Structure design and forming method for improving the interface bonding strength of fiber-metal hybrid materials

Abstract

The structure design and forming method for improving the interface bonding strength of fiber-metal heterogeneous material is a kind of composite forming process which is obtained by optimizing the combination of metal plastic forming, metal plate machining, fiber prepreg laying, composite laminate densification treatment and thermal curing treatment technology. Firstly, the multi-layer metal plate is formed by using metal plastic forming die and device; then, the multi-layer metal plate is machined according to the designed processing trajectory to form the local structure with meshing features; then, the metal plate is chemically treated on the surface to passivate; then, the fiber metal composite laminate obtained according to the designed laying mode is subjected to densification treatment in the forming device to make the fiber prepreg fill the metal local features and ensure the uniformity of the fiber prepreg laying thickness; finally, the fiber metal composite preform is subjected to vacuum bag-autoclave hot pressing process to obtain the fiber metal composite laminate part with high structural integration.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of forming of fiber metal multi-heterogeneous composite laminates, in particular to a local structure design and forming method of a laminate with improved interfacial bonding strength between fiber layers and metal layers. BACKGROUND

[0002] Fiber metal laminates (FMLs) are a kind of interlaminar hybrid composites formed by alternating layers of fiber reinforced resin-based composites and metal substrates, which are cured under certain temperature and pressure, also known as super hybrid laminates. FMLs combine the high strength, low density characteristics, good fatigue resistance, corrosion resistance and flame resistance of fiber reinforced resin-based composites, and also have good ductility and processability of metals. FMLs have been successfully applied in the field of aerospace due to their excellent comprehensive performance, and FMLs have developed four generations so far.

[0003] The interfacial bonding strength between the layers in the fiber metal laminates makes the composite laminate structure have high integrity and uniformity, so that the excellent mechanical and physical properties of each component can be maximally utilized. The interfacial bonding of composites has various forms, including mechanical bonding, chemical bonding, molecular bonding and diffusion bonding. FMLs have multiple interfaces, the fiber layers are bonded by chemical bonds and molecular bonds formed by resin curing, and the metal layers and fiber layers are mainly bonded by mechanical engagement, which mainly affects the interlaminar shear resistance and peel resistance of the fiber metal laminates, and the former has stronger bonding force than the latter. Poor interfacial performance can cause delamination damage, which in turn causes the overall stiffness and strength of the FMLs to decrease, so improving the interfacial bonding performance of fiber layers / metal layers is of great significance in practical engineering. The mechanical engagement process between the metal layers and the fiber layers is actually a connection process achieved through mechanical adhesion, which mainly involves the filling of liquid adhesive into the etch pits or holes on the surface of the metal layer, followed by solidification to produce engagement connection or anchoring effect. The connection force is unrelated to the intermolecular force between the adhesive and the adherend, and is often greatly affected by the surface roughness of the metal layer and the local features of the part. When the fiber metal laminates are subjected to external alternating loads, the metal layers and the fiber layers are prone to debonding and delamination, which weakens the overall interlaminar shear resistance of the laminates and seriously affects the overall strength and stiffness of the composite laminates, thereby limiting the application of fiber metal laminates to parts such as aircraft wings and fuselages, and developing composite laminates with excellent interlaminar shear resistance and forming methods are particularly important in the field of aerospace. SUMMARY

[0004] In order to solve the above problems, the purpose of the present application is to provide a structure design and forming method for improving the interface bonding strength of fiber-metal heterogeneous materials, covering metal plastic forming, metal plate machining, fiber pre-impregnated layer laying, composite laminate densification treatment and heat curing treatment technology, which can realize the improvement of the interlaminar shear resistance of fiber reinforced metal laminate.

[0005] In order to achieve the above purpose, the structure design and forming method for improving the interface bonding strength of fiber-metal heterogeneous materials provided by the present application comprises the following steps in order:

[0006] 1) First, according to the designed fiber metal composite laminate part structure, the number of metal laminates is selected, and then the four edges are aligned and stacked. The neatly stacked metal laminates are placed in a forming device with an upper die and a lower die. The upper die moves downward with the movement device and closes with the lower die, and at the same time the forming device applies a certain pressure to the upper die and the lower die, so that the metal laminates are plastically deformed and adhere to the die surface to obtain the required shape of the metal part. The metal layers in the fiber metal laminate are laid with a certain thickness of fiber pre-impregnated material, so the curvature radius of each layer of metal laminate part after forming is different. Using traditional metal plastic forming process, different forming dies are needed to form each layer of metal part, which increases the production cost and the forming process. Taking the multi-layer plate integral forming, then according to the local structure design form and the thickness of the fiber pre-impregnated material, the metal laminate is machined, which can realize the different curvatures of different metal laminates, greatly saving the production cost.

[0007] 2) Place the obtained multi-layer metal part in the machining center, design the machining path of the tool according to the thickness of the fiber pre-impregnated material between the metal laminates and the interlaminar shear stress distribution theoretical model, and process the tooth-like local structure on the contact surface of the adjacent two metal laminates. Through the structure form of mechanical engagement, the purpose of increasing the tangential resistance of heterogeneous materials and reducing the risk of delamination and debonding of composite materials is achieved, which can play the role of fiber pre-impregnated material and improve the overall performance of fiber metal laminate. At the same time, continuous machining of multi-layer metal parts can ensure the accuracy of local structure engagement, so that the thickness of fiber pre-impregnated material is uniform when laid between metal layers, and the integrity and continuity of fiber metal laminate structure and performance are realized.

[0008] 3) The surface of the machined metal part is cleaned with acetone, and then surface phosphoric acid anodization treatment is carried out, which comprises five processes in sequence, namely, alkaline cleaning, deoxidization, phosphoric acid anodization, rinsing and drying. After the surface of the metal part is treated by the phosphoric acid anodization, nanoscale rough morphology is generated, which can provide more contact area when contacting with the fiber prepreg, and can improve the bonding performance of the metal layer and the resin interface in the fiber prepreg to some extent. Meanwhile, the resin is embedded into the holes like a "fiber", and when subjected to external force to produce delamination expansion, the "fiber" is destroyed at the same time, and the stress concentration of the crack tip in the interface layer is also relieved, so that the fiber-metal interface can absorb more energy when the crack expands, and the "reinforcing" effect of the fiber prepreg is more obvious.

[0009] 4) The fiber prepreg layer plate is placed between the metal parts subjected to mechanical machining and surface chemical treatment according to the designed layup mode, to form a fiber metal composite part. Then, the fiber metal composite part is placed in a forming device of a shaped metal part, the upper die moves downward to close the lower die, and the forming device applies a certain pressure to the upper die and the lower die, so that a fiber metal composite layer plate preform part with uniform thickness, good bonding quality and compactness is obtained. Because of the local engagement structure of the metal part, the equipment working load is limited by using the traditional vacuum bag-hot press forming method, and under a certain pressure, the fiber prepreg cannot overcome the large flow resistance and cannot completely fill the local structure of the metal, resulting in discontinuity of the composite layer plate structure and function. The fiber metal composite layer plate preform part is compacted by a mechanical device before heat curing, which can ensure that the fiber prepreg fills the local features on the metal layer plate under the action of external mechanical pressure, and a compact composite layer plate part is obtained.

[0010] 5) The compact and continuous fiber metal composite layer plate preform part obtained in step 4) is made into a vacuum bag system, and then placed in a hot press tank, and temperature T and pressure P are set to make the fiber prepreg cure to obtain a compact and practical fiber metal composite layer plate part.

[0011] The structure design and forming method for improving the bonding strength of the fiber-metal heterogeneous material interface provided by the application is based on the interlaminar shear failure mechanism of the fiber metal layer plate, and from the aspects of structure design and forming, a composite process covering metal plastic forming, metal plate machining, fiber prepreg layup, composite layer plate densification treatment and heat curing treatment is provided. The purpose is to design and manufacture a local structure which can realize the compact bonding of the fiber layer and the metal layer, increase the relative sliding resistance between the two materials, improve the interlaminar shear resistance, and ultimately improve the service performance and life of the composite layer plate. At the same time, the energy consumption of the aircraft and weapon equipment is reduced, and the endurance and maneuverability are greatly improved, which has important national defense significance.

[0012] The definition is: first, according to the laminated structure of the fiber metal composite part, the number of metal laminates is determined, the whole plastic forming scheme is adopted, all metal laminates are formed at one time, and the mechanical processing of the adjacent two metal parts is carried out according to the thickness and local structure characteristics of the fiber prepreg, that is, the metal laminates with different layers and different curvature radii can be obtained, which can save the number of metal forming molds and production cost; then, according to the interlaminar shear stress theoretical distribution model, the local characteristics of the metal laminates are designed, the heterogeneous materials still maintain good bonding quality under the action of tangential load, and the risk of delamination and debonding is reduced. Combined with the material thickness of the fiber prepreg, the local feature processing of the metal laminate is completed by the machining center at the same time, the different curvature radii of different laminates are realized, so that when the fiber metal composite part is cured, the fiber prepreg has uniform thickness between the metal layers, which ensures the integrity and continuity of the fiber metal laminate structure and performance; then, the surface of the metal laminate processed by the machining center is subjected to phosphoric acid anodic oxidation treatment, so that it is passivated, the roughness is increased, and the contact area between the metal layer and the resin layer is increased, realizing the "micro-mechanical bonding" and "physical-mechanical locking" effect between the two, and improving the interfacial bonding capacity between the two; then, the fiber prepreg is placed and combined with the metal laminate subjected to surface chemical treatment according to the designed layering scheme, to form a fiber metal composite part, which is placed in a forming device provided with an upper mold and a lower mold, the mold is closed and a certain pressure is applied, the fiber layer and the metal layer are bonded together, because the load is uniformly applied, the consistency of the thickness of the fiber prepreg can be ensured, and a complete fiber metal composite laminate preform part is formed. Because of the local tooth-shaped features on the metal laminate, the pressure value is small, and the traditional vacuum bag-hot press tank hot pressing technology cannot meet the requirement of completely filling the local features of the fiber prepreg during the layering process of the fiber layer and the metal layer; finally, the compacted fiber metal composite laminate preform part is subjected to vacuum bag-hot press tank hot pressing process under the action of temperature T and pressure P, the fiber prepreg is completely cured, and a practical fiber metal composite laminate part with improved interlaminar shear resistance is formed.

[0013] Fiber metal laminates combine the high strength, low density characteristics of fiber reinforced resin matrix composites, good fatigue resistance, corrosion resistance and flame resistance, etc. performance, while the metal has good ductility, processability, has excellent comprehensive performance, but due to the adhesion between metal and resin, mainly rely on the "micro-mechanical adhesion" and "physical-mechanical locking" between the two, resulting in the problem of weak shear resistance of fiber-metal interface. Through the structure design and forming method of improving the bonding strength of fiber-metal heterogeneous material interface, the key technologies such as high-efficiency forming of metal laminates, precision machining of multi-layer metal local structure, densification control of fiber prepreg layer, integration of forming and structure design, etc. can be broken through, the application range of high-performance lightweight materials in aerospace and national defense industry field can be expanded, which has important national defense and military strategic significance. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 The structure design and forming method of improving the bonding strength of fiber-metal heterogeneous material interface provided by the present application;

[0015] Figure 2 The multi-layer metal plate one-time forming process provided by the present application;

[0016] Figure 3 The multi-layer metal plate local structure mechanical machining process provided by the present application;

[0017] Figure 4 The metal part surface treatment process provided by the present application;

[0018] Figure 5 The fiber prepreg layer and composite laminate densification treatment process provided by the present application;

[0019] Figure 6 The vacuum bag-heat press tank heat curing treatment process of the fiber metal composite prefabricated part provided by the present application.

[0020] In the figure: 1 - multi-layer raw metal plate material, 2 - metal plate forming upper die, 3 - metal plate forming lower die, 4 - metal plate forming device, 5 - multi-layer metal plate part, 6 - local structure section machining profile, 7 - multi-layer metal plate part with local structure, 8 - multi-layer metal plate part with local structure after surface treatment, 9 - fiber prepreg layer, 10 - fiber metal composite laminate prefabricated part, 11 - vacuum bag system, 12 - heat press tank. DETAILED DESCRIPTION

[0021] The structure design and forming method of improving the bonding strength of fiber-metal heterogeneous material interface provided by the present application will be described in detail below in combination with the drawings and specific embodiments.

[0022] As Figure 1 -Figure 6 As shown, the structural design and forming method for improving the interface bonding strength of fiber-metal heterogeneous material provided by the present application comprises the following steps in sequence:

[0023] 1) According to the designed structure of the fiber-metal composite panel part, the number of metal panels is selected, and then the four edges are aligned and stacked. The neatly stacked multi-layer raw metal panel (1) is placed in the forming device (4) with the upper die (2) and the lower die (3), the upper die (2) moves downward with the movement device and closes with the lower die (3), at the same time, the forming device (4) applies a certain pressure to the upper die (2) and the lower die (3), so that the multi-layer raw metal panel (1) is plastically deformed and adheres to the die surface to obtain a multi-layer metal panel part (5) with the required shape.

[0024] 2) The multi-layer metal panel part (5) obtained in step 1) is placed in the machining center, and the local structure cross-section machining profile (6) is designed according to the fiber prepreg thickness between the metal panels and the interlaminar shear stress distribution theoretical model, and the tooth-like local structure is machined on the contact surface of the adjacent two metal panels in the longitudinal direction L of the metal panel to obtain a multi-layer metal panel part (7) with local structure.

[0025] 3) The surface dirt of the multi-layer metal panel part (7) with local structure is removed with acetone, and then surface phosphoric acid anodizing treatment is carried out, which sequentially includes five processes of alkali washing, deoxidation, phosphoric acid anodizing, rinsing and drying, to obtain a multi-layer metal panel part (8) with local structure after surface treatment. After the surface of the metal part is treated by phosphoric acid anodizing, a nano-scale rough morphology is generated, which can provide more contact area when contacting with the fiber prepreg, and can improve the bonding performance of the metal layer and the resin interface in the fiber prepreg to a certain extent.

[0026] 4) The fiber prepreg panel (9) is placed between the metal parts after mechanical machining and surface chemical treatment according to the designed lay-up method to form a fiber-metal composite panel part. Then, the fiber-metal composite panel part is placed in the metal panel forming device (4), the upper die (2) moves downward to close with the lower die (3), at the same time, the forming device (4) applies a certain pressure to the upper die (2) and the lower die (3), so as to obtain a fiber-metal composite panel preform part (10) with uniform thickness, good bonding quality and good compactness.

[0027] 5) The compact and structure continuous fiber-metal composite panel preform part (10) obtained in step 4) is placed in the vacuum bag system (11), and then placed in the autoclave (12) after vacuumizing and sealing, and the fiber prepreg is cured by setting the temperature T and pressure P, so as to obtain a fiber-metal composite panel part with practical value and compact structure.

Claims

1. A method for improving the interfacial bond strength of a fiber-metal hybrid material, characterized by: The composite process of the optimized combination of metal plastic forming, metal plate mechanical processing, fiber prepreg layering, composite layer densification treatment and thermal curing treatment comprises the following steps in sequence: 1) According to the designed structure of the fiber metal composite layer part, the number of metal layers is selected, then the four edges are aligned and stacked, and the neatly stacked multi-layer raw metal plate (1) is placed in the forming device (4) with the upper die (2) and the lower die (3), the upper die (2) moves downward with the movement device and closes with the lower die (3), at the same time, the forming device (4) applies a certain pressure to the upper die (2) and the lower die (3), so that the multi-layer raw metal plate (1) is plastically deformed and adheres to the die profile, and a multi-layer metal plate part (5) with the required shape is obtained; 2) The multi-layer metal plate part (5) obtained in step 1) is placed in the machining center, and the local structure cross-section machining profile (6) is designed according to the fiber prepreg thickness between the metal layers and the interlaminar shear stress distribution theoretical model, and the tooth-shaped local structure is machined on the contact surface of the adjacent two metal layers in the longitudinal direction L of the metal layer, and a multi-layer metal plate part (7) with local structure is obtained; 3) The surface dirt of the multi-layer metal plate part (7) with local structure is removed with acetone, and then surface phosphoric acid anodizing treatment is carried out, which sequentially includes five processes of alkali washing, deoxidization, phosphoric acid anodizing, rinsing and drying, to obtain a multi-layer metal plate part (8) with local structure after surface treatment, and after the surface of the metal part is treated by phosphoric acid anodizing, a nano-scale rough morphology is generated, which can provide more contact area when contacting with the fiber prepreg, and can improve the bonding performance of the metal layer and the resin interface in the fiber prepreg to a certain extent; 4) The fiber prepreg layer (9) is placed between the metal parts treated by mechanical processing and surface chemical treatment according to the designed layering method to form a fiber metal composite layer part, and then the fiber metal composite layer part is placed in the metal plate forming device (4), the upper die (2) moves downward to close with the lower die (3), at the same time, the forming device (4) applies a certain pressure to the upper die (2) and the lower die (3), so as to obtain a fiber metal composite layer preform part (10) with uniform thickness, good bonding quality and good density; 5) The compact and structure continuous fiber metal composite layer preform part (10) obtained in step 4) is placed in the vacuum bag system (11), and the vacuum bag system (11) is sealed after vacuumizing, and then placed in the hot press tank (12), and the fiber prepreg is cured by setting the temperature T and the pressure P, so as to obtain a practical fiber metal composite layer part with compact structure.

2. The method of claim 1, wherein: The metal layers in the fiber metal laminates are laid with a certain thickness of fiber prepreg, so the curvature radius of each layer of the metal laminates after forming is different. Using traditional metal plastic forming process, different forming dies are needed to form each layer of metal parts, which increases the production cost and forming process. Taking the multi-layer plate one-time integral forming, and then according to the local structure design form and the thickness of the fiber prepreg, the metal laminates are machined, which can realize the different curvatures of different metal laminates, and greatly save the production cost.

3. The method of claim 1, wherein: The mechanical engagement structure form obtained by machining center on the multi-layer metal plate parts can achieve the effect of increasing the tangential resistance of heterogeneous materials, reducing the risk of delamination and debonding of composite materials, and playing the role of fiber prepreg reinforcement, realizing the purpose of improving the overall performance of fiber metal laminates.

4. The method of claim 1, wherein: Synchronous and continuous processing of multi-layer metal plate parts can ensure the accuracy of local structure engagement, so that the thickness of fiber prepreg is uniform when laid between metal layers, and realize the integrity and continuity of fiber metal laminate structure and performance.

5. The method of claim 1, wherein: Because of the special local engagement structure on the metal plate parts, when using traditional vacuum bag-hot press tank hot pressing process for the thermal curing treatment of fiber metal laminates, due to the limited working load capacity of the equipment, the fiber prepreg cannot overcome the large flow resistance and cannot completely fill the local structure of the metal plate parts, which affects the final thermal curing effect of the composite laminates. Before thermal curing, the fiber metal composite laminate preform parts are compacted by mechanical device, which can ensure that the fiber prepreg fills the local features on the metal plate under the action of external mechanical pressure, and obtain a composite laminate part with dense structure. Then, using the traditional vacuum bag-hot press tank process, a fiber metal composite laminate part with uniform and dense structure and continuous performance can be obtained, the interlaminar shear resistance is improved, and the service performance and service life of the material are further improved.

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