Method for manufacturing composite material components, including fatigue design.

Abstract

The present invention provides a method for manufacturing a component (1) made of a composite material, which includes one or more plies (2,3) that are associated with each other. [Solution] The method comprises a series of steps (4) for fatigue design of a member (1), namely (A) a first step in which a discretized model (5) is generated through a finite element model of the member (1), wherein in the discretized model (5), at least a first ply (2) and optionally at least a second ply (3) are divided into two or more first parts (6) and two or more second parts (7), respectively; (B) a second step in which the locations of one or more first damage initiation sites (8) and one or more second damage initiation sites (9) are defined within each of the two or more first parts (6) and within each of the two or more second parts (7), respectively; (C) a third step in which fatigue strength parameters are assigned to each damage initiation site; and (D) a fourth step in which a load history to be simulated for the member is established based on specific load conditions, the total number of cycles (NC) to be simulated is divided into discrete cycle blocks, and load conditions are assigned to each cycle block.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for manufacturing a member made of a composite material, comprising a step of fatigue design.

[0002] As used herein, the term "composite material member" means an artifact comprising one or more plies reinforced with, for example, continuous fibers, discontinuous fibers, or particulate fibers, which are associated with one another according to a series of specific superpositions such that the respective reinforcements are oriented in a specific manner relative to a reference direction, and the series of superpositions of the plies is referred to as a "laminate".

[0003] As used herein, the term "lay-up" means a series of information intended to define the configuration of a laminate, and the above information may include, for example, the matrix material of each ply, the reinforcement material of each ply, the elastic properties of each ply, the orientation of the reinforcement of each ply relative to the reference direction, the thickness of each ply, and a series of superpositions of the plies. PRIOR ART DOCUMENTS PATENT DOCUMENTS

[0004] PATENT DOCUMENT 1 European Patent No. 2803968 Specification NON-PATENT DOCUMENTS

[0005] NON-PATENT DOCUMENT 1 Carraro PA, Quaresimin M, A damage-based model for crack initiation in unidirectional composites under multiaxial cyclic loading, Composites Science and Technology 2014; 99:154-163 NON-PATENT DOCUMENT 2 Maragoni L, Carraro PA, Quaresimin M, A novel method to include crack-induced delamination in a fatigue damage predictive procedure for composite laminates, Composites Science and Technology 2023; 238:110011 [Non-Patent Document 3] Carraro PA, Quaresimin M, A stiffness degradation model for cracked multidirectional laminates with cracks in multiple layers, International Journal of Solids and Structures 2015; 58:34-51 [Non-Patent Document 4] Carraro PA, Maragoni L, Quaresimin M, Stiffness degradation of symmetric laminates with off-axis cracks and delamination: an analytical model, International Journal of Solids and Structures 2021; 213:50-62 [Overview of the Initiative]

[0006] The method according to the present invention can be used to manufacture various types of structural elements, such as wind turbine blades, bicycle frames, pressure vessels, and vehicle or aircraft components.

[0007] When subjected to time-varying loads, composite laminates gradually deteriorate. This gradual deterioration means that the stiffness of the laminate decreases from the first load application cycle, while the final failure of the component (separation into two or more parts) may occur only after a very large number of load cycles (sometimes millions).

[0008] It should be noted that the main damage events in composite material laminates may include matrix cracks, delamination (separation between adjacent plies), and fracture of reinforcing materials.

[0009] Currently, a method for manufacturing composite material laminates is known that uses a so-called "damage evolution" model and an initial fatigue design step based on a so-called "damage-tolerant" approach.

[0010] Fatigue design based on a damage tolerance approach is carried out while tolerating the presence of damage events, but it should be noted that this is conditional on these damage events not reducing the stiffness of the member below a certain threshold, for example, or impairing the member's ability to withstand a given operating load.

[0011] It should also be noted that the damage progression model is a model that makes it possible to predict both the change in stiffness over time and the fatigue life of composite material laminates.

[0012] Patent document 1, held by Siemens, describes a method for manufacturing structural elements made of composite materials, including, for example, fatigue design for predicting the fatigue life of a structure. This fatigue design involves several steps. In the first step, the structure is modeled by a series of calculation points. For each point, the stresses and deformations caused by the load cycle, as well as the hysteresis branches that define them, are determined. Next, the cumulative damage due to the load cycle is predicted and recorded. For this prediction, first, the change in stress along a portion of the hysteresis branches is calculated as a function of the load that changes over time using a hysteresis operator, and second, the change in damage is calculated using the change in stress and the recorded cumulative damage. Next, the change in properties, including the stiffness of the structure, is also calculated. Then, based on these changes in properties, further changes in stress and deformation are calculated, and newly adapted hysteresis branches are determined. Next, further changes in stress along further portions of the adapted hysteresis branches are calculated as a function of the load that changes over time.

[0013] At the end of the process, if no fatigue failure occurs, the structure is manufactured with the materials, properties, and dimensions specified in the model. Otherwise, the model is adapted, and the life performance prediction is repeated.

[0014] Patent Document 1 describes how finite element analysis is used to determine the stress state in a structure, such as a composite structure. A series of loads are applied to the structure, and in each iteration, a continuous damage parameter is calculated for each element based on the local stress. Based on this damage parameter, the stiffness of the material is updated, and the occurrence of final failure is evaluated.

[0015] However, the method described in the Siemens patent mentioned above has several limitations.

[0016] In practice, this method predicts the stiffness of a laminate by relating it through an empirical relationship to a single continuous damage parameter (continuum damage mechanics approach), without considering the presence of individual damage events such as matrix cracks, delamination, and reinforcement failure. This type of approach first requires a series of costly experiments to obtain the relationship between the damage parameter and the elastic properties of the laminate, and this relationship can also vary depending on the layup of the laminate and the type of load it is subjected to. Furthermore, because this approach uses a continuous relationship between the number of cycles and the stiffness of the laminate, it assumes that the damage is uniformly distributed within a given physical region (such as an element or member in finite element analysis). This does not allow for accurate prediction of fatigue damage to structural elements, especially when the shape of the structural element is relatively irregular or when the element contains discontinuities such as holes or surface irregularities. Discontinuities are important in real-world applications, as they are areas where very steep high stress gradients exist, causing localization of damage.

[0017] The main objective of this invention is to overcome the aforementioned drawbacks, and in particular, to manufacture composite material components from fatigue life designs that enable more accurate damage prediction by predicting individual damage events as clearly defined entities in space and time ("discrete damage mechanics" approach) and correlating the stiffness of the laminate with their presence. This approach can provide accurate predictions even in the presence of very steep stress gradients. A further advantage is that, given that some basic material properties are known, the behavior of the component can be predicted even when the laminate layup and loading conditions change.

[0018] Within the scope of the above-mentioned problems, the object of the present invention is to accelerate the design and, consequently, the manufacturing of composite material components optimized to withstand loads that change over time, by providing accurate prediction of the progression of physical damage, and further reducing the time and cost associated with experimental characterization of materials and design verification testing.

[0019] One aspect of the present invention relates to a method for producing a composite material member having the features of claim 1.

[0020] Further advantageous features of the present invention are set out in the dependent claims.

[0021] The features and advantages of the present invention will become more apparent from the following exemplary and non-limiting description, with reference to the accompanying schematic drawings of an embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] [Figure 1] It is a diagram schematically showing a regularly shaped member having two plies by way of example. [Figure 2] It is a diagram schematically showing a discretization model generated from the member of FIG. 1, for example using the finite element method. [Figure 3] It is a diagram schematically showing the discretization model of FIG. 2, with the damage initiation site highlighted. [Figure 4] It is a diagram schematically showing a block diagram of a method according to the present invention. [Figure 5] It is a diagram schematically showing step (A) shown in the block diagram of FIG. 4. [Figure 6] It is a diagram schematically showing step (B) shown in the block diagram of FIG. 4. [Figure 7] It is a diagram schematically showing step (C) shown in the block diagram of FIG. 4. [Figure 8] It is a diagram schematically showing step (D) shown in the block diagram of FIG. 4. [Figure 9] It is a diagram schematically showing sub-step (D1) shown in the block diagram of FIG. 8. [Figure 10] It is a diagram schematically showing sub-step (D2) shown in the block diagram of FIG. 8. [Figure 11] It is a diagram schematically showing sub-step (D3) shown in the block diagram of FIG. 8. [Figure 12] It is a diagram schematically showing sub-step (D4) shown in the block diagram of FIG. 8. [Modes for carrying out the invention]

[0023] The present invention relates to a method for manufacturing a composite material member 1 comprising at least a first ply 2 and optionally at least a second ply 3 that are associated with one another.

[0024] Advantageously, the first ply 2 and / or the second ply 3 are reinforced, for example, with continuous fibers, discontinuous fibers, or particulate fibers appropriately oriented with respect to the reference direction 11. As described above, it should be noted that the method according to the present invention can also be used to manufacture structural elements comprising a single ply or structural elements comprising multiple plies.

[0025] In this specification, the configuration of the laminate constituting member 1 (also called "layup") is defined, for example, by a series of one or more plies 2, 3 constituting the member, the orientation of the reinforcing material of each ply 2, 3 with respect to a reference direction 11, the thickness of each ply 2, 3, the matrix material, the reinforcing material of each ply 2, 3 (e.g., continuous fibers), and the elastic properties of each ply.

[0026] The method according to the present invention includes a series of steps 4 in which a fatigue design of member 1 is performed.

[0027] The above series of steps 4 includes a first step A in which a discretized model 5 is generated through, for example, a finite element model of member 1, in which a first (or single) ply 2 and / or a second ply 3 are divided into two or more first parts 6 and two or more second parts 7, respectively.

[0028] In an advantageous embodiment of the method according to the present invention, a virtual three-dimensional model of member 1 (not shown in the accompanying drawings) can be generated using any commercially available three-dimensional modeling software (CAD).

[0029] In the advantageous embodiment described above, first information is provided to finite element software (SW-FEM) through a virtual three-dimensional model, with the aim of describing the overall shape of member 1. Next, the virtual three-dimensional model can be discretized through the finite element software SW-FEM according to finite element discretization, thereby obtaining a discretized model 5.

[0030] In another advantageous embodiment of the method according to the present invention, finite element modeling can be performed entirely within the finite element software SW-FEM.

[0031] In an advantageous embodiment, within the finite element software SW-FEM, second information relating to the layup of the laminate 1, and third information intended to describe the elastic properties of the first ply 2 and the second ply 3, can be assigned to the discretized model 5. The third information may include, for example, the Young's modulus, shear modulus, Poisson's ratio, and shear modulus for each of the plies 2 and 3.

[0032] Advantageously, the following are stored in the first database DB1: first information intended to describe the overall shape of member 1, fourth information intended to describe the finite element discretization of discretization model 5, i.e., the division into two or more first parts 6 and two or more second parts 7, second information concerning the layup of laminate 1, and third information intended to describe the elastic properties of the first ply 2 and the second ply 3.

[0033] The series of steps 4 described above further includes a second step B, which defines the locations of one or more first damage initiation sites 8 and one or more second damage initiation sites 9 within each of the two or more first parts 6 and each of the two or more second parts 7, respectively.

[0034] In an advantageous embodiment, the locations of one or more first damage initiation sites 8 and one or more second damage initiation sites 9 in each of two or more first parts 6 and each of two or more second parts 7 are defined based on fourth information intended to describe the finite element discretization of the discretization model 5 stored in a first database DB1, via a suitable computational tool SW-CAL. For example, the locations of one or more first damage initiation sites 8 and one or more second damage initiation sites 9 may be the same as the centroids of one or more first subdivisions 61 and one or more second subdivisions 71, respectively, and the shape of the subdivisions may be determined by the user.

[0035] The locations of one or more first damage initiation sites 8 and one or more second damage initiation sites 9 are advantageously stored in the first database DB1.

[0036] The above locations can be arbitrarily selected and may refer to, for example, the start of a matrix crack, delamination, or reinforcing failure. Existing damage events can also be inserted into the structure as needed.

[0037] The series of steps 4 described above further includes a third step C, which assigns fatigue strength parameters to the first damage initiation site 8 and the second damage initiation site 9, respectively, based on a fifth piece of information intended to describe the fatigue behavior of the material, for example. This fifth piece of information is stored in a second database DB2, which is interconnected with the first database DB1.

[0038] In advantageous embodiments, the fifth piece of information may include the relationship between fatigue intensity and the number of cycles to the onset of a damage event (SN curve), the statistical distribution of fatigue intensity, the initial dimensions of the damage event, and the damage progression rule (e.g., the relationship between the progression rate and the rate of elastic energy release).

[0039] The sequence of steps 4 further includes a fourth step D in which the load history to be simulated on the member is established, the total number of simulated cycles NC is divided into discrete cycle blocks, and load conditions are assigned to each cycle block. The fewer cycles each block contains, the more accurate the damage prediction becomes, but the analysis time increases.

[0040] For each cycle block, a calculation is performed that includes the following steps: -(D1) For each element of the discretized model, calculate one or more load parameters. -Then, perform the following steps in parallel as needed. -(D2) For each damage initiation site, the damage initiation parameter PID is calculated using the fatigue damage initiation model M1. If the parameter reaches a predetermined initiation value for one or more initiation sites, a damage event is placed at the initiation site. Furthermore, if the dimensions of the placed damage event exceed the periphery of the element where the damage initiation site is located, the excess portion of the damage event is placed on an adjacent element. -(D3) For each damage event initiated in any previous cycle block, the damage progression control parameter PCPD is calculated using the fatigue damage progression model M3, and then the dimensions of each damage event are updated. If the dimensions of the damage event after progression exceed the periphery of the element where the end of the damage event was located before progression, the excess portion is placed in an adjacent element. -(D4) Using the appropriate model M4, calculate the updated elastic properties of each portion (6,7) of each ply based on the damage events located at that portion (6,7).

[0041] Step D is performed in detail as follows: The calculation of one or more load parameters for each element in substep D1 is performed through a finite element analysis performed on discretized model 5, which applies the load conditions related to the cycle block under analysis to discretized model 5 and is based on the elastic properties (or initial properties, if calculations are performed for the first cycle block) of each part of each ply (first ply 2 and second ply 3) calculated at the end of the previous cycle block. The load parameters are stored in a third database DB3.

[0042] Preferably, in substep D2, a damage initiation parameter PID is calculated for each of one or more first damage initiation sites 8 and each of one or more second damage initiation sites 9, using an appropriate damage initiation model M1 for fatigue damage and a stress redistribution model M2 in the presence of damage, based on the load parameters acting on the element where the damage initiation site is located. Damage events to be considered for stress redistribution and PID calculations are damage events within the element where the initiation site is located, and, if necessary, damage events within adjacent elements up to a distance that can be set by the user, for example, based on the characteristics of the laminate. For one or more of the first damage initiation sites 8 or one or more of the second damage initiation sites 9, when the initiation parameter reaches a determined initiation value, the damage event is placed at the initiation site via information adapted to define the location of one or more parts of the damage event in one or more parts of the relevant ply.

[0043] In conclusion, in substep D2, all damage events that started within the cycle block being analyzed are placed.

[0044] The above information is collected in the fourth database, DB4.

[0045] Preferably, in substep D3, for each damage event initiated in the previous cycle block, the damage progression control parameter PCPD is calculated using the fatigue damage progression model M3 and the stress redistribution model M2 in the presence of damage. Damage events to be considered for stress redistribution and PCPD calculations are damage events located in the element where the end of the damage event was located before progression, and, if necessary, damage events in adjacent elements up to a distance that can be set by the user based on the characteristics of the laminate. Based on the progression, the dimensions of each damage event initiated in the previous cycle block (e.g., the position of the apex in the case of a crack) are updated. This information is collected in a fourth database DB4.

[0046] If the dimensions of a propagated damage event exceed the periphery of the element where the end of the damage event was located before propagation, the excess portion is placed in an adjacent element. For example, a propagated crack may have a vertex whose coordinates are outside the periphery of the element where it ended before propagation. In this case, the excess distance beyond the periphery is reflected in an adjacent element.

[0047] Preferably, substep D4 calculates the first updated elastic properties and the second updated elastic properties (or properties at the end of the cycle block being analyzed) for each portion, based on the model M4 described above for calculating the apparent elastic properties based on damage events located in each portion of the first ply 2 and optionally the second ply 3.

[0048] In practice, the elastic properties of each ply are updated based on the current damage. For this purpose, Model M4 is provided as input to calculate the apparent elastic properties of the plies in the laminate. The elastic properties of the damaged plies of each element are updated within the finite element software based on the newly calculated values.

[0049] Step D specifies that substeps D1 to D4 are repeated until an unacceptable condition is reached or the user-specified number of cycles NC is reached. Furthermore, in step D, known external models M1 to M4 are used as input to the method. For example, model M1 for matrix crack initiation and delamination initiation are described in Non-Patent Literature 1 and Non-Patent Literature 2, respectively. For example, models M2 and M4 are described in Non-Patent Literature 3 and Non-Patent Literature 4. Model M3 can be expressed, for example, by the relationship between the propagation rate of the damage event and the rate of elastic energy release.

[0050] Finally, step E specifies that member 1 is manufactured when a certain number of load cycles are reached without any specific non-acceptable conditions occurring.

[0051] For the purposes of the present invention, non-acceptable conditions may mean, for example, failure of a reinforcing material in any element of the member, or a decrease in member stiffness to below a certain value, or the initiation of a certain number (which may be as few as one) of damage events.

[0052] During the first calculation cycle, the initial elastic properties are those of a ply in an undamaged state, or those with existing damage already present. For the cycles following the first calculation cycle, the initial elastic properties are equal to the updated elastic properties calculated during substep (D4) of the previous cycle.

[0053] Thus, the method according to the present invention has been found to solve the above-mentioned problems and objectives.

[0054] In fact, this method tracks the location and dimensions of individual damage events over time, and allows for their interactions between elements (interactions in terms of both the initiation and progression of damage events).

[0055] This enables more accurate damage prediction and allows for better handling of areas with high stress gradients (e.g., holes), which are important in real-world applications.

[0056] These regions are characterized by significant localization of damage that cannot be included by the continuous damage method.

[0057] Compared to discrete damage methods available for complex structures, this method allows numerical stress calculation tools to interact with analysis models (M1-M4) for predicting individual damage events. This method manages the stress analysis of the structure (which remains in the numerical model) and the progression of damage (the information of which is contained in an appropriate database) in separate environments. However, these environments remain closely interconnected because models M1-M4 use the results of the numerical analysis and provide the numerical analysis with updated local elastic properties based on the existing damage. This separate management significantly reduces computation time compared to currently available discrete damage prediction methods for complex structures.

Claims

1. A method for manufacturing a composite material member (1) consisting of one or more plies (2, 3) that are associated with each other, The method is characterized by including a series of steps (4) for fatigue design of the member (1), the series of steps (4) being: (A) For example, a first step in which a discretized model (5) is generated through a finite element model of the member (1), wherein in the discretized model (5), at least a first ply (2) and optionally at least a second ply (3) are divided into two or more first parts (6) and two or more second parts (7), (B) A second step in which the locations of one or more first damage initiation sites (8) and one or more second damage initiation sites (9) are defined within each of the two or more first parts (6) and within each of the two or more second parts (7), (C) A third step in which fatigue strength parameters are assigned to each injury initiation site (8, 9), (D) A fourth step in which a simulated load history is established for the member based on specific load conditions, the total number of simulated cycles (NC) is divided into discrete cycle blocks, and load conditions are assigned to each cycle block, For each cycle block, the following substeps are performed: - (D1) A substep in which one or more load parameters are calculated as resulting forces and moments for each element of the discretized model. Next, - (D2) For each damage initiation site, calculate the damage initiation parameter PID using the fatigue damage initiation model (M1), and if the damage initiation parameter reaches a predetermined initiation value for one or more initiation sites, place a damage event at the damage initiation site, and if the dimensions of the placed damage event exceed the periphery of the element where the damage initiation site is located, place the excess portion of the damage event on an adjacent element. And, - (D3) For each damage event initiated in any previous cycle block, the damage progression control parameter (PCPD) is calculated using the fatigue damage progression model (M3), then the dimensions of the damage event are updated, and if the dimensions of the damage event after progression exceed the periphery of the element where the end of the damage event was located before progression, the excess portion is placed on an adjacent element. Substeps which are performed in parallel with each other as needed, - (D4) A substep of calculating the updated elastic properties of each portion (6, 7) of each ply based on the damage events located in each portion (6, 7) of the ply, using an appropriate model (M4). The fourth step involves performing a calculation that includes, (E) A step of manufacturing the member (1) when a specific number of cycles (NC) is reached without any specific non-acceptable conditions occurring, Methods that include...

2. The calculation of one or more load parameters for each element in substep (D1) is performed, for example, through analysis using the finite element method. In the analysis, the elastic properties of the portion of the ply calculated at the end of the previous cycle block (or, if the calculation is performed for the first cycle block, the initial properties) are used, and the load conditions related to the cycle block under analysis are applied to the discretized model (5). The method according to claim 1.

3. The first step (A) and the substep (D1) are performed using first finite element software, and the second step (B) and the third step (C), as well as the substeps (D2), (D3), and (D4) are performed using a different computational tool than the structural analysis step performed using the first finite element software. The method according to claim 1.

4. The calculation of the damage initiation parameter (PID) in substep (D2) is performed using an appropriate fatigue damage initiation model (M1) and a stress redistribution model (M2) in the presence of a damage event, wherein the damage event to be considered for stress redistribution and PID calculations is a damage event within the element where the damage initiation site is located, and, if necessary, a damage event within an adjacent element up to a user-configurable distance based on the characteristics of the laminate. The method according to one or more of claims 1 to 3.

5. The calculation of the damage progression control parameter (PCPD) in substep (D3) is performed using a fatigue damage progression model (M3) and a stress redistribution model (M2) in the presence of a damage event, wherein the damage event to be considered for stress redistribution and PCPD calculations is a damage event located in the element where the end of the damage event was located before progression, and, if necessary, a damage event located in an adjacent element up to a user-configurable distance based on, for example, the characteristics of the laminate. The method according to one or more of claims 1 to 4.

6. The aforementioned non-acceptable conditions are that, before reaching a certain number of cycles, events occur such as failure of a reinforcing material in any element of the member, a decrease in member stiffness to below a certain value, or the initiation of a certain number of damage events. The method according to one or more of claims 1 to 5.

7. In the first step (A) above, information relating to the discretized model (5), such as first information relating to the shape of the entire laminate, second information relating to the layup of the member (1), and third information intended to describe the initial elastic properties (e.g., Young's modulus, Poisson's ratio, and shear modulus) of the first ply (2) and optionally the second ply (3), is provided in the finite element software SW-FEM. The method according to claim 1.

8. In the second step (B), the positions of the one or more first damage initiation sites (8) and the one or more second damage initiation sites (9) may be the same as the center of gravity of one or more first subdivisions (61) and, if necessary, the center of gravity of one or more second subdivisions (71), and the shapes of the first and second subdivisions may be determined by the user. The method according to claim 1.

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