Effect of Hypervelocity Impact on Microcellular Ceramic Foams from a Preceramic Polymer

Abstract

Orbiting spacecrafts and satellites are exposed to hypervelocity impacts against orbiting objects of various nature (natural, such as meteorites, or deriving from human artifacts, such as molten sodium and potassium metal alloys, aluminum and alumina particles or plastics), traveling at speed of up to 15 km s ±1 . [1] Hence, special protecting measures have to be implemented to reduce the risk of damages to satellites and spacecraft components. Suitable shields have to perform several functions, from the fragmentation of the projectiles to the stopping of the resulting debris cloud, while at the same time playing a role in the structural support as well as in the thermal management of the entire structure. [2] The use of lightweight cellular materials represents a novel way to increase the ballistic efficiency of meteoroid and orbital debris (M/OD) shields. In fact, the large number of cell walls that a projectile impacting a cellular material will find along its path provides a good way of inducing a high number of consecutive shocks on the impactor, thus effectively absorbing its energy and reducing the penetration depth of the debris inside the structure. Ceramic foams represent a good candidate for meteoroid and debris protection shields (MDPS) since they offer a unique combination of properties such as low density, high stiffness, high relative strength, high melting point, and very good shock absorption capability. Moreover, these properties can be tailored to specific space applications through a careful design of the material's microstructure and morphology.In analogy to microcellular plastics, [3] a microcellular ceramic foam is defined as a material in which the cell size is below about 30 lm, and the cell density is greater than 10 9 cells cm ±3 . Silicon oxycarbide (SiOC) microcellular foams possess a compressive strength higher than that of macrocellular foams of similar density, [4] and thus are well suited candidates for impact resistance applications.Several efforts have been recently made to enhance the effectiveness of sandwich panels in case of hypervelocity impacts, but they seem to be still vulnerable with respect to high energy impacts. [5] The recent interest of the European Space Agency (ESA) towards cellular materials for multifunctional space applications will certainly encourage further research activities in this field. Microcellular foams were produced using a silicone resin (SR) preceramic polymer (Oxycarbide A, Starfire Systems, Watervliet, NY) and poly(methyl methacrylate) (PMMA) microbeads, with an average dimension of 9.45 ± 1.82 lm, as a sacrificial pore-forming agent (A 910W, Cray Valley Waterborne Polymers Department, Atofina Italia, Milan, Italy). They were dry mixed in a ball mill in a weight ratio PMMA/ SR = 80/20. Samples with dimension of 80 65 20 mm were uniaxially pressed at room temperature, applying a pressure of 100 MPa. The PMMA microbeads were eliminated by slowly heating the samples in air up to 250±350 C and holding them at temperature for one hour. Subsequently,...

Protecting Earth-orbiting spacecraft against micro-meteoroid/orbital debris impact damage using composite structural systems and materials: An overview

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The Exploitation of Superplasticity in the Successful Foaming of Ceramics after Sintering

“…This is because sintering after foaming reduces the porosity, and inevitably, the sintering process results in the exclusion of some pores. The mechanical properties of ceramics dominated by open pores have been improved, [10][11][12] but they are still inadequate, owing to weak inter-grain bonding in addition to the smaller bulk area.…”

Si–O–C nanotubes from pyrolyzing polycarbosilane in a mesoporous template

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