C. M. Gill, Manchester University, Manchester, United Kingdom

Summary:

Low plasticity burnishing (LPB) is a recently developed mechanical surface treatment. A spherical rolling element is used to plasticity deform the surface layers of a component, introducing a deep layer of compressive residual stress with minimal cold work. The results are comparable to laser shock peening, but at significantly lower cost. It has been suggested that the reduced cold work enhances the thermal stability of the residual stresses introduced compared to those from conventional shot peening. A potential application for this technique is in compressor blade aerofoils, which experience elevated temperatures and must be able to withstand damage from objects ingested by the engine.

Residual elastic strain and stress distributions arising from LPB have been characterized using laboratory and synchrotron X-ray diffraction. The penetration of high energy synchrotron radiation allows through-thickness measurements, so subsurface balancing tensile strains can be observed directly. Lab. XRD with layer removal has been used to assess the thermal relaxation of the residual stresses at typical service temperatures. The geometry of a treated component may affect the stress field resulting from a mechanical surface treatment. Synchrotron XRD strain measurements have been made in a real compressor blade, treated with LPB along the leading edge. Two dimensional mapping of principal residual elastic strains has been used to visualize the effects of LPB in the blade geometry.