CN114417634A - A multi-scale prediction method for damp-heat aging properties of plant fiber/polylactic acid composites based on mesoscopic modeling - Google Patents

Abstract

A plant fiber/polylactic acid composite material wet heat aging performance multi-scale prediction method based on mesoscopic modeling comprises the following steps: 1) carrying out an aging test on the plant fiber/polylactic acid composite material 2) establishing a change rule function of the water absorption of each aging material along with aging time at different temperatures; 3) establishing a function of the change rule of the strength of each component at different temperatures along with the aging time; 4) respectively establishing a relation function between the strength of each component and the water absorption rate and the temperature; 5) establishing a composite material mesoscopic RVE model; 6) defining and introducing an environmental degradation factor; 7) calculating the elastic property of the composite material; 8) calculating the failure strength of the composite material; 9) and predicting the wet heat aging performance of the macroscopic composite material. The invention fully considers the coupling effect of multiple scales and factors and provides a model and a method for predicting the mechanical property of the green composite material after aging in practical application.

Description

A multi-scale prediction method for damp-heat aging properties of plant fiber/polylactic acid composites based on mesoscopic modeling

technical field

The invention belongs to the technical field of detection of composite materials, and in particular relates to a multi-scale prediction method for the damp-heat aging performance of a plant fiber/polylactic acid composite material based on mesoscopic modeling.

Background technique

Degradability is one of the most important advantages of plant fiber reinforced composites. However, due to the hygroscopicity of plant fibers and the degradable properties of polylactic acid, its durability in service environments such as humidity and damp heat still faces great challenges. At present, the aging research of composite materials for automobile service conditions mainly focuses on traditional synthetic fiber reinforced resins, such as carbon fiber, glass fiber reinforced epoxy resin, and phenolic resin. For plant fiber-reinforced polylactic acid composites, due to the unique hydrophilicity and typical multi-scale and multi-level microstructure of plant fibers, as well as the degradable characteristics of polylactic acid itself, the research on environmental aging is more complicated and difficult.

The mechanical properties of plant fiber-reinforced composites are very sensitive to hot and humid environments. Experimental studies have shown that both moisture absorption and hydrothermal aging can significantly reduce the mechanical properties of plant fiber-reinforced composites and affect their service life. In plant fibers, the main component responsible for absorbing water is hemicellulose. The higher the hemicellulose content, the higher the degree of water absorption and degradation. Different plant fiber structures also have an impact on water diffusion. Usually, the water absorption law of plant fiber reinforced composites at room temperature follows the Fickian diffusion law, and the initial change is linear, and the water absorption gradually slows down and tends to be saturated after a long time. At higher temperatures, the hygroscopic behavior is significantly accelerated, and the water saturation time is greatly shortened.

Due to the hydrophilicity and complex structural characteristics of plant fibers, as well as the degradability of the PLA matrix, the long-term humid and heat environment often causes changes in the properties of each component (fiber, matrix, and fiber-matrix interface) in the composite material. At present, most of the research on aging prediction models and methods only focus on fibers and matrix, ignoring the self-degradation of fibers/matrix and the interface separation phenomenon caused by them, and cannot fully respond and analyze short plant fiber reinforcement from the micro-fine-macro level. Effects of fiber, matrix and interface component recession on the mechanical properties of composite materials.

SUMMARY OF THE INVENTION

Aiming at the design requirements of lightweight parts for low-carbon automobiles, the present invention provides a multi-scale prediction method for the damp-heat aging performance of plant fiber/polylactic acid composite materials based on mesoscopic modeling, which is a useful tool for plant fiber/polylactic acid green composite materials in practical engineering. Design applications for reference and guidance.

In order to achieve the above-mentioned purpose of the invention, the present invention provides the following technical solutions: a multi-scale prediction method for the wet-heat aging performance of plant fibers/polylactic acid composite materials based on mesoscopic modeling, comprising the following steps:

1) Prepare the plant fiber/PLA composite material, and conduct aging tests on the composite material, the PLA matrix and the plant fiber respectively: select typical plant fiber as the filling phase, and degradable PLA as the matrix material to prepare the plant fiber/PLA composite material ; Referring to the accelerated aging standard for parts in the automotive industry, put the pre-dried plant fiber, polylactic acid matrix, plant fiber\polylactic acid composite material into a constant temperature water tank with different temperatures for artificial accelerated aging, and obtain different aging temperatures and aging times. aged materials;

2) Establish the regular function of the water absorption rate of each material at different temperatures with aging time: The water absorption rate of the aging material obtained in step 1) is tested. The water absorption rate of the plant fiber is measured indirectly by the water absorption rate of the polylactic acid matrix and the composite material, and the variation law of the material water absorption rate with the aging time at each temperature is fitted to obtain the water absorption rate (M) of the three materials and the aging temperature. (T) and aging time (t) as a function of fiber M _f (t, T), PLA matrix M _m (t, T) and composite M _i (t, T), respectively;

3) Establish the regular function of the strength of each component at different temperatures with aging time: The strength test is performed on the aging material obtained in step 1): wherein, the polylactic acid matrix is subjected to a dumbbell tensile test, and the plant fiber is subjected to single fiber pulling The tensile test was carried out, and the single fiber pull-out test was carried out on the composite material, and the function of the strength of the polylactic acid matrix, plant fiber and composite material with aging time at different temperatures was obtained: S _m (t, T), S _f (t, T) and _Si (t, T);

4) Establish the relationship function between the strength of each component of polylactic acid matrix, plant fiber, and composite material, water absorption rate, and temperature: Integrate the previously obtained data, and obtain plant fiber, polylactic acid matrix and fiber- The three strengths of the matrix interface as a function of water absorption and aging temperature are respectively fiber S _f (M, T), matrix S _m (M, T) and fiber-matrix interface _Si (M, T);

5) Establishment of the microscopic RVE model of the composite material: sampling from the unaged plant fiber/polylactic acid composite material, performing X-ray tomography to obtain a tomographic grayscale image containing the microstructure information of the material; 3D visualization analysis of the tomographic image to establish 3D view and geometric simplification and cleaning of fibers and PLA matrix are completed, the reconstructed geometric model is imported into finite element analysis software, and the meso RVE model of plant fiber/PLA composite material is established;

6) Definition and introduction of environmental degradation factors: Compose the constitutive relationship of plant fibers, polylactic acid matrix, and composite interface simulation elements, define the properties of the meso-RVE model of composite materials, and construct the environmental degradation factors of each component based on the strength change function ( D) function,

where S(M', T') is the strength when the temperature is T' and the moisture absorption is M', and S(M ⁰ , T ⁰ ) is the initial strength of the material. From the above formula, the degradation factor function D _f (M, T) of the fiber, the degradation factor function D _m (M, T) of the matrix and the degradation factor function D _i (M, T) of the fiber-matrix interface can be obtained;

7) Calculation of elastic properties of composite materials: Introduce a degradation factor to correct the elastic performance parameters of each component; under periodic boundary conditions, apply a linear uncorrelated displacement load to the RVE model and simulate it to obtain macroscopic images of different temperatures and water absorption rates. composite elastic properties;

8) Calculation of failure strength of composite materials: For the three components of plant fiber, polylactic acid matrix and composite interface in the mesoscopic model, the corresponding initial failure criterion and damage expansion criterion are respectively defined, and the degradation factor is introduced to correct the failure parameters. , and carry out numerical simulation to obtain the failure strength of macroscopic composites under different water absorption rates and temperatures;

9) Prediction of the wet-heat aging performance of macroscopic composite materials: establish a macroscopic model of composite tensile and three-point bending specimens, and simulate the macroscopic elastic performance function and failure strength function of composite materials that depend on water absorption and temperature changes based on the microscopic RVE model simulation. , substituted into the macro model, set up the damp-heat environment for finite element analysis, and predicted the mechanical properties of plant fiber/polylactic acid composites with different aging degrees under damp-heat aging conditions.

In step 1), the plant fiber/polylactic acid composite material is prepared from jute fiber and polylactic acid particles by injection molding.

In step 5), the finite element software is Abaqus software; the three-dimensional visualization analysis adopts Avizo9.0 software.

In step 8), the maximum stress criterion is adopted as the failure criterion of the fiber; the generalized Mises failure criterion is adopted as the failure criterion of the polylactic acid matrix; and the secondary stress criterion is adopted for the fiber-matrix interface in the composite material.

Compared with the prior art, the beneficial effects of the present invention are:

1) The present invention focuses on the construction goals of “carbon peaking” and “carbon neutrality” in my country, aiming at the current needs of energy conservation, emission reduction and environmental protection, and conducts multi-scale aging performance of plant fiber/polylactic acid green composite materials for low-carbon vehicles. Research on forecasting methods, explore new paths for crop raw materials, solve the dilemma of oil and energy crisis, and provide reference and foundation for the further application of plant fiber/polylactic acid green composite materials in the field of auto parts.

2) At present, the research on the damp-heat aging of short plant fiber/polylactic acid composites pays more attention to the establishment and improvement of the theoretical model of water diffusion and the analysis of internal stress of the structure, etc., but a systematic and effective prediction model and method for mechanical properties after aging has not been formed. The invention starts from the mesoscopic modeling considering the performance of each component, constructs the fiber, matrix and interface performance correction function dependent on the water absorption rate variable, and realizes the elastic performance of the short plant fiber/polylactic acid composite material after aging under the coupling influence of multiple factors and failure strength prediction, which provides a new idea for the performance prediction of composite materials.

3) In the long-term service process, affected by the environment, load, wear and other factors, the structure of auto parts has different degrees of aging, which needs to be updated and maintained regularly. Compared with materials such as metal and traditional plastics, the plant fiber/PLA composite material is more sensitive to service conditions, and the aging phenomenon is more obvious. If the service life of the components is exceeded, the use function may be lost, and even serious safety accidents may be caused. However, updating and maintaining in advance before reaching the limit of service life will also cause great waste of manpower and materials, and significantly increase the cost of use. The aging performance simulation and life prediction method provided by the invention can effectively support the structural design theory of green composite material parts, and provide a reference for formulating reasonable maintenance cycles and methods, thereby reducing economic costs.

Description of drawings

Fig. 1 is a process flow diagram of the multi-scale prediction method of the wet-heat aging performance of plant fiber/polylactic acid composite material based on mesoscopic modeling of the present invention.

Detailed ways

The multi-scale prediction method for wet-heat aging performance of plant fiber/polylactic acid composite material based on mesoscopic modeling of the present invention is further described in detail:

A multi-scale prediction method of plant fiber/polylactic acid composites based on mesoscopic modeling for damp-heat aging properties, as shown in Figure 1, includes the following steps:

1) plant fiber/polylactic acid composite material preparation and aging test: the present invention selects jute fiber as filling phase, selects degradable polylactic acid as matrix material, removes moisture from jute fiber and polylactic acid particles in a vacuum drying oven, and uses alkali/ The jute fiber is treated with a silane coupling agent, and the jute fiber and the polylactic acid particles are fully mixed according to the ratio of 1:9 (the ratio described in this example is only for illustrating the model establishment, and the present invention is applicable to any ratio) to obtain the jute fiber/polylactic acid particle. Lactic acid composite. The jute fiber/polylactic acid particles were prepared by a twin-screw extruder, and after drying, the required samples were prepared by a plastic injection molding machine; at the same time, pure jute fiber samples and polylactic acid samples were prepared by the above method, respectively. Select 25 ℃, 40 ℃, 55 ℃ water baths as aging conditions, respectively, carry out wet heat accelerated aging on polylactic acid, jute fiber and composite materials, and dry the samples after aging;

2) Establish the law function of the water absorption rate of each aging material at different temperatures with aging time: calculate the water absorption rate of pure PLA matrix and composite materials by electronic scale weighing method, and regularly monitor jute fiber/polylactic acid composite material, jute fiber and the average water absorption of pure PLA until reaching the equilibrium water absorption M _∞ in Fickian formula, the water absorption M in the composite material and pure PLA material is calculated according to the ASTM D5229 standard.

The water absorption of the fiber is obtained by the following formula

ΔM _c =ΔM _f ×V _f +ΔW _m (1-V _f )

Through experiments, the saturated water absorption rates of jute fiber/PLA composite material, jute fiber and pure PLA at different temperatures were obtained, respectively.

Table 1 Saturated water absorption of each aged material at different temperatures

Integrate the test data to obtain the changing law of the water absorption of the composite material, PLA matrix and jute fiber with aging time under different aging temperatures;

3) Establish a function of the variation law of the strength of each component at different temperatures with aging time: select materials with different aging temperatures and aging times for mechanical property tests, single-fiber pull-out tests for composite materials, and single-fiber tensile tests for fibers , Carry out the dumbbell tensile test on the polylactic acid matrix, and obtain the strength reduction ratio of the three components when they reach the saturated water absorption rate, as shown in the following table:

Table 2 Changes in the strength of each component at different temperatures (percentage decrease compared to the initial strength)

By integrating the data obtained from the test, the law of the strength of the matrix-fiber interface changing with aging temperature and aging time, the law of fiber strength changing with aging temperature and aging time, and the changing law of polylactic acid matrix strength with aging temperature and aging time were obtained. ;

4) Establish the relationship function between the strength of each component of the polylactic acid matrix, fiber and composite material, water absorption, and temperature: Integrate the data obtained before, and obtain the plant fiber, polylactic acid matrix and fiber-matrix by fitting the data. Interfacial triad strength as a function of water absorption and aging temperature

S _f (M,T)＝14.82787+0.9456T-0.03143M-0.01163T ² -0.02714M ² -0.00991MT

S _m (M,T)＝42.16438+0.49302T-17.52793M-0.0065T ² -24.68074M ² +0.37515MT

S _i (M,T)＝-1.23196+3.11211T+9.87753M-0.03748T ² -1.82922M ² -0.3378MT

5) Establishment of the microscopic RVE model of the composite material: sampling from the unaged plant fiber/polylactic acid composite material, performing X-ray tomography to obtain a tomographic gray image containing the microstructure information of the material; using Avizo9.0 software to analyze the plant fiber/polylactic acid composite material. The tomographic images of PLA composites were analyzed for 3D visualization. In order to remove the influence of impurities in the image, the original image was filtered and simplified by median filtering technology; then, the repair function in Avizo 9.0 software was used to close and clean the pores on the surface of natural fibers, and the repaired plant fiber voxel model was The surface is smoothed; finally, the reconstructed geometric model is imported into the finite element analysis software Abaqus software to establish the meso RVE model of the composite material;

6) Definition and introduction of environmental degradation factors: Compose the constitutive relationship of fiber, matrix, and interface simulation element, and define the properties of the meso-scale RVE model of composite materials. Constructing the environmental degradation factor (D) function of each component based on the intensity change function

The degradation factor functions of the fibers are obtained respectively

D _f (M,T)=0.46337+0.02955T-0.00098m-0.00036T ² -0.00085M ² +0.00031MT,

Degradation factor function of the matrix

D _m (M,T)＝0.84329+0.00986T-0.35056m-0.00013T ² -0.49361M ² +0.00750MT,

Degradation factor function of fiber-matrix interface

D _i (M,T)=-0.02124+0.05366T+0.17030m-0.00065T ² -0.03154M ² -0.00582MT,

The degradation factor is introduced into the corresponding constitutive to realize the correction of the constitutive parameters of each component based on the aging effect;

7) Calculation of elastic properties of composite materials: By introducing degradation factors, the elastic performance parameters of each component are corrected; under periodic boundary conditions, linear uncorrelated displacement loads are applied to the RVE model and simulated to obtain different temperature and water absorption conditions The elastic properties of macroscopic composites under

8) Calculation of the failure strength of composite materials: Since the research scale is very small in the mesoscopic state, the short plant fiber is regarded as an isotropic material in the mesoscopic model, and the plant fiber is expressed as a linear elastic constitutive, the failure criterion of the fiber The maximum stress criterion is adopted; the PLA matrix is usually considered as an isotropic elastic-plastic material, and the generalized Mises failure criterion is adopted for the failure criterion; the cohesive force constitutive and the quadratic stress criterion are adopted for the fiber-matrix interface; Numerical simulation was carried out to obtain the failure strength of macroscopic composites under different water absorption rates and temperatures;

9) Prediction of the wet-heat aging performance of macroscopic composite materials: establish a macroscopic model of composite tensile and three-point bending specimens. Among them, the tensile standard of composite materials adopts ISO 527-2, and the three-point bending standard adopts EN ISO14125, which will be based on the microscopic RVE The macro-elastic properties and failure strengths of composites that depend on changes in water absorption obtained from the model simulation are substituted into the macro-model, and the damp-heat environment is set for finite element analysis. The performance is predicted, and the results show that the tensile test error is 7.86%, and the three-point bending test error is 8.13%, which shows that the prediction method of the present invention has certain practical significance in predicting the wet heat aging performance of the plant fiber/polylactic acid composite material.

Claims (4)

1. a multi-scale prediction method based on the plant fiber/polylactic acid composite material damp heat aging performance based on mesoscopic modeling, is characterized in that, comprises the following steps: 1) Prepare a plant fiber/polylactic acid composite material, and carry out an aging test on the composite material, the polylactic acid matrix and the plant fiber, respectively, to obtain aging materials with different aging temperatures and aging times; 2) Carry out a water absorption test on the aging material obtained in step 1), and obtain the function of the water absorption of the plant fiber, the polylactic acid matrix and the composite material changing with the aging time under different aging temperatures: M _f (t, T), M _m (t, T) and M _i (t, T); 3) The strength test is carried out on the aged material obtained in step 1), wherein the polylactic acid matrix is subjected to a dumbbell tensile test, the plant fiber is subjected to a single fiber tensile test, and the composite material is subjected to a single fiber pull-out test, respectively to obtain different The function of the strength of PLA matrix, plant fiber and composite material as a function of aging time at temperature: S _m (t, T), S _f (t, T) and _Si (t, T); 4) The relationship function between the strength of each component of PLA matrix, plant fiber, and composite material, water absorption rate, and temperature was established respectively; by fitting the data, the three strengths of plant fiber, PLA matrix and fiber-matrix interface were obtained with water absorption rate. and aging temperature changes: S _f (M, T), S _m (M, T) and t _i (M, T); 5) Establishment of the microscopic RVE model of the composite material: sampling from the unaged plant fiber/polylactic acid composite material, performing X-ray tomography to obtain a tomographic grayscale image containing the microstructure information of the material; 3D visualization analysis of the tomographic image to establish 3D view and geometric simplification and cleaning of fibers and PLA matrix are completed, the reconstructed geometry is imported into finite element analysis software, and a meso RVE model of plant fiber/PLA composite material is established; 6) Definition and introduction of environmental degradation factors: Compose the constitutive relations of plant fibers, polylactic acid matrix, and composite interface simulation elements, and define the properties of the mesoscopic RVE model of composite materials; construct environmental degradation factors of each component based on the strength change function ( D) function,

Among them, S(M', T') is the strength when the temperature is T' and the moisture absorption is M', and S(M ⁰ , T ⁰ ) is the initial strength of the material; the degradation factor function D _f of the fiber can be obtained from the above formula (M, T), the degradation factor function D _m (M, T) of the PLA matrix and the degradation factor function D _i (M, T) of the fiber-matrix interface in the composite; 7) Calculate the elastic properties of composite materials: Introduce a degradation factor to modify the elastic performance parameters of each component; under periodic boundary conditions, apply a linear uncorrelated displacement load to the RVE model and simulate it to obtain different temperatures and water absorption rates. Macroscopic composite elastic properties; 8) Calculate the failure strength of the composite material: For the three components of the plant fiber, the polylactic acid matrix and the interface of the composite material in the mesoscopic model, the corresponding initial failure criterion and damage expansion criterion are respectively defined, the degradation factor is introduced, and the failure parameters are calculated. Correction and numerical simulation are carried out to obtain the failure strength of macroscopic composites under different water absorption rates and temperatures; 9) Prediction of the wet-heat aging performance of macroscopic composites: establish a macroscopic model of composite tensile and three-point bending specimens, and simulate the macroscopic elastic performance function and failure strength of composites dependent on water absorption and temperature changes based on the microscopic RVE model simulation. The function is substituted into the macro model, and the damp-heat environment is set for finite element analysis to predict the mechanical properties of plant fiber/polylactic acid composites with different aging degrees under damp-heat aging conditions. 2. a kind of plant fiber/polylactic acid composite material moisture-heat aging performance multi-scale prediction method based on mesoscopic modeling according to claim 1, is characterized in that, in step 1), described plant fiber/polylactic acid composite material It is prepared from jute fiber and polylactic acid particles by injection molding. 3. a kind of plant fiber/polylactic acid composite material moisture-heat aging performance multi-scale prediction method based on mesoscopic modeling according to claim 1, is characterized in that, in step 5), described finite element software is Abaqus software; The three-dimensional visualization analysis was performed using Avizo 9.0 software. 4. a kind of plant fiber/polylactic acid composite material moisture-heat aging performance multi-scale prediction method based on mesoscopic modeling according to claim 1, is characterized in that, in step 8), the failure criterion of fiber adopts maximum stress criterion; The generalized Mises failure criterion is adopted for the failure criterion of PLA matrix; the quadratic stress criterion is adopted for the fiber-matrix interface in the composite material.

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