LXXIII. Thermal stresses in turbine blades

Abstract

Summary A theory of thermal stress in turbine blades is developed, on the assumption that at each point of the blade planform the stresses are approximately those that would be set up in a free infinite slab of uniform thickness equal to the thickness of the blade at that point. To justify this assumption it is shown that the thermal stresses in a wedge, assuming plane strain and infinite heat transfer coefficient, differ from those based on the approximate theory by terms which tend to zero uniformly with the wedge angle. More general arguments are also given in § 6. Consequences of the theory are that in cooling the maximum stress occurs at all times near the position of maximum thickness, but that in heating the largest stresses are initially near an edge, though as time goes on their position moves alongthe blade towards the position of maximum thickness, and their magnitude increases. Maximum stress is inversely proportional to thermal conductivity for the lower heat transfer rates, but is less sensitive to it at higher rates. Application to a specific material and comparison with experiment are given in § 7.