Method and system for predicting compressive residual strength of intercalation toughened composite after impact

Abstract

The application provides a method and system for predicting the compressive residual strength of an intercalation toughened composite material after impact, and belongs to the technical field of electric digital data processing. The application determines the interlayer fracture toughness through experiments and establishes a finite element model, adopts the progressive damage theory combined with the Hashin criterion and the cohesive force method to accurately capture the initiation and evolution of the intralayer and interlayer damage, extracts the damage state variables of each unit after impact, imports the deformed grid into a compression model, and simultaneously reduces the modulus, strength and fracture energy based on the damage variables to construct a high-precision post-damage material constitutive relation, and finally obtains the residual strength through compression simulation. The application avoids the initial oscillation and residual stress interference in the traditional "restarting" method, realizes the automatic damage mapping and performance reduction by using a Python script, significantly improves the calculation efficiency and universality, and provides a reliable simulation tool for the optimization design of the toughened layer.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of digital data processing, and relates to a method using finite elements in computer-aided design, to design optimization, verification or simulation, to composite materials, to force analysis or optimization, and in particular to a method and system for predicting the compressive residual strength of interlaminar toughened composite materials after impact. BACKGROUND

[0002] Currently, composite materials are widely used in high-tech fields such as aerospace. However, when they are subjected to impact from foreign objects during production and use, internal invisible damage may occur, which will cause a significant decrease in the strength of the structure when subjected to further loading (such as in-plane compression). The industry also considers the compressive residual strength after impact as an important indicator for evaluating the damage tolerance of composite materials, and adds a toughening layer to the composite material as a technical means to improve the interlaminar fracture toughness. However, due to the high production cost of interlaminar toughened composite materials and the strong designability of the toughening layer arrangement scheme, the efficiency of researching them through experimental methods is low. Therefore, it is particularly important to use simulation calculations to guide the design of the toughening layer arrangement by predicting the response of the compressive mechanical behavior of composite materials after impact under different toughening layer arrangement schemes through a finite element model, which will greatly improve the research efficiency.

[0003] In the existing finite element simulation method, the paper “Liu X Y, Zhang Y, Li X L, et al. Simulation analysis of composite laminates after impact and compression [J]. Aviation Computing Technology, 2024, 54(4): 106-109. DOI: 10.3969 / j.issn.1671-654X.2024.04.021.” discloses a numerical simulation method that unifies the impact and compression processes. This method uses the data transfer function of ABAQUS to transfer the damage, stress, strain and displacement state after impact to the compression model as initial conditions, and uses a three-dimensional Hashin failure criterion and stiffness reduction to simulate damage.

[0004] However, the above-mentioned literature recording scheme still has some inherent defects when applied to the prediction of the compressive strength of interlaminar toughened composite materials after impact:

[0005] (1) Insufficient comprehensiveness of damage mapping: The existing modeling method focuses on stiffness reduction of damaged elements when introducing impact damage into the compression model. However, after damage, the strength properties (such as tensile, compressive, shear strength) and fracture energy of composite materials also decrease significantly. The existing method ignores the degradation of these key mechanical properties, resulting in incomplete damage characterization, prediction results deviating from the actual material's post-damage behavior, and difficulty in accurately reflecting the actual effect of the toughening layer in the damage evolution process.

[0006] (2) The initial state interference exists in the calculation process: the above-mentioned document adopts the "restart" calculation method, that is, the boundary conditions are directly changed after the impact analysis for compression analysis. This method will cause the structure oscillation and residual stress generated by the impact to be brought into the compression stage. In order to suppress the oscillation, it is often necessary to introduce additional artificial damping, which not only increases the calculation cost, but also makes the initial stress state of the compression model inconsistent with the actual static state of the specimen after impact, thereby affecting the accuracy of the residual strength prediction.

[0007] (3) The model generality and implementation efficiency need to be improved: such methods usually rely on the user-defined material subroutine (such as UMAT) to realize the complex constitutive model and damage evolution law. Different material systems or failure criteria need to modify or even redevelop the subroutine, the applicability is limited, and the programming ability of the user is required, the model development and debugging period is long, and the calculation cost is relatively high.

[0008] In addition, the paper "Zhu Weirao. Research on residual strength and fatigue performance of composite laminates after low-speed impact [D]. Nanjing University of Aeronautics and Astronautics, 2012." discloses the damage evolution law, residual strength attenuation characteristics and compression-compression fatigue life prediction method of composite laminates under low-speed impact. Through experiments and numerical simulation, an analysis model for evaluating the safety of the structure is proposed.

[0009] However, the scheme recorded in the above-mentioned document still has some inherent defects when applied to the impact compression strength prediction of intercalation toughened composite materials:

[0010] (1) The unit performance reduction of the above-mentioned document is also only for the stiffness attenuation of the in-plane unit, and does not fully consider the influence of the strength and fracture energy attenuation of the in-plane unit.

[0011] (2) The damage mapping method of the impact and compression finite element model in the above-mentioned document only considers the reduction of the unit performance, and does not fully consider the change of the geometric characteristics of the sample after being subjected to impact. The initial mesh model does not contain the mesh deformation caused by the initial impact damage, which will cause some differences in the subsequent buckling behavior from the actual.

[0012] (3) The method proposed in the above-mentioned document also extracts the damage state of each unit, but the performance reduction part still needs to be realized through the VUMAT subroutine.

[0013] In summary, the modeling method of the intercalation toughened composite material impact compression residual strength prediction model at the present stage mainly has the following defects:

[0014] (1) Existing intercalation toughening composite material research is mostly based on costly experiments, and there are few reports on the finite element simulation model establishment method for quickly predicting the compression residual strength of the composite material after impact. The mechanism of the toughening effect of the composite material under different toughening layer arrangement schemes in low-speed impact and the compression mechanical behavior after impact is not clear.

[0015] (2) The existing modeling method of the composite material after impact compression mostly deletes damaged elements or equivalent damaged areas to reduce performance, which fails to consider the degradation of strength and fracture energy simultaneously, and it is also difficult to accurately quantify and introduce the interlaminar delamination damage caused by the initial impact. These simplifications limit the accuracy of the prediction model.

[0016] (3) The existing calculation process (such as the restart method) introduces unrealistic initial states (residual stress, oscillation), and relies on the writing of complex finite element subprograms, resulting in low calculation efficiency and weak universality, which is not conducive to rapid application in engineering design and material selection.

[0017] (4) In the simulation of intercalation toughening composite materials, the existing technology usually treats it as a homogeneous or conventional laminate, which fails to effectively reflect the specific influence of the toughening layer on the interlaminar fracture toughness, damage initiation and propagation behavior, resulting in an inaccurate description of the toughening mechanism and difficulty in guiding the optimization design of the toughening layer.

[0018] (5) In the process of transferring impact damage to the compression model, the existing technology mostly focuses on the reduction of material stiffness, but fails to fully consider the influence of geometric deformation (such as dents, pre-buckling local shape) caused by impact on subsequent compression stability and failure mode, limiting the model's ability to capture the real failure behavior.

[0019] (6) The simulation process of the existing technology usually relies on multiple software platforms and manual operations, and the damage data transfer, performance reduction and model reconstruction process from impact simulation to compression analysis is complicated, lacking an integrated and automated simulation system, which affects the analysis efficiency and reliability of the results. SUMMARY

[0020] The present application is carried out to solve the above problems, and aims to provide an intercalation toughening composite material impact compression residual strength prediction method and system.

[0021] The application provides a method for predicting the compressive residual strength of an intercalation toughened composite material after impact, which has the characteristics that the initial impact damage of the intercalation toughened composite material is considered, and comprises the following steps: S10, interlaminar fracture toughness of the intercalation toughened composite material is measured by actual test, and interlaminar cohesive contact properties are determined; S20, after a low-speed impact finite element model of the intercalation toughened composite material is established in a finite element modeling software, the interaction force between the interlaminar layers of the intercalation toughened composite material is defined by the interlaminar cohesive contact properties; S30, the low-speed impact finite element model is run to simulate that the intercalation toughened composite material is impacted by an impactor at low speed, whether the intercalation toughened composite material is damaged is judged based on a composite material progressive damage theory, and damage state variables of each unit of the intercalation toughened composite material are extracted, the damage state variables include intralaminar damage state variables and interlaminar damage state variables; S40, the grid model corresponding to the intercalation toughened composite material in the low-speed impact finite element model after running is imported into a new post-impact compression finite element model, and the intralaminar mechanical properties and the interlaminar mechanical properties corresponding to the post-impact compression finite element model are reduced according to the intralaminar damage state variables and the interlaminar damage state variables; S50, the boundary conditions of the post-impact compression finite element model after reduction are set to be consistent with actual compression conditions, and the post-impact compression finite element model is run, and the compression stress corresponding to the peak load in the compression process is taken as the compressive residual strength of the intercalation toughened composite material.

[0022] In the method for predicting the compressive residual strength of the intercalation toughened composite material after impact provided by the application, the actual test in step S10 can further comprise a double cantilever beam experiment and an end notched flexure experiment, and the interlaminar fracture toughness can further comprise type I interlaminar fracture toughness and type II interlaminar fracture toughness.

[0023] In the method for predicting the compressive residual strength of the intercalation toughened composite material after impact provided by the application, the low-speed impact finite element model in step S20 can further comprise: a plurality of shell elements for constructing the intercalation toughened composite material; and a plurality of rigid body elements for constructing an impactor for impacting the intercalation toughened composite material at low speed.

[0024] In the method for predicting the compressive residual strength of the intercalation toughened composite material after impact provided by the application, the boundary conditions of the impactor in step S20 can be set to only generate displacement in the impact direction of the intercalation toughened composite material, and the displacement and / or rotation in other directions are kept as 0.

[0025] The method for predicting the residual compressive strength of intercalated toughened composite materials after impact provided by this invention may also have the following feature: In step S30, during the operation of the low-speed impact finite element model, the stress tensor of each element of the intercalated toughened composite material is extracted, and the Hashin failure criterion is used to determine whether intralaminar damage has occurred: when the longitudinal stress tensor... When the value is ≥0, the fiber is considered to have suffered tensile damage, and the failure criterion expression is: , X represents the fiber tensile damage variable. T Indicates longitudinal tensile strength. S represents the tangential stress tensor. L Represents the longitudinal shear strength, where α is the shear failure coefficient used to represent the effect of tangential force on fiber tensile damage, 0≤α≤1, when the longitudinal stress tensor... When the value is ≤0, the fiber is considered to have suffered compressive damage, and the failure criterion expression is: , X represents the fiber compression damage variable. C Represents longitudinal compressive strength, when the transverse stress tensor When the value is ≥0, tensile damage to the matrix is ​​considered to have occurred, and the failure criterion expression is: , Y represents the matrix tensile damage variable. T Represents transverse tensile strength, when the transverse stress tensor... When the value is ≤0, the matrix is ​​considered to have undergone compressive damage, and the failure criterion expression is: , S represents the matrix compression damage variable. T Y represents the transverse shear strength. C It represents the transverse compressive strength, and the damage state variable within the layer is the maximum value among the fiber tensile damage variable, fiber compressive damage variable, matrix tensile damage variable, and matrix compressive damage variable.

[0026] The method for predicting the residual compressive strength of intercalated toughened composite materials after impact provided by this invention may also have the following feature: In step S30, during the operation of the low-speed impact finite element model, the cohesive force method is used to capture the interlaminar damage behavior of the intercalated toughened composite material to determine the interlaminar damage state variables. The initiation conditions for interlaminar damage in the intercalated toughened composite material are: , This represents the interlaminar stress tensor in the i-direction of the interlaminar toughened composite material. The term represents the interlaminar material strength in the i-direction of the interlaminar toughened composite material, where i is n, s, or t, and n, s, and t represent the normal and two shear directions, respectively. The interlaminar damage state variables are: , denotes the equivalent displacement when the interlaminar failure is complete, i.e. denotes the maximum displacement, denotes the equivalent displacement when the delamination damage is just initiated.

[0027] In the method for predicting the compressive residual strength of the intercalation toughened composite material after impact provided by the application, the method can further have the following characteristics: in step S30, the interlaminar damage state variable d inter denotes the severity of the interlaminar damage, inter =0 indicates no damage, d inter =1 indicates complete interlaminar failure.

[0028] In the method for predicting the compressive residual strength of the intercalation toughened composite material after impact provided by the application, the method can further have the following characteristics: in step S40, the reduction is performed in the following manner: the intralaminar modulus, the intralaminar strength, and the intralaminar fracture energy of each element in the post-impact compression finite element model are respectively multiplied by the intralaminar damage state variable of the element; and the interlaminar modulus, the interlaminar strength, and the interlaminar fracture energy of each element in the post-impact compression finite element model are respectively multiplied by the interlaminar damage state variable of the element.

[0029] In the method for predicting the compressive residual strength of the intercalation toughened composite material after impact provided by the application, the method can further have the following characteristics: in step S30, the extraction of the intralaminar damage state variable and the interlaminar damage state variable is automatically performed using a Python script; and in step S40, the reduction operation of the intralaminar mechanical properties and the interlaminar mechanical properties is automatically performed using a Python script.

[0030] The application further provides a system for predicting the compressive residual strength of an intercalation toughened composite material after impact, which has the characteristics that the system uses any of the methods for predicting the compressive residual strength of an intercalation toughened composite material after impact, and comprises: a data input module for allowing a user to input cohesive contact properties determined through actual tests; a low-speed impact modeling module connected with the data input module, for establishing a low-speed impact finite element model of the intercalation toughened composite material in finite element modeling software, and defining the interaction force between the intercalation toughened composite material through the cohesive contact properties; a damage simulation module connected with the low-speed impact modeling module, for running the low-speed impact finite element model to simulate the low-speed impact process, judging the damage state based on the progressive damage theory of the composite material, and extracting damage state variables; a performance reduction module connected with the damage simulation module, for importing the grid model after impact into a new post-impact compression finite element model, and reducing the in-layer mechanical properties and interlayer mechanical properties according to the damage state variables; and a compression simulation module connected with the performance reduction module, for allowing the user to set the boundary conditions of the post-impact compression finite element model to match the actual compression working conditions, running the post-impact compression finite element model, and obtaining the compression stress corresponding to the peak load as the compressive residual strength.

[0031] The application has the following beneficial effects:

[0032] (1) The application constructs a high-precision damage prediction model, and realizes accurate simulation of the post-impact compression behavior. The method is based on the progressive damage theory of the composite material, and comprehensively uses the Hashin failure criterion and the cohesive force method, which can accurately capture and distinguish the initiation and evolution process of the in-layer damage (tensile / compression damage of fibers / substrate) and the interlayer damage (delamination). Compared with the prior art which only considers stiffness reduction, the application simultaneously considers the degradation of modulus, strength and fracture energy caused by damage, which makes the characterization of the damage state more complete, and the prediction result is more consistent with the experimental result.

[0033] (2) The application innovatively solves the initial state interference problem in the traditional simulation process, and improves the calculation efficiency and accuracy. The traditional "restarting" method will bring the residual stress and structure oscillation caused by impact into the compression stage, which affects the accuracy of the result. The application directly imports the deformed grid model after impact into a new compression model, and only reduces the performance of the damaged units, which fundamentally avoids the problem of unrealistic initial stress and oscillation. The application does not need to introduce additional artificial damping, which not only saves the calculation cost, but also ensures that the initial state of the compression simulation is consistent with the real post-impact static specimen state.

[0034] (3) The present application realizes a high-universality and high-efficiency automatic modeling process, and reduces the technical threshold. The present application automatically performs the extraction of damage variables and the reduction operation of mechanical properties through a Python script, replacing the dependence on a complex user subroutine (such as UMAT / VUMAT) in the traditional method. The automatic process is not dependent on a specific unit type (applicable to shell elements, solid elements, etc.), is applicable to different material systems and failure criteria, significantly improves the universality of the model, shortens the model development and debugging period, and is more beneficial to engineering application.

[0035] (4) The present application fully considers the multidimensional influence of impact damage, and significantly improves the capturing ability of the model to the real damage behavior. The present application imports the grid deformation caused by impact into the compression model, so that the prediction of subsequent buckling behavior and damage mode is more realistic. The present application can clearly reveal the quantitative relationship between the distribution of the toughening layer and the compression strength after impact through parameterized analysis, clarify the micro-mechanical mechanism of toughening, and provide direct and strong theoretical basis and data support for the optimization design of the toughening layer. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is a flowchart of an intercalation toughened composite material post-impact compression residual strength prediction method of an embodiment of the present application.

[0037] Figure 2 is a low-speed impact finite element model and its boundary conditions of step S21 of an embodiment of the present application.

[0038] Figure 3 is a reduced post-impact compression finite element model and its boundary conditions of step S50 of an embodiment of the present application.

[0039] Figure 4 is an architecture diagram of an intercalation toughened composite material post-impact compression residual strength prediction system of an embodiment of the present application.

[0040] Figure 5 is the post-impact compression load-displacement prediction result and the measured result of the laminate 1 of the test example of the present application.

[0041] Figure 6 is the post-impact compression load-displacement prediction result and the measured result of the laminate 2 of the test example of the present application. DETAILED DESCRIPTION

[0042] In order to make the technical means, creative features, purposes and effects realized by the present application easy to understand, the following embodiments will specifically describe a intercalation toughened composite material post-impact compression residual strength prediction method and system of the present application in conjunction with the drawings.

[0043] EMBODIMENT

[0044] Figure 1 is a flow chart of the method for predicting the compressive residual strength of an intercalation toughened composite material after impact according to an embodiment of the present application.

[0045] As shown in Figure 1 , the embodiment provides a method for predicting the compressive residual strength of an intercalation toughened composite material after impact, which takes into account the initial impact damage of the intercalation toughened composite material, and includes the following steps:

[0046] S10, the interlaminar fracture toughness of the intercalation toughened composite material is measured by actual test, and the interlaminar cohesive contact property is determined therefrom.

[0047] The actual test includes double cantilever beam experiment and end notched flexure experiment, and the interlaminar fracture toughness includes mode I interlaminar fracture toughness and mode II interlaminar fracture toughness.

[0048] S20, after establishing the low-speed impact finite element model of the intercalation toughened composite material in the finite element modeling software, the interlaminar interaction force of the intercalation toughened composite material is defined by the cohesive contact property determined in step S10, including the following sub-steps S21-S22:

[0049] S21, finite element modeling:

[0050] In the Explicit module of Abaqus software, the finite element model of the intercalation toughened composite material is established using shell elements, and the finite element model of the impactor for low-speed impact on the finite element model of the intercalation toughened composite material is established using rigid body elements. The above two are collectively used as the low-speed impact finite element model.

[0051] The boundary conditions of the finite element model of the intercalation toughened composite material are set according to the experimental conditions, the external nodes of the bottom elements are fixedly constrained, and the interlaminar interaction force is directly defined by the cohesive contact property; the boundary conditions of the finite element model of the impactor are set to have only Z-direction displacement, X and Y-direction displacement, and three-direction rotation are all kept as zero, as shown in Figure 2 .

[0052] S22, changing the cohesive contact property:

[0053] The finite element model of the intercalation toughened composite material in step S21 is changed using the cohesive contact property determined in step S10.

[0054] S30, running the low-speed impact finite element model to simulate the low-speed impact of the intercalation toughened composite material by the impactor, and automatically extracting damage state variables (intra-layer damage state variables and interlaminar damage state variables) using Python script, including the following sub-steps S31-S35:

[0055] S31, run the low-speed impact finite element model to simulate the intercalation toughened composite material being impacted by an impactor at a low speed.

[0056] S32, according to the progressive damage theory of the composite material, there are four kinds of intralaminar damage variables of the composite material, which are fiber tensile damage variable , fiber compression damage variable , matrix tensile damage variable , and matrix compression damage variable . Therefore, during the running of step S31, the stress tensor of each element of the finite element model of the intercalation toughened composite material is extracted and it is judged whether intralaminar damage occurs according to the Hashin failure criterion:

[0057] (1) When the longitudinal stress tensor ≥ 0, it is considered that the fiber is tensile damaged, and the failure criterion expression is:

[0058] .

[0059] In the above formula, X T represents the longitudinal tensile strength, represents the stress tensor of the tangential direction, S L represents the longitudinal shear strength, and a is a shear failure coefficient for representing the influence of the tangential force on the fiber tensile damage, 0 ≤ a ≤ 1.

[0060] (2) When the longitudinal stress tensor ≤ 0, it is considered that the fiber is compression damaged, and the failure criterion expression is:

[0061] .

[0062] In the above formula, X C represents the longitudinal compression strength.

[0063] (3) When the transverse stress tensor ≥ 0, it is considered that the matrix is tensile damaged, and the failure criterion expression is:

[0064] .

[0065] In the above formula, Y T represents the transverse tensile strength.

[0066] (4) When the transverse stress tensor ≤ 0, it is considered that the matrix is compression damaged, and the failure criterion expression is:

[0067] ,

[0068] In the above formula, S Trepresents the transverse shear strength, Y C represents the transverse compressive strength.

[0069] S33, taking the maximum value among the fiber tensile damage variable , the fiber compressive damage variable , the matrix tensile damage variable and the matrix compressive damage variable as the interlaminar damage state variable of the interlaminar toughened composite:

[0070] .

[0071] In the above formula, d intra represents the interlaminar damage state variable, and Max represents taking the maximum value for the data in the set.

[0072] S34, during the running of step S31, the interlaminar damage behavior of the interlaminar toughened composite is captured by using the cohesive method, and the following formula is used as the initiation condition of the interlaminar damage:

[0073] .

[0074] wherein, represents the stress tensor of the interlaminar of the interlaminar toughened composite in the i direction, represents the material strength of the interlaminar of the interlaminar toughened composite in the i direction, i is n, s or t, and n, s, t represent the normal and two shear directions.

[0075] S35, using the interlaminar damage state variable d inter to quantify the severity of delamination:

[0076] .

[0077] wherein, represents the equivalent displacement when the interlaminar completely fails, i.e. the delamination completely occurs, represents the maximum displacement, represents the equivalent displacement when the delamination just initiates, before the delamination initiates, d inter will always remain 0; and when the load rises, d inter will gradually rise until 1, at which time the interlaminar toughened composite will completely delaminate, at which time the interlaminar almost loses the bonding effect and peels off.

[0078] S40, the grid model corresponding to the interlaminar toughened composite in the low-velocity impact finite element model after running is imported into a new post-impact compression finite element model, each unit is marked after using the Python script, and the mechanical performance reduction is carried out according to d intra and d inter :

[0079] .

[0080] In the above formula, 、 and respectively represent the in-layer strength, in-layer modulus and in-layer fracture energy of each unit in the post-impact compression finite element model; 、 and respectively represent the reduced 、 and ; 、 and respectively represent the interlayer strength, interlayer modulus and interlayer fracture energy of each unit in the post-impact compression finite element model; 、 and respectively represent the reduced 、 and .

[0081] S50, the boundary conditions of the reduced post-impact compression finite element model are set to be consistent with the actual compression working condition, as shown in Figure 3 . Then run the post-impact compression finite element model, and take the compression stress corresponding to the peak load in the compression process as the compression residual strength of the intercalation toughened composite material.

[0082] In this embodiment, specifically: the left node of the reduced post-impact compression finite element model is connected to the left reference point through coupling constraint, so as to uniformly constrain the displacement and rotation of the left boundary. The displacement constraints in horizontal and vertical directions are defined on the reference point, so as to prevent the overall displacement or rotation of the specimen (reduced post-impact compression finite element model) from occurring during compression loading, and ensure that the loading direction is consistent with the longitudinal direction of the specimen.

[0083] Figure 4 is the architecture diagram of the intercalation toughened composite material post-impact compression residual strength prediction system of the embodiment of the present application.

[0084] As shown in Figure 4 , the present embodiment also provides an intercalation toughened composite material post-impact compression residual strength prediction system, which uses the intercalation toughened composite material post-impact compression residual strength prediction method in the present embodiment.

[0085] The intercalation toughened composite material post-impact compression residual strength prediction system 100 in the present embodiment comprises a data input module 10, a low-speed impact modeling module 20, a damage simulation module 30, a performance reduction module 40 and a compression simulation module 50.

[0086] a data input module 10 for inputting the cohesive contact properties determined by the actual test in step S10.

[0087] a low-velocity impact modeling module 20 connected with the data input module 10 for defining the interlaminar interaction force of the interlayered toughened composite material according to the cohesive contact properties determined by the data input module 10 after the user establishes the low-velocity impact finite element model of the interlayered toughened composite material in the finite element modeling software according to the method of step S20.

[0088] a damage simulation module 30 connected with the low-velocity impact modeling module 20 for running the low-velocity impact finite element model to simulate the low-velocity impact process, judging the damage state based on the progressive damage theory of the composite material, and extracting the damage state variable according to the method of step S30.

[0089] a performance reduction module 40 connected with the damage simulation module 30 for importing the grid model after impact into a new post-impact compression finite element model and marking each unit of the post-impact compression finite element model using a Python script and reducing the intralaminar and interlaminar mechanical properties according to the damage state variable according to the method of step S40.

[0090] a compression simulation module 50 connected with the performance reduction module 40 for setting the boundary conditions of the post-impact compression finite element model to match the actual compression working condition and running the post-impact compression finite element model to obtain the compression stress corresponding to the peak load as the compression residual strength according to the method of step S50.

[0091] Test Example

[0092] In this test example, the interlayered toughened composite material post-impact compression residual strength prediction system 100 in the embodiment is used to perform actual testing according to the interlayered toughened composite material post-impact compression residual strength prediction method in the embodiment.

[0093] In this test example, two carbon fiber reinforced epoxy resin-based composite laminates are used for actual testing, which are respectively referred to as laminate 1 and laminate 2.

[0094] The size of the laminate 1 and the laminate 2 is 150mm x 100mm x 5.92mm, and the layup mode is [45, 0, -45, 90] 4s , and the single-layer thickness is 0.185mm.

[0095] The laminate 1 is used as a control group and is not interlayered, and only epoxy resin exists between the layers.

[0096] The laminated plate 2 is taken as a research group, and is subjected to interlayer toughening layer by layer, and the interlayer material is a thermoplastic non-woven felt. Considering that the interlayer toughening is an interlaminar toughening process, the performance in the layer is hardly affected, and thus the interlaminar fracture toughness of the laminated plate 2 is changed only compared with the laminated plate 1.

[0097] The interlaminar fracture toughness of the laminated plate 1 and the laminated plate 2 is completed through double cantilever beam tests and end notched flexure tests.

[0098] According to steps S10-S50, the laminated plate 1 and the laminated plate 2 are actually tested, and the I-type interlaminar fracture toughness values of the laminated plate 1 and the laminated plate 2 are 0.2477 kJ / m 2 and 0.2576 kJ / m 2 , respectively, and the II-type interlaminar fracture toughness values are 1.1733 kJ / m 2 and 1.9383 kJ / m 2 , respectively. Subsequently, low-speed impact and post-impact compression finite element model calculation are performed, and the post-impact compression load-displacement prediction results and the actual test results of the laminated plate 1 are shown in Figure 5 , and the post-impact compression load-displacement prediction results and the actual test results of the laminated plate 2 are shown in Figure 6 .

[0099] Figure 5 is the post-impact compression load-displacement prediction results and the actual test results of the laminated plate 1 of the test example of the present application; Figure 6 is the post-impact compression load-displacement prediction results and the actual test results of the laminated plate 2 of the test example of the present application.

[0100] As shown in Figure 5 and Figure 6 , the predicted compression stress-displacement curves obtained during the loading process are very close to the three groups of true stress-displacement curves, and before the final failure, the stress increases linearly with the displacement, thereby proving that the method has high accuracy for predicting the failure displacement and residual strength of the samples before and after toughening. The interlayer toughening composite impact post-compression residual strength prediction method and system of the embodiment can effectively predict the impact post-compression residual strength of the carbon fiber reinforced composite laminated plate under various interlayer toughening design schemes, and subsequently, the interlayer scheme can be further optimized according to the working condition requirements, such as adjusting the laminated plate material system, the toughening layer material system, the toughening layer insertion scheme, thereby providing effective help for the composite material toughening layer design.

[0101] Those skilled in the art should understand that the present application is not limited to the above-mentioned embodiments, and the above-mentioned embodiments and descriptions in the specification are only to illustrate the principles of the present application, and various changes and improvements can be made without departing from the spirit and scope of the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for predicting the residual compressive strength after impact of intercalated toughened composite materials, characterized in that, The initial impact damage of intercalated toughened composite materials was considered, including the following steps: S10, the interlaminar fracture toughness of the intercalated toughened composite material was measured by actual test, and the cohesive contact properties of its interlaminar layers were determined accordingly. S20. After establishing a low-speed impact finite element model of the intercalated toughened composite material in the finite element modeling software, the interlayer interaction force of the intercalated toughened composite material is defined by the cohesive contact property. S30, run the low-speed impact finite element model to simulate the intercalated toughened composite material being impacted at low speed by the impactor, and determine whether the intercalated toughened composite material is damaged based on the progressive damage theory of composite materials and extract the damage state variables of each element. The damage state variables include intra-layer damage state variables and inter-layer damage state variables. S40, import the mesh model corresponding to the intercalated toughened composite material in the low-speed impact finite element model after running into the new post-impact compression finite element model, and reduce the corresponding intralayer mechanical properties and interlayer mechanical properties in the post-impact compression finite element model according to the intralayer damage state variables and the interlayer damage state variables. S50, after setting the boundary conditions of the reduced post-impact compression finite element model to be consistent with the actual compression conditions, the post-impact compression finite element model is run, and the compressive stress corresponding to the peak load during the compression process is taken as the compressive residual strength of the intercalated toughened composite material.

2. The method for predicting the residual compressive strength of intercalated toughened composite materials after impact according to claim 1, characterized in that: in, In step S10, the actual test includes a double cantilever beam test and an end-notch bending test. The interlaminar fracture toughness includes Type I interlaminar fracture toughness and Type II interlaminar fracture toughness.

3. The method for predicting the residual compressive strength of intercalated toughened composite materials after impact according to claim 1, Its features are: In step S20, the low-speed impact finite element model includes: The intercalated toughened composite material is constructed from several shell units; and An impactor constructed from several rigid body units for subjecting the intercalated toughened composite material to low-speed impact.

4. The method for predicting the residual compressive strength of intercalated toughened composite materials after impact according to claim 3, characterized in that: in, In step S20, the boundary conditions of the impactor are set to produce displacement only in the impact direction of the intercalated toughened composite material, while displacement and / or rotation in other directions remain 0.

5. The method for predicting the residual compressive strength of intercalated toughened composite materials after impact according to claim 1, characterized in that: in, In step S30, during the running of the low-speed impact finite element model, the stress tensor of each element of the intercalated toughened composite material is extracted, and the presence of intralaminar damage is determined according to the Hashin failure criterion. When the longitudinal stress tensor When the value is ≥0, the fiber is considered to have suffered tensile damage, and the failure criterion expression is: ， X represents the fiber tensile damage variable. T Indicates longitudinal tensile strength. S represents the tangential stress tensor. L The longitudinal shear strength is represented by α, which is the shear failure coefficient used to represent the effect of tangential force on fiber tensile damage, where 0 ≤ α ≤ 1. When the longitudinal stress tensor When the value is ≤0, the fiber is considered to have suffered compressive damage, and the failure criterion expression is: ， X represents the fiber compression damage variable. C Indicates longitudinal compressive strength. When the transverse stress tensor When the value is ≥0, tensile damage to the matrix is ​​considered to have occurred, and the failure criterion expression is: ， Y represents the matrix tensile damage variable. T Indicates transverse tensile strength. When the transverse stress tensor When the value is ≤0, the matrix is ​​considered to have undergone compressive damage, and the failure criterion expression is: ， S represents the matrix compression damage variable. T Y represents the transverse shear strength. C Indicates lateral compressive strength. The intralayer damage state variable is the maximum value among the fiber tensile damage variable, the fiber compressive damage variable, the matrix tensile damage variable, and the matrix compressive damage variable.

6. The method for predicting the residual compressive strength of intercalated toughened composite materials after impact according to claim 1, characterized in that: in, In step S30, during the running of the low-speed impact finite element model, the cohesive force method is used to capture the interlaminar damage behavior of the intercalated toughened composite material, thereby determining the interlaminar damage state variables. The initiation conditions for interlaminar damage in the intercalated toughened composite material are as follows: , This represents the interlaminar stress tensor in the i-direction of the intercalated toughened composite material. The term represents the interlaminar material strength of the interlayer toughened composite material in the i-direction, where i is n, s, or t, and n, s, and t represent the normal direction and two shear directions, respectively. The interlaminar damage state variables are: , This represents the equivalent displacement when interlayer failure occurs completely, i.e., when delamination damage has fully occurred. Indicates the maximum displacement. This represents the equivalent displacement at the initial stage of layered damage.

7. The method for predicting the residual compressive strength of intercalated toughened composite materials after impact according to claim 6, characterized in that: in, In step S30, the interlaminar damage state variable d inter Used to quantify the severity of interlaminar damage, d inter =0 indicates no damage, d inter =1 indicates complete layering failure.

8. The method for predicting the residual compressive strength of intercalated toughened composite materials after impact according to claim 1, characterized in that: in, In step S40, the reduction is performed as follows: Multiply the intralaminar modulus, intralaminar strength, and intralaminar fracture energy of each element in the post-impact compression finite element model by the intralaminar damage state variable of that element; and The interlaminar modulus, interlaminar strength, and interlaminar fracture energy of each element in the post-impact compression finite element model are multiplied by the interlaminar damage state variable of that element.

9. The method for predicting the residual compressive strength of intercalated toughened composite materials after impact according to claim 1, characterized in that: in, In step S30, a Python script is used to automatically extract the intra-layer damage state variables and the inter-layer damage state variables. In step S40, a Python script is used to automatically perform the reduction operations of the intralayer mechanical properties and the interlayer mechanical properties.

10. A system for predicting the residual compressive strength after impact of intercalated toughened composite materials, characterized in that, The method for predicting the residual compressive strength of intercalated toughened composite materials after impact, as described in any one of claims 1 to 9, includes: The data input module is used for users to input the cohesive contact properties determined through actual experiments; The low-speed impact modeling module, connected to the data input module, is used to establish the low-speed impact finite element model of the intercalated toughened composite material in the finite element modeling software, and to define the interlayer interaction force of the intercalated toughened composite material through the cohesive contact property. The damage simulation module is connected to the low-velocity impact modeling module and is used to run the low-velocity impact finite element model to simulate the low-velocity impact process, determine the damage state based on the progressive damage theory of composite materials, and extract the damage state variables. A performance reduction module, connected to the damage simulation module, is used to import the post-impact mesh model into a new post-impact compression finite element model, and to reduce the intra-layer mechanical properties and inter-layer mechanical properties according to the damage state variables; and The compression simulation module, connected to the performance reduction module, is used by the user to set the boundary conditions of the post-impact compression finite element model to match the actual compression conditions, run the post-impact compression finite element model, and obtain the compressive stress corresponding to the peak load as the residual compressive strength.

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