The Development Of A Fiber-Reinforced Titanium Matrix Composite Low Pressure Turbine Shaft For Turboshaft Engines

Higher power density requirements for future turboshaft engines necessitate higher pressures and operating temperatures. This results in higher shaft speeds and the need for smaller shaft diameters to reduce disk bore stresses. Higher rotational speed and smaller shaft diameters lower the critical speed of the shafts relative to the operating speed of the engine, resulting in supercritical operation. Preliminary results of a cooperative program to design, develop and fabricate a titanium matrix composite (TMC) low pressure turbine (LPT) shaft for application in a turboshaft engine, and to demonstrate improved frequency characteristics of this shaft relative to a conventional all-metallic shaft, were presented in a previous paper. This paper will focus on the design, test results and metallographic analysis of the TMC barrels and shafts manufactured during the program. Four TMC barrels and two LPT shafts were manufactured and subjected to an array of thermal-mechanical tests. The results of the testing indicated that a defect free TMC barrel has significantly higher mechanical properties than required for the selected engine application requirements. Modal tests of the fabricated shaft verified analytical predictions of the critical speed benefits.