Calculation method for durability design of aircraft rivet hole structure

Abstract

The invention belongs to the field of structural design, and particularly relates to a calculation method for durability design of an aircraft rivet hole structure, which comprises the following steps: firstly, based on information such as geometry, material and load of the rivet hole structure, carrying out durability analysis on the rivet hole structure, deducing a fatigue influence coefficient expression, and obtaining a fatigue durability stress index; furthermore, a durability profit index and a load spectrum coefficient are obtained according to the actual load working condition of the rivet hole structure, and the strength margin of the structure is given by adopting a method similar to static strength. The method has the advantages that a mathematical expression for measuring the capacity of resisting repeated loads without damage is given, and the column has the advantages of being continuous, differentiable, simple and universal and can be applied to various design structures. And the durability margin is effectively controlled, fatigue cracking of the rivet hole structure in the service period is avoided, the service life of equipment is prolonged, and the safety of the equipment is improved.

Description

Technical Field

[0001] The present application belongs to the field of structural design, and in particular relates to a calculation method for durability design of aircraft rivet hole structures. Background Art

[0002] With the development of aviation, the multi-purpose, high performance and high manufacturing cost of advanced aircraft require that aircraft must have high reliability, long life, high attendance rate and low maintenance cost. The durability analysis method of aircraft structure is a new technology developed to meet the above goals. Structural durability is a basic quality of aircraft structure. It represents the ability of aircraft structure to resist fatigue cracking, corrosion (including stress corrosion) and cracking caused by accidental damage within the specified service life. The US Air Force has begun research on the durability of aircraft structures since the 1980s. At present, my country has carried out research on the durability of aircraft structures and applied it to the design of newly developed aircraft and the reliability assessment of the service life of existing aircraft.

[0003] At present, in the preliminary design stage of new aircraft, empirical design is mainly used for structural durability (fatigue) design. Since it is impossible to conduct durability analysis and evaluation of the structure in the preliminary design stage, it is more difficult to change the key structural design in the detailed design stage, and the aircraft design cycle is increased. However, in the preliminary design stage of new aircraft, it is costly to conduct durability design for all aircraft structures, and it is necessary to screen typical key structures for durability analysis in a targeted manner. Due to the requirements of lightweight aircraft and easy maintenance, riveting process is the most widely used connection method for aircraft. Stress concentration is prone to occur at the rivet hole position, and the rivet hole structure is prone to fatigue failure under fatigue load. The rivet hole structure is a typical key structure for aircraft durability design. Therefore, it is necessary to establish a calculation method for the durability design of aircraft rivet hole structure. Summary of the invention

[0004] The purpose of this application is to provide a calculation method for the durability design of aircraft rivet hole structures to solve the problem that rivet hole structures are prone to fatigue failure under fatigue loads.

[0005] The technical solution of the present application is: a calculation method for durability design of aircraft rivet hole structure, comprising:

[0006] According to the geometric parameters of the rivet hole structure and the load conditions, the influence coefficient of the countersunk nail hole, the influence coefficient of the open hole, the influence coefficient of the bidirectional stress field, the influence coefficient of the nail-loaded hole and the influence coefficient of the nail bending are calculated respectively, and then the stress concentration factor K of the rivet hole is calculated. T ;

[0007] According to the geometric parameters, material parameters and process type of the rivet hole structure, the allowable peak stress K of the rivet hole is determined. TFand correction factors;

[0008] According to the fatigue load spectrum, the fatigue load during the entire flight process is converted into an equivalent equal-amplitude load to determine the spectrum severity factor G. DI ;

[0009] According to the actual load condition, the maximum stress under the reference load condition is obtained, and the durability stress index f is determined by combining the spectral severity coefficient. DI ;

[0010] According to the fatigue durability allowable stress index F of the rivet hole structure DI and durability stress index f DI , calculate the durability margin DM of the structure;

[0011] The durability margin DM is obtained to determine the current fatigue life. DM>0 means that under the assumed analysis conditions, fatigue cracking will not occur in the structure during service; while DM<0 indicates that the structure needs to be modified so that DM is minimized to 0 to meet the requirements of the design objectives and complete the durability design of the preliminary design stage of the structure.

[0012] Preferably, the stress concentration factor K T The calculation formula is:

[0013]

[0014] Among them, α is the nail load ratio, KTCSK is the influence coefficient of the countersunk nail hole, and the calculation formula is:

[0015] K TCSK =1.26-0.48exp[-0.25(t / d)]*[0.57-1.82(tc / t)(t / d) 0.6 +0.56(tc / t) 2 (t / d) 0.3 ]

[0016] K TG is the opening influence coefficient, and the calculation formula is:

[0017]

[0018] K TBI is the influence coefficient of the bidirectional stress field, and the calculation formula is:

[0019] K TBI =1-(σ2 / σ1) / 3

[0020] K TBRG is the influence coefficient of the nail-loaded hole, and the calculation formula is:

[0021]

[0022] K TPB is the influence coefficient of nail bending, and the calculation formula is:

[0023]

[0024] Where D is the diameter of the nail hole, t is the thickness of the connection area, tc is the countersunk thickness, s is the nail hole spacing, and α is the nail load ratio.

[0025] Preferably, the load condition includes the total load P, the bypass load PBP, the nail load PPL, and the nail load ratio α=P PL / P.

[0026] Preferably, the correction factor includes a size correction factor C SE , Surface treatment influence factor C ST , Cold work hardening influence coefficient C CW , Connector installation influence coefficient C FI , Material fiber direction correction factor C GO , Heat treatment thickness coefficient C HTT , slope influence coefficient S and fracture influence coefficient m.

[0027] Preferably, the material parameters include material, brand, and fastening type.

[0028] Preferably, the fatigue durability allowable stress index F of the rivet hole structure is DI The calculation formula is:

[0029]

[0030] Where DSG is the target life of the design service period, LSF is the dispersion coefficient, if the rivet hole structure is the main structure, LSF = 5, if the rivet hole structure is the secondary structure, LSF = 3.

[0031] Preferably, the spectral severity coefficient G DI The calculation formula is:

[0032]

[0033] Among them, n z is overload, T0 is the flight hours corresponding to a random spectrum block, is the equivalent damage corresponding to the i-th cycle in the random spectrum, It is the equivalent damage corresponding to one equivalent equal-amplitude cyclic action.

[0034] Preferably, the durability stress index f DI The calculation formula is:

[0035] f DI =GDI ·f REF

[0036] Among them, f REF It is the maximum stress under the reference load condition with 1g overload.

[0037] Preferably, the durability margin DM calculation formula is:

[0038]

[0039] The calculation method for durability design of aircraft rivet hole structure of the present application has the following advantages:

[0040] 1. A mathematical expression for measuring the ability to resist repeated loads without damage is given. The expression is continuous, differentiable, simple and universal, and can be applied to various design structures.

[0041] 2. The durability margin is effectively controlled to ensure that the rivet hole structure will not suffer from fatigue cracking during service, thereby improving the service life and safety of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solution provided by the present application, the following is a brief introduction to the accompanying drawings. Obviously, the accompanying drawings described below are only some embodiments of the present application.

[0043] Figure 1 This is the overall flow chart of this application;

[0044] Figure 2 This is a top view schematic diagram of the rivet hole structure of this application;

[0045] Figure 3 This is a cross-sectional view of the rivet hole structure of this application;

[0046] Figure 4 This is a loaded cross-sectional view of the rivet hole structure of the present application;

[0047] Figure 5 The influence coefficient K of the countersunk nail hole for this application TCSK Curve fitting diagram;

[0048] Figure 6 The opening influence coefficient K for this application TG Schematic diagram of curve fitting. DETAILED DESCRIPTION

[0049] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] A calculation method for durability design of aircraft rivet hole structure. The existing technology mainly guarantees the economic life of the structure by controlling the damage tolerance through a large number of experiments, and does not provide an indicator to measure whether the structure will not be damaged when resisting repeated loads. This application first analyzes the durability of the rivet hole structure based on the geometry, material, load and other information of the rivet hole structure, derives the expression of the fatigue influence coefficient, obtains the fatigue durability stress index, and further obtains the durability profit index and load spectrum coefficient according to the actual load condition of the rivet hole structure, and uses a method similar to static strength to give the strength margin of the structure.

[0051] like Figure 1 As shown, the following steps are included:

[0052] Step S100, according to the geometric parameters of the rivet hole structure and the load conditions, respectively calculate the influence coefficient of the countersunk nail hole, the influence coefficient of the open hole, the influence coefficient of the bidirectional stress field, the influence coefficient of the nail load hole and the influence coefficient of the nail bending; then calculate the stress concentration factor K of the rivet hole through the influence coefficient of the countersunk nail hole, the influence coefficient of the open hole, the influence coefficient of the bidirectional stress field, the influence coefficient of the nail load hole and the influence coefficient of the nail bending T .

[0053] Stress concentration factor K T The calculation formula is:

[0054]

[0055] Among them, α is the nail load ratio, KTCSK is the influence coefficient of the countersunk nail hole, and the calculation formula is:

[0056] K TCSK =1.26-0.48exp[-0.25(t / d)]*[0.57-1.82(tc / t)(t / d) 0.6 +0.56(tc / t) 2 (t / d) 0.3 ] (2)

[0057] K TG is the opening influence coefficient, and the calculation formula is:

[0058]

[0059] KTBI is the influence coefficient of the bidirectional stress field, and the calculation formula is:

[0060] K TBI =1-(σ2 / σ1) / 3 (4)

[0061] K TBRG is the influence coefficient of the nail-loaded hole, and the calculation formula is:

[0062]

[0063] K TPB is the influence coefficient of nail bending, and the calculation formula is:

[0064]

[0065] Where D is the diameter of the nail hole, t is the thickness of the connection area, tc is the countersunk thickness, s is the nail hole spacing, and α is the nail load ratio.

[0066] Preferably, the load condition includes the total load P, the bypass load PBP, the nail load PPL, and the nail load ratio α=P PL / P.

[0067] Step S200, determining the allowable peak stress K of the rivet hole according to the geometric parameters, material parameters and process type of the rivet hole structure TF And the correction factor, the correction factor includes the size correction factor C SE , Surface treatment influence factor C ST , Cold work hardening influence coefficient C CW , Connector installation influence coefficient C FI , Material fiber direction correction factor C GO , Heat treatment thickness coefficient C HTT , slope influence coefficient S and fracture influence coefficient m.

[0068] Preferably, the material parameters include material, brand, fastening type, etc. The material information is generally divided into three types: aluminum, iron, and titanium, and the brand corresponds to the material.

[0069] Step S300, according to the stress concentration factor K of the rivet hole T , allowable peak stress K TF And the correction factor to determine the fatigue durability allowable stress index F of the rivet hole structure DI , the calculation formula is:

[0070]

[0071] Where DSG is the target life of the design service period, LSF is the dispersion coefficient, if the rivet hole structure is the main structure, LSF = 5, if the rivet hole structure is the secondary structure, LSF = 3.

[0072] Step S400: According to the fatigue load spectrum, the fatigue load in the entire flight process is converted into an equivalent constant amplitude load to determine the spectrum severity coefficient G DI , the calculation formula is:

[0073]

[0074] Among them, n z is overload, T0 is the flight hours corresponding to a random spectrum block, is the equivalent damage corresponding to the i-th cycle in the random spectrum, It is the equivalent damage corresponding to one equivalent equal-amplitude cyclic action.

[0075] Step S500, obtaining the maximum stress under the reference load condition according to the actual load condition, and determining the durability stress index f in combination with the spectral severity coefficient DI , the calculation formula is:

[0076] f DI =G DI ·f REF (9)

[0077] Among them, f REF It is the maximum stress under the reference load condition with 1g overload.

[0078] Step S600, based on the fatigue durability allowable stress index F of the rivet hole structure DI and durability stress index f DI , calculate the durability margin DM of the structure, the calculation formula is:

[0079]

[0080] Step S700, obtain the durability margin DM to determine the current fatigue life. DM>0 means that under the assumed analysis conditions, the structure will not suffer fatigue cracking during service (DSG). DM<0 indicates that the structure needs to be modified to minimize DM to 0 to meet the requirements of the design target and complete the durability design of the preliminary design stage of the structure.

[0081] Through the above design, this application has the following advantages:

[0082] 1. A mathematical expression for measuring the ability to resist repeated loads without damage is given. The expression is continuous, differentiable, simple and universal, and can be applied to various design structures.

[0083] 2. The durability margin is effectively controlled to ensure that the rivet hole structure will not suffer from fatigue cracking during service, thereby improving the service life and safety of the equipment.

[0084] As a specific implementation method, a specific example is used below to illustrate the model structure diagram. Figure 2-3 As shown:

[0085] Step S100: Determine the geometric parameters of the rivet hole structure, where the rivet hole diameter D = 5mm, the connection area thickness t = 2.3mm, the countersunk thickness tc = 1.2mm, the rivet hole spacing s = 24mm, and the structure type is the main structure. Set the load condition of the structure, determine the condition type as unstable simple shear, and the nail load ratio α = P PL / P=0.35, load diagram as shown Figure 4 shown.

[0086] From formula (2), we can get the influence coefficient K of the countersunk nail hole: TCSK =1.22, the fitting diagram of formula (2) is as follows Figure 5 As shown; from formula (3), the opening influence coefficient K can be obtained TG =3, such as Figure 6 As shown; from formula (4), the influence coefficient K of the bidirectional stress field can be obtained TBI =0.78; From formula (5), we can get the influence coefficient K of the nail hole TBRG =1.38; From formula (6), we can get the influence coefficient of nail bending K TPB =1.4.

[0087] Stress concentration factor K of rivet hole structure T for:

[0088]

[0089] Step S200: Material parameters of the rivet hole structure, the material is 2198, the grade is T851, the plate thickness is <3mm, the fastening type is standard rivet material, determine the allowable peak stress K TF =540Mpa, and the correction factor includes the size correction factor C SE =0.98, surface treatment influence factor C ST =0.81, cold work hardening influence coefficient C CW =1.35, connector installation influence coefficient C FI =1.3, Material fiber direction correction factor C GO =1, Heat treatment thickness coefficient C HTT =1, slope influence coefficient S=5.6 and fracture influence coefficient m=0.6.

[0090] Step S300: According to the rivet hole structure type as the main structure, the dispersion coefficient LSF = 5, according to steps 1-2, the fatigue durability allowable stress index F of the connection hole is determined. DI , the calculation formula is:

[0091]

[0092] Step S400: According to the fatigue load spectrum, the fatigue load in the entire flight process is converted into an equivalent equal-amplitude load to determine the spectrum severity coefficient G DI :

[0093]

[0094] Step S500: According to the actual load condition, the maximum principal stress f under the reference load condition under 1g overload REF =41.85Mpa, durability stress index f DI‘

[0095] f DI =G DI ·f REF =45Mpa

[0096] Step S600: Combine steps S300 and S500 to calculate the durability margin DM of the structure. The calculation formula is:

[0097]

[0098] Step S700: DM>0 means that under the assumed analysis conditions, the structure will not suffer fatigue cracking during service (DSG). DM is minimized to 0 to meet the requirements of the design objectives and complete the durability design of the preliminary design stage of the structure.

[0099] Finally, it should be noted that: the drawings of the embodiments disclosed in the present invention only involve structures related to the embodiments disclosed in the present invention, and other structures can refer to the general design. In the absence of conflict, the same embodiment and different embodiments of the present invention can be combined with each other;

[0100] Finally: 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 in the protection scope of the present invention.

Claims

1. A calculation method for durability design of aircraft rivet hole structure, characterized in that: include: According to the geometric parameters of the rivet hole structure and the load conditions, the influence coefficient of the countersunk nail hole, the influence coefficient of the open hole, the influence coefficient of the bidirectional stress field, the influence coefficient of the nail-loaded hole and the influence coefficient of the nail bending are calculated respectively, and then the stress concentration factor K of the rivet hole is calculated. T ; According to the geometric parameters, material parameters and process type of the rivet hole structure, the allowable peak stress K of the rivet hole is determined. TF and correction factors; According to the rivet hole structure type as the main structure, the dispersion coefficient LSF = 5, according to steps 1-2, determine the fatigue durability allowable stress index F of the connection hole DI ; According to the fatigue load spectrum, the fatigue load during the entire flight process is converted into an equivalent equal-amplitude load to determine the spectrum severity factor G. DI ; According to the actual load condition, the maximum stress under the reference load condition is obtained, and the durability stress index f is determined by combining the spectral severity coefficient. DI ; According to the fatigue durability allowable stress index F of the rivet hole structure DI and durability stress index f DI , calculate the durability margin DM of the structure; Obtain the durability margin DM to determine the current fatigue life. DM>0 means that under the assumed analysis conditions, the structure will not suffer from fatigue cracking during service. If DM<0, it means that the structure needs to be modified so that DM is minimized and approaches 0 to meet the requirements of the design objectives and complete the durability design of the preliminary design stage of the structure.

2. The calculation method for durability design of aircraft rivet hole structure according to claim 1, characterized in that: The stress concentration factor K T The calculation formula is: Among them, α is the nail load ratio, KTCSK is the influence coefficient of the countersunk nail hole, and the calculation formula is: K TCSK =1.26-0.48exp[-0.25(t / d)]*[0.57-1.82(tc / t)(t / d) 0.6 +0.56(tc / t) 2 (t / d) 0.3 ] K TG is the opening influence coefficient, and the calculation formula is: K TBI is the influence coefficient of the bidirectional stress field, and the calculation formula is: K TBI =1-(σ2 / σ1) / 3 K TBRG is the influence coefficient of the nail-loaded hole, and the calculation formula is: K TPB is the influence coefficient of nail bending, and the calculation formula is: Where D is the diameter of the nail hole, t is the thickness of the connection area, tc is the countersunk thickness, s is the nail hole spacing, and α is the nail load ratio.

3. The calculation method for durability design of aircraft rivet hole structure according to claim 2, characterized in that: The load conditions include total load P, bypass load PBP, nail load PPL, nail load ratio α=P PL / P.

4. The calculation method for durability design of aircraft rivet hole structure according to claim 1, characterized in that: The correction factor includes the size correction factor C SE , Surface treatment influence factor C ST , Cold work hardening influence coefficient C CW , Connector installation influence coefficient C FI , Material fiber direction correction factor C GO , Heat treatment thickness coefficient C HTT , slope influence coefficient S and fracture influence coefficient m.

5. The calculation method for durability design of aircraft rivet hole structure according to claim 4, characterized in that: The material parameters include material, brand, and fastening type.

6. The calculation method for durability design of aircraft rivet hole structure according to claim 4, characterized in that: The fatigue durability allowable stress index F of the rivet hole structure DI The calculation formula is: Where DSG is the target life of the design service period, LSF is the dispersion coefficient, if the rivet hole structure is the main structure, LSF = 5, if the rivet hole structure is the secondary structure, LSF = 3.

7. The calculation method for durability design of aircraft rivet hole structure according to claim 1, characterized in that: The spectral severity coefficient G DI The calculation formula is: Among them, n z is overload, T0 is the flight hours corresponding to a random spectrum block, is the equivalent damage corresponding to the i-th cycle in the random spectrum, It is the equivalent damage corresponding to one equivalent equal-amplitude cyclic action.

8. The calculation method for durability design of aircraft rivet hole structure according to claim 1, characterized in that: The durability stress index f DI The calculation formula is: f DI =G DI ·f REF Among them, f REF It is the maximum stress under the reference load condition with 1g overload.

9. The calculation method for durability design of aircraft rivet hole structure according to claim 1, characterized in that: The durability margin DM calculation formula is:

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