CN113627012B - Method for predicting fracture strength of carbon fiber/metal layered structure after surface scratch - Google Patents
Method for predicting fracture strength of carbon fiber/metal layered structure after surface scratch Download PDFInfo
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Abstract
The invention discloses a method for predicting breaking strength of a carbon fiber/metal layered structure after surface scratch, which comprises the steps of selecting a carbon fiber plate with the same size as a carbon fiber layer in a carbon fiber/metal layered composite structure test piece to be predicted; carrying out a direct tensile test on the carbon fiber plate, loading the carbon fiber plate to the test piece to be completely broken and destroyed, and recording a load/displacement curve of the carbon fiber plate; further, the direct tensile strength f of the carbon fiber plate is obtained t‑T The method comprises the steps of carrying out a first treatment on the surface of the Direct tensile Strength f through carbon fiber Board t‑T Tensile strength f of carbon fiber/metal layered composite structure test piece in place of fracture strength analysis model t Breaking strength P of test piece with carbon fiber/metal layered composite structure to be predicted max The calculation can effectively solve the problems of complex steps, large test error and size effect in the prior art.
Description
Technical Field
The invention belongs to the field of mechanical properties of engineering structures, and relates to a method for predicting fracture strength of a carbon fiber/metal layered structure after surface scratch.
Background
The Carbon Fiber (CFRP) has large brittleness and poor impact resistance, and the CFRP formed by cementing contains about 30 percent of brittle resin matrix, so that the mechanical property of the CFRP is obviously influenced by micro defects on the surface or in the matrix, the size effect of the mechanical property is obvious, when the CFRP plate is used for pasting and reinforcing mechanical equipment or metal structures, micro damage defects, such as shallow scratches, are easily generated on the surface of the brittle CFRP plate in the operation stage, and whether the mechanical property of the carbon fiber/steel layered composite structure test piece with the surface damage can still continuously meet the use requirement or not can be ensured.
At present, most of the methods for predicting the breaking strength are single materials, because the carbon fiber is a brittle material, a damage area can appear in the carbon fiber/metal lamellar composite structure after the surface of the carbon fiber is scratched, the damage mode is complex and various, a large number of parameters are needed due to more consideration factors, the prediction method is complex in process and low in accuracy, and no good prediction method is available for the breaking strength of the carbon fiber/metal lamellar composite structure.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides a method for predicting the fracture strength of a carbon fiber/metal layered structure after surface scratch, which can effectively solve the problems of complex steps, large test error and size effect in the prior art.
In order to achieve the purpose, the invention is realized by adopting the following technical scheme:
a method for predicting the fracture strength of a carbon fiber/metal layered structure after surface scratch comprises the following steps:
s1, selecting a carbon fiber plate consistent with a carbon fiber layer in a carbon fiber/metal layered composite structure test piece to be predicted;
s2, performing a direct tensile test on the carbon fiber board, loading the carbon fiber board to the test piece to be completely broken and destroyed, and recording a load/displacement curve of the carbon fiber board;
s3, analyzing and calculating a load/displacement curve to obtain the direct tensile strength f of the carbon fiber plate t-T ；
S5, breaking strength P of carbon fiber/metal lamellar composite structure test piece to be predicted max And (3) performing calculation:
wherein B is the width of the carbon fiber/metal layered composite structure test piece; x is the distance from the internal bending moment M of the midspan section of the carbon fiber/metal layered composite structure test piece to the interface between the carbon fiber layer and the metal layer; n is the ratio of the elastic modulus of the metal layer to that of the carbon fiber layer; h is a 1 Is the thickness of a metal layer in the carbon fiber/metal lamellar composite structure test piece, h 2 The thickness of the carbon fiber layer in the carbon fiber/metal layered composite structure test piece; s is para-carbon fiber/goldA fulcrum span which belongs to a layered composite structure test piece and is subjected to three-point bending loading; a, a 0 The initial crack length of the surface of the carbon fiber layer of the carbon fiber/metal layered composite structure test piece; Δa fic C is the crack extension length of the carbon fiber/metal lamellar composite structure test piece ch The structural characteristic parameters of the carbon fiber/metal layered composite structure test piece; a, a e Equivalent crack length of the carbon fiber/metal layered composite structure test piece;
the characteristic crack length of the carbon fiber/metal lamellar composite structure test piece; sigma (sigma) n Virtual crack delta a of carbon fiber/metal lamellar composite structure test piece fic Nominal stress in the range; f (f) t Is the tensile strength of the carbon fiber layer in the carbon fiber/metal layered composite structure, wherein f t By f t-T Instead of.
Preferably, the structural feature parameter C ch The calculation process of (1) is as follows:
Δa fic ＝β·G＝1.5C ch
where β is a discrete coefficient, assuming normal distribution is obeyed, β is taken as 1.5, and g is a second structural feature parameter.
Preferably, the equivalent crack length a of the carbon fiber/metal layered composite structure test piece e The calculation process of (1) is as follows:
wherein alpha is a 0 Total thickness h of test piece with carbon fiber/metal layered composite structure 1 +h 2 Y (alpha) is a geometric factor, alpha is less than 1, and Y (alpha) is 1.12.
Preferably, the characteristic crack length of the carbon fiber/metal layered composite structure test piece
The calculation process of (1) is as follows:
wherein K is IC The fracture toughness of the carbon fiber/metal lamellar composite structure test piece.
Preferably, the virtual crack delta a of the carbon fiber/metal layered composite structure test piece fic Nominal stress sigma within a range n The calculation process of (1) is as follows:
preferably, the balance relation between the bending moment M in the midspan section of the carbon fiber/metal layered composite structure test piece and the stress and strain on the section is as follows:
wherein the stress at the upper surface of the metal layer is sigma s The method comprises the steps of carrying out a first treatment on the surface of the The stress at the interface of the metal layer and the carbon fiber layer is sigma' s Strain is epsilon' s The method comprises the steps of carrying out a first treatment on the surface of the The strain of the carbon fiber layer in the damaged area of the crack tip is epsilon n The equivalent elastic modulus of the carbon fiber layer is E n 。
Preferably, the mid-span section internal bending moment M of the carbon fiber/metal layered composite structure and the peak load P of the carbon fiber/metal layered composite structure test piece max-i The relation of (2) is:
a system for predicting fracture strength of a carbon fiber/metal layered structure after surface scratch, comprising;
the carbon fiber plate selecting module is used for selecting a carbon fiber plate consistent with a carbon fiber layer in the carbon fiber/metal layered composite structure test piece to be predicted;
the load/displacement curve acquisition module is used for carrying out a direct tensile test on the carbon fiber board, loading the carbon fiber board to the test piece to be completely broken and destroyed, and recording the load/displacement curve of the carbon fiber board;
the direct tensile strength calculation module is used for analyzing and calculating the load/displacement curve to obtain the direct tensile strength f of the carbon fiber board t-T ；
The breaking strength calculation module is used for calculating the breaking strength P of the carbon fiber/metal layered composite structure test piece to be predicted max And (3) performing calculation:
wherein B is the width of the carbon fiber/metal layered composite structure test piece; x is the distance from the internal bending moment M of the midspan section of the carbon fiber/metal layered composite structure test piece to the interface between the carbon fiber layer and the metal layer; n is the ratio of the elastic modulus of the metal layer to that of the carbon fiber layer; h is a 1 Is the thickness of a metal layer in the carbon fiber/metal lamellar composite structure test piece, h 2 The thickness of the carbon fiber layer in the carbon fiber/metal layered composite structure test piece; s is a fulcrum span for carrying out three-point bending loading on the carbon fiber/metal layered composite structure test piece; a, a 0 The initial crack length of the surface of the carbon fiber layer of the carbon fiber/metal layered composite structure test piece; Δa fic C is the crack extension length of the carbon fiber/metal lamellar composite structure test piece ch The structural characteristic parameters of the carbon fiber/metal layered composite structure test piece; a, a e Equivalent crack length of the carbon fiber/metal layered composite structure test piece;
the characteristic crack length of the carbon fiber/metal lamellar composite structure test piece; sigma (sigma) n Virtual crack delta a of carbon fiber/metal lamellar composite structure test piece fic Nominal stress in the range; f (f) t Is the tensile strength of the carbon fiber layer in the carbon fiber/metal layered composite structure, wherein f t By f t-T Instead of.
A computer device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, the processor implementing the steps of the method for predicting breaking strength of a carbon fiber/metal layered structure after surface scoring as defined in any one of the preceding claims when the computer program is executed.
A computer readable storage medium storing a computer program which when executed by a processor performs the steps of the method for predicting fracture strength of a carbon fiber/metal layered structure after surface scoring as set forth in any one of the preceding claims.
Compared with the prior art, the invention has the following beneficial effects:
the invention is based on boundary effect theory, considers complex damage area of carbon fiber surface and processing and manufacturing process, establishes a breaking strength analysis model of the carbon fiber/metal lamellar composite structure test piece, the established analysis model is simple, carries out three-point bending test on the carbon fiber/metal lamellar composite structure, brings geometric parameters into the analysis model to obtain the tensile strength of the carbon fiber in the composite structure, replaces the tensile strength of the carbon fiber/metal lamellar composite structure test piece in the breaking strength analysis model by the direct tensile strength of the carbon fiber plate, and can predict the breaking strength of the carbon fiber/metal lamellar composite structure test piece after surface damage by the direct tensile strength of the carbon fiber plate, the required parameters are less, the breaking strength prediction of the lamellar composite structure is realized, the damage tolerance design is realized, and the tensile strength f of the carbon fiber/metal lamellar composite structure test piece is realized t Direct tensile strength with carbon fiber sheet f t-T By contrast, the deviation between the two is less than 10%, and the error of the method is smaller.
Drawings
FIG. 1 is a schematic structural view of a carbon fiber/metal layered composite structure test piece according to the present invention;
FIG. 2 is a stress-strain diagram of a cross section of a crack in a carbon fiber layer according to the present invention;
FIG. 3 is a schematic illustration of a polished cross-section of a carbon fiber layer of the present invention;
FIG. 4 is a graph of crack propagation length under a metallographic microscope at A-A of a first sample of the present invention;
FIG. 5 is a graph showing crack growth lengths under a metallographic microscope at B-B of a first sample of the present invention;
FIG. 6 is a graph of crack propagation length under a metallographic microscope at A-A of a second sample of the present invention;
FIG. 7 is a graph showing crack growth length under a metallographic microscope at B-B of a second sample of the present invention;
FIG. 8 is a P of a carbon fiber/steel composite structure according to the present invention max -A e A graph;
FIG. 9 is a diagram of the sigma of the carbon fiber/steel composite structure of the present invention n -a e A graph;
FIG. 10 shows the P of the carbon fiber/steel composite structure of the present invention max -A e A curve prediction graph;
FIG. 11 is a diagram showing the sigma of the carbon fiber/steel composite structure of the present invention n -a e Curve predictive graph.
Wherein: 1-a metal layer; 2-carbon fiber layer.
Detailed Description
The invention is described in further detail below with reference to the attached drawing figures:
as shown in fig. 1, a carbon fiber/metal layered composite structure test piece according to the present invention is shown.
The size of the carbon fiber/metal layered composite structure test piece was (h 1 +h 2 ) X B x L, W is the specimen height; b is the width of the test piece; l is the length of the test piece, h 1 Is the thickness h of the metal layer 1 in the composite structure test piece 2 Is the thickness of the carbon fiber layer 2 in the composite structure test piece.
As shown in FIG. 2, the initial crack length of the carbon fiber surface of the carbon fiber/metal layered composite structure test piece is a 0 The method comprises the steps of adopting a loading mode of three-point bending, wherein the fulcrum span is S, carrying out static test on a carbon fiber/metal layered composite structure test piece on an electronic universal testing machine, stopping loading when the load of the testing machine is reduced by about 10%, recording the peak load of each test piece in each group during the test, and recording as P max-i 。
The carbon fiber layer 2 of the carbon fiber/metal layered composite structure test piece is taken down to be re-combined withFlattening the steel sheet for bonding, performing sample insertion and side polishing, and calculating crack propagation length delta a by observing and measuring the crack depth difference between two adjacent fracture surfaces fic Further determining structural characteristic parameter C ch The method comprises the steps of carrying out a first treatment on the surface of the Calculating the equivalent crack length a of the carbon fiber/metal lamellar composite structure test piece e 。
Calculating the characteristic crack length of the carbon fiber/metal lamellar composite structure test piece
Calculating virtual crack delta a of carbon fiber/metal lamellar composite structure test piece fic Nominal stress sigma within a range n The method comprises the steps of carrying out a first treatment on the surface of the Calculating a balance relation between the internal bending moment M of the midspan section of the carbon fiber/metal layered composite structure test piece and the stress and strain on the section; calculating the internal bending moment M and the peak load P of the midspan section of the carbon fiber/metal lamellar composite structure test piece max-i Is a relation of (2); obtaining the tensile strength f of the carbon fiber layer 2 in the carbon fiber/metal layered composite structure test piece t 。
The breaking strength analysis model is as follows:
order the
Wherein x is the distance from the bending moment M in the midspan section of the carbon fiber/metal layered composite structure test piece to the interface between the carbon fiber layer 2 and the metal layer 1; n is the ratio of the elastic modulus of the metal layer 1 to that of the carbon fiber layer 2; h is a 1 Is the thickness h of the metal layer 1 in the carbon fiber/metal lamellar composite structure test piece 2 Is the thickness of the carbon fiber layer 2 in the carbon fiber/metal layered composite structure test piece.
Manufacturing a group of carbon fiber plate test pieces with the dimensions of W multiplied by B multiplied by L, wherein W is the height of the test piecesAnd the number of the carbon fiber layers 2 of the tensile carbon fiber plate test piece and the carbon fiber/metal layered composite structure test piece are kept consistent. Carrying out a direct tensile test on a carbon fiber board test piece on an electronic universal testing machine, loading the test piece to be completely broken and destroyed, and recording a load/displacement curve of each test piece; analyzing and calculating the load/displacement curve to obtain the elastic modulus E of the carbon fiber plate n And direct tensile strength f t-T 。
Tensile strength f of carbon fiber/metal layered composite structural test piece t Direct tensile strength with carbon fiber sheet f t-T In contrast, the deviation between the two is less than 10%, the direct tensile strength f through the carbon fiber plate t-T Tensile strength f of carbon fiber/metal layered composite structure test piece in place of fracture strength analysis model t . The breaking strength of the carbon fiber/metal layered composite structure test piece after the surface damage can be predicted through the direct tensile strength of the carbon fiber plate.
Structural feature parameter C ch The calculation formula is as follows:
Δa fic ＝β·G＝1.5C ch
beta is a discrete coefficient, assuming normal distribution is obeyed, and the beta mean value is taken to be 1.5;
equivalent crack length a e The calculation formula is as follows:
alpha is a 0 Total thickness h of test piece with carbon fiber/steel layered composite structure 1 +h 2 Y (α) is a geometric factor, and α is much smaller than 1, Y (α) is approximately 1.12, since this patent predicts the surface microcrack fracture strength of the layered sheet.
Characteristic crack length
The calculation formula is as follows:
K IC fracture toughness of the carbon fiber/metal layered composite structure.
Virtual crack deltaa based on boundary effect theory fic Nominal stress sigma within a range n The calculation formula of (2) is as follows:
as shown in fig. 2, the equation of the equilibrium relation between the internal bending moment M of the midspan section and the stress and strain on the section is:
as shown in FIG. 2, the internal bending moment M of the midspan section and the peak load P obtained in the step (5) max-i The formula of the relation is:
as shown in fig. 2, the calculation formula of x is:
n is the ratio of the elastic modulus of the metal to the carbon fiber, and x is the distance from the mid-span section M to the carbon fiber to the metal interface.
For the d-group (d=1, 2,3 … …) test results, the test yielded d-group P max-i Thus, d group f can be obtained by testing t-i Similar to the random nature of β, assume P max-i Obeys normal distribution, thus f t-i ～N(μ，σ 2 )；
Example 1: the selected metal material is a steel plate with the model of Q235, the carbon fiber cloth is in 2D plain weave, the model is A-38/3K, the length L of the carbon fiber plate in a direct tensile test is 150mm, and the width B is 25mm. The length L of the carbon fiber/steel lamellar composite structure test piece is 150mm, the width B is 25mm, and the h of the steel plate 1 The number of the carbon fiber layers of the direct tensile test and the number of the carbon fiber layers 2 of the carbon fiber/steel layered composite structure test piece are 8, and the number of the effective test pieces of the carbon fiber plate of the direct tensile test is 6.
The initial crack depths of 0.2mm and 0.4mm are manufactured on the surface of the carbon fiber/steel layered composite structure test piece by using a nicking tool, and each group of test pieces is 8.
The CFRP plate is directly tensile tested by using a 100kN electronic universal testing machine in a displacement control mode of 1mm/min, and an extensometer YYU-25/50 is arranged to test the elastic modulus of the CFRP plate in the tensile load direction, after a test piece breaks, the elastic modulus and breaking load results are shown in Table 1, and the CFRP plate is obtained, wherein the mean value of the direct tensile strength of the CFRP plate is f t-T 424.31MPa and elastic modulus of 41GPa, i.e. E n ＝41GPa。
TABLE 1 results of CFRP plate direct tensile test
And (2) adopting a loading mode of three-point bending, wherein the span of a fulcrum is 96mm, carrying out a static test on the carbon fiber/steel layered composite structure test piece on an electronic universal testing machine, and stopping loading when the load of the testing machine is reduced by about 10%, wherein the data of the three-point bending test of the carbon fiber/steel layered composite structure test piece are shown in Table 2.
Table 2 three-point bending test data for carbon fiber/steel layered composite structural test pieces
Layering carbon fiber/steelThe carbon fiber plate of the composite structure test piece is taken down to be adhered with the flat steel sheet again, then the sample is inlaid and the side surface is polished, and the crack propagation length delta a is calculated by observing and measuring the crack depth difference between two adjacent fracture surfaces fic Further determining structural characteristic parameter C ch The method comprises the steps of carrying out a first treatment on the surface of the The specific observation method is as follows: (1) Taking down the carbon fiber plate of the carbon fiber/steel layered composite structure test piece after the test is completed, bonding with the flat steel sheet again, then carrying out sample embedding and side polishing treatment, and observing and measuring under a metallographic microscope; (2) The polishing observation schematic diagram is shown in fig. 3, fig. 4-7 are respectively adjacent carbon fiber bundle sections of two different samples, it can be seen from fig. 4 and 6 that the crack of the carbon fiber plate is expanded into the transverse carbon fiber bundle area, the area is closed after re-flattening and bonding treatment, while the crack is expanded into the longitudinal carbon fiber area in fig. 5 and 7, and the crack is not closed due to shrinkage after the carbon fiber bundle is broken, so that the crack expansion length can be determined by observing and measuring the difference of the crack depth between the adjacent two fracture surfaces, namely the virtual crack expansion length deltaa in the boundary effect theoretical model fic . Thus, the crack lengths of FIGS. 4 and 6 are 103.4 μm and 92.52 μm, and the crack lengths of FIGS. 5 and 7 are 196.91 μm and 142.66 μm, respectively, and then the crack propagation lengths of the two samples are 196.91-103.4=93.51 μm and 142.66-92.52=50.14 μm, respectively, and the average crack propagation length is taken to be 72 μm, and the structural feature parameter C is obtained from the formula (II) ch 48 μm.
Obtaining the carbon fiber/steel lamellar composite structure test piece
Curve sum sigma n -a e Curves, as shown in figures 8 and 9. Because the carbon fiber is a heterogeneous material, random factors such as size deviation, defect difference and the like exist among each sample, certain dispersity exists among the data of the samples with the same initial crack depth, and the sample data is still in the range of 95% confidence interval through reliability evaluation, so that the analysis model can describe the fracture behavior of the 2D-carbon fiber/steel lamellar composite structure test piece with crack damage on the surface of the carbon fiber layer. In FIG. 8, for two different typesPerforming least square fitting on test data of the carbon fiber/steel lamellar composite structure test piece with initial crack length, wherein the slope of a fitted curve is 427.88MPa, and f can be obtained by analyzing model sample estimation t 430.20MPa, the relative error of the two is 0.54%, which shows that the analytical model analysis result and the linear least square fitting result are good in consistency. As can be seen from Table 4, the tensile strength f was measured by comparing the direct tensile test t-T The average tensile strength of the carbon fiber plate measured by the side crack three-point bending test is 430.20MPa, the relative error of the two is 1.39%, and the deviation is small, so that the effectiveness of the analysis model is shown.
Ultimate bearing capacity P of carbon fiber/steel lamellar composite structure test piece with initial crack length of 0.001mm, 0.01mm and 0.1mm respectively max Making predictions as shown in fig. 10; sigma (sigma) n -a e The predicted graph is shown in fig. 11, and the upper and lower limit values of the ultimate bearing capacity for 95% reliability are obtained as shown in table 3.
TABLE 3 ultimate bearing capacities P of carbon fiber/Steel layered composite Structure test pieces with different surface crack lengths max Predictive value
| Initial notch depth/mm | Upper limit of ultimate bearing capacity/N | Lower limit of ultimate bearing capacity/N | Average value of ultimate bearing capacity/N | Average |
| 0 | 3274.20 | 2711.28 | 2992.74 | / |
| 0.001 | 3262.51 | 2701.60 | 2982.06 | 0.36％ |
| 0.01 | 3163.28 | 2619.43 | 2891.36 | 3.39％ |
| 0.1 | 2532.87 | 2097.41 | 2315.14 | 22.64％ |
| 0.2 | 2084.79 | 1809.17 | 1996.98 | 33.27％ |
| 0.4 | 1859.02 | 1539.40 | 1699.21 | 43.22％ |
The implementation also discloses a system for predicting the fracture strength of the carbon fiber/metal layered structure after surface scratch, which comprises the following steps of;
and the carbon fiber plate selecting module is used for selecting the carbon fiber plate with the same size as the carbon fiber layer 2 in the carbon fiber/metal layered composite structure test piece to be predicted.
And the load/displacement curve acquisition module is used for carrying out a direct tensile test on the carbon fiber board, loading the carbon fiber board to the test piece to be completely broken and destroyed, and recording the load/displacement curve of the carbon fiber board.
The direct tensile strength calculation module is used for analyzing and calculating the load/displacement curve to obtain the direct tensile strength f of the carbon fiber board t-T 。
The breaking strength calculation module is used for calculating the breaking strength P of the carbon fiber/metal layered composite structure test piece to be predicted max And (3) performing calculation:
wherein B is the width of the carbon fiber/metal layered composite structure test piece; x is the distance from the internal bending moment M of the midspan section of the carbon fiber/metal layered composite structure test piece to the interface between the carbon fiber layer 2 and the metal layer 1; n is the ratio of the elastic modulus of the metal layer 1 to that of the carbon fiber layer 2; h is a 1 Is the thickness h of the metal layer 1 in the carbon fiber/metal lamellar composite structure test piece 2 The thickness of the carbon fiber layer 2 in the carbon fiber/metal layered composite structure test piece; s is a fulcrum span for carrying out three-point bending loading on the carbon fiber/metal layered composite structure test piece; a, a 0 The initial crack length of the surface of the carbon fiber layer 2 of the carbon fiber/metal layered composite structure test piece; Δa fic C is the crack extension length of the carbon fiber/metal lamellar composite structure test piece ch The structural characteristic parameters of the carbon fiber/metal layered composite structure test piece; a, a e Equivalent crack length of the carbon fiber/metal layered composite structure test piece;
the characteristic crack length of the carbon fiber/metal lamellar composite structure test piece; xn virtual crack delta a of carbon fiber/metal lamellar composite structure test piece fic Nominal stress in the range; f (f) t Is the tensile strength of the carbon fiber layer 2 in the carbon fiber/metal layered composite structure, wherein f t By f t-T Instead of.
The implementation also discloses a computer device, which comprises a memory, a processor and a computer program stored in the memory and capable of running on the processor, wherein the processor realizes the steps of the method for predicting the fracture strength of the carbon fiber/metal layered structure after surface scratches.
The present implementation also discloses a computer readable storage medium storing a computer program which, when executed by a processor, implements the steps of the method for predicting fracture strength of a carbon fiber/metal layered structure after surface scratches as described above.
The above is only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited by this, and any modification made on the basis of the technical scheme according to the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (10)
1. The method for predicting the fracture strength of the carbon fiber/metal layered structure after surface scratch is characterized by comprising the following steps of:
s1, selecting a carbon fiber plate consistent with a carbon fiber layer (2) in a carbon fiber/metal layered composite structure test piece to be predicted;
s2, performing a direct tensile test on the carbon fiber board, loading the carbon fiber board to the test piece to be completely broken and destroyed, and recording a load/displacement curve of the carbon fiber board;
s3, analyzing and calculating a load/displacement curve to obtain the direct tensile strength f of the carbon fiber plate t-T ；
S5, breaking strength P of carbon fiber/metal lamellar composite structure test piece to be predicted max And (3) performing calculation:
wherein B is the width of the carbon fiber/metal layered composite structure test piece; x is the distance from the internal bending moment M of the midspan section of the carbon fiber/metal layered composite structure test piece to the interface between the carbon fiber layer (2) and the metal layer (1); n is the ratio of the elastic modulus of the metal layer (1) to that of the carbon fiber layer (2); h is a 1 Is the thickness of the metal layer (1) in the carbon fiber/metal lamellar composite structure test piece, h 2 The thickness of the carbon fiber layer (2) in the carbon fiber/metal layered composite structure test piece; s is a fulcrum span for carrying out three-point bending loading on the carbon fiber/metal layered composite structure test piece; a, a 0 The initial crack length of the surface of the carbon fiber layer (2) of the carbon fiber/metal layered composite structure test piece; Δa fic C is the crack extension length of the carbon fiber/metal lamellar composite structure test piece ch The structural characteristic parameters of the carbon fiber/metal layered composite structure test piece; a, a e Equivalent crack length of the carbon fiber/metal layered composite structure test piece;
the characteristic crack length of the carbon fiber/metal lamellar composite structure test piece; sigma (sigma) n Virtual crack delta a of carbon fiber/metal lamellar composite structure test piece fic Nominal stress in the range; f (f) t Is the tensile strength of the carbon fiber layer (2) in the carbon fiber/metal layered composite structure, wherein f t By f t-T Instead of.
2. The method for predicting fracture strength of carbon fiber/metal layered structure after surface scratches as claimed in claim 1, wherein the structural characteristic parameter C ch The calculation process of (1) is as follows:
Δa fic ＝β·G＝1.5C ch
where β is a discrete coefficient, assuming normal distribution is obeyed, β is taken as 1.5, and g is a second structural feature parameter.
3. The method for predicting fracture strength of carbon fiber/metal layered structure after surface scratches as claimed in claim 1, wherein the carbon fiber/metal layered structure is compoundedEquivalent crack length a of composite structural test piece e The calculation process of (1) is as follows:
wherein alpha is a 0 Total thickness h of test piece with carbon fiber/metal layered composite structure 1 +h 2 Y (alpha) is a geometric factor, alpha is less than 1, and Y (alpha) is 1.12.
4. The method for predicting fracture strength of carbon fiber/metal layered structure after surface scratches as claimed in claim 1, wherein the characteristic crack length of the carbon fiber/metal layered composite structure test piece
The calculation process of (1) is as follows:
wherein K is IC The fracture toughness of the carbon fiber/metal lamellar composite structure test piece.
5. The method for predicting fracture strength of carbon fiber/metal layered structure after surface scratch according to claim 1, wherein the virtual crack Δa of the carbon fiber/metal layered composite structure test piece fic Nominal stress sigma within a range n The calculation process of (1) is as follows:
6. the method for predicting the fracture strength of the carbon fiber/metal layered structure after surface scratches according to claim 1, wherein the equilibrium relation between the internal bending moment M of the midspan section of the carbon fiber/metal layered composite structure test piece and the stress and strain on the section is:
wherein the stress at the upper surface of the metal layer (1) is sigma s The method comprises the steps of carrying out a first treatment on the surface of the The stress at the interface of the metal layer (1) and the carbon fiber layer (2) is sigma' s Strain is epsilon' s The method comprises the steps of carrying out a first treatment on the surface of the The strain of the carbon fiber layer (2) in the damaged area of the crack tip is epsilon n The equivalent elastic modulus of the carbon fiber layer (2) is E n 。
7. The method for predicting fracture strength of carbon fiber/metal layered structure after surface scratches as claimed in claim 1, wherein the mid-span section internal bending moment M of the carbon fiber/metal layered composite structure and the peak load P of the carbon fiber/metal layered composite structure test piece max-i The relation of (2) is:
8. a system for predicting fracture strength of a carbon fiber/metal layered structure after surface scratch, comprising;
the carbon fiber plate selecting module is used for selecting a carbon fiber plate consistent with the carbon fiber layer (2) in the carbon fiber/metal layered composite structure test piece to be predicted;
the load/displacement curve acquisition module is used for carrying out a direct tensile test on the carbon fiber board, loading the carbon fiber board to the test piece to be completely broken and destroyed, and recording the load/displacement curve of the carbon fiber board;
the direct tensile strength calculation module is used for analyzing and calculating the load/displacement curve to obtain the direct tensile strength f of the carbon fiber board t-T ；
The breaking strength calculation module is used for calculating the breaking strength P of the carbon fiber/metal layered composite structure test piece to be predicted max And (3) performing calculation:
wherein B is the width of the carbon fiber/metal layered composite structure test piece; x is the distance from the internal bending moment M of the midspan section of the carbon fiber/metal layered composite structure test piece to the interface between the carbon fiber layer (2) and the metal layer (1); n is the ratio of the elastic modulus of the metal layer (1) to that of the carbon fiber layer (2); h is a 1 Is the thickness of the metal layer (1) in the carbon fiber/metal lamellar composite structure test piece, h 2 The thickness of the carbon fiber layer (2) in the carbon fiber/metal layered composite structure test piece; s is a fulcrum span for carrying out three-point bending loading on the carbon fiber/metal layered composite structure test piece; a, a 0 The initial crack length of the surface of the carbon fiber layer (2) of the carbon fiber/metal layered composite structure test piece; Δa fic C is the crack extension length of the carbon fiber/metal lamellar composite structure test piece ch The structural characteristic parameters of the carbon fiber/metal layered composite structure test piece; a, a e Equivalent crack length of the carbon fiber/metal layered composite structure test piece;
the characteristic crack length of the carbon fiber/metal lamellar composite structure test piece; sigma (sigma) n Virtual crack delta a of carbon fiber/metal lamellar composite structure test piece fic Nominal stress in the range; f (f) t Is the tensile strength of the carbon fiber layer (2) in the carbon fiber/metal layered composite structure, wherein f t By f t-T Instead of.
9. A computer device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that the processor, when executing the computer program, carries out the steps of the method for predicting breaking strength of a carbon fiber/metal layered structure after surface scoring according to any one of claims 1 to 7.
10. A computer-readable storage medium storing a computer program, wherein the computer program when executed by a processor performs the steps of the method for predicting breaking strength of a carbon fiber/metal layered structure after surface scoring according to any one of claims 1 to 7.
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