Glossary

What are transonic airfoils, and what is the active clearance control? Check out our technical dictionary and find out more about engine technology terms – from active clearance control to velocity triangle.

Scanning electron microscopy Shaped holes Shot peening Silencer Silver-plating Single-crystal turbine blades Skeleton line Slurry coatings Soft annealing Solid-film lubricants Specific work of a stage Stage Steel shot peening STEM drilling

Straight cascade Stress-relieving Sulphuric acid DC anodizing Supersonic aircraft

Shot peening

High-pressure and low-pressure turbine blades must exactly fit into the corresponding slots in the turbine disks. The interface between blade and disk is the serrated blade root, also called fir-tree root or dovetail root depending on the profile form selected. The high rotational speeds during engine operation cause high centrifugal forces which act on the blade roots and may be up to 17 tons in extreme cases. The blade roots are therefore shot peened to improve their mechanical strength.

In the process small steel balls are directed onto the root surfaces at a high pressure. Thus, so-called residual compressive stresses are produced in the near-surface zone which increase the tensile strength of the blade root and reduce its susceptibility to cracking.