Study Of Ballistic Limit Of Dual-Wall Shielding Structures Against Space Debris

With the development of human's space technology and activities, the space debris environment is getting more and more deteriorated, which results in a great threaten to the safety of on-orbit space vehicles. The severe situation of space debris environment makes it necessary and inevitable to design shielding for spacecraft. Furthermore, the development and activities of the nation's space technoloty, espetially those on manned spacecraft and spacecraft rendezvous, propose an urgent demand to design effective shielding for spacecraft against space debris.The relative impact velocity between space debris and spacecraft is about 1km/s to 16km/s. Due to their numerousness and the resulting high probability of collision, the emphasis of shielding design is small space debris with diameter less than 1cm, whose mass density is about 2.8g/cm3, which is close to that of aluminium or aluminium alloy.The most basic shielding structure is dual-wall shielding structure, which is also widely adopted in the International Space Station. Dual-wall shielding structure, also called Whipple shielding structure, consists of a front wall and a rear wall, which represent the bumper and the module of spacecraft respectively. Generally, the materials of dual-wall shielding structure are aluminium or aluminium alloy.Ballistic limit is used for decribing shielding structure's critical status between failure and not failure when subjected to the impact of space debris. To access the space debris impact risk in designing shielding structure, it's necessary and inevitable to obtain the shielding structure's ballistic limit. Nevertheless, there exists no complete ballistic limit equations domistically that can be applied in engineering, due to the lack of relative data of impact characteristic.This paper takes space debris shielding design as the engineering application background, takes dual-wall shielding structure against space debris of millimeters as research object. Due to the characteristic that the ballistic limit of dual-wall shielding structure can be divided into different sections under different parameters, based on analysis on the impact effects of different ranges, by considering the damage process and mechanism of the front and rear wall under different ballistic limit ranges, this paper establishes a mechanical model for the different ballistic limit ranges of dual-wall shielding structure under impacts by space debris. As a result of the models, this paper obtains the functional relation of critical thickness to prevent the failure of the rear wall when impacted by space debris, establishes the ballistic limit equations for the three velocity ranges. The main contents of the paper are as follows:The paper studies the impact phenomenon under different velocities and observes the characteristic of dual-wall shielding structure that the ballistic limit can be divided into different sections under different impact velocity ranges. Based on the individual analysis of impact effects under different ballistic limit ranges, the paper proposes the modelling method to establish the ballistic limit equations for different velocity ranges.In the ballistic range, semi-infinite plate subjected to impact by projectile is investigated. Base on conservation of energy and the feature that after impacting the front wall, the projectile will not change its mass and a hole is generated in the front wall, the remnant velocity of the projectile after perforating the front wall is investigated, as a result of which the paper obtains the crater depth of the rear semi-infinite plate. Making use of the relation between crater depth of semi-infinite plate and critical thickness of rear wall, the paper establishes the ballistic limit equation in the ballistic range.In the shatter range, the debris cloud is analyzed. Due to the feature that the debris cloud consists of solid particles, the crater depth of the semi-infinite rear wall is decomposed into two parts, one caused by the largest particle and one caused by the rest cloud particles. Base on the analysis of debris cloud cratering, the paper gives a non-dimensional expression for crater depth of semi-infinite rear wall. As sequence, the paper establishes the ballistic limit equation for shatter range. At the same time, the paper also gives the non-dimensional expression of the diameter of the largest debris particle.In the melt/vaporize range, debris cloud after impact consists of gas or liquid particles. For simplification, the paper assumes that the rear wall is subjected to uniform load when impacted by the debris cloud. Base on bending theory of plates and by Rize method, the paper obtains the approximate displacement of simple-supported circle plate subjected to partial uniform load. Afterward, the paper establishes the ballistic limit equation for melt/vaporize range through the analysis of the plate.The paper also studies the division of velocity ranges for the ballistic limit analysis of dual-wall structures. Using dimensional analysis, the paper establishes a non-dimensional empirical expression for fragmentation-initiation velocity of the projectile, which is valid for different projectile materials.By dividing into different sections, the paper establishes mechanical models for different ballistic limit ranges to reveal the physical process that dual-wall shielding structure responses differently under impacts of different velocity ranges. Existing basic research results on cratering and perforation are adopted. As a result, the paper establishes the ballistic limit equations for the three velocity ranges, the predictions of which agree well with experimental data. The research findings of the paper has some significant meanings and is valuable in engineering applications and providing theoretical guidelines. It provides technical foundation for risk assessment and shielding design applications. It reveals the physical process and mechanism of impact effects. And for developing new multilayer shielding structure, it also provides theoretical foundations for studying the hypervelocity impact characteristics.