Low-Cycle Thermal Fatigue

120 стр.
NASA Technical Memorandum 87225
Lewis Research Center, Cleveland? Ohio, 1986
Low-cycle thermal fatigue (LCTF) 1s one of the dominant failure modes 1n high temperature structural components. In fact, the problem 1s Intensifying 1n aeronautical gas turbine blades and vanes as greater emphasis 1s placed on Internal cooling of hollow airfoils to permit higher gas temperatures. The resultant thermal gradients at thin leading and trailing edges become greater, and the propensity for thermal fatigue cracking Increases. As greater performance Is demanded of gas turbines, operating temperatures Increase, rotational speeds Increase, thermal transients Intensify, and durability suffers. As a case 1n point, the United States Space Shuttle Main Engine utilizes turbo- machinery that extracts over seven hundred horsepower per turbine blade. Yet, the blade airfoil 1s only about the size of a thumb. Their durability Is measured 1n Just thousands of seconds of operation during which time low-cycle thermal fatigue cracks Initiate and grow to readily detectable proportions.