Method for preparing honeycomb sandwich structure based on laser collaborative explosion welding

Abstract

The present invention provides a method for preparing a honeycomb sandwich structure based on laser-assisted explosive welding, which belongs to the field of explosive welding technology. The method comprises: performing laser pretreatment on the surface of the honeycomb core to form a periodically distributed micron-scale pit array; constructing submicron-scale holes inside the micron-scale pit array based on nanoimprinting; applying an energetic material layer to the surface of the surface material, and utilizing the shock wave generated by the detonation of the energetic material layer to explosively weld the surface material and the pretreated honeycomb core to obtain a honeycomb sandwich structure; laser pretreatment uses femtosecond laser processing with a power density of 10 6 W / cm 2 ~10 7 W / cm 2 The pulse width is 100fs to 500fs, and the scanning path spacing is 10μm to 50μm. This invention utilizes the synergistic effects of laser pretreatment, nanoimprinting, and explosive welding to form a metallurgical bonding layer and residual compressive stress field at the interface between the honeycomb core and the surface material, inhibiting crack propagation, improving joint fatigue life, and reducing thermal damage.

Description

Technical Field

[0001] The invention belongs to the technical field of explosive welding, and in particular relates to a method for preparing a honeycomb sandwich structure based on laser-assisted explosive welding. Background Art

[0002] The honeycomb sandwich structure consists of two layers of material and a honeycomb core in the middle. It has the advantages of high material utilization, light weight, high strength, and strong impact resistance, and is therefore widely used in aerospace, construction, transportation and other fields.

[0003] In the process of preparing honeycomb sandwich structures, how to combine the honeycomb core and the surface material is a key step that affects the performance of the honeycomb sandwich structure. At present, the methods for connecting the interface of the honeycomb core and the surface material mainly include gluing and welding. The traditional gluing process has defects such as aging of the adhesive layer and high-temperature thermal damage. Welding includes brazing, laser welding, explosion welding, etc. Among them, brazing requires a fusible brazing material, which has poor heat resistance and limited bonding strength; laser welding is prone to collapse of the honeycomb core due to excessive heat input. Conventional explosion welding is suitable for welding plates with a planar contact interface; while the contact interface between the honeycomb core and the surface material in the honeycomb sandwich structure is non-planar, and the existing explosion welding technology has problems such as a large heat-affected zone, uneven interface bonding strength, and poor metallurgical compatibility of dissimilar materials. The bonding interface is prone to cracks or delamination, which reduces the bonding strength of the interface between the honeycomb core and the surface material. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a method for preparing a honeycomb sandwich structure based on laser collaborative explosion welding, aiming to solve at least one technical problem in the background technology.

[0005] The present invention is achieved in that:

[0006] The present invention provides a method for preparing a honeycomb sandwich structure based on laser collaborative explosion welding, wherein the honeycomb sandwich structure includes two groups of surface materials and a honeycomb core sandwiched between the two groups of surface materials; the method comprises the following steps:

[0007] Laser pretreatment is performed on the surface of the honeycomb core to form a periodically distributed array of micron-scale pits;

[0008] Constructing submicron-scale holes inside micron-scale pit arrays based on nanoimprinting;

[0009] An energetic material layer is coated on the surface of the face material, and the face material and the pre-treated honeycomb core are explosively welded using the shock wave generated by the detonation of the energetic material layer to form a connection interface and obtain a honeycomb sandwich structure;

[0010] The laser pretreatment adopts femtosecond laser treatment, and the power density of the femtosecond laser is 10 6 W / cm 2 ~107 W / cm 2 , the pulse width is 100fs~500fs, and the scanning path spacing is 10μm~50μm.

[0011] Preferably, the honeycomb core is made of aluminum alloy or titanium alloy; and the surface material is made of a metal-based composite material.

[0012] Preferably, the energetic material layer is made of modified ammonium nitrate explosive, metal-nitrocellulose material, RDX-polymer-based explosive or PETN-polymer-based explosive.

[0013] Preferably, in the micron-scale pit array, the pit depth is 10 μm to 200 μm, the pit diameter is set to 50 μm to 200 μm; the spacing between two pits is 1.5 to 3 times the pit diameter, and the inner wall of the pit has a multi-level rough structure.

[0014] Preferably, the outer surface of the pit is an oxide layer and the inner surface is a melt recrystallization layer.

[0015] Preferably, the diameter of the submicron pores is set to 200 nm-800 nm; the submicron pores are distributed in the interface area between the melt recrystallization layer and the matrix of the honeycomb core.

[0016] Preferably, the thickness of the energetic material layer is 10 μm-100 μm.

[0017] Preferably, the explosion velocity of the energetic material layer is controlled to be 1500m / s-3000m / s.

[0018] Preferably, the explosion shock wave pressure of the energetic material layer is controlled to be 0.5 GPa-5 GPa.

[0019] Preferably, the connection interface forms a metallurgical bonding layer and a residual compressive stress field.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention utilizes the synergistic effect of laser pretreatment, nanoimprinting and explosive welding to form a metallurgical bonding layer and a residual compressive stress field at the interface between the honeycomb core and the surface material, thereby inhibiting crack propagation, improving joint fatigue life and reducing thermal damage.

[0022] 2. The present invention forms a micro-nano structure on the surface of the honeycomb core through femtosecond laser, thereby enhancing the mechanical interlocking effect of the interface between the honeycomb core and the surface material and improving the interface connection effect.

[0023] 3. The present invention optimizes the detonation velocity of energetic materials, controls the shock wave pressure distribution and thermal-mechanical coupling effect, and suppresses the expansion of the heat-affected zone. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a demonstration diagram of the femtosecond laser scanning pretreatment of the honeycomb core surface in the present invention;

[0025] Figure 2 It is a schematic diagram of the assembly of the explosion welding operation in the present invention;

[0026] Figure 3 3 is a comparison curve of the shear strength-absolute mass density of the honeycomb core material of Example 1 and the comparative group 3. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific implementation cases described herein are only used to explain the present invention and are not intended to limit the present invention.

[0028] A method for preparing a honeycomb sandwich structure based on laser collaborative explosion welding, wherein the honeycomb sandwich structure includes two groups of surface materials and a honeycomb core sandwiched between the two groups of surface materials; the material of the honeycomb core is an aluminum alloy or a titanium alloy, and the material of the surface materials is a metal-based composite material, such as copper, stainless steel, etc.; the method includes steps S1-S3.

[0029] S1, such as Figure 1 As shown, the surface (opening surface) of the honeycomb core 2 is pretreated by using a femtosecond laser emitted by a laser 1, and a periodically distributed micron-scale pit array is formed on the surface of the honeycomb core 2;

[0030] The power density of the femtosecond laser is 10 6 W / cm 2 ~10 7 W / cm 2 , the pulse width is 100fs~500fs, and the scanning path spacing is 10μm~50μm.

[0031] In the micron-scale pit array, the pit depth is 10 μm to 200 μm, the diameter range is usually 50 μm to 200 μm, the spacing between two pits is 1.5 to 3 times the pit diameter, and the inner wall of the pit has a multi-level rough structure.

[0032] During femtosecond laser treatment of the honeycomb core 2, a composite metal layer is formed due to the laser thermal effect. Specifically, it includes a melt-recrystallized layer and an oxide layer. The oxide layer is the outermost layer covering the honeycomb core surface, which inhibits further oxidation of the honeycomb core material and improves interfacial bonding strength. The melt-recrystallized layer is located between the oxide layer and the honeycomb core surface. Its formation mechanism is the grain refinement and element segregation caused by the melting-solidification process. The grain size is ≤200nm, and the melt-recrystallized layer thickness is 10μm-50μm.

[0033] S2. Construct submicron-scale holes inside the micron-scale pit array based on nanoimprinting method.

[0034] Submicron pores mainly exist inside the melt recrystallization layer and at the interface of the honeycomb core matrix, with a pore diameter of 200nm-800nm and a surface roughness of Ra<50nm.

[0035] The periodically distributed micron-scale pits formed by S1 and the submicron-scale holes constructed by S2 form functional units of different scales but with a synergistic relationship. They are mainly used to optimize macroscopic mechanical properties, which can increase the compressive strength of the honeycomb core by 30% and the thermal stress dispersion efficiency by 40%.

[0036] S3, covering the surface of the face material with an energetic material layer, and utilizing the shock wave generated by the detonation of the energetic material layer to explosively weld the face material and the honeycomb core pretreated in S1 and S2 to form a connection interface, thereby obtaining a honeycomb sandwich structure;

[0037] Before explosive welding, a thermal-mechanical coupled finite element model can be established to determine the magnitude and distribution of the shock wave pressure generated by the explosion of the energetic material layer. This is done to match the critical shock pressure required for explosive welding and suppress the expansion of the heat-affected zone. The detonation velocity of the energetic material layer is set at 1500m / s-3000m / s, and the shock wave pressure generated by the detonation is controlled to 0.5GPa-5GPa.

[0038] The specific steps to establish the thermal-mechanical coupling finite element model are:

[0039] (1) Geometric modeling and meshing: A three-dimensional geometric model of the energetic material layer is established, including the charge structure, the constrained shell, and the contact interface. The explosion reaction zone (detonation point, interface contact zone) is locally encrypted (mesh size ≤ 0.5 mm) through a non-uniform meshing strategy, and the non-reaction zone uses a 1 mm to 3 mm mesh size to ensure computational efficiency.

[0040] (2) Multi-field coupled material constitutive model, including:

[0041] Mechanical properties: Johnson-Cook plasticity model is used to describe dynamic response;

[0042] Thermochemical properties: embedded in Arrhenius reaction kinetics equation;

[0043] Detonation products: Apply the JWL equation of state.

[0044] (3) Boundary conditions and load application, including:

[0045] Thermal boundary conditions: initial temperature 300K, explosion reaction zone is set as adiabatic boundary (heat flux density = 0);

[0046] Mechanical boundary conditions: The fixed end of the shell is fully constrained, the free end is allowed to expand and deform, and the friction coefficient of the contact interface is set to 0.2-0.4‌36;

[0047] Explosive load: Apply transient impact pressure load (pressure rise time ≤ 1μs, peak pressure ≥ 2GPa).

[0048] (4) Using the central difference method for explicit dynamics solution and verification, including:

[0049] Set the time step to ≤1μs, calculate the total time to cover the shock wave propagation to 3 times the charge diameter, and use the TNT equivalent empirical formula (Z=R / W 1 / 3 , Z represents the radius of the destruction range, R represents the equivalent of the explosive to be calculated, and W represents a constant related to the environment and target characteristics) to verify the shock wave overpressure attenuation law, with the error controlled within ±15%.

[0050] (5) Shock wave parameter calibration and output, used to extract shock wave pressure distribution characteristics:

[0051] A virtual sensor array is arranged radially along the explosion center, the pressure time history curve is recorded, the peak pressure and attenuation gradient are marked, and a three-dimensional pressure cloud map is generated to identify the maximum overpressure area (0.5D-1.5D range from the explosion center) and anisotropic distribution (axial / radial pressure ratio ≥1.5:1).

[0052] (6) Optimize the charge structure based on energy release efficiency: Use the integral method to calculate the total energy release of the chemical reaction heat source term and evaluate its proportion (if the total energy release proportion is ≥85%, it is considered qualified). Adjust the pit array distribution parameters (diameter 50μm-200μm) to improve the uniformity of the shock wave pressure by ≥30%.

[0053] The energetic material layer 6 is made of modified ammonium nitrate explosive, metal-nitrocellulose material, RDX-polymer-based explosive or PETN-polymer-based explosive. Modified ammonium nitrate explosive refers to an energetic material formed by adding a photothermal conversion agent such as aluminum powder or silicon carbide powder to ammonium nitrate explosive, which can improve the absorption efficiency of laser energy and the detonation velocity can be adjusted to 2500m / s-3000m / s. RDX-polymer-based explosive or PETN-polymer-based explosive is an energetic material combining RDX or PETN with a photosensitive resin, which can improve the material's impact resistance (fracture toughness is increased by 20%-30%). Metal-nitrocellulose material is a modified nitrocellulose film composed of a metal foil (such as aluminum foil or titanium-nickel composite foil) and nitrocellulose (NC). It has self-sustaining combustion capability when the nitrogen content is greater than 12%.

[0054] In the following embodiments, the energetic material layer 6 is illustrated by a modified nitrocellulose film formed by a composite of titanium-nickel composite foil and nitrocellulose (NC), but the invention is not limited to the materials listed, and other materials not listed are also applicable.

[0055] Since the honeycomb sandwich structure requires connecting two sets of surface materials to both open surfaces of the honeycomb core, double-sided welding can be performed simultaneously or separately in step S3. The following description will be based on separate welding.

[0056] like Figure 2 As shown, from top to bottom are the restraining plate 7, energetic material layer 6, face material 3, spacer 5, pre-treated honeycomb core 2, and support plate 4. The spacer 5 is disposed in the outer edge region between the face material 3 and the honeycomb core 2 to create a gap between the face material 3 and the honeycomb core 2. The energetic material layer 6 is then detonated to generate a shock wave, which drives the face material 3 toward the honeycomb core 2, causing them to contact and bond to form a connection interface. Plastic flow and a high-speed jet flow occur at the contact surface between the two, and the oxide layer is ejected under the action of the high-speed jet flow. A metallurgical bonding layer and a residual compressive stress field (-50 MPa to -200 MPa) are formed at the connection interface, completing the explosive welding of the face material 3 and the honeycomb core 2 on one side. The above operation is repeated to explosively weld the face material 3 on the other side to the pre-treated honeycomb core 2, resulting in a honeycomb sandwich structure.

[0057] The bonding strength of the explosive welding connection interface is ≥200MPa, and the joint shear strength is ≥95MPa; the dynamic impact energy absorption rate is increased by more than 30% compared with traditional welding, and the heat-affected zone is reduced to within 50μm.

[0058] Example 1

[0059] This embodiment uses a honeycomb core made of AA6061 aluminum alloy with a pore diameter of 3 mm, a wall thickness of 0.26 mm, and a height of 11.84 mm; two sets of copper plates with a thickness of 0.5 mm are used as surface materials.

[0060] The method for preparing a honeycomb sandwich structure based on laser collaborative explosion welding is as follows:

[0061] S1. Laser pretreatment of the honeycomb core opening surface. Laser parameters include: power density of 3×10 6 W / cm2, a pulse width of 200 fs, and a scanning pitch of 20 μm; after laser pretreatment, a periodically distributed micron-scale pit array (pit depth 50 μm, diameter 30 μm) is formed on the surface of the honeycomb core opening, and an oxide layer with a thickness of 2 μm to 5 μm is formed;

[0062] S2, constructing submicron-scale holes (pore diameter 300nm, surface roughness Ra < 50nm) inside the pits through nanoimprinting process;

[0063] S3. Establish a thermal-mechanical coupling finite element model to simulate the shock wave pressure distribution under different detonation velocities and determine the critical pressure threshold of 1.2 GPa; set a modified nitrocellulose film with a thickness of 50 μm as the energetic material layer 6; from top to bottom, there are the constraint plate 7, the energetic material layer 6, the surface material 3, the spacer 5, the pretreated honeycomb core 2, and the support plate 4. Detonate the energetic material layer 6 to generate a shock wave with a detonation velocity of 2000 m / s, and collide the surface material 3 with the honeycomb core 2 to make them contact and bond to form a connection interface; repeat the operation, and bond another set of surface materials to the other side of the pretreated honeycomb core 2 in the same way; obtain a honeycomb sandwich structure.

[0064] The properties of the honeycomb sandwich structure prepared in this embodiment were tested, including the bonding strength of the connection interface, the shear strength of the welded joint, the dynamic impact energy absorption rate, and the range of the heat-affected zone.

[0065] Among them, bonding strength is a key indicator for evaluating the bonding quality between honeycomb panels. The peel test can be used to detect the bonding strength between the core material and the panel.

[0066] Tensile force is applied to the upper and lower surfaces of the metal honeycomb core sandwich structure, and its shear strength is evaluated by measuring the shear stress and corresponding displacement generated during the stretching process.

[0067] Combined drop hammer impact test and Charpy impact test to test dynamic impact energy absorption rate.

[0068] Comprehensive hardness gradient analysis and microstructure observation, supplemented by ultrasonic / X-ray non-destructive testing, test the heat-affected zone and observe whether there are cracks.

[0069] Comparative Groups 1 to 3, which were subjected to explosion welding without laser pretreatment and / or nanoimprint pretreatment, were compared with Example 1. The performance comparison is shown in Table 1.

[0070] Table 1

[0071]

[0072] As can be seen from the data in Table 1, the present invention adds laser pretreatment and nanoimprinting steps before explosive welding, which greatly increases the connection interface bonding strength, weld joint shear strength, and dynamic impact energy absorption rate of the target product and reduces the range of the heat-affected zone.

[0073] Among them, laser pretreatment has a greater impact on product performance. Taking Example 1 of the present invention and Comparative Group 3 as comparison objects, the relationship between the shear strength of the welded joint and the absolute mass density of the honeycomb core material is analyzed. The comparison curves of the two are as follows: Figure 3 shown by Figure 3It can be seen that as the absolute mass density of the honeycomb core material changes, the shear strength of Example 1 after laser pretreatment is higher than that of the comparison group 3.

[0074] Example 2

[0075] In this embodiment, the material of the honeycomb core is replaced with titanium alloy based on the embodiment 1. The steps of preparing the honeycomb sandwich structure by laser collaborative explosion welding are as follows:

[0076] S1. Laser pretreatment of the honeycomb core opening surface. Laser parameters include: power density of 4×10 6 W / cm 2 , pulse width of 300fs, scanning spacing of 15μm; after laser pretreatment, a periodically distributed micron-scale pit array (pit depth 40μm, diameter 25μm) is formed on the surface of the honeycomb core opening, and an oxide layer with a thickness of 3μm~6μm is formed;

[0077] S2, constructing submicron-scale holes (pore diameter 400nm, surface roughness Ra < 50nm) inside the pits through nanoimprinting process;

[0078] S3. Establish a thermal-mechanical coupling finite element model to simulate the shock wave pressure distribution under different detonation velocities and determine the critical pressure threshold of 1.8 GPa; set a modified nitrocellulose film with a thickness of 60 μm as the energetic material layer 6; from top to bottom, there are the constraint plate 7, the energetic material layer 6, the surface material 3, the spacer 5, the pretreated honeycomb core 2, and the support plate 4. Detonate the energetic material layer 6 to generate a shock wave with a detonation velocity of 2200 m / s, and collide the surface material 3 with the honeycomb core 2 to make them contact and bond to form a connection interface; repeat the operation, and bond another set of surface materials to the other side of the pretreated honeycomb core 2 in the same way; obtain a honeycomb sandwich structure.

[0079] The same test method as in Example 1 was used to test the performance of the honeycomb sandwich structure prepared in Example 2. Comparison groups 4 to 6 without laser pretreatment and / or nanoimprint pretreatment and subjected to explosion welding were compared with Example 2, and the performance comparison is shown in Table 2.

[0080] Table 2

[0081]

[0082] As can be seen from the data in Table 2, the present invention adds laser pretreatment and nanoimprinting steps before explosive welding, which greatly increases the connection interface bonding strength, weld joint shear strength, and dynamic impact energy absorption rate of the target product.

[0083] Example 3

[0084] In this embodiment, based on the embodiment 1, the power density of the laser pretreatment in S1 is adjusted to 10 6 W / cm 2 , 5×10 6 W / cm 2 , 8×10 6 W / cm 2 , 10 7 W / cm 2 , 2×10 7 W / cm 2 , other reaction steps and parameters are consistent with Example 1, and the effects of laser pretreatments with different power densities on the performance of the honeycomb sandwich structure are analyzed. The test results are shown in Table 3.

[0085] Table 3

[0086]

[0087] The data in Table 3 show that as the power density of laser pretreatment in S1 increases, the performance of the interface between the honeycomb core and the surface material first improves and then decreases, and there is an optimal power density range.

[0088] Too low a power density leads to a significant decrease in interfacial bonding strength and shear strength. This is due to: insufficient energy input, insufficient micron-scale pit depth (only 30 μm), and insufficient oxide layer thickness (1 μm to 3 μm). Physical adsorption is the primary mechanism of interfacial bonding, making it difficult to form an effective metallurgical bond.

[0089] Excessive power density leads to a decrease in the dynamic impact energy absorption rate and an expansion of the heat-affected zone to 65μm. The reasons are: the ultra-high energy causes local ablation of the honeycomb core (oxide layer thickness > 8μm), which increases the brittleness of the oxide layer and induces microcracks. At the same time, the excessive heat input causes grain coarsening (grain size > 10μm), weakening the interface's shear resistance and energy absorption capacity.

[0090] Therefore, the present invention sets the power density of laser pretreatment in S1 to 10 6 W / cm 2 ~10 7 W / cm 2 .

[0091] Example 4

[0092] In this example, based on Example 1, the pulse width of the laser pretreatment in S1 was adjusted to 50 fs, 100 fs, 300 fs, 400 fs, 500 fs, and 600 fs, respectively. The other reaction steps and parameters were consistent with those in Example 1. The effects of laser pretreatment with different pulse widths on the performance of the honeycomb sandwich structure were analyzed, and the test results are shown in Table 4.

[0093] Table 4

[0094]

[0095] The data in Table 4 show that as the pulse width of the laser pretreatment in S1 increases, the performance of the interface between the honeycomb core and the surface material first increases and then decreases, and there is an optimal pulse width range.

[0096] Too short a pulse width (50fs-100fs) leads to a significant decrease in interface bonding strength and dynamic impact absorption rate. This is due to insufficient ultrashort pulse energy input, which results in substandard micron-scale pit depth (≤35μm) and oxide layer continuity (thickness 1μm-3μm). Consequently, interface bonding is primarily physical adsorption, preventing effective mechanical and metallurgical bonding.

[0097] Excessive pulse width (600 fs) causes the heat-affected zone to expand to 50 μm and the shear strength to decrease by 18%. The reasons are: the excessive pulse width causes local overheating of the aluminum alloy, and the oxide layer is too thick (>8 μm), which leads to brittle phase transformation (the microcrack density of the Al2O3 layer increases to 5.2×10 3 mm -2 ), while grain coarsening (size > 12 μm) weakens the interface shear resistance‌.

[0098] Therefore, the present invention sets the pulse width of the laser pretreatment in S1 to 100fs~500fs.

[0099] Example 5

[0100] In this embodiment, based on Example 1, the scanning path spacing of the laser pretreatment in S1 was adjusted to 5 μm, 10 μm, 30 μm, 40 μm, 50 μm, and 55 μm. The other reaction steps and parameters were consistent with those in Example 1. The effects of laser pretreatment with different scanning path spacings on the performance of the honeycomb sandwich structure were analyzed, and the test results are shown in Table 5.

[0101] Table 5

[0102]

[0103] It can be seen from the data in Table 5 that as the scanning path of the laser pretreatment in S1 increases, the performance of the connection interface between the honeycomb core and the surface material shows a trend of first improving and then decreasing, and there is an optimal parameter range (10μm~50μm).

[0104] The scan path is too small (5 μm), resulting in a significant decrease in the interface bonding strength and dynamic impact energy absorption rate (185 MPa, 14.0 kJ / m²). The reason is that the ultra-dense scan path causes the accumulation of laser energy per unit area, resulting in local ablation of the honeycomb core surface (oxide layer thickness > 8 μm), and an increase in the density of microcracks (up to 4.1×103 mm -2 ), the interface brittle phase transition is intensified;

[0105] A scanning path that is too large (55 μm) causes the heat-affected zone to expand to 53 μm and the shear strength to decrease by 23.5% (75 MPa). The reasons are: the sparse scanning path results in insufficient pit coverage (≤60%), the oxide layer is discontinuous (thickness fluctuation >3 μm), and the interface bonding is mainly discrete mechanical bite, which cannot form a uniform stress transfer path.

[0106] Therefore, the present invention sets the scanning path of the laser pre-processing in S1 to 10 μm to 50 μm.

[0107] Example 6

[0108] In this embodiment, based on Example 1, the detonation velocity of the energetic material layer 6 in S3 was adjusted to 1000 m / s, 1500 m / s, 2000 m / s, 2500 m / s, 3000 m / s, and 3500 m / s. The other reaction steps and parameters were consistent with those in Example 1. The effects of different detonation velocities on the performance of the honeycomb sandwich structure were analyzed, and the test results are shown in Table 6.

[0109] Table 6

[0110]

[0111] It can be seen from the data in Table 6 that with the increase of detonation velocity, the performance of the interface between the honeycomb core and the surface material shows a trend of first strengthening and then weakening, and there is an optimal detonation velocity range (1500m / s~3000m / s).

[0112] The low detonation velocity (1000 m / s) leads to a significant decrease in the interface bonding strength and dynamic impact energy absorption rate (160 MPa, 10.5 kJ / m²). The reasons are: the energetic material layer releases insufficient energy at low detonation velocity, the interface metallurgical bonding ratio is low (the oxide layer thickness is only 3 μm to 5 μm), and the microcrack density is high (up to 2.8 × 10 3 mm -2 ), the interface is mainly mechanically biting and cannot form a continuous stress transfer path;

[0113] The high detonation velocity (3500 m / s) caused the heat-affected zone to expand to 53 μm and the bond strength to drop by 23.6% (195 MPa). The reasons are: the ultra-high detonation velocity caused local energy overload, the oxide layer was too thick (>8 μm) and the grains were coarsened (size>15 μm), and the microcrack density increased sharply (4.2×10 3 mm -2 ), the interface brittle phase transformation (Al3Ti phase ratio > 12%) dominates, weakening the bonding stability‌.

[0114] Therefore, the present invention sets the detonation velocity to 1500m / s-3000m / s.

[0115] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for preparing a honeycomb sandwich structure based on laser collaborative explosion welding, wherein the honeycomb sandwich structure comprises two sets of surface materials and a honeycomb core sandwiched between the two sets of surface materials; characterized in that: The method comprises the following steps: Laser pretreatment is performed on the surface of the honeycomb core to form a periodically distributed array of micron-scale pits; Constructing submicron-scale holes inside micron-scale pit arrays based on nanoimprinting; An energetic material layer is coated on the surface of the face material, and the face material and the pre-treated honeycomb core are explosively welded using the shock wave generated by the detonation of the energetic material layer to form a connection interface and obtain a honeycomb sandwich structure; The laser pretreatment adopts femtosecond laser treatment, and the power density of the femtosecond laser is 10 6 W / cm 2 ~10 7 W / cm 2 , pulse width is 100fs~500fs, and scanning path spacing is 10μm~50μm; The laser thermal effect of the laser pretreatment forms a composite metal layer of an oxide layer and a melt recrystallization layer. The outer surface of the pit is an oxide layer, and the inner surface is a melt recrystallization layer. The oxide layer is the outermost layer covering the surface of the honeycomb core, and the melt recrystallization layer is located between the oxide layer and the surface of the honeycomb core. The melt recrystallization layer is the result of grain refinement and element segregation during the melting-solidification process. The submicron-scale pores are distributed in the interface area between the melt-recrystallized layer and the matrix of the honeycomb core.

2. The method for preparing a honeycomb sandwich structure based on laser collaborative explosion welding according to claim 1, characterized in that: The material of the honeycomb core is aluminum alloy or titanium alloy; the material of the surface material is a metal-based composite material.

3. The method for preparing a honeycomb sandwich structure based on laser collaborative explosion welding according to claim 1, characterized in that: The material used in the energetic material layer is modified ammonium nitrate explosive, metal-nitrocellulose material, RDX-polymer-based explosive or PETN-polymer-based explosive.

4. The method for preparing a honeycomb sandwich structure based on laser collaborative explosion welding according to claim 1, characterized in that: In the micron-scale pit array, the pit depth is 10 μm to 200 μm, the pit diameter is set to 50 μm to 200 μm; the spacing between two pits is 1.5 to 3 times the pit diameter, and the inner wall of the pit has a multi-level rough structure.

5. The method for preparing a honeycomb sandwich structure based on laser collaborative explosion welding according to claim 4, characterized in that: The pore diameter of the submicron pores is set to 200nm-800nm.

6. The method for preparing a honeycomb sandwich structure based on laser collaborative explosion welding according to claim 3, characterized in that: The thickness of the energetic material layer is 10 μm-100 μm.

7. The method for preparing a honeycomb sandwich structure based on laser collaborative explosion welding according to claim 3, characterized in that: The explosion speed of the energetic material layer is controlled to be 1500m / s-3000m / s.

8. The method for preparing a honeycomb sandwich structure based on laser collaborative explosion welding according to claim 3, characterized in that: The explosion shock wave pressure of the energetic material layer is controlled to be 0.5 GPa-5 GPa.

9. The method for preparing a honeycomb sandwich structure based on laser collaborative explosion welding according to claim 1, characterized in that: The connection interface forms a metallurgical bonding layer and a residual compressive stress field.

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