Background technology
Show according to external satellite statistical data: " stuck " that the driven unit insufficient lubrication causes is the one of the main reasons that causes satellite to lose efficacy, and the rubbing wear of driven unit is the key reason that causes the rotating mechanism performance to descend.The space flight driven unit is the critical product of restriction satellite long-life in rail flight, and its high reliability and long-life are to the development of novel long-life satellite and use most important.
Usually the life characteristics of product is to obtain through the method for doing the life-span test under normal operation.But for the satellite driven unit; If adopt the method for ordinary life test often need expend very long test period and lot of test expense; Even needed test period is far longer than the lead time; Can not before coming into operation, accomplish the life-span checking, so accelerated life test receives people's attention gradually.
At present, the durability test of space flight driven unit is in vacuum chamber, to apply temperature stress and load stress (radiation and other environmental stresses are not considered because of difficult simulation event), and durability test is accomplished till the life characteristics value of driven unit at 1: 1.The temperature stress variation range that is applied is normally-50 ℃ to 70 ℃, and rate of temperature change is set according to operating mode and testing equipment actual conditions; Load applies inertia usually and often is worth load, applies load as adopting the inertia dish, with the load capacity of examination space flight driven unit.The ground experiment of satellite driven unit checking at present lacks relevant test figure and experience accumulation, and the surplus of its space environment adaptive faculty is not known the real situation, and is mainly reflected in following two aspects:
One, the anti-environment temperature design of driven unit is conservative relatively, and storage and working temperature scope of design are narrower.Present completed simulation only is confined to the environmental baseline of designing requirement at rail environmental work reliability assessment, does not draw partially and knows the real situation verification experimental verification;
Two, the existing verification experimental verification level of driven unit has been supported the life requirements that synchronous orbit 8 years, accumulative total were worked 2000 hours basically; For the longer performance requirement with the accumulative total working time, there are not direct test figure checking and test method assessment in the rail life-span.
But along with the raising of satellite, test profile efficiently need be provided, to realize the life appraisal of accelerated life test at the rail index of aging.
Accelerated life test is under the prerequisite that does not change product failure mechanism, through strengthening the way of stress, accelerates product bug, shortens test period, dopes the method for product life characteristics under the normal stress effect in the short period of time.Not changing failure mechanism is the prerequisite of accelerated life test, and strengthening environmental stress or working stress that product bore is the necessary means of carrying out accelerated life test.Accelerated life test is to shorten test period through strengthening stress, if but stress is excessive, changed the failure mechanism of product, and then accelerated life test has just lost meaning.If stress is less than normal, it is also not obvious then can to cause test period to shorten, and accelerated life test can't obtain best effect.The actual condition that how to combine product, the accelerated life test section of confirming not change product failure mechanism and playing accelerating effect preferably is puzzlement designer's a difficult problem always.
Can retrieve the reference of external product accelerated life test at present, but concentrate on the research of statistical method mostly, considerably less about the test profile design content.In view of China's correlation technique being taked the sealing policy abroad; How we design the accelerated life test section to external space flight driven unit is had no way of learning; China is also at the early-stage to the research of the accelerated life test of space flight driven unit, and up to the present China does not have the accelerated life test section method for designing of the space flight driven unit that is suitable for practical applications as yet.
Summary of the invention
The present invention is in order to solve under the prerequisite that does not change space flight driven unit failure mechanism; The accelerated life test that realizes the space flight driven unit has the purpose of acceleration effect preferably; A kind of space flight driven unit combined stress accelerated life test section method for designing is proposed; For the space flight driven unit provides a kind of practicality, can operate, not change failure mechanism and the comparatively tangible accelerated life test section method for designing of acceleration effect, for space flight driven unit life appraisal provides effective accelerated method.
A kind of space flight driven unit combined stress accelerated life test section method for designing that the present invention proposes is specially:
Step 1, the test of knowing the real situation, definite the most extreme stress value that does not change space flight driven unit failure mechanism;
Step 2, based on stress level quantity l, confirm respectively to quicken each stress value stress level under, the value size of each stress under i acceleration stress level is all definite based on following formula:
Specified stress value+(the most extreme stress value-specified stress value) * i/l, 1≤i≤l, i, l are positive integer;
Step 3, confirm the single cycle time T of stress T=0.01T to be set
0, T
0Life expectancy index for space flight driven unit under the conventional stress;
Step 4, carry out the design of combined stress accelerated test section; Specifically: all exemplars that carry out the combined stress accelerated life test bear same test profile; All be protracted test single cycle time T under the acceleration stress level that step 2 obtains successively, this process that circulates again again is until off-test;
Step 5, if need to increase new stress; At first confirm newly-increased stress at the rail physical condition according to the space flight driven unit; Then according to cumulative damage theory; Adopt rain stream method to increase the section establishment of stress newly; With increasing the comprehensive acceleration stress test section stack that stress section and step 4 obtain newly, obtain final combined stress accelerated life test section, all exemplars that carry out the space flight driven unit of combined stress accelerated life test are made an experiment on the final combined stress accelerated life test section that obtains.
Advantage of the present invention and good effect are:
(1) under the situation that ordinary life test load spectrum is confirmed, can quicken space flight driven unit crashed process largely, accelerate to obtain the speed of Test to Failure sample;
(2) the comprehensive accelerated life test section of varying stress method for designing is provided, can have reflected space flight driven unit actual motion load section better;
(3) when design synthesis accelerated life test section,, guarantee not change the failure mechanism of space flight driven unit through the amplitude and the time of adjustment stress.
Embodiment
Below in conjunction with accompanying drawing and embodiment combined stress accelerated life test section method for designing of the present invention is elaborated.
Accelerated life test section method for designing of the present invention mainly comprises two parts: based on the accelerated life test section method for designing under the ordinary life test load spectrum, and newly-increased stress loading section method for designing.
As shown in Figure 1, the inventive method is on the basis that existing ordinary life test profile is confirmed, the method for carrying out the design of accelerated life test section is following:
Step 1, the test of knowing the real situation, definite the most extreme stress value that does not change space flight driven unit failure mechanism.Confirming that durability test quickens to a certain stress, other stress values to be fixed earlier on the basis of stress, the amplitude of this stress is being improved on the basis of specified stress.Generally can the test exemplar be divided into several groups, every group is promoted to different numerical, confirms through all kinds of both macro and micro analytical approachs and means whether failure mechanism changes, and then is not changed the extreme value of this stress of failure mechanism.Definite extreme value that does not change other acceleration stress of failure mechanism uses the same method.And then the extreme value of respectively quickening stress that will obtain is comprehensive, analyzes whether failure mechanism changes under this combined stress.If change; Then must adjust by the counter stress combined value; The extreme stress value of each stress is all reduced the size of (the extreme stress value of stress-specified stress value under the single stress situation) * 10% at every turn; Failure mechanism until the space flight driven unit does not change, and obtains the desired the most extreme stress value that respectively quickens stress this moment.Adjustment can be carried out as follows: with two acceleration stress is example, establishes specified stress value and is respectively V
0, P
0, extreme stress value is respectively V under the single stress situation
m, P
m, can extreme stress value be reduced to V respectively
0+ 0.9 (V
m-V
0), P
0+ 0.9 (P
m-P
0) analyze again.If failure mechanism still changes, then combined stress is reduced to V
0+ 0.8 (V
m-V
0), P
0+ 0.8 (P
m-P
0), by that analogy.
Step 2, definite stress level that quickens.The combined stress accelerated life test need be set stress level quantity l according to physical conditions such as experimental facilitiess, and l general desirable 3 to 5.The value size of each stress under i stress level is all definite according to following formula: specified stress value+(extremely stress value-specified stress value) * i/l, and 1≤i≤l, i, l are positive integer.Still quickening with two stress is example, gets l=4.If the extreme stress value of the combination that obtains in the
step 1 is respectively V
n, P
n, then can set 4 acceleration stress levels and be respectively
{ V
2, P
2}={ V
0+ 0.5 (V
n-V
0), P
0+ 0.5 (P
n-P
0), { V
3, P
3}={ V
0+ 0.75 (V
n-V
0), P
0+ 0.75 (P
n-P
0), { V
4, P
4}={ V
n, P
n.
Step 3, confirm the single cycle time T of stress.If the life expectancy index of assembly is T under the specified stress value
0, then can get T=0.01T
0
Step 4, carry out the design of combined stress accelerated test section.According to the single cycle time of quickening stress level and stress, can confirm combined stress accelerated life test stress section.All exemplars that carry out the combined stress accelerated life test bear same test profile; All be to carry out following process of the test: the time T of protracted test single cycle successively under the acceleration stress level that step 2 obtains, and then this process of the test that circulates again is until off-test.Still quickening with the two stress in step 1 and the step 2 is example, and the combined stress test profile is { V
1, P
1, { V
2, P
2, { V
3, P
3, { V
4, P
4Continuing the T time successively, each combined stress test profile that circulates again again is until off-test.
Step 5, newly-increased stress loading section designing technique.If the stress section according to above step design does not still reach extraordinary acceleration effect, then can in the combined stress test profile, increase stress newly.Newly-increased stress is confirmed at the rail physical condition according to the space flight driven unit.For example adopt two stress of rotating speed and axial load to quicken,, then can further apply temperature stress if still there is not good acceleration effect to bearing with solid lubricant.At first obtain the temperature stress section that born in the longer cycle of space flight driven unit when rail.Increase the establishment of stress section newly according to cumulative damage theory again.According to cumulative damage theory; Load change all causes a certain amount of damage to mechanism each time; The stress profile change is big more; The amount of damage that is caused is also big more, when all damage accumulations to reaching a certain particular value together when (often being called total damage), the critical component of mechanism promptly takes place to destroy and causes losing efficacy.When carrying out the establishment of stress section, adopt rain stream method according to cumulative damage theory.
Rain stream method is to have considered material stress-coping behavior and a kind of counting method of proposing by people such as Matsuiski and Endo.This method thinks that the existence of plasticity is the necessary condition of fatigue damage, and its plastic property shows as the lag loop of stress-strain.Generally speaking, though nominal stress is in elastic range, from the viewpoint of measures part, microcosmic, plastic yield still exists.
The stress section that bears for certain space flight driven unit shown in Figure 2, its corresponding cyclic stress-strain curve is shown among Fig. 3.Constitute two little and big lag loops respectively by visible two the partial circulating 2-3-2 ' of figure, 5-6-5 ' and systemic circulation 1-4-7.If fatigue damage is as sign, and suppose that a caused damage of big range does not receive to accomplishing the influence that a little lag loop blocks, then can from whole strain-time history, extract than partial circulating constituting one by one, make up again.Like this, Fig. 2 strain-time history will be reduced to the form of Fig. 4, and think that the two fatigue damage that material is caused is equivalent.Rain stream method is promptly counted based on above-mentioned principle.Be illustrated in figure 5 as the stress section that another space flight driven unit bears, the sub-fraction that here only begins with section is that example describes, and the time of getting is ordinate, and vertically downward, load-time history shape is like a pagoda roof.Raindrop Yi Feng, paddy are starting point, flow downward.According to the trace that raindrop flow, confirm load cycle, the title of rain stream method promptly gets thus.For realizing its counting principle, the special regulation as follows of doing.At first, from certain 1: 0 beginning, all rain stream that originates in trough runs into than its lower valley (algebraic value) and just stops.The rain stream that for example originates in trough 0 terminates in the horizontal line of trough f, because the valley of trough is lower than the valley of trough 0.Similarly, all rain stream that originates in crest runs into than its higher peak value and just stops, and the rain stream that for example originates in crest a terminates in the horizontal line of crest e.In addition, in the raindrop flow process, also just stop during the raindrop that flowing down above all running into, the rain stream that for example originates in crest c terminates in crest b '; The rain stream that originates in trough d terminates in a '.Like this, based on starting point and the terminal point that raindrop flow, can delineate out complete one by one circulation.Like b-c-b ' and a-d-a ' etc.The circulation that all are complete extracts one by one, and writes down its peak value and valley.
Table 1 has provided the count results of the complete stress section at the place of the stress section shown in Fig. 5 being carried out rain stream method.Peakreading and valley reading are divided into 11 groups in the table, and the group distance is 2.In group limit one hurdle, only indicated lower limit: 0,2,4 ..., 20.Numeral circulation frequency in the square formation, for example peak value (class mean) is 11, valley (class mean) is that 9 load cycle takes place 45 times altogether, can design the loading spectrum of newly-increased stress thus.
Table 1 rain stream method count results
The stack of stress section and former test profile will be increased newly, final combined stress accelerated life test section can be obtained.
The counting characteristics of rain stream method are that alternate load-time history and the ess-strain response of material under alternate load have corresponding relation, and its count results and material stress-coping behavior are in full accord, and this is its a big advantage place; Its essence is the complete cycle number and half period of record test profile, when the test profile time history of dealing with complicated, adopts rain stream method very convenient.According to above principle,, can effectively carry out the design of combined stress accelerated life test section according to the actual condition of space flight driven unit.
Embodiment
Adopt the inventive method as follows to certain model bearing with solid lubricant accelerated life test section design:
At first analyze the working environment of bearing with solid lubricant and the stress that bears, and quicken the selection of stress.Bearing with solid lubricant is a kind of basic space flight driven unit, is widely used in each quasi-instrument and mechanism of spacecraft.The environmental stress that bearing with solid lubricant bears mainly contains temperature, radiation etc., and working stress mainly contains rotating speed, radial load, axial load etc.
In the real work, how bearing with solid lubricant is caused by insufficient lubrication or wearing and tearing if losing efficacy.Solid lubricant film is attrition gradually, and destruction of lubricating film and cause bearing moment to increase or vibration increases finally causes losing efficacy.When carrying out the bearing with solid lubricant accelerated life test, mainly select rotating speed and axial load as quickening stress.
The carrying out of (1) knowing the real situation and testing
With the rotating speed is example, on the basis of bearing rated speed, progressively increases rotating speed, simultaneously the moment of friction of bearing, temperature, vibration etc. is monitored.Monitoring result is compared and analyzes to confirm not change the maximum stress of space flight driven unit failure mechanism.
With certain model angular contact bearing with solid lubricant is example, and the rated speed of its work is 1000rpm, and axial load is 7.84N.Existing test speed begins from 1000rpm to its test of knowing the real situation, and pressing 1000rpm upwards increases the vibration signal of monitoring test bearing on some fixed angles gradually.Distinguish one section vibration signal such as Fig. 6 a~6c of intercepting when 2000rpm, 5000rpm, 6000rpm.
Contrast through Fig. 6 a~6c can obtain, and vibration signal was less when rotating speed was 2000rpm, and vibration signal slightly increased when rotating speed was 5000rpm, but changes also not obvious.Rotating speed for 6000rpm time vibration very violent.So can select rotating speed V
m=5000rpm is as the maximum speed that does not change failure mechanism.Method through approximate can obtain the maximum axial stress P that does not change failure mechanism that this model bearing with solid lubricant can bear
m=11.84N.Again with { V
m, P
mBe applied in 2 bearing with solid lubricant exemplars, the result finds that failure mechanism does not change under this combined stress.So can obtain extreme combined stress value { V
n, P
n}={ 5000rpm, 11.84N}.
(2) confirm to quicken stress level.Get stress level quantity l=4.Can obtain 4 acceleration stress levels and be respectively { V
1, P
1}={ 2000rpm, 8.84N}, { V
2, P
2}={ 3000rpm, 9.84N}, { V
3, P
3}={ 4000rpm, 10.84N}, { V
4, P
4}={ 5000rpm, 11.84N}.
(3) confirm the single cycle time T of stress.The life expectancy index of this model bearing with solid lubricant is T under the conventional stress
0=2000h.So T=0.01T
0=20h.
(4) comprehensively quicken the design of stress test section.The combined stress test profile is { V
1, P
1, { V
2, P
2, { V
3, P
3, { V
4, P
4Continue 20h successively, circulate until off-test again again.
Adopt the inventive method that certain model bearing with solid lubricant is carried out accelerated life test, finally obtaining speedup factor is 4, has obtained acceleration effect preferably, so need on the basis of the stress section that designs, not increase stress condition newly.Surface topography analysis after the experiment shows that above-mentioned accelerated life test section method for designing can not change the failure mechanism of bearing with solid lubricant; The comprehensive accelerated life test of varying stress; Can reflect better that space flight driven unit actual motion load section quickens space flight driven unit crashed process, and obtain acceleration effect preferably.
The present invention takes all factors into consideration working stress and the environmental stress that the space flight driven unit is born, and in the process of design accelerated life test section, the factor that takes into full account size, frequency, the order of stress and four aspects that distribute is to guarantee the validity of loading spectrum.Actual applying working condition according to the space flight driven unit; Confirm the maximal value of each stress and stress combination under the critical failure mechanism; Consider coupled relation and decoupling zero effect thereof between each stress simultaneously; Increase stress amplitude by frequency distribution and probability size equal proportion, accomplish not change its stress distribution order as far as possible.Quicken effectively expedite product crashed process of stress frequency; But also may introduce coupling new between stress, might destroy the failure mechanism that changes product, therefore will combine the test of knowing the real situation; Select suitable acceleration start frequency, but the test period under the extreme stress is adjusted to allowed band.In the time need on the basis of combined stress section, increasing stress condition newly,, adopt " rain stream method " to carry out new acceleration stress section design according to cumulative damage theory.