Micromechanical modeling of unidirectional fibrous composite plies and laminates

Several micromechanics-based procedures are developed and implemented within the framework of laminated plate analysis to extend the prediction of laminate response beyond its elastic limit. Both the classical first order shear deformable laminated plate theory and the refined laminated plate theory by Mau are introduced to tackle various micromechanical problems which arise in the design of composite materials. Of particular interest are problems of interfacial decohesion, such as debonding and sliding at fiber-matrix and/or coating-matrix interfaces.; The classical laminated plate theory is used to analyze the behavior of symmetric and balanced laminates under uniform overall thermomechanical loading. A variant of the Mori-Tanaka method is then called upon to provide estimates of the local stresses within the plies. The quantities of interest are both the average matrix and fiber stresses, and their distribution at or in the vicinity of the fiber-matrix or coating-matrix interfaces. In the present study, the information about extreme values of the stress components are presented in the form of initial failure maps. Such maps not only identify the allowable overall stress states that maintain the integrity of the microstructure, but also provide valuable information about various failure modes.; The initial failure maps indicate that in most ceramic and metal matrix composite laminates the onset of damage is caused by interfacial decohesion. A simple interface constitutive model is developed to reflect such damage mechanisms. Detailed prediction of decohesion processes is then obtained numerically using the finite element method (FEM). The approach used herein employs the periodic hexagonal array (PHA) model (Teply and Dvorak (1988)). Within the context of the FEM, the interface constitutive model is incorporated into representative unit cell via appropriate interface element and the local fields are obtained with the ABAQUS program. Essential features of the unit cell response are then utilized in the transformation field analysis method (Dvorak (1992)) to extend modeling of interfacial decohesion into large laminated structures.; Under certain loading conditions such as bending or torsion the classical laminated plate theory become inadequate in predicting an accurate overall response of both symmetric and antisymmetric laminates, particularly at low span-to-depth ratios. To obtain more accurate prediction of laminate response under such conditions the refined laminated plate theory by Mau is used instead. To utilize the full potential of this method a "multi-layered" finite plate element is developed and implemented. This opens a way to modeling of arbitrary composite laminates with complex geometries and variety of loading conditions.