Aircraft composite lattice sandwich energy-absorbing structure and performance prediction method thereof

Abstract

The application provides an aircraft composite lattice sandwich energy-absorbing structure and a performance prediction method thereof, and belongs to the technical field of composite materials. The application takes a tensile-dominant octagonal truss lattice as a basic lattice structure, fuses a body-centered cubic lattice, simple cubic point mechanics characteristics of tensile-dominant and bending-dominant to strengthen mechanical properties, forms a new hybrid lattice structure, establishes an optimal arrangement strategy of the lattice structure inspired by a bionic bone microstructure, combines the characteristics of the two lattice structures, effectively improves the mechanical properties of the sandwich structure, including higher peak load, average load, specific energy absorption and more stable crushing force efficiency, and establishes a prediction model of the effective stiffness and relative density of the two-phase lattice, effectively realizes customized mechanical properties, and widens the application of the lattice sandwich structure in aircraft structures.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, specifically relating to an energy-absorbing structure of composite material lattice sandwich for aircraft and its performance prediction method. Background Technology

[0002] In the modern aviation field, rotorcraft, helicopters, and large and medium-sized civil aircraft are increasingly intertwined with people's daily lives. With the booming development of the aviation industry, aircraft safety and lightweight design have received significant attention. The increasing maturity of aviation manufacturing technology and the widespread application of advanced composite materials have propelled aircraft structural design to new heights. During flight and takeoff / landing, aircraft frequently encounter complex situations such as airflow impacts and collisions, posing a significant threat to their safety. Energy-absorbing structures, as a key design element capable of effectively responding to impact energy and protecting the main structure of the aircraft and its internal personnel and equipment, can convert, absorb, and dissipate impact energy through their unique structural characteristics and material properties when encountering dangers such as impacts, providing crucial protection for the safe and stable operation of the aircraft. This makes energy-absorbing structures one of the most studied directions in current aircraft structural design research.

[0003] Composite sandwich structures hold great promise for engineering applications, particularly in aerospace, marine equipment, and automotive fields. They consist of upper and lower panels and a lightweight core material. Carbon fiber reinforced polymer (CFRP) is increasingly used in sandwich structures due to its high specific stiffness, strength, and energy absorption capacity. The core material plays a crucial role in determining performance, driving a strong pursuit of high-performance sandwich structures. However, the complexity and uncertainty of core material failure mechanisms pose significant challenges to improving their performance. Traditional sandwich structures include corrugated cores, honeycomb cores, and foam cores. Cell size, the fracture toughness of the adhesive, and the strength of the sandwich skin determine the critical load capacity of the sandwich structure. This means that the performance of sandwich structures still has the potential for continuous improvement. Summary of the Invention

[0004] This invention provides a composite material lattice sandwich energy-absorbing structure for aircraft and a method for predicting its performance. While ensuring the lightweight nature of the structure, it effectively improves the mechanical properties of the sandwich structure in terms of impact resistance, energy absorption, etc., thereby solving at least one of the technical problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the present invention is implemented as follows:

[0006] A composite material lattice sandwich energy-absorbing structure for aircraft includes two parallel and spaced carbon fiber plates and a core material sandwiched between the two carbon fiber plates. The core material includes a first layer, a middle layer, and a last layer stacked sequentially along the Z direction. The first layer, the middle layer, and the last layer are all formed by connecting multiple column units arranged sequentially along the X direction. The column units include staggered hard phase array units and soft phase array units. The hard phase array units are formed by connecting multiple hybrid lattice structures arranged sequentially along the Y direction. The soft phase array units are formed by connecting multiple octagonal truss lattice structures arranged sequentially along the Y direction. The hybrid lattice is formed by nesting octagonal truss lattice with body-centered cubic lattices and simple cubic lattices. The X direction is the length direction of the core material, the Y direction is the width direction of the core material, and the Z direction is the thickness direction of the core material.

[0007] As a preferred improvement, the construction process of the hybrid lattice is as follows: taking the octagonal truss lattice as the base phase, aligning the center points of the body-centered cubic lattice and the simple cubic lattice with the center point of the octagonal truss lattice, and aligning each face of the body-centered cubic lattice and the simple cubic lattice with one face of the octagonal truss lattice for combination and nesting.

[0008] As a preferred improvement, each layer of the carbon fiber sheet and the core material are bonded together with an adhesive.

[0009] As a preferred improvement, the first layer has one column of hard phase array units, and the remaining columns are all soft phase array units, symmetrically distributed on the left and right sides of the hard phase array units; the middle layer has two columns of hard phase array units, with one column of soft phase array units between the two columns of hard phase array units, and the remaining columns are all soft phase array units, symmetrically distributed outside the two columns of hard phase array units; the last layer has three columns of hard phase array units, with one column of soft phase array units between two adjacent hard phase array units, and the remaining columns are all soft phase array units, symmetrically distributed outside the two outer columns of hard phase array units.

[0010] As a preferred improvement, the core material is made of lightweight material using 3D printing technology, and the lightweight material is selected from any one of aluminum-titanium alloy, stainless steel, polylactic acid, and nylon.

[0011] As a preferred improvement, the carbon fiber plate is formed by stacking multiple layers of carbon fiber cloth using a hand lay-up process.

[0012] A method for predicting the performance of a composite lattice sandwich energy-absorbing structure for aircraft, as described above, includes the following steps:

[0013] Step S1: Based on the nesting mechanism of the hybrid lattice, a 45° load is added to the octagonal truss lattice to calculate the effective elastic stiffness and collapse strength of the hybrid lattice.

[0014] Step S2 uses hybrid rules to explain the compressive deformation characteristics of each lattice structure in the core material and predicts the effective stiffness of any layer.

[0015] As a preferred improvement, for octagonal truss lattice cells, the effective elastic stiffness is... Represented as:

[0016]

[0017] In the formula, t represents the thickness of the strut in the octagonal truss lattice cell; l represents the length of the cell; E S Indicates the Young's modulus of the substrate;

[0018] Collapse strength of octagonal truss lattice cell Represented as:

[0019]

[0020] In the formula, σ ys The yield stress of the octagonal truss lattice represents the plastic strain.

[0021] Effective elastic stiffness of hybrid lattice Represented as:

[0022]

[0023] Collapse strength of hybrid lattice Represented as:

[0024]

[0025] As a preferred improvement, step S2 specifically includes the following steps:

[0026] Assuming equal compressive stress in each layer, the compressive deformation characteristics of each lattice structure in the core material can be explained using the mixing rule, as follows:

[0027]

[0028] In the formula, E ini The initial stiffness of the i-th layer, i.e., the effective elastic stiffness, is calculated through step S1; n represents the total number of layers, with a value of 3. This represents the volume fraction of the i-th layer; This represents the stiffness of the i-th layer after compression;

[0029] Considering the plastic strain of each lattice structure layer, the stiffness of the i-th layer after compression is redefined as:

[0030]

[0031] In the formula, λ D λ represents a coefficient describing the compression size; for a hybrid lattice, λ D by The reciprocal approximation, for an octagonal truss lattice, λ D by The reciprocal of is used as an approximation;

[0032] The plastic strain process of each lattice structure is divided into two stages. The first stage is the middle of the plastic deformation stage, and the coefficient describing the magnitude of compression is λ. D1 The second stage is the later stage of densification, and the coefficient describing the size of the compression is λ. D2 , where λ D1 >λ D2 ;

[0033] The strain assumption for the i-th layer is derived from the following equation:

[0034]

[0035] In the formula, σ represents the strain of the i-th layer; σ represents the stress.

[0036] Based on the above formula, the effective plastic strain of the i-th layer can be derived as follows:

[0037]

[0038] Assuming the i-th layer is in the elastic deformation stage, then the (i-1)-th layer is in the first stage, and the (i-2)-th layer is in the second stage. Therefore, the general prediction formula for the effective stiffness of different layers is:

[0039]

[0040] In the formula, m and k represent the summation index. m requires traversing the terms from 1 to n in the summation and performing cumulative calculations on the related terms; k requires traversing the terms from 1 to i-2 in the summation and performing cumulative calculations on the related terms.

[0041] The beneficial effects of this invention are as follows:

[0042] (1) A composite material lattice sandwich energy-absorbing structure for aircraft structures is provided, which combines the characteristics of two lattice structures (tension-dominated and bending-dominated) to effectively improve the mechanical properties of the sandwich structure, including higher peak load, average load, specific energy absorption and more stable crushing force efficiency.

[0043] (2) It provides mechanical prediction models such as effective stiffness and relative density, effectively realizing customized mechanical properties. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0045] Figure 1 This is a cross-sectional schematic diagram of the composite material lattice sandwich energy-absorbing structure for aircraft provided by the present invention;

[0046] Figure 2 This invention provides a combined design process for hybrid lattice cells;

[0047] Figure 3 The specific arrangement strategy for each layer of the biphase lattice provided by the present invention;

[0048] Figure 4 A front view of a composite material lattice sandwich energy-absorbing structure for use in aircraft structures, provided by the present invention;

[0049] Figure 5 A comparison of theoretical and experimental values ​​for the effective stiffness analysis of the two-phase lattice sandwich structure provided by this invention;

[0050] Figure 6 A load-displacement comparison diagram of a three-point bending test between a two-phase lattice sandwich structure and a single-phase lattice sandwich structure provided by the present invention;

[0051] Figure 7 A comparison diagram of peak load and post-peak average load between the two-phase lattice sandwich structure and the single-phase lattice sandwich structure provided by the present invention.

[0052] Figure 8 A comparison diagram of the energy absorption capabilities of the two-phase lattice sandwich structure and the single-phase lattice sandwich structure provided by the present invention.

[0053] Figure 9 A comparison diagram of the average load and breaking force efficiency between the two-phase lattice sandwich structure and the single-phase lattice sandwich structure provided by the present invention.

[0054] Figure 10 The figure shows the fitting curves of stress oscillation factor and load stability for different types of lattices in the two-phase lattice sandwich structure provided by the present invention. Detailed Implementation

[0055] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] Example 1

[0057] like Figures 1-10 As shown, this embodiment provides an energy-absorbing structure for a composite material lattice sandwich structure for aircraft, including two parallel and spaced carbon fiber plates 1 and a core material 2 sandwiched between the two carbon fiber plates 1. Each carbon fiber plate 1 and the core material 2 are bonded and fixed together by an adhesive.

[0058] The core material 2 is made of lightweight materials using 3D printing technology, such as aluminum-titanium alloy, stainless steel, polylactic acid, and nylon. 3D printing technology has advantages such as high precision, low cost, and a wide range of material choices, making it well-suited for molding the core material 2.

[0059] In this embodiment, the core material is designed to be 99mm long, 33mm wide, and 33mm high.

[0060] The carbon fiber plate 1 is prepared by hand lay-up, which involves cutting eight layers of 20cm×20cm carbon fiber cloth and stacking them. The fibers are then bonded together using an adhesive formed by mixing resin and curing agent. After compression at 1.5MPa for 12 hours, a carbon fiber plate with a thickness of 2mm is prepared, which is then cut into 101mm×34mm dimensions.

[0061] The core material 2 comprises a first layer 21, an intermediate layer 22, and a last layer 23 stacked sequentially along the Z direction. Each of the first, intermediate, and last layers 23 is formed by connecting multiple column units 20 arranged sequentially along the X direction. Each column unit 20 includes staggered hard phase array units 201 and soft phase array units 202. The hard phase array units 201 are formed by connecting multiple hybrid lattice structures arranged sequentially along the Y direction, and the soft phase array units 202 are formed by connecting multiple octagonal truss lattice structures arranged sequentially along the Y direction. It should be noted that the X direction is the length direction of the core material 2, the Y direction is the width direction of the core material 2, and the Z direction is the thickness direction of the core material 2.

[0062] The hybrid lattice structure is formed by nesting an octagonal truss lattice with tensile dominance as the base phase, combined with body-centered cubic lattices and simple cubic lattices with bending dominance. The construction process of the hybrid lattice is as follows: using the octagonal truss lattice as the base phase, the center points of the body-centered cubic lattices and simple cubic lattices are aligned with the center point of the octagonal truss lattice; each face of the body-centered cubic lattice and simple cubic lattice is aligned with one face of the octagonal truss lattice for nesting. The octagonal truss lattice, body-centered cubic lattice, and simple cubic lattice can all adopt conventional structures in the art, and this embodiment does not impose any limitations on them.

[0063] Structurally, the octagonal truss lattice, body-centered cubic lattice, and simple cubic lattice are all centrally symmetrical hexahedral structures. Therefore, during the combination and nesting process, the center points of the octagonal truss lattice, body-centered cubic lattice, and simple cubic lattice are aligned, and the six faces are aligned respectively. During the nesting process, there is a certain degree of overlap between the supports of each lattice. For example, the edges of the simple cubic lattice intersect with the edges of the "cross-shaped" outer support frame of the octagonal truss lattice, and the included angle at the intersection is 90°; the supports of the body-centered cubic lattice intersect with the supports on the inner side of the octagonal truss lattice, and the included angle at the intersection is also 90°.

[0064] In the hybrid lattice structure, the octagonal truss lattice features have high strength and can effectively resist impact loads, thereby improving the tensile mechanical characteristics of the core material 2; the body-centered cubic lattice and simple cubic lattice have stable plateau stress, which is conducive to continuous energy absorption and can improve the bending mechanical characteristics of the core material 2.

[0065] The hard phase column units 201 and soft phase column units 202 are arranged in an alternating pattern. The hard phase column units 201 play a crucial role in hindering relative dislocation movement, thereby altering the shear strip paths and expanding them to enhance energy dissipation. Specifically:

[0066] In the first layer 21, there is a column of hard phase column units 201, and the remaining columns are all soft phase column units 202, which are symmetrically distributed on the left and right sides of the hard phase column units 201.

[0067] In the intermediate layer 22, there are two columns of hard phase column units 201, and a column of soft phase column units 202 is arranged between the two columns of hard phase column units 201. The remaining columns are all soft phase column units 202, symmetrically distributed on the outside of the two columns of hard phase column units 201.

[0068] In the last layer 23, three columns of hard phase array units 201 are provided, and a column of soft phase array units 202 is provided between two adjacent hard phase array units 201. The remaining columns are all soft phase array units 202, symmetrically distributed outside the two outer columns of hard phase array units 201.

[0069] The staggered arrangement strategy has the following advantages:

[0070] (1) Cooperative load-bearing: The staggered or regular arrangement of each layer can make the overall structure more uniformly stressed in all directions, thus enhancing stability;

[0071] (2) Stress dispersion: The changes in the pattern and structure of different layers can change the crack propagation path and reduce the risk of structural cracking or deformation due to stress concentration;

[0072] (3) Energy absorption: When deformed by external force, the layers will interact to limit excessive deformation, and the small displacement and deformation between layers can consume the impact energy.

[0073] Example 2

[0074] This embodiment provides a performance prediction method for the composite material lattice sandwich energy-absorbing structure of an aircraft in Embodiment 1, including the following steps:

[0075] Step S1: Based on the nesting mechanism of the hybrid lattice, a 45° load is added to the octagonal truss lattice to calculate the effective elastic stiffness and collapse strength of the hybrid lattice.

[0076] For an octagonal truss lattice cell, the effective elastic stiffness Represented as:

[0077]

[0078] In the formula, t represents the thickness of the strut in the octagonal truss lattice cell; l represents the length of the cell; E S Indicates the Young's modulus of the substrate;

[0079] Collapse strength of octagonal truss lattice cell Represented as:

[0080]

[0081] In the formula, σ ys This represents the yield stress of the octagonal truss lattice under plastic strain.

[0082] The hybrid lattice is obtained by adding horizontal and vertical supports to an octagonal truss lattice. Rotating the hybrid lattice by 45° produces an octagonal truss lattice. Therefore, the effective elastic stiffness of the hybrid lattice can be calculated by adding a 45° load to the octagonal truss lattice. and collapse intensity

[0083] Then, the effective elastic stiffness of the hybrid lattice Represented as:

[0084]

[0085] Collapse strength of hybrid lattice Represented as:

[0086]

[0087] Step S2 uses hybrid rules to explain the compressive deformation characteristics of each lattice structure in the core material and predicts the effective stiffness of any layer.

[0088] Assuming equal compressive stress in each layer, the compressive deformation characteristics of each lattice structure in the core material are explained using the Mixture Rule (ROM), as follows:

[0089]

[0090] In the formula, E ini The initial stiffness of the i-th layer, i.e., the effective elastic stiffness, is calculated through step S1; n represents the total number of layers, which is 3. This represents the volume fraction of the i-th layer; This represents the stiffness of the i-th layer after compression;

[0091] During compression, when the i-th layer has just reached the elastic deformation stage, the (i-1)-th layer is in its plastic deformation stage. The load transmitted by the i-th layer can induce plastic strain in the (i-1)-th layer. This plastic strain is significant because the stiffness of the (i-1)-th layer is greatly reduced. As compression continues, the increasing stress forces the (i-1)-th layer to compress into a compact structure, increasing its corresponding elastic modulus. To describe this change, this invention redefines the stiffness of the i-th layer after compression as:

[0092]

[0093] In the formula, λ D A coefficient representing the compression size.

[0094] At the beginning of each plastic deformation stage, the effective stiffness is weakest, therefore λ D Maximum; the more it is compressed, the higher λ becomes. D The smaller the value, the better. When the layer is completely compressed into a compact substrate, the stiffness of the layer can be considered as the Young's modulus of the substrate. Therefore, for a hybrid lattice, λ... D It can be approximated by the formula The reciprocal of λ for the octagonal truss lattice D It can be approximated by the formula The reciprocal of.

[0095] The plastic strain process of each lattice structure is divided into two stages. The first stage is the middle of the plastic deformation stage, and the coefficient describing the magnitude of compression is λ. D1 The second stage is the later stage of densification, and the coefficient describing the size of the compression is λ. D2 , where λ D1 >λ D2 .

[0096] The strain assumption can be derived from the following equation:

[0097]

[0098] In the formula, σ represents the strain of the i-th layer; σ represents the stress.

[0099] The effective plastic strain can be derived from the above formula:

[0100]

[0101] Assuming the i-th layer is in the elastic deformation stage, then the (i-1)-th layer is in the first stage, and the (i-2)-th layer is in the second stage. Therefore, the general formula for calculating the effective stiffness of different layers is:

[0102]

[0103] In the formula, m and k represent the summation index. m requires traversing the terms from 1 to n in the summation and performing cumulative calculations on the related terms; k requires traversing the terms from 1 to i-2 in the summation and performing cumulative calculations on the related terms.

[0104] To verify the effectiveness of the prediction method provided by this invention, the corresponding... and Substituting the ratios into the above equation, the effective stiffness ratio is calculated to be 3.12:0.84:0.87:0.85.

[0105] Divide the effective stiffness ratio of experimental prediction to theoretical prediction by Normalization is performed to eliminate the influence of differences in initial stiffness between different layers. Directly comparing the absolute values ​​of the effective stiffness of each layer makes it difficult to reflect the relative changes due to differences in initial stiffness. This is achieved by dividing by the initial stiffness of the bottom layer. The effective stiffness of each layer is converted into a ratio relative to the bottom layer, thereby eliminating the benchmark difference and highlighting the decreasing or increasing trend of stiffness of each layer relative to the bottom layer.

[0106] Theoretical and experimental results of normalized stiffness are as follows: Figure 5 As shown. From Figure 5It can be seen that the stiffness prediction method provided by this invention successfully solves the problem of the decreasing stiffness trend and explains the sudden increase in the stiffness of the third layer. The results comparison shows that the prediction method provided by this invention is quite close to the experimental values, with the difference within the range of 0.1, proving the effectiveness of the prediction method of this invention.

[0107] In this embodiment, a three-point bending (3PB) test was conducted using a general-purpose electronic testing machine to test the bending load-displacement response of the sandwich structure. A span of 47 mm was established, and the quasi-static displacement loading was controlled at a consistent rate of 5 mm / min throughout all tests. A high-resolution camera was used to record the bending response process of the sandwich structure. Figure 6 The figures show the bending load-displacement curves for a two-phase lattice sandwich structure and a single-phase lattice sandwich structure. These two curves exhibit similar trends and can be divided into four stages: the first stage is the elastic deformation stage; the second stage includes the fracture of both the panel and the lattice core material; the third stage is mainly characterized by fracture deformation of the lattice core material; and the fourth stage is characterized by stable deformation. The fracture stage of the composite sandwich structure is significantly shorter, which is beneficial for effective energy absorption.

[0108] Example 3

[0109] This embodiment uses an experimental approach to verify the performance of the composite material lattice sandwich energy-absorbing structure for aircraft provided in Implementation 1:

[0110] (1) Relative density is used as an indicator to evaluate the lightweighting of composite lattice sandwich energy-absorbing structures in aircraft.

[0111] The relative density is determined by the density ρ of the lattice structure. l or volume V l Density ρ of the parent material p or volume V p The ratio determines this.

[0112]

[0113] The relative density of an octagonal truss lattice with cylindrical supports can be expressed as:

[0114]

[0115] In the formula, t1 and l1 represent the diameter and length of the octagonal truss lattice, respectively. Geometry can be used to calculate the first coefficient in the above equation. When the relative density is high (>0.1), the overlapping volume at the joints of the lattice members must be considered. Therefore, the second coefficient needs to be fitted into the CAD calculation to obtain a correction factor of 6.825. Similarly, the relative density of the novel hybrid lattice structure with a cylindrical diameter of t2 and a length of l2 can be expressed as:

[0116]

[0117] For a two-phase lattice structure, its relative density can be calculated using the following formula.

[0118]

[0119] In the formula, and As the corresponding volume fractions of the base phase and the reinforcing phase, where, and These represent the volumes of the base phase octagonal truss lattice and the reinforcing phase hybrid lattice in the two-phase lattice, respectively. The total volume of the two-phase lattice is V. P .

[0120] The volume V of the lattice structure obtained in the experiment e It is given by the following formula:

[0121]

[0122] In the formula, ρ is the density of the material itself, and m is obtained by weighing.

[0123] The relative density of the experiment was calculated as follows:

[0124]

[0125] In the formula, V is the experimental volume obtained through actual measurement and calculation.

[0126] The calculated relative densities of the octagonal lattice cell and the mixed lattice cell are 21.2% and 39.0%, respectively. The theoretical relative density of the single-phase lattice core material is 21%, and the actual relative density after preparation is 20.5%, with an error of 2.4%. The theoretical relative density of the two-phase lattice core material is 24%, and the actual relative density after preparation is 25.7%, with an error of 6.6%. These results effectively meet the lightweight requirements of the sandwich structure, and the errors are within an acceptable range.

[0127] (2) Energy absorption and specific energy absorption are used as indicators to evaluate the mechanical properties of composite lattice sandwich energy-absorbing structures for aircraft.

[0128] The calculation process for energy absorption W is expressed as follows:

[0129]

[0130] In the formula, s represents the compressive displacement; d represents the total compressive displacement; and F(s) represents the bending load.

[0131] Specific energy absorption refers to the energy absorbed per unit mass of a structure, and the calculation process is expressed as follows:

[0132]

[0133] In the formula, m represents the mass of the lattice.

[0134] (3) The crushing load stability (CLS) is used as an indicator to evaluate the energy absorption stability of the composite lattice sandwich structure of the aircraft.

[0135] The calculation process for crushing load stability (CLS) is expressed as follows:

[0136]

[0137] In the formula, F avg The value represents the average force; P represents the peak load; SD represents the load reading relative to the average force F throughout the crushing process. avg The standard deviation.

[0138] Crushing load CLS relative to F avg coefficient It should be as small as possible. If the coefficient The horizontal load is then considered the most ideal for stability. Values ​​of CFE and CLS close to 1 indicate more stable breakage behavior throughout the process. Furthermore, higher breakage stability (higher CLS) allows the pipe to dissipate energy more effectively and increases the total energy absorption (EA).

[0139] (4) The stress oscillation factor is used as an indicator to evaluate the mechanical properties of the crystal structure.

[0140] The calculation process for the stress oscillation factor Δ is expressed as follows:

[0141]

[0142] In the formula, σ p Indicates peak stress; σ v The stress valley represents the stress peak, and the subscript coefficient is the effective number of stress peaks and valleys, denoted by q. The stress oscillation factor Δ and CLS can simultaneously and effectively predict the stability of different lattice types of structures in the energy absorber during the energy absorption process.

[0143] In this embodiment, as Figures 7-10 As shown, compared with traditional single-phase lattice sandwich structures, the present invention exhibits higher peak load (+24.8%), post-peak average load (42.6%), energy absorption (+42.0%), average force (+41.2%), and specific energy absorption (+21.1%). In terms of crushing force efficiency, the two-phase lattice sandwich structure has a value of 1.18, almost close to 1. The stress oscillation factor shows a good fit with the load stability curve, effectively predicting the energy absorption stability of the sandwich structure.

[0144] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of the present invention.

Claims

1. A composite material lattice sandwich energy-absorbing structure for aircraft, characterized in that, The material comprises two parallel layers of carbon fiber plates and a core material sandwiched between the two layers of carbon fiber plates. The core material includes a first layer, a middle layer, and a last layer stacked sequentially along the Z direction. Each of the first, middle, and last layers is formed by connecting multiple column units arranged sequentially along the X direction. Each column unit includes staggered hard phase column units and soft phase column units. The hard phase column units are formed by connecting multiple hybrid lattice structures arranged sequentially along the Y direction. The soft phase column units are formed by connecting multiple octagonal truss lattice structures arranged sequentially along the Y direction. The hybrid lattice is formed by nesting and combining octagonal truss lattices with body-centered cubic lattices and simple cubic lattices. The X direction is the length direction of the core material, the Y direction is the width direction of the core material, and the Z direction is the thickness direction of the core material. The construction process of the hybrid lattice is as follows: taking the octagonal truss lattice as the base phase, aligning the center points of the body-centered cubic lattice and the simple cubic lattice with the center point of the octagonal truss lattice, and aligning each face of the body-centered cubic lattice and the simple cubic lattice with one face of the octagonal truss lattice for combination and nesting. In the first layer, there is one column of hard phase array units, and the remaining columns are all soft phase array units, symmetrically distributed on the left and right sides of the hard phase array units; in the middle layer, there are two columns of hard phase array units, with one column of soft phase array units between the two columns of hard phase array units, and the remaining columns are all soft phase array units, symmetrically distributed outside the two columns of hard phase array units; in the last layer, there are three columns of hard phase array units, with one column of soft phase array units between two adjacent hard phase array units, and the remaining columns are all soft phase array units, symmetrically distributed outside the two outer columns of hard phase array units.

2. The composite material lattice sandwich energy-absorbing structure for aircraft according to claim 1, characterized in that, Each layer of carbon fiber sheet and the core material are bonded and fixed together by adhesive.

3. The composite material lattice sandwich energy-absorbing structure for aircraft according to claim 1, characterized in that, The core material is made of lightweight material using 3D printing technology. The lightweight material is selected from any one of aluminum-titanium alloy, stainless steel, polylactic acid, and nylon.

4. The aircraft composite material lattice sandwich energy-absorbing structure according to claim 1, characterized in that, The carbon fiber plate is formed by stacking multiple layers of carbon fiber cloth using a hand lay-up process.

5. A method for predicting the performance of an aircraft composite material lattice sandwich energy-absorbing structure as described in any one of claims 1-4, characterized in that, Includes the following steps: Step S1: Based on the nesting mechanism of the hybrid lattice, a 45° load is added to the octagonal truss lattice to calculate the effective elastic stiffness and collapse strength of the hybrid lattice. Step S2 uses hybrid rules to explain the compressive deformation characteristics of each lattice structure in the core material and predicts the effective stiffness of any layer.

6. The performance prediction method for the composite material lattice sandwich energy-absorbing structure of an aircraft according to claim 5, characterized in that, For an octagonal truss lattice cell, the effective elastic stiffness Represented as: ； ； In the formula, This indicates the thickness of the struts in the octagonal truss lattice cell; Indicates the length of the unit cell; Indicates the Young's modulus of the substrate; Collapse strength of octagonal truss lattice cell Represented as: ； In the formula, The yield stress of the octagonal truss lattice represents the plastic strain. Effective elastic stiffness of hybrid lattice Represented as: ； Collapse strength of hybrid lattice Represented as: 。 7. The performance prediction method for the composite material lattice sandwich energy-absorbing structure of an aircraft according to claim 6, characterized in that, Step S2 specifically includes the following steps: Assuming equal compressive stress in each layer, the compressive deformation characteristics of each lattice structure in the core material can be explained using the mixing rule, as follows: ； In the formula, Indicates the first The initial stiffness of the layer, i.e. the effective elastic stiffness, is calculated through step S1; This indicates the total number of floors, with a value of 3. Indicates the first The volume fraction of the layer; Indicates the first Stiffness after layer compression; Considering the plastic strain of each lattice structure, the first The stiffness after layer compression is redefined as: ； In the formula, This represents a coefficient describing the compression size; for hybrid lattices, by The reciprocal approximation is used for octagonal truss lattice points. by The reciprocal of is used as an approximation; The plastic strain process of each lattice structure is divided into two stages. The first stage is the middle of the plastic deformation stage, and the coefficient describing the magnitude of compression is... The second stage is the later stage of densification, and the coefficient describing the size of the compression is... ,in > ; No. The strain assumption of the layer is derived from the following equation: ； In the formula, Indicates the first Strain of the layer; Indicates stress; Based on the above formula, we can derive the... Effective plastic strain of the layer: ； Assume the first If the first layer is in the elastic deformation stage, then the second layer... The layer is in the first stage, the first Since the layer is in the second stage, the general prediction formula for the effective stiffness of different layers is: ； In the formula, m and k This represents the index of the summation sequence. m The summation process involves iterating through the terms from 1 to n and performing cumulative calculations on the relevant terms. k The requirement is to iterate through the terms from 1 to i-2 in the summation process and perform cumulative calculations on the relevant terms.

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