Research On High Velocity Impact Damage And Fatigue Of Defected Spacecraft Protection Structure

With the development of space industry,the environment of space debris is getting worse and worse,which seriously threatens the safe operation of on-orbit spacecraft.In order to deal with the threat of space debris to spacecraft,one or more thin plate protective screens are installed at a certain distance outside the bulkhead to break the space debris and disperse its impact energy,so as to achieve the purpose of protecting the safety of spacecraft.Among them,aluminum alloy sheets are widely used to make protective screens and bear the impact of space debris directly.At the same time,due to the lack of atmospheric protection,the spacecraft in orbit is subject to radiation fluctuations,and the thermal stress in the shield changes dramatically.For the protection structure of spacecraft,after years of research and development,people have a deep understanding of its protection performance.New materials are also applied to the protection structure of spacecraft,which greatly improves its performance.However,the spacecraft’s protective structure may be impacted by space debris more than once during its operation.Sometimes the impact occurs at the same point or the two impact points are close to each other.When the second and subsequent impact occurs,the protective structure can not be regarded as a complete one.In addition,defects such as bubbles and indentations may also occur in the production process of aluminium alloy sheets.These defects caused by impact or production will affect the performance of the protective shield,and the defects will lead to stress concentration or strain concentration of the protective shield,thus affecting the fatigue strength of the protective shield.Based on the above background,aiming at the phenomenon of high-speed impact and thermal fatigue effect of the protective structure of defective spacecraft,this paper focuses on the protective performance of Whipple aluminum alloy protective structure with crater,bubble and crack defects,as well as the thermal fatigue effect of the protective screen with perforation and crater defects.Firstly,two-stage light gas gun loading technology was applied to carry out the experimental study on the high-speed impact of projectile on Whipple protective structure of aluminum alloy with crater and crack defects.The high-speed impact damage characteristics of Whipple protective structure of aluminum alloy with crater and crack defects were obtained.Compared with the high-speed impact damage characteristics of Whipple protective structure of aluminum alloy,the impact damage characteristics of crater and crack defects on Whipple protective knot of aluminum alloy were analyzed.Effects of high-speed impact damage on structures.Secondly,based on the ballistic limit equation summarized by predecessors,the impact limit curves of Al-alloy Whipple protective structures with craters,bubbles and cracks are obtained by numerical simulation.Compared with the impact limit curves of Al-alloy Whipple protective structures,the effects of craters,bubbles and cracks on the performance of Al-alloy Whipple protective structures are summarized.Thirdly,by comparing the projectile shape,stress wave propagation,velocity change and energy conversion of the system after the projectile impacts on the protective shield with craters,bubbles and cracks,the mechanism of the impact of the defect on the performance of the spacecraft protective structure is analyzed.Finally,related theory of thermal fatigue is introduced.The effects of perforation and crater defects on the fatigue strength of protective shield are studied by numerical simulation.The parameters of Paris zone with perforation and crater defects are calculated,and the influence of residual stress on the fatigue strength of protective shield is analyzed.Empirical parameters of residual stress on the fatigue strength of protective shield are summarized by numerical simulation.