Measurement Method for Plastic Deformation Zone at Crack Tip of Composite Material

Abstract

The present invention provides a method for measuring the plastic deformation zone at the crack tip of a composite material, which comprises the following steps: S1. Lay multiple prepreg layers or bonded flat specimens, and after curing and forming, cut each prepreg layer or bonded flat specimen into multiple test pieces; S2. Conduct laminating on the test pieces in sequence; S3. Package the completed laminates according to the encapsulation system; S4. Place the vacuum bag of the encapsulated test pieces into an autoclave for curing; S5. Mark the cured test pieces and conduct cutting; S6. Conduct performance testing on the test pieces; S7. Measure the length of the plastic zone at the crack tip of the weak bond; S8. Plot the curve of the length of the plastic zone at the crack tip versus the weak bond ratio; S9. Determine the length of the plastic zone at the crack tip of the reference test piece. By accurately measuring the size of the plastic deformation zone under different weak bond ratios, the present invention provides support for the theory and model of composite material damage and failure, fatigue life assessment, and parameter optimization selection of interlayer toughening.

Description

Technical Field

[0001] The present invention relates to the field of experimental research on fracture mechanics models of composite materials, and particularly to a method for measuring the plastic deformation zone at the crack tip of composite materials. Background Art

[0002] In the prior art, the interlayer, fiber-matrix interface, and adhesive interface of composite materials are the weakest positions in the structural performance of composite materials. The fracture toughness of the interface layer and the adhesive layer is an important index for measuring the initiation and propagation of damage in these weak areas during processing, assembly, and service loads.

[0003] Based on the fracture mechanics theory of composite material damage failure analysis, and a very important parameter in the model is the length of the plastic deformation zone of the matrix or adhesive layer adjacent to the crack tip of the interface layer and the adhesive layer. This length determines parameters such as the minimum mesh size required for stable calculation of the analysis model, the attenuation rate of the unit mesh performance in fatigue analysis, and the toughening spacing required for interlayer toughening technology.

[0004] For a long time, due to the lack of directly detectable characteristic changes in the plastic deformation zone at the crack tip, it has been impossible to accurately measure. In various theories and models, only artificial assumptions of numerical values can be used for fitting calculations. Whether this assumption is reasonable in terms of physical phenomena urgently requires appropriate experimental methods for measurement and correction.

[0005] In view of this, those skilled in the art have designed a method for measuring the plastic deformation zone at the crack tip of composite materials in order to overcome the above technical problems. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for measuring the plastic deformation zone at the crack tip of composite materials in order to overcome the defect in the prior art that the characteristic changes in the plastic deformation zone at the crack tip cannot be directly detected and only artificial assumptions of numerical values can be used for fitting calculations.

[0007] The present invention solves the above technical problems through the following technical solutions:

[0008] A method for measuring the plastic deformation zone at the crack tip of composite materials, characterized in that the plastic deformation zone measurement method includes the following steps:

[0009] S1. Lay multiple prepreg plies or bonded flat specimens, and after curing and forming, cut each of the prepreg plies or the bonded flat specimens into a plurality of test pieces;

[0010] S2. Lay the plurality of test pieces formed by cutting in sequence;

[0011] S3. Package the laid plies in step S2 according to the encapsulation system;

[0012] S4. Place the vacuum bag of the encapsulated test piece into an autoclave for curing;

[0013] S5. Cure the identification of the test piece and perform cutting;

[0014] S6. Conduct performance testing on the test piece;

[0015] S7. Measure the length of the plastic zone at the crack tip of the weak bond;

[0016] S8. Plot the curve of the length of the plastic zone at the crack tip versus the weak bond ratio;

[0017] S9. Determine the length of the plastic zone at the crack tip of the reference test piece.

[0018] According to an embodiment of the present invention, the specific steps in step S2 include the following steps:

[0019] S 21 ., Use a prepreg cutting machine or manually cut a number of prepregs and lay them into a unidirectional ply;

[0020] S 22 ., Cut out a slice using a prefabricated film, and cut one side of the slice into a shape with multiple tail strips, each of the tail strips being located at the center of the corresponding test piece;

[0021] S 23 ., Align the left side of the prefabricated film with the tail strips after cutting and lay it above the unidirectional ply or the bonded flat specimen; Record the end position of the prefabricated film and the end position of the tail strips at the edge of the unidirectional ply or the bonded flat specimen;

[0022] S 24 ., Lay another unidirectional ply above the unidirectional ply or the bonded flat specimen with the prefabricated film, evacuate and compact it, and wait for curing;

[0023] S 25 ., Repeat step S 21 to step S 24 to lay other test pieces.

[0024] According to an embodiment of the present invention, the specific steps in step S4 include the following steps:

[0025] S 41 ., Conduct vacuum treatment on the workpiece;

[0026] S 42 ., Use an autoclave to pressurize to 7 bar;

[0027] S 43When the autoclave pressure reaches 1 bar, reduce the vacuum degree to -0.2 bar;

[0028] S 44 Set the heating rate to 1 - 2 °C / min and heat up to 180 °C ± 5 °C;

[0029] S 45 Insulate for (120 ± 5) min at a temperature of 180 °C ± 5 °C;

[0030] S 46 The cooling rate is 2 - 5 °C / min;

[0031] S 47 Release the autoclave pressure when the temperature of the workpiece reaches below 60 °C.

[0032] According to an embodiment of the present invention, in step S5, it specifically includes: after the pre - placed film is cured, mark the end position line of the pre - placed film and the boundary line of the defect - free bonding area at the end of the pre - placed film tape on the surface of the specimen with a marking line according to the end position of the pre - placed film and the end position of the tail tape, and obtain the test piece by cutting.

[0033] According to an embodiment of the present invention, in step S6, it specifically includes: testing test pieces with different tail - tape widths, and the corresponding weak - bonding ratios of the test pieces are 0%, 10%, 20%, 30%, 40% and 50%, where the 0% weak - bonding ratio is a reference comparison test piece without pre - placed defects;

[0034] Record the inflection point where the load first decreases and then starts to increase after crack propagation for test pieces with different weak - bonding ratios and the crack - propagation positions of test pieces with weak - bonding ratios of 10%, 20%, 30%, 40% and 50% respectively.

[0035] According to an embodiment of the present invention, in step S7, it specifically includes: measuring the length of the crack - propagation position from the boundary line of the defect - free bonding area.

[0036] According to an embodiment of the present invention, in step S8, it specifically includes: measuring the length of the crack - tip plastic zone for test pieces with weak - bonding ratios of 10%, 20%, 30%, 40% and 50% respectively, and plotting the relationship curve between the length of the crack - tip plastic zone and the weak - bonding ratio.

[0037] According to an embodiment of the present invention, the pre - placed film is a polytetrafluoroethylene film.

[0038] According to an embodiment of the present invention, the thickness of the pre - placed film is less than 20 microns.

[0039] According to an embodiment of the present invention, the width of the tail strip of each test piece is 5 mm, 7.5 mm, 10 mm, or 12.5 mm.

[0040] The positive and progressive effects of the present invention are as follows:

[0041] The method for measuring the plastic deformation zone at the crack tip of the composite material of the present invention provides an experimental measurement and verification method for the assumption of the size of the plastic deformation zone at the crack tip required for fracture mechanics theory and model analysis to predict the crack initiation and propagation process of composite materials and their bonded structures. By accurately measuring the size of the plastic deformation zone under different weak bonding ratios, it provides strong support for the improvement and perfection of the composite material damage failure theory and model, fatigue life assessment, and parameter optimization selection of interlayer toughening. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The above and other features, properties, and advantages of the present invention will become more apparent from the following description in conjunction with the drawings and embodiments, in which like reference numerals always represent the same features, where:

[0043] Figure 1 It is a schematic diagram of the test piece manufacturing for pre-setting a weak bonding zone in the method for measuring the plastic deformation zone at the crack tip of the composite material of the present invention.

[0044] Figure 2 It is a schematic diagram of the test piece manufacturing process for pre-setting a weak bonding zone in the method for measuring the plastic deformation zone at the crack tip of the composite material of the present invention.

[0045] Figure 3 It is a schematic diagram of the curing curve with a porosity of less than 1% in the method for measuring the plastic deformation zone at the crack tip of the composite material of the present invention.

[0046] Figure 4 It is a schematic diagram of the test piece with a pre-set weak bonding zone and a marked defect-free bonding boundary line O in the method for measuring the plastic deformation zone at the crack tip of the composite material of the present invention.

[0047] Figure 5 It is a schematic diagram of the test load-displacement curve with different weak bonding ratios and the crack propagation position corresponding to the inflection point where the load changes from decreasing to increasing after crack propagation in the method for measuring the plastic deformation zone at the crack tip of the composite material of the present invention.

[0048] Figure 6 It is a schematic diagram of measuring the size of the plastic deformation zone at the crack tip in the method for measuring the plastic deformation zone at the crack tip of the composite material of the present invention.

[0049] Figure 7 It is a schematic diagram of the relationship between the length of the plastic deformation zone at the crack tip and the weak bonding ratio in the method for measuring the plastic deformation zone at the crack tip of the composite material of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0050] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following provides a detailed description of the specific embodiments of the present invention in conjunction with the accompanying drawings.

[0051] Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Preferred embodiments of the present invention will now be described in detail, which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to represent the same or similar parts.

[0052] In addition, although the terms used in the present invention are selected from well-known and commonly used terms, some of the terms mentioned in the specification of the present invention may be selected by the applicant according to his or her judgment, and their detailed meanings are described in the relevant parts of the description herein.

[0053] In addition, it is required to understand the present invention not only through the actual terms used, but also through the meaning implied by each term.

[0054] Figure 1 Schematic diagram for manufacturing a test piece with a pre-set weak bonding area in the method for measuring the plastic deformation zone at the crack tip of a composite material of the present invention. Figure 2 Schematic diagram of the manufacturing process of a test piece with a pre-set weak bonding area in the method for measuring the plastic deformation zone at the crack tip of a composite material of the present invention. Figure 3 Schematic diagram of the curing curve with a porosity of less than 1% in the method for measuring the plastic deformation zone at the crack tip of a composite material of the present invention. Figure 4 Schematic diagram of a test piece with a pre-set weak bonding area and a defect-free bonding boundary line O marked in the method for measuring the plastic deformation zone at the crack tip of a composite material of the present invention.

[0055] Figure 5 Schematic diagram of the test load-displacement curve with different weak bonding ratios and the crack propagation position corresponding to the inflection point where the load changes from decreasing to increasing after crack propagation in the method for measuring the plastic deformation zone at the crack tip of a composite material of the present invention. Figure 6 Schematic diagram for measuring the size of the plastic deformation zone at the crack tip in the method for measuring the plastic deformation zone at the crack tip of a composite material of the present invention. Figure 7 Schematic diagram of the relationship between the length of the plastic deformation zone at the crack tip and the weak bonding ratio in the method for measuring the plastic deformation zone at the crack tip of a composite material of the present invention.

[0056] As Figures 1 to 7 shown, the present invention discloses a method for measuring the plastic deformation zone at the crack tip of a composite material, characterized in that the plastic deformation zone measurement method includes the following steps:

[0057] Step S1: Lay multiple prepreg plies or bonded flat specimens, and after curing and forming, cut each of the prepreg plies or the bonded flat specimens into multiple test pieces.

[0058] As Figure 1 shown, preferably, the requirements for the overall dimensions of the test specimens are as follows: According to the dimensions of the double cantilever beam bending (DCB) test specimens for testing the mode I interlaminar critical fracture energy release GIC in ASTM D5528 standard, multiple prepreg plies or bonded flat specimens (such as 6 pieces) are laid.

[0059] For example, Figure 1 the specimen dimensions shown in are preferably 190 mm in length, 190 mm in width, and 3 mm in thickness. After curing and forming, each large plate can be cut into Figure 1 5 test specimens with a length of 150 mm, a width of 25 mm, and a thickness of 3 mm shown in the dashed area in. Among them, the width of the cutting seam is preferably Wc = 3 - 5 mm, and the machining allowance We at the four edges is preferably 15 - 25 mm to ensure that the curing quality and thickness uniformity of the test specimens are not affected by the edge overflow effect. The dimensions of the test specimens within the dashed line, where L S = 150 mm is the length of the test specimen, L C = 65 mm is the length of the pre-crack, L Weak = 15 mm is the length of the pre-weak bond, L Weak > 10 mm. W S is the width of the test specimen, W P is the width of the pre-weak bond of the test specimen, W P / W S is the weak bond ratio.

[0060] Step S2: Lay the multiple test specimens formed by cutting in sequence.

[0061] Preferably, the step S2 specifically includes the following steps:

[0062] S 21 Cut several prepregs by a prepreg cutting machine or manually, and lay them into a unidirectional ply;

[0063] S 22 Cut out a slice from a prefabricated film, and cut one side of the slice into a shape with multiple tail strips, and each tail strip is located at the center of the corresponding test specimen;

[0064] S 23 Lay the left side of the prefabricated film with tail strips after cutting on top of the unidirectional ply laid well; Record the end position of the prefabricated film and the end position of the tail strip at the edge of the unidirectional ply or the bonded flat specimen;

[0065] S 24, lay a unidirectional ply on top of the prepreg ply or the bonded flat specimen with the pre-placed film, evacuate and compact it, and wait for curing;

[0066] More specifically, the process of laying the test piece is as follows: Cut several 190mm x 190mm square prepregs with a prepreg cutting machine or manually, and lay them into a unidirectional ply (UD) with a cured thickness of 1.5mm. Cut a slice of pre-placed film (such as PTFE film or an equivalent pre-placed delamination film of other materials) with a width of 190mm and a length of 95mm. The film thickness is preferably less than 20 microns.

[0067] As Figure 1 shown in Region 1, cut the pre-placed film (such as PTFE or a film of equivalent material) into a shape with a width of 190mm and a length of 80mm, with 5 slender tails having a length L weak = 15mm and a width W P = 2.5mm. Each slender tail is located at the center of a corresponding 25mm-wide cut test piece.

[0068] Align the left side of the pre-placed film with the tails with the laid unidirectional ply, and lay it on top of the prepreg ply or the bonded flat specimen (as Figure 2 shown). Use a white oil-based pen to record the tail end position C and the tail tip position O of the pre-placed film on the edge of the prepreg ply. Then, lay another unidirectional ply with a cured thickness of 1.5mm on top of the prepreg with the pre-placed film, evacuate and compact it, and wait for curing.

[0069] S 25 Repeat step S 21 to step S 24 to lay other test pieces.

[0070] Then, for laying other test pieces: Repeat step S 21 to step S 24 Cut four kinds of pre-placed films (such as PTFE or films of equivalent material) with tail widths of W P = 5.0mm, 7.5mm, 10.0mm, 12.5mm and one pre-placed film without tails (such as PTFE or a film of equivalent material). The sizes of the parts of the films without tails are all 190mm wide and 8mm long.

[0071] As Figure 1As shown, a pre - placed film (such as a film of PTFE or equivalent material) with the shape shown in area 1 is pre - placed on the adhesive film 2 at the mid - plane of the prepreg ply or the bonding interface, and the thickness of the film is less than 20 microns. Use a white oil - based pen to record the end position C of the pre - placed film and the end position O of the trailing tape at the edge of the prepreg ply. After the prepreg ply or the bonded sample is laid and pasted, evacuate and compact it, and wait for curing.

[0072] Step S3: Encapsulate the laid - up ply completed in step S2 according to the encapsulation system.

[0073] Step S4: Put the vacuum bag of the encapsulated test piece into an autoclave for curing.

[0074] For example, for the IM7 / M91 material system, in order to obtain a porosity of < 1%, the curing curve is as Figure 3 shown, and the specific curing process is:

[0075] S 41 、Perform a vacuum treatment on the workpiece, preferably - 1.0 bar;

[0076] S 42 、Use the autoclave to pressurize to 7 bar;

[0077] S 43 、When the autoclave pressure reaches 1 bar, reduce the vacuum degree to - 0.2 bar;

[0078] S 44 、Set the heating rate at 1 - 2 °C / min and heat up to 180 °C ± 5 °C;

[0079] S[[ID=3...]] 45 、Insulate at a temperature of 180 °C ± 5 °C for (120 ± 5) min;

[0080] S 46 、The cooling rate is 2 - 5 °C / min;

[0081] S 47 、When the temperature of the workpiece reaches below 60 °C, release the autoclave pressure.

[0082] Step S5: Cure the identification of the test piece and perform cutting.

[0083] Preferably, step S5 specifically includes: after the pre - placed film plate is cured, according to the end position of the pre - placed film and the end position of the trailing tape, use a marking line to mark the end position line of the pre - placed film and the boundary line of the defect - free bonding area at the end of the pre - placed film trailing tape on the surface of the specimen, and obtain the test piece through cutting.

[0084] More specifically, after the pre-set thin film plate is cured, according to the fiducial points C and O on both sides of the layup, the end position line CC of the pre-set thin film and the boundary line OO of the defect-free bonding area at the end of the trailing tape of the pre-set thin film are marked on the surface of the specimen with light-colored marking lines, and according to Figure 1 the cutting line to obtain Figure 4 the test specimens (such as DCB test specimens) shown.

[0085] Step S6: Perform performance testing on the test specimens.

[0086] Preferably, in the step S6, it specifically includes: testing test specimens with different trailing tape widths, and the corresponding weak bonding ratios of the test specimens are 0%, 10%, 20%, 30%, 40% and 50%, where the 0% weak bonding ratio is the reference comparison test specimen without pre-set defects;

[0087] Record the inflection points where the load first decreases and then starts to increase after crack propagation for the test specimens with different weak bonding ratios and the crack propagation positions of the test specimens with weak bonding ratios of 10%, 20%, 30%, 40% and 50% respectively.

[0088] More specifically, the process of testing the performance of the test specimens is as follows: Test the test specimens with the above different trailing tape (such as 6 trailing tapes) widths according to the ASTM D5528 standard, and each test specimen has multiple samples (such as 5). Assume that the weak bonding ratios corresponding to the 6 trailing tape widths are W P / W S = 0%, 10%, 20%, 30%, 40% and 50%, and their typical load-displacement curves are as Figure 5 shown. Among them, the 0% weak bonding ratio is the reference comparison test specimen without pre-set defects. The load-displacement curves of the test specimens with the remaining non-zero weak bonding ratios all show a trend of first decreasing, then slowly rising to a load level similar to that of the reference test specimen, and then slowly decreasing with a load characteristic similar to that of the reference test specimen after the pre-set crack starts to propagate.

[0089] As Figure 5 shown, record the inflection points 3, 4, 5, 6, 7 where the load first decreases and then starts to increase after crack propagation for the test specimens with different weak bonding ratios and the crack propagation positions A of the test specimens with weak bonding ratios of 10%, 20%, 30%, 40% and 50% respectively.

[0090] Step S7: Measure the length of the plastic zone at the crack tip of the weak bond.

[0091] Preferably, in the step S7, it specifically includes: measuring the length L COZ between the crack propagation position A and the boundary line O of the defect-free bonding area, which is the length of the plastic zone at the crack tip corresponding to the corresponding weak bonding ratio.

[0092] Step S8: draw a curve of the length of the crack tip plastic zone and the weak bonding ratio.

[0093] Preferably, step S8 specifically includes: measuring the lengths of the crack tip plastic zone of test pieces with weak bonding ratios of 10%, 20%, 30%, 40% and 50%, respectively, and drawing a relationship curve between the lengths of the crack tip plastic zone and the weak bonding ratio.

[0094] More specifically, if Figure 7 As shown, the crack tip plastic zone length and weak bonding ratio curve are plotted as follows: Repeat the above step S7 method to measure the crack tip plastic zone length L of DCB specimens with weak bonding ratios of 10%, 20%, 30%, 40% and 50% respectively COZ , plot this length versus the weak bond ratio W P / W S relationship curve.

[0095] S9. Determine the length of the plastic zone at the crack tip of the reference test piece.

[0096] More specifically, the length of the plastic zone at the crack tip of the benchmark specimen is determined as: Figure 7 W P / W S It can be seen from the relationship curve that when the weak bonding ratio is less than a certain value, the length of the plastic zone at the crack tip converges to the same value as the crack length of the defect-free benchmark test piece.

[0097] The convergence threshold in this example is a weak bonding ratio of 20%. Different material systems may have different convergence thresholds. In order to accurately measure the L COZ Convergence weak bonding ratio threshold, need to be drawn Figure 7 The length to which the crack length converges as the weak bonding ratio decreases is the length of the plastic zone at the crack tip of the benchmark specimen.

[0098] According to the above description, the method for measuring the plastic deformation zone at the crack tip of a composite material of the present invention can be extended to the end-preset crack bending test (ENF) for measuring the type II critical fracture release energy, the mixed mode bending test (MMB) of type I and type II, and other types of tests for measuring the performance of the interface layer and adhesive interface of the composite material, to measure the size of the plastic deformation zone at the crack tip of the corresponding mode.

[0099] The method for measuring the plastic deformation zone at the crack tip of the composite material of the present invention is a physical test measurement method for the length of the plastic deformation zone at the crack tip of the interface layer and the adhesive layer of the composite material. By setting partial weak adhesive layers in the test piece for measuring the critical fracture release energy of the interface layer and the adhesive layer of the composite material cracking, when recording that the load continuously changes from the load-bearing characteristic of the weak adhesive to the load-bearing characteristic of the defect-free adhesive during the loading process, the distance between the crack tip position and the leading edge of the defect-free adhesive layer is measured to obtain the size of the plastic zone at the crack tip under different weak adhesive ratios. The length of the plastic deformation zone at the crack tip of the defect-free interface layer and the adhesive layer is obtained by extrapolating the correlation curve of the plastic zone size and the weak adhesive ratio.

[0100] In summary, the method for measuring the plastic deformation zone at the crack tip of the composite material of the present invention provides a test measurement and verification method for the assumption of the size of the plastic deformation zone at the crack tip required for the fracture mechanics theory and model to analyze and predict the crack initiation and propagation process of the composite material and its bonded structure. By accurately measuring the size of the plastic deformation zone under different weak adhesive ratios, it provides strong support for the improvement and perfection of the composite material damage failure theory and model, fatigue life assessment, and parameter optimization selection of interlayer toughening.

[0101] Although the specific implementation manners of the present invention have been described above, those skilled in the art should understand that these are only examples, and the protection scope of the present invention is defined by the appended claims. Without departing from the principle and essence of the present invention, those skilled in the art can make various changes or modifications to these implementation manners, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. A method for measuring the plastic deformation zone at the crack tip of a composite material, characterized in that, The method for measuring the plastic deformation zone includes the following steps: S1. Lay multiple prepreg layers or bonded flat specimens, and after curing and forming, cut each of the prepreg layers or the bonded flat specimens into multiple test pieces; S2. Lay the multiple test pieces formed by cutting in sequence; S3. Package the layers after laying in step S2 according to the encapsulation system; S4. Put the vacuum bag of the packaged test pieces into an autoclave for curing; S5. Cure the identification of the test pieces and perform cutting; S6. Perform performance testing on the test pieces; S7. Measure the length of the plastic zone at the crack tip of the weak bond; S8. Plot the curve of the length of the plastic zone at the crack tip versus the weak bond ratio; S9. Determine the length of the plastic zone at the crack tip of the reference test piece.

2. The method for measuring the plastic deformation zone at the crack tip of the composite material according to claim 1, characterized in that The specific steps in step S2 include the following steps: S 21 , cut several prepregs using a prepreg cutting machine or manually, and lay them into a unidirectional ply; S 22 、Cut out a slice from a prefabricated film, and cut one side of the slice into a shape with multiple tail strips, each of the tail strips being located at the center of the corresponding test piece; S 23 Lay the unidirectional ply of the pre-cut preformed film with a tail strip on top of the prepreg ply or the bonded flat plate specimen with the left side aligned; record the position of the end of the preformed film and the position of the end of the tail strip at the edge of the prepreg ply or the bonded flat plate specimen. S 24 、Lay a unidirectional ply on top of the prepreg ply or the bonded flat specimen with the pre-set film, evacuate and compact it, and wait for curing; S 25 Repeat step S 21 to step S 24 for paving other test pieces.

3. The method for measuring the plastic deformation zone at the crack tip of the composite material according to claim 1, wherein, The specific steps in step S4 include the following steps: S 41 , subject the workpiece to vacuum treatment; S 42 、Pressurize to 7 bar using an autoclave; S 43 When the autoclave pressure reaches 1 bar, reduce the vacuum to -0.2 bar; S 44 Set the heating rate to 1 - 2 °C / min and heat up to 180 °C ± 5 °C; S 45 、Keep warm at a temperature of 180°C ± 5°C for (120 ± 5) min; S 46 and the cooling rate is 2 - 5 °C / min; S 47 Release the autoclave pressure when the temperature of the workpiece reaches below 60°C.

4. The method for measuring the plastic deformation zone at the crack tip of the composite material according to claim 2, characterized in that, The specific steps in step S5 include: After curing the preset thin film flat plate, mark the end position line of the preset thin film and the boundary line of the defect-free bonding area at the end of the preset thin film tail band on the surface of the specimen according to the end position of the preset thin film and the end position of the tail band, and obtain the test piece by cutting.

5. The method for measuring the plastic deformation zone at the crack tip of the composite material according to claim 2, characterized in that, The specific steps in step S6 include: Test multiple test pieces with different tail band widths, and the corresponding weak bond ratios of the test pieces are 0%, 10%, 20%, 30%, 40%, and 50%, where the 0% weak bond ratio is the reference comparison test piece without preset defects; Record the inflection points where the load first decreases and then starts to increase after crack propagation for the test pieces with different weak bond ratios and the crack propagation positions of the test pieces corresponding to the weak bond ratios of 10%, 20%, 30%, 40%, and 50% respectively.

6. The method for measuring the plastic deformation zone at the crack tip of the composite material according to claim 5, characterized in that, The specific steps in step S7 include: Measure the length between the crack propagation position and the boundary line of the defect-free bonding area.

7. The method for measuring the plastic deformation zone at the crack tip of the composite material according to claim 5, characterized in that, The specific steps in step S8 include: Measure the lengths of the plastic zones at the crack tips of the test pieces with weak bond ratios of 10%, 20%, 30%, 40%, and 50% respectively, and plot the relationship curve of the length of the plastic zone at the crack tip versus the weak bond ratio.

8. The method for measuring the plastic deformation zone at the crack tip of the composite material according to claim 2, characterized in that The preset thin film is a polytetrafluoroethylene thin film.

9. The method for measuring the plastic deformation zone at the crack tip of the composite material according to claim 2, characterized in that The thickness of the preset thin film is less than 20 microns.

10. The method for measuring the plastic deformation zone at the crack tip of the composite material according to claim 5, wherein, The width of the tail band of each test piece is 5mm, 7.5mm, 10mm, or 12.5mm.

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