CN102184326A - Method for estimating calendar life of aircraft structure - Google Patents

Abstract

The invention discloses a method for estimating calendar life of an aircraft structure, belonging to the technical field of aircraft life estimation and particularly relating to improvement on the method for estimating the calendar life of the aircraft structure. The method mainly comprises three steps of: 1, compiling a fatigue load spectrum under the condition of considering influence of calendar time; 2, establishing relation between the calendar time and fatigue life; and 3, estimating the calendar life of the structure by using a linear accumulated damage theory. The method has the advantages that: influences of the calendar time and an environmental factor are simultaneously considered during estimation of fatigue life; a load-environment process which is actually suffered by the aircraft structure can be really reflected; a few parameters are required to be determined; and engineering application is facilitated.

Description

A kind of aircaft configuration calendar life evaluation method

Technical field

The invention belongs to the aircraft life evaluation technical field, be specifically related to improvement aircaft configuration calendar life evaluation method.

Background technology

Aircaft configuration calendar life appraisal procedure mainly contains following several at present:

(1) determines the empirical method of body calendar life

At present both at home and abroad mainly determine calendar entire life and overhaul the cycle, how much relevant to the statistics of the quality of Aircraft Structural Life evaluation and aircraft with estimator's experience itself according to the practice of the statistics of aircraft natural selection and the leading flight of part aircraft and overhaul experience.

(2) corrosion damage linear accumulation model

By setting up the corrosive medium temperature and critical etching time concerns the T-H curve, be parameter with structure/material critical etching extent Dc under the identical text temperature not, when the accumulated damage amount to 1 the time, think the material damage and failure.This model is similar to the Miner rule in form, easy to understand, and its computation process is also simple.But this model only relates to pure corrosion damage, owing to lack main aircraft construction material T-H curve, the definition of critical corrosion damage does not descend with the strength of materials/fatigue behaviour yet and connects, and still is difficult to be put to engineering and uses.

(3) the anti-pushing manipulation of environment equivalent conversion curve

This method proposes to obtain the acceleration environment spectrum with the metal erosion electric current as the scale of measurement with the method for controlling the metal surface wetting time, providing equivalent conversion curve (COE curve) by calculating and equivalent conversion test.Be Equivalent Spectrum under the experimental enviroment condition with this curve with the conversion of the equivalent environment of practical structures spectrum then, calendar time that just can anti-push out test Equivalent Spectrum representative.This method provides a kind of simple and direct approach for the equivalence of equivalent environment spectrum is composed for accelerated test, can be used as one of approach of the preliminary acceleration environment spectrum of establishment.But this method can not be reacted the influence of calendar time to the fatigue of materials characteristic.

(4) corrosion fatigue method

This method comprises the corrosion fatigue model, corrosion fatigue crack extended model, corrosion-tired overall process model of the tired model of stress corrosion, strain control etc., more than these models when can be used for the aircraft airflight under corrosion environment and the coefficient situation of fatigue load, but can't consider that ground parks the corrosion damage that is brought.Employed material of all models of corrosion fatigue or test specimen fatigue lifetime data or curve mostly obtain in the laboratory accelerated tests, and this test is equivalent to how long the natural environment corrosion aging effect is unknown.And model relates to corrosion kinetics parameter, electrochemical reaction parameter and breaking mechanics parameter etc. between metal and environment, and parameter is more and be not easy to obtain, and using to engineering makes troubles.

(5) permanance assessment method

Aluminium alloy and high-strength steel pitch corrosion hole are regarded as the initial fatigue quality of equivalent, be incorporated in the permanance model, estimate fatigue lifetime with the probabilistic fracture mechanics method.These class methods belong to the fracturing mechanics research contents, the initial fatigue quality test figure support of still needing on engineering is used.

Summary of the invention

The objective of the invention is: propose a kind of engineering method of new aircaft configuration calendar life evaluation, the method can be considered the influence to the aircaft configuration fatigue behaviour of calendar time and fatigue load simultaneously, and assessment method is simple, remedies the deficiency of existing engineering method.

Technical scheme of the present invention is: a kind of aircaft configuration calendar life evaluation method, it is characterized in that, and comprise the steps:

The first, considering that calendar time influences under the situation, the establishment fatigue load spectrum;

Flight training cycle of aircraft comprises m flight rises and falls (or flight number of times), is total to the T pilot time,

In calendar time Y, finish (as shown in Figure 1).

Airborne hours and ground parking time are continuous process that hockets.

Certain in-flight the characterising parameter of certain one-level loaded-up condition i should comprise: load parameter S _iAnd time t _i(or period n _i), all the air environment factor ∑ E before the state i _AjWith ground parking environment factor ∑ E _GjAnd the calendar of this moment moment y _j(∑ is not to sue for peace and the expression standort here).For military secret, can omit air environment factor ∑ E _AjAnd each flight back ground environment factor E _G1, E _G2... E _GmBe considered as a kind of environment (average environment of available this calendar year of ambient zone replaces), each flight load spectrum is linked in sequence just obtains Fig. 2 and calendar loading spectrum shown in Figure 3 again.

Among Fig. 2, the k time in-flight, and the characterising parameter of i loaded-up condition is S _i, n _i, y _j, y wherein _jFollowing calculating:

y _j＝Y ₁+Y ₂+…+Y _k-1 (1)

The second, set up the relation of calendar time and fatigue lifetime

Experiment on fatigue properties data or the accelerated test data of typical structure material after the corrosion of aircraft military service region ground environment are introduced computation model.By setting up y-S-N (time-stress level-fatigue lifetime) curve or C-y curve (median fatigue life that C is defined as structure under the time y is that 0 o'clock structure same load is composed the ratio of median life down with calendar time), curvilinear correlation fatigue lifetime of calendar time and material is got up.

The 3rd, utilize linear cumulative damage law estimation structure calendar life

The fatigue damage that each load cycle causes is:

$D_{\mathrm{ij}}\left(y_j\right)=\frac{1}{N_{\mathrm{ij}}\left(y_j\right)}---\left(3\right)$

Here D _Ij(y _j) be at calendar time y _jFollowing the i time load cycle damage, N _Ij=N _Ij(y _j) be structured material exposure test calendar time y in the atmospheric corrosion environment _jAfter, corresponding to the fatigue lifetime of structure under the i level stress level.Under the maneuvering load spectrum, the accumulated damage when the calendar moment of k load cycle and correspondence thereof l is:

$D(k,l)=\underset{j=0}{\overset{l}{\mathrm{\Σ}}}\underset{i=1}{\overset{k}{\mathrm{\Σ}}}{D}_{\mathrm{ij}}\left(y_j\right)---\left(4\right)$

When accumulated damage is 1, promptly think structure to the longevity, can solve corresponding calendar time l according to (4) formula simultaneously, thereby can obtain the calendar life of aircraft.

The invention has the beneficial effects as follows: the advantage of this method is in the estimation of fatigue life process, calendar time and Effect of Environmental have been considered simultaneously, can more truly react the actual load that suffers of aircaft configuration-environment course, need definite parameter less, make things convenient for engineering to use.

Description of drawings

Fig. 1: aircraft utilization load-environment synoptic diagram

Fig. 2: the calendar loading spectrum synoptic diagram of a life cycle of certain ambient zone

Fig. 3: aircraft is at the calendar loading spectrum synoptic diagram in varying environment district

Fig. 4: the approximate processing of life-span attenuation ratio curve

Embodiment

Example one:

The estimation of LY12CZ center pit fatigue Life

A) under the influence of considering calendar time, the establishment fatigue load spectrum

This loading spectrum is spectral pattern at random, and a loading cycle comprises 2110 peak-to-valley values, and each piece spectrum is 0.05 to total damage of structure.Loading spectrum was finished in a calendar year, here in order to simplify calculating, suppose that 2110 load peak valleys are uniformly distributed in the one-year age (this distribution is intended to illustrate computation process, in fact should be on active service by aircraft/training plan, each time is risen dropping in the one-year age distribution and come).

Can be expressed as at the fatigue load spectrum of considering calendar time:

f(S，n，y _j)＝f(S，2110，y _j)(j＝1，……，k)

B) set up the relation of calendar time and fatigue lifetime

According to LY12CZ sheet material atmospheric aging test findings, under certain corrosion environment, relation its calendar time and stress level and fatigue lifetime can be expressed as:

${1.0028e}^{0.0194y}\·N\·S_{\max }^m=A---\left(5\right)$

Wherein, m=3.53, A=3.16E+13

C) utilize linear cumulative damage law estimation structure calendar life

The calendar life of this structure is not 1/0.05=20 when obviously, having corrosion.

Because material is comparatively slow with the variation of calendar time the fatigue lifetime under the atmospheric environment corrosion environment, therefore, can be with calendar time at y _iWith y _I+1Between mean lifetime replace interval y _i～y _I+1Life-span, according to (5) formula, during y=0, its damage is 0.05, then has:

${\mathrm{<figure-callout\; id="0"\; label="D"\; filenames="HSA00000487967800021.png"\; state="\{\{state\}\}">D</figure-callout>}}_0=\frac{1}{{\mathrm{<figure-callout\; id="0"\; label="N"\; filenames="HSA00000487967800021.png"\; state="\{\{state\}\}">N</figure-callout>}}_0}=\frac{S_{\max }^m}{A}=0.05$

The damage of i is:

$D_i=\frac{1}{N_i}=\frac{S_{\max }^{m}1.0028e^{0.0194i}}{A}=0.05\&times;1.0028e^{0.0194i}$

According to (4) formula, when

The time, structure then can be obtained l=16 to the longevity, is promptly considering that the calendar life of this structure is 16 years under the corrosion influence.

Example two:

The estimation of fatigue life of certain aircraft wing body joint

The terminal lug sheet material is the LC4CS forging, and the connector fatigue test loading spectrum is eight grades of program block spectrums (table 1).The joint simulating piece torture test life-span (during the 0.5mm crackle of limit, auricle hole) is the 50-80 piece.

Table 1: wing body joint program block spectrum (200 pilot time)

The load level

1

2

3

4

5

6

7

8

S max(MPa)	92.1	196.0	33.4	423.7	383.5	274.6	191.2	161.8
									S min(MPa)	41.2	49.0	41.2	41.2	41.2	41.2	47.8	41.2
Period	145	146	59	1	13	234	137	40

At first the median life that calculates joint with determinacy method fatigue lifetime is 59, and this result conforms to the test life result.In order to consider environmental corrosion influence, suppose that aircraft finished the flight training of a spectrum in 1 year.Because the life-span attenuation ratio of atmospheric environment corrosion back material is comparatively slow with the decline curve variation of calendar time, therefore, can be with calendar time at y _iWith y _I+1Between the mean lifetime attenuation ratio replace interval y _i～y _I+1Increase the longevity ratio, i.e. piece-wise linearization C～y curve as shown in Figure 4.Calculation procedure is as follows:

The first step: the Fatigue Damage Calculation when not considering to corrode

Second step: when considering environmental corrosion, get the life-span attenuation ratio by Fig. 4, then the damage of every spectrum is modified to:

$D_{\mathrm{bi}}^{*}=\frac{1}{C(y=i-1,i)}{D}_{\mathrm{bi}}---\left(5\right)$

Make by determinacy Miner criterion:

Then can get fatigue lifetime is 39.3.As get factor of life scatter L _f=3.0, the safe life when then not considering environmental corrosion and considering environmental corrosion is about 20 calendar years and 13 calendar years respectively.(in fact, after material corroded in atmospheric environment, factor of life scatter may increase, and the then actual tired safe life that provides is shorter possibly than 13 years).

Claims (1)

1. an aircaft configuration calendar life evaluation method is characterized in that, comprises the steps:

The first, considering that calendar time influences under the situation, the establishment fatigue load spectrum;

Flight training cycle of aircraft comprises m flight rises and falls (or flight number of times), altogether the T pilot time, finishes in calendar time Y.

Airborne hours and ground parking time are continuous process that hockets.

Certain in-flight the characterising parameter of certain one-level loaded-up condition i should comprise: load parameter S _iAnd time t _i(or period n _i), all the air environment factor ∑ E before the state i _AjWith ground parking environment factor ∑ E _GjAnd the calendar of this moment moment y _j(∑ is not to sue for peace and the expression standort here).For military secret, can omit air environment factor ∑ E _AjAnd each flight back ground environment factor E _G1, E _G2... E _GmBe considered as a kind of environment (average environment of available this calendar year of ambient zone replaces), each flight load spectrum is linked in sequence just obtains the calendar loading spectrum again.

The k time in-flight, and the characterising parameter of i loaded-up condition is S _i, n _i, y _j, y wherein _jFollowing calculating:

y _i＝Y ₁+Y ₂+…+Y _k-1(1)

The second, set up the relation of calendar time and fatigue lifetime

Experiment on fatigue properties data or the accelerated test data of typical structure material after the corrosion of aircraft military service region ground environment are introduced computation model.By setting up y-S-N (time-stress level-fatigue lifetime) curve or C-y curve (median fatigue life that C is defined as structure under the time y is that 0 o'clock structure same load is composed the ratio of median life down with calendar time), curvilinear correlation fatigue lifetime of calendar time and material is got up.

The 3rd, utilize linear cumulative damage law estimation structure calendar life

The fatigue damage that each load cycle causes is:

$D_{\mathrm{ij}}\left(y_j\right)=\frac{1}{N_{\mathrm{ij}}\left(y_j\right)}---\left(3\right)$

Here D _Ij(y _j) be at calendar time y _jFollowing the i time load cycle damage, N _Ij=N _Ij(y _j) be structured material exposure test calendar time y in the atmospheric corrosion environment _jAfter, corresponding to the fatigue lifetime of structure under the i level stress level.Under the maneuvering load spectrum, the accumulated damage when the calendar moment of k load cycle and correspondence thereof l is:

$D(k,l)=\underset{j=0}{\overset{l}{\mathrm{\&Sigma;}}}\underset{i=1}{\overset{k}{\mathrm{\&Sigma;}}}{D}_{\mathrm{ij}}\left(y_j\right)---\left(4\right)$

When accumulated damage is 1, promptly think structure to the longevity, can solve corresponding calendar time l according to (4) formula simultaneously, thereby can obtain the calendar life of aircraft.

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