A failure analysis method for a thermoplastic composite laminate structure

Abstract

The present invention discloses a method for failure analysis of a thermoplastic composite laminate structure, comprising: Step 1, establishing an in-plane elastic damage model of the thermoplastic composite to obtain the stress-strain level of in-plane elastic damage; Step 2, establishing an in-plane shear elastic-plastic model of the thermoplastic composite to obtain the stress-strain level of in-plane shear elastic-plasticity; Step 3, determining the in-plane initial damage of the thermoplastic composite laminate structure and the form of stiffness degradation after in-plane initial damage according to the stress-strain levels obtained in Step 1 and Step 2; Step 4, determining the interlaminar initial damage of the thermoplastic composite laminate structure and the form of stiffness degradation after interlaminar initial damage. The technical solution provided by the embodiments of the present invention solves the problem that the existing composite damage theory mainly focuses on the research of thermosetting composites, resulting in difficulty in effectively predicting the progressive failure of thermoplastic composite laminate structures.

Description

Technical Field

[0001] This application relates to, but is not limited to, the technical field of damage tolerance design for thermoplastic composite structures, and particularly refers to a method for failure analysis of thermoplastic composite laminated structures. Background Art

[0002] Compared with thermosetting composites, thermoplastic composites have higher impact resistance and fracture toughness.

[0003] The existing research on composite damage theory mainly focuses on thermosetting composites. During the damage failure process of thermosetting composites, there is no plastic deformation, and the damage failure criterion is also independent of plastic influencing factors. Currently, the failure mechanism of fiber-reinforced thermoplastic composites is not clear, and the constitutive relationship and damage model are also not perfect. Therefore, the existing composite damage theory for thermosetting composites is difficult to effectively predict the progressive failure of thermoplastic composite laminated structures. Summary of the Invention

[0004] Objective of the Invention: To solve the above technical problems, embodiments of the present invention provide a method for failure analysis of thermoplastic composite laminated structures to solve the problem that it is difficult to effectively predict the progressive failure of thermoplastic composite laminated structures due to the existing composite damage theory mainly focusing on the research of thermosetting composites.

[0005] Technical Solution of the Invention: Embodiments of the present invention provide a method for failure analysis of thermoplastic composite laminated structures, wherein the in-plane stress of the thermoplastic composite includes elastic stress and shear plastic stress; the failure analysis method includes:

[0006] Step 1, establish an in-plane elastic damage model for the thermoplastic composite to obtain the stress-strain level of in-plane elastic damage;

[0007] Step 2, establish an in-plane shear elastic-plastic model for the thermoplastic composite to obtain the stress-strain level of in-plane shear elastic-plasticity;

[0008] Step 3, determine the in-plane initial damage of the thermoplastic composite laminated structure and the form of stiffness degradation after in-plane initial damage according to the stress-strain levels obtained in Step 1 and Step 2;

[0009] Step 4, determine the interlayer initial damage of the thermoplastic composite laminated structure and the form of stiffness degradation after interlayer initial damage.

[0010] Optionally, in the failure analysis method of the thermoplastic composite laminated structure as described above, Step 1 includes:

[0011] Under the condition of plane stress state, the model of the elastic stress-strain relationship for the performance degradation of thermoplastic composites is as follows:

[0012]

[0013] Wherein, d1 is the damage variable in the fiber 1 direction, d2 is the damage variable in the fiber 2 direction, and d 12 is the shear damage variable; E1 is the elastic modulus of the laminate in the 1 direction, E2 is the elastic modulus of the laminate in the 2 direction; ε1 is the strain in the 1 direction, ε2 is the strain in the 2 direction, and ε 12 el is the shear strain; σ1 is the stress in the 1 direction, σ2 is the stress in the 2 direction, and σ 12 is the shear stress; and the damage variable in the 1 direction and the damage variable in the 2 direction are:

[0014]

[0015] Wherein, d + is the damage variable generated during the tensile process, and d - is the damage variable generated during the compression process.

[0016] Optionally, in the failure analysis method of the thermoplastic composite laminate structure as described above, the total strain of the thermoplastic composite is equal to the elastic strain plus the plastic strain; the step 2 includes:

[0017] According to the classical plastic model of the isotropic hardening law and based on the setting that there is only plastic strain in the shear strain, the in-plane shear elasto-plastic model of the thermoplastic composite is obtained as:

[0018] R(ε 12 pl ) = C(ε 12 pl ) p ;

[0019] Wherein, R(ε 12 pl ) is an isotropic hardening function about the plastic cumulative strain ε 12 pl , and C and p are obtained by fitting the shear stress-strain curve through experiments.

[0020] Optionally, in the failure analysis method of the thermoplastic composite laminate structure as described above, the step 3 includes:

[0021] Step 31, determine the in-plane initial damage criterion of the thermoplastic composite laminate structure according to the stress-strain levels obtained in step 1 and step 2;

[0022] Step 32, after determining the in-plane initial damage of the thermoplastic composite laminate structure according to the in-plane initial damage criterion, determine the form of in-plane damage stiffness degradation.

[0023] Optionally, in the failure analysis method of the thermoplastic composite laminate structure as described above, the initial damage criterion determined in step 31 includes:

[0024] Determine the initial damage criterion for each failure mode respectively from the failure modes of radial fiber tensile failure, radial fiber compressive failure, circumferential fiber tensile failure, circumferential fiber compressive failure, and in-plane matrix shear failure.

[0025] Optionally, in the failure analysis method of the thermoplastic composite laminate structure as described above, the initial damage criterion for each failure mode in step 31 includes:

[0026] Failure criterion 1, the radial tensile failure factor for failure criterion in the radial fiber tensile mode is:

[0027]

[0028] Failure criterion 2, the radial compressive failure factor for failure criterion in the radial fiber compressive mode is:

[0029]

[0030] Failure criterion 3, the circumferential tensile failure factor for failure criterion in the circumferential fiber tensile mode is:

[0031]

[0032] Failure criterion 4, the circumferential compressive failure factor for failure criterion in the circumferential fiber compressive mode is:

[0033]

[0034] Failure criterion 5, the shear failure factor for failure criterion in the in-plane matrix shear mode is:

[0035]

[0036] Among them, when each failure factor is equal to 1, initial failure occurs;

[0037] X t is the tensile strength of the fiber in the radial direction, X c is the compressive strength of the fiber in the radial direction; Y t is the tensile strength of the fiber in the circumferential direction, Y c is the compressive strength of the fiber in the circumferential direction; S 12 is the in-plane shear strength.

[0038] Optionally, in the failure analysis method of the thermoplastic composite laminate structure as described above, the in-plane stiffness degradation forms of the thermoplastic composite laminate structure determined in step 32 include:

[0039] The in-plane tensile stiffness of the thermoplastic composite degrades into a linear degradation form based on the fracture toughness of the material;

[0040] The in-plane compressive stiffness of the thermoplastic composite degrades into a linear degradation form based on the fracture toughness of the material;

[0041] The in-plane shear failure stiffness of the thermoplastic composite degrades into an attenuation mode fitted based on test data.

[0042] Optionally, in the failure analysis method of the thermoplastic composite laminate structure as described above, in the thermoplastic composite laminate structure, there is an adhesive layer between each layer, and step 4 includes:

[0043] Step 41, determining the interlayer initial damage criterion of the thermoplastic composite laminate structure;

[0044] Step 42, after determining that the adhesive layer of the thermoplastic composite laminate structure has initial damage according to the interlayer initial damage criterion, determining the interlayer damage stiffness degradation form.

[0045] Optionally, in the failure analysis method of the thermoplastic composite laminate structure as described above, the interlayer initial damage criterion in step 41 includes:

[0046] The damage initiation criterion for determining whether the adhesive layer starts to have adhesive layer element failure is:

[0047]

[0048] where t n is the normal stress that the adhesive layer finite element unit can bear, and t s , t t are the shear stresses that the adhesive layer finite element unit can bear; t n 0 , t s 0 , t t 0 are the strengths of the interfaces in each orthogonal direction respectively.

[0049] Optionally, in the failure analysis method of the thermoplastic composite laminate structure as described above, the interlayer damage stiffness degradation form in step 42

[0050] The damage propagation criterion for determining whether the adhesive layer element is completely failed and damaged is:

[0051]

[0052] Among them, G T = G n + G s + G t ; G S = G s + G t .

[0053] G n 、G s 、G t are the energies for doing work on the normal stress, the first shear stress, and the second shear stress respectively; are the normal critical energy release rate and the shear critical energy release rate respectively, and G C is the total energy at failure.

[0054] Advantages of the present invention: The failure analysis method for the thermoplastic composite laminate structure provided in the embodiments of the present invention is specifically a brand-new progressive failure analysis method for composite materials. This failure analysis method respectively establishes an in-plane elastic damage model and an in-plane shear elastic-plastic model for the thermoplastic composite material to obtain the stress-strain levels of in-plane elastic damage and in-plane shear elastic-plasticity. Subsequently, based on the above stress-strain levels, not only can the in-plane initial damage of the thermoplastic composite laminate structure and the form of stiffness degradation after the in-plane initial damage be determined, but also the interlaminar initial damage of the thermoplastic composite laminate structure and the form of stiffness degradation after the interlaminar initial damage can be determined. The technical solution of the embodiments of the present invention effectively predicts the progressive failure process of the composite material under quasi-static and impact loads, providing a basis for the design, analysis, and verification of aircraft thermoplastic composite structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The drawings are used to provide a further understanding of the technical solution of the present invention and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solution of the present invention and do not constitute a limitation to the technical solution of the present invention.

[0056] Figure 1 is a flowchart of a failure analysis method for a thermoplastic composite laminate structure provided in an embodiment of the present invention;

[0057] Figure 2 is a schematic diagram of a typical shear hardening curve provided in the prior art;

[0058] Figure 3 is a schematic diagram of the shear stress-strain curve of the composite material in the failure analysis method for the thermoplastic composite laminate structure provided in an embodiment of the present invention;

[0059] Figure 4Schematic diagram of the constitutive relationship of in-plane tensile stiffness degradation in the embodiments of the present invention;

[0060] Figure 5 Schematic diagram of the degradation of in-plane shear damage variable in the embodiments of the present invention;

[0061] Figure 6 Schematic diagram of the constitutive model of the adhesive layer in the embodiments of the present invention;

[0062] Figure 7 Schematic diagram of the finite element calculation model of AS4D / PEEK open-hole laminate;

[0063] Figure 8 Schematic diagram of the comparison of simulation test results of AS4D / PEEK open-hole laminate under compressive load;

[0064] Figure 9 Schematic diagram of the impact analysis results of thermoplastic composites - overall stress distribution;

[0065] Figure 10 Schematic diagram of the impact analysis results of thermoplastic composites - failure situation of cohesive elements. Detailed implementation manners

[0066] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, without conflict, the embodiments and features in the embodiments of the present application can be combined arbitrarily with each other.

[0067] As described in the above background art, the existing research on composite material damage theory mainly focuses on thermosetting composites. However, since thermosetting composites do not exhibit plastic deformation during the damage failure process and the damage failure criterion is also independent of plastic influencing factors, it is difficult to effectively predict the progressive failure of thermoplastic composite laminated structures using the existing composite material damage theory.

[0068] In view of the above problems, the embodiments of the present invention provide a failure analysis method for thermoplastic composite laminated structures, which can effectively predict the progressive failure of thermoplastic composite laminated structures and provide a basis for the design, analysis and verification of aircraft thermoplastic composite structures.

[0069] The present invention provides the following specific embodiments that can be combined with each other. For the same or similar concepts or processes, they may not be repeated in some embodiments.

[0070] Figure 1Flow chart of a failure analysis method for a thermoplastic composite laminate structure provided by an embodiment of the present invention. First of all, it should be noted that the in-plane stress of the thermoplastic composite includes elastic stress and shear plastic stress. The failure analysis method for the thermoplastic composite laminate structure provided by the embodiment of the present invention may include the following steps:

[0071] Step 1, establish an in-plane elastic damage model for the thermoplastic composite to obtain the stress-strain level of in-plane elastic damage; this step is for the elastic tensile and compressive stress-strain of a single layer;

[0072] Step 2, establish an in-plane shear elastic-plastic model for the thermoplastic composite to obtain the stress-strain level of in-plane shear elastic-plasticity; this step is for the shear elastic-plastic stress-strain of a single layer.

[0073] Both the above Step 1 and Step 2 are for a single layer to obtain the stress-strain level.

[0074] Step 3, determine the in-plane initial damage of the thermoplastic composite laminate structure and the form of stiffness degradation after the in-plane initial damage occurs according to the stress-strain levels obtained in Step 1 and Step 2;

[0075] Step 4, determine the interlayer initial damage of the thermoplastic composite laminate structure and the form of stiffness degradation after the interlayer initial damage occurs.

[0076] In addition, it is necessary to explain the assumption basis of the failure analysis method provided by the embodiment of the present invention:

[0077] a) Fiber and shear damage modes are decoupled;

[0078] b) The damage variables of the fiber in the 1 direction (set as the fiber direction) and the 2 direction (set as the direction perpendicular to the fiber direction) are different;

[0079] c) The damage of a single layer of material is irreversible, that is, the damage variable remains unchanged after unloading until a higher damage load is reapplied;

[0080] d) Damage propagation does not necessarily lead to final failure;

[0081] e) The total strain of a single layer is divided into elastic strain and plastic strain, which is different from that of thermosetting composites;

[0082] f) Plastic strain is only related to the in-plane shear response mainly based on the matrix;

[0083] g) Adopt a classical plastic model and apply the elastic domain function and the isotropic hardening law to calculate the effective stress of the damaged material;

[0084] h) Assume that the plastic strain increment is positive in the elastic domain function.

[0085] The following details the specific implementation of each step in the failure analysis method of the thermoplastic composite laminate structure provided by the embodiments of the present invention.

[0086] Step 1: Establish an in-plane elastic damage model for the thermoplastic composite

[0087] The specific implementation of this step is as follows: Under the condition of plane stress state, the model of the elastic stress-strain relationship with performance degradation of the thermoplastic composite is:

[0088]

[0089] where d1 is the damage variable in the fiber 1 direction, d2 is the damage variable in the fiber 2 direction, and d 12 is the shear damage variable; E1 is the elastic modulus of the laminate in the 1 direction, E2 is the elastic modulus of the laminate in the 2 direction; ε1 is the strain in the 1 direction, ε2 is the strain in the 2 direction, and ε 12 el is the shear strain; σ1 is the stress in the 1 direction, σ2 is the stress in the 2 direction, and σ 12 is the shear stress.

[0090] To distinguish between the tensile and compressive failure modes in the fiber direction, the above 1-direction damage variable and 2-direction damage variable can be rewritten as:

[0091]

[0092] where d + is the damage variable generated during the tensile process, and d - is the damage variable generated during the compression process.

[0093] Step 2: Establish an in-plane shear elastoplastic model for the thermoplastic composite

[0094] Since the total strain of the thermoplastic composite is equal to the elastic strain plus the plastic strain, i.e., ε = ε e + ε p , where the elastic strain ε e is given by the above formula (1). Under the plane stress model, it is assumed that there is only plastic strain in the shear strain, i.e., ε1 = ε2 = 0. Therefore, only ε 12 el in the above formula (1) is not zero.

[0095] Adopt the classical plastic model of the isotropic hardening law of conventional metal materials (plastic strain plus elastic strain), and the yield function is defined as:

[0096]

[0097] In the above formula (3), is the initial shear yield stress threshold, and R(ε 12 pl ) is an isotropic hardening function with respect to the plastic cumulative strain ε 12 pl . This function is a typical power-law function, and C and p are obtained by fitting the experimental shear stress-strain curve.

[0098] R(ε 12 pl ) = C(ε 12 pl ); (4) p ; (4)

[0099] As Figure 2 shown, it is a schematic diagram of a typical shear hardening curve provided in the prior art. As Figure 3 shown, it is a schematic diagram of the composite material shear stress-strain curve in the failure analysis method of the thermoplastic composite material laminated structure provided by the embodiment of the present invention.

[0100] Step 3: Determine the in-plane initial damage of the thermoplastic composite material laminated structure and the form of stiffness degradation after the in-plane initial damage occurs;

[0101] First, according to the stress-strain levels obtained in Step 1 and Step 2, determine the in-plane initial damage criterion of the thermoplastic composite material laminated structure. The determination method includes: respectively determining the initial damage criteria under each failure mode from the failure modes of radial fiber tensile failure, radial fiber compressive failure, circumferential fiber tensile failure, circumferential fiber compressive failure, and matrix in-plane shear failure.

[0102] The failure mechanism of the composite material is complex. The maximum stress material failure criterion is one of the most commonly used failure judgment criteria, which can comprehensively consider the effects of failure modes such as radial fiber tensile failure, radial fiber compressive failure, circumferential fiber tensile failure, circumferential fiber compressive failure, and matrix in-plane shear failure. The failure of the material is represented by the failure factor , and the corresponding failure criteria are as follows:

[0103] Failure criterion 1, the radial tensile failure factor for failure criterion in the radial fiber tensile mode is:

[0104]

[0105] Failure criterion 2, the radial compressive failure factor for failure criterion in the radial fiber compressive mode is:

[0106]

[0107] Failure criterion 3, the circumferential tensile failure factor for failure criterion in the circumferential fiber tensile mode is:

[0108]

[0109] Failure criterion 4. The warp compression failure factor for the failure criterion in the warp fiber compression mode is as follows:

[0110]

[0111] Failure criterion 5. The shear failure factor for the failure criterion in the matrix in-plane shear mode is as follows:

[0112]

[0113] In the above formulas, X t is the tensile strength in the fiber radial direction, and X c is the compressive strength in the fiber radial direction; Y t is the tensile strength in the fiber warp direction, and Y c is the compressive strength in the fiber warp direction; S 12 is the shear strength; and when each failure factor is equal to 1, initial failure (i.e., initial damage) occurs.

[0114] Secondly, after determining that initial in-plane damage occurs in the thermoplastic composite laminate structure according to the in-plane initial damage criterion, determine the in-plane damage stiffness degradation form.

[0115] After the material satisfies the failure criterion at a certain integration point, the material undergoes initial failure, but the stiffness does not immediately drop to 0. The mechanical properties of the material are degraded. The progressive failure analysis of the composite material is usually represented by the stiffness degradation of the material. The failure analysis method provided in the embodiments of the present invention is based on the fracture toughness of the material. On the one hand, according to the previous test data, the damage variables d1 and d2 of the tensile / compressive failure of the material are linearly attenuated; on the other hand, for thermoplastic composites with large shear strains, linear attenuation is not applicable. Therefore, the material shear damage variable d 12 adopts an attenuation method fitted based on test data.

[0116] In addition, if finite element calculation is used, after damage occurs to the smallest element of the finite element mesh, a local strain reduction phenomenon will occur, which will lead to strain localization, making the energy dissipation during the calculation too dependent on the mesh size. Therefore, it is necessary to introduce the element characteristic length L to reduce the sensitivity of the material stiffness degradation to the element mesh size. The stiffness degradation methods for the three quantities are described separately as follows:

[0117] (1) In-plane tensile failure stiffness degradation:

[0118] The in-plane tensile stiffness degradation is a linear degradation form based on the fracture toughness of the material. The specific degradation form is as follows:

[0119]

[0120] In Equation (10), ε is the current strain, ε 0 is the strain at damage initiation; ε f+ is the ultimate tensile strain; as Figure 4 shown, it is a schematic diagram of the constitutive relationship of in-plane tensile stiffness degradation in the embodiments of the present invention.

[0121] (2) In-plane compressive failure stiffness degradation:

[0122] The compressive stiffness degradation is similar to the tensile law, and it is also a linear degradation form based on the fracture toughness of the material. However, when the compressive strain reaches the ultimate strain, it still has a load-bearing capacity, and the damage variable reaches the maximum d max , and the specific degradation form is:

[0123]

[0124] In Equation (11), ε is the current strain ε 0 is the strain at damage initiation; ε f- is the ultimate compressive strain; d max is the maximum damage variable in compressive damage failure.

[0125] (3) In-plane shear failure stiffness degradation, that is, the degradation of the material shear damage variable d 12 :

[0126] After the initial shear damage occurs, the equivalent shear stress is:

[0127]

[0128] For thermoplastic composites with large shear strains, linear attenuation is not applicable, and the logarithm of the effective shear stress is linearly related to the shear damage variable d 12 , as Figure 5 shown, it is a schematic diagram of the degradation of the in-plane shear damage variable in the embodiments of the present invention, where the shear initiation damage stress S can be calculated from the damage variable and the shear stress, and d 12 can be obtained from the shear cyclic loading test.

[0129] That is

[0130] Here, α 12 is Figure 5 in the linear fitting slope of the curve.

[0131] Step 4, determine the initial interlayer damage of the thermoplastic composite laminate structure and the stiffness degradation form after the initial interlayer damage occurs.

[0132] Before explaining the initial interlayer damage and the form of stiffness degradation after the initial interlayer damage in this step, the interlayer structural characteristics and the interlayer damage constitutive model will be described first.

[0133] Based on the interlayer structure with an adhesive layer, a bilinear interlayer damage constitutive model is selected. The finite element unit of the adhesive layer simulated by CZM can bear the normal stress t n and the shear stress t s 、t t , and the constitutive relationship is linear elastic before its damage failure. The stress-strain relationship of the cohesive zone of the adhesive layer is:

[0134]

[0135] When damage occurs in the adhesive layer element, the material shows a softening stage of damage. At this time, the constitutive relationship is:

[0136]

[0137] In the formula, K i (i = n, s, t) is the elastic modulus in each stress direction, δi (i = n, s, t) is the strain in each stress direction, D is the damage coefficient, and its value ranges from 0 to 1. When D is 0, it means that the adhesive layer element has not suffered damage failure. When D is 1, it means that the adhesive layer element has completely failed and lost its bearing capacity.

[0138] It can be seen from the description of the adhesive layer constitutive model that there are mainly two damage failure criteria for the adhesive layer interface element: (1) the damage initiation criterion for determining whether the adhesive layer starts to have adhesive layer element failure; (2) the damage propagation criterion for determining whether the adhesive layer element has completely failed. In the embodiments of the present invention, the quadratic nominal traction criterion is selected as the damage initiation criterion. Specifically:

[0139]

[0140] In the formula, t n 0 、t s 0 、t t 0 are the strengths of the interfaces in each orthogonal direction respectively.

[0141] The selection of the damage propagation evolution criterion for the adhesive layer element is based on the energy-based B-K criterion. Specifically:

[0142]

[0143] Among them, G T =Gn +G s +G t ; G S = G s +G t .

[0144] In the above formula, G n , G s , G t are the energies of the work done by the normal stress, the first shear stress (longitudinal), and the second shear stress (transverse), respectively; are the critical energy release rates in the I direction (normal) and the II direction (shear), respectively, and G C is the total energy at failure.

[0145] As Figure 6 shown, it is a schematic diagram of the constitutive model of the adhesive layer in the embodiment of the present invention.

[0146] The failure analysis method of the thermoplastic composite laminate structure provided by the embodiment of the present invention is specifically a brand-new thermoplastic progressive failure analysis method for composites. This failure analysis method obtains the stress-strain levels of in-plane elastic damage and in-plane shear elastoplasticity by respectively establishing an in-plane elastic damage model and an in-plane shear elastoplastic model of the thermoplastic composite. Subsequently, based on the above stress-strain levels, not only can the in-plane initial damage of the thermoplastic composite laminate structure and the form of stiffness degradation after in-plane initial damage be determined, but also the interlayer initial damage of the thermoplastic composite laminate structure and the form of stiffness degradation after interlayer initial damage can be determined. The technical solution of the embodiment of the present invention effectively predicts the progressive failure process of the composite under quasi-static and impact loads, providing a basis for the design, analysis, and verification of aircraft thermoplastic composite structures.

[0147] The following uses a specific embodiment to schematically illustrate the failure analysis method of the thermoplastic composite laminate structure provided by the embodiment of the present invention.

[0148] As Figures 7 to 10 shown, among them, Figure 7 is a schematic diagram of the finite element calculation model of the AS4D / PEEK open-hole laminate, Figure 8 is a schematic diagram of the comparison of the simulation test results of the AS4D / PEEK open-hole laminate under compressive load, Figure 9 is a schematic diagram of the impact analysis result of the thermoplastic composite - overall stress distribution, Figure 10 is a schematic diagram of the impact analysis result of the thermoplastic composite - the failure situation of the cohesive element.

[0149] The progressive failure analysis of the thermoplastic composite in this specific embodiment.

[0150] 1. The geometric information of the thermoplastic composite AS4D / PEEK open-hole laminate is as follows:

[0151] Geometric dimensions of the open-hole plate: 300 mm * 36 mm, with a hole diameter of 6.0 mm

[0152] Ply layup: [(+45) / 0 / (-45) / 90]4s, with a thickness t = 4.0 mm.

[0153] Based on the above information, the in-plane initial damage and the rigid degradation form after the in-plane initial damage of the thermoplastic composite AS4D / PEEK open-hole laminate can be obtained.

[0154] 2. Establish a finite element calculation model for the AS4D / PEEK open-hole laminate

[0155] Establish a finite element model for the thermoplastic composite AS4D / PEEK open-hole laminate according to the geometric information. As Figure 7 shown, the continuous shell element S4R is used for the ply material, and the Cohesive element is used for the adhesive layer. The element type is C3D8R. The adhesive layer and the ply are connected by co-nodes. In the software, the stiffness degradation index SDEG (Scalar Stiffness Degradation) of the adhesive layer is defined to simulate the damage and its propagation of debonding. When SDEG > 0, it indicates that damage begins to occur in the adhesive layer, and when SDEG = 1, the adhesive layer completely fails.

[0156] 3. Compare and analyze the test results. As Figure 8 shown, it is the comparison of the simulation test results

[0157] Comparing the simulation test results of the open-hole compression laminate, the damage forms are mainly edge delamination cracking and fiber extrusion fracture of the hole. Under the compression load, delamination cracking and fiber extrusion phenomena first occur at the hole edge. As the compression load continuously increases, the delamination damage gradually expands, and the fiber extrusion damage continuously increases until the specimen is extruded and broken.

[0158] 4. Impact analysis of thermoplastic composites (dynamic analysis)

[0159] The modeling method is the same as that of the AS4D / PEEK open-hole laminate. The continuous shell element S4R is used for the ply material, and the Cohesive element is used for the adhesive layer. The element type is C3D8R. The analysis results are shown in Figure 9 (stress diagram) and Figure 10 shown (damage diagram).

[0160] Although the embodiments disclosed in the present invention are as described above, the content described is only an embodiment adopted for the convenience of understanding the present invention and is not used to limit the present invention. Any person skilled in the art within the scope of the present invention can make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in the present invention. However, the scope of patent protection of the present invention shall still be subject to the scope defined by the appended claims.

Claims

1. A failure analysis method for a thermoplastic composite laminate structure, characterized in that, The in-plane stress of the thermoplastic composite includes elastic stress and shear plastic stress; The failure analysis method includes: Step 1: Establish an in-plane elastic damage model of the thermoplastic composite to obtain the stress-strain level of in-plane elastic damage; Step 2: Establish an in-plane shear elastic-plastic model of the thermoplastic composite to obtain the stress-strain level of in-plane shear elastic-plasticity; Step 3: Determine the in-plane initial damage of the thermoplastic composite laminate structure and the form of stiffness degradation after in-plane initial damage according to the stress-strain levels obtained in Step 1 and Step 2; Step 4: Determine the interlaminar initial damage of the thermoplastic composite laminate structure and the form of stiffness degradation after interlaminar initial damage; Among them, Step 3 includes: Step 31: Determine the in-plane initial damage criterion of the thermoplastic composite laminate structure according to the stress-strain levels obtained in Step 1 and Step 2; Step 32: Determine the form of in-plane damage stiffness degradation after in-plane initial damage of the thermoplastic composite laminate structure according to the in-plane initial damage criterion; The initial damage criterion determined in Step 31 includes: From the failure modes of radial fiber tensile failure, radial fiber compressive failure, circumferential fiber tensile failure, circumferential fiber compressive failure, and matrix in-plane shear failure, determine the initial damage criterion for each failure mode respectively; In the thermoplastic composite laminate structure, there is an adhesive layer between each layer. Step 4 includes: Step 41: Determine the interlaminar initial damage criterion of the thermoplastic composite laminate structure; Step 42: Determine the form of interlaminar damage stiffness degradation after initial damage of the adhesive layer of the thermoplastic composite laminate structure according to the interlaminar initial damage criterion.

2. The failure analysis method of the thermoplastic composite laminate structure according to claim 1, characterized in that, Step 1 includes: Under the condition of plane stress state, the model of the elastic stress-strain relationship of the performance degradation of the thermoplastic composite is: where d1 is the damage variable in the fiber 1 direction, d2 is the damage variable in the fiber 2 direction, and d 12 is the shear damage variable; E1 is the elastic modulus of the laminate in the 1 direction, E2 is the elastic modulus of the laminate in the 2 direction; ε1 is the strain in the 1 direction, ε2 is the strain in the 2 direction, and ε 12 el is the shear strain; σ1 is the stress in the 1 direction, σ2 is the stress in the 2 direction, and σ 12 is the shear stress; and the damage variables in the 1 direction and 2 direction are: Among them, d + is the damage variable generated during the stretching process, and d - is the damage variable generated during the compression process.

3. The failure analysis method of the thermoplastic composite laminate structure according to claim 2, characterized in that, The total strain of the thermoplastic composite is equal to the elastic strain plus the plastic strain. Step 2 includes: According to the classical plastic model of the isotropic hardening law and based on the setting that only the shear strain has plastic strain, the in-plane shear elastic-plastic model of the thermoplastic composite is obtained as: R(ε 12 pl ) = C(ε 12 p l)p ; where, R(ε 12 pl ) is an isotropic hardening function with respect to the plastic cumulative strain ε 12 pl , and C and p are obtained by fitting the experimental shear stress-strain curve.

4. The failure analysis method of the thermoplastic composite laminate structure according to claim 3, characterized in that, The initial damage criterion for each failure mode in Step 31 includes: Failure criterion 1, the radial tensile failure factor for failure criterion in the radial fiber tensile mode is: Failure criterion 2, the radial compressive failure factor for failure criterion in the radial fiber compressive mode is: Failure criterion 3, the circumferential tensile failure factor for failure criterion in the circumferential fiber tensile mode is: Failure criterion 4, the circumferential compressive failure factor for failure criterion in the circumferential fiber compressive mode is: Failure criterion 5, the shear failure factor for failure criterion in the matrix in-plane shear mode is: Among them, when each failure factor is equal to 1, initial failure occurs; X t is the tensile strength in the radial direction of the fiber, X c is the compressive strength in the radial direction of the fiber; Y t is the tensile strength in the weft direction of the fiber, Y c is the compressive strength in the weft direction of the fiber; S 12 is the in-plane shear strength.

5. The failure analysis method of the thermoplastic composite laminate structure according to claim 4, characterized in that, The form of in-plane stiffness degradation of the thermoplastic composite laminate structure determined in Step 32 includes: The in-plane tensile stiffness of the thermoplastic composite degrades into a linear degradation form based on the fracture toughness of the material; The in-plane compressive stiffness of the thermoplastic composite degrades into a linear degradation form based on the fracture toughness of the material; The in-plane shear failure stiffness degradation of the thermoplastic composite material follows an attenuation pattern fitted based on experimental data.

6. The failure analysis method of the thermoplastic composite material laminated structure according to any one of claims 1 to 5, characterized in that, The interlayer initial damage criterion in step 41 includes: The damage initiation criterion for determining whether the adhesive layer starts to experience adhesive layer element failure is: where t n is the normal stress that the finite element unit of the adhesive layer can withstand, and t s , t t are the shear stresses that the finite element unit of the adhesive layer can withstand; t n 0 , t s 0 , t t 0 are the strengths of the interfaces in each orthogonal direction, respectively.

7. The failure analysis method of the thermoplastic composite laminate structure according to claim 6, characterized in that The interlayer damage stiffness degradation form in step 42 The damage propagation criterion for determining whether the adhesive layer element is completely failed and damaged is: Among them, G T = G n + G s + G t ; G S = G s + G t ; G n and G s and G t are the energies that do work on the normal stress, the first shear stress, and the second shear stress, respectively; are the normal critical energy release rate and the shear critical energy release rate, respectively. G C is the total energy at failure.

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