Methods for Controlling Surface Forces to Increase the Reliability of AdvanceCeramics and their Composites Via Colloidal Processing

摘要

During FY 95, we have discovered a number of important phenomena towards ourresearch goal. Tech. Rept. Number 15 shows that elastic modulus and yield stress measurements can be used the particle pair potential, and shows that the a modified version of the classic DLVO theory could be used to explain the short-range repulsive potential produced by salt additions to dispersed, aqueous slurries. Tech. Rept. Number 13 shows that the bodies reformed via the VibraForming Method previous developed under this program (US Patent: US 5,188,780) could be gel by changing the pH in-situ via a urea decomposition. Tech. Rept. Number 12 and 16 show that cracking can be avoided in laminar composites, despite large differential strain that are produce either during processing or cooling, if the layers are less than a critical thickness. Tech. Rept Number 17 shows that laminar composites can be produced were thin layers under biaxial compressive stress cause cracks to bifurcate instead of passing through the layer. This is the first time that residual stresses have been shown to cause crack bifurcation. Laminate were prepared with crack bifurcating layers failed by sequential crack extension; specimens could be unloaded prior to failure.