NEAR-SURFACE RESIDUAL STRESS-PROFILING WITH HIGHFREQUENCY EDDY CURRENT CONDUCTIVITY MEASUREMENT

摘要

The lifetime of aero engine components can be extended by applying an additionalstrain to the material. Typical aero engine-alloys like Nickel-Base superalloys or Titanium alloys canbe surface-treated by use of shot peening to induce the compressive strain near the surface.However, in order to use the additional life for critical aero engine components, a quantitativedetermination of strain gradients near the surface has to be carried out periodically. We propose tomeasure the depth-profile of residual stresses non-destructively by use of high frequency eddycurrent techniques. This paper presents results obtained with an experimental set-up based on a highprecision impedance analyzer. Test samples prepared from IN718 by shot peening of differentintensities can be easily distinguished. By sweeping the frequency from 100 kHz up to 100 MHz adepth profile for the electrical conductivity from 50 pm to 500 gm can be obtained. The measuredconductivity profile is a resultant from residual stresses, cold work, surface roughness and thetexture of the material. In addition, first results for strain profiling obtained with industry applicableNDE instrument will be presented.