Thermal Shock Tests on Gas Turbine Materials: A Study of the Effects of Severe Temperature Fluctuations on Rotor Blades and Nozzle Segments

UNDER steady load conditions, materials in gas turbines are subject to various forms of static and alternating stresses. Changes in the operating conditions such as starting, load variations and shut down cause additional thermal stresses which limit the permissible rate of these changes in service. In stationary plants these effects can be minimized by adjustment of the starting and shut down procedure or by protection of the sensitive parts with a cooling flow. In gas turbines for propulsion purposes load changes are governed by external conditions, are more frequent and take place at a higher rate. The consequent thermal stresses are then referred to as thermal shocks. Various methods for testing the resistance of materials to thermal shocks have already been suggested and applied. However, they differ very widely, and no quantitative, or even comparable figures are available as yet.