Application of three-dimensionally reinforced carbon–carbon composites to dovetail joint structures

In development of an air-turbo-ramjet engine with an expander cycle (ATREX) for a space plane, application of carbon–carbon (C/C) composites plays an important role to achieve high performance. Above all, dovetail joints are one of the key structures to realize the turbine system made of C/C composites. In this study, the feasibility of dovetail joints made of three-dimensionally reinforced C/C composites was investigated. Tensile tests were carried out on simplified dovetail joint models. The shoulder angles of the dovetail joint and fiber volume fractions of the C/C composites were taken as parameters to optimize the shape of the dovetail joint. Finite element analyses were also carried out for various cases. Comparison between the experimental and the calculated results suggests that fracturing of the dovetail joint was controlled by the average shear stress, which implies that the shear stress concentration on the shoulder was relaxed during the fracture process. It was also shown that the dovetail joint made of C/C composites is feasible for use in the ATREX engine.