CN114357729A - Fatigue load spectrum compiling method based on damage characterization sky point - Google Patents
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Abstract
The invention belongs to the technical field of aircraft structure fatigue load spectrum compilation, and particularly relates to a fatigue load spectrum compilation method based on damage characterization sky points. The method is characterized in that a damage characterization sky point of each key component is determined, and a proper sky point combination proportion is determined, so that a compiled load spectrum meets the damage severity requirements of all key components, and the damage of individual components is not too large, namely the fatigue damage of all key components under the load spectrum is balanced.
Description
Technical Field
The invention belongs to the technical field of aircraft structure fatigue load spectrum compilation, and particularly relates to a fatigue load spectrum compilation method based on damage characterization sky points.
Background
Military aircraft structural strength specifications (GJB67.6A-2008) require that durability design use load spectra be compiled to reflect severe use cases of the aircraft within the design use distribution so that 90% of the aircraft in the fleet are expected to meet the design service life. The load spectrum reflecting the severe use case is generally referred to as the severe spectrum, and the load spectrum reflecting the average use case is referred to as the average spectrum. Load spectrum compiling methods in the existing specifications/manuals are all directed at average spectrums, and no clear and uniform serious spectrum compiling method exists at present.
The design and use of an aircraft is generally represented by a mission profile. The mission profile is a mission sequence table consisting of several mission segments and performance parameters, thus constituting one complete flight for each mission. The traditional fatigue load spectrum compiling method is a flight-continuation-flight method based on typical mission profile combination, also called a mission analysis method, and reflects different mission profile combinations and different maneuvering strength combinations in service life.
The fatigue load spectrum compiling method based on the damage characterization sky point is different from a task analysis method, can meet the requirement that the load spectrum reflects the serious use condition in the airplane design use distribution, and is balanced in the severity of all key components. This method reflects typical sky-point combinations, not mission profile combinations. The typical sky point is the sky position and the basic flight state when the aircraft performs basic maneuver flight. A typical airspace point consists of a set of specific altitudes, mach numbers, weights, and external configurations.
Disclosure of Invention
The purpose of the invention is as follows: in order to compile a load spectrum which can reflect the serious use condition in the use distribution of the airplane design and balance the fatigue damage of all key parts, the invention provides a fatigue load spectrum compiling method based on damage characterization sky points.
The technical scheme of the invention is as follows:
the invention discloses a fatigue load spectrum compiling method based on damage characterization sky-space points, which is characterized in that the damage characterization sky-space point of each key component is determined and a proper sky-point combination proportion is determined, so that the compiled load spectrum meets the damage severity requirements of all key components, the damage of individual components is not overlarge, and the fatigue damage of all key components under the load spectrum is balanced.
The requirement for severity of damage means: for each key component, fatigue damage under a damage characterization sky point load spectrum is taken as a reference damage, the compiled fatigue load spectrum is required to reach a reference damage level of a specific proportion, the proportion is usually 80% for a wing main girder, 50% to 80% for a fuselage and 35% to 45% for a control surface. The damage characterizing sky-point refers to the sky-point where the damage to the part is the most severe among all typical sky-points. The damage characterization sky points for different structural components are usually different unless there is a large correlation between the loads of certain components.
A fatigue load spectrum compiling method based on damage characterization sky points comprises the following steps:
s1: assuming that a typical task section and a time proportion thereof, basic maneuvers and occurrence times thereof in a life cycle are determined (or known), according to task segment definitions of the typical task section, the task segments are merged into n typical sky points according to the principle of similarity of characteristic parameters, and m key component loads are selected from all component load types;
in one possible embodiment, in said step S1, the basic maneuver, also called basic maneuver layer, represents a continuous time-of-flight history of the aircraft completing a set of specific flight parameters, continuously changing from a certain possible minimum load value to a certain possible maximum load value.
In one possible embodiment, in the step S1, the characteristic parameters refer to the height, mach number, weight and configuration of the mission segment. One mission profile may contain multiple typical sky points, and different mission profiles may have the same typical sky points.
In one possible embodiment, in step S1, the critical component load refers to a load that has the greatest impact on the fatigue damage of the critical component, such as: wing root bending moment, wing half-span long bending moment, vertical tail root bending moment, front/middle/rear fuselage key section bending moment, movable control surface hinge moment and the like.
S2: for each sky point, assuming that all basic maneuvering actions occur under the sky point in a life cycle, acquiring the load of a key component in a typical load state of each maneuvering by adopting a six-degree-of-freedom flight simulation method and a flight parameter analysis method, compiling the load spectrum of each key component under the sky point by adopting a probability sampling method, and finally obtaining n x m groups of single sky point load spectrums;
in a possible embodiment, in step S2, a probability sampling method is used to compile a load spectrum of each key component under the sky point, and the specific steps are as follows:
according to the occurrence frequency of each basic maneuver in a life cycle, random sampling arrangement is carried out on the maneuvers by adopting a mixed multiplication-simultaneous-remainder method to form a basic maneuver spectrum under a single day vacancy point. Then, the key component loads of each maneuvering typical load state are arranged according to the sequence of the basic maneuvering spectrum, and the load spectrum of each key component under a single sky point can be obtained.
S3: for each key component load, respectively calculating fatigue damage of typical structure details under n groups of single sky point load spectrums, and selecting a sky point with the maximum fatigue damage as a damage characterization sky point; selecting the maximum value of the fatigue damage as a reference damage, calculating the relative damage ratio (namely the fatigue damage degree) of the fatigue damage and the reference damage under the load spectrum of other single day empty points, sorting the fatigue damage degrees from large to small, and finally selecting the first g empty points, wherein g is 1/8-1/4 n;
in one possible embodiment, in the step S3, the fatigue damage calculation process for the typical structural details is as follows:
1) counting the maximum load values in n groups of single sky point load spectrums, dividing the n groups of load spectrums by the maximum value, and converting the n groups of load spectrums into n groups of coefficient spectrums;
2) selecting typical structure detail types (such as lugs and fastening holes) of the key parts, and determining a proper reference stress level by adopting a strain life analysis method (also called a local stress-strain method), so that the shortest crack initiation life under n groups of single sky point coefficient spectrums is close to the designed service life of the airplane;
3) calculating the strain fatigue damage of n groups of single sky point coefficient spectrums under the reference stress level determined in the step 2).
In one possible embodiment, in the step S3, the relative damage ratio (i.e., the fatigue damage degree) of the fatigue damage to the reference damage under the loading spectrum of other single sky points is calculated according to the following formula:
wherein DR represents the degree of fatigue damage, DiRepresenting the strain fatigue damage under the load spectrum of the ith single sky point, and n is the number of typical sky points.
S4: taking and collecting g sky points selected by each key component load in the step S3, and if the quantity of the collected sky points is greater than 2 x g, further comprehensively screening f sky points according to the principle that the fatigue damage degree of the main key component load under the sky points is as large as possible, wherein f is 1.5 x g-2 x g; if the number of the collected sky points is less than 2 x g, directly selecting all the collected sky points;
in one possible embodiment, in said step S4, the main critical component loads are typically taken as wing root bending moments and/or wing half span length bending moments and/or mid-fuselage bending moments.
S5: based on the f sky points screened in the step S4 and the fatigue damage degrees of the loads of the key components obtained in the step S3 under the sky points, a damage linear superposition method is adopted to perform preliminary combination analysis of the sky points, and a plurality of sky point combinations are initially selected on the basis that the total fatigue damage degree of the loads of the main key components reaches a specific value (usually at least 80%);
in one possible embodiment, in the step S5, the specific process of the preliminary sky point combination analysis is as follows:
1) j represents the number of sky points in the sky point combination, and j < f is satisfied;
2) randomly selecting j space points from the f space points, and assuming a group of possible probability combinations to represent the flight time proportion of each space point, wherein the total time proportion is 1;
3) and calculating the total fatigue damage degree of each key component load under the sky point combination and probability combination by adopting a damage linear superposition method (as shown in a formula), wherein the total fatigue damage degree of the main key component load (usually, wing root bending moment and/or wing half-span length bending moment and/or middle fuselage bending moment) is required to reach a specific value (usually at least 80%), and thus, a plurality of sky point combinations (including flight time proportion) are initially selected.
Wherein DRiRepresenting the fatigue damage degree p of a certain key component load under the ith sky point in the current sky point combinationiRepresenting the time-of-flight proportion, p, of the ith sky point in the current sky point combinationiThere are various combinations of values, usually adjusted in 10% increments. Such as: assuming that j is 2, then piThe combination may be 10%/90%, 20%/80%, 30%/70%, 40%/60%, and so on; assuming that j is 3, then piThe combination may be 10%/10%/80%, 10%/20%/70%, 10%/30%/60%, 10%/40%/50%, and so on.
S6: based on the initially selected sky point combinations in the step S5, probability distribution is performed on the occurrence frequency of each maneuver in a lifetime according to the flight time proportion of each sky point, then a probability sampling method is adopted to compile a key component load spectrum of each sky point combination, and then the fatigue damage of the key component load spectrum of each sky point combination is calculated by adopting the typical structure detail fatigue damage calculation method in the step S3, so that the final sky point combination and the corresponding load spectrum thereof are determined on the basis of meeting the damage severity requirement of each key component.
In a possible embodiment, in step S6, the probability distribution of the occurrence number of each maneuver in a lifetime is performed according to the proportion of the flight time of each sky point, and the calculation formula of the probability distribution is as follows.
Wherein N isk,iRepresenting the number of occurrences of the kth maneuver assigned to the ith sky-point in the current sky-point combination, NkRepresenting the total number of occurrences of the kth maneuver over a lifetime, piRepresenting the proportion of time-of-flight for the ith sky point in the current sky point combination.
In a possible embodiment, in step S6, a probability sampling method is used to compile a key component load spectrum of each sky point combination, and the specific steps are as follows:
according to the occurrence frequency of each sky point in a life cycle, random sampling arrangement is carried out on the sky points by adopting a mixed multiplication-congruence method, then random arrangement is carried out on each maneuver action in each sky point according to the occurrence frequency of each maneuver action by adopting the same random sampling method, and a basic maneuver spectrum under the combination of the sky points is formed. Then, the key component loads of each maneuvering typical load state are arranged according to the sequence of the basic maneuvering spectrum, and the load spectrum of each key component under each sky point combination can be obtained.
The invention has the beneficial effects that: the fatigue load spectrum is compiled based on the damage characterization sky points, the method can quantitatively evaluate the damage severity of each key part under all the sky points, the finally compiled load spectrum can meet the requirement that the load spectrum reflects the severe use condition in the design use distribution of the airplane, and the severity of the load spectrum to all key parts is balanced.
Drawings
FIG. 1 is a flow chart of the method of the present invention
FIG. 2 is a wing load spectrum sequence of an embodiment.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Taking a certain type of airplane load spectrum compilation as an example, the method disclosed by the invention is specifically implemented by the following steps:
1) according to step s1, 16 typical sky points and 6 critical component loads are selected,
2) according to the step s2, 16 x 6 groups of component load spectrums under the single sky points are compiled,
3) according to the step s3, calculating fatigue damage degrees under all single sky point load spectrums by adopting the strain life method, and respectively selecting the first 3 sky points of each key component load;
4) according to step s4, 6 sky points are further selected by comprehensive screening. Table 1 lists the fatigue damage levels of each key component load under these 6 single sky point load spectra.
TABLE 1 fatigue damage degree of each key component load under single sky point load spectrum
| Space point numbering | Wing root M | Wing half-spread length M | Front body M | Middle fuselage M | Root of vertical fin M | Flap HM |
| PITS1 | 0.5 | 0.44 | 0.4 | 0.53 | 0.43 | 0.28 |
| PITS2 | 0.88 | 0.9 | 1 | 0.72 | 0.29 | 0.88 |
| PITS3 | 0.56 | 0.59 | 0.54 | 0.93 | 0.62 | 0.17 |
| PITS4 | 0.31 | 0.28 | 0.42 | 1 | 0.72 | 0.12 |
| PITS5 | 0.91 | 0.92 | 0.35 | 0.84 | 0.44 | 0.2 |
| |
1 | 1 | 0.39 | 0.82 | 0.56 | 0.35 |
5) And according to the step s5, performing preliminary sky point combination analysis by adopting a damage linear superposition method, and initially selecting 15 groups of sky point combinations meeting the damage requirement. Tables 2-4 illustrate the critical part load total fatigue damage results for 3 sets of preliminary sky point combinations.
TABLE 2 Total fatigue damage of critical component load for initial selection of sky-point combination in group 1 (Linear superposition method)
TABLE 3 Total fatigue damage of critical component load for initial selection of sky-point combination in group 2 (Linear superposition method)
TABLE 4 Total fatigue damage of critical component load for initial selection of sky-point combination in group 3 (Linear superposition method)
6) According to the step s6, key component load spectrums of 15 groups of primarily selected sky point combinations are compiled by adopting a probability sampling method, fatigue damage of typical structure details under each load spectrum is calculated, and finally the 2 nd group of sky point combinations and corresponding component load spectrums are selected on the basis of meeting the requirement of the damage severity degree of each key component. Table 5 illustrates the key component load total fatigue damage results for group 2 sky point combinations. The spectrum sequence of the bending moment load of the root part of the wing in a service life is shown in figure 2, and the ordinate is normalized. The damage severity degree is 80% for wing bending moment, 50% -80% for fuselage bending moment and 35% -45% for vertical fin/control surface.
TABLE 5 Total fatigue damage for critical part load for group 2 sky point combinations (typical detail fatigue damage calculation)
The foregoing is merely a detailed description of the embodiments of the present invention, and some of the conventional techniques are not detailed. The scope of the present invention is not limited thereto, and any changes or substitutions that can be easily made by those skilled in the art within the technical scope of the present invention will be covered by the scope of the present invention. The protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (8)
1. A fatigue load spectrum compiling method based on damage characterization sky points is characterized by comprising the following steps:
s1: assuming that a typical task section and a time proportion thereof, basic maneuvers and occurrence times thereof in a life cycle are determined, according to task segment definitions of the typical task section, the task segments are merged into n typical sky points according to the principle of similarity of characteristic parameters, and m key component loads are selected from all component load types;
s2: for each sky point, assuming that all basic maneuvering actions occur under the sky point in a life cycle, acquiring the load of a key component in a typical load state of each maneuvering by adopting a six-degree-of-freedom flight simulation method and a flight parameter analysis method, compiling the load spectrum of each key component under the sky point by adopting a probability sampling method, and finally obtaining n x m groups of single sky point load spectrums;
s3: for each key component load, respectively calculating fatigue damage of typical structure details under n groups of single sky point load spectrums, and selecting a sky point with the maximum fatigue damage as a damage characterization sky point; selecting the maximum value of fatigue damage as reference damage, calculating the relative damage ratio of the fatigue damage to the reference damage under the load spectrum of other single day empty points, namely the fatigue damage degree, sorting the fatigue damage degrees from large to small, and finally selecting the first g empty points, wherein g is 1/8-1/4 n;
s4: taking and collecting g sky points selected by each key component load in the step S3, and if the quantity of the collected sky points is greater than 2 x g, further comprehensively screening f sky points according to the principle that the fatigue damage degree of the main key component load under the sky points is as large as possible, wherein f is 1.5 x g-2 x g; if the number of the collected sky points is less than 2 x g, directly selecting all the collected sky points;
s5: based on the f sky points screened in the step S4 and the fatigue damage degrees of the loads of the key components obtained in the step S3 under the sky points, performing preliminary combination analysis on the sky points by adopting a damage linear superposition method, and initially selecting a plurality of sky point combinations on the basis that the total fatigue damage degree of the loads of the main key components reaches a specific value;
s6: based on the initially selected sky point combinations in the step S5, probability distribution is performed on the occurrence frequency of each maneuver in a lifetime according to the flight time proportion of each sky point, then a probability sampling method is adopted to compile a key component load spectrum of each sky point combination, and then the fatigue damage of the key component load spectrum of each sky point combination is calculated by adopting the typical structure detail fatigue damage calculation method in the step S3, so that the final sky point combination and the corresponding load spectrum thereof are determined on the basis of meeting the damage severity requirement of each key component.
2. The method for compiling the fatigue load spectrum based on the damage characterization sky point of claim 1, wherein in the step S2, the probability sampling method is adopted to compile the load spectrum of each key component under the sky point, and the specific steps are as follows:
randomly sampling and arranging all maneuvers by adopting a hybrid multiplication-residue method according to the occurrence frequency of each basic maneuver in a life cycle to form a basic maneuver spectrum under a single day empty point; then, the key component loads of each maneuvering typical load state under the sky point are arranged according to the sequence of the basic maneuvering spectrum, and the load spectrum of each key component under a single sky point can be obtained.
3. The method for formulating a fatigue load spectrum based on damage characterization sky point as claimed in claim 1, wherein in said step S3, the fatigue damage calculation process of typical structure details is as follows:
1) counting the maximum load values in n groups of single sky point load spectrums, dividing the n groups of load spectrums by the maximum value, and converting the n groups of load spectrums into n groups of coefficient spectrums;
2) selecting typical structure detail types of the key parts, and determining a reference stress level by adopting a strain life analysis method to ensure that the shortest crack initiation life under n groups of single sky point coefficient spectrums is close to the design service life of the airplane;
3) calculating the strain fatigue damage of n groups of single sky point coefficient spectrums under the reference stress level determined in the step 2).
4. The method of claim 1, wherein in the step S3, the fatigue damage ratio of the fatigue damage to the reference damage under the other single sky point load spectrum, i.e. the fatigue damage degree, is calculated according to the following formula (one):
wherein DR represents the degree of fatigue damage, DiRepresenting fatigue damage under the loading spectrum of the ith single sky point, and n is the number of typical sky points.
5. The method for compiling the fatigue load spectrum based on the damage characterization sky point according to claim 1, wherein in the step S4, the main critical component loads are wing root bending moment and/or wing half-span length bending moment and/or mid-fuselage bending moment.
6. The method of claim 1, wherein in the step S5, the detailed procedure of the preliminary analysis of sky point combination is as follows:
1) j represents the number of sky points in the sky point combination, and j < f is satisfied;
2) randomly selecting j space points from the f space points, and assuming a group of possible probability combinations to represent the flight time proportion of each space point, wherein the sum of the time proportions is 1;
3) and calculating the total fatigue damage degree of each key component load under the sky point combination and the probability combination by adopting a damage linear superposition method, wherein the total fatigue damage degree of the main key component load is required to reach a specific value, the main key component load is wing root bending moment and/or wing half-span length bending moment and/or middle fuselage bending moment, and the total fatigue damage degree is at least 80%, so that a plurality of sky point combinations and flight time proportions are initially selected.
Wherein DRiRepresenting the fatigue damage degree p of a certain key component load under the ith sky point in the current sky point combinationiRepresenting the proportion of time-of-flight for the ith sky point in the current sky point combination.
7. The method for formulating a fatigue load spectrum based on damage characterization sky-point as claimed in claim 6, wherein in step S6, the probability distribution of the occurrence number of each maneuver in a lifetime is performed according to the proportion of the time of flight of each sky-point, and the formula (iii) of the probability distribution is as follows:
wherein N isk,iRepresenting the number of occurrences of the kth maneuver assigned to the ith sky-point in the current sky-point combination, NkRepresenting the total number of occurrences of the kth maneuver over a lifetime, piRepresenting the proportion of time-of-flight for the ith sky point in the current sky point combination.
8. The method for compiling a fatigue load spectrum based on the damage characterization sky point of claim 6, wherein in the step S6, a probability sampling method is adopted to compile a key component load spectrum of each sky point combination, and the specific steps are as follows:
randomly sampling and arranging the sky points by adopting a hybrid multiplicative congruence method according to the occurrence frequency of each sky point in a life cycle, and randomly arranging each maneuver action in each sky point by adopting the same random sampling method according to the occurrence frequency of each maneuver action to form a basic maneuver spectrum under the combination of the sky points; then, the key component loads of each maneuvering typical load state are arranged according to the sequence of the basic maneuvering spectrum, and the load spectrum of each key component under each sky point combination can be obtained.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114878123A (en) * | 2022-07-12 | 2022-08-09 | 中国飞机强度研究所 | Acceleration model-based combined load spectrum compilation method in aircraft fatigue strength test |
| CN117454511A (en) * | 2023-10-26 | 2024-01-26 | 北京航空航天大学 | 5X 5 spectrum compiling method of transport aircraft based on longhorn beetle whisker searching method and interior point method |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114878123A (en) * | 2022-07-12 | 2022-08-09 | 中国飞机强度研究所 | Acceleration model-based combined load spectrum compilation method in aircraft fatigue strength test |
| CN114878123B (en) * | 2022-07-12 | 2022-09-16 | 中国飞机强度研究所 | Acceleration model-based combined load spectrum compilation method in aircraft fatigue strength test |
| CN117454511A (en) * | 2023-10-26 | 2024-01-26 | 北京航空航天大学 | 5X 5 spectrum compiling method of transport aircraft based on longhorn beetle whisker searching method and interior point method |
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