CN115906541B - Fastening connection system reliability forward design method based on multiple competition failure modes - Google Patents
Fastening connection system reliability forward design method based on multiple competition failure modes Download PDFInfo
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Abstract
The invention provides a method for forward designing the reliability of a fastening connection system based on a multi-competition failure mode, which comprises the following steps: failure mode and mechanism analysis of the fastening connection system; based on a single threaded connection reliability model in a single failure mode; a multiple contention failure mode based fastening connection system reliability model; the connection system is designed in the forward direction. The invention has the beneficial effects that: the invention provides a forward design method for reliability of a fastening connection system based on a multi-competition failure mode, which is based on stress-strength data, takes a k-out-of-n model as a framework, combines probability distribution functions and combines reliability design indexes, and solves the problem that the conventional design based on a safety coefficient method is difficult to accurately design stress-strength matching of complex working conditions at present; the method is simple and convenient to calculate and easy to implement, accords with engineering practice, is convenient for engineering technicians to master and use, is scientific and is convenient to apply and popularize.
Description
Technical Field
The invention belongs to the technical field of equipment connection system reliability forward design and the like, and particularly relates to a fastening connection system reliability forward design method based on a multi-competition failure mode.
Background
In the model in the fields of aerospace, aviation, aeronautics and the like, the connecting modes such as threaded connection, riveting, welding, adhesive connection and the like are commonly adopted among all the components, and the threaded connection is widely adopted by the advantages of good connecting rigidity, light weight, simple structure, convenient assembly and disassembly and the like, so that the threaded connection is the most main connecting mode adopted in the current engine. Such as an aircraft engine spool threaded connector, is a key important component of an aircraft engine and is a life-prolonging element, which is an important influencing factor for the reliability level of the aircraft engine. The threaded connector of the engine disc shaft has the characteristics of complex application working conditions, severe service environment, variable bearing load and the like, and therefore, the fastening connection system needs to have good mechanical properties, high precision and high reliability. Due to high precision requirements, high processing difficulty, and limited equipment and manufacturing process capabilities of manufacturing enterprises, threaded connectors are becoming key components in various models. And along with the compactness of the whole machine structure, the strength is higher and higher, and how to make the threaded connection more reliable and more accurate becomes the key for guaranteeing the performance of equipment such as an engine and the like.
In the whole life cycle of the fastening connection system, various stresses in the complex environment of the fastening connection system affect the reliability, and aiming at the characteristics of the fastening connection system that the environment profile is subjected to multiple stresses, multiple failure modes and the like, the fault mode analysis and the fault diagnosis method research are developed based on typical faults such as connection fracture, looseness, coating falling of a connecting piece and the like. Considering that the current threaded connection piece adopts technical means such as high temperature resistant design, fatigue resistant design, anti-loose design and the like in design, the traditional design based on the safety coefficient method is difficult to accurately perform stress-strength matching design under complex working conditions. In order to comprehensively evaluate the connection safety of the fastening connection system, the invention provides a forward design method of the reliability of the threaded connection, a reliability model and a design and evaluation method of the system are constructed from the perspective of a fastener, and based on the main failure mode of the fastening connection system in a service period, a multi-failure mode competition mechanism is adopted on the basis of a single stress-intensity interference model to develop the forward design method research of the reliability of the fastening connection system. The invention is helpful for realizing the reliable forward design of the threaded connection system, and can ensure the proper reliability level through accurate process control.
Disclosure of Invention
In view of the foregoing, the present invention is directed to a forward design method for reliability of a fastening connection system based on multiple competitive failure modes, so as to solve the problem that it is difficult to accurately design stress-strength matching under complex working conditions according to the conventional design based on the safety factor method.
In order to achieve the above purpose, the technical scheme of the invention is realized as follows:
a fastening connection system reliability forward design method based on a multi-competition failure mode comprises the following steps:
s1, analyzing a failure mode and a mechanism of a fastening connection system to obtain stress and strength of the fastening connection system in each failure mode;
s2, calculating a single threaded connection reliability model based on a single fault mode by using the stress and the strength of each fault mode in the step S1;
s3, calculating a fastening connection system reliability model based on a multi-competition failure mode under a k-out-of-n model by using the single threaded connection reliability model based on the single failure mode in the step S2;
s4, establishing a joint probability distribution function through a fastening connection system reliability model based on multiple competition failure modes, and carrying out forward design of the fastening connection system by combining the reliability design indexes of the fastening connection system.
Further, the calculation in step S2 is based on a single threaded connection reliability model in a single failure mode, comprising the steps of:
s21, respectively carrying out distribution inspection on stress and strength data according to the stress and strength of the fastening connection system in each fault stage, and determining the distribution of final stress and the distribution of final strength;
s22, substituting the distribution of the final stress and the distribution of the final strength into the formula (1), and calculating a single threaded connection reliability model based on a single failure mode.
Further, the expression of the formula (1) is:
when the stress and the intensity are subjected to normal distribution, probability density functions are respectively as follows:
in formula (1), define
Random variable->
Subject to mean and standard deviation of respectively
and />
Normal distribution of (1) at this point->
The reliability of (2) is:
when the stress and the intensity are subjected to exponential distribution, probability density functions are respectively as follows:
the reliability of R at this time is:
wherein ,
for single screw connection reliability in single failure mode, +.>
For stress->
For strength (I)>
and />
Probability density functions of stress and intensity, respectively, and +.>
And->
Independent of each other.
Further, the k-out-of-n model in step S3 is a relationship between the reliability of the fastening connection system and the reliability of the threaded connection.
Further, the calculating in step S3 is based on the fastening connection system reliability model of the multiple contention failure mode, including the steps of:
s31, assuming that the fastening connection system consists of n threaded connectors, setting the reliability of the n threaded connectors based on the mth failure mode to be respectively
；
S32, when any k screw connectors in the n screw connectors fail, the reliability of the fastening connection system in the mth failure mode is represented by a formula (4);
s33, obtaining a fastening connection system reliability model based on the multi-competition failure mode through the formula (4) and the formula (5).
Further, the expression of the formula (4) is:
wherein ,
based on the reliability of the nth-kth threaded connection in the mth failure mode, respectively, said
Is the reliability of the fastening connection system in the mth failure mode.
Further, the expression of the formula (5) is:
wherein ,
fastening connection system reliability in mth failure mode, respectively, +.>
Is a secure connection system reliability model based on multiple contention failure modes.
Further, in step S33, assuming that the threaded connections of the fastening connection system are equally distributed in stress, when there are k threaded connections failed, the stress originally divided into n threaded connections is divided into (n-k) threaded connections, and when the stress and the strength are both subjected to normal distribution, the stress probability density function of the threaded connections
Updated to
Intensity probability density function of threaded connection>
Unchanged;
definition of the definition
Random variable->
Subject to mean and standard deviation of respectively
and />
The reliability of the threaded connection at this time is updated as: />
；
If the fastening connection system is
And if 1 of the remaining (n-k) threaded connectors fail and the fastening connection system fails, the reliability of the fastening connection system based on the multi-competition failure mode is as follows:
wherein ,
is a secure connection system reliability model based on multiple contention failure modes.
Compared with the prior art, the forward design method of the reliability of the fastening connection system based on the multi-competition failure mode has the following advantages:
the invention provides a reliability forward design method of a fastening connection system based on a multi-competition failure mode, which is based on stress-strength data, takes a k-out-of-n model as a framework, combines probability distribution functions and combines reliability design indexes, thereby solving the problem that the conventional design based on a safety coefficient method is difficult to accurately design the stress-strength matching of complex working conditions; the method provided by the invention is simple and convenient to calculate and easy to realize, accords with engineering practice, is convenient for engineering technicians to master and use, is scientific and is convenient for application and popularization.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention. In the drawings:
FIG. 1 is a schematic diagram of a stress-intensity interference model according to an embodiment of the present invention;
FIG. 2 is a schematic view of an exemplary hub connection structure according to an embodiment of the present invention;
FIG. 3 shows the target preload multiple b and reliability according to the embodiment of the invention
A function curve diagram of the relation;
FIG. 4 is a diagram illustrating a pretightening force range with a reliability of 0.9999 according to an embodiment of the present invention;
FIG. 5 is a diagram of a pretightening force range with a reliability of 0.99999 according to an embodiment of the present invention;
FIG. 6 is a diagram illustrating a range of pretightening force with a reliability of 0.999999 according to an embodiment of the present invention;
fig. 7 is a schematic diagram of a pretightening force range with reliability 0.9999999 according to an embodiment of the present invention.
Detailed Description
It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other.
In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are merely for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first", "a second", etc. may explicitly or implicitly include one or more such feature. In the description of the present invention, unless otherwise indicated, the meaning of "a plurality" is two or more.
In the description of the present invention, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art in a specific case.
The invention will be described in detail below with reference to the drawings in connection with embodiments.
As shown in fig. 1 to 7, the method for designing the reliability forward direction of the fastening connection system based on the multiple contention failure mode is specifically implemented as follows:
step one: failure mode and mechanism analysis for fastening connection systems
And analyzing the failure mode, the reason, the influence and the mechanism of the fastening connection system according to the basic steps of the FMECA, determining the main failure mode and the failure mechanism, and obtaining the actual stress and strength data of the fastening connection system in the main failure mode.
Step two: threaded connection reliability model based on single fault mode
And combining the main failure modes of the fastening connection system, and establishing a reliability model of the fastening connection system in a multi-competition failure mode based on the stress intensity interference relation in each failure mode and the competition mechanism among the failure modes. After the bolt strength data and stress profile are given, respectively carrying out distribution inspection on the stress and strength data according to the actual stress and strength data of the fastening connection system in each fault stage, determining proper stress and strength distribution, then substituting the distribution of the stress and strength into the formula (1), and calculating the reliability of the single threaded connection based on the single fault mode
。
wherein 
The reliability of (2) is: />
（1）
Stress
And intensity->
The probability density functions of (2) are +.>
and />
And->
And->
Is independent of each other,
when the stress and the intensity are subjected to normal distribution, probability density functions are respectively as follows:
definition of the definition
Random variable->
Obeying mean and standard deviation to be +.>
And
normal distribution of (1) at this point->
The reliability of (2) is: />
When the stress and the intensity are subjected to the exponential distribution, the probability densities are respectively as follows:
at this time
The reliability of (2) is:
step three: fastening connection system reliability model based on multiple competition failure modes under k-out-of-n model
The fastening connection system is composed of
The group of threaded connections is formed, and the relationship between the reliability of the fastening connection system and the reliability of the threaded connections can be regarded as a k-out-of-n model, since the threaded connections together take on the connection. Since the number of bolts for connection of the fastening connection system of different model parts is variable, it is assumed that the fastening connection system is composed of n threaded connection pieces, reliability of each threaded connection piece +>
Can be obtained by calculation in the second step. Wherein:
since the distribution form of the stress applied to each of the n threaded connectors is not necessarily the same, the reliability of the n threaded connectors based on the mth failure mode is set to be respectively
。
Based on this, when any k screw connectors out of the n screw connectors fail, the fastening connection system reliability in the mth failure mode is:
the multiple contention failure mode based fastening connection system reliability model:
assuming an even distribution of the stresses on the threaded connections of the threaded connection (i.e., the fastening connection system), when there are k threaded connections that fail, the stresses originally divided into n threaded connections are divided into (n-k) threaded connections, and when the stresses and the strengths are both subject to normal distribution, the probability density function of the stresses on the threaded connections
To be updated to
Intensity probability density function of threaded connection>
Unchanged, definition->
Random variable->
Obeying mean and standard deviation to be +.>
and />
The reliability of the threaded connection at this time is updated as:
. If screw connectionThe device is
The system, namely that any 1 screw thread connecting piece in the remaining (n-k) screw thread connecting pieces is invalid, and the screw thread connecting piece is invalid, the reliability of the fastening connecting system based on the multi-competition failure mode is as follows:
step four: establishing a joint probability distribution function, and combining reliability design indexes to carry out forward design of a connection system
Judging the correlation between each design variable and the reliability model of the fastening connection system, analyzing the influence of each failure mode by the conditional probability, and obtaining the design influence factor of each failure mode
(mutual independence or coupling relation among influence factors) and reliability index of fastening connection system +.>
And (3) combining the reliability design index of the fastening connection system, carrying out forward design of the connection system, and selecting the optimal design influence factor range or parameter combination under the condition of conforming to the reliability design index.
Through the steps, the screw connection piece is taken as an element, the stress-intensity data is taken as a basis, the k-out-of-n model is taken as a bridge, the forward design method of the reliability of the fastening connection system based on the multi-competition failure mode is provided, the problem that the traditional design based on the safety coefficient method is difficult to accurately perform the stress-intensity matching design of the complex working condition is solved, the effectiveness of the model is ensured by combining the inspection method, the engineering practical situation is met, the calculation is simple, an effective and feasible technical means is provided for engineering technicians, and important application value exists.
Firstly, analyzing a main failure mode of a threaded connection, judging the correlation among multiple degradation failure modes based on the main failure mode and failure criteria of a fastening connection system, and establishing a threaded connection reliability evaluation model of the single failure mode by analyzing the influence among the failure modes through conditional probability on the basis of a single stress-intensity interference model; and then, based on the composition structure of the fastening connection system, combining a k-out-of-n model, establishing a reliability model of the fastening connection system based on multiple competition failure modes, finally, judging the correlation between each design variable and the reliability model of the fastening connection system, analyzing the influence of each failure mode through conditional probability, establishing a joint probability distribution function, combining reliability design indexes, carrying out forward design of the connection system, and selecting the optimal design parameters.
The invention has the following advantages:
Example 1
The invention will be described in further detail below with reference to a connector comprising 24 sets of threaded connectors for connecting a turbine disk to an compressor shaft in an aero-engine.
The most critical part of an aeroengine is its core, which typically includes three components, a compressor, a combustor, and a turbine. Among these three components, the disk shaft threaded connector is a type of fastening connection system that connects components of an engine turbine disk, a compressor disk, a turbine shaft, a compressor shaft, etc. into one piece by means of threaded mating connectors. A typical disc shaft connection structure is shown in FIG. 1, and a specific disc shaft structure test model is shown in FIG. 2.
Taking a high-pressure turbine disc and a high-pressure compressor rear journal connector as an example, the disc shaft is connected by 24 groups of uniformly distributed threaded connectors, each group of threaded connectors consists of a D-type high-pressure rotor bolt and a twelve-angle high-pressure rotor self-locking nut, and considering that in the actual use process, the situation that a single threaded connector fails and the whole threaded connector still operates normally can exist.
The invention provides a screw connector reliability forward design method based on a multi-competition failure mode, which comprises the following specific implementation steps:
step one: failure mode and mechanism analysis for fastening connection systems
Through the failure mode analysis to the disc shaft threaded connector, the main reason of the connection failure is determined to be caused by connection loosening due to the fact that the stress exceeds the allowable strength of the bolt and the installation pre-tightening force is insufficient, and the main failure mode of the disc shaft threaded connector is finally determined to be as follows: the bolt/nut breaks and the thread pair loosens. Actual product strength data for the disc shaft threaded connection is collected, see table 1.
TABLE 1 found tensile resistance value (kN) of MJ14 bolt
Step two: establishing a threaded connection reliability model based on a single failure mode
Establishing a disc shaft threaded connector reliability model based on two failure modes of stress fracture and connection loosening
(1) Establishing a disc shaft threaded connection reliability model based on stress fracture modes
Based on the intensity data of Table 1, the intensity can be estimated
Obeys normal distribution: />
. Considering that the maximum dangerous load is 42.23kN and the variation coefficient is 0.12 (standard deviation/mean) in the actual use process, the stress +.>
Obeys normal distribution: />
The method comprises the steps of carrying out a first treatment on the surface of the The pretightening force is +.>
Variance is->
，/>
For the pretension control multiple, the pretension distribution is +.>
Is->
Distribution of maximum risk load+preload as stress +.>
Is->
. Set random variable->
It obeys a normal distribution: />
From this, the single threaded connection reliability based on stress fracture failure mode can be calculated as: />
(2) Establishing a reliability model of a disc shaft threaded connector based on a connection loosening failure mode
Considering that the pre-tightening force can be used for preventing loosening, taking the pre-tightening force as strength data and the maximum dangerous load as stress data, and taking the strength at the moment
Obeys normal distribution: />
. Stress->
Obeys normal distribution:
. Set random variable->
It obeys a normal distribution:
from this, the single threaded connection reliability based on the connection release failure mode can be calculated as:
step three: fastening connection system reliability model based on multi-competition failure mode under k-out-of-n model
Establishing a disc shaft threaded connection reliability model based on two failure modes of stress fracture and connection loosening
Considering that the threaded connection needs to be reliable in two parts, because each threaded connector of the disc shaft threaded connector is stressed consistently, the reliability of a single threaded connector is as follows:
wherein ：
is a pretension multiple->
, wherein />
The pre-tightening force precision is achieved.
The disc shaft threaded connector consists of 24 groups of threaded connectors, namely when any one threaded connector does not fail, the reliability of the disc shaft threaded connection system based on two competing failure modes is as follows:
wherein ：
is a pretension multiple->
, wherein />
The pre-tightening force precision is achieved.
Step four: establishing a joint probability distribution function, and combining reliability design indexes to carry out forward design of a connection system
(1) Establishing a target pretightening force multiple according to the influence factors of stress fracture and connection loosening failure modes
And reliability->
Function curve of relation
As can be seen from FIG. 3 (FIG. 3 illustrates that, due to the accuracy of the calculation, more than 50 9 readings are shown as 1, the middle is shown as a flat line), the reliability of the threaded connector for the disc shaft consisting of 24 MJ14 specification bolts
Along with pretension multiple->
The increase in (c) increases until it reaches a peak and then decreases. It can also be seen from fig. 3 that the accuracy of the pretension is +.>
Is (i.e. is +.>
Closer), reliability corresponding to the boundary line +.>
Also has an increasing trend. It can also be seen from FIG. 3 that the reliability maximum centerline +.>
Corresponding +.>
Is 1.11, i.e. optimal pretension->
Design target pretightening force of 1.11 times>
The two are deviated to a certain extent, and the target pretightening force designed to be given is usually the optimal pretightening force, so that the original target pretightening force is optimized to be
。
(2) Forward design of reliability of a connection system is carried out according to probability distribution functions, and pretightening force design index recommendation under different reliability is established
According to the reliability index distribution of the aero-engine, the reliability requirement of the disc shaft threaded connector is not lower than 0.9999 (4 9); while combining engineering applications of mechanical reliability, typically too rarely exceed 0.9999999999 (10 9); in view of this, a pretightening force design index with reliability in the range of 0.9999-0.9999999, the number of allowable failure bolts and the recommendation of the installation method are given, as shown in fig. 4-7, pretightening force control ranges under different reliability, and fig. 4 is pretightening force range with reliability of 0.9999; FIG. 5 is a pre-load range with a reliability of 0.99999; FIG. 6 is a pre-load range with a reliability of 0.999999; fig. 7 shows the range of pretension with a reliability of 0.9999999.
Table 2 recommendation of design index of pretightening force of disc shaft threaded connector composed of 24 MJ14 specification bolts
According to the model and the curve, in a wider pretightening force precision control range, a higher reliability level can be maintained, and the highest reliability value exceeds 50 levels of 9, which indicates that the safety margin of the connection scheme is higher; under the same failure condition, the reliability level of 1 9 can be improved every 2% -4% of installation accuracy; also under the same reliability level, the number of failures allowed by the improvement of the installation precision is increased; according to the control precision of the pretightening force corresponding to different reliability indexes, the conventional torque installation method can reach 5-6 reliability levels of 9, which indicates that the 24-group screw pair connection design scheme has high tolerance to pretightening force errors and the maximum allowable tolerance
The error of 32% is stronger, and the tolerance capability is stronger, and belongs to a robust design scheme with higher safety coefficient.
The above example shows that the invention takes a connector formed by 24 groups of threaded connectors of a turbine disk and an air compressor shaft connected by an aeroengine as a research object, establishes a disk shaft threaded connector universal reliability model based on multiple competition failure modes such as stress fracture, connection looseness and the like through research, can develop forward design of a typical disk shaft threaded connector structure based on the reliability model, obtains the highest achievable reliability level of the structure, and recommends a corresponding pretightening force design value; and simultaneously, the corresponding pretightening force precision control range can be recommended according to different reliability indexes.
In summary, the present invention provides a forward design method for reliability of a fastening connection system based on multiple failure modes. Firstly, analyzing a main failure mode of a threaded connection pair, judging the correlation among multiple degradation failure modes based on the main failure mode and failure criteria of a fastening connection system, and establishing a threaded connection reliability evaluation model based on the single failure mode by analyzing the influence among the failure modes through conditional probability based on a single stress-intensity interference model; and then, based on a threaded connector composition structure, combining a k-out-of-n model, establishing a threaded connector reliability model based on multiple competition failure modes, finally, judging the correlation between each design variable and the threaded connector reliability model, analyzing the influence of each failure mode through conditional probability, establishing a joint probability distribution function, combining reliability design indexes, carrying out forward design of a connecting system, and selecting the optimal design parameters. The problem of missing of the reliability forward design method of the equipment connection system can be effectively solved.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the invention.
Claims (5)
1. The forward design method for the reliability of the fastening connection system based on the multiple competition failure modes is characterized by comprising the following steps of: the method comprises the following steps:
s1, analyzing a failure mode and a mechanism of a fastening connection system to obtain stress and strength of the fastening connection system in each failure mode;
s2, calculating a single threaded connection reliability model based on a single fault mode by using the stress and the strength of each fault mode in the step S1;
s3, calculating a fastening connection system reliability model based on a multi-competition failure mode under a k-out-of-n model by using the single threaded connection reliability model based on the single failure mode in the step S2;
s4, establishing a joint probability distribution function through a fastening connection system reliability model based on a multi-competition failure mode, and carrying out forward design of the fastening connection system by combining reliability design indexes of the fastening connection system; the calculation in step S2 is based on a single threaded connection reliability model in a single failure mode, comprising the steps of:
s21, respectively carrying out distribution inspection on stress and strength data according to the stress and strength of the fastening connection system in each fault stage, and determining the distribution of final stress and the distribution of final strength;
s22, substituting the distribution of the final stress and the distribution of the final strength into a formula (1), and calculating a single threaded connection reliability model based on a single failure mode;
the expression of the formula (1) is:
when the stress and the intensity are subjected to normal distribution, probability density functions are respectively as follows:
in equation (1), y=δ -s is defined, then the random variable y obeys the mean and standard deviation, respectively, as μ y ＝μ δ -μ s And
the reliability of R at this time is:
when the stress and the intensity are subjected to exponential distribution, probability density functions are respectively as follows:
the reliability of R at this time is:
wherein R is the reliability of a single threaded connection in a single failure mode, s is stress, delta is strength, and f s(s) and fδ (delta) is a probability density function of stress and strength, respectively, and s and delta are independent of each other;
in step S4, a joint probability distribution function is established through a fastening connection system reliability model based on multiple contention failure modes, and a fastening connection system forward design is performed in combination with a fastening connection system reliability design index, which includes the following contents:
judging the correlation between each design variable and the reliability model of the fastening connection system, analyzing the influence of each failure mode through conditional probability, and obtaining the design influence factor x of each failure mode 1 ，x 2 ，x 3 .....，x m And (3) carrying out forward design of the connecting system by combining the probability distribution function of the reliability index RS of the fastening connecting system and the reliability design index of the fastening connecting system, and selecting the optimal design influence factor range or parameter combination under the condition of conforming to the reliability design index, wherein the design influence factors are mutually independent or have a coupling relation.
2. The positive design method for reliability of a fastening connection system based on a multiple contention failure mode according to claim 1, wherein: the k-out-of-n model in step S3 is the relation between the reliability of the fastening connection system and the reliability of the threaded connection.
3. The positive design method for reliability of a fastening connection system based on a multiple contention failure mode according to claim 2, wherein: the calculation in step S3 is based on a multiple contention failure mode fastening connection system reliability model, comprising the steps of:
s31, assuming that the fastening connection system consists of n threaded connectors, setting the reliability of the n threaded connectors based on the m failure mode as follows
S32, when any k screw connectors in the n screw connectors fail, the reliability of the fastening connection system in the mth failure mode is represented by a formula (4);
s33, obtaining a fastening connection system reliability model based on the multi-competition failure mode through the formula (4) and the formula (5).
4. The positive design method for reliability of a fastening connection system based on multiple contention failure modes according to claim 3, wherein: the expression of the formula (4) is:
wherein ,
to be based on the reliability of the n-k th threaded connection in the mth failure mode, the R' m Is the reliability of the fastening connection system in the mth failure mode.
5. The positive design method for reliability of a fastening connection system based on multiple contention failure modes according to claim 3, wherein: the expression of the formula (5) is:
R S ＝R’ 1 ×R’ ２ ×.......×R’ m (5)
wherein ,R’m Reliability of fastening connection system in mth failure mode, R S Is a secure connection system reliability model based on multiple contention failure modes.
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