A method for predicting the mechanical properties of resin matrix composites with large thickness

Abstract

The present invention discloses a method for predicting the mechanical properties of a large-thickness resin matrix composite material, belonging to the field of mechanical property testing of composite materials. The present invention uses finite element simulation software to establish a multi-field coupling curing model for large-thickness composite materials, simulates the entire curing process and extracts the temperature peak value during the curing process; conducts mechanical property tests on composite material samples with a certain thickness gradient to obtain the strength values of samples with different thicknesses; introduces a temperature damage factor to correct the Bazant strength size effect law, thereby realizing the prediction of the mechanical properties of large-thickness resin matrix composite materials. The strength size effect law corrected by this method can effectively improve the prediction accuracy of the mechanical properties of large-thickness resin matrix composite materials, and at the same time can broaden the applicable range of this size effect law.

Description

Technical Field

[0001] The present invention belongs to the field of mechanical property testing of composite materials, and particularly relates to a method for predicting the mechanical properties of thick resin matrix composite materials. Background Technique

[0002] With the wide application of composite materials in the fields of aircraft main load-bearing components, engine fan blades, submarines and ships, etc., the size and thickness of composite structural components are increasing day by day. As a quasi-brittle material, the mechanical property testing of resin matrix composite materials has large dispersion, and there is an obvious size effect on the strength of resin matrix composite materials. Therefore, for large composite components, an accurate and simple mechanical property prediction method is needed.

[0003] The classical two-parameter Weibull statistical size effect theory is based on the weakest link model and is widely used to describe the size effect of the mechanical properties of composite materials. This theory believes that the failure of a single material unit is only related to the stress received by this unit, and has nothing to do with the stress conditions and loading history of other units in the structure, which obviously violates the actual situation during the testing of composite materials. Therefore, it needs to be corrected based on non-local theory. Bazant's size effect theory is based on the energy release theory, and by solving the nominal stress of the sample, it further describes the size effect of composite materials. The results of Bazant's size effect theory are closer to the experimental results, but when the thickness is large, they will be higher than the experimental results. This is mainly because the thermal conductivity of composite materials is low, and a large amount of heat released during the resin curing process cannot be dissipated in time, resulting in the center temperature of thick composite materials being much higher than the set temperature, thus causing the deterioration of resin properties and further affecting the mechanical properties. Therefore, it is necessary to consider the influence of temperature overshoot during the curing process of thick resin matrix composite materials. Summary of the Invention

[0004] Aiming at the above problems in the prior art, the present invention proposes a method for predicting the mechanical properties of thick resin matrix composite materials. Starting from the basic mechanical property testing of composite materials, combining numerical analysis and finite element simulation, introducing the temperature damage factor T, and establishing a modified Bazant size effect model for thick resin matrix composite materials, the prediction of the mechanical properties of thick resin matrix composite materials is accurately and efficiently realized.

[0005] The specific technical solution adopted by the present invention is as follows:

[0006] The present invention provides a method for predicting the mechanical properties of thick resin matrix composite materials, which is used to predict the mechanical properties of thick resin matrix composite materials with a thickness not within the standard test range, specifically as follows:

[0007] S1: Based on the curing kinetics model and thermophysical parameters of prepreg, establish the temperature distribution model of the curing process of thick resin matrix composite materials;

[0008] S2: Embed the temperature sensor into the center of the laminate of the thick resin matrix composite material, and verify the temperature distribution model of the curing process by monitoring the temperature change at the center of the laminate in real time;

[0009] S3: Conduct mechanical property tests on the thick composite material sample group with a certain thickness gradient to obtain the strength values of samples with different thicknesses;

[0010] S4: Conduct a temperature distribution simulation test during the curing process on the thick composite material sample group with a certain thickness gradient in S3 to obtain the temperature peak values during the curing process of samples with different thicknesses. The temperature difference between the temperature peak value and the temperature of the second heat preservation platform in the curing regime used in the temperature distribution simulation test of the curing process is defined as the temperature overshoot ΔT;

[0011] S5: Cut standard thickness samples from the central regions of thick composite material laminates with different thicknesses and conduct mechanical property tests to obtain their strength values; subsequently, compare the strength values with those of samples cut from standard thickness composite material laminates to obtain the percentage value of strength reduction caused by temperature overshoot at different thicknesses. This percentage value is the actual value of the temperature damage factor at the current thickness;

[0012] S6: Based on the results obtained in S3, according to the actual values of the temperature damage factors at different thicknesses obtained in S5, fit to obtain the temperature damage factor T applicable to different thicknesses, and introduce T into the Bazant strength size effect law for correction, so as to realize the accurate prediction of the mechanical properties of thick resin matrix composites.

[0013] Preferably, the mechanical properties include the short beam shear and three-point bending properties of thick resin matrix composites and the compression properties of thick resin matrix composites.

[0014] Preferably, in S1, the Abaqus finite element simulation software is used to establish the temperature distribution model of the curing process.

[0015] Preferably, the verification of the temperature distribution model in S2 is carried out at least once. It is preferred to conduct three verifications on thick resin matrix composites with thicknesses of 10 mm, 20 mm, and 30 mm respectively, so that the error between the experimental results of the temperature peak value during the curing process and the simulation results obtained according to the temperature distribution model of the curing process does not exceed 5%.

[0016] Preferably, the thick composite material sample group with a certain thickness gradient in S3 includes at least 5 kinds of samples with different thicknesses; it is preferred that the initial thickness is 2 mm and the thickness gradient is 3 mm.

[0017] Preferably, the samples described in S3 are all cut and processed from a large-thickness resin matrix composite laminate. The lengths and widths of all the large-thickness resin matrix composite laminates are the same, and only the thicknesses are different.

[0018] Preferably, the large-thickness composites with different thicknesses described in S5 include at least 3 thicknesses and the thicknesses are not less than 10 mm. Preferably, large-thickness resin matrix composite laminates with thicknesses of 10 mm, 20 mm, and 30 mm are used.

[0019] Preferably, the unmodified Bazant strength size effect law described in S6 is as shown in the following formula:

[0020]

[0021] In the formula: σ N is the nominal strength, is the average tensile strength of the boundary layer, 2D b is the thickness of the boundary layer, D is the thickness of the sample, and 2D b are obtained by fitting the formula.

[0022] Furthermore, the expression of the temperature damage factor T at different thicknesses described in S6 is obtained by fitting the percentage value of the strength drop caused by temperature overshoot at several thicknesses obtained through S5 by numerical analysis software, as shown in the following formula:

[0023]

[0024] In the formula: T max is the maximum strength drop caused by temperature overshoot, ΔT is the temperature overshoot, is the temperature constant, T max and are obtained by fitting the formula.

[0025] Even further, the modified Bazant strength size effect law described in S6 is as shown in the following formula:

[0026]

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] On the one hand, the steps of the present method are not only applicable to large-thickness resin matrix composite systems with existing curing kinetics models, but also applicable to large-thickness resin matrix composite systems without curing kinetics models, and the application range is relatively wide; on the other hand, the present method simultaneously considers the influence of energy release and temperature overshoot, and proposes a method and process for predicting the mechanical properties of large-thickness resin matrix composites through finite element simulation and the Bazant strength size effect law, which is accurate and efficient. Description of the Drawings

[0029] Figure 1 It is a verification diagram of the curing temperature distribution model of the large-thickness resin matrix composite material in the embodiment;

[0030] Figure 2 It is the short beam shear strength values of samples with different thicknesses in the embodiment;

[0031] Figure 3 It is the temperature overshoot values of laminates with different thicknesses in the embodiment;

[0032] Figure 4 It is the fitting curve of the temperature damage factor T in the embodiment;

[0033] Figure 5 It is a comparison diagram of the uncorrected and corrected Bazant strength size effect ratios in the embodiment. Detailed Embodiments

[0034] The present invention will be further described and illustrated below in conjunction with the drawings and specific embodiments. The technical features of each embodiment in the present invention can be combined correspondingly without conflict.

[0035] In the present invention, so-called curing kinetics models, short beam shear, three-point bending, temperature overshoot, etc. are well-known technical terms in the art and do not need any limitation.

[0036] In the present invention, a method for predicting the mechanical properties of large-thickness resin matrix composite materials is provided, which is used to predict the mechanical properties of large-thickness resin matrix composite materials with thicknesses not within the standard test range, and it includes the following steps:

[0037] S1: Using Abaqus finite element simulation software, based on the curing kinetics model of prepreg and other thermophysical parameters, establish a temperature distribution model of the curing process of large-thickness resin matrix composite materials.

[0038] In this step, the specific method for establishing the temperature distribution model of the curing process of large-thickness resin matrix composite materials is prior art and will not be elaborated herein.

[0039] S2: Conduct experimental verification of the temperature distribution model. Specifically, bury temperature sensors in the center of the large-thickness resin matrix composite laminate to monitor the temperature change at the center point in real time.

[0040] In this step, the verification of the temperature distribution model should be carried out at least once. Preferably, three verifications are carried out on large-thickness resin matrix composite materials with thicknesses of 10 mm, 20 mm, and 30 mm. It should be ensured that the error between the experimental results and the simulation results of the temperature peak value during the curing process does not exceed 5%.

[0041] S3: Conduct mechanical property tests on large-thickness composite material samples with a certain thickness gradient to obtain the strength values of samples with different thicknesses.

[0042] In this step, to ensure the effectiveness of the mechanical property prediction model, it is necessary to ensure that the samples for testing include at least 5 thicknesses. Preferably, the initial thickness is 2 mm and the thickness gradient is 3 mm, which can not only ensure sufficient experimental data for curve fitting but also avoid waste of experimental materials.

[0043] S4: Simulate the temperature distribution during the curing process of large-thickness composite laminates with a certain thickness gradient to obtain the temperature peaks during the curing process of laminates with different thicknesses. The temperature difference between the temperature peak and the temperature of the second heat preservation platform in the curing regime used in the temperature distribution simulation test during the curing process is defined as the temperature overshoot ΔT.

[0044] In this step, the temperature distribution model during the curing process of composite laminates with different thicknesses is exactly the same as the aforementioned model in terms of material properties, boundary conditions, curing regime, etc., only with the difference in thickness. The samples described in S3 and S5 are all cut and processed from a whole large-thickness resin-based composite laminate, and the length and width of all whole large-thickness resin-based composite laminates should be kept consistent.

[0045] S5: Cut standard-thickness samples from the central regions of large-thickness composite laminates with different thicknesses and conduct mechanical property tests to obtain their strength values; then compare this strength value with the strength value of the sample cut from the standard-thickness composite laminate to obtain the percentage value of the strength decrease caused by temperature overshoot at different thicknesses. This percentage value is the actual value of the temperature damage factor at the current thickness.

[0046] Since both size effect and temperature overshoot will affect the strength value of the sample, in this step, to only consider verifying the influence of temperature overshoot, mechanical property tests are conducted on the standard-thickness samples cut from the central regions of large-thickness composite laminates with different thicknesses.

[0047] In addition, to ensure the accuracy of fitting the temperature damage factor, the large-thickness composites with different thicknesses described in S5 should include at least 3 thicknesses and the thickness should not be less than 10 mm. Preferably, large-thickness resin-based composite laminates with thicknesses of 10 mm, 20 mm, and 30 mm are used, and the experimental and simulation data in S2 can both be used. Compare the strength value of the standard-thickness sample cut from the central region of the large-thickness composite laminate with different thicknesses with the strength value of the sample cut from the standard-thickness composite laminate to obtain the percentage value of the strength decrease caused by temperature overshoot at different thicknesses. This percentage value is the actual value of the temperature damage factor at the current thickness.

[0048] S6: Based on the results obtained in S3, according to the actual values of the temperature damage factor at different thicknesses obtained in S5, the temperature damage factor T applicable to different thicknesses is obtained by fitting, and T is introduced into the Bazant strength size effect law for correction to achieve accurate prediction of the mechanical properties of thick resin matrix composites.

[0049] In this step, the uncorrected Bazant strength size effect law is shown as the following formula:

[0050]

[0051] In the formula: σ N is the nominal strength, is the average tensile strength of the boundary layer, 2D b is the thickness of the boundary layer, and D is the thickness of the sample.

[0052] The expression of the temperature damage factor T at different thicknesses in S6 is obtained by fitting the percentage value of the strength drop caused by temperature overshoot at several thicknesses obtained in S5 through numerical analysis software, as shown in the following formula:

[0053]

[0054] In the formula: T max is the maximum strength drop caused by temperature overshoot, ΔT is the temperature overshoot, is the temperature constant.

[0055] The corrected Bazant strength size effect law is shown as the following formula:

[0056]

[0057] The above prediction method and process of the present invention are applicable not only to thick resin matrix composite systems with existing curing kinetics models, but also to thick resin matrix composite systems without curing kinetics models.

[0058] In order to further enable those skilled in the art to better understand the specific implementation process and technical effects of this prediction method, the above method will be applied to a specific embodiment below.

[0059] Embodiment

[0060] This embodiment provides a method and process for predicting the mechanical properties of thick resin matrix composites. The steps of this method are as follows:

[0061] (1) Establish a temperature distribution model for the curing process of thick resin matrix composites with effective sizes of 350×350×10 mm, 350×350×20 mm, and 350×350×30 mm, and simulate the temperature change of its center point during the entire curing process.

[0062] (2) The temperature sensors were embedded at the center points of resin matrix composites with large thicknesses of 350×350×10 mm, 350×350×20 mm, and 350×350×30 mm to monitor the temperature changes during the entire curing process in real time. The experimental results of the 350×350×30 mm sample and the simulation results are as Figure 1 shown.

[0063] Figure 1 In it, Cure Cycle represents the curing regime used for curing, Experiment represents the experimental results of the temperature changes at the center points of the resin matrix composites with large thicknesses, Simulation represents the finite element simulation results of the temperature changes at the center points of the resin matrix composites with large thicknesses, and Cure degree α represents the finite element simulation results of the curing degree changes at the center points of the resin matrix composites with large thicknesses. It can be seen from the figure that the experimental results of the temperature changes at the center points are in good agreement with the finite element simulation results, and the error between the experimental results and the simulation results of the temperature peak value during the curing process does not exceed 5%, which proves the effectiveness of this finite element model.

[0064] (3) Short beam shear tests were carried out on large thickness composite samples with thicknesses of 2.4 mm, 5.4 mm, 8.4 mm, 10.8 mm, 13.2 mm, and 16.2 mm to obtain the short beam shear strength values of samples with different thicknesses. The sample sizes refer to the standard ASTM D2344, and the results are as Figure 2 shown. It can be seen from the figure that as the thickness increases, the short beam shear strength of samples with different thicknesses decreases from 81.34 MPa to 63.14 MPa.

[0065] (4) The curing processes of composite laminates with thicknesses of 2.4 mm, 5.4 mm, 8.4 mm, 10.8 mm, 13.2 mm, and 16.2 mm and lengths and widths of 350×350 mm were simulated to obtain the temperature overshoot ΔT of the center points at each thickness during the entire curing process. The results are as Figure 3 shown. It can be seen from the figure that as the thickness increases, the temperature overshoot of samples with different thicknesses rises from 0.2 °C to 10.2 °C.

[0066] (5) Short beam shear tests were carried out on samples with a thickness of 5 mm cut from the central regions of large thickness composite laminates of 350×350×10 mm, 350×350×20 mm, and 350×350×30 mm to obtain their strength values, and they were compared with the strength values of samples cut from a 350×350×5.4 mm composite laminate to obtain the percentage value T of the strength decrease caused by the temperature overshoot.

[0067] (6) The temperature damage factor T was obtained by fitting with numerical analysis software, as Figure 4As shown, the temperature loss factor T is expressed as:

[0068]

[0069] (7) The modified Bazant strength size effect law is fitted through numerical analysis software, and the comparison with the unmodified result is as Figure 5 shown. It can be seen from the figure that the fitting coefficient is increased from 0.87 to 0.93, and the modified Bazant strength size effect law is expressed as:

[0070]

[0071] Thus, it can be seen that the strength size effect law modified by the method of the present invention can effectively improve the prediction accuracy of the mechanical properties of thick resin matrix composites, and at the same time can broaden the applicable range of this size effect law.

[0072] The above-described embodiments are only a preferred solution of the present invention, but they are not intended to limit the present invention. Those of ordinary skill in the relevant technical fields can still make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all technical solutions obtained by means of equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A method for predicting the mechanical properties of a resin matrix composite with a large thickness, characterized in that, It is used to predict the mechanical properties of thick resin matrix composites with thicknesses outside the standard test range, specifically as follows: S1: Based on the curing kinetics model and thermophysical parameters of prepreg, establish a temperature distribution model for the curing process of thick resin matrix composites; S2: Embed temperature sensors into the center of the laminate of thick resin matrix composites, and verify the temperature distribution model of the curing process by real-time monitoring of the temperature changes at the center of the laminate; S3: Conduct mechanical property tests on a group of thick composite samples with a certain thickness gradient to obtain the strength values of samples with different thicknesses; S4: Conduct a temperature distribution simulation test of the curing process on the group of thick composite samples with a certain thickness gradient in S3 to obtain the temperature peaks during the curing process of samples with different thicknesses. The temperature difference between the temperature peak and the temperature of the second heat preservation platform in the curing regime used in the temperature distribution simulation test of the curing process is defined as the temperature overshoot ΔT; S5: Cut standard thickness samples from the central region of thick composite laminates with different thicknesses and conduct mechanical property tests to obtain their strength values; Subsequently, compare this strength value with the strength value of the sample cut from the standard thickness composite laminate to obtain the percentage value of the strength decrease caused by the temperature overshoot at different thicknesses. This percentage value is the actual value of the temperature damage factor at the current thickness; S6: Based on the results obtained in S3, according to the actual values of the temperature damage factors at different thicknesses obtained in S5, fit to obtain the temperature damage factor T applicable to different thicknesses, and introduce T into the Bazant strength size effect law for correction, thereby realizing the accurate prediction of the mechanical properties of thick resin matrix composites.

2. The mechanical property prediction method of a large-thickness resin matrix composite material according to claim 1, characterized in that The mechanical properties include the short beam shear and three-point bending properties of thick resin matrix composites and the compression properties of thick resin matrix composites.

3. A method for predicting the mechanical properties of a thick resin matrix composite material according to claim 1, characterized in that, In S1, use Abaqus finite element simulation software to establish a temperature distribution model for the curing process.

4. A method for predicting the mechanical properties of a large-thickness resin matrix composite according to claim 1, characterized in that, In S2, the verification of the temperature distribution model is carried out at least once. Select thick resin matrix composites with thicknesses of 10 mm, 20 mm, and 30 mm respectively for three verifications, so that the error between the experimental results of the temperature peak during the curing process and the simulation results obtained according to the temperature distribution model of the curing process does not exceed 5%.

5. A method for predicting the mechanical properties of a thick resin matrix composite material according to claim 1, characterized in that, In S3, the group of thick composite samples with a certain thickness gradient contains at least 5 types of samples with different thicknesses.

6. A method for predicting the mechanical properties of a thick resin matrix composite material according to claim 1, characterized in that, In S3, the initial thickness of the group of thick composite samples is 2 mm, and the thickness gradient is 3 mm.

7. A method for predicting the mechanical properties of a thick resin matrix composite material according to claim 1, characterized in that In S3 and S5, the samples are all cut and processed from a whole thick resin matrix composite laminate. The lengths and widths of all whole thick resin matrix composite laminates are the same, and only the thicknesses are different.

8. A method for predicting the mechanical properties of a thick resin matrix composite material according to claim 1, characterized in that, In S5, the thick composites with different thicknesses contain at least 3 types of thicknesses and the thickness is not less than 10 mm.

9. A method for predicting the mechanical properties of a thick resin matrix composite material according to claim 1, characterized in that In S5, thick resin matrix composite laminates with thicknesses of 10 mm, 20 mm, and 30 mm are used.

10. A method for predicting the mechanical properties of a large-thickness resin matrix composite according to claim 1, characterized in that, The Bazant strength size effect law in S6 is shown as the following formula: Where: σ N is the nominal strength, f r 0 is the average tensile strength of the boundary layer, 2D b is the thickness of the boundary layer, D is the thickness of the sample, f r 0 and 2D b are obtained by fitting with the formula.

11. A method for predicting the mechanical properties of a thick resin matrix composite material according to claim 10, characterized in that, The expression of the temperature damage factor T at different thicknesses described in S6 is obtained by fitting the percentage values of strength decrease caused by temperature overshoot at several thicknesses obtained through S5 using numerical analysis software, as shown in the following formula: Where: T max is the maximum intensity decrease caused by temperature overshoot, ΔT is the temperature overshoot, is the temperature constant, T max and are obtained by fitting with the formula.

12. A method for predicting the mechanical properties of a large-thickness resin matrix composite according to claim 11, characterized in that, The modified Bazant strength size effect law described in S6 is shown in the following formula:

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