A method and device for calculating the residual strength of a composite foam sandwich structure

Abstract

This invention relates to a method and apparatus for calculating the residual strength of a composite foam sandwich structure. The method includes establishing a damage analysis model of the composite foam sandwich structure, which includes a composite panel layer, a foam core layer, and an interlayer adhesive layer; performing explicit dynamic simulation of high-speed fragment impact on the damage analysis model to obtain the damage state of the composite foam sandwich structure after impact, thereby detecting the damage state through the damage analysis model; transferring the model parameters and damage state of the damage analysis model to a residual compressive strength simulation model for residual compressive strength calculation and analysis, obtaining the residual compressive strength of the composite foam sandwich structure after fragment impact damage, thereby predicting the residual compressive strength of the composite foam sandwich structure after fragment impact damage through the residual compressive strength simulation model, improving the accuracy of performance evaluation.

Description

Technical Field

[0001] This invention relates to the field of composite foam sandwich structure testing technology, and in particular to a method and apparatus for calculating the residual strength of composite foam sandwich structures. Background Technology

[0002] Composite sandwich panels offer significant advantages in structural optimization, lightweighting, and improved overall structural performance, leading to their widespread application in ship superstructures and various longitudinal and transverse bulkheads. In actual combat environments, ships face threats from various loads, including shock waves and fragmentation. Therefore, the stability and strength of composite sandwich panels under these loads are crucial. Under high-speed fragmentation impact loads, even if a composite sandwich panel is not completely penetrated, it may suffer hidden damage such as delamination, fiber breakage, or matrix cracking. Crucially, the residual strength loss caused by this type of damage directly determines whether the damaged structure can continue to bear the operational loads of critical equipment such as radar and communications systems. Since ship structures must maintain the integrity of their combat systems after an attack, insufficient residual strength can lead to local structural instability or even overall functional paralysis, thereby jeopardizing the ship's battlefield survivability. Therefore, quantitatively assessing the residual load-bearing capacity after impact damage is a vital technical indicator for ensuring the ability of composite shipbuilding to operate even with damage.

[0003] Composite sandwich panels consist of fiber layups, interlayer interfaces, and a foam core. The fragmentation damage mode of composite sandwich panel structures has long been a focus of attention. Impact compression properties (CAI) are used as a unified characterization of the impact resistance and damage performance of composite materials. Currently, there is no numerical prediction method that can simultaneously monitor the residual strength of the sandwich panel after fragmentation damage while considering fragmentation damage to the composite foam core structure.

[0004] Therefore, there is an urgent need to propose a method and device for calculating the residual strength of composite foam sandwich structures, in order to solve the technical problem that existing technologies cannot consider the residual strength of composite foam sandwich structures after fragment damage and monitor the residual strength of sandwich panels after fragment damage. Summary of the Invention

[0005] In view of this, it is necessary to provide a method and apparatus for calculating the residual strength of composite foam sandwich structures, so as to solve the technical problem that the existing numerical prediction method cannot consider the residual strength of composite foam sandwich structures after fragment damage and monitor the residual strength of sandwich panels after fragment damage.

[0006] To address the aforementioned problems, in a first aspect, the present invention provides a method for calculating the residual strength of a composite foam sandwich structure, comprising:

[0007] A damage analysis model for a composite foam sandwich structure is established, wherein the composite foam sandwich structure includes a composite panel layer, a foam core layer, and an interlayer adhesive layer. The damage analysis model was subjected to explicit dynamic simulation of high-speed impact of fragments to obtain the damage state of the composite foam sandwich structure after impact. The model parameters of the damage analysis model and the damage state are transferred to the residual compressive strength simulation model to calculate and analyze the residual compressive strength, thereby obtaining the residual compressive strength of the composite foam sandwich structure after fragment impact damage.

[0008] In one possible implementation, the explicit dynamic simulation of high-speed impact on the damage analysis model to obtain the damage state of the composite foam sandwich structure after impact includes: After dividing the mesh in the damage analysis model according to the optimal meshing scheme, the damage status and stiffness reduction of the composite material panel layer in the damage analysis model are judged and the damage coefficient is reduced based on the three-dimensional progressive damage analysis method to obtain the damage coefficient, and the damage state of the composite material panel layer is determined according to the damage coefficient. The mechanical behavior of the foam core layer under high-speed impact load is described based on the isotropic hardening compressible foam model and the failure criterion, and the dynamic strength and dynamic modulus are obtained. The damage state of the foam core layer is determined based on the dynamic strength and the dynamic modulus. The cohesive force model based on fracture mechanics describes the damage and propagation process between the composite panel layer and the interlayer adhesive layer, and obtains the damage state of the interlayer adhesive layer.

[0009] In one possible implementation, the damage coefficient is obtained by judging the failure status and stiffness reduction of the composite panel layer in the damage analysis model based on the three-dimensional progressive damage analysis method, including: The damage condition of the composite panel layer in the damage analysis model is judged based on the three-dimensional progressive damage analysis method, and the fiber tensile damage value, fiber compressive damage value, matrix tensile damage value and matrix compressive damage value are obtained. The damage process evolution of the composite foam sandwich structure is analyzed based on the fiber tensile damage value, the fiber compressive damage value, the matrix tensile damage value, and the matrix compressive damage value to obtain the damaged composite panel layer; The stiffness of the damaged composite panel layer is reduced according to the failure criterion to obtain the damage coefficient.

[0010] In one possible implementation, the fracture mechanics-based cohesive model describes the damage and propagation process between the composite panel layer and the interlayer adhesive layer, obtaining the damage state of the interlayer adhesive layer, including: The cohesive model based on fracture mechanics describes the damage and propagation process between the composite panel layer and the interlayer adhesive layer, and obtains the stress state. The performance degradation and crack propagation of the interlayer adhesive layer are determined based on the secondary stress criterion, the BK criterion, and the stress state, thereby obtaining the damage state of the interlayer adhesive layer.

[0011] In one possible implementation, the description of the mechanical behavior of the foam core layer under high-speed impact load based on the isotropic hardening compressible foam model and the failure criterion, to obtain dynamic strength and dynamic modulus, includes: The mechanical behavior of the foam core layer under high-speed impact load is described based on the isotropic hardening compressible foam model and the failure criterion, and the current stress at each moment is obtained. The true strain rate at each moment is obtained based on the current stress. The actual strain rate at each time step is calculated based on the dynamic enhancement factor parameterization model to obtain the corresponding dynamic enhancement factor. Based on the dynamic reinforcement factor and the strength and modulus of the composite material under quasi-static conditions, the dynamic strength and dynamic modulus under dynamic conditions are obtained.

[0012] In one possible implementation, the process of determining the optimal mesh partitioning scheme includes: By adjusting the mesh size of the fragments and key areas of the foam core layer, and using the remaining velocity of the fragments as the convergence criterion, the optimal mesh partitioning scheme is determined.

[0013] In one possible implementation, the step of transferring the model parameters of the damage analysis model and the damage state to the residual compressive strength simulation model for residual compressive strength calculation and analysis, to obtain the residual compressive strength of the composite foam sandwich structure after fragment impact damage, includes: Using the restart analysis function of the finite element software, the model parameters, damage state transmission, and stiffness degradation matrix of the damage coefficient of the damage analysis model are used as initial conditions to transfer to the residual compressive strength simulation model for residual compressive strength calculation and analysis, so as to obtain the residual compressive strength of the composite foam sandwich structure after fragment impact damage.

[0014] In one possible implementation, after performing explicit dynamic simulation of high-speed impact on the damage analysis model to obtain the damage state of the composite foam sandwich structure after impact, the method further includes: The ballistic limiting velocity of the composite foam sandwich structure is fitted and predicted to obtain the verification results of the damage state; If the verification result is reliable, calculate the remaining compressive strength.

[0015] In one possible implementation, the remaining compressive strength is calculated as follows:

[0016] In the formula, P is the residual compressive strength after impact, in MPa; A is the cross-sectional area, in mm2; and Fmax is the maximum compressive force before compression failure.

[0017] Secondly, the present invention also provides a device for calculating the residual strength of a composite foam sandwich structure, comprising: The model building module is used to establish a damage analysis model of a composite foam sandwich structure, which includes a composite panel layer, a foam core layer, and an interlayer adhesive layer. The damage simulation module is used to perform explicit dynamic simulation of high-speed impact on the damage analysis model to obtain the damage state of the composite foam sandwich structure after impact. The strength calculation module is used to transmit the model parameters of the damage analysis model and the damage state to the residual compressive strength simulation model to calculate and analyze the residual compressive strength, so as to obtain the residual compressive strength of the composite foam sandwich structure after fragment impact damage.

[0018] The beneficial effects of this invention are as follows: A damage analysis model for a composite foam sandwich structure is established, comprising a composite panel layer, a foam core layer, and an interlayer adhesive layer; explicit dynamic simulation of high-speed impact on the damage analysis model is performed to obtain the damage state of the composite foam sandwich structure after impact, thereby detecting the damage state through the damage analysis model; the model parameters and damage state of the damage analysis model are transferred to a residual compressive strength simulation model for residual compressive strength calculation and analysis, obtaining the residual compressive strength of the composite foam sandwich structure after fragment impact damage, thus predicting the residual compressive strength of the composite foam sandwich structure after fragment impact damage through the residual compressive strength simulation model, improving the accuracy of performance evaluation. Attached Figure Description

[0019] Figure 1 A schematic flowchart of an embodiment of the method for calculating the residual strength of composite foam sandwich structures provided by the present invention; Figure 2 A schematic diagram of an embodiment of the composite material foam sandwich structure provided by the present invention; Figure 3 For the present invention Figure 1 A schematic diagram of an embodiment of step S102; Figure 4 For the present invention Figure 3 A schematic flowchart of an embodiment of step S302; Figure 5 A schematic diagram of an embodiment of the experimental system provided by the present invention; Figure 6 A schematic diagram of a structure for comparing three-view drawings of finite element simulation and experimental results provided by the present invention; Figure 7 This is a schematic diagram of an embodiment of the composite material foam sandwich structure residual strength calculation device provided by the present invention. Detailed Implementation

[0020] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0021] like Figure 1 As shown, a specific embodiment of the present invention discloses a method for calculating the residual strength of a composite foam sandwich structure, including: S101. Establish a damage analysis model for composite foam sandwich structures, which include composite panel layers, foam core layers, and interlayer adhesive layers.

[0022] The embodiments of this invention can be applied to modern ship design. Composite material foam sandwich structures, due to their excellent specific strength, specific stiffness, and energy absorption characteristics, are widely used in the protective armor of superstructures, bulkheads, and critical components. Composite material foam sandwich structures are as follows... Figure 2 As shown, composite foam sandwich structures consist of a face layer, an interlayer adhesive layer, and a foam core material. Such structures are highly susceptible to localized damage when subjected to high-speed fragments (such as metal fragments) from close-in weapon explosions. This damage not only weakens the structure's local protective capabilities but can also lead to a significant decrease in the overall load-bearing capacity (such as bending, shear, and compressive stability) due to stress concentration in the damaged area, threatening the ship's survivability and safety. Traditional methods struggle to accurately simulate the coupled failure process of multi-component materials under high-speed impact, and are unable to quantitatively assess the impact damage on the structure's remaining load-bearing capacity.

[0023] All analysis processes in this invention embodiment are performed in ABAQUS / Explicit. A refined finite element model, i.e., a damage analysis model, is established for the target composite foam sandwich structure. The model clearly distinguishes and establishes the composite panel layer, the foam core layer, and the interlayer adhesive layer. The composite panel layer is typically a carbon fiber or glass fiber reinforced laminate. A constitutive model and failure criteria are assigned to this layer. The foam core layer is typically a polymer foam such as PVC or PMI. An isotropically hardened compressible foam model and failure criteria are assigned to this layer. The interlayer adhesive layer inserts cohesive elements between the panel and the core layer. A damage initiation criterion and a damage evolution criterion are assigned to this interface layer, with the secondary nominal stress criterion used as the damage initiation criterion.

[0024] S102. Perform explicit dynamic simulation of high-speed impact on the damage analysis model to obtain the damage state of the composite foam sandwich structure after impact.

[0025] Before conducting formal impact simulation, this invention first determines the optimal mesh generation scheme through mesh convergence analysis. Based on this optimal mesh model, the initial velocity and impact position of the fragments are set in an explicit dynamic solver such as ABAQUS / Explicit, and high-speed impact simulation calculations are performed on the model to obtain the damage state of the composite foam sandwich structure after impact.

[0026] S103. Transfer the model parameters and damage state of the damage analysis model to the residual compressive strength simulation model to calculate and analyze the residual compressive strength, and obtain the residual compressive strength of the composite foam sandwich structure after fragment impact damage.

[0027] This invention utilizes the data transfer (or restart analysis) function of finite element software to transfer the model parameters and damage state of the entire model after the impact simulation in step S102 to the residual compressive strength simulation model for residual compressive strength calculation and analysis. The residual compressive strength simulation model is the second-stage calculation carrier in the entire integrated "impact-damage-residual strength" prediction process. Essentially, it is a finite element analysis model that carries the accurate initial state of impact damage and is used to simulate the final failure of the structure under static or quasi-static compressive loads. Analysis using the residual compressive strength simulation model can output the residual compressive strength of the composite foam sandwich structure after fragment impact damage.

[0028] Compared with existing technologies, this embodiment provides a damage analysis model for a composite foam sandwich structure, which includes a composite panel layer, a foam core layer, and an interlayer adhesive layer. The damage analysis model is subjected to explicit dynamic simulation of high-speed fragment impact to obtain the damage state of the composite foam sandwich structure after impact, thereby detecting the damage state through the damage analysis model. The model parameters and damage state of the damage analysis model are then transferred to a residual compressive strength simulation model for residual compressive strength calculation and analysis, obtaining the residual compressive strength of the composite foam sandwich structure after fragment impact damage. This residual compressive strength simulation model can then predict the residual compressive strength of the composite foam sandwich structure after fragment impact damage, improving the accuracy of performance evaluation.

[0029] Furthermore, based on the ABAQUS software platform, the analysis and judgment theory of composite material panel layer, foam core layer and interlayer interface adhesive layer of damage theory model was written into VUMAT subroutine.

[0030] In some embodiments of the present invention, the process of determining the optimal mesh partitioning scheme includes: The optimal meshing scheme is determined by adjusting the mesh size of key areas in the fragments and foam core layer, using the remaining velocity of the fragments as the convergence criterion.

[0031] In the mesh generation of this invention, mesh convergence analysis is required during calculation. Various different mesh sizes are set. Specifically, the mesh size of the cubic fragment and the overall size or local refinement size of the composite foam core structure are changed. The remaining velocity after the fragment penetrates the composite foam core structure is used as a reference benchmark to finally obtain the optimal mesh generation scheme.

[0032] In some embodiments of the present invention, such as Figure 3 As shown, step S102 includes: S301. After dividing the mesh in the damage analysis model according to the optimal meshing scheme, the damage status and stiffness reduction of the composite material panel layer in the damage analysis model are judged based on the three-dimensional progressive damage analysis method to obtain the damage coefficient, and the damage state of the composite material panel layer is determined according to the damage coefficient.

[0033] In the integrated numerical prediction method for impact and residual strength of composite foam sandwich structures, the damage evolution of the composite panel layer is crucial to the structural performance. To accurately simulate its complex failure behavior under high-speed impact and subsequent compressive loading, a damage criterion capable of distinguishing different failure modes must be employed for real-time assessment. This embodiment specifically illustrates how to use a three-dimensional progressive damage analysis method and the three-dimensional Hashin criterion to assess the damage of the composite panel layer elements and obtain quantified damage values.

[0034] In some embodiments of the present invention, step S301 includes: The damage status of the composite panel layer in the damage analysis model is judged based on the three-dimensional progressive damage analysis method, and the fiber tensile damage value, fiber compressive damage value, matrix tensile damage value and matrix compressive damage value are obtained.

[0035] In each time step t of this invention, the solver passes the stress tensor of the current element integration point to the VUMAT subroutine. σ ( t Its components include σ 11 , σ 22 , σ 33 , σ 12 , σ 13 Wherein, direction 1 (11) represents the fiber direction, and direction 2 (22) and direction 3 (33) represent the in-plane transverse and thickness directions. The VUMAT subroutine calculates and judges whether the three-dimensional Hashin criterion theory (three-dimensional progressive damage analysis method) is satisfied according to the current stress state, as shown in the following formula: (a) Fiber tensile damage: when When the fiber tensile damage factor is calculated, it is shown in formula (1); (1) If the fiber tensile damage factor is ≥1, then the fiber tensile damage is determined to have started at that point in the material.

[0036] (b) Fiber compression damage: when When the fiber compression damage factor is calculated, it is shown in formula (2); (2) If the fiber compression damage factor is ≥1, then fiber compression damage is considered to have started at that point in the material. Where, X C It represents the compressive strength in the fiber direction.

[0037] (c) Matrix tensile damage: when When the matrix tensile damage factor is calculated, it is shown in formula (3); (3) If the matrix tensile damage factor is ≥1, then the matrix tensile damage initiation is determined to have occurred at this point in the material.

[0038] (d) Matrix compression damage: when When calculating the matrix compression damage factor, as shown in formula (4); (4) In the formula, , This indicates the tensile and compressive strength of the composite panel layer along the fiber direction. , This indicates the tensile and compressive strength of the composite panel layer in the transverse direction. , and This represents the shear strength of the composite panel layer in three directions. If the matrix compressive damage factor is ≥1, then the matrix compressive damage initiation is determined to have occurred at that point in the material.

[0039] Once a damage mode is identified, the corresponding damage variable will start from 0 and increase to obtain the damage value of each damage variable at each time point, namely, the fiber tensile damage value, fiber compressive damage value, matrix tensile damage value, and matrix compressive damage value, following a predefined damage evolution law (usually based on fracture energy or equivalent displacement). This is the core of "gradual".

[0040] The damage process evolution of the composite foam sandwich structure is analyzed based on the fiber tensile damage value, fiber compressive damage value, matrix tensile damage value, and matrix compressive damage value to obtain the damaged composite panel layer.

[0041] This invention uses a continuous damage variable to describe the damage evolution process of a composite foam sandwich structure after reaching the initial damage criterion, thereby obtaining the damaged composite panel layer.

[0042] The stiffness of the damaged composite panel layer is reduced according to the failure criteria to obtain the damage coefficient.

[0043] In this embodiment of the invention, the stiffness reduction factor, i.e. the damage factor, after the onset of damage in the laminate is calculated, which includes various damage variables in the stiffness degradation matrix, is used to simulate the entire process of laminate damage from the beginning to complete failure, and to establish the stiffness degradation matrix of progressive damage of three-dimensional composite laminate, as shown in formulas (5) and (6): (5) , (6) In the formula, This represents the fiber damage variable in a composite laminate element. and Represents the fiber tensile and compressive damage variables of composite laminate units; This represents the matrix damage variable of a composite laminate element. and Represents the matrix tensile and compressive damage variables of composite laminate unit cells; and These represent the matrix tensile and compressive damage failure coefficients of the element. Typically, the two coefficients are 0.9 and 0.5.

[0044] When the material reaches the initial damage criterion, damage occurs in the fibers of the composite laminate. At this point, the corresponding material point damage variable changes from 0 to 1. For example, when the material experiences fiber tensile damage... Substituting into the formula, we can obtain Thus obtain d i =0, at which point the material is completely damaged. When the damage variable value of the material is 0, it means that the material has not been damaged. When the damage variable value of the material is 1, it means that the material is completely damaged. The three-dimensional progressive damage stiffness degradation matrix simulates the stiffness softening process of the material by calculating the stiffness softening coefficient of the composite laminate after being subjected to load, from the beginning of damage to complete failure.

[0045] S302. Based on the isotropic hardening compressible foam model and failure criteria, the mechanical behavior of the foam core layer under high-speed impact load is described, the dynamic strength and dynamic modulus are obtained, and the damage state of the foam core layer is determined based on the dynamic strength and dynamic modulus.

[0046] In the high-speed impact simulation of composite foam sandwich structures, the foam core layer is the main energy-absorbing component, and its mechanical behavior exhibits significant strain rate sensitivity, meaning that its strength and modulus increase with increasing loading rate. Ignoring this effect would severely underestimate the dynamic load-bearing capacity and energy absorption characteristics of the foam. This embodiment details how to combine a crushable foam model with a dynamic reinforcement factor model to achieve an accurate description of the mechanical response of the foam core layer under high strain rate impact loads, providing accurate stress states and dynamic material parameters for subsequent damage assessment.

[0047] In some embodiments of the present invention, such as Figure 4 As shown, step S302 includes: S401. Based on the isotropic hardening compressible foam model and failure criteria, the mechanical behavior of the foam core layer under high-speed impact load is described, and the current stress at each moment is obtained.

[0048] The failure criterion of this invention can be the yield criterion of foam, at time step t The VUMAT subroutine receives the current element strain from the solver. ε ( t The specific process is as follows: the isotropic hardening compressible foam model describes the mechanical behavior of the foam core layer under high-speed impact load, and judges the process of mechanical behavior according to the yield criterion of foam. When yielding occurs, the current stress at the corresponding moment is output.

[0049] S402. Obtain the true strain rate at each moment based on the current stress.

[0050] In this embodiment of the invention, at this time step t Based on the strain increment Δ provided by the solver ε and time increment Δ t Calculate the current true strain rate ( t ), ( t ) ≈ Δ ε / Δ t .

[0051] S403. Calculate the actual strain rate at each moment according to the dynamic enhancement factor parameterization model to obtain the corresponding dynamic enhancement factor.

[0052] The embodiments of the present invention obtain the true strain rate Substituting into the dynamic enhancement factor parameterization model, the dynamic enhancement factor at the current time is calculated, and the dynamic enhancement effect quantification characterization equation is shown in formula (7): (7) In the formula, A, B, and C are empirical constants describing the strain rate effect. The reference strain rate is set to a value of =1s-1; This represents the true strain rate of the composite material.

[0053] S404. Based on the dynamic reinforcement factor and the strength and modulus of the composite material under quasi-static conditions, the dynamic strength and dynamic modulus under dynamic conditions are obtained.

[0054] The expressions for the strength and modulus considering the strain rate effect in the embodiments of the present invention are described as shown in formulas (8) and (9), respectively: (8) (9) The values ​​of strength and modulus at different strain rates can be obtained from the above two equations. and The dynamic strength and dynamic modulus of a material under dynamic conditions are given by formulas (10) and (11) as follows: (10) (11) In the formula, and These are the quasi-static strength and modulus of the corresponding composite materials, respectively, and are known inputs. XT This represents the dynamic tensile strength along the fiber direction. X C The dynamic compressive strength is oriented in the fiber direction. Y T It represents the dynamic tensile strength in the transverse direction of the plane. Y C The dynamic compressive strength is the in-plane transverse force. Z T This represents the dynamic tensile strength in the thickness direction. Z C The dynamic compressive strength is in the thickness direction. S 12 The dynamic shear strength in the plane (planes 1-2) is the in-plane (planes 1-2). S 23 The dynamic shear strength of the transverse plane (planes 2-3) S 31 The dynamic shear strength of the longitudinal-thickness plane (3-1 plane) is given. E 11 Dynamic elastic modulus in the fiber direction. E 22 It represents the in-plane, transverse dynamic elastic modulus. E 33 This represents the dynamic elastic modulus in the thickness direction. G 12 This refers to the dynamic shear modulus in the plane (planes 1-2). G 23 The dynamic shear modulus of the transverse plane (2-3 planes) is given. G 31 The dynamic shear modulus of the longitudinal-thickness plane (3-1 plane).

[0055] S303. The cohesive force model based on fracture mechanics describes the damage and propagation process between the composite panel layer and the interlayer adhesive layer, and obtains the damage state of the interlayer adhesive layer.

[0056] In this embodiment of the invention, during high-speed impact and subsequent compression of a composite foam sandwich structure, the interfacial adhesive layer between the panel and the core layer is a critical weak point. The initiation and propagation of delamination damage in this layer significantly reduces the overall integrity, stiffness, and load-bearing capacity of the structure. To accurately simulate this interfacial failure process, this embodiment employs a cohesive force model based on fracture mechanics, using physically defined damage initiation and evolution criteria to calculate and determine the stress state and damage state of the interfacial layer in real time.

[0057] In some embodiments of the present invention, step S303 includes: The cohesive model based on fracture mechanics describes the damage and propagation process between the composite panel layer and the interlayer adhesive layer, and obtains the stress state.

[0058] The cohesive force model in this invention is a numerical simulation method based on fracture mechanics, used to describe the entire process of crack (or delamination) initiation, propagation, and final fracture within a material or at the interface between different materials. At the time step... t The program obtains the relative separation displacement vector between the upper and lower surfaces of the current cohesive model. δ The stress state of the interface element is calculated based on the linear elastic cohesive constitutive relation, as shown in formula (12): (12) In the formula, the relative separation displacement vector δ include , , , For normal separation displacement, , These are two tangential separation displacements; K The adhesive stiffness (i.e., the initial (undamaged) stiffness matrix) is usually assumed to be a diagonal matrix, where K nn For normal stiffness, K ss and K tt This represents the shear stiffness. The output of this step is the stress state of the interface at the current moment. σ n , σ s , σ t}

[0059] The performance degradation and crack propagation of the interlayer adhesive layer are determined based on the secondary stress criterion, the BK criterion, and the stress state, thus obtaining the damage state of the interlayer adhesive layer.

[0060] In this embodiment of the invention, to determine whether interface damage has begun (i.e., adhesion degradation has begun), a second nominal stress criterion is used as the damage initiation criterion. A damage initiation factor is calculated. If the calculated damage initiation factor is less than 1, the interface remains intact, the stiffness remains unchanged, and the damage variable... D =0. If the calculated damage initiation factor is greater than or equal to 1, then the material point is considered to have reached the damage initiation condition, and the interface properties begin to degrade. The program records the separation displacement at this moment. δ 0, and enter the damage evolution stage. Once damage begins, the interfacial stiffness starts to degrade, and the stress-displacement relationship enters the softening stage. Damage evolution is controlled by fracture energy, and the BK (Benzeggagh-Kenane) criterion is used to determine crack propagation in the mixed mode, defining energy-based damage variables. DIt monotonically increases from 0 (damage initiation point) to 1 (complete failure), and the damage state at the current moment is determined by this damage variable. D ( t Quantification (0≤) D ≤1). According to D The stiffness matrix is ​​reduced. When D When the value is 1, the stiffness completely degrades. σ =0, the interface is completely invalid, and the crack propagation judgment result is obtained.

[0061] The cohesive model in this invention dynamically describes the entire process of an interface from linear elastic response to damage initiation, then to stiffness degradation (damage evolution), and finally to complete failure (crack propagation), and outputs the stress state at each moment. By using the quadratic nominal stress criterion and the BK criterion, it physically determines when damage begins and how it evolves, ultimately obtaining the damage state at each interface point, i.e., the damage variable. D The spatiotemporal distribution. At the end of the impact simulation. D Spatial cloud maps clearly show the extent, shape, and severity of the stratification. D The region where =1 indicates complete debonding, and 0< D Areas with a value <1 indicate partial damage). This complete... D The field, as a key initial damage condition, is seamlessly transferred to the residual strength analysis to assess the impact of stratification on compressive stability.

[0062] In some embodiments of the present invention, after step S102, the method further includes: The ballistic limiting velocity of the composite foam sandwich structure was fitted and predicted, and the verification results of the damage state were obtained. When the verification result is reliable, proceed with the step of "transferring the model parameters and damage state of the damage analysis model to the residual compressive strength simulation model to calculate and analyze the residual compressive strength, and obtaining the residual compressive strength of the composite foam sandwich structure after fragment impact damage".

[0063] This invention analyzes the damage characteristics and damage mechanism of composite foam sandwich structures under high-speed impact, and then studies their ballistic limit velocity using finite element simulation. Specifically, the energy absorbed by the composite foam sandwich structure during penetration is the same as the kinetic energy reduced by the fragments, as shown in formula (13): (13) In the formula, It is the initial penetration velocity of the fragments. It is the remaining penetration speed of the fragments. It is the mass of the fragment. The ballistic limit of the composite foam sandwich structure can be fitted by the following formula as shown in formula (14): (14) In the formula, a and p are bullet parameters. According to the Recht-Ipson model, for an immutable rigid body fragment, a is 1 and p is 2. This is the ballistic limit velocity.

[0064] After obtaining the ballistic limit velocity, this predicted value is compared with the experimentally measured actual ballistic limit. If the two match well, it strongly proves that the entire material model, failure criteria, and parameter settings used are accurate and can reproduce the real physical process. This means that the "damage state" calculated by this model is reliable. If reliable, proceed to step S103. If unreliable, perform a model calibration and verification cycle on the damage analysis model. The specific settings can be configured according to the actual situation, and this embodiment of the invention does not impose any limitations.

[0065] In some embodiments of the present invention, step S103 includes: By utilizing the restart analysis function of the finite element software, the model parameters, damage state transmission, and stiffness degradation matrix of the damage analysis model are used as initial conditions to transfer to the residual compressive strength simulation model for residual compressive strength calculation and analysis, thereby obtaining the residual compressive strength of the composite foam sandwich structure after fragment impact damage.

[0066] In this embodiment of the invention, after the impact calculation is completed, the data transfer function (restart analysis) of the ABAQUS / Explicit software is used to transfer the geometric dimensions, material parameters, layup method, mesh generation and element type of the composite sandwich panel from the high-speed impact finite element simulation calculation of the composite foam sandwich structure to the residual compressive strength finite element simulation calculation of the composite foam sandwich structure. The calculation result of the high-speed impact resistance of the composite foam sandwich structure is used as the initial condition for the calculation of the residual compressive strength, and the element damage and element stiffness degradation at the end of the high-speed impact calculation are maintained. The calculation of the residual compressive strength is shown in formula (15): (15) In the formula, P The remaining compressive strength after impact, in MPa; A This represents the cross-sectional area, in mm². F max This represents the maximum compressive force before compression failure.

[0067] This invention, based on ABAQUS software and combined with failure assessment theories for composite material panel layers, foam core layers, and interlayer adhesive layers, analyzes the compression damage characteristics of composite foam sandwich structures after high-speed impact. First, the compression process and overall damage of the composite foam sandwich structure are analyzed. Subsequently, the damage to the carbon fiber / glass fiber panel, foam core layer, and interlayer adhesive layers is analyzed separately.

[0068] The ballistic impact testing system designed in this embodiment of the invention is as follows: Figure 5 As shown in Table 1, finite element simulation calculations were performed on the high-speed impact test of 45 steel fragments on composite sandwich panels under working conditions 1 to 3 respectively. The residual velocity of the fragments was extracted from the calculation and compared with the residual velocity of the fragments after high-speed impact in the response working condition test.

[0069] Table 1. Test conditions and maximum compressive load results of the test plate

[0070] like Figure 6 As shown, Figure 6 Figure a shows the incoming surface, figure b shows the side surface, and figure c shows the outgoing surface. Comparing the finite element simulation results with the experimental results under the three views, we can see that the same damage mode and damage effect occurred. The incoming surface showed a tear with an approximate fragment shape, and the surface glass fiber was broken, concave inward, exposing the internal carbon fiber; the side surface shows that the fiber protruded outward after the tear occurred; the outgoing surface shows a tear slightly larger than the fragment size, with the surface glass fiber protruding outward.

[0071] Impact damage in composite foam sandwich structures, as described in this invention, is a highly complex process involving multiple materials such as fiber-reinforced composites, adhesive layers, and foam, resulting in diverse damage modes. This invention proposes a numerical calculation method for the impact performance and residual strength after impact of foam sandwich structures, simultaneously considering fiber panel failure, core material failure, interlayer delamination, and interfacial debonding. Damage theoretical models for each component of the composite foam sandwich structure are established. A three-dimensional progressive damage analysis method is employed, using the three-dimensional Hashin criterion to assess the failure status of fiber-reinforced composite elements, followed by corresponding stiffness reduction for the failed elements. An isotropic hardening compressible foam model is used to describe the mechanical behavior of the foam sandwich under high-speed impact loads. A cohesive force model based on fracture mechanics is employed to describe the formation and propagation process of interlayer and interfacial adhesive layer damage.

[0072] Composite sandwich structures exhibit multi-mechanism coupled damage behavior under dynamic penetration loading, including fiber fracture, matrix cracking, and interfacial delamination failure. Traditional single-failure-mode modeling methods are insufficient to characterize this multi-physics coupling effect, leading to significant theoretical biases in impact load-bearing performance predictions. Therefore, this invention utilizes ABAQUS / Explicit damage state transfer technology to achieve the transfer of impact damage to the initial damage in residual compressive strength analysis.

[0073] To better implement the method for calculating the residual strength of composite foam sandwich structures in this invention, this invention also provides a device for calculating the residual strength of composite foam sandwich structures, based on the method for calculating the residual strength of composite foam sandwich structures. Figure 7 As shown, the residual strength calculation device 700 for composite foam sandwich structures includes: Model building module 701 is used to establish a damage analysis model of composite foam sandwich structure, which includes composite panel layer, foam core layer and interlayer interface adhesive layer. Damage simulation module 702 is used to perform explicit dynamic simulation of high-speed impact on the damage analysis model to obtain the damage state of the composite foam sandwich structure after impact. The strength calculation module 703 is used to transfer the model parameters and damage state of the damage analysis model to the residual compressive strength simulation model for residual compressive strength calculation and analysis, so as to obtain the residual compressive strength of the composite foam sandwich structure after fragment impact damage.

[0074] The composite material foam sandwich structure residual strength calculation device 700 provided in the above embodiments can realize the technical solutions described in the above composite material foam sandwich structure residual strength calculation method embodiments. The specific implementation principles of each module or unit can be found in the corresponding content in the above composite material foam sandwich structure residual strength calculation method embodiments, which will not be repeated here.

[0075] The above provides a detailed description of the method and apparatus for calculating the residual strength of composite foam sandwich structures provided by the present invention. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for calculating the residual strength of a composite foam sandwich structure, characterized in that, include: A damage analysis model for a composite foam sandwich structure is established, wherein the composite foam sandwich structure includes a composite panel layer, a foam core layer, and an interlayer adhesive layer. The damage analysis model was subjected to explicit dynamic simulation of high-speed impact of fragments to obtain the damage state of the composite foam sandwich structure after impact. The model parameters of the damage analysis model and the damage state are transferred to the residual compressive strength simulation model to calculate and analyze the residual compressive strength, thereby obtaining the residual compressive strength of the composite foam sandwich structure after fragment impact damage.

2. The method for calculating the residual strength of a composite foam sandwich structure according to claim 1, characterized in that, The damage analysis model is subjected to explicit dynamic simulation of high-speed impact fragmentation to obtain the damage state of the composite foam sandwich structure after impact, including: After dividing the mesh in the damage analysis model according to the optimal meshing scheme, the damage status and stiffness reduction of the composite material panel layer in the damage analysis model are judged and the damage coefficient is reduced based on the three-dimensional progressive damage analysis method to obtain the damage coefficient, and the damage state of the composite material panel layer is determined according to the damage coefficient. The mechanical behavior of the foam core layer under high-speed impact load is described based on the isotropic hardening compressible foam model and the failure criterion, and the dynamic strength and dynamic modulus are obtained. The damage state of the foam core layer is determined based on the dynamic strength and the dynamic modulus. The cohesive force model based on fracture mechanics describes the damage and propagation process between the composite panel layer and the interlayer adhesive layer, and obtains the damage state of the interlayer adhesive layer.

3. The method for calculating the residual strength of a composite foam sandwich structure according to claim 2, characterized in that, The three-dimensional progressive damage analysis method is used to determine the damage status and stiffness reduction of the composite material panel layer in the damage analysis model, and the damage coefficient is obtained, including: The damage condition of the composite panel layer in the damage analysis model is judged based on the three-dimensional progressive damage analysis method, and the fiber tensile damage value, fiber compressive damage value, matrix tensile damage value and matrix compressive damage value are obtained. The damage process evolution of the composite foam sandwich structure is analyzed based on the fiber tensile damage value, the fiber compressive damage value, the matrix tensile damage value, and the matrix compressive damage value to obtain the damaged composite panel layer; The stiffness of the damaged composite panel layer is reduced according to the failure criterion to obtain the damage coefficient.

4. The method for calculating the residual strength of a composite foam sandwich structure according to claim 2, characterized in that, The cohesive model based on fracture mechanics describes the damage and propagation process between the composite panel layer and the interlayer adhesive layer, obtaining the damage state of the interlayer adhesive layer, including: The cohesive model based on fracture mechanics describes the damage and propagation process between the composite panel layer and the interlayer adhesive layer, and obtains the stress state. The performance degradation and crack propagation of the interlayer adhesive layer are determined based on the secondary stress criterion, the BK criterion, and the stress state, thereby obtaining the damage state of the interlayer adhesive layer.

5. The method for calculating the residual strength of a composite foam sandwich structure according to claim 2, characterized in that, The mechanical behavior of the foam core layer under high-speed impact load is described based on the isotropic hardening compressible foam model and the failure criterion, resulting in dynamic strength and dynamic modulus, including: The mechanical behavior of the foam core layer under high-speed impact load is described based on the isotropic hardening compressible foam model and the failure criterion, and the current stress at each moment is obtained. The true strain rate at each moment is obtained based on the current stress. The actual strain rate at each time step is calculated based on the dynamic enhancement factor parameterization model to obtain the corresponding dynamic enhancement factor. Based on the dynamic reinforcement factor and the strength and modulus of the composite material under quasi-static conditions, the dynamic strength and dynamic modulus under dynamic conditions are obtained.

6. The method for calculating the residual strength of a composite foam sandwich structure according to claim 2, characterized in that, The process of determining the optimal mesh partitioning scheme includes: By adjusting the mesh size of the fragments and key areas of the foam core layer, and using the remaining velocity of the fragments as the convergence criterion, the optimal mesh partitioning scheme is determined.

7. The method for calculating the residual strength of a composite foam sandwich structure according to claim 2, characterized in that, The step of transferring the model parameters of the damage analysis model and the damage state to the residual compressive strength simulation model for residual compressive strength calculation and analysis, to obtain the residual compressive strength of the composite foam sandwich structure after fragment impact damage, includes: Using the restart analysis function of the finite element software, the model parameters, damage state transmission, and stiffness degradation matrix of the damage coefficient of the damage analysis model are used as initial conditions to transfer to the residual compressive strength simulation model for residual compressive strength calculation and analysis, so as to obtain the residual compressive strength of the composite foam sandwich structure after fragment impact damage.

8. The method for calculating the residual strength of a composite foam sandwich structure according to claim 1, characterized in that, After performing explicit dynamic simulation of high-speed impact on the damage analysis model to obtain the damage state of the composite foam sandwich structure after impact, the method further includes: The ballistic limiting velocity of the composite foam sandwich structure is fitted and predicted to obtain the verification results of the damage state; If the verification result is reliable, calculate the remaining compressive strength.

9. The method for calculating the residual strength of a composite foam sandwich structure according to claim 1, characterized in that, The remaining compressive strength is calculated as follows: In the formula, P The remaining compressive strength after impact, in MPa; A This refers to the cross-sectional area, in mm². 2 ; F max This represents the maximum compressive force before compression failure.

10. A device for calculating the residual strength of a composite foam sandwich structure, characterized in that, include: The model building module is used to establish a damage analysis model of a composite foam sandwich structure, which includes a composite panel layer, a foam core layer, and an interlayer adhesive layer. The damage simulation module is used to perform explicit dynamic simulation of high-speed impact on the damage analysis model to obtain the damage state of the composite foam sandwich structure after impact. The strength calculation module is used to transmit the model parameters of the damage analysis model and the damage state to the residual compressive strength simulation model to calculate and analyze the residual compressive strength, so as to obtain the residual compressive strength of the composite foam sandwich structure after fragment impact damage.

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