Thermal Analysis of Composite Integral Armor

The notion of utilizing composite material designs to fabricate the exterior skin of armored vehicles has been implemented since the 1980s by countries such as England, Israel, Germany, and France. The many advantages afforded by using composite armor greatly assist the U.S. Army's transformation to a lighter and more deployable force. In order to field the innovative concept of composite armor, extensive testing of ballistics, survivability, and structural integrity must be performed. Nested within structural integrity analysis, the thermal properties of composite armor must be investigated to ensure the equipment is capable of operation in extreme climates. In this paper, a thermal analysis of proposed composite specimens for vehicle protection was conducted to compare the thermal strains in several composite material recipes. Titanium, aluminum, and an S2-glass blend were each used for the armor backplate. These backplate materials were bonded to an exterior ceramic tile of silicon carbide to form the composite armor. In order to reduce the thermal stresses of the composite material, an intermediate rubber layer was bonded between the backplate and ceramic tile. The purpose of the rubber layer was to reduce the thermal strain mismatch near the interface due to the dissimilar coefficients of thermal expansion. The rubber layer would theoretically provide a more compliant layer between the top and bottom plates. Experiments were conducted on several configurations of composite armor specimens exposing them to temperature ranges from -51.1 °C (-60 °F) to 82.2 °C (180 °F). Strain gages were attached to the composite materials to determine thermal deformations and strains. In addition, finite element analysis was conducted using ANSYS 8.1 which modeled the laminar composite material. Furthermore, a theoretical model using Composite Materials Analysis of Plates (CMAP) was used to determine strains using classical laminar plate theory. Strains calculated from the finite element model and CMAP were compared to the strains from the experiment. The results served to verify the current thermal properties of the composite armor recipes, helping to integrate thermal effects into ballistic and other structural testing for FCS armor research.