Papers by Author: Hugues Guerault

Abstract: Roughness influence on the residual stress gradient evaluation in the case of a grazing incidence X-ray diffraction setup is considered. In this geometry the surface roughness changes essentially the X-ray wave fields of the transmitted and diffracted beams inside the coatings and subsurface regions of bulk samples, and thus influences the refractive properties of the investigated sample area. In turn, the change in the refraction index enforces the re-scale of the informational depth and, consequently, the evaluated stress depth profile. The diffracted amplitude from the crystalline grain located beneath the surface is calculated. The surface roughness is shown to contribute into reconstruction of the real stress gradient profile of the coating.

Abstract: Alumina-zirconia multilayered ceramics have been proposed as an alternative for the design of structural ceramics with improved fracture toughness and strength reliability. During the processing of these laminates, significant residual stresses may arise due to the thermal expansion mismatch between adjacent layers. The correct evaluation of such stress distribution in the laminate may determine its range of application. In this work, the residual stress state in a layered material designed with five thick alumina layers of approximately 650 microns alternated with four thin alumina-zirconia layers of approximately 140 microns was estimated using different methods. A finite element analysis (FEM) was performed for stress evaluation in the bulk and an indentation method and X-Ray diffraction to account for stresses at the surface. Experimental findings show a constant stress distribution within the bulk for each layer, while at the surface stress position dependence is observed in the alumina layers, being the maximum tensile stresses near the layer interface. The accuracy of the results provided by each technique is discussed.