MEASUREMENT OF RESIDUAL-STRESSES IN AL2O3/NI LAMINATED COMPOSITES USING AN X-RAY-DIFFRACTION TECHNIQUE

Using an X-ray diffraction technique, macro-residual stresses were measured in laminated composites consisting of alternating layers of alpha-Al2O3 and nickel. The in-plane thermal mismatch stresses which develop during fabrication were found to be compressive and tensile in the alpha-Al2O3 and nickel layers, respectively. The magnitude of the in-plane stresses was found to be approximate to 110 MPa. Models of laminate structures predict the stress state to be biaxial in the plane of the layers. However, substantial stresses were observed perpendicular to the plane of the laminate; this stress might be due to the hot-pressing procedure used to fabricate the samples. The stress on the side surface of a laminate was measured using the indentation method and the results were consistent with those obtained by the X-ray method. Three samples were heated to 700, 900 and 1000 degrees C, respectively, and then cooled to test the effect of stress relaxation of the residual stresses due to the thermal expansion. The heat treatments (700-1000 degrees C) had no effect on the measured stress states of the laminates.