Overview of research on functionally graded materials for reusable launch vehicle applications

Functionally Graded Materials (FGMs) are considered to have important applications for future reusable space transportation vehicles, which cyclically encounter extremely high heat loads in their engines and airframes. Under the actual heat loading conditions affecting such FGMs, it is necessary to evaluate the thermal fatigue properties of FGMs induced by macroscopic and microscopic thermal stress due to high temperature differences. The thermal fatigue characteristics of the FGMs with a diameter of 30 mm by exposing them under the large-temperature-difference conditions have been studied in vacuum and hot gas environments. Several studies on FGMs are under way for practical applications. Thrusters made of Ni-ZiO2 FGM and C/C composite covered with SiC-C FGM layer have been studied. The durability was-confirmed from the tests.