture.

[0046] Isocyanate release: After the microcapsules rupture, the isocyanate repair agent encapsulated within is released into the epoxy resin matrix. The repair agent then flows into the cracks through capillary action.

[0047] The reaction between isocyanates and epoxy resins is a crucial step in self-healing. Isocyanate molecules contain multiple isocyanate functional groups (NCO), while epoxy resins contain multiple hydroxyl functional groups (OH). The isocyanate functional groups (NCO) in the isocyanate react with the hydroxyl functional groups (OH) in the epoxy resin through an addition reaction, forming new chemical bonds. This reaction is called the isocyanate-isocyanate (NCO-OH) reaction. This reaction leads to the repair of damaged sites because it introduces new cross-linking sites and chemical bonds.

[0048] Damage Repair: The reaction between isocyanate and epoxy resin forms new bonds around the damaged area, filling cracks or defects and thus repairing the damage. This repair process can restore the interlayer adhesive strength and integrity, reducing the adverse effects of damage on material properties.

[0049] When a crack occurs, the interior is considered to be a vacuum with a pressure difference. Under direct compression or impact, the pressure difference causes the microcapsule to rupture for repair, preventing premature rupture of the microcapsule due to excessive temperature.

[0050] The method for preparing the fiber metal plate with added microcapsule self-healing layer of the present invention specifically includes the following steps:

[0051] 1) Treatment of the metal substrate: Select a metal substrate such as aluminum alloy or titanium, and first perform degreasing treatment. Place the metal sample in an acetone solution and treat it in a water bath at 60°C for 20 minutes, then rinse with clean water. Next, use fine and coarse sandpaper to polish the surface of the metal substrate to increase the surface roughness and increase the bonding area.

[0052] 2) Selection of fiber prepreg layer: Epoxy resin-based carbon fiber prepreg is selected as the fiber prepreg. Since an epoxy resin matrix is ​​used, the interface reinforcement film layer 2 does not need to use a high-temperature resistant polymer material, and a polyimide film with good thermal and chemical stability can be selected.

[0053] 3) Microcapsule preparation: To reduce the porosity of the resin and improve its density, the microcapsule particle size needs to be sufficiently small. Polyurethane microcapsules were prepared using a microemulsion system combined with interfacial polymerization. Prepolymer preparation: A mixture of p-toluene diisocyanate, cyclohexanone, and butanediol in a mass ratio of 1:6.5:0.2 was prepared. The p-toluene diisocyanate was dissolved in the cyclohexanone solution. While slowly adding butanediol, the solution was heated and stirred at 70°C. After complete reaction, the prepolymer was obtained by distillation.

[0054] Isophorone diisocyanate (IPDI) was dissolved in ethyl acetate at a ratio of 3.5:1 as the core material and prepolymer to form an oil phase, and the mixture was stirred thoroughly.

[0055] Mix deionized water and emulsifier (natural emulsifier O / W) and stir thoroughly to form an emulsion;

[0056] The oil phase is added to the emulsion at an appropriate rate to form an oil-in-water (O / W) emulsion system;

[0057] Then, butylene glycol was slowly added, the entire system was heated to 60°C and stirred at 1500 rpm for 1.5 hours to obtain a microcapsule suspension;

[0058] After washing, filtration and vacuum drying, microcapsule samples with a diameter of 2 to 5 micrometers were obtained that met the requirements.

[0059] 4) Preparation of microcapsule coating: The microcapsule sample was mixed with epoxy resin-based varnish, wherein the mass fraction of the microcapsule sample was 1.5 wt%. After mixing, it was coated on the fiber prepreg layer and allowed to dry.

[0060] 5) Shaping and Curing: The fiber prepreg layer containing the microcapsule coating, along with the polyimide film and metal substrate, is placed in a vacuum bag and hot-pressed for curing (130-140℃) until the desired shape is formed, resulting in a fiber-metal laminate with an added microcapsule self-healing layer. During this process, a certain pressure is applied, but it will not cause the microcapsule shells to rupture or the IPDI core material to leak.

[0061] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A fiber-metal laminate with an added microcapsule self-healing layer, comprising a metal substrate layer, an interface-reinforcing film layer, and a fiber prepreg layer, characterized in that, The fiber-metal laminate further includes a microcapsule coating. The laminate employs an alternating layer structure of metal substrate layer / interface reinforcement film layer / microcapsule coating / fiber prepreg layer / microcapsule coating / interface reinforcement film layer / metal substrate layer. The metal substrate layer is at least one of aluminum alloy, magnesium alloy, and titanium alloy, with a thickness not exceeding 0.5 mm. The fiber prepreg layer is composed of fibers and resin, and the fibers are at least one of glass fiber, carbon fiber, and aramid fiber. The resin is a thermosetting epoxy resin. The microcapsule coating is uniformly applied to both sides of the fiber prepreg layer by a coating method. The microcapsule coating is formed by dispersing micron-sized microcapsules in an epoxy resin-based varnish through stirring or ultrasonication followed by coating. The microcapsules are internally encapsulated. The compound is isocyanate (IPDI), the capsule shell material is polyurethane, and the micron-sized microcapsules account for 1.5 wt% of the epoxy resin-based varnish; the thickness of the microcapsule coating is tens of micrometers; the average diameter of the micron-sized microcapsules is 2-5 μm, and the micron-sized microcapsules do not agglomerate in the epoxy resin-based varnish and can be uniformly dispersed on the fiber prepreg layer; the preparation method of the fiber metal layer includes the following steps: 1) Treatment of the metal substrate: the metal substrate is degreased, and then polished with fine and coarse sandpaper; 2) Selection of fiber prepreg layer: epoxy resin-based fiber prepreg is selected, and polyimide film is selected for the interface reinforcement film layer; 3) Preparation of microcapsules: a microemulsion system combined with interfacial polymerization is used. The process for preparing polyurethane microcapsules includes: Prepolymer preparation: A mixture of p-toluene diisocyanate, cyclohexanone, and butanediol in a mass ratio of 1:6.5:0.2 is prepared. P-Toluene diisocyanate is dissolved in cyclohexanone. While slowly adding butanediol, the solution is heated and stirred at 60-80°C. After sufficient reaction, the prepolymer is obtained by distillation. Isophorone diisocyanate (IPDI) is used as the core material and dissolved in ethyl acetate at a ratio of 3.5:1 with the prepolymer to form an oil phase, which is then thoroughly stirred. Deionized water and an emulsifier are mixed and thoroughly stirred to form an emulsion. The oil phase is added to the emulsion at an appropriate rate to form an oil-in-water (O / W) emulsion system. Butanediol is then slowly added, and the entire system is heated to 60°C and heated to 1500°C. Stirring at rpm for 1.5 hours yields a microcapsule suspension; after washing, filtration, and vacuum drying, microcapsule samples with a diameter of 2-5 μm are obtained; 4) Preparation of microcapsule coating: The microcapsule sample is mixed with epoxy resin-based varnish, wherein the mass fraction of the microcapsule sample is 1.5 wt%, and after mixing, it is coated onto the fiber prepreg layer and dried; 5) Shaping and curing: The fiber prepreg layer containing the microcapsule coating, polyimide film, and metal substrate are placed in a vacuum bag and hot-pressed for curing until the desired shape is formed, obtaining a fiber metal plate with added microcapsule self-healing layer; The hot-pressing curing temperature is 130-140℃, and the applied pressure will not cause the microcapsule shell to rupture or the IPDI core material to leak.

2. The fiber-reinforced metal laminate according to claim 1, characterized in that, The fiber layup angle in the fiber-metal laminate is 0°, 90°, or ±45°; the micron-sized microcapsules are spherical and have a core-shell structure.

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