CN106919758B - Service life prediction method for electric propulsion hollow cathode based on tungsten top hole failure - Google Patents
Service life prediction method for electric propulsion hollow cathode based on tungsten top hole failure Download PDFInfo
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Abstract
A service life prediction method for an electrically-propelled hollow cathode based on tungsten top hole failure relates to the technical field of hollow cathode detection. The method aims to solve the problem that the service life of the hollow cathode is difficult to evaluate. The method for predicting the service life comprises the steps of firstly establishing a tungsten top hole corrosion model, putting hollow cathodes for simulation into the tungsten top hole corrosion model for simulation to obtain a change curve of internal gas pressure of the hollow cathode tungsten top hole along with time of each simulation, then carrying out a high-acceleration stress degradation test on each hollow cathode with the service life to be predicted to obtain a change curve of the internal gas pressure of the hollow cathode tungsten top hole along with time, finally comparing the change curves, if the change curves are consistent with each other, taking the hollow cathode with the maximum and minimum internal pressure of the tungsten top hole in the hollow cathode with the service life to be predicted as a standard hollow cathode, taking the service life corresponding to the two standard hollow cathodes as the end point value of the service life range of the hollow cathode with the service life to be predicted, and further obtaining the service life range of the hollow cathode with the service life to be predicted.
Description
Technical Field
The invention belongs to the technical field of hollow cathode detection.
Background
As more and more electric propulsion devices enter an engineering application stage from an early design and development stage, the reliability becomes an important factor for limiting the electric propulsion devices from entering space, an electric propulsion hollow cathode is an electron source, is applied to two current mainstream space electric propulsion devices of ions and Hall and is an essential component in two propulsion systems, the hollow cathode has a harsh working environment and becomes a weak point in a thruster system, the service life of the hollow cathode directly limits the reliability of the whole set of electric propulsion devices, namely the heart of the whole electric propulsion device, and therefore the reliability of the service life of the hollow cathode has important significance for researching the service life of the hollow cathode.
Because the hollow cathode has the characteristics of high manufacturing cost, high reliability, long service life (the service life can even reach tens of thousands of hours), extremely slow change of various performance parameters and the like, in the process of researching the service life of the hollow cathode, the ground test time of 1:1, the economic cost, the labor cost and the material cost are all quite high, the number of samples allowed to be input in the experiment is very limited, and the ground test time is also limited. Although the traditional statistical inference method is simple and intuitive, in the absence of a large number of subsamples, only a performance degradation mechanism of the hollow cathode can be obtained, and the exact service life and failure confidence data of the product cannot be obtained, which brings serious difficulty to the service life evaluation of the hollow cathode.
In addition, after a batch of cathodes are produced, because large-batch long-time experimental verification cannot be carried out, how to judge which cathodes have the service lives meeting the design requirements is also an urgent problem to be solved, otherwise, accurate screening is difficult to carry out, and therefore, a novel hollow cathode service life prediction method is imperative to be researched.
Disclosure of Invention
The invention provides a method for predicting the service life of an electrically propelled hollow cathode based on tungsten top hole failure, aiming at solving the problems that the hollow cathode cannot obtain exact service life and failure confidence data and service life evaluation is difficult.
A life prediction method for an electrically-propelled hollow cathode based on tungsten apical pore failure, the life prediction method comprising the steps of:
establishing a model: the internal air pressure of the cathode tube is taken as a performance characteristic parameter of the tungsten top hole, the performance characteristic parameter is input into COMSOL software, the software is utilized to establish a tungsten top hole corrosion model for the hollow cathode,
simulation experiment: keeping the mean value of the aperture of the hollow cathode tungsten top hole for simulation to be 0.35mm, putting the hollow cathode for simulation into a tungsten top hole corrosion model for n times of simulation to obtain the change curve of the internal air pressure of the hollow cathode tungsten top hole for each simulation along with time, wherein n is a positive integer,
degradation test: carrying out high-accelerated stress degradation test on each hollow cathode with the service life to be predicted, recording the change curve of the internal air pressure of the tungsten top hole of the hollow cathode along with time and the test service life of each hollow cathode with the service life to be predicted,
and (3) life prediction: comparing the change curve obtained by the degradation test with the change curve obtained by the simulation test, if the change curve and the change curve are consistent, taking the hollow cathode with the maximum and minimum internal pressure of the tungsten top hole in the hollow cathode with the service life to be predicted as a standard hollow cathode, taking the service lives corresponding to the two standard hollow cathodes as the end point value of the service life range of the hollow cathode with the service life to be predicted, further obtaining the service life range of the hollow cathode with the service life to be predicted, and completing the service life prediction; otherwise, the degradation test is performed again.
In the simulation experiment, the variance of the simulated air pressure values for n times in the same time is obtained according to the change curve of the air pressure in the tungsten top hole of the hollow cathode along with the time, and the variance is convergent.
In the simulation, n is 20.
In the degradation test, a 10-hour high-accelerated stress degradation test was performed for each hollow cathode whose life was to be predicted.
The invention provides a service life prediction method based on a short-term experiment of a tungsten top hole, aiming at solving the problem of service life prediction of a hollow cathode according to the failure mechanism of the hollow cathode. The invention provides a method for evaluating the service life of a cathode by means of the failure rule of a tungsten top hole of the cathode in the service life test process, combining a theoretical model to carry out simulation prediction and utilizing the change condition of characteristic parameter dispersion (variance), which is used for solving various service life evaluation problems of cathode screening, design verification and the like.
Drawings
FIG. 1 is a graph showing the change of the internal pressure of the tungsten top hole of the hollow cathode with time in a simulation experiment;
FIG. 2 is a graph showing the change of the internal gas pressure of the tungsten top hole of the hollow cathode in the degradation test with time;
FIG. 3 is a graph showing the trend of the variance of the internal gas pressure of the tungsten top hole of the hollow cathode with time.
Detailed Description
The failure modes of the hollow cathode mainly comprise heating wire evaporation failure, tungsten top hole reaming corrosion, emitter evaporation failure and the like. Once the aperture of the tungsten top is changed, the whole characteristics of the cathode are obviously changed along with the change of the aperture of the tungsten top, such as the increase of ignition time and oscillation, and finally the whole cathode fails because the ignition cannot be performed or the oscillation during work is too large. The relationship between the tungsten ceiling pore diameter and the cathode lifetime will be specifically described below by the following embodiments.
The first embodiment is as follows: the embodiment is described in detail with reference to fig. 1 to 3, the method for predicting the service life of the electrically-propelled hollow cathode based on tungsten top hole failure in the embodiment,
and (3) establishing a small hole corrosion model for the hollow cathode to be detected by utilizing COMSOL software, wherein the experimental model can see the air pressure change condition and the small hole corrosion appearance.
Utilize the aperture corrosion process of this aperture corrosion model simulation experiment component, the tungsten apical pore corrodes and leads to the aperture grow, and the aperture grow leads to inside atmospheric pressure to diminish, and atmospheric pressure is little to a certain extent can cause whole negative pole because unable ignition or work to vibrate too big and inefficacy. The lifetime of the cathode is thus associated with corrosion of pinholes. The corrosion of the pores corresponds to the change of the pore diameter, the pore diameter change affects the internal air pressure of the cathode, the specific corrosion condition of the pores cannot be directly measured during specific experiments, and the corrosion is related to the air pressure, and the change of the air pressure is measured in the specific experiments, so that the service life problem is reflected.
And in n times of simulation, the initial value of the aperture is about 0.35mm respectively, so that the average value is 0.35 mm. After the simulation is finished, the air pressure change of each simulation is obtained, and the variance change condition of the air pressure value of n times of simulation at the same time is calculated. The variance was found to converge and more towards unity.
The simulated change curve of the internal gas pressure of the tungsten top hole of the hollow cathode along with the time, as shown in fig. 1, shows that for the corrosion of the small hole of the hollow cathode, the characteristic of the deceleration corrosion is obvious, namely, after the corrosion is carried out to a certain degree, the corrosion rate is reduced to a low enough magnitude, even can be ignored.
And (3) carrying out a high-acceleration stress degradation test on a batch of hollow cathodes to be detected, wherein the degradation test adopts a hole diameter of 0.35mm and a hole depth of 1mm, the hollow cathodes circularly work for 10 hours under a 7.8A high-current working condition, the gas supply flow adopts 3sccm, and the change conditions of various parameters of the cathodes are observed.
Obtaining variance variation condition of characteristic parameters of a test sample by using test data within 10h in the initial stage of the test, wherein the process is to obtain a test data value and calculate to obtain a mean variance, and the characteristic parameters are the internal air pressure of the cathode tube;
the degradation test finds that the variance of the air pressure value of the test piece of the batch is indeed converged and tends to be more and more consistent, the comsol simulation result is proved to be credible, the rule is correct, and the dispersion condition of the characteristic quantity (air pressure value) in the small hole corrosion process of the cathode of the batch is converged along with the time development, namely the dispersion condition of the characteristic quantity (air pressure value) in the small hole corrosion process of the cathode of the batch is converged along with the time development
Wherein the content of the first and second substances,
the method refers to the upper limit of the internal pressure value of the cathode at the beginning of an experiment in the same batch of cathodes;
Pt,nthe upper limit of the internal pressure value of the corresponding cathode at time t in the same batch of cathodes is referred to;
Pt,n′refers to the lower limit of the internal pressure value of the cathode corresponding to the time t in the same batch of cathodes.
Thus, to
And
the corresponding lifetime is more conservative as the lifetime range of this batch of cathodes. The initial internal air pressure value of the corresponding cathode experiment is set as
And
the tungsten top hole is subjected to a high accelerated stress degradation experiment to obtain two life values, namely the life range of the batch of cathodes.
The main failure modes of the tungsten top hole include two types, namely tungsten top hole reaming corrosion caused by high-energy ion bombardment and tungsten top hole reaming corrosion caused by high-temperature evaporation.
The high energy ion bombardment erosion rate is two orders of magnitude higher than the high temperature evaporation rate, thus neglecting the high temperature evaporation mechanism at the tungsten tip. In the embodiment, only the tungsten top hole reaming corrosion caused by the high-energy ion bombardment corrosion is considered.
Because the tungsten top hole is small in size (the diameter is smaller than 1mm), the physical process is extremely complex during discharging, and the internal physical parameters can not be obtained by the existing detection method, so that great difficulty is brought to the research on the corrosion process of the tungsten top hole.
At present, the method mainly comprises a destructive test method, namely: the corroded tungsten top hole is cut from the middle by means of linear cutting and the like and is placed under a microscope to observe the appearance of the small hole, although the final appearance of the small hole can be obtained, the appearance of the small hole cannot correspond to the performance of the tungsten top hole, the change process of the throttling performance of the small hole in the whole service life cannot be obtained, and the change process is the most important basic data in the performance degradation test method. There is therefore a critical need for a measurable characteristic parameter to characterize the degradation process of pore performance with increasing lifetime. In view of the problem of the lack of the performance characteristic parameter, the present embodiment proposes a method for evaluating the performance degradation process of the small hole based on the air pressure change, that is, the air pressure inside the cathode tube is used as the performance characteristic parameter of the small hole, and the change of the throttling performance of the small hole is evaluated by monitoring the change of the air pressure value of the small hole during the service life.
In fact, a number of experiments have demonstrated that for hollow cathode pitting corrosion, there is a significant deceleration corrosion characteristic, i.e. when the corrosion has progressed to a certain extent, the corrosion rate will have decreased to a sufficiently low level, even negligible.
In order to verify the process, a pore corrosion model is established for a cathode with the aperture of 0.35mm by utilizing COMSOL (multi-physical-field numerical simulation) software, the model is consistent with the prior models in a direct current discharge module, a laminar flow module and a heat transfer module and only has difference in numerical value, and a deformation geometric body module is added into the corrosion model on the basis of the model so as to simulate the pore corrosion process.
According to the change data of the air pressure along with the time in the COMSOL simulation model, an equation of the change of the air pressure along with the time is obtained through an exponential fitting function in origin (function drawing software):
P＝P0+A*exp(-t/x)
wherein, P0The discharge pressure of the cathode at which the pitting corrosion rate decreases to a negligible level is related to the operating characteristics and operating parameters of the cathode;
x is a normal number, and represents a time characteristic quantity;
a-a function related to the level of acceleration stress, characterizing the rate of degradation;
for different cathodes, the degradation curve forms of the characteristic parameters are consistent under different working conditions, and only the exponential function parameters are different.
Claims (4)
1. A life prediction method for an electrically-propelled hollow cathode based on tungsten apical pore failure is characterized by comprising the following steps:
establishing a model: the internal air pressure of the cathode tube is taken as the performance characteristic parameter of the tungsten top hole, the performance characteristic parameter is input into COMSOL software, the software is utilized to establish a tungsten top hole corrosion model for the hollow cathode, a deformation geometric body module is added into the corrosion model so as to simulate the small hole corrosion process,
simulation experiment: keeping the mean value of the aperture of the hollow cathode tungsten top hole for simulation to be 0.35mm, putting the hollow cathode for simulation into a tungsten top hole corrosion model for n times of simulation to obtain the change curve of the internal air pressure of the hollow cathode tungsten top hole for each simulation along with time, wherein n is a positive integer,
equation of air pressure over time:
P＝P0+A*exp(-t/x)
wherein, P0The discharge pressure of the cathode when the pitting corrosion rate is reduced to a negligible level, x-the normal number, A-a function related to the level of the accelerating stress, t-time, P-the gas pressure,
degradation test: carrying out high-accelerated stress degradation test on each hollow cathode with the service life to be predicted, recording the change curve of the internal air pressure of the tungsten top hole of the hollow cathode along with time and the test service life of each hollow cathode with the service life to be predicted,
and (3) life prediction: comparing the change curve obtained by the degradation test with the change curve obtained by the simulation test, if the change curve and the change curve are consistent, taking the hollow cathode with the maximum and minimum internal pressure of the tungsten top hole in the hollow cathode with the service life to be predicted as a standard hollow cathode, taking the service lives corresponding to the two standard hollow cathodes as the end point value of the service life range of the hollow cathode with the service life to be predicted, further obtaining the service life range of the hollow cathode with the service life to be predicted, and completing the service life prediction; otherwise, the degradation test is performed again.
2. The method for predicting the service life of the electrically-propelled hollow cathode based on the tungsten top hole failure as claimed in claim 1, wherein in the simulation experiment, the variance of the simulated air pressure values n times in the same time is obtained according to the change curve of the air pressure in the tungsten top hole of the hollow cathode along with the time, and the variance is convergent.
3. The method for predicting the service life of the electrically-propelled hollow cathode based on the tungsten apical pore failure is characterized in that n in a simulation experiment is 20.
4. The method for predicting the service life of the electrically-propelled hollow cathode based on the tungsten top hole failure as claimed in claim 1, wherein a 10-hour high-accelerated stress degradation test is performed on each hollow cathode with the service life to be predicted in the degradation test.
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| CN109766626B (en) * | 2019-01-08 | 2020-10-09 | 北京航空航天大学 | Degradation modeling and service life prediction method considering effective impact under intermittent stress |
| CN112444725B (en) * | 2019-09-05 | 2024-01-26 | 中车株洲电力机车研究所有限公司 | Through hole welding spot contrast accelerated life test method |
| CN112084688B (en) * | 2020-08-18 | 2023-10-03 | 中国电子产品可靠性与环境试验研究所（（工业和信息化部电子第五研究所）（中国赛宝实验室）） | Cathode life prediction method |
| CN112329201B (en) * | 2020-09-30 | 2022-11-04 | 兰州空间技术物理研究所 | Integrated ionic electric propulsion simulation model and method |
| CN112395805B (en) * | 2020-10-27 | 2023-10-03 | 中国电子产品可靠性与环境试验研究所（（工业和信息化部电子第五研究所）（中国赛宝实验室）） | EBSM cathode life assessment method |
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