A New Theoretical Model for Development of Damage Tolerant Composites

Abstract

A new model for design of multilayer ceramic composite (MLC) with both high failure energy and fracture toughness is developed in the present work. The model considers, for the sake of simplicity, the failure process under three point bend loading for a notched MLC beam comprised of N number of matrix layers separated by (N—1) very thin interfacial layers. The theory is developed on the basis of changes in stored elastic energy as well as compliance of the MLC beam as a function of crack growth process. Finally, the model predicts the interfacial toughness and the amount of energy consumed per unit volume, E_{con MLC}, during controlled propagation of interfacial cracks and through thickness cracks in the MLC beam. The predictions of the model for an optimally designed MLC beam comprised of 20 number of 150 μm thick alumina matrix layers separated by 19 number of very thin (7 μm) lanthanum phosphate interface layers compared favourably with experimental data from literature as well as our own work. Further, it is illustrated that working with our proposed model, the optimally designed MLC beam can achieve significant toughening. The influence of material properties and the fabrication process design parameters on failure energy and fracture toughness is also considered for designing MLC beam.

Keywords:

• Multilayer ceramic composite
• Weak interface
• Modelling
• Alumina
• Lanthanum phosphate