| Abstract [eng] |
This masters thesis is aimed at numerically studying Whipple shield improvements for protection against hyper-velocity impacts. Whipple shields are used to protect the hull of a spacecraft against high-speed space debris impacts. Upon impact, debris particles disintegrate into small fragments – a debris cloud. The following debris cloud’s impact into the spacecraft is considered very dangerous, due to the possible penetration of the material. Studied literature shows, that decreasing the probability of such penetration is achieved by improving the structural characteristics of Whipple shields. Such improvements are aimed at increasing the impacting particle‘s kinetic energy loss and increasing the spread of the resulting debris cloud. This work employs a numerical modelling approach in AUTODYN-2D software – the program’s hydrocode functions allow for accurate simulation of material mechanical behaviour under large deformations. In the models, material bodies are assigned with smoothed-particle hydrodynamics computational method, to represent the shield’s and the impacting particle’s material medium with point-particles, and a Lagrangian mesh element method for the back-plate. Impacting particles are assigned with aliuminium alloy Al 6061-T6, shields are assigned with aliuminium alloy Al 7075-T6 and titanium Ti-6Al-4V. To determine the appropriateness of applied materials and numerical methods, an impact verification model is created, which imitates an experimental hyper-velocity impact test. The verification model’s results – the debris cloud, impacting particle deformation and Whipple shield damage – display high correlation to their experimental counterparts. This establishes the relevancy of this work’s results. To determine the effectiveness characteristics of a single-plate Whipple shield, basic effectiveness tests are performed. Effectiveness characteristics are defined as the damage sustained by the backplate after the resulting debris cloud impact. Three tests are chosen to be used with improved shields – the tests’ condition allow for an objective measurement of effectiveness increase: 3 mm diameter particle impact at 3.5 km/s, 6 mm at 7.0 km/s and 9 mm at 9.0 km/s. Two-plate, improved thickness, structure, material and spacing shields are investigated – such improvements increased the basic shield’s effectiveness in all tests. To establish, how structural parameters of mentioned improvements influence their effectiveness characteristics, additional two-plate, improved structure, and material tests are performed. The tests reveal that the largest effectiveness increase is achieved by utilizing a two-shield structure – the second plate decreases the damage of the back-plate in all tests. The structural characteristic of this shield – distance between the front and the second plate – heavily influences such shield’s effectiveness. Improved structure and improved spacing shields were determined to have the second and third highest effectiveness increase, respectively. It was noted, that in all tests, shield plates experienced large damage, which negatively affected their further use. To create the highest effectiveness shield, all five analysed improvements were combined into a single structure. Such shield is comprised of an improved material front-plate, and three-section, improved thickness, spacing and structure, second plate. To decrease the large damage tendency of the second plate, the mentioned improvements are applied in an optimal way, to compensate one improvement‘s disadvantages with other’s advantages. The combined improvements shield displayed exceptional effectiveness - in all tests, the second plate stopped the debris cloud from impacting the back-plate. The second plate experienced non-critical damage in low- and medium-speed test but received critical damage in the high-speed one. An additional test was made, which revealed how this shield’s structural parameters influence debris cloud formation – this warrants further optimization and analysis of the combined improvements shield. |
