A molecular dynamics evaluation method for crack propagation resistance at the plant fiber / inorganic matrix interface

Abstract

This invention discloses a molecular dynamics evaluation method for crack propagation resistance at the plant fiber / inorganic matrix interface. This method simulates interfacial debonding using a full-atom model of the interface, introduces gridded analysis in the interfacial region, and quantitatively identifies the debonding regions under different separation displacements based on the changing characteristics of interfacial interaction energy and the number of contact atoms. Furthermore, it combines a multi-parameter linkage criterion of traction force, interfacial binding energy, and debonding area ratio to achieve interfacial failure mode discrimination. A curve relating external force work to interfacial debonding area is further established, and linear fitting is performed on the stable crack propagation stage to obtain the effective interfacial crack propagation energy release rate, which is used for quantitative evaluation of interfacial crack propagation resistance. This method enables a unified comparison of the interfacial toughening effects under different modification strategies, providing a scientific quantitative basis for the quantitative screening of plant fiber surface modification processes and the interfacial design of reinforced geopolymer composites.

Description

Technical Field

[0001] This invention belongs to the field of composite material interface performance characterization and evaluation technology, specifically involving a quantitative evaluation method for crack propagation resistance at the plant fiber / inorganic matrix interface based on molecular dynamics simulation, used to predict the energy release rate during nanoscale interface crack propagation under different modification methods. Background Technology

[0002] Slag-based geopolymers are three-dimensional inorganic cementitious materials formed from active aluminosilicate precursors through an alkali-activated reaction. They possess outstanding characteristics such as high early strength, excellent mechanical properties, high temperature resistance, corrosion resistance, and good durability, showing broad application prospects in green building materials, solid waste resource utilization, and low-carbon infrastructure construction. However, geopolymer matrices are typically brittle, easily prone to crack initiation and rapid propagation under load, severely limiting their widespread application in load-bearing structures and long-term service environments. Plant fibers, with their advantages of wide availability, renewability, low density, high specific strength and specific stiffness, biodegradability, and environmental friendliness, can be used as reinforcing components in geopolymer-based composites to improve the crack resistance and toughness of the matrix.

[0003] In plant fiber-reinforced geopolymer composites, the interfacial bonding performance between the plant fibers and the geopolymer matrix is ​​a crucial factor affecting the mechanical properties and service stability of the composite. Due to the abundance of polar groups and strong hydrophilicity on the surface of plant fibers, their interfacial compatibility with the inorganic geopolymer matrix is ​​poor. Under stress, the weak interface easily leads to fiber debonding, interfacial slippage, and crack propagation along the interface, thus severely weakening the reinforcing effect of the fibers. Therefore, modifying the surface of plant fibers to optimize interfacial bonding performance is a core approach to improving the performance of this material.

[0004] To improve the interfacial compatibility between plant fibers and inorganic matrices, existing technologies typically employ methods such as alkali treatment, silane coupling agent treatment, chemical functionalization, or nano-coating modification to modify the fiber surface. However, current evaluations of plant fiber modification effects largely rely on traditional experimental methods such as macroscopic mechanical testing, water absorption experiments, or microscopic morphology observation. While these methods can reflect changes in the overall properties of the composite material, they cannot directly and quantitatively obtain core microscopic fracture parameters such as crack propagation resistance at the plant fiber / inorganic matrix interface under different modification methods. This results in the selection and optimization of modification schemes still heavily relying on empirical experiments, leading to low evaluation efficiency and a lack of unified and comparable quantitative criteria between different modification methods.

[0005] In recent years, molecular dynamics simulations have been widely used to construct microscopic interface models of plant fiber-geopolymer inorganic gel phases and to calculate interfacial interactions. However, existing molecular dynamics-based interface evaluation methods mostly use parameters such as interfacial adsorption configuration, number of hydrogen bonds, interaction energy, or local structural changes as evaluation indicators. These indicators can reflect the strength of interfacial interactions to a certain extent, but they cannot be directly converted into interfacial crack propagation resistance parameters such as fracture toughness and critical energy release rate required for mesoscopic or macroscopic fracture mechanics analysis, making it difficult to effectively support the quantitative comparison of crack propagation resistance under different modification methods.

[0006] In summary, existing technologies have at least the following shortcomings: First, the evaluation of the surface modification effect of plant fibers mainly relies on experimental results, lacking quantitative evaluation methods for interfacial crack propagation resistance under different modification methods; second, existing molecular dynamics simulation evaluation indicators mostly remain at the level of indirect parameters such as interaction energy, number of hydrogen bonds, or structural changes, lacking quantitative fracture parameters that can be used to characterize interfacial crack propagation resistance. Therefore, it is necessary to provide a quantitative evaluation method for the interfacial crack propagation resistance of plant fibers / inorganic matrices based on molecular dynamics simulation, so as to achieve a unified and comparable evaluation of interfacial crack propagation resistance under different modification methods, and provide a scientific quantitative basis for the optimization of plant fiber surface modification schemes and the design of composite material interface strengthening and toughening. Summary of the Invention

[0007] The purpose of this invention is to provide a molecular dynamics evaluation method for the crack propagation resistance at the plant fiber / inorganic matrix interface, in order to solve the problems in the prior art where the evaluation of the effect of plant fiber surface modification mainly relies on empirical experiments, there is a lack of unified quantitative evaluation methods for the crack propagation resistance at the interface under different modification methods, and the existing molecular dynamics simulation results are difficult to directly convert into interface fracture mechanics parameters.

[0008] Therefore, the technical solution provided by the present invention is as follows: A molecular dynamics method for evaluating the crack propagation resistance at the plant fiber / inorganic matrix interface includes the following steps: Step 1) Construct a cellulose crystal model of plant fiber and a calcium aluminosilicate hydrate (CASH) model representing the main phase of the inorganic matrix, respectively; Step 2) Construct a modified cellulose crystal model by replacing atoms or functional groups; Step 3) Construct the cellulose crystal / CASH interface structure based on the CASH gel phase model and the modified cellulose crystal model; Step 4) Perform energy minimization and equilibrium molecular dynamics simulations on the cellulose crystal / CASH interface structure to obtain a stable initial interface configuration; Step 5) Simulate the process of cellulose crystals peeling off from the CASH gel phase interface using controlled molecular dynamics simulation to obtain the simulation trajectory file and traction force. F Interface separation displacement D Cumulative potential potential (PMF) and interfacial bonding energy E I and obtain FD curves and E I - D curve; Step 6) Identify the debonding area of ​​the cellulose crystal / CASH interface region based on the trajectory file, and count the different separation displacements. D The interface debonding area below A ( D ); Step 7) Work done on the system by the PMF as an external force W(D) ,Establish W ( D ) and the debonding area of ​​the interface A ( D The relationship curve between ) is obtained W ( D )- A ( D )curve; Step 8) W ( D )- A ( D Linear fitting was performed on the curve during the interface stability and debonding stage, and the resulting slope represents the effective interface crack propagation energy release rate. G eff A quantitative evaluation of the resistance to interface crack propagation was completed.

[0009] The method of this invention can quantitatively characterize the energy release rate of crack propagation at the plant fiber / inorganic matrix interface at the molecular scale, and can be used as a systematic method to guide the surface modification of plant fibers and the design of crack resistance of composite materials.

[0010] The effective interfacial crack propagation energy release rate defined in this invention has a clear cross-scale mechanical and physical significance, serving as a cross-scale bridge connecting molecular dynamics simulations with mesoscopic / macroscopic mechanical failures. The core advantage of this parameter lies in its quantitative transformation from discrete molecular-scale dynamic evolution to energy parameters related to fracture mechanics in continuous media. Microscopically, it characterizes the total energy dissipation during interfacial delamination when multi-component molecular interactions such as hydrogen bonds, ionic coordination bonds, electrostatic compatibility, and van der Waals forces are disrupted. Macroscopically, as a standard physical quantity, it can be directly introduced into cohesive zone models, phase-field fracture models, or finite element numerical analyses to characterize and predict crack evolution under macroscopic load conditions. Therefore, this invention provides a method for quantitatively obtaining the crack propagation energy release rate at the plant fiber / inorganic matrix interface based on molecular dynamics simulations, successfully establishing an intrinsic quantitative correlation between the regulation of functional groups on the plant fiber surface, the evaluation of microscopic interfacial fracture resistance, and the design of macroscopic composite material interface strengthening and toughening.

[0011] Furthermore, step 6) also includes interface debonding determination and interface failure mode determination.

[0012] Furthermore, the interface debonding determination includes mesh debonding determination and a count of the number of debonded mesh cells: A mesh cell is considered to have debonded when it simultaneously meets the following conditions: (1) and (2) in, i Indicates the first i One grid cell; , These represent the interfacial interaction energy and the number of contact atoms within each grid cell during the debonding process; , These represent the initial interfacial interaction energy and the initial number of contact atoms of the corresponding grid cell in equilibrium state, respectively. α 1 and α 2 represents the preset single-mesh debonding threshold. α The value of 1 ranges from 0.1 to 0.25. α The value of 2 ranges from 0.1 to 0.2.

[0013] Furthermore, the debonding area identification process described in step 6) is as follows: An analytical region with a thickness of 1.5 nm to 4 nm was selected in the interface area and divided into several grid cells with a grid size of a. The number of CASH atoms within each grid cell that are adjacent to cellulose crystal atoms within a cutoff distance of 0.8 nm to 1.2 nm was counted and defined as the number of contact atoms between CASH and cellulose crystals within that grid cell. ,in, i Indicates the first i Each grid cell.

[0014] Furthermore, the debonding area A ( D ) is represented as: (3) In the formula, C ( D ) for statistical separation of displacement D The number of mesh elements that debond. a This refers to the grid cell size.

[0015] The method for identifying the debonding area of ​​an interface based on simulated trajectory files includes establishing a gridded analysis region in the interface area and combining the interface interaction energy and the change in the number of contact atoms to determine whether each grid cell has debonded under different separation displacements, thereby obtaining the debonding area of ​​the interface.

[0016] Furthermore, the interface failure determination process is as follows: Displacement at the interface D Greater than peak displacement D Fmax Then, the peak displacement D Fmax To achieve maximum traction F max The corresponding interface separation displacement occurs when the traction force satisfies: (4) Alternatively, the interface combination can satisfy: (5) The interface separation process then enters the failure determination stage. in, E I ( D ) represents the separation displacement D The interface integration performance is as follows. E I (0) represents the initial interfacial binding energy in equilibrium. and To preset the failure threshold, The value ranges from 0.1 to 0.3. The value ranges from 0.05 to 0.25.

[0017] Furthermore, in the failure determination stage, based on the debonding area ratio R D Determine the interface failure mode, the debonding area ratio ,in, A (0) represents the initial interface area; the interface failure modes include surface debonding failure, cohesive failure, and mixed failure modes.

[0018] Furthermore, when When the interface failure mode is determined to be interface debonding failure; when When the interface failure mode is determined to be cohesion failure; when When the interface failure mode is determined to be a hybrid destruction mode; in, and This is the preset interface de-adhesion threshold.

[0019] This invention provides a method for determining interface failure modes based on traction force, interfacial bonding energy, and the ratio of interfacial debonding area. It classifies the failure modes of the modified plant fiber / CASH interface into interfacial debonding failure, cohesive failure, and mixed failure, and achieves quantitative identification of failure modes through preset thresholds.

[0020] For the unmodified cellulose crystal / CASH interface, since its failure mode is interfacial debonding failure, when the failure mode of the modified cellulose crystal / CASH interface changes to mixed failure or cohesive failure, it indicates that the modification treatment can effectively enhance the interfacial bonding ability between the cellulose crystal and the CASH gel phase. Based on this, this invention is used to evaluate the effect of different surface functional group modifications on the energy release rate of interfacial crack propagation in the interfacial debonding failure system.

[0021] Furthermore, The value ranges from 0.1 to 0.25. The value ranges from 0.7 to 0.85.

[0022] For systems determined to be exhibiting interfacial debonding failure, different separation displacements are statistically analyzed based on trajectory files obtained from controlled molecular dynamics simulations. D The interface debonding area below A ( D In controlled molecular dynamics simulations, the cumulative potential (PMF) is obtained by integrating the traction force along the separation displacement, and its physical meaning characterizes the work done by the external force on the system. W ( D Therefore, it is possible to establish that external forces do work. W (D ) and the debonding area of ​​the interface A ( D The relationship curve between ) W ( D )- A ( D )curve.

[0023] Based on this, W ( D )- A ( D Linear fitting was performed on the interface stability debonding stage of the curve, and the resulting slope was used as the effective interface crack propagation energy release rate. G eff This parameter reflects the ability of the cellulose crystal / CASH interface to resist crack propagation under different surface modification methods. Using this method, atomic-scale information such as traction force, separation displacement, and force potential obtained from molecular dynamics simulations can be transformed into interface fracture evaluation parameters with significance in continuous fracture mechanics, thereby achieving a quantitative evaluation of the fracture resistance of the modified plant fiber / inorganic matrix interface.

[0024] The beneficial effects of this invention are as follows: This invention establishes a microscopic interface model between modified cellulose crystals and the CASH gel phase, and combines controlled traction molecular dynamics simulation, interface debonding area identification, and effective energy release rate calculation to achieve quantitative evaluation of the microscopic debonding behavior of plant fiber / inorganic matrix interfaces with different surface functional groups.

[0025] This invention utilizes trajectory files obtained from controlled molecular dynamics simulations to introduce an innovative three-dimensional meshed dynamic analysis method in the interface region. By capturing the transient responses of interfacial interaction energy and contact atom number within the mesh cells in real time, it achieves precise quantitative identification of the debonding region at different separation displacements. Based on traction force, interfacial binding energy, and the ratio of debonding area, this method establishes a multi-parameter linkage criterion, enabling the classification of cellulose crystal / CASH interface failure modes into interfacial debonding failure, cohesive failure, and mixed failure, thus achieving quantitative discrimination of interface failure modes.

[0026] This invention establishes work done by external force. W ( D ) and the debonding area of ​​the interface A ( D The relationship curve between the two was obtained, and a linear fit was performed on the crack propagation stage. The slope of the obtained curve was defined as the effective interface crack propagation energy release rate. G effThis method can transform atomic-scale information such as traction force, separation displacement, and force potential obtained from controlled molecular dynamics simulations into evaluation parameters characterizing interfacial fracture resistance, thereby establishing a relationship between atomic-scale interfacial separation behavior and crack propagation energy release rate in continuous fracture mechanics.

[0027] This invention enables quantitative characterization at the molecular scale of crack propagation energy release rate at the plant fiber / CASH gel interface after modification with different surface functional groups, thus paving the way for "design of plant fiber surface functional groups". Characterization of micro-interface crack propagation resistance A cross-scale technical approach of "interfacial toughening design of macroscopic composite materials" has been proposed. This method effectively eliminates the over-reliance on traditional macroscopic empirical experiments in the selection of modification schemes, and provides solid quantitative theoretical support for the interfacial structure design and performance optimization of high-performance plant fiber reinforced geopolymer composites. Attached Figure Description

[0028] Figure 1 This invention provides a quantitative determination process for predicting interface failure modes based on molecular dynamics simulations. Figure 2 This invention is based on molecular dynamics simulations to predict the effective interfacial crack propagation energy release rate in interfacial debonding failure systems. G eff The process; Figure 3 Here are the mechanical responses during the debonding process at the cellulose crystal (CNC) / CASH interface: (a) Traction force F -Interfacial debonding displacement D (a) Relationship diagram; (b) Interface bonding energy E I -Interfacial debonding displacement D Relationship diagram; Figure 4 When cellulose crystals (CNC) / CASH debond at a preset interface ( D = 14.6 ), the identification results of the debonding area of ​​the interface; Figure 5 It is the debonding area during the debonding process of cellulose crystal (CNC) / CASH interface. A -Interfacial debonding displacement D Relationship diagram; Figure 6 The interfacial separation displacement of cellulose crystals (CNC) / CASH is 14.6. The interface structure indicates that its failure mode is interface debonding failure mode; Figure 7 It is the work done by external forces during the debinding process of cellulose crystals (CNC) / CASH interface.W -Interfacial debonding area A Relationship diagram; Figure 8 This is a diagram illustrating the mechanical effects during the debonding process at the interface of amide-modified cellulose crystals (CNC-CONH2) / CASH: (a) traction force F -Interfacial debonding displacement D (a) Relationship diagram; (b) Interface bonding energy E I -Interface debonding displacement D relationship diagram; Figure 9 When amide-modified cellulose crystals (CNC-CONH2) / CASH debond at a preset interface (D = 15), ), the identification results of the debonding area of ​​the interface; Figure 10 It is the debonding area during the debonding process of amide-modified cellulose crystals (CNC-CONH2) / CASH interface. A -Interfacial debonding displacement D Relationship diagram; Figure 11 The interface structure of amide-modified cellulose crystal (CNC-CONH2) / CASH with an interfacial separation displacement of 15 Å indicates that its failure mode is a mixed failure mode. Figure 12 This is a diagram illustrating the mechanical effects during the debonding process at the CNC-COOH / CASH interface: (a) traction force F -Interfacial debonding displacement D (a) Relationship diagram; (b) Interface bonding energy E I -Interface debonding displacement D relationship diagram; Figure 13 It is the debonding area during the debonding process at the carboxyl-modified cellulose crystal (CNC-COOH) / CASH interface. A -Interface debonding displacement D relationship diagram; Figure 14 It is the work done by external forces during the debonding process of carboxyl-modified cellulose crystals (CNC-COOH) / CASH interface. W -Interfacial debonding area A Relationship diagram. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0030] To address the technical problems in existing technologies, such as the over-reliance on macroscopic empirical experiments to evaluate the effects of plant fiber surface modification, the lack of direct quantitative characterization methods for microscopic interface crack propagation resistance, and the difficulty in directly converting atomic-scale simulation indicators into mesoscopic / macroscopic fracture mechanics parameters for cross-scale model transfer, this invention provides a molecular dynamics evaluation method for crack propagation resistance at the plant fiber / inorganic matrix interface. First, a cellulose crystal model, a modified cellulose crystal model, and a CASH gel phase model are constructed, and based on these, a cellulose crystal / CASH interface structure is established. Subsequently, energy minimization and equilibrium molecular dynamics simulations are performed on the interface structure to obtain a stable initial interface configuration. Then, a controlled molecular dynamics simulation method is used to simulate the process of cellulose crystal peeling from the CASH gel phase interface, obtaining simulation trajectory files and traction forces. F Interface separation displacement D Cumulative potential potential (PMF) and interfacial bonding energy E I .

[0031] The above data is processed to obtain the traction force-separation displacement curve, i.e. FD The curve, and the interface bonding energy-separation distance curve, i.e. E I - D curve.

[0032] Furthermore, based on trajectory files obtained from controlled molecular dynamics simulations, the debonding area of ​​the cellulose crystal / CASH interface region was identified. Specifically, an analysis region with a thickness of 2 nm was selected in the interface region and divided into several grid cells with a grid size of 0.5 nm. At each separation displacement D, the number of CASH atoms within each grid cell that are adjacent to cellulose crystal atoms within a cutoff distance of 0.85 nm was counted and defined as the number of contact atoms between CASH and cellulose crystal within that grid cell. ,in, i Indicates the first i Each grid cell.

[0033] The interfacial interaction energy within each grid cell during the debinding process and the number of contact atoms The initial interface interaction energy of the corresponding mesh element in equilibrium state. and the number of initial contact atoms A comparison is performed. A mesh cell is considered to have debonded when it simultaneously meets the following conditions: (1) and (2) in, α 1 and α 2 represents the preset single-mesh debonding threshold, preferably... α The value of 1 ranges from 0.1 to 0.25. α 2 is set to a value between 0.1 and 0.2. Based on this, the separation displacement is statistically analyzed. D The number of mesh elements that debonded is denoted as C ( D ), then the interfacial debonding area under this separation displacement. A ( D This can be represented as: (3) in, a This refers to the grid cell size.

[0034] Displacement at the interface D Greater than peak displacement D Fmax Then, the peak displacement D Fmax To achieve maximum traction F max The corresponding interface separation displacement occurs when the traction force satisfies: (4) Alternatively, the interface combination can satisfy: (5) The interface separation process then enters the failure determination stage. E I ( D ) represents the separation displacement D The interface integration performance is as follows. E I (0) represents the initial interfacial binding energy in equilibrium. and To preset the failure threshold, preferably, The value ranges from 0.1 to 0.3. The value ranges from 0.05 to 0.25.

[0035] In the failure determination stage, based on the interface debonding area A (D ) and initial interface area A The ratio of (0) is used to determine the interface failure mode. Preferably, the debonding area ratio is defined as: (6) when When the interface failure mode is determined to be interface debonding failure; when When the interface failure mode is determined to be cohesion failure; when When the interface failure mode is determined to be a hybrid failure mode, then... and This is a preset interface debonding threshold. Preferably, The value ranges from 0.1 to 0.25. The value ranges from 0.7 to 0.85. For example... Figure 1 As shown.

[0036] For systems determined to be exhibiting interfacial debonding failure, different separation displacements are statistically analyzed based on trajectory files obtained from controlled molecular dynamics simulations. D The interface debonding area below A ( D In controlled molecular dynamics simulations, the potential molecular force (PMF) is obtained by integrating the traction force along the separation displacement, and its physical meaning can characterize the work done by the external force on the system. W ( D Therefore, it is possible to establish that external forces do work. W ( D ) and the debonding area of ​​the interface A ( D The relationship curve between ) W ( D )- A ( D ( ) curve. For example Figure 2 As shown.

[0037] Based on this, W ( D )- A ( D Linear fitting was performed on the interface stability debonding stage of the curve, and the resulting slope was used as the effective interface crack propagation energy release rate. G eff This parameter reflects the ability of the cellulose crystal / CASH interface to resist debonding and propagation under different surface modification methods. Using this method, atomic-scale information such as traction force, separation displacement, and force potential obtained from molecular dynamics simulations can be transformed into interface fracture evaluation parameters with significance in continuous fracture mechanics, thereby achieving a quantitative evaluation of the fracture resistance of the modified plant fiber / non-polar matrix interface.

[0038] Example 1 Cellulose crystal / CASH interface debonding: First, a CASH model was constructed in Materials Studio based on the tobermorite 14 Å crystal structure. Specifically, an orthogonal structure model was constructed by cleaving along the (100) crystal plane of tobermorite 14 Å, and eight units were repeated along the silicon-oxygen chain direction. Subsequently, bridging silicon dioxide units were randomly removed, and Q was modulated by replacing silicon atoms with aluminum atoms at tetrahedral sites. n (mAl) structure distribution. The resulting charged aluminosilicate framework was then balanced by adding hydrogen atoms. The final CASH model had Ca / Si and Al / Si ratios of 1.16 and 0.22, respectively, and a size of 60. × 60 × 33 .

[0039] Select crystalline cellulose I β As a representative model of cellulose fibers, its lattice parameters are a = 7.8 , b =8.2 , c = 10.4 , = 96.5°. Subsequently, the cellulose crystal structure was periodically repeated along the chain length direction, and its interface cross-sectional area was matched with the CASH model to construct a cellulose crystal / CASH interface model. The interface force field was used to describe the interaction between the cellulose crystal and the atoms in CASH.

[0040] Before the interface separation simulation, the energy of the cellulose crystal / CASH interface model was first minimized using the conjugate gradient algorithm to eliminate unreasonable contacts in the initial structure. Subsequently, the model was balanced at 298 K under an isothermal and isochoric ensemble to obtain a stable initial interface structure.

[0041] In this embodiment, controlled molecular dynamics is used to simulate the peeling process of the cellulose crystal / CASH interface. This method is equivalent to connecting a virtual spring between the CASH centroid and the cellulose crystal centroid. During the simulation, a 1.5 nm region at the bottom of the CASH is fixed, and traction is applied to the cellulose crystal centroid in a direction perpendicular to the interface, causing the virtual spring to... The crystals move at a speed of / ps, thereby driving the cellulose crystals to gradually peel off the CASH substrate. During the peeling process, the traction force is recorded. F Interface separation displacement DThe cumulative potential potential (PMF) and the interfacial interaction energy between cellulose crystals and CASH. E I The changes include, among which, the interface separation displacement. D Defined as the change in distance between the CASH centroid and the cellulose crystal centroid relative to the initial equilibrium state.

[0042] Based on the trajectory file and traction force obtained from the above controlled molecular dynamics simulations F -Interface separation displacement D Curve (e.g.) Figure 3 (as shown in a), and interface bonding energy E I -Interface separation displacement D Curve (e.g.) Figure 3 As shown in b), different separation displacements during the interface peeling process are identified using formulas (1)-(2). D The interface is in a detached state (e.g.) Figure 4 As shown), the debonding area at the interface is calculated using formula (3). A ( D )( Figure 5 As shown), where and All values ​​were set to 0.15.

[0043] The interface failure mode is determined using formulas (4)-(6), and the interface debonding area ratio is calculated. R D It is 0.80. R D If the value is greater than 0.75, the interface failure mode is determined to be interface debonding failure. Select 0.3, Select 0.15, Select 0.2, Selecting 0.75, this judgment result is consistent with the microstructure evolution analysis results during the interface peeling process, such as... Figure 6 As shown. Simultaneously, the work done by external forces on the system is obtained based on the change in PMF. W ( D ), and establish W ( D )- A ( D Relationship curve (e.g.) Figure 7 (As shown). A linear fit was performed on the curve during the interface stabilization and debonding stage, and the resulting slope was defined as the effective interface crack propagation energy release rate of the cellulose crystal / CASH interface. G eff 31 This is used to characterize the interface's ability to resist debonding and propagation.

[0044] Example 2 The effect of grafting amide groups onto the surface of cellulose crystals on interfacial debonding behavior The construction methods for the CASH structure and cellulose crystal structure are described in Implementation Case 1. Surface functionalization of the cellulose crystal is performed at the C6 hydroxyl site of the glucose molecule. Specifically, the hydroxyl groups on the C6 sites of the glucose units on the surface of the cellulose crystal are removed, and amide functional groups are introduced at the corresponding C6 carbon sites to construct an amide-modified cellulose crystal model.

[0045] Subsequently, following the method described in Implementation Case 1, energy minimization, isothermal and isochoric ensemble equilibrium, and controlled molecular dynamics interface peeling simulations were performed on the amide-modified cellulose crystal / CASH interface model to obtain trajectory files and traction forces. F -Interface separation displacement D Curve (e.g.) Figure 8 (as shown in a), and interface bonding energy E I -Interface separation displacement D Curve (e.g.) Figure 8 (as shown in b). Using formulas (1)-(2), different separation displacements during the interface peeling process are identified. D The interface is in a detached state (e.g.) Figure 9 As shown), the debonding area at the interface is calculated using formula (3). A ( D )( Figure 10 (As shown). Following the method in Implementation Case 1, based on the traction force obtained from simulation... F Interface separation displacement D Interface integration E I The interface failure mode was determined using formulas (4)-(6) based on the trajectory file. The results show that, in the event of interface failure, the interface debonding area ratio... R D A value of 0.38 indicates that the interface failure mode of this system is a mixed failure mode. This judgment result is consistent with the results of the microstructure evolution analysis during the interface peeling process, such as... Figure 11 As shown.

[0046] Example 3 The effect of carboxyl groups grafted onto the surface of cellulose crystals on interfacial debonding behavior The construction methods for the CASH structure, cellulose crystal structure, and modified cellulose crystal / CASH interface model are the same as in Implementation Case 2. The difference is that in this implementation case, the C6 hydroxyl site of glucose molecules on the surface of cellulose crystals is replaced with a carboxyl functional group, thereby constructing a carboxyl-modified cellulose crystal model.

[0047] Subsequently, following the method described in Implementation Case 1, energy minimization, isothermal and isochoric ensemble equilibrium, and controlled molecular dynamics interface peeling simulations were performed on the carboxyl-modified cellulose crystal / CASH interface model. The obtained trajectory files and traction forces... F -Interface separation displacement D Curve (e.g.) Figure 12 (as shown in a), and interface bonding energy E I -Interface separation displacement D Curve (e.g.) Figure 12 (as shown in b). Different separation displacements during the interface peeling process are calculated using formulas (1)-(3). D The interface debonding area below A ( D )( Figure 13 (As shown).

[0048] Following the method in Implementation Case 1, based on the simulated traction force, interface separation displacement, interface bonding energy, and trajectory file, the interface failure mode is determined using formulas (4)-(6). The results show that, in the event of interface failure, the interface debonding area ratio... R D The value of 0.77 indicates that the interface failure mode of this system is interface debonding failure. Furthermore, following the method in Implementation Case 1, the work done by external forces is established. W ( D ) and the debonding area of ​​the interface A ( D The relationship curve between ) (e.g.) Figure 14 (As shown), and linear fitting was performed on the interface stabilization and debonding stage to obtain the effective interface crack propagation energy release rate of the carboxyl-modified cellulose crystal / CASH interface. G eff 39 This is used to evaluate the interface's ability to resist debonding and expansion.

[0049] To further broaden the scope of application of this invention and clarify the scope of protection of this invention, the following supplementary explanations are provided: The inorganic matrix described in this invention is not limited to the geopolymer matrix in the embodiments, but can also be extended to cement matrix or other inorganic cementitious material matrix.

[0050] The main inorganic phase described in this invention is not limited to the CASH gel in the examples, but is also applicable to other base-activated product phases or hydration product phases such as calcium silicate hydrate (CSH) gel and sodium aluminosilicate hydrate (NASH) gel.

[0051] The plant fiber (or its representative cellulose crystal) described in this invention is only a typical example of the reinforcing phase, and it can be completely replaced by other conventional micro-reinforcing fibers such as glass fiber, carbon fiber, and basalt fiber, or equivalently replaced by nano-carbon materials such as carbon nanotubes and graphene.

[0052] The surface functional groups described in this invention are intended to cover all chemical groups capable of altering fiber surface properties, and are not limited to the specific groups listed in the embodiments. Other modified functional groups introduced by those skilled in the art based on actual process requirements are all within the scope of protection of this invention.

Claims

1. A molecular dynamics evaluation method for crack propagation resistance at the plant fiber / inorganic matrix interface, characterized in that, Includes the following steps: Step 1) Construct a cellulose crystal model of plant fibers and a CASH gel phase model representing the main phase of the inorganic matrix, respectively; Step 2) Construct a modified cellulose crystal model by replacing atoms or functional groups; Step 3) Construct the cellulose crystal / CASH interface structure based on the CASH gel phase model and the modified cellulose crystal model; Step 4) Perform energy minimization and equilibrium molecular dynamics simulations on the cellulose crystal / CASH interface structure to obtain a stable initial interface configuration; Step 5) Simulate the process of cellulose crystals peeling off from the CASH gel phase interface using controlled molecular dynamics simulation to obtain the simulation trajectory file and traction force. F Interface separation displacement D Cumulative potential potential (PMF) and interfacial bonding energy E I and obtain FD curves and E I - D curve; Step 6) Identify the debonding area of ​​the cellulose crystal / CASH interface region based on the trajectory file, and count the different separation displacements. D The interface debonding area below A ( D ); Step 7) Work done on the system by the PMF as an external force W(D) ,Establish W ( D ) and the debonding area of ​​the interface A ( D The relationship curve between ) is obtained W ( D )- A ( D )curve; Step 8) W ( D )- A ( D Linear fitting was performed on the curve during the interface stability and debonding stage, and the resulting slope represents the effective interface crack propagation energy release rate. G eff A quantitative evaluation of the resistance to interface crack propagation was completed.

2. The molecular dynamics evaluation method for crack propagation resistance at the plant fiber / inorganic matrix interface according to claim 1, characterized in that, Step 6) also includes interface debonding determination and interface failure determination.

3. The molecular dynamics evaluation method for crack propagation resistance at the plant fiber / inorganic matrix interface according to claim 2, characterized in that, The interface debonding determination includes mesh debonding determination and counting of the number of debonded mesh cells: A mesh cell is considered to have debonded when it simultaneously meets the following conditions: （1） and （2） in, i Indicates the first i One grid cell; , These represent the interfacial interaction energy and the number of contact atoms within each grid cell during the debonding process; , These represent the initial interfacial interaction energy and the initial number of contact atoms of the corresponding grid cell in equilibrium state, respectively. α 1 and α 2 represents the preset single-mesh debonding threshold. α The value of 1 ranges from 0.1 to 0.

25. α The value of 2 ranges from 0.1 to 0.

2.

4. The molecular dynamics evaluation method for crack propagation resistance at the plant fiber / inorganic matrix interface according to claim 1, characterized in that, The debonding area identification process described in step 6) is as follows: An analysis region with a thickness of 1.5 nm–4 nm was selected in the interface region, and this region was divided into several grid cells with a grid size of [missing information]. a The number of CASH atoms within each grid cell that are adjacent to cellulose crystal atoms in the cutoff distance range of 0.8 nm to 1.2 nm is counted and defined as the number of contact atoms between CASH and cellulose crystal within that grid cell. ,in, i Indicates the first i Each grid cell.

5. The molecular dynamics evaluation method for crack propagation resistance at the plant fiber / inorganic matrix interface according to claim 1, characterized in that, Debonding area A ( D ) is represented as: （3） In the formula, C ( D ) for statistical separation of displacement D The number of mesh elements that debond. a This refers to the grid cell size.

6. The molecular dynamics evaluation method for crack propagation resistance at the plant fiber / inorganic matrix interface according to claim 2, characterized in that, The interface failure determination process is as follows: Displacement at the interface D Greater than peak displacement D Fmax Then, the peak displacement D Fmax To achieve maximum traction F max The corresponding interface separation displacement occurs when the traction force satisfies: (4) Alternatively, the interface combination can satisfy: (5) The interface separation process then enters the failure determination stage. in, For separation displacement D The interface integration performance is as follows. This represents the initial interfacial binding energy in equilibrium. and To preset the failure threshold, The value ranges from 0.1 to 0.

3. The value ranges from 0.05 to 0.

25.

7. The molecular dynamics evaluation method for crack propagation resistance at the plant fiber / inorganic matrix interface according to claim 6, characterized in that, In the failure determination stage, based on the debonding area ratio R D Determine the interface failure mode, the debonding area ratio ,in, A (0) represents the initial interface area; the interface failure modes include surface debonding failure, cohesive failure, and mixed failure modes.

8. The molecular dynamics evaluation method for crack propagation resistance at the plant fiber / inorganic matrix interface according to claim 7, characterized in that, when When the interface failure mode is determined to be interface debonding failure; when When the interface failure mode is determined to be cohesion failure; when When the interface failure mode is determined to be a hybrid destruction mode; in, and This is the preset interface de-adhesion threshold.

9. The molecular dynamics evaluation method for crack propagation resistance at the plant fiber / inorganic matrix interface according to claim 7, characterized in that, The value ranges from 0.1 to 0.

25. The value ranges from 0.7 to 0.85.

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