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,...

Deformation of dry and wet sandstone targets during hypervelocity impact experiments, as revealed from the MEMIN Program

“…5.2), the zones of shock deformation (e.g., zone of localized deformation) are not spherical. The elongation of the isobars along the impact axis is in good agreement with observations in highly porous targets (Colombo et al. 2003; Onose et al.…”

Light and Strong SiC Networks

“…However, the bulk of the structure remains stable and is still able to sustain the applied load. This type of behavior has been observed in other porous ceramics and microlattices …”

Mechanical properties of highly porous alumina foams

“…It is important to note that all these samples were intact and maintained their mechanical integrity after passing the apparent yield strength. Such a behavior has already been reported by Colombo et al 25 who compared the mechanical properties of macrocellular and microcellular silicon oxycarbide (SiOC) (with pore sizes below 30 lm). They found that microcellular SiOC exhibits no macroscopic crack propagation after reaching the yield stress and crushes only gradually, as compared with its macrocellular counterpart, which suddenly develops macroscopic cracks.…”