An equal-strength scale design method for aircraft connecting structure
By calculating the strength equivalence similarity conditions of rivet size and position in the scaled-down design of aircraft connection structures, the problem that traditional scaled-down models cannot accurately simulate the strength of prototype connection structures is solved, thus achieving accurate verification of scaled-down models and reducing testing costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NORTHWESTERN POLYTECHNICAL UNIV
- Filing Date
- 2023-06-13
- Publication Date
- 2026-07-24
Smart Images
Figure CN116776465B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of aircraft structure / strength testing technology, specifically to a method for scaled-down design of aircraft connection structures with equal strength. Background Technology
[0002] Large-scale engineering structural strength impact tests, exemplified by aircraft crash tests, are noteworthy but costly. If the strength of a prototype structure could be predicted through scaled-down tests, thus replacing prototype tests, testing costs could be significantly reduced.
[0003] In large-scale structural impact strength tests, such as those involving aircraft crashes, damage to connecting structures has always played a significant role. Numerous instances of rivet pull-out and shearing occur at the joints. Therefore, researching scaling methods for rivet structures is an important component in completing the scaling of complex aircraft structures.
[0004] However, traditional aircraft structure scaling often requires the scaled-down model to be scaled strictly according to a scaling factor for the geometry and dimensions of the structural prototype. This imposes significant limitations on the design of scaled-down models. Sometimes, due to engineering manufacturing realities, some dimensions of thin-walled structures and connectors cannot be scaled strictly according to the scale when scaling down. In this case, the traditional impact similarity method loses its effectiveness. Therefore, traditional scaled-down models cannot effectively simulate the prototype, resulting in the inability to accurately verify the strength of the connection structure when conducting strength simulation tests.
[0005] Therefore, there is a need to provide a structural design method for aircraft connection structures with reduced strength to solve the above problems. Summary of the Invention
[0006] This invention provides a scaled-down design method for aircraft connection structures with equivalent strength. The scaled-down design method requires that the scaled-down model be equivalent to the prototype. Based on the scaling, the dimensions of the rivets and the distance between the rivets and the end face of the thin plate on the connection structure are accurately calculated according to the strength equivalence criterion, thereby obtaining an accurate scaled-down model. This solves the problem that existing scaled-down model design methods cannot effectively simulate the prototype, resulting in the inability to accurately verify the strength of the connection structure during impact simulation.
[0007] The present invention provides a method for equal-strength scaled-down design of aircraft connection structures, which adopts the following technical solution: including: Based on the characteristic parameters that affect the strength of the connection structure, the failure force equations corresponding to the connection structure under different failure modes are obtained. Based on the failure force equation, the strength equivalence similarity conditions between the scaled-down model and the prototype of the connected structure under each failure mode of load are obtained; According to the scaling factor of the characteristic parameters of the connection structure, the geometric dimensions of the scaled thin plate of the connection structure are obtained; according to the geometric dimensions of the scaled thin plate, the number of columns and rows of rivets, and the strength equivalence similarity condition, the rivet shank diameter and the distance of the rivet from the end face of the thin plate of the scaled connection structure are obtained. Based on the rivet shank diameter, rivet distance from the end face of the thin plate, the geometric dimensions of the thin plate, and the number of columns and rows of rivets after scaling up the connection structure, the final scaled-down model of the connection structure is obtained.
[0008] Preferably, the steps of obtaining the rivet shank diameter and the distance between the rivet and the end face of the thin plate after scaling the connection structure include: Preset the number of columns and rows for a set of rivets; Substitute the number of columns and rows of rivets, as well as the scaled geometric dimensions of the thin plate, into the strength equivalence similarity conditions corresponding to the load of the second failure mode to obtain the rivet shank diameter of the scaled rivets. Determine whether the shank diameter conforms to the actual shank diameter range of the rivet. If not, redesign the number of columns and rows of the rivet. Based on the scaled-down sheet geometry and the redesigned number of columns and rows of the rivet, obtain the scaled-down shank diameter of the rivet until the scaled-down shank diameter and the corresponding number of columns of the rivet are obtained when they conform to the actual shank diameter range of the rivet. Substituting the scaled-down sheet geometry, rivet shank diameter, and corresponding rivet column number into the strength equivalence similarity condition under the load of the first failure mode, we obtain the scaled-down rivet distance from the sheet end face.
[0009] Preferably, the step of redesigning the number of columns and rows of a set of rivets includes: When the shank diameter of the scaled rivet is smaller than the minimum value in the range of actual rivet shank diameters, the number of columns and rows of the previous set of rivets is reduced by one row or one column, respectively, to obtain the number of columns and rows of the redesigned set of rivets. When the shank diameter of the scaled rivet is greater than the maximum value in the range of actual rivet shank diameters, the number of columns and rows of the previous set of rivets is increased by one row or one column respectively, resulting in a redesigned set of rivets with a new set of columns and rows.
[0010] Preferably, the characteristic parameters affecting the strength of the connection structure include: the length, width, and thickness of the thin plate, the number of rows and columns of rivets on the thin plate, the diameter of the rivet shank, and the distance between the rivet and the end face of the thin plate.
[0011] Preferably, the failure modes of the connection structure are pull-out failure of the rivet head and shear failure of the rivet shank. Pull-out failure of the rivet head is denoted as the first failure mode, and shear failure of the rivet shank is denoted as the second failure mode.
[0012] Preferably, the step of obtaining the failure force equations corresponding to the connection structure under loads with different failure modes includes: Under the first type of failure load, the failure force equation of the connected structure is:
[0013] In the formula, This represents the destructive force of the connection structure under load in the form of pull-out failure of the rivet head, i.e., the tangential force at the end of the thin plate of the connection structure; This indicates the distance between the rivet on the thin plate and the end face of the thin plate in the connecting structure; Indicates the number of columns of rivets on the thin plate of the connecting structure; Indicates the diameter of the rivet shank; Indicates the tensile strength of the rivet material; Represents a constant; Under the second type of failure load, the failure force equation of the connected structure is:
[0014] In the formula, It represents the destructive force of the connection structure under load in the shear failure mode of the rivet shank, that is, the normal force at the end of the thin plate of the connection structure; Indicates the number of columns of rivets on the thin plate of the connecting structure; Indicates the number of rows of rivets on the thin plate of the connecting structure; Indicates the diameter of the rivet shank; Represents a constant; This indicates the shear strength of the rivet material.
[0015] Preferably, the step of obtaining the strength equivalence similarity conditions between the scaled-down model and the prototype of the connected structure under load for each failure mode includes: Under the load of the first type of failure, the strength equivalence similarity condition between the scaled-down model and the prototype of the connection structure is as follows:
[0016] Under the second type of failure load, the strength equivalence similarity condition between the scaled-down model and the prototype of the connected structure is as follows:
[0017] In the formula, The distance scaling factor is the ratio of the distance between the rivet and the end face of the thin plate in the scaled-down model of the connection structure to the distance between the rivet and the end face of the thin plate in the prototype. The ratio of the shank diameter of the rivet in the scaled-down model of the connection structure to the shank diameter of the rivet in the prototype is called the diameter scaling factor when the shank diameter of the rivet is scaled down. This represents the ratio of the plate length in the scaled-down model of the connection structure to the plate length in the prototype, i.e., the length scaling factor when the plate length is scaled down. The ratio of the number of rows of rivets on the thin plate of the scaled-down model of the connection structure to the number of rows of rivets on the thin plate of the prototype is the column scaling factor when the number of rows of rivets on the thin plate is scaled down. This represents the ratio of the number of rows of rivets on the thin plate of the scaled-down model of the connection structure to the number of rows of rivets on the thin plate of the prototype, i.e., the scaling factor of the number of rows of rivets on the thin plate when scaled down.
[0018] Preferably, it also includes: validity verification of the final scaled-down model, the validity verification steps being: When the scaled-down model and prototype of the connection structure are similar, the relationship between the scaling factors of various physical quantities during the loading process is obtained. Based on the relationship between the scaling factors and the scaling factor, the dynamic response loading conditions of the connection structure are scaled to obtain the target dynamic response loading conditions of the connection structure. The final scaled-down model was simulated based on the target dynamic response loading conditions to obtain the destructive force of the final scaled-down model. Under each type of load, when the final scaled-down model of the connection structure and the prototype satisfy the strength equivalence similarity condition, the proportional similarity relationship between the destructive forces of the final scaled-down model of the connection structure and the prototype is obtained. Based on the destructive force of the final scaled-down model and the aforementioned proportional similarity relationship, the predicted destructive force of the prototype is calculated. By comparing the destructive force of the prototype with the predicted destructive force, the effectiveness of the final scaled-down model can be determined.
[0019] Preferably, the step of obtaining the proportional similarity relationship between the destructive forces of the final scaled-down model of the connection structure and the prototype includes:
[0020] In the formula, This represents the ratio of the destructive force of the final scaled-down model of the connection structure to that of the prototype under the load of the first type of failure, i.e., the tangential force similarity scaling factor; This represents the ratio of the destructive force of the final scaled model of the connection structure to that of the prototype under the load of the second failure mode, i.e., the shear force similarity scaling factor; The ratio of the loading force of the final scaled model of the connection structure to that of the prototype during dynamic response loading is called the loading force scaling factor. The final scaled-down model of the connection structure represents the geometry of the thin plate of the prototype. The ratio, geometric dimensions Take length ,width Or thickness Any one of them; This represents the ratio of the plate length in the final scaled-down model of the connection structure to the plate length in the prototype, i.e., the length scaling factor when the plate length is scaled down.
[0021] Preferably, the step of obtaining the relationship between the scaling factors of various physical quantities during loading when the scaled-down model and prototype of the connection structure are similar includes: The physical quantities of the connection structure include: the dimensions of the connection structure, the loading force, the stress at various points of the connection structure during loading, the loading time, the strain at various points of the connection structure during loading, the loading speed, and the mass. Based on the structural impact similarity law, the relationship between the scaling factors of various physical quantities during the loading process is obtained.
[0022] The beneficial effects of the aircraft connection structure equal-strength scaled-down design method of the present invention are: 1. The scaling design method of the connection structure requires that the scaled model and the prototype be equivalent. That is, using the scaling method of the present invention, the rivet size and the distance between the rivet and the end face of the thin plate on the connection structure are accurately calculated based on the strength equivalence criterion after scaling. In this way, while achieving strength equivalence between the prototype and the scaled model of the connection structure, it is ensured that it conforms to the actual engineering processing and manufacturing. That is, the scaled model can accurately predict the damage and failure response of the prototype. In other words, the final scaled model designed using the method of the present invention realizes the accurate verification of the strength of the connection structure.
[0023] 2. Predicting the damage response of the prototype of the connection structure by using a scaled-down model, that is, using a scaled-down model to replace the prototype for testing, can effectively reduce testing costs and shorten the testing cycle, and provide guidance for the design of scaled-down impact and crash tests of aircraft structures.
[0024] 3. Since the damage and failure modes of rivet connection structures in real aircraft impact crashes are divided into two types: rivet pull-out and rivet shearing, this invention considers the strength equivalence under both rivet pull-out and rivet shear loads in the scaled-down connection design, so as to be applicable to the scaled-down model design under tension-shear coupled composite load. Attached Figure Description
[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0026] Figure 1 A flowchart of an equal-strength scaled-down design method for aircraft connection structures according to the present invention; Figure 2 This is a front view of an aircraft connection structure according to the present invention; Figure 3 This is a top view of an aircraft connection structure according to the present invention; Figure 4 The prototype and scaled-down model of the connection structure are shown as the damage and failure surfaces under the first and second failure modes of load. Detailed Implementation
[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0028] An embodiment of the present invention provides a method for equal-strength scaled-down design of aircraft connection structures, such as... Figure 1 The steps shown include: S1. Obtain the failure force equations of the connection structure under loads with different failure modes; Specifically, because the strength of an aircraft connection structure is related to some characteristic parameters of the structure itself, the destructive force it experiences varies under different failure modes of load. A typical aircraft connection structure is a single lap joint, such as... Figure 2As shown, the structure is composed of two square thin plates and multiple rivets arranged side by side and overlapped. The entire structure is made of metal materials commonly used in the aerospace field. The structural boundary conditions are that the lower plate is fixed at both ends and the upper plate is loaded at one end. The actual damage and failure modes of the connection structure can be divided into two types: rivet head pull-out failure and rivet shank shear failure. The loads corresponding to the two failure modes are the tangential load and the normal load at the end, respectively. Therefore, this embodiment obtains the failure force equations corresponding to the connection structure under different failure modes based on the characteristic parameters affecting the strength of the connection structure.
[0029] Among them, such as Figure 2 and Figure 3 As shown, the characteristic parameters affecting the strength of the connection structure specifically include: the length of the thin plate. ,width ,thickness The number of rows of rivets on a thin plate and row number rivet shank diameter and the distance between the rivet and the end face of the thin plate. .
[0030] In the case of tangential load, the thin plate of the connecting structure is lifted upwards from the end, causing the rivet head to be pulled off. The phenomenon of the rivet closest to the end being stressed until it is pulled off and fails can be simplified to a model where the tangential force at the end of the cantilever structure causes a moment that leads to root failure. According to the formula for calculating the force at the end of the cantilever structure, the failure force equation of the connecting structure under the first failure mode is expressed as:
[0031] In the formula, This represents the destructive force of the connection structure under load in the form of pull-out failure of the rivet head, i.e., the tangential force at the end of the thin plate of the connection structure; This indicates the distance between the rivet on the thin plate and the end face of the thin plate in the connecting structure; Indicates the number of columns of rivets on the thin plate of the connecting structure; Indicates the diameter of the rivet shank; Indicates the tensile strength of the rivet material; Represents a constant; Under normal load, the connection structure exhibits relative displacement between the two thin plates. The rivet shank deforms under stress, leading to shearing. Based on the empirical formula for shear failure of lap joints, the failure force equation for the connection structure under the second failure mode is expressed as:
[0032] In the formula, It represents the destructive force of the connection structure under load in the shear failure mode of the rivet shank, that is, the normal force at the end of the thin plate of the connection structure; Indicates the number of columns of rivets on the thin plate of the connecting structure; Indicates the number of rows of rivets on the thin plate of the connecting structure; Indicates the diameter of the rivet shank; Represents a constant; This indicates the shear strength of the rivet material.
[0033] S2. Obtain the strength equivalence similarity conditions between the scaled-down model and the prototype of the connection structure; Specifically, based on the destructive force equation, the strength equivalence similarity conditions between the scaled-down model and the prototype of the connection structure under load for each of the aforementioned failure modes are obtained.
[0034] It should be noted that, since the scaled-down model uses the same material as the prototype, this embodiment will... , Treating it as a constant, we analyze the two failure force equations in step S1 using the equation analysis method, thus obtaining the strength equivalence similarity condition between the scaled-down model and the prototype of the connected structure under the load of the first failure mode (tangential load):
[0035] In the formula, The distance scaling factor is the ratio of the distance between the rivet and the end face of the thin plate in the scaled-down model of the connection structure to the distance between the rivet and the end face of the thin plate in the prototype. The ratio of the number of rows of rivets on the thin plate of the scaled-down model of the connection structure to the number of rows of rivets on the thin plate of the prototype is the column scaling factor when the number of rows of rivets on the thin plate is scaled down. The ratio of the shank diameter of the rivet in the scaled-down model of the connection structure to the shank diameter of the rivet in the prototype is the diameter scaling factor when the shank diameter of the rivet is scaled down. This represents the ratio of the plate length in the scaled-down model of the connection structure to the plate length in the prototype, i.e., the length scaling factor when the plate length is scaled down. Specifically, under the second type of failure load (normal load), the strength equivalence similarity condition between the scaled-down model and the prototype of the connected structure is as follows:
[0036] The ratio of the shank diameter of the rivet in the scaled-down model of the connection structure to the shank diameter of the rivet in the prototype is the diameter scaling factor when the shank diameter of the rivet is scaled down. This represents the ratio of the plate length in the scaled-down model of the connection structure to the plate length in the prototype, i.e., the length scaling factor when the plate length is scaled down. The ratio of the number of rows of rivets on the thin plate of the scaled-down model of the connection structure to the number of rows of rivets on the thin plate of the prototype is the column scaling factor when the number of rows of rivets on the thin plate is scaled down. This represents the ratio of the number of rows of rivets on the thin plate of the scaled-down model of the connection structure to the number of rows of rivets on the thin plate of the prototype, i.e., the row number scaling factor when the number of rows of rivets on the thin plate is scaled down.
[0037] S3. Obtain the scaled geometric dimensions of the thin plate, the rivet shank diameter, and the distance between the rivet and the end face of the thin plate; Specifically, according to the scaling factor preset for the characteristic parameters of the connection structure, the geometric dimensions of the thin plate after scaling (in this embodiment, scaling refers to reduction) of the connection structure are obtained; based on the reduced geometric dimensions of the thin plate, the preset number of columns and rows of rivets, and the strength equivalence similarity condition, the rivet shank diameter and the distance between the rivet and the end face of the thin plate after the reduction of the connection structure are obtained.
[0038] Among them, based on the characteristic parameters affecting the strength of the connection structure: the length of the thin plate ,width ,thickness 1. Rivet shank diameter Distance between rivets and the end face of the thin plate The scaling factor for each feature parameter is obtained. Specifically, in this embodiment, the scaling factor for each feature parameter is defined as the ratio of the feature parameter of the scaled-down model of the connection structure to the corresponding feature parameter on the prototype. It should be noted that the scaling factors for the three feature parameters of the thin plate are the same.
[0039] In the formula, This represents the scaling factor for the length of the thin plate when the connection structure is scaled. This represents the scaling factor of the thin plate when the connection structure is scaled. This represents the thickness scaling factor of the thin plate when the connection structure is scaled. Rivet feature size scaling factor Rivet end distance scaling factor Rivet column scaling factor Rivet row scaling factor In the formula, Represents the prototype. This represents a scaled-down model. That is, the diameter of the rivet shank in the prototype. That is, the shank diameter of the rivet in the scaled-down model; That is, the distance between the rivet and the end face of the thin plate in the prototype. That is, the distance between the rivet and the end face of the thin plate in the scaled-down model; The number of rivet rows for the prototype The number of rivet columns in the scaled-down model; The number of rivet rows for the prototype This represents the number of rivet rows in the scaled-down model.
[0040] Specifically, when obtaining the geometric dimensions of the scaled-down thin plate of the connecting structure, the length dimension and length scaling factor of the thin plate of the prototype connecting structure are known. Since the length scaling factor, width scaling factor, and thickness scaling factor are the same, the geometric dimensions of the scaled-down thin plate can be obtained.
[0041] Specifically, the steps for obtaining the rivet shank diameter and the distance between the rivet and the thin plate end face after scaling (reduced in this embodiment) of the connection structure include: presetting a set of rivet column and row numbers, i.e., setting the rivet column and row numbers according to empirical values; substituting the rivet column and row numbers, as well as the scaled (reduced in this embodiment) geometric dimensions of the thin plate, into the strength equivalence similarity conditions corresponding to the load of the second failure mode to obtain the scaled (reduced in this embodiment) rivet shank diameter; determining whether the rivet shank diameter conforms to the actual rivet shank diameter range, and if not, redesigning a set of rivet column and row numbers. The scaled (reduced) rivet shank diameter is obtained based on the scaled sheet geometry and the number of columns and rows of the redesigned rivets. This process continues until the scaled (reduced) rivet shank diameter, which conforms to the actual rivet shank diameter range, is obtained, along with the corresponding number of rivet columns. The scaled (reduced) sheet geometry, rivet shank diameter, and corresponding number of rivet columns are substituted into the strength equivalence similarity condition under the load of the first failure mode to obtain the scaled (reduced) rivet distance from the sheet end face.
[0042] The steps for redesigning the number of columns and rows of a set of rivets are as follows: when the shank diameter of the scaled (reduced in this embodiment) rivet is less than the minimum value in the range of actual rivet shank diameters, the number of columns and rows of the previous set of rivets is reduced by one row or one column respectively to obtain the number of columns and rows of the redesigned set of rivets; when the shank diameter of the scaled (reduced in this embodiment) rivet is greater than the maximum value in the range of actual rivet shank diameters, the number of columns and rows of the previous set of rivets is increased by one row or one column respectively to obtain the number of columns and rows of the redesigned set of rivets.
[0043] S4. Obtain the final scaled-down model; Specifically, based on the rivet shank diameter, the distance between the rivet and the end face of the thin plate, the geometric dimensions of the thin plate, and the number of columns and rows of rivets after scaling up (referred to as scaling down in this embodiment) the connection structure, the final scaled-down model of the connection structure is obtained.
[0044] It should be noted that when scaling (reducing in this embodiment), the form, position, and type of the boundary conditions of the final scaled model should be consistent with the prototype. In this embodiment, the prototype's boundary conditions are: the lower thin plate is fully fixed at both ends, the upper plate is free and unconstrained at one end, and a uniformly distributed load is applied at the other end; the sides of both plates are free and unconstrained. Therefore, the boundary conditions of the scaled model must also be consistent. Furthermore, when scaling, the load form of the final scaled model must also be consistent with the prototype. The load magnitude is scaled according to the corresponding load force scaling factor. In this embodiment, the prototype structure is loaded at the ends. The first failure mode's load force (applied force) is an upward uniformly distributed shear force on the end face, and the second failure mode's load force (applied force) is a uniformly distributed shear force acting outwards from the normal to the end face. The final scaled model maintains this consistency. The load magnitude is scaled according to the geometric scaling factor of the corresponding physical quantity. The prototype structure's load force in the first and second failure modes increases linearly with time, and the load force is scaled according to the load force scaling factor (applied force scaling factor). Scaling is applied, with time scaled according to a time scaling factor. Scaling is performed.
[0045] In addition, this embodiment also includes: validity verification of the final scaled-down model. The specific steps of validity verification are as follows: In this embodiment, the load fracture force when the prototype and the scaled-down structure are damaged is used as the basis for judging the strength equivalence similarity between the prototype and the scaled-down model. The fracture force of the scaled-down model should be divided by the load force scaling factor and then compared with the fracture force of the prototype to verify validity. Therefore, the relationship between the scaling factors of each physical quantity during the loading process is first obtained when the scaled-down model and the prototype of the connection structure are similar. According to the relationship between the scaling factors and the scaling factor, the dynamic response loading conditions of the connection structure are scaled to obtain the target dynamic response loading conditions of the connection structure. The final scaled-down model is then scaled according to the target dynamic response loading conditions. The model undergoes simulation experiments to obtain the destructive force of the final scaled-down model. Based on the destructive force of the final scaled-down model and the aforementioned proportional similarity relationship, the predicted destructive force of the prototype is calculated. The magnitudes of the prototype's destructive force and the predicted destructive force are compared. In this embodiment, the deviation between the predicted and predicted destructive forces of the prototype from the scaled-down model is kept within 10%. Based on the difference between the predicted and predicted destructive forces of the prototype, it is determined whether the difference is less than or equal to 10% of the prototype's destructive force. If so, it is valid; otherwise, it is invalid. The validity of the final scaled-down model is determined. If invalid, the process returns to step S3 for redesign. According to the verification of the specific embodiment, the fracture force prediction error of this method can be controlled within 10%, which is relatively accurate in predicting the fracture force response of the prototype. Figure 4 As shown, Figure 4 For the prototype and scaled-down model under the first failure mode of load ( The second type of load ( The damage and failure surfaces under the model show that, based on the strength equivalence design, the scaled-down model exhibits high similarity in fracture force response between the prototype and the scaled-down model under the first failure mode load, the second failure mode load, and the simultaneous mixed loading of the first and second failure modes loads in component form. The data results indicate that, in the validity verification results, the fracture force prediction error is generally less than 10%, with a maximum of no more than 13.3%. This means that the predicted failure force of the prototype using the final scaled-down model is similar to the failure force of the prototype. Therefore, it can be concluded that the scaled-down model can predict the fracture force response of the prototype well, and the prediction error can meet the engineering requirements.
[0046] Specifically, the proportional similarity relationship between the final scaled-down model and the prototype of the connection structure under each failure mode of load is as follows:
[0047] In the formula, This represents the ratio of the destructive force of the final scaled-down model of the connection structure to that of the prototype under the load of the first type of failure, i.e., the tangential force similarity scaling factor; This represents the ratio of the destructive force of the final scaled model of the connection structure to that of the prototype under the load of the second failure mode, i.e., the shear force similarity scaling factor; The ratio of the loading force of the final scaled model of the connection structure to that of the prototype during dynamic response loading is called the loading force scaling factor. The final scaled-down model of the connection structure represents the geometry of the thin plate of the prototype. The ratio, geometric dimensions Take length ,width Or thickness Any one of them, in this embodiment Take the length of the thin plate , that is, the length scaling factor; The ratio of the plate length of the final scaled-down model of the connection structure to the plate length of the prototype is the length scaling factor when the plate length is scaled down.
[0048] It should be noted that when the strength equivalence similarity condition is met, that is, the scaled-down model and the prototype are similar, the destructive force of the scaled-down model and the prototype of the connection structure under the same load should also be similar. That is, the ratio of the destructive force of the scaled-down model to the prototype is equal to the ratio of the loading force of the scaled-down model to the prototype, and the ratio of the loading force is equal to the square of the scaling factor of the geometric dimensions of the thin plate.
[0049] The physical quantities of the connection structure include: dimension L, force F, stress σ, time t, strain ε, velocity V, and mass M. In this paper, dimension L refers to the length, width, and thickness of the connecting plate; force F refers to the loading force of the connection structure; stress σ refers to the stress at various points in the connection structure; time t refers to the loading time; strain ε refers to the strain at various points in the connection structure; and velocity V refers to the loading velocity. It should be noted that the physical quantities here are not limited to a certain specific quantity or a particular actual quantity; all quantities conforming to the corresponding physical dimensions are referred to by the above quantities. Furthermore, the scaling method of the designed connection structure is not limited to a certain loading method. For example, when the connection structure is subjected to a mass impact, the impact mass is referred to by the mass M. The scaling factor is the ratio of the physical quantities corresponding to the scaled-down model and the prototype of the connection structure. The relationships between the scaling factors are as follows: the strain scaling factor and the stress scaling factor are both 1; the length scaling factor, the displacement scaling factor, and the time scaling factor are equal; the loading force scaling factor is equal to the square of the dimension scaling factor; and the mass scaling factor is equal to the cube of the dimension scaling factor. That is to say, according to the structural impact similarity law, when performing the loading response, the scaling factors of each physical quantity during the loading process are: dimension scaling factor. Force proportionality factor Displacement scaling factor Stress proportionality factor Time scaling factor strain ratio factor Speed scaling factor quality ratio factor In the formula Represents the original model. This represents a scaled-down model. This refers to the dimensions of the original model, where the dimensions include length, width, and thickness. When the scaled-down model of the connecting structure is similar to the prototype, the scaling factors of each physical quantity during loading should satisfy the following: .
[0050] Based on steps S1 to S4, this embodiment provides the prototype dimensions of the connection structure and performs simulations on the prototype and scaled-down model of the connection structure under the first failure mode and the load of the first failure mode. The prototype and scaled-down model use the same metal material for all parts; the nail material is 2024 aerospace aluminum alloy, and the plate material is 7150 aerospace aluminum alloy. Specifically, the length, width, and thickness of the thin plate in the prototype of the connection structure are as follows: =70mm, =40mm, =3mm; Rivet diameter =4mm, number of rivet rows =2, number of rivet rows =3, and then scale the dimensions of the prototype's feature parameters according to the geometric scaling factor given by the engineering requirements. In this embodiment, the length scaling factor is taken when the dimension is the length, that is... = =1 / 3. Therefore, the scaling factor when scaling the prototype structure is... = =1 / 3, = =1 / 3, = =1 / 3, thus obtaining the scaled geometric dimensions of the thin plate: , , Take a set of rivet column and row numbers. In this embodiment, first perform proportional scaling so that the rivet arrangement of the scaled-down model is consistent with the prototype, that is, the number of rivet column and row numbers of the scaled-down model is equal to that of the prototype: , ;but Substituting the strength equivalence similarity condition under the second failure mode, we obtain... =1 / 9, the scaled diameter of the nail rod Next, check if the rivet diameter matches the actual rivet shank diameter range. Common aircraft rivet diameters range from 2mm to 10mm. In this case, take 2mm to 10mm as the actual rivet shank diameter range, and then determine the scaled-down rivet shank diameter. This does not meet the requirements. Therefore, it is necessary to adjust the number of rivet columns and rows. By adjusting the number of rivet columns and rows each time, and calculating the scaled rivet shank diameter after each adjustment, the process continues until the scaled rivet shank diameter meets the actual rivet shank diameter range. This will ultimately determine the number of rivet columns for the scaled-down model. Number of rivet rows The corresponding rivet diameter at this time mm, then, the obtained scaled rivet diameter mm, number of rivet rows Number of rivet rows The scaled-down geometric dimensions of the thin plate: , , Substituting this into the strength equivalence similarity condition under the first failure mode, we obtain... =0.8667mm, which is the scaled distance between the rivet and the end face of the thin plate. Finally, based on the scaled rivet diameter mm, number of rivet rows Number of rivet rows The scaled-down geometric dimensions of the thin plate: , , And the distance between the scaled-down rivet and the end face of the thin plate. This will give you the final scaled-down model.
[0051] In summary, the present invention provides a scaled-down design method for aircraft connection structures with equivalent strength. This method requires the scaled-down model to be equivalent to the prototype. Specifically, using the scaling-down method of this invention, the dimensions of the rivets and the distance between the rivets and the end face of the thin plate on the connection structure are accurately calculated based on the strength equivalence criterion after scaling down the proportions. This ensures that the scaled-down structure conforms to actual engineering manufacturing practices, achieving strength equivalence between the prototype and the scaled-down model of the connection structure. The scaled-down model accurately predicts the damage and failure response of the prototype. In other words, the final scaled-down model designed using the method of this invention accurately verifies the strength of the connection structure. Predicting the damage and failure response of the prototype of the connection structure using the scaled-down model replaces actual testing, effectively reducing testing costs and shortening the testing cycle, and providing guidance for the design of scaled-down impact and crash tests for aircraft structures.
[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for proportionally scaling aircraft connection structures, characterized in that, include: Based on the characteristic parameters that affect the strength of the connection structure, the failure force equations corresponding to the connection structure under different failure modes are obtained. Based on the failure force equation, the strength equivalence similarity conditions between the scaled-down model and the prototype of the connection structure under each failure mode of load are obtained; According to the scaling factor preset for the characteristic parameters of the connection structure, obtain the geometric dimensions of the scaled thin plate of the connection structure; Based on the scaled geometric dimensions of the thin plate, the preset number of columns and rows of rivets, and the strength equivalence similarity condition, the rivet shank diameter and the distance of the rivet from the end face of the thin plate are obtained after scaling the connection structure. Based on the rivet shank diameter, the distance of the rivet from the end face of the thin plate, the geometric dimensions of the thin plate, and the number of columns and rows of rivets after scaling up the connection structure, the final scaled-down model of the connection structure is obtained. The failure modes of the connection structure are pull-out failure of the rivet head and shear failure of the rivet shank. Pull-out failure of the rivet head is recorded as the first failure mode, and shear failure of the rivet shank is recorded as the second failure mode. The steps for obtaining the failure force equations for connected structures under loads with different failure modes include: Under the first type of failure load, the failure force equation of the connection structure is: In the formula, This represents the destructive force of the connection structure under load in the form of pull-out failure of the rivet head, i.e., the tangential force at the end of the thin plate of the connection structure; This indicates the distance between the rivet on the thin plate and the end face of the thin plate in the connecting structure; Indicates the number of columns of rivets on the thin plate of the connecting structure; Indicates the diameter of the rivet shank; Indicates the tensile strength of the rivet material; Represents a constant; Under the second type of failure load, the failure force equation of the connection structure is: In the formula, It represents the destructive force of the connection structure under load in the shear failure mode of the rivet shank, that is, the normal force at the end of the thin plate of the connection structure; Indicates the number of columns of rivets on the thin plate of the connecting structure; Indicates the number of rows of rivets on the thin plate of the connecting structure; Indicates the diameter of the rivet shank; Represents a constant; Indicates the shear strength of the rivet material; The steps for establishing the strength equivalence similarity conditions between the scaled-down model and the prototype of the connected structure under each of the aforementioned failure modes of loading include: Under the load of the first type of failure, the strength equivalence similarity condition between the scaled-down model and the prototype of the connection structure is as follows: Under the second type of failure load, the strength equivalence similarity condition between the scaled-down model and the prototype of the connection structure is as follows: In the formula, The distance scaling factor is the ratio of the distance between the rivet and the end face of the thin plate in the scaled-down model of the connection structure to the distance between the rivet and the end face of the thin plate in the prototype. The ratio of the shank diameter of the rivet in the scaled-down model of the connection structure to the shank diameter of the rivet in the prototype is the diameter scaling factor when the shank diameter of the rivet is scaled down. This represents the ratio of the plate length in the scaled-down model of the connection structure to the plate length in the prototype, i.e., the length scaling factor when the plate length is scaled down. The ratio of the number of rows of rivets on the thin plate of the scaled-down model of the connection structure to the number of rows of rivets on the thin plate of the prototype is the column scaling factor when the number of rows of rivets on the thin plate is scaled down. This represents the ratio of the number of rows of rivets on the thin plate of the scaled-down model of the connection structure to the number of rows of rivets on the thin plate of the prototype, i.e., the row number scaling factor when the number of rows of rivets on the thin plate is scaled down.
2. The method for equal-strength scaled-down design of aircraft connection structures according to claim 1, characterized in that, The steps of obtaining the rivet shank diameter and the distance of the rivet from the end face of the thin plate after scaling the connection structure include: Preset the number of columns and rows for a set of rivets; Substitute the number of columns and rows of rivets, as well as the scaled geometric dimensions of the thin plate, into the strength equivalence similarity conditions corresponding to the load of the second failure mode to obtain the rivet shank diameter of the scaled rivets. Determine whether the shank diameter conforms to the actual shank diameter range of the rivet. If not, redesign the number of columns and rows of the rivet. Based on the scaled-down sheet geometry and the redesigned number of columns and rows of the rivet, obtain the scaled-down shank diameter of the rivet until the scaled-down shank diameter and the corresponding number of columns of the rivet are obtained when they conform to the actual shank diameter range of the rivet. Substituting the scaled-down sheet geometry, rivet shank diameter, and corresponding rivet column number into the strength equivalence similarity condition under the first failure mode load, we obtain the scaled-down rivet distance from the end face of the sheet.
3. The method for equal-strength scaled-down design of aircraft connection structures according to claim 2, characterized in that, The steps of redesigning the number of columns and rows of a set of rivets include: When the shank diameter of the scaled rivet is smaller than the minimum value in the range of actual rivet shank diameters, the number of columns and rows of the previous set of rivets is reduced by one row or one column, respectively, to obtain the number of columns and rows of the redesigned set of rivets. When the shank diameter of the scaled rivet is greater than the maximum value in the range of actual rivet shank diameters, the number of columns and rows of the previous set of rivets is increased by one row or one column respectively, resulting in a redesigned set of rivets with a new set of columns and rows.
4. The method for equal-strength scaled-down design of aircraft connection structures according to claim 1, characterized in that, The characteristic parameters affecting the strength of the connection structure include: the length, width, and thickness of the thin plate; the number of columns and rows of rivets on the thin plate; the diameter of the rivet shank; and the distance of the rivet from the end face of the thin plate.
5. The method for equal-strength scaled-down design of aircraft connection structures according to claim 1, characterized in that, Also includes: The validity verification of the final scaled-down model includes the following steps: When the scaled-down model and prototype of the connection structure are similar, the relationship between the scaling factors of various physical quantities during the loading process is obtained. Based on the relationship between the scaling factors and the scaling factor, the dynamic response loading conditions of the connection structure are scaled to obtain the target dynamic response loading conditions of the connection structure. The final scaled-down model was simulated based on the target dynamic response loading conditions to obtain the destructive force of the final scaled-down model. Under each type of load, when the final scaled-down model of the connection structure and the prototype satisfy the strength equivalence similarity condition, the proportional similarity relationship between the destructive forces of the final scaled-down model of the connection structure and the prototype is obtained. Based on the destructive force of the final scaled-down model and the aforementioned proportional similarity relationship, the predicted destructive force of the prototype is calculated. By comparing the destructive force of the prototype with the predicted destructive force, the effectiveness of the final scaled-down model can be determined.
6. The method for equal-strength scaled-down design of aircraft connection structures according to claim 5, characterized in that, The steps for obtaining the proportional similarity relationship between the final scaled-down model of the connection structure and the prototype in terms of destructive force include: In the formula, This represents the ratio of the destructive force of the final scaled-down model of the connection structure to that of the prototype under the load of the first type of failure, i.e., the tangential force similarity scaling factor; This represents the ratio of the destructive force of the final scaled model of the connection structure to that of the prototype under the load of the second failure mode, i.e., the shear force similarity scaling factor; The ratio of the loading force of the final scaled model of the connection structure to that of the prototype during dynamic response loading is called the loading force scaling factor. The final scaled-down model of the connection structure represents the geometry of the thin plate of the prototype. The ratio, geometric dimensions Take length ,width Or thickness Any one of them; The ratio of the plate length of the final scaled-down model of the connection structure to the plate length of the prototype is the length scaling factor when the plate length is scaled down.
7. The method for equal-strength scaled-down design of aircraft connection structures according to claim 5, characterized in that, The steps for determining the relationship between the scaling factors of various physical quantities during loading when obtaining a scaled-down model and a prototype of the connection structure include: The physical quantities of the connection structure include: the dimensions of the connection structure, the loading force, the stress at various points of the connection structure during loading, the loading time, the strain at various points of the connection structure during loading, the loading speed, and the mass. Based on the structural impact similarity law, the relationship between the scaling factors of various physical quantities during the loading process is obtained.