A new model for multilayer ceramic composites

An attempt was made in the present work, to develop a model for design of multilayer ceramic composites (MLC) with high failure energy. The model considered the failure process of a notched MLC beam comprised of N number of matrix layers of thickness t(m) each, separated by (N-1) very thin interfacial layer of thickness t(i) (<< t(m)) and loaded in a three-point bend configuration. The model was developed on the basis of changes in compliance and stored elastic energy of the MLC beam as a function of crack growth process. Finally, the amount of energy consumed per unit volume, E-con MLC, during controlled propagation of interfacial cracks in the MLC beam was evaluated by the proposed model. The main advantage of the controlled interfacial crack growth process was that the amount of energy consumed per unit volume by the MLC could also enhance substantially with the number of failed matrix layers. The predictions of the model were made for a strong matrix/weak interface design of MLC system. The optimally designed MLC beam was comprised of 20 numbers of 150 mu m alumina matrix layers separated by 19 numbers of very thin (7 mu m) lanthanum phosphate interfaces. For the purpose of verification, it was put under a three-point bend configuration with a loading span of 38mm. The predictions compared favorably with experimental data from literature as well as our own work. Further, it was found out that in the present alumina/lanthanum phosphate/alumina MLC system, the predicted failure energy (57.9KJm(-3)), improved by a factor of 8.68times over that (6.67KJm(-3)) of the matrix alumina layer phase. This enhancement in failure energy suggested the achievement of significant toughening in the proposed new design of the chosen MLC system. Finally, the influence of key design parameters like the total number of layers, layer thickness, etc., and of inherent material properties like failure stress of matrix, strain energy release rate of interface, etc. on the mechanical behavior of the proposed alumina/lanthanum phosphate/alumina MLC design were also discussed.