CN105260584A - Method for determining served airplane structure residual durability safe life - Google Patents

Abstract

The invention provides a method for determining served airplane structure residual durability safe life. The method is divided into two situations, wherein the first situation is that airplane structure fatigue life complies with logarithmic normal distribution, and the second situation is that the airplane structure fatigue life complies with two-parameter Weibull distribution. The method comprises the following specific steps: determining median fatigue life [N50], determining a fatigue dispersion coefficient, and determining the served airplane structure residual durability safe life. The method solves the problem of the value acquisition of the fatigue dispersion coefficient when the airplane structure residual durability safe life is determined, and the determination of a logarithm standard deviation and the fatigue dispersion coefficient is improved. According to a served airplane structure fatigue/ durability test result, the airplane structure residual durability safe life is determined again, and a purpose that the airplane structure service life is prolonged can be achieved.

Description

One has been on active service used aircaft configuration residue permanance safe life defining method

Technical field

The present invention relates to and the invention belongs to aircraft structural reliability life search technical field, be specifically related to one and be on active service used aircaft configuration residue permanance safe life defining method.

Background technology

The cost of present generation aircraft is very expensive, makes people always think fully to excavate the life-span potentiality of every airplane, allows its as far as possible long service, namely extends its serviceable life or claim serviceable life of being on active service, thus obtains distinct economic.

At present, domestic each type is determined longevity employing permanance safe life and is determined longevity method, also adopts the management method based on permanance safe life to the management of Aircraft life.Group of planes permanance safe life method refers to the requirement by " strength of aircraft rigidity specifcation ", carry out a series of activities such as the full-scale fatigue/endurancing of aircraft, crack expansion test, residual intensity test and permanance/damage tolerance computational analysis, then the tired critical risk position of aircaft configuration and time between overhauls(TBO), maintenance content is provided, with fatigue/permanance overall test hourage divided by tired dispersion coefficient, draw the permanance safe life conclusion of a group of planes.Because aircraft structure fatigue/fracture failure process exists the impact of a large amount of uncertain factor, therefore determine in longevity process, to introduce tired dispersion coefficient at aircraft.Generally only choosing 1 airplane carries out full size structure fatigue/endurancing.

When group of planes military service aircraft has flown to originally given group of planes permanance safe life, if re-used, carry out prolongation aircaft configuration with regard to needs to be on active service serviceable life, namely expand the use restriction of aircraft, now life extension test machine extracts usually all at random from a used group of planes of being on active service.Or sometimes due to odjective cause, need to determine its residue permanance safe life to the group of planes aircraft of being on active service, fatigue now/endurancing aircraft is also randomly drawed from used aircraft of being on active service.So how to determine to be on active service, used aircaft configuration residue permanance safe life is very important problem in Aircraft life management engineering.At present, used aircaft configuration of being on active service residue permanance safe life adopts life extension test machine fatigue/endurancing result to estimate that the median fatigue life obtained is determined divided by tired dispersion coefficient.

Aircraft structure fatigue/viability it has been generally acknowledged that obeys logarithm normal distribution or Weibull distribution.Can median fatigue life be obtained according to life extension test machine fatigue/endurancing result, if know the value of tired dispersion coefficient, just can determine used aircaft configuration residue permanance safe life of being on active service.

The problem being difficult to determine tired dispersion coefficient value is there is in prior art when determining aircaft configuration residue permanance safe life.

Summary of the invention

For fully excavating the military service potentiality in serviceable life of aircaft configuration, the present invention proposes one to be on active service used aircaft configuration residue permanance safe life defining method, object be for extend aircaft configuration be on active service serviceable life, ensure that aircraft safety flight provides a set of theoretical method.The method is divided into two kinds of situations:

(1) situation during aircraft structure fatigue life-span obeys logarithm normal distribution

When aircraft structure fatigue/viability obeys logarithm normal distribution, suppose used aircaft configuration remanent fatigue life also obeys logarithm normal distribution of being on active service, concrete steps are as follows:

Step 1: median fatigue life [N ₅₀] determination

According to life extension test machine fatigue/endurancing result determination median fatigue life [N ₅₀]; Generally only choosing 1 frame life extension test machine carries out fatigue/endurancing, so median fatigue life [N ₅₀] be exactly that life extension test machine carries out fatigue/endurancing result;

Step 2: the determination of tired dispersion coefficient

The form of the tired dispersion coefficient of aircraft structure fatigue life-span obeys logarithm normal distribution is:

$L_f={10}^{(\frac{u_{\mathrm{\γ}}}{\sqrt{n}}-u_p)\mathrm{\σ}}$

Wherein: L _ffor tired dispersion coefficient; σ is logarithm life standard error; u _pfor standardized normal distribution adds up functional value, determined by the fiduciary level selected; u _γfor standardized normal distribution adds up functional value, determined by the confidence level selected; N is sample size;

When not knowing group of planes aircaft configuration remanent fatigue life, determine that the method for remanent fatigue life logarithm standard deviation σ is as follows:

Get the logarithmic fatigue life expectation value of logarithm as former group of planes parent of the full machine of new machine/parts fatigue/endurancing result; The logarithm standard deviation determined according to specification is as the logarithm standard deviation σ of former group of planes parent;

According to law of great number, when Sample Size n be greater than certain several time, just can represent parent by sample estimated value; In order to determine the logarithm standard deviation σ of group of planes aircaft configuration remanent fatigue life, the random number of stochastic generation j group obeys logarithm normal distribution, often group has k random number, represents the increment data of group of planes aircraft fatigue/viability; The same used time is deducted to these random numbers simultaneously, represents the increment data of group of planes aircaft configuration remanent fatigue life, the logarithm standard deviation σ of statistic computer swarming machine structure residual fatigue lifetime; Logarithm standard deviation σ according to group of planes aircaft configuration remanent fatigue life can calculate tired dispersion coefficient;

Step 3: the determination of used aircaft configuration of being on active service residue permanance safe life

According to the median fatigue life [N determined in step 1 ₅₀] with the tired dispersion coefficient L that determines in step 2 _fcalculate permanance safe life N _p:

$N_P=\frac{\left[N_{50}\right]}{L_f}$

(2) situation during aircraft structure fatigue life-span obedience Two-parameter Weibull Distribution

When aircraft structure fatigue/viability obeys Two-parameter Weibull Distribution, used aircaft configuration remanent fatigue life of supposing to be on active service also obeys Two-parameter Weibull Distribution, and concrete steps are as follows:

Step 1: median fatigue life [N ₅₀] determination

According to life extension test machine fatigue/endurancing result determination median fatigue life [N ₅₀]; When testpieces number n is 1, the point estimation of the characteristics life parameter of two-parameter Weibull be exactly fatigue/endurancing result, so tired median life is:

$\left[N_{50}\right]=\frac{\widehat{\mathrm{\η}}}{{\left(\ln \frac{1}{0.5}\right)}^{-\frac{1}{m}}}$

Wherein m is profile shape parameter;

When not knowing group of planes aircaft configuration remanent fatigue life, determine that the method for the profile shape parameter m of remanent fatigue life is:

According to the profile shape parameter m of the determined profile shape parameter of specification as former group of planes parent; And take the full machine of new machine/parts fatigue/endurancing result as the characteristics life parameter value of former group of planes parent fatigue lifetime;

According to law of great number, when Sample Size n be greater than certain several time, just can represent parent by sample estimated value; In order to determine the profile shape parameter m of group of planes aircaft configuration remanent fatigue life, stochastic generation p group obeys the random number of Two-parameter Weibull Distribution, and often group has q random number, represents the increment data of group of planes aircraft fatigue/viability; Same used time or equivalent time are deducted to these random numbers simultaneously, represents the increment data of group of planes aircaft configuration remanent fatigue life, the profile shape parameter m of statistic computer swarming machine structure residual fatigue lifetime; Profile shape parameter m according to group of planes aircaft configuration remanent fatigue life can calculate median fatigue life [N ₅₀];

Step 2: the determination of tired dispersion coefficient

The form that the aircraft structure fatigue life-span obeys the tired dispersion coefficient of Two-parameter Weibull Distribution is:

$L_f=S_c\·{\left(\frac{-\ln R}{\ln 2}\right)}^{-\frac{1}{m}}$

Wherein: L _ffor tired dispersion coefficient; S _cfor confidence factor; R is fiduciary level;

When m is known, S _cobtain by following formula:

${\∫}_0^{S_c}\frac{m\·n^n}{\mathrm{\Γ}\left(n\right)}{x}^{\mathrm{mn}-1}\·e^{-n\·x^m}\mathrm{dx}=\mathrm{\γ}$

Step 3: the determination of used aircaft configuration of being on active service residue permanance safe life

The according to circumstances determined median fatigue life [N of step 1 in (two) ₅₀] with the tired dispersion coefficient L that determines in step 2 _fcalculate permanance safe life N _p:

$N_P=\frac{\left[N_{50}\right]}{L_f}$

In one embodiment of the invention, Sample Size n >=50.

In one embodiment of the invention, can the random number of stochastic generation j group obeys logarithm normal distribution in the step 2 of situation (one), j >=50.

In one embodiment of the invention, stochastic generation p group the random number of Two-parameter Weibull Distribution can be obeyed, p >=50 in the step 2 of situation (two).

In one embodiment of the invention, the j group random number of stochastic generation in the step 2 of situation (one), often group has k random number, k >=50.

In one embodiment of the invention, the p group random number of stochastic generation in the step 2 of situation (two), often group has q random number, q >=50.

The invention solves the problem of tired dispersion coefficient value when determining aircaft configuration residue permanance safe life, the determination of logarithm standard deviation and tired dispersion coefficient is improved.Redefine aircaft configuration residue permanance safe life according to used aircraft structure fatigue/endurancing result of being on active service, the object extending aircaft configuration and be on active service serviceable life can be reached.

Accompanying drawing explanation

Fig. 1 illustrates of the present invention to used aircaft configuration residue permanance safe life constant current journey really of being on active service.

Embodiment

(1) situation during aircraft structure fatigue life-span obeys logarithm normal distribution

When aircraft structure fatigue/viability obeys logarithm normal distribution, suppose used aircaft configuration remanent fatigue life also obeys logarithm normal distribution of being on active service, therefore can provide one to be on active service used aircaft configuration residue permanance safe life defining method, as shown in Figure 1.

The method step is as follows:

Step 1: median fatigue life [N ₅₀] determination

According to life extension test machine fatigue/endurancing result determination median fatigue life [N ₅₀].Generally only choosing 1 frame life extension test machine carries out fatigue/endurancing, so median fatigue life [N ₅₀] be exactly that life extension test machine carries out fatigue/endurancing result.

Step 2: the determination of tired dispersion coefficient

The form of the tired dispersion coefficient of aircraft structure fatigue life-span obeys logarithm normal distribution is:

$L_f={10}^{(\frac{u_{\mathrm{\γ}}}{\sqrt{n}}-u_p)\mathrm{\σ}}$

Wherein: L _ffor tired dispersion coefficient; σ is logarithm life standard error; u _pfor standardized normal distribution adds up functional value, determined by the fiduciary level selected; u _γfor standardized normal distribution adds up functional value, determined by the confidence level selected; N is sample size.

Visible, when sample size, fiduciary level, confidence level and standard deviation are known, just tired dispersion coefficient can be calculated.

When deducting identical military service service time (or equivalent time) with a same model group of planes all aircraft fatigue life-span, the average of group of planes aircaft configuration residual life can change, logarithmic fatigue life standard deviation also changes, even if then fiduciary level, confidence level, sample size are constant, tired dispersion coefficient also can change.So, logarithm standard deviation when determining initial group of planes permanance safe life and tired dispersion coefficient should not be adopted here.And analysis must be re-started to logarithm standard deviation and tired dispersion coefficient.

Actual fatigue/the viability supposing n frame military service aircraft under same load/Environmental Spectrum is N ₁, N ₂..., N _n, a group of planes used time of being on active service is N _p, as initial endurance safe life etc., then this n frame military service aircaft configuration remanent fatigue life is N ₁-N _p, N ₂-N _p..., N _n-N _p.Its logarithmic fatigue life increment average and increment standard deviation are:

$\stackrel{\‾}{X}=\frac{1}{n}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\lg (N_i-N_p)$

$s=\sqrt{\frac{1}{n-1}(\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\lg (N_i-N_p)-{n\stackrel{\‾}{X}}^2)}$

Strictly speaking, S is had inclined as parent standard deviation estimate amount, so in fatigue statisic, usually it is revised.Standard deviation correction factor is:

$\hat{k}=\sqrt{\frac{n-1}{2}}\·\frac{\mathrm{\Γ}\left(\frac{n-1}{2}\right)}{\mathrm{\Γ}\left(\frac{n}{2}\right)}$

Then the unbiased esti-mator formula of normal state parent standard deviation is:

$\widehat{\mathrm{\σ}}=\hat{k}\·s$

Also can not revise in common engineering application.Particularly, when n>=50, time, generally do not need to revise.

Discussing below when not knowing group of planes aircaft configuration remanent fatigue life, determining remanent fatigue life logarithm standard deviation.

In real work, due to 1 test specimen that fatigue/durability test machine is for determining initial group of planes permanance safe life, one group of fatigue test piece under same loading spectrum effect, their life-span has very large dispersiveness, but they follow lognormal distribution rule in middle lifetime region, according to lognormal distribution rule, its life-span is that minimum and maximum probability is extremely low, the probability being tending towards intermediate value or mean value is high, in other words, in this fatigue test piece, the life-span randomly drawing 1 testpieces is tending towards the Probability maximum of mean value.So we get the logarithmic fatigue life expectation value of logarithm as former group of planes parent of the full machine of new machine/parts fatigue/endurancing result here.

According to specification, when supposing aircraft structure fatigue/viability obeys logarithm normal distribution, the most model aircraft of China determines the longevity, and all to get tired dispersion coefficient be 4.0, correspond to logarithm standard deviation 0.1402, fiduciary level 99.87%, confidence level 90% and sample size 1 are foundation.So can using 0.1402 as the logarithm standard deviation of former group of planes parent.

According to law of great number, when Sample Size n be greater than certain several time, just can represent parent by sample estimated value; In order to determine the logarithm standard deviation σ of group of planes aircaft configuration remanent fatigue life, the random number of stochastic generation j group obeys logarithm normal distribution, often group has k random number, represents the increment data of group of planes aircraft fatigue/viability; The same used time is deducted to these random numbers simultaneously, represents the increment data of group of planes aircaft configuration remanent fatigue life, the logarithm standard deviation σ of statistic computer swarming machine structure residual fatigue lifetime; Logarithm standard deviation σ according to group of planes aircaft configuration remanent fatigue life can calculate tired dispersion coefficient.

Step 3: the determination of used aircaft configuration of being on active service residue permanance safe life

According to the median fatigue life [N determined in step 1 ₅₀] with the tired dispersion coefficient L that determines in step 2 _fcalculate permanance safe life N _p:

$N_P=\frac{\left[N_{50}\right]}{L_f}$

(2) situation during aircraft structure fatigue life-span obedience Two-parameter Weibull Distribution

When aircraft structure fatigue/viability obeys Two-parameter Weibull Distribution, as when long life range, used aircaft configuration remanent fatigue life of supposing to be on active service also obeys Two-parameter Weibull Distribution, then can provide one and be on active service used aircaft configuration residue permanance safe life defining method as shown in Figure 1.

Step 1: median fatigue life [N ₅₀] determination

According to life extension test machine fatigue/endurancing result determination median fatigue life [N ₅₀].Generally only choosing 1 frame life extension test machine carries out fatigue/endurancing, then the point estimation of the characteristics life parameter of two-parameter Weibull for:

$\widehat{\mathrm{\η}}={\left[\frac{1}{n}\left(\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{N}_i^m\right)\right]}^{\frac{1}{m}}$

Wherein n is testpieces number, and m is profile shape parameter, N _ibe i-th testpieces fatigue/viability.

Visible, when testpieces number n is 1, the point estimation of the characteristics life parameter of two-parameter Weibull be exactly fatigue/endurancing result, so tired median life is:

$\left[N_{50}\right]=\frac{\widehat{\mathrm{\η}}}{{\left(\ln \frac{1}{0.5}\right)}^{-\frac{1}{m}}}$

Wherein m is profile shape parameter.

When deducting the identical service time of military service or equivalent time to all aircraft fatigue life-spans, profile shape parameter can change, so, profile shape parameter when determining initial group of planes permanance safe life should not be adopted here.

Discussing below when not knowing group of planes aircaft configuration remanent fatigue life, how to determine the profile shape parameter of remanent fatigue life.

According to specification, when supposing that aircraft structure fatigue/viability all obeys Two-parameter Weibull Distribution, the most model aircraft of China determines the longevity, and all to get tired dispersion coefficient be 4.0, correspond to profile shape parameter 2.6706, fiduciary level 95%, confidence level 95% and sample size 1 are foundation.So can using 2.6706 as the profile shape parameter of former group of planes parent.And take the full machine of new machine/parts fatigue/endurancing result as the characteristics life parameter value of former group of planes parent fatigue lifetime.

According to law of great number, when Sample Size n be greater than certain several time, just can represent parent by sample estimated value; In order to determine the profile shape parameter m of group of planes aircaft configuration remanent fatigue life, stochastic generation p group obeys the random number of Two-parameter Weibull Distribution, and often group has q random number, represents the increment data of group of planes aircraft fatigue/viability; Same used time or equivalent time are deducted to these random numbers simultaneously, represents the increment data of group of planes aircaft configuration remanent fatigue life, the profile shape parameter m of statistic computer swarming machine structure residual fatigue lifetime; Profile shape parameter m according to group of planes aircaft configuration remanent fatigue life can calculate median fatigue life [N ₅₀].

Step 2: the determination of tired dispersion coefficient

The form that the aircraft structure fatigue life-span obeys the tired dispersion coefficient of Two-parameter Weibull Distribution is:

$L_f=S_c\·{\left(\frac{-\ln R}{\ln 2}\right)}^{-\frac{1}{m}}$

Wherein: L _ffor tired dispersion coefficient; M is profile shape parameter; S _cfor confidence factor; R is fiduciary level.

When m is known, S _cobtain by following formula:

${\∫}_0^{S_c}\frac{m\·n^n}{\mathrm{\Γ}\left(n\right)}{x}^{\mathrm{mn}-1}\·e^{-n\·x^m}\mathrm{dx}=\mathrm{\γ}$

When confidence level is 95%, S _ccan approximate expression be a note: this formula is that Chinese aircraft structure strength research institute Xue Jingchuan researcher provides:

$S_c=3^{\frac{1}{m}}-\frac{1}{m}\mathrm{lgn}$

Visible, when sample size, fiduciary level, confidence level and profile shape parameter are known, tired dispersion coefficient can be calculated.

Step 3: the determination of used aircaft configuration of being on active service residue permanance safe life

According to the median fatigue life [N determined in step 1 ₅₀] with the tired dispersion coefficient L that determines in step 2 _fcalculate permanance safe life N _p:

$N_P=\frac{\left[N_{50}\right]}{L_f}$

(3) specific embodiment

Now the invention will be described further in conjunction with specific embodiments.

Suppose aircraft structural fatigue/viability obeys logarithm normal distribution, then be on active service and used the aircaft configuration remanent fatigue life obeys logarithm normal distribution of same time (or equivalent time), and the pilot fight hourage that the full machine of the new machine of this type aircraft under test load spectral condition/parts fatigue/endurancing is experienced is 10000h.According to specification, when determining this type Airplane Structure Durability safe life, tired dispersion coefficient gets 4.0, so group of planes permanance safe life is 2500h.Need reenlist serviceable life after aircraft to longevity or expand to use restriction.

Step 1: median fatigue life [N ₅₀] determination

That randomly draws that 1 frame flown 2500h completes the fatigue/endurancing of full machine to longevity aircraft.Suppose that life extension test machine fatigue/endurancing result is 6000h, then aircaft configuration residue median fatigue life [N ₅₀] be 6000h.

Step 2: the determination of tired dispersion coefficient

Here we get the expectation value of logarithm as former parent of the full machine of new machine/parts fatigue/endurancing result 10000h.According to specification, when determining this type Airplane Structure Durability safe life, tired dispersion coefficient gets 4.0.When fiduciary level is 99.87%, confidence level is 90%, and when Sample Size is 1, adopting the tired dispersion coefficient computing formula of lognormal distribution can obtain standard deviation is 0.1402.So can using 0.1402 as the logarithm standard deviation of former parent.With the random number of this stochastic generation 50 groups of obeys logarithm normal distribution, often group has 50 random numbers, represents the increment data in group of planes aircraft fatigue life-span.Deduct 2500h to these random numbers, represent the increment data of group of planes aircaft configuration remanent fatigue life, the logarithm standard deviation of group of planes aircaft configuration remanent fatigue life is often organized in statistical computation, as shown in table 1 simultaneously.

The logarithm standard deviation often organizing group of planes aircaft configuration remanent fatigue life of table 1 obeys logarithm normal distribution

Average to the logarithm standard deviation of 50 groups of group of planes aircaft configuration remanent fatigue lifes, the logarithm standard deviation of known group of planes aircaft configuration remanent fatigue life is 0.1919.Tired dispersion coefficient then under fiduciary level 99.87% with confidence level 90% is:

$L_f={10}^{(\frac{u_{\mathrm{\γ}}}{\sqrt{n}}-u_p)\mathrm{\σ}}={10}^{(\frac{1.282}{\sqrt{1}}+3)\×0.1919}=6.6$

Step 3: the determination of used aircraft of being on active service residue permanance safe life

According to the median fatigue life [N determined in step 1 ₅₀] with the tired dispersion coefficient L that determines in step 2 _fcalculate permanance safe life N _p:

$N_P=\frac{\left[N_{50}\right]}{L_f}=\frac{6000}{6.6}=909h$

When fiduciary level and degree of confidence constant when, according to being on active service, the residue permanance safe life of used aircraft residue permanance safe life defining method this type aircraft known after reaching initial group of planes permanance safe life 2500h is 909h, namely can continue to expand for a test load spectrum group of planes and use restriction, reenlist serviceable life or equivalent military service 909h in serviceable life.

When hypothesis aircraft structural fatigue/viability obeys Two-parameter Weibull Distribution, then be on active service and used the aircaft configuration remanent fatigue life of same time or equivalent time also to obey Two-parameter Weibull Distribution, and the pilot fight hourage that the full machine of the new machine of this type aircraft under test load spectral condition/parts fatigue/endurancing is experienced is 10000h.According to specification, when determining this type Airplane Structure Durability safe life, tired dispersion coefficient gets 4.0, so group of planes permanance safe life is 2500h.Need reenlist serviceable life after aircraft to longevity or expand to use restriction.

Step 1: median fatigue life [N ₅₀] determination

Get the characteristics life value of the full machine of new machine/parts fatigue/endurancing result 10000h as former parent.According to specification, when supposing that aircraft structure fatigue/viability all obeys Two-parameter Weibull Distribution, the most model aircraft of China determines the longevity, and all to get tired dispersion coefficient be 4.0.When fiduciary level is 95%, confidence level is 95%, and when Sample Size is 1, adopting the tired dispersion coefficient computing formula of Two-parameter Weibull Distribution can obtain profile shape parameter is 2.6706.So can using 2.6706 as the profile shape parameter of former parent.Obey the random number of Two-parameter Weibull Distribution with this stochastic generation 50 groups, often group has 50 random numbers, represents the increment data of group of planes aircraft.Deduct 2500h to these random numbers, represent the increment data of group of planes aircaft configuration remanent fatigue life, the profile shape parameter of group of planes aircaft configuration remanent fatigue life is often organized in statistical computation, as shown in table 2 simultaneously.

The profile shape parameter often organizing group of planes aircaft configuration remanent fatigue life of Two-parameter Weibull Distribution obeyed by table 2

Average to the profile shape parameter of 50 groups of group of planes aircaft configuration remanent fatigue lifes, the profile shape parameter of known group of planes aircaft configuration remanent fatigue life is 1.9631.

That randomly draws that 1 frame flown 2500h completes the fatigue/endurancing of full machine to longevity aircraft.Suppose that life extension test machine fatigue/endurancing result is 6000h, so get the characteristics life value of life extension test machine fatigue/endurancing result 6000h as group of planes aircaft configuration remanent fatigue life.

Then tired median life is:

$\left[N_{50}\right]=\frac{\widehat{\mathrm{\η}}}{{\left(\ln \frac{1}{0.5}\right)}^{-\frac{1}{m}}}=\frac{6000}{{\left(\ln \frac{1}{0.5}\right)}^{-\frac{1}{1.9631}}}=4978h$

Step 2: the determination of tired dispersion coefficient

When confidence level is 95%, S _ccan approximate expression be:

$S_c=3^{\frac{1}{m}}-\frac{1}{m}\mathrm{lgn}=3^{\frac{1}{1.9631}}=1.75$

Tired dispersion coefficient then under fiduciary level 95% with confidence level 95% is:

$L_f=S_c\·{\left(\frac{-\ln R}{\ln 2}\right)}^{-\frac{1}{m}}=1.75\×{\left(\frac{-\ln 0.95}{\ln 2}\right)}^{-\frac{1}{1.9631}}=6.59$

Step 3: the determination of used aircraft of being on active service residue permanance safe life

According to the median fatigue life [N determined in step 1 ₅₀] with the tired dispersion coefficient L that determines in step 2 _fcalculate permanance safe life N _p:

$N_P=\frac{\left[N_{50}\right]}{L_f}=\frac{4978}{6.59}=755h$

When fiduciary level and degree of confidence constant when, according to being on active service, the residue permanance safe life of used aircraft residue permanance safe life defining method this type aircraft known after reaching initial group of planes permanance safe life 2500h is 755h, namely can continue to expand for a test load spectrum group of planes and use restriction, reenlist serviceable life (or equivalent is on active service serviceable life) 755h.

Claims (6)

1. used aircaft configuration of being on active service a residue permanance safe life defining method, the method is divided into two kinds of situations:

(1) situation during aircraft structure fatigue life-span obeys logarithm normal distribution

When aircraft structure fatigue/viability obeys logarithm normal distribution, suppose used aircaft configuration remanent fatigue life also obeys logarithm normal distribution of being on active service, concrete steps are as follows:

Step 1: median fatigue life [N ₅₀] determination

According to life extension test machine fatigue/endurancing result determination median fatigue life [N ₅₀]; Generally only choosing 1 frame life extension test machine carries out fatigue/endurancing, so median fatigue life [N ₅₀] be exactly that life extension test machine carries out fatigue/endurancing result;

Step 2: the determination of tired dispersion coefficient

The form of the tired dispersion coefficient of aircraft structure fatigue life-span obeys logarithm normal distribution is:

Wherein: L _ffor tired dispersion coefficient; σ is logarithm life standard error; u _pfor standardized normal distribution adds up functional value, determined by the fiduciary level selected; u _γfor standardized normal distribution adds up functional value, determined by the confidence level selected; N is sample size;

When not knowing group of planes aircaft configuration remanent fatigue life, determine that the method for remanent fatigue life logarithm standard deviation σ is as follows:

Get the logarithmic fatigue life expectation value of logarithm as former group of planes parent of the full machine of new machine/parts fatigue/endurancing result; The logarithm standard deviation determined according to specification is as the logarithm standard deviation σ of former group of planes parent;

According to law of great number, when Sample Size n be greater than certain several time, just can represent parent by sample estimated value; In order to determine the logarithm standard deviation σ of group of planes aircaft configuration remanent fatigue life, the random number of stochastic generation j group obeys logarithm normal distribution, often group has k random number, represents the increment data of group of planes aircraft fatigue/viability; The same used time is deducted to these random numbers simultaneously, represents the increment data of group of planes aircaft configuration remanent fatigue life, the logarithm standard deviation σ of statistic computer swarming machine structure residual fatigue lifetime; Logarithm standard deviation σ according to group of planes aircaft configuration remanent fatigue life can calculate tired dispersion coefficient;

Step 3: the determination of used aircaft configuration of being on active service residue permanance safe life

According to the median fatigue life [N determined in step 1 ₅₀] with the tired dispersion coefficient L that determines in step 2 _fcalculate permanance safe life N _p:

(2) situation during aircraft structure fatigue life-span obedience Two-parameter Weibull Distribution

When aircraft structure fatigue/viability obeys Two-parameter Weibull Distribution, used aircaft configuration remanent fatigue life of supposing to be on active service also obeys Two-parameter Weibull Distribution, and concrete steps are as follows:

Step 1: median fatigue life [N ₅₀] determination

According to life extension test machine fatigue/endurancing result determination median fatigue life [N ₅₀]; When testpieces number n is 1, the point estimation of the characteristics life parameter of two-parameter Weibull be exactly fatigue/endurancing result, so tired median life is:

Wherein m is profile shape parameter;

When not knowing group of planes aircaft configuration remanent fatigue life, determine that the method for the profile shape parameter m of remanent fatigue life is:

According to the profile shape parameter m of the determined profile shape parameter of specification as former group of planes parent; And take the full machine of new machine/parts fatigue/endurancing result as the characteristics life parameter value of former group of planes parent fatigue lifetime;

According to law of great number, when Sample Size n be greater than certain several time, just can represent parent by sample estimated value; In order to determine the profile shape parameter m of group of planes aircaft configuration remanent fatigue life, stochastic generation p group obeys the random number of Two-parameter Weibull Distribution, and often group has q random number, represents the increment data of group of planes aircraft fatigue/viability; Same used time or equivalent time are deducted to these random numbers simultaneously, represents the increment data of group of planes aircaft configuration remanent fatigue life, the profile shape parameter m of statistic computer swarming machine structure residual fatigue lifetime; Profile shape parameter m according to group of planes aircaft configuration remanent fatigue life can calculate median fatigue life [N ₅₀];

Step 2: the determination of tired dispersion coefficient

The form that the aircraft structure fatigue life-span obeys the tired dispersion coefficient of Two-parameter Weibull Distribution is:

Wherein: L _ffor tired dispersion coefficient; S _cfor confidence factor; R is fiduciary level;

When m is known, S _cobtain by following formula:

Step 3: the determination of used aircaft configuration of being on active service residue permanance safe life

The according to circumstances determined median fatigue life [N of step 1 in (two) ₅₀] with the tired dispersion coefficient L that determines in step 2 _fcalculate permanance safe life N _p:

。

2. used aircaft configuration residue permanance safe life defining method of being on active service according to claim 1, wherein Sample Size n >=50.

3. used aircaft configuration residue permanance safe life defining method of being on active service according to claim 1, wherein can the random number of stochastic generation j group obeys logarithm normal distribution in the step 2 of situation (one), j >=50.

4. used aircaft configuration residue permanance safe life defining method of being on active service according to claim 1, wherein can the random number of stochastic generation p group obedience Two-parameter Weibull Distribution in the step 2 of situation (two), p >=50.

5. used aircaft configuration residue permanance safe life defining method of being on active service according to claim 1, wherein the j group random number of stochastic generation in the step 2 of situation (one), often group has k random number, k >=50.

6. used aircaft configuration residue permanance safe life defining method of being on active service according to claim 1, wherein the p group random number of stochastic generation in the step 2 of situation (two), often group has q random number, q >=50.