Introduction to creep Reprint PDF

INTRODUCTION

There are many practical examples where materials are required to survive for long periods under load at high temperatures. For instance, consider the turbine blades of jet engines. The principles of operation of aeroengine gas turbines are illustrated in Figure 1. Air enters into the compressor stage and the compressed air is forced into the combustion chamber where it is mixed with kerosene (paraffin) and burnt. This creates a very large volume of hot combustion gases. The hot gases then exit from the rear of the engine to provide the thrust, just as air escaping from a punctured balloon drives the balloon in the opposite direction. However, before leaving the engine, the hot gases pass through a turbine stage which acts like a high temperature windmill. Since the turbine is connected by a shaft to the compressor, rotation of the turbine drives the compressor to supply a continuous flow of air for combustion. The blades of the turbine must therefore operate under the stresses generated by the high rotational speeds of the engine in the hot gas stream from the combustion chamber. With modem jet engines, the materials from which the turbine blades are made must then be capable of serving under stress at temperatures of up to about 1300K, at least for several thousand hours between overhauls.

Edited by: R.W. Evans, B. Wilshire