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Thermo-Mechanical Behavior of Spatially Tailored Functionally Graded Materials in a High Temperature Environment



Airframes operating in hypersonic regime are subjected to complex structural and thermal loads. Structural loads are a result of aggressive high-g maneuvers, rapid vehicle acceleration, and dynamic pressure. Thermal loads are a result of aerodynamic heating. Thus, hypersonic airframes are typically designed with external insulation, active cooling or a thermal protection system (TPS) is added to the structure. TPS may consist of adhesively bonded, pinned, and bolted thermal protection layers over exterior panels. These types of attachments create abrupt change in thermal expansion and stiffness that make the structure susceptible to cracking and debonding. Functionally graded materials (FGMs) with metal-rich interior surfaces and ceramicrich exterior surfaces can potentially overcome the issues related to high thermal gradients and stress concentrations as well as selectively provide enhancements in strength and toughness and, thus, are a particularly appealing solution for thermal protection of structures operating at extreme temperatures. In this paper thermo-mechanical response of metal-ceramic Ti-6Al-4V/TiB2 functionally graded composite structural panels is studied and compared against a Titanium structural panel with Exelis AcusilĀ® syntactic foam TPS. Effective thermal and mechanical properties of Ti-6Al-4V/Ti-B2 composite are obtained using micromechanical models and finite element analysis (FEA) of representative volume elements. The results of the micromechanical modeling are incorporated into the structural analysis of the Ti-6Al-4V/TiB2 FGM panels subjected to extreme thermomechanical loading. Realistic structural and thermal loads and time history, obtained by hypersonic flight trajectory simulation, are used in the analysis. The obtained computational results indicate reduction in deflection and weight with an increase in stiffness when Ti-6Al-4V with TPS is replaced with Ti-6Al-4V/TiB2 metal-ceramic functionally graded composite.

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