Thermoplastic composite corrugated sandwich structure and welding method thereof

Abstract

The invention discloses a thermoplastic composite material corrugated sandwich structure and a welding method thereof, and relates to the technical field of ultrasonic welding, the corrugated sandwich structure comprises a thermoplastic composite material upper panel, a thermoplastic composite material core layer and a thermoplastic composite material lower panel; the thermoplastic composite material upper panel is welded above the thermoplastic composite material core layer through an energy transmission film; and the thermoplastic composite material lower panel is welded below the thermoplastic composite material core layer through an energy transmission film. Original achievements are obtained in the aspects of design and manufacturing and mechanical property characterization of the thermoplastic composite material sandwich structure, and guidance is provided for engineering application of the thermoplastic composite material sandwich structure.

Description

Technical Field

[0001] The invention belongs to the technical field of ultrasonic welding, and in particular relates to a thermoplastic composite material corrugated sandwich structure and a welding method thereof. Background Art

[0002] Ultrasonic welding is a technology for quickly connecting thermoplastic composite materials, which has the characteristics of high strength, short cycle, and no interface heterogeneity. The welding head applies 20kHz high-frequency and 20μm-100μm low-amplitude mechanical vibration to the welding interface, and generates heat at the welding interface through surface friction and viscoelastic heating, which causes the energy-conducting item to melt on the welding surface to form a weld.

[0003] Existing studies have shown that the single lap shear test is the most typical experimental method to characterize the mechanical properties of ultrasonic welded interfaces. In contrast, other mechanical characterization methods are very rare. The results show that when subjected to shear loads, the bearing capacity of spot welded joints is comparable to that of high-lock bolts of the same size, and has higher structural connection stiffness. In addition, the failure modes of the welded interfaces under the two load conditions are also significantly different. At present, due to the limitations of the welding process on the structural configuration, the experimental characterization methods for the mechanical properties of TPC ultrasonic welded structures are still very simple. In addition, although TPC has excellent fracture toughness and impact resistance, research on the dynamic response and failure mechanism of its welded structure under impact loads is still a blank. Summary of the invention

[0004] The present invention aims to solve the deficiencies of the prior art and provides the following solutions:

[0005] A thermoplastic composite corrugated sandwich structure, comprising: a thermoplastic composite upper panel, a thermoplastic composite core layer and a thermoplastic composite lower panel;

[0006] The thermoplastic composite upper panel is welded above the thermoplastic composite core layer through an energy transmission film;

[0007] The thermoplastic composite lower panel is welded below the thermoplastic composite core layer via an energy transmission membrane.

[0008] Preferably, the core layer of the thermoplastic composite material is any one of a corrugated structure, a lattice structure and a honeycomb structure.

[0009] Preferably, the material of the energy transmission membrane is a thermoplastic resin or a fiber-reinforced thermoplastic composite material;

[0010] The matrix of the thermoplastic resin is any one of polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyamide, polyoxymethylene, polycarbonate, polyetheretherketone, polyphenylene ether, polysulfone, and rubber;

[0011] The fiber in the fiber-reinforced thermoplastic composite material is any one of glass fiber, carbon fiber, graphite fiber, boron fiber, ceramic fiber, polyethylene fiber, polyamide fiber, PBO fiber and natural fiber.

[0012] The present invention also provides a welding method for a thermoplastic composite corrugated sandwich structure, the welding method is used to weld the corrugated sandwich structure described in any one of the above items, and comprises the following steps:

[0013] placing the energy transmission membrane between the upper thermoplastic composite material panel and the thermoplastic composite material core layer, and between the lower thermoplastic composite material panel and the thermoplastic composite material core layer;

[0014] Fixing the thermoplastic composite material core layer to the thermoplastic composite material upper panel and the thermoplastic composite material lower panel respectively by means of a fixture;

[0015] Based on a preset ultrasonic welding thermal-mechanical coupling model, setting working parameters of the ultrasonic generator, as well as the thicknesses of the thermoplastic composite upper panel, the thermoplastic composite core layer, the thermoplastic composite lower panel and the energy transmission membrane;

[0016] Melting the energy transmission film at the interface by an ultrasonic generator and applying pressure simultaneously;

[0017] The fixture is removed, and the connection between the face and the core is welded to obtain the thermoplastic composite material corrugated sandwich structure.

[0018] Preferably, the ultrasonic welding thermal-mechanical coupling model includes:

[0019] At the beginning of welding, the energy transfer film and the surface of the composite material produce interface friction under high-frequency ultrasonic oscillation, which is expressed by the Coulomb friction equation:

[0020]

[0021] Among them, Q fric is the interface friction heat dissipation, α is the hammer coefficient, ω is the vibration frequency, μ is the friction system, σ yy (x) is the vertical stress on the horizontal interface, and u(x) is the displacement;

[0022] When the interface temperature generated by the interface friction is higher than the glass transition temperature of the thermoplastic polymer, the energy transfer film begins to melt, and the heat generation mechanism is transformed into the viscoelastic flow of the thermoplastic polymer chain molecules, which is expressed by the viscoelastic flow equation:

[0023]

[0024] Among them, Q visco is the viscoelastic heat dissipation, E′ is the loss modulus of the material, ε * is the strain tensor, and α is the hammer coefficient.

[0025] Preferably, the working parameters of the ultrasonic generator include: the working frequency is 20kHz, the ultrasonic amplitude is 50μm-100μm, and the magnitude of the applied pressure is 800N.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention proposes to use ultrasonic welding technology to connect thermoplastic composite corrugated sandwich structures, establish a thermal-mechanical coupling model at the ultrasonic welding interface of thermoplastic composite corrugated sandwich structures, clarify the influence of process parameters and structural configuration on the thermodynamic behavior of the interface, develop process mechanics and quality evaluation methods for ultrasonic welding of thermoplastic composite corrugated structures, reveal the inherent response law between welding process and structural strength, carry out out-of-plane compression and drop hammer impact experiments to characterize the mechanical properties of welded corrugated structures, and reveal the failure mode and destruction mechanism of the structure; the present invention obtains original results in the design and manufacture of thermoplastic composite sandwich structures and the characterization of mechanical properties, and provides guidance for their engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0029] Figure 1 This is a schematic diagram of a single corrugated sandwich structure according to an embodiment of the present invention;

[0030] Figure 2 A schematic diagram of a welding method flow chart of an embodiment of the present invention;

[0031] Figure 3 A flowchart of a welding method according to an embodiment of the present invention;

[0032] Figure 4 This is a schematic diagram of welding the core layer and the lower panel according to an embodiment of the present invention;

[0033] Figure 5 Schematic diagram of welding the core layer and the upper panel according to an embodiment of the present invention.

[0034] Description of reference numerals:

[0035] 1. Ultrasonic generator; 2. Thermoplastic composite upper panel; 3. Energy transmission membrane; 4. Thermoplastic composite core layer; 5. Thermoplastic composite lower panel; 6. Fixture; 7. Support block. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] Embodiment 1

[0039] In this embodiment, if Figure 1 As shown, a thermoplastic composite corrugated sandwich structure comprises: a thermoplastic composite upper panel 2, a thermoplastic composite core layer 4 and a thermoplastic composite lower panel 5. The thermoplastic composite upper panel 2 is welded to the upper part of the thermoplastic composite core layer 4 through an energy transmission membrane 3; the thermoplastic composite lower panel 5 is welded to the lower part of the thermoplastic composite core layer 4 through an energy transmission membrane 3.

[0040] The thermoplastic composite core layer 4 is any one of a corrugated structure, a lattice structure, and a honeycomb structure. The material of the energy transfer membrane 3 is a thermoplastic resin or a fiber-reinforced thermoplastic composite material, wherein the matrix of the thermoplastic resin is any one of polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyamide, polyoxymethylene, polycarbonate, polyetheretherketone, polyphenylene ether, polysulfone, and rubber, and the fiber in the fiber-reinforced thermoplastic composite material is any one of glass fiber, carbon fiber, graphite fiber, boron fiber, ceramic fiber, polyethylene fiber, polyamide fiber, PBO fiber, and natural fiber.

[0041] Due to the presence of the core layer between the upper and lower panels, the sandwich structure has a greater specific stiffness than a single-layer solid structure of equal mass, and can thus withstand higher static loads. When subjected to out-of-plane loads such as compression and impact, the core layer structure will undergo plastic deformation such as bending and buckling, thereby absorbing a large amount of energy. Therefore, the sandwich structure has a better energy absorption effect than the traditional laminate structure.

[0042] Embodiment 2

[0043] In this embodiment, if Figure 2 , Figure 3 , Figure 4 and Figure 5 As shown, a welding method for a thermoplastic composite corrugated sandwich structure comprises the following steps:

[0044] S1. An energy transmission membrane 3 is placed between the upper thermoplastic composite panel 2 and the thermoplastic composite core layer 4 and between the lower thermoplastic composite panel 5 and the thermoplastic composite core layer 4.

[0045] S2. Fix the thermoplastic composite core layer 4 to the thermoplastic composite upper panel 2 and the thermoplastic composite lower panel 5 respectively by means of a fixture 6. In this embodiment, a support block 7 is also used to support the thermoplastic composite core layer 4.

[0046] S3. Based on the preset ultrasonic welding thermal-mechanical coupling model, set the working parameters of the ultrasonic generator 1, as well as the thicknesses of the thermoplastic composite upper panel 2, the thermoplastic composite core layer 4, the thermoplastic composite lower panel 5 and the energy transfer membrane 3.

[0047] The thermal-mechanical coupling model of ultrasonic welding includes: at the initial stage of welding, the energy transmission membrane 3 and the surface layer of the composite material produce interface friction under high-frequency ultrasonic oscillation, which is expressed by the Coulomb friction equation:

[0048]

[0049] Among them, Q fric is the interface friction heat dissipation, α is the hammer coefficient, ω is the vibration frequency, μ is the friction system, σ yy (x) is the vertical stress of the horizontal interface, and u(x) is the displacement. When the interface temperature generated by the interface friction is higher than the glass transition temperature of the thermoplastic polymer, the energy transfer film 3 begins to melt, resulting in the activation of the thermoplastic polymer chain molecules. The heat generation mechanism is transformed into the viscoelastic flow of the thermoplastic polymer chain molecules, which is expressed by the viscoelastic flow equation:

[0050]

[0051] Among them, Q visco is the viscoelastic heat dissipation, E′ is the loss modulus of the material, ε * is the strain tensor, and α is the hammer coefficient. The working parameters of the ultrasonic generator 1 include: the working frequency is 20kHz, the ultrasonic amplitude is 50μm-100μm, and the applied pressure is 800N.

[0052] In order to numerically model the surface-core connection of the corrugated sandwich structure, the following Figure 1configuration. The model mainly includes three parts: ultrasonic welding head, TPC upper and lower panels and core layer, and energy transfer membrane 3 at the interface. The composite material plate and the core layer use the same material parameters, and the energy transfer membrane 3 uses the same material resin. Modeling is performed using the finite element software COMSOL Multiphysics. In order to improve the computational efficiency, a 1 / 2-size two-dimensional model is constructed according to the symmetry of the configuration. It consists of the upper composite attachment, half of the lower core layer, and 1 / 2 of the energy transfer membrane 3. At the same time, the ultrasonic welding head applies uniform pressure and vertical displacement on the top of the panel. At the same time, horizontal boundary condition constraints are imposed on the panel, and horizontal and vertical constraints are imposed on the core layer to ensure the stability of the structure during vibration. Among them, the friction heat source and the elastic thin layer are applied to the contact interface between the energy transfer membrane 3 and the panel and core layer, and the viscoelastic heat source is applied to the energy transfer membrane 3. All couplings are processed using the Newton iteration method to ensure a strict solution at the convergence. Large geometric changes are handled within the Euler framework. When the lowest temperature in the film exceeds T m The resolution stops at ℃. Under the same welding conditions, that is, the welding pressure is 800N and the maximum amplitude is 4μm, we carried out numerical simulations on core layers with different thicknesses (1mm, 2mm, 3mm) and energy conduction terms with different thicknesses (0.2mm, 0.4mm, 0.5mm) to analyze their effects on the temperature field of the corrugated sandwich structure.

[0053] S4. The energy transmission film 3 is melted at the interface by the ultrasonic generator 1, and pressure is applied simultaneously.

[0054] S5. Remove the fixture 6 and weld the connection between the face and the core to obtain a thermoplastic composite corrugated sandwich structure.

[0055] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A thermoplastic composite corrugated sandwich structure, characterized in that: include: A thermoplastic composite upper panel, a thermoplastic composite core layer, and a thermoplastic composite lower panel; The thermoplastic composite upper panel is welded above the thermoplastic composite core layer through an energy transmission film; The thermoplastic composite lower panel is welded below the thermoplastic composite core layer via an energy transmission membrane.

2. A thermoplastic composite corrugated sandwich structure according to claim 1, characterized in that: The core layer of the thermoplastic composite material is any one of a corrugated structure, a lattice structure and a honeycomb structure.

3. A thermoplastic composite corrugated sandwich structure according to claim 1, characterized in that: The material of the energy transmission membrane is a thermoplastic resin or a fiber-reinforced thermoplastic composite material; The matrix of the thermoplastic resin is any one of polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyamide, polyoxymethylene, polycarbonate, polyetheretherketone, polyphenylene ether, polysulfone, and rubber; The fiber in the fiber-reinforced thermoplastic composite material is any one of glass fiber, carbon fiber, graphite fiber, boron fiber, ceramic fiber, polyethylene fiber, polyamide fiber, PBO fiber and natural fiber.

4. A welding method for a thermoplastic composite corrugated sandwich structure, the welding method being used for welding the corrugated sandwich structure according to any one of claims 1 to 3, characterized in that: The following steps are involved: placing the energy transmission membrane between the upper thermoplastic composite material panel and the thermoplastic composite material core layer, and between the lower thermoplastic composite material panel and the thermoplastic composite material core layer; Fixing the thermoplastic composite material core layer to the thermoplastic composite material upper panel and the thermoplastic composite material lower panel respectively by means of a fixture; Based on a preset ultrasonic welding thermal-mechanical coupling model, setting working parameters of the ultrasonic generator, as well as the thicknesses of the thermoplastic composite upper panel, the thermoplastic composite core layer, the thermoplastic composite lower panel and the energy transmission membrane; Melting the energy transmission film at the interface by an ultrasonic generator and applying pressure simultaneously; The fixture is removed, and the connection between the face and the core is welded to obtain the thermoplastic composite material corrugated sandwich structure.

5. A welding method for a thermoplastic composite corrugated sandwich structure according to claim 4, characterized in that: The ultrasonic welding thermal-mechanical coupling model includes: At the beginning of welding, the energy transfer film and the surface of the composite material produce interface friction under high-frequency ultrasonic oscillation, which is expressed by the Coulomb friction equation: Among them, Q fric is the interface friction heat dissipation, α is the hammer coefficient, ω is the vibration frequency, μ is the friction system, σ yy (x) is the vertical stress on the horizontal interface, and u(x) is the displacement; When the interface temperature generated by the interface friction is higher than the glass transition temperature of the thermoplastic polymer, the energy transfer film begins to melt, and the heat generation mechanism is transformed into the viscoelastic flow of the thermoplastic polymer chain molecules, which is expressed by the viscoelastic flow equation: Among them, Q visco is the viscoelastic heat dissipation, E′ is the loss modulus of the material, ε * is the strain tensor, and α is the hammer coefficient.

6. A welding method for a thermoplastic composite corrugated sandwich structure according to claim 4, characterized in that: The working parameters of the ultrasonic generator include: the working frequency is 20kHz, the ultrasonic amplitude is 50μm-100μm, and the magnitude of the applied pressure is 800N.

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