Role of Interfaces and Interphases in the Evolution Mechanics of Material Systems

The general objective of this investigation was to apply the discipline of mechanics to the prediction and description of the long-term behavior of composite materials by developing experimental information, conceptual understanding, and analytical representations of the evolution of the properties of constituent materials and interfaces in composite material systems as a function of time during the application of time-variable mechanical, thermal, and chemical loadings. The general approach to this objective was to develop mechanistic representations of the state of the material under those conditions, and to join those descriptions with micromechanical descriptions of the state of stress in critical elements to support an estimate of remaining strength, and thereby, to predict remaining life. The current program focused on the Role of Interfaces and Interphases in the Evolution Mechanics of material Systems. The objective of the program was to achieve accurate and realistic representations of the geometry, arrangement, properties, and property distributions as a function of space associated with the region between fibers and matrix material in continuous and short fiber reinforced composite materials, to develop engineering methods of characterizing the interphasal strength, and to use a critical element method to extend these findings to the prediction of the changes in stiffness and strength.