Energy determination method for low-velocity impact crack damage of composite material

Abstract

The present application relates to the field of composite material design, in particular to a kind of energy determination method of composite material low-speed impact crack damage, comprising: the first calculation formula for determining the impact damage of composite laminated plate is constructed, wherein R indicates the variable after the impact of composite laminated plate, E v Indicate the energy absorption existing in the impact process of composite laminated plate, E a Indicate the energy dissipated in the impact process of composite laminated plate, D i Indicate the dent depth formed after impact, D P Indicate the penetration thickness of composite laminated plate;The numerical value of E v , E a , D i , D P Is obtained respectively, and R is calculated according to the first calculation formula.The method is used to obtain E v , E a By low-speed impact test of composite material;D i , D P Is obtained by detecting impact damage, the ratio of E v , E a And the product of the ratio of D i , D P Is calculated, impact damage assessment is carried out, so that the prediction result is more obvious and more accurate.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of composite material design, and particularly relates to a method for determining the energy of low-speed impact crack damage of a composite material. BACKGROUND

[0002] Composite materials have become the best materials today due to their high specific stiffness and strength ratio. These composite structures may be subjected to repeated impacts such as hail impacts, debris impacts, etc. during use. Although a single low-speed impact may not cause obvious external damage, it will inevitably deteriorate the mechanical properties of the composite structure to some extent.

[0003] Woven fabric reinforced composite materials, especially carbon fiber reinforced composite materials, have high structural stability and good damage resistance, and are also widely used in aerospace structures. However, the anisotropy of unidirectional laminated plates and woven fiber layers, the complex geometry, and the existence of mixed failure mechanisms under impact load of the composite materials make it challenging to predict their impact resistance and failure behavior. SUMMARY

[0004] The first object of the present application is to provide a method for determining the energy of low-speed impact crack damage of a composite material, comprising:

[0005] constructing a first calculation formula for determining the impact damage of a composite laminated plate wherein R represents a variable of the composite laminated plate after impact, E v represents the energy absorption existing in the process of impact of the composite laminated plate, E a represents the energy dissipation in the process of impact of the composite laminated plate, D i represents the crater depth formed after impact, D P represents the through-thickness of the composite laminated plate;

[0006] respectively obtaining the numerical values of E v , E a , D i , and D P , and calculating R according to the first calculation formula;

[0007] In the first calculation formula, E v is calculated by a second calculation formula E v = |E a -E0|, wherein E0 represents the energy dissipation of the inelastic process;

[0008] In the first calculation formula and the second calculation formula, E a is obtained by detection;

[0009] In the second calculation formula, E0 is calculated according to the structure of the composite laminated plate.

[0010] Further, E0 is calculated at least according to the following: (a) the composite laminated plate is a unidirectional layer structure, and E0 is calculated by a third calculation formula , wherein R C represents the radius of the dent formed after impact, G IIC represents the mode II crack fracture toughness, E C represents the energy required for fiber tensile load failure, D i represents the dent depth formed after impact, E mt represents the cracking energy per unit volume of the matrix of the composite material, V m represents the volume fraction of the matrix of the composite material, and l represents the overall thickness of the composite laminated plate; (b) the composite laminated plate is a woven fiber layer structure, and E0 is calculated by a fourth calculation formula , wherein r represents the radius of the carbon fiber, and σ f represents the tensile strength of the composite laminated plate, E f represents the tensile modulus of the composite laminated plate.

[0011] Further, in the third calculation formula and the fourth calculation formula, R C , G IIC , E C , D i , E mt , V m , l, r, σ f , E f are obtained by detection.

[0012] The second object of the present application is to provide a specific calculation step of the energy determination method, comprising:

[0013] S1, database establishment

[0014] S101, impact performance detection of the composite laminated plate

[0015] The composite laminated plate is prepared, and the parameters l, V m , E mt , E C , G IIC , E f , σ f , r of the composite laminated plate are measured.

[0016] The change of the absorbed energy of the composite laminated plate under impact is measured, and the parameters D i , R C , E i , E a are detected.

[0017] S102, calculation of crack energy absorption

[0018] E0 is calculated according to whether the composite laminated plate comprises a unidirectional layer structure and a woven fiber layer structure, and E0 represents energy dissipation of an inelastic process;

[0019] S2, damage determination

[0020] According to the first calculation formula R is calculated, R represents a variable after the composite laminated plate is impacted, and the damage of the composite laminated plate after being impacted is determined.

[0021] A third object of the present application is to provide an application of a composite material low-speed impact crack damage energy determination method, and the composite material low-speed impact crack damage energy determination method is applied to predict the damage condition of a carbon fiber reinforced composite material plate.

[0022] A fourth object of the present application is to provide an application of a composite material low-speed impact crack damage energy determination method, and the composite material low-speed impact crack damage energy determination method is applied to predict the damage condition of a plain woven cloth product.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] (1) The method of the present application is used to perform a low-speed impact test on a composite material to obtain E v , E a ; the impact damage is detected to obtain D i , D P ; and the product of the ratio of E v , E a and the ratio of D i , D P is calculated by using the first calculation formula, and the impact damage is evaluated. The method effectively amplifies the impact damage by establishing the corresponding relationship between E v -E a and D i -D P , and the internal damage degree of the composite material product is evaluated by the proportion of crack damage energy in the impact energy process, which reduces the harm caused by damage in the subsequent service process, because the invisible crack damage factor is increased, and the damage evaluation is more obvious and more accurate.

[0025] (2) the method of the present application is used to calculate the low-speed impact crack damage of the composite material, and the energy damage of the composite material after impact can be evaluated according to the calculation result of the R value: 1. when the composite laminated plate has no visual damage, the R value is proportional to the crack number, inversely proportional to the fiber damage degree, and inversely proportional to the matrix damage degree, that is, the greater the R value, the greater the crack ratio, the smaller the fiber and matrix damage, and the relatively lighter the overall damage degree of the composite plate; 2. when the composite laminated plate begins to have visual damage, the R value is proportional to the crack damage ratio, proportional to the fiber damage degree, and proportional to the matrix damage degree, that is, the greater the R value, the greater the crack damage ratio, the more obvious the fiber and matrix damage, and the more serious the overall damage degree of the composite plate.

[0026] (3) the method of the present application is used to calculate the low-speed impact crack damage of the composite material, and the R value and the visual damage of the composite laminated plate obtained by comprehensive calculation can be used to compare and evaluate the overall damage degree of two laminated plate composite parts under the same impact energy, because the influence of internal invisible crack damage on overall damage determination is considered, so that the damage evaluation is more obvious and more accurate. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 It is a typical energy-time curve diagram in the low-speed impact performance detection experiment of the present application;

[0028] Figure 2 It is a flowchart of the low-speed impact performance detection experiment of the present application;

[0029] Figure 3 It is a schematic diagram of the main fiber and secondary fiber range and impact range in the low-speed impact performance detection experiment of the present application;

[0030] Figure 4 It is a schematic diagram of the actual impact damage of A and B laminated plates in Example 1 of the present application;

[0031] Figure 5 It is a schematic diagram of the actual impact damage of A and C laminated plates in Example 2 of the present application;

[0032] Figure 6 It is a schematic diagram of the actual impact damage of B and C laminated plates in Example 3 of the present application;

[0033] Figure 7 It is an energy-time change diagram of A, B and C laminated plates in Examples 1-3 of the present application respectively in the process of 4J energy impact;

[0034] Figure 8 It is a modal test result diagram of A, B and C laminated plates in Examples 1-3 of the present application respectively after the process of 4J energy impact. DETAILED DESCRIPTION

[0035] The application will be further described below in connection with specific embodiments. The following examples are only used to more clearly illustrate the technical solutions of the application, and cannot be used to limit the protection scope of the application. Any content not described in detail in the patent application of the application can be understood as common knowledge in the art.

[0036] Based on the defects of the existing damage prediction and determination methods mentioned in the background art, the application aims to provide a composite low-speed impact crack damage energy determination method. In the determination process, the crack dissipation energy is introduced, and the absorbed energy is combined as a damage index to evaluate the impact damage degree of the carbon fiber reinforced composite (CFRP) plate. The evaluation index can be used to represent the performance of the crack in the overall damage, and can also predict the damage state of the plate to a certain extent. The index can also be used to predict the damage of plain woven cloth to a certain extent.

[0037] As shown in Figure 2 The first object of the application is to provide a composite low-speed impact crack damage energy determination method, comprising:

[0038] S1, database establishment

[0039] S101, impact performance detection of composite laminated plate

[0040] (1) Preparation of composite laminated plate

[0041] According to the material, composite method and forming process of the known carbon fiber reinforced composite to be detected, a composite laminated plate is prepared, and different composite laminated plates are labeled for identification.

[0042] The carbon fiber reinforced composite takes resin as the matrix and carbon fiber as the reinforcing body. The layup angle of the unidirectional layup can include but is not limited to commonly used standard layup angles such as 0°, 45° and 90°, as well as special layup angles. Each layer is placed according to the design direction. The woven fiber layer can be cross-woven by two fiber bundles. Unless otherwise specified, only one type of carbon fiber is used for cross-woven in each layer. The forming process includes but is not limited to hot pressing.

[0043] (2) Measurement of parameters of composite laminated plate

[0044] The parameters of the composite laminated plate are measured: l, V m , E mt , E C , G IIC , E f , σ f , r.

[0045] Among them:

[0046] l represents the overall thickness of the composite laminate, D P D represents the through-thickness of the composite laminate, numerically. P =l;

[0047] V m Indicates the matrix volume fraction of the composite material;

[0048] E mt This represents the cracking energy per unit volume of the composite matrix;

[0049] r represents the radius of the carbon fiber;

[0050] E C This represents the energy required for fiber failure under tensile load;

[0051] E f Indicates the tensile modulus of composite laminates;

[0052] σ f Indicates the tensile strength of composite laminates;

[0053] G IIC This indicates the fracture toughness of type II cracks.

[0054] (3) Measuring the energy absorption change of composite laminates under impact

[0055] After non-destructive testing confirmed that the composite laminate was free of internal defects, it was subjected to impacts with different impact energies. Typical energy-time curves are shown below. Figure 1 As shown, and detect relevant parameters: D i R C E i E a .

[0056] in:

[0057] D i Indicates the depth of the dent formed after the impact;

[0058] R C Indicates the radius of the dent formed after the impact;

[0059] E i This represents the maximum impact energy corresponding to the maximum contact force;

[0060] E a This represents the absorbed energy, that is, the energy dissipated during the impact, which can be determined according to... Figure 1 The location of the absorbed energy value is read from the specific impact test energy-time variation graph. a The specific value.

[0061] S102, Calculation of crack energy absorption

[0062] In the process of impact on carbon fiber reinforced composite laminates (CFRP), the energy conversion and absorption of composite laminates includes three stages: 1. laminate deformation stage, 2. laminate damage stage, 3. impact rebound stage.

[0063] In these three stages, E e represents the elastic specific energy in the laminate deformation stage, E d represents the damage energy absorption in the laminate damage stage, and E r represents the punch rebound energy in the impact rebound stage.

[0064] E0 represents the energy dissipation of non-elastic process; in the actual impact process of composite laminates, E0 mainly represents the energy absorbed due to delamination and matrix cracking, so E0 = E e +E d .

[0065] E v represents other energy absorption methods such as micro-cracks existing in the impact process; in the impact process of composite laminates, the absorbed energy E a =E e +E d +E v =E0+E v , since the calculation range is expanded, the absolute value E v =|E a -E0| is taken, which is defined as the second calculation formula.

[0066] (1) For unidirectional laminated composite laminates

[0067] E DL represents the energy absorbed by delamination of composite laminates, which is calculated by the formula E DL =πR C 2 G ⅡC D i , the premise of using this formula is that the absorbed energy is negative, the friction energy is not counted, and the failure mechanism is uniform throughout the thickness, each layer of fiber is independent, the failure of one layer of fiber does not affect other layers, and the material properties do not change during impact, the strain rate does not change, according to the damage range of the concave pit section, this calculation formula is obtained.

[0068] E MC represents the energy of matrix cracking, which is calculated by the formula E MC =πR C 2 E mt lV m .

[0069] E TF represents the energy absorption of fiber tensile failure in the whole failure area of unidirectional laminate; generally, fiber fracture is mainly in the tensile mode, so E TF can be calculated by the formula .

[0070] Therefore, for the composite laminate with unidirectional laminate structure, E0=E DL +E MC +E TF , and further calculation gives This is defined as the third calculation formula.

[0071] (2) For the composite laminate with woven fiber layer

[0072] As shown in Figure 3 , for the composite laminate with woven fiber layer, the carbon fibers along the X-axis and Y-axis directions of the impacted area are defined as the primary yarns, i.e., the main fibers, and the rest of the carbon fibers are defined as the secondary yarns, i.e., the secondary fibers.

[0073] E MC represents the energy of matrix cracking of the woven structure, which can be calculated by the formula .

[0074] E ED represents the energy absorbed by the secondary yarns in unit area in elastic deformation; in the woven fiber layer structure, the fracture of the primary yarns will cause the release of a certain amount of elastic strain energy and transfer to the surrounding of the dent, assuming that the radius from the impact center of the composite laminate to the delamination zone boundary is and the strain in the secondary yarns inside the boundary of the delamination zone of the composite laminate changes linearly from the impact center of the composite laminate, and the main load is tensile load, then E ED can be calculated by the formula .

[0075] Therefore, for the composite laminate with woven structure, E0=E DL +E MC +E TF +E ED , and further calculation gives This is defined as the fourth calculation formula.

[0076] S2, damage determination

[0077] R represents the variable of the composite laminate after impact, and the damage determination can be performed, which can be calculated by the first calculation formula ; wherein: D P represents the through-thickness of the composite laminate, and the value of DP = l, D i D represents the dent depth formed after impact.

[0078] After impact, the plate of the composite laminate begins to have different degrees of cracks. When the cracks are obvious damage visible to the naked eye, the greater the R value, the greater the proportion of crack damage, the more obvious the fiber damage and the more obvious the matrix damage. When the plate has no visible damage to the naked eye, the greater the R value, the greater the proportion of crack damage, the smaller the fiber damage and the smaller the matrix damage. Therefore, according to the R value and whether there is a visible crack, the crack damage in the low-speed impact test of the composite laminate is determined.

[0079] Functional features: crack energy absorption E is calculated V The results represent the crack damage of the laminate under a certain impact energy, and the overall energy absorption E a and dent depth D i The R value is calculated, and the value and the visible damage of the plate can be used to compare and evaluate the overall damage of two composite laminate parts under the same impact energy, because the influence of internal invisible crack damage on overall damage determination is considered, and the damage evaluation is more obvious and more accurate.

[0080] In some specific embodiments, the energy determination method of the crack damage of the composite material described above can be applied to predict the damage of the carbon fiber reinforced composite plate. In other specific embodiments, it can also be applied to predict the damage of the plain woven cloth product, and the judgment process is also shown in Figure 2 .

[0081] Example 1

[0082] This embodiment determines the energy of the low-speed impact crack damage of the T300 carbon fiber reinforced composite material.

[0083] S1, database establishment

[0084] S101, impact performance detection of the composite laminate

[0085] (1) Preparation of the composite laminate

[0086] The composite laminate is prepared and marked as plate A, and the plate A is a T300 carbon fiber composite laminate with a plain weave structure.

[0087] (2) Measurement of parameters of the composite laminate

[0088] The parameters of the composite laminate are measured: l, V m , E mt , E C , G IIC , E f, σ f , r. Record the carbon fiber radius r of plate A (A) = 7 μm, the thickness D of plate A p(A) = 1 (A) = 4.44 mm, the parameter V m = 0.4, E mt = 1 Kg / m 2 , E C = 12.5 Kg / m 2 , G IIC = 0.34, E f = 184.771 GPa, σ f = 2890 MPa.

[0089] (3) Measure the absorbed energy of the composite laminated plate under impact

[0090] Impinge the composite laminated plate with 4J energy, measure the absorbed energy of the composite laminated plate under impact, and detect the relevant parameters: D i , R C , E i , E a . Record D i(A) = 0.9 mm, R C(A) = 1.61 mm, E i(A) = 4.18 J, E a(A) = 2.16 J.

[0091] S102, Calculation of crack absorbed energy

[0092] During the impact of the carbon fiber reinforced composite laminated plate, the energy conversion and absorption of the composite laminated plate includes three stages: 1. Laminated plate deformation stage, 2. Laminated plate destruction stage, 3. Impact rebound stage.

[0093] Since plate A is a composite laminated plate with plain weave structure, calculate E0 by E0 = E DL + E MC + E TF + E ED According to the fourth calculation formula , calculate E 0(A) = 2.55 J.

[0094] According to the second calculation formula E v = |E a -E0|, calculate E v(A) = 0.39 J.

[0095] S2, Damage determination

[0096] Calculate E v(A) , E a(A) , Di(A) , D p(A) The numerical value of D is substituted into the first calculation formula The calculation obtains R (A) = 0.03659.

[0097] Example 2

[0098] This example determines the energy of low-speed impact crack damage of T300 carbon fiber reinforced composite material.

[0099] S1, database establishment

[0100] S101, impact performance detection of composite laminated plate

[0101] (1) Preparation of composite laminated plate

[0102] The composite laminated plate is prepared, marked as plate B, and the plate B is a T300 carbon fiber composite laminated plate with unidirectional layer structure.

[0103] (2) Measurement of parameters of composite laminated plate

[0104] The parameters of the composite laminated plate are measured, and the carbon fiber radius r of the plate B is recorded (B) = r (A) = 7 μm, the thickness D of the plate B p(B) = 1 (B) = 3.71 mm. The parameters V m , E mt , E C , G IIC of the plate A and the plate B are the same, V m = 0.4, E mt = 1 Kg / m 2 , E C = 12.5 Kg / m 2 , G IIC = 0.34, E f = 138 GPa, σ f = 3258 MPa.

[0105] (3) Measurement of absorbed energy change of composite laminated plate under impact

[0106] The composite laminated plate is impacted by 4J energy, the absorbed energy change of the composite laminated plate under impact is measured, the related parameters are detected, and D i(B) = 0.976 mm, R C(B) = 1.67 mm, E i(B) = 4.17 J, E a(B) = 2.7 J.

[0107] S102, calculation of crack absorbed energy

[0108] The plate B is a T300 carbon fiber composite material laminated plate with unidirectional layer structure, so E0=E DL +E MC +E TF E0is calculated by the third calculation formula E is calculated 0(B) =2.94J.

[0109] According to the second calculation formula E v =|E a -E0|E is calculated v(B) =0.24J.

[0110] S2, damage determination

[0111] The values of E v(B) , E a(B) , D i(B) , D p(B) are substituted into the first calculation formula R is calculated (B) =0.02338.

[0112] Example 3

[0113] In this embodiment, the energy determination of low-speed impact crack damage of T300 carbon fiber reinforced composite material is carried out.

[0114] S1, establishment of database

[0115] S101, impact performance detection of composite laminated plate

[0116] (1) Preparation of composite laminated plate

[0117] The composite laminated plate is prepared and marked as plate C, and the plate C is a T300 carbon fiber composite laminated plate with more +45 / -45 layer direction.

[0118] (2) Measurement of parameters of composite laminated plate

[0119] The parameters of the composite laminated plate are measured, and the carbon fiber radius r of the plate C is recorded (C) =7μm, the thickness D p(C) of the plate C is (C) =3.71mm, the parameter V m =0.4, E mt =1Kg / m 2 , E C =12.5Kg / m 2 , G IIC =0.34, E f =138GPa, σ f =3258MPa.

[0120] (3) Measurement of absorbed energy change of the composite laminate under impact

[0121] The composite laminate was impacted by 4J energy, the absorbed energy change of the composite laminate under impact was measured, and the relevant parameters were detected: D i , R C , E i , E a . The values of D i(C) =1.01mm, R C(C) =1.69mm, E i(C) =4.17J, E a(C) =2.76J were recorded.

[0122] S102, calculation of crack absorbed energy

[0123] Since the plate C is a composite laminate with more +45 / -45 layer directions, E0 is calculated by E0=E DL +E MC +E TF , and the third calculation formula E 0(C) =3.08J.

[0124] According to the second calculation formula E v =|E a -E0|, E v(C) =0.32J is calculated.

[0125] S2, damage determination

[0126] The values of E v(C) , E a(C) , D i(C) , D p(C) are substituted into the first calculation formula , and R (C) =0.03256 is calculated.

[0127] Test Example 1

[0128] The damage of the laminates of Examples 1-3 was determined, and the results are shown in Figure 4 , Figure 5 , Figure 6 , Figure 7 , the actual impact damage of the laminates is shown in the two-by-two comparison diagram Figures 4-6 , and the energy-time change diagram of the plate A, plate B and plate C during 4J energy impact is shown in Figure 7 . From these diagrams, it can be observed that:

[0129] Plate A absorbs the least energy under a 4J impact. Based on the principle that the absorbed energy should result in less damage, the damage to plates B and C should be greater than that to plate A. This also aligns with the visually apparent damage levels. Figure 4 , Figure 5 Plate A has a shallower pit and less visual damage. Furthermore, modal testing was performed on plates A, B, and C, yielding... Figure 8 ,according to Figure 8 It can be seen that at the low order levels (1-3), the modal frequency values ​​of the three plates are not significantly different, with plate A's mode being slightly higher than that of plates B and C. At the high order levels (4-5), a significant difference begins to appear, with plate A's mode being significantly lower than that of plates B and C. This is because high-order modal frequencies are sensitive to damage caused by microcracks; the higher the frequency, the less damage from cracks, and the lower the frequency, the more damage from cracks. Therefore, high-order modes can reflect the damage caused by microcracks inside the laminate to a certain extent. Plate A's high-order modes are lower than those of plates B and C, meaning that it contains more microcracks than plates B and C. This aligns with the judgment based on the R value that the damage state of plate A is slightly worse than that of plates B and C, taking into account the influence of microcracks on the damage.

[0130] Plate B absorbs less energy than plate C but more energy than plate A during a 4J energy impact. Figure 4 , Figure 6 There are more matrix cracks on the back side. Visually, the damage is less than that of plate C and more than that of plate A. Judging from the absorbed energy, the damage of plate B should also be less than that of plate C and less than that of plate A, because plate A has no obvious visual damage at this time. Therefore, the larger the R of plate A, the smaller the fiber crack damage. Plates B and C already have visible crack damage. Therefore, the damage of plate B is less than that of plate C and less than that of plate A.

[0131] Plate C absorbs more energy than plates A and B under a 4J energy impact, such as Figure 5 , Figure 6 The exterior also has the most cracks and scratches, while the interior has more damage. Layered propagation leads to more crack initiation and the absorption of the most energy. Based on the damage energy, the damage degree is the greatest. The modal test results also show that the higher-order mode of plate C is less than that of plate B but greater than that of plate A. Similarly, based on the R value, the R value of plate C is less than that of plate A but greater than that of plate B. Therefore, the damage degree of plate C is greater than that of plate B but less than that of plate A.

[0132] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for determining the energy of low velocity impact crack damage of a composite material, characterized by, The application relates to a composite material low-speed impact crack damage energy determination method. Construction of a first calculation formula for determining impact damage of a composite laminate wherein R represents a variable after the composite laminate is impacted, E v represents energy absorption present during the impact of the composite laminate, E a represents energy dissipated during the impact of the composite laminate, D i represents a dent depth formed after the impact, D P represents a through-thickness of the composite laminate; The values of E v , E a , D i , and D P are obtained respectively, and R is calculated according to the first calculation formula; In the first calculation formula, the E v By the second calculation formula E v = |E a -E0| is calculated, wherein E0 represents the energy dissipation of the inelastic process; the E0 is calculated at least according to the following: (a) the composite laminated plate is a unidirectional layup structure, and the E0 is calculated by a third calculation formula wherein, R C represents the dent radius formed after impact, G IIC represents the mode II crack fracture toughness, E C represents the energy required for fiber tensile load failure, D i represents the dent depth formed after impact, E mt represents the cracking energy per unit volume of the composite matrix, V m represents the volume fraction of the composite matrix, and l represents the overall thickness of the composite laminated plate; (b) the composite laminate is a woven fiber layer structure, and the E0 is calculated by a fourth calculation formula wherein r represents the radius of the carbon fiber, and σ f represents the tensile strength of the composite laminate, E f represents the tensile modulus of the composite laminate; In the first calculation formula and the second calculation formula, the E a The value is obtained by detection. In the second calculation formula, the E0 is calculated according to the structure of the composite material laminated plate.

2. The energy decision method of claim 1, wherein, In the third and fourth calculation formulas, the R C , G IIC , E C , D i , E mt , V m , l, r, σ f , E f values are obtained by detection.

3. A method of calculating the energy criterion of low-velocity impact crack damage of the composite material according to any one of claims 1-2, characterized in that, The application relates to a composite material low-speed impact crack damage energy determination method. S1, database establishment S101, impact performance detection of the composite material laminated plate A composite material laminate is prepared and parameters l, V of the composite material laminate are measured m , E mt , E C , G IIC , E f , σ f , r; Measuring the absorbed energy of a composite laminate under impact, detecting the parameter D i , R C , E i , E a ; S102, crack energy absorption calculation The E0 is calculated according to whether the composite material laminated plate comprises a unidirectional layer structure and a woven fiber layer structure, and the E0 represents energy dissipation in a non-elastic process; S2, damage determination According to the first calculation formula The R is calculated, and R represents a variable of the composite laminated plate after impact, and the damage of the composite laminated plate after impact is determined.

4. Use of a method of determining the energy of low-velocity impact crack damage of a composite material, characterized in that, The composite material low-speed impact crack damage energy determination method according to any one of claims 1-2 is applied to predict the damage condition of a carbon fiber reinforced composite material plate.

5. Use of a method of determining the energy of low-velocity impact crack damage of a composite material, characterized in that, The composite material low-speed impact crack damage energy determination method according to any one of claims 1-2 is applied to predict the damage condition of a plain woven cloth product.

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