Prestressing of components

#The invention relates to a method of prestressing a component or material and particularly to a method of prestressing an aerofoil, such as an aerofoil section of a gas turbine engine compressor or turbine blade or vane. The invention further relates to a prestressed component and particularly to a prestressed aerofoil, such as an aerofoil section of a gas turbine engine compressor or turbine blade or vane.

#Gas turbine engine components are susceptible to damage caused by foreign object ingestion and general fatigue. Such damage may result in stress concentrations and cracks which limit the components' lives. This is a particular problem in aerofoil leading and trailing edges in both compressor and turbine blades and vanes. One known solution is to increase the thickness of the aerofoil section in the leading and trailing edges. However, this adds weight and adversely affects the aerodynamic performance of the blade, reducing the efficiency of the engine.

#It has also previously been proposed to introduce regions of residual compressive stress into aerofoils, ideally resulting in the entire cross-section of the leading and trailing edges being under compression. By creating such “through thickness compression” whereby the residual stresses in the edges of the aerofoil are purely compressive, the tendency for cracks to grow is severely reduced. The stress field is equalised out in the less critical remainder of the blade.

#An embodiment of the invention will now be described with reference to the accompanying drawings in which:

#FIG. 1 is a diagrammatic sectional view of a ducted fan gas turbine engine;

#FIG. 2 is a diagrammatic sectional view indicating a first embodiment of the invention;

#With reference to FIG. 1, a ducted fan gas turbine engine generally indicated at 10 comprises, in axial flow series, an air intake 12, a propulsive fan 14, an intermediate pressure compressor 16, a high pressure compressor 18, combustion equipment 20, a high pressure turbine 22, an intermediate pressure turbine 24, a low pressure turbine 26 and an exhaust nozzle 28.

#The gas turbine engine 10 works in the conventional manner so that air entering the intake 12 is accelerated by the fan 14 to produce two air flows, a first air flow into the intermediate pressure compressor 16 and a second air flow which provides propulsive thrust. The intermediate pressure compressor 16 compresses the air flow directed into it before delivering the air to the high pressure compressor 18 where further compression takes place.

#The compressed air exhausted from the high pressure compressor 18 is directed into the combustion equipment 20 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through and thereby drive the high, intermediate and low pressure turbines 22, 24 and 26 before being exhausted through the nozzle 28 to provide additional propulsive thrust. The high, intermediate and low pressure turbines 22, 24 and 26 respectively drive the high and intermediate pressure compressors 16 and 18 ad the fan 14 by suitable interconnecting shafts.