微流星體高速撞擊航天器Whipple防護結構損傷特性研究

朱凼凼，龐寶君，孫英超，賈 斌，張澤華，程燕平

(1．哈爾濱工業大學，哈爾濱150001;2．中國空間技術研究院研究發展中心，北京100094)

0 Introduction

Meteoroid is one kind of solid particles which come from comets and asteroids，and move in interstellar space［1－2］．In Earth orbit，the meteoroids and space debris may occur and impact the spacecraft and lead to damage．Therefore，they are often known as the M/OD(Meteoroid/Orbital Debris)and considered together．Space debris does not exist outside of the Earth＇s orbit．Meteoroid has become the only damage threat that impact spacecraft．Some study materials on meteoroid［3］showed that:a．Meteoroids have high speed and the average relative impact velocity is 20 km/s(twice the speed of space debris)．High-speed impact might lead to the breakdown of spacecraft surface and be danger to payload and control system(such as electronic devices become invalid due to plasma discharge)within the spacecraft;b．mm-class meteoroid might damage spacecraft surface materials，and will cause shock waves which cause the surface of spacecraft protective coating off and damage sensitive detector on the spacecraft surface;c．With regard to high-pressure containers，cracks may lead to leakage or even explosion，or seriously affect the safety of the manned capsule．

For space debris research，generally aluminum projectile is used as a typical source of space debris．For meteoroids，more of them are non-metallic or mineral-based，while the physical and chemical compositions are very different．So it is difficult to find a unified typical projectile simulation material．But we can do research according to some typical situations．In this paper，as a high-brittle，high melting point of typical meteoroid simulation materials，diamond is used to do hypervelocity impact tests on typical spacecraft structures，and analysis of bulkhead damage has also been done．

1 Test Method

The test used non-gunpowder-driven two-stage light gas-gun of Hypervelocity Impact Research Center in Harbin Institute of Technology as launchers and Laser velocimetry device．Whipple structure(Figure 1)is made of 1mm thick shield(front plate)and 3 mm thick bulkhead plate(rear plate)and the interval spacing is 100 mm．The shield and the bulkhead plate are 200 mm×200 mm square．The shield is 2A12 aluminum alloy plate，and the bulkhead plate is 5A06 aluminum alloy plate［6］．The range of the minimum diameter of diamond projectile is between 1．1 mm and 2．1 mm，and the range of the Maximum diameter is between 1．9 mm and 2．6 mm．The quality scope of projectile is between 0．0108g and 0．0178g．The impact velocity is between 0．9 km/s and 4．3 km/s．

The diamond sands used in this experiment are purchased from South Africa and Shanghai respectively(Figure 2)．Shanghai Diamond has low intensity，and can＇t guarantee the integrity of projectile in high-speed stage，so it is fit to be used in low-speed stage．Compared to South Africa Diamond，Shanghai Diamond has high strength．The South African diamond intensity is 6GPa;strain-rate is about 2000 s－1tested by Hopkinson bar apparatus under moving in Hypervelocity Impact Research Center in Harbin Institute of Technology．So it is fit for high-speed impact stage［4－5］．

Fig．1 Whipple shield

Fig．2 Diamond

2 Test Analyses

2．1 Test Result

The tests conducted nine hypervelocity impact tests，four typical phases is given after the analysis and the each elected by a typical example is as follows:

(1)Shanghai Diamond speed is 0．91 km/s

Shown in Figure 3，when Shanghai Diamond impact velocity is 0．91km/s，there is a hole in the front plate and crimped．Because the shape of diamond is irregular，the edge of the hole of the front plate is also irregular，which has something with the shape of diamond．A single crater is formed in the rear plate whose surface is smooth．And we can see a diamond bullet traces clearly．All these indicate that the projectile is basically intact after it goes through the front plate and rebound after it crashes on the rear plate．

Fig．3 Damage on the front and rear plate

(2)Shanghai Diamond speed is 1．47 km/s

When Shanghai Diamond impact velocity is 1．47 km/s，because the maximum and the minimum diameter of diamond are not very different，which is closer to round bullet，the edge of hole formed by projectile of the front plate is relatively smooth and round．The diamond is broken and inlaid in the rear plate，which forms a cone-shaped diamond accumulation whose midst is high and border is low．And there are black powders around the crater on the rear plate，referring to Figure 4．

Fig．4 Damage on the front and rear plate

(3)South African Diamond speed is 2．53 km/s

When South African Diamond impact velocity is 2．53 km/s，compared the maximum diameter with the minimum diameter of diamond，there are much difference relatively．But the edge of the hole of the front plate closes to the circular，whose curling is more evident than the first two．Diamond crystal can＇t be observed with the naked eye in the rear plate，but dispersed and clustered．This fully demonstrates that the diamond breaks and scatters after the projectile impacts on the front plate and brings high temperature and high pressure，which make broken diamond come into graphite，referring to Figure 5．

Fig．5 Damage on the front and rear plate

(4)South African Diamond speed is 4．3 km/s

When South African Diamond impact velocity is 4．3 km/s，compared the largest diameter with the minimum diameter of diamond，there are much difference relatively．But the edge of the hole of the front plate closes to the circular and comes to double crimping there．There is more obvious the phenomenon of cluster dispersion on the rear plate．There are apparent ignition，burning bright and!melt surface in the middle of each cluster，which indicates the high temqerature debris cloud generated after diamond hypervelocity impact on the front plate．Then the damage on the rear plate by the diamond is no longer a leading role．And the front plate aluminum debris cloud is a major factor to damage on the rear plate，referring to Figure 6．

2．2 Damage Analysis

Fig．6 Damage on the front and rear plate

Spacecraft bulkhead perforation causes a great threat to the safe operation of the spacecraft，especially for manned spacecraft capsule．So the depth of bulkhead damage is an important indicator for the safe operation of spacecraft．We carry out the damage analysis on the deepest hole of rear plate by three-dimensional microscopy in laboratory of Hypervelocity Impact Research Center in Harbin Institute of Technology．The deepest pit formed on the rear plate is hit by diamond or debris cloud．Diamond deepest pit is generated by the diamond impaction．As shown in Figure 7，H is the distance from bottom of the deepest hole to the crimping top and h is the distance from the bottom of the deepest hole to the surface of the bulkhead．

Fig．7 Rear plate＇s pit chart

Hypervelocity crash test data on Whipple protective structures as follows:

The debris cloud contains diamond and aluminum of front plate after diamond passes through the first plate．After the overall analysis on the rear plate，we can get the relationship between speed and largest damage by the diamond．From the Figure 8，we can see the change of state of diamond under different speeds can be divided into five clear sections，each section，summed up the situation after the board injuries as shown in Table 2．

Table 1 Impact test data of diamond

Table 2 Diamond hypervelocity impact phenomena on rear plate

Fig．8 The deepest pit of diamond

3 Conclusions

Firstly，after diamond hypervelocity impact on the former board，the impact effect of high temperature and high pressure in different speeds by corresponding is different．The effect of high temperature and high pressure become more obvious with increasing speed that lead to diamond pellet changes from the complete diamond into mixture of graphite and diamond and then transition to full graphite components．

Secondly，diamond broken chips change into smaller particles and the material change of diamond at high-speed stage are two factors which reduce the rear plate damage．So at high-speed stage，the former aluminum plate debris cloud has become a major factor of the damage of the rear plate．

Thirdly，at the stage of three speed such as v＜0．91 km/s，v=2．53 km/s or so，v＞4．3 km/s，the damage on the rear plate of Whipple projective structure is obviously．So the three distinct stages are the focus of structural protection design．

Finally，diamond damage on the protective structure is reflected at the low-speed stage，when the impact velocity is greater than 4．3 km/s，the burn injury on the rear plate is extremely significant．Therefore at the stage of high-speed，prevent protective structure from high temperature damage has been the focus of design．

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