3.2 X-ray Bragg Peak Profile Analysis 
The X-ray Bragg Peak Profile Analysis (XPA) utilizes the intensity-profiles from the Bragg 
reflections to represent various defects in the crystalline structure. The broadening of the reflections 
permits the assumption type and density of existing lattice defects (primarily lattice displacements), 
while shifted reflections, i.e. asymmetrical reflection broadening, are caused by residual stresses of 
the second and third order [4]. Contradictory to elastic stresses of the first order, and related to 
macroscopic specimen areas that can be analyzed using conventional X-ray stress analysis, stresses 
of the second order only cover a single grain of a polycrystal. Stresses of the third order are found in 
the sub-micrometer range [5], and are associated with the inhomogeneous displacement 
distributions within a single grain. High-performance X-ray generators and Synchrotron radiation 
permit the improvement of the lateral resolution from 500um to 10pm [6]. For this research project, 
the XPA technique was primarily used to determine stresses of the second order. 
3.3 Barkhausen Noise Eddy Current Microscope (BEMI) 
The Barkhausen Noise Eddy Current Microscope [7, 8, 9] allows measurement of the magnetic 
Barkhausen Noise or attainment of eddy current data with a lateral resolution of 10um or smaller, 
depending on the material to be tested and the selected sensor. A very powerful manipulation The rest 
system provides high precision miniature-sensor placement (within 11m) to the examination display® 
surface. Data acquisition time for a single data point is about 1.0 second for the Barkhausen Noise 
technique and approximately 0.3 seconds for eddy current, including sensor positioning. In the 
Barkhausen Noise mode, the sample is magnetized by an electromagnet and the tangential field 
strength is recorded by the Hall sensor mounted under the sample. 
4. Measurement Results 
The Barkhausen Noise Eddy Current Microscope demonstrated the ability to detect residual micro- 
stresses in the individual grains of a polycrystalline nickel specimen. To calibrate the system, 
defined residual stresses (in the elastic range) were applied to the samples using a tensile testing 
machine. Stresses of the second order were determined for grains with varying orientation using a 
radiographic residual stress measurement method. For system calibration, all electromagnetic 
quantities of the grains were recorded and correlated to the quantities determined radiographically 
and evaluated using a multiparameter regression analysis. The electromagnetic values are displayed 
in Figure 1 as a function of tensile stresses. Variations of the slope of the straight lines are caused 
by varying elasticity modules of the grains. In addition, the Barkhausen Noise measurements 
detected specimen areas with different initial residual stress states. The values of these initial 
residual stress states varied linearly with the applied load ol, just as would be physically expected. 
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