Structural stress level control method based on life index constraint

Abstract

The invention belongs to the field of structural strength design, and particularly relates to a structural stress level control method based on life index constraint, which comprises the following steps: selecting one structural fatigue key part characteristic to determine the range of a stress concentration coefficient Kt of the corresponding structural fatigue key part; constructing an initial stress spectrum of a fatigue key part of the aircraft structure; carrying out initial calculation on the fatigue life of the aircraft structure to obtain the initial life of the aircraft structure corresponding to the key part; judging whether the fatigue life requirement of the aircraft structure is met or not, and if yes, fitting the range of a stress concentration coefficient Kt and a stress level Kt-sigma curve for fatigue key parts of other structures; rapid multi-discipline and multi-scheme comprehensive analysis based on fatigue and other disciplines in the scheme stage can be achieved, the design period is greatly shortened, the capability of rapidly evaluating and obtaining the optimal layout scheme by combining the service life index of the aircraft is formed, the design requirements for the ultra-low structure weight coefficient and the high service life index of a new generation of aircrafts in the future are met, and the design efficiency is improved. And the economy of a new generation of aircrafts is effectively improved.

Description

Technical Field

[0001] The present application belongs to the field of structural strength design, and in particular relates to a structural stress level control method based on life index constraints. Background Art

[0002] In order to achieve the ultra-low structural weight coefficient design and high life indicators of new fighters, the design-verification-redesign process in traditional aircraft structural design can no longer meet the research and development requirements of the agility of modern fighters. It is necessary to instill verification opinions at the aircraft scheme stage and make corresponding suggestions for the scheme layout from the perspectives of load, structure, strength, etc. From the perspective of the development process, the design of aircraft structure layout has gradually moved towards automation, speed, and topology. In the development process of Chinook CH-47 transport helicopter, Airbus A380 aircraft, and F35 fighter, the automated, fast, and topological structural layout design concept has achieved good structural weight benefits. In the aircraft scheme design stage, since the load-bearing layout scheme needs to be frequently iterated according to multi-professional opinions, the verification requirements for its structural strength are gradually moving towards lightweight and speed. In the existing scheme design, the analysis processes and results of various disciplines such as fatigue, stability, and flutter are independent of each other, and multi-disciplinary and multi-scheme comprehensive analysis cannot be effectively carried out, making it difficult to quickly evaluate and obtain the optimal layout scheme. Therefore, a method is needed to control the structural stress level in combination with the life index. In the aircraft design stage, the critical stress levels of different materials under a given life are calculated to provide a stress index based on fatigue analysis. Summary of the invention

[0003] The purpose of this application is to provide a structural stress level control method based on life index constraints to solve the problem that the design-verification-redesign process in traditional aircraft structural design can no longer meet the requirements of modern fighter aircraft agility research and development.

[0004] The technical solution of the present application is: a structural stress level control method based on life index constraint, comprising:

[0005] According to the aircraft structure layout plan, determine the materials and characteristics of the aircraft structural fatigue key parts, select one of the structural fatigue key parts to determine the range of the stress concentration factor Kt of the corresponding structural fatigue key part; obtain the aircraft's typical flight mission profile and compile the center of gravity overload spectrum of the whole aircraft; give the unit initial value according to the center of gravity overload spectrum of the whole aircraft, and construct the initial stress spectrum of the aircraft structural fatigue key parts through the unit initial value;

[0006] According to the initial stress spectrum of the key fatigue parts of the aircraft structure and the range of the stress concentration factor Kt, the initial calculation of the fatigue life of the aircraft structure is performed to obtain the initial life of the aircraft structure at the corresponding key parts; whether the initial life of the aircraft structure meets the requirements of the fatigue life of the aircraft structure is judged, if not, the unit initial value is adjusted, the stress level of the key parts, the overload spectrum of the center of gravity of the whole aircraft and the initial stress spectrum are re-obtained, after iterating the aircraft stress level, the current fatigue life of the aircraft structure is recalculated, and the judgment is made again, if not, the stress level of the key parts of the aircraft is continued to be iterated until the critical value level of the fatigue life of the aircraft structure is met;

[0007] According to the determined range of stress concentration factor Kt of key structural fatigue parts, other key structural fatigue parts are selected in turn to obtain the range of stress concentration factor Kt and stress level of all key structural fatigue parts, and the range of stress concentration factor Kt and stress level Kt-σ curve are fitted to form a structural stress level control method based on the constraints of aircraft structure fatigue life indicators.

[0008] Preferably, the aircraft structure fatigue critical parts include nail holes, bosses, fillets and thickness transition areas.

[0009] Preferably, the specific method for obtaining the range of the stress concentration factor Kt includes an experimental method, an engineering chart method and an empirical formula method.

[0010] Preferably, when the experimental method is used, the corresponding structural fatigue key part characteristics are obtained, the corresponding test piece is made, a stress test is performed, the stress concentration data is obtained, and then the structural parameters of the test piece are compared and calculated with the stress concentration data to obtain the corresponding range of the stress concentration factor Kt.

[0011] Preferably, the unit initial value is the initial value of the 1g stress level σi corresponding to the key structural fatigue position. When adjusting the unit initial value, if the currently calculated initial life of the aircraft structure is lower than the aircraft structure life index, σ0 is reduced to σ1, where σ0 is the adjusted 1g stress level; if the currently calculated initial life of the aircraft structure is higher than the aircraft structure life index, σ0 is increased to σ1.

[0012] Preferably, when performing the initial calculation of the fatigue life of the aircraft structure, the nominal stress analysis method is used to obtain the SN curve data of the key parts of the material, and the stress concentration factor K is given. t1 And the unit initial values ​​of the corresponding key parts are obtained after calculation.

[0013] The structural stress level control method based on life index constraints in this application can realize rapid multidisciplinary and multi-scheme comprehensive analysis based on fatigue and other disciplines in the scheme stage, significantly reduce the design cycle, and form the ability to quickly evaluate the aircraft combined with life index to obtain the optimal layout plan, meet the design requirements of ultra-low structural weight coefficient and high life index of the future new generation of aircraft, and effectively improve the economy of the new generation of aircraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] 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.

[0015] Figure 1 This is a schematic diagram of the overall process of this application;

[0016] Figure 2 This is a schematic diagram of the range of the stress concentration factor Kt and the stress level Kt-σ curve of this application. DETAILED DESCRIPTION

[0017] 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.

[0018] A structural stress level control method based on life index constraint, such as Figure 1 As shown, the following steps are included:

[0019] Step S100, compiling stress spectrum based on the characteristics of key parts of structural fatigue

[0020] According to the aircraft structure layout plan, determine the materials and features of the aircraft structure's key fatigue parts, such as nail holes, bosses, fillets, thickness transition zones and other areas prone to stress concentration. Select one of the key structural fatigue part features to determine the range of the stress concentration factor Kt of the corresponding key structural fatigue part.

[0021] Preferably, specific methods for obtaining the range of the stress concentration factor Kt include experimental methods, engineering chart methods, and empirical formula methods; when the experimental method is used, the corresponding characteristics of the key parts of the structural fatigue are obtained, the corresponding test pieces are made, stress tests are carried out, stress concentration data are obtained, and then the structural parameters of the test pieces are compared and calculated with the stress concentration data to obtain the corresponding range of the stress concentration factor Kt.

[0022] The typical flight mission profile of the aircraft is obtained, and the center of gravity overload spectrum of the whole aircraft is compiled. The initial value of the 1g stress level σi of the corresponding key structural fatigue parts is given according to the center of gravity overload spectrum of the whole aircraft, and the unit initial value is obtained. The initial stress spectrum of the key parts of the aircraft structure fatigue is constructed through the unit initial value.

[0023] Step S200: Structural critical stress level analysis method based on life index constraint

[0024] According to the initial stress spectrum of the key parts of the aircraft structure fatigue and the range of the stress concentration factor Kt, the nominal stress analysis method is used to obtain the SN curve data of the key parts material, and the stress concentration factor Kt is given. t1 And the unit initial values ​​of the corresponding key parts are used to perform the initial calculation of the fatigue life of the aircraft structure and obtain the initial life of the aircraft structure corresponding to the key parts.

[0025] Determine whether the initial life of the aircraft structure meets the aircraft structure fatigue life requirements. If not, adjust the 1g stress level σ0 (if the currently calculated initial life of the aircraft structure is lower than the aircraft structure life index, reduce σ0 to σ1, otherwise increase it), and re-acquire the stress level of key parts, the overload spectrum of the center of gravity of the whole aircraft, and the initial stress spectrum. After iterating the aircraft stress level, recalculate the current fatigue life of the aircraft structure and make another judgment. If not, continue to iterate the stress level of the key parts of the aircraft until the 1g stress level σ i The corresponding aircraft structure fatigue life meets the critical value level of aircraft structure fatigue life, and the 1g stress level σ is determined i The stress concentration factor is K t0 The design allowable value of aircraft structure fatigue strength at .

[0026] Step S300: Structural stress level control method based on life index constraint

[0027] According to the determined range of stress concentration factor Kt of key structural fatigue parts, the above method is repeated to obtain the range of stress concentration factor Kt and stress level (Kt) of all key structural fatigue parts. ti ,σ i ), and fit the range of stress concentration factor Kt and stress level Kt-σ curve, such as Figure 2 , forming a structural stress level control method based on the constraints of aircraft structure fatigue life indicators.

[0028] In summary, this application can achieve rapid multidisciplinary and multi-scheme comprehensive analysis based on fatigue and other disciplines in the scheme stage, significantly reduce the design cycle, and form the ability to quickly evaluate the aircraft combined with life indicators to obtain the optimal layout plan, meet the design requirements of ultra-low structural weight coefficient and high life indicators of the future new generation of aircraft, and effectively improve the economy of the new generation of aircraft.

[0029] 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;

[0030] 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 structural stress level control method based on life index constraint, characterized in that: include: According to the aircraft structure layout plan, determine the materials of the aircraft structure fatigue key parts and the characteristics of the structure fatigue key parts, select one of the structure fatigue key part characteristics to determine the range of the stress concentration factor Kt of the corresponding structure fatigue key part; Obtain the typical flight mission profile of the aircraft and compile the center of gravity overload spectrum of the whole aircraft; give the unit initial value according to the center of gravity overload spectrum of the whole aircraft, and construct the initial stress spectrum of the key parts of the aircraft structure fatigue through the unit initial value; According to the initial stress spectrum of the key fatigue parts of the aircraft structure and the range of the stress concentration factor Kt, the initial calculation of the fatigue life of the aircraft structure is performed to obtain the initial life of the aircraft structure at the corresponding key parts; Determine whether the initial life of the aircraft structure meets the requirements of the fatigue life of the aircraft structure. If not, adjust the initial value of the unit, re-acquire the stress level of key parts, the overload spectrum of the center of gravity of the whole aircraft, and the initial stress spectrum. After iterating the aircraft stress level, recalculate the current fatigue life of the aircraft structure and make a judgment again. If not, continue to iterate the stress level of the key parts of the aircraft until the critical value level of the fatigue life of the aircraft structure is met; According to the determined range of stress concentration factor Kt of key structural fatigue parts, other key structural fatigue parts are selected in turn to obtain the range of stress concentration factor Kt and stress level of all key structural fatigue parts, and the range of stress concentration factor Kt and stress level Kt-σ curve are fitted to form a structural stress level control method based on the constraints of aircraft structure fatigue life indicators.

2. The structural stress level control method based on life index constraint according to claim 1, characterized in that: The aircraft structure fatigue critical parts include nail holes, bosses, fillets and thickness transition areas.

3. The structural stress level control method based on life index constraint according to claim 1, characterized in that: The specific methods for obtaining the range of the stress concentration factor Kt include experimental method, engineering chart method and empirical formula method.

4. The structural stress level control method based on life index constraint according to claim 3 is characterized in that: When the experimental method is used, the corresponding key fatigue part characteristics of the structure are obtained, the corresponding test pieces are made, stress tests are carried out, stress concentration data are obtained, and then the structural parameters of the test pieces are compared and calculated with the stress concentration data to obtain the corresponding range of the stress concentration factor Kt.

5. The structural stress level control method based on life index constraint according to claim 1, characterized in that: The unit initial value is the initial value of the 1g stress level σi corresponding to the key structural fatigue position. When adjusting the unit initial value, if the currently calculated initial life of the aircraft structure is lower than the aircraft structure life index, σ0 is reduced to σ1, where σ0 is the adjusted 1g stress level; if the currently calculated initial life of the aircraft structure is higher than the aircraft structure life index, σ0 is increased to σ1.

6. The structural stress level control method based on life index constraint according to claim 1, characterized in that: When performing the initial calculation of the fatigue life of aircraft structures, the nominal stress analysis method is used to obtain the SN curve data of the key parts of the material and give the stress concentration factor K t1 And the unit initial values ​​of the corresponding key parts are obtained after calculation.

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