Characterization of random composites using moving-window technique

Many critical damage phenomena in composite materials, including cracking, are related to local stresses that are linked to local variations in materi al properties associated with composite microstructure. Relatively little r esearch, however, has been done on the effects of randomness in microstruct ural configuration on the material behavior of composites. For many enginee ring applications, it is assumed that small-scale fluctuations in material properties are averaged when evaluating macroscopic behavior. This assumpti on is generally valid when evaluating quantities such as displacements, ave rage strain, or even average stress, but this approach does not provide any information about local stresses. The analysis of local stresses requires a method of characterizing material properties in terms of material microst ructure. This characterization is made more difficult by the inherent rando mness in composite microstructure. A methodology is presented whereby the m icromechanics model known as the generalized method of cells is used in com bination with a moving-window technique to produce material property fields , for elastic and inelastic material properties, associated with the random microstructure of a composite material. In this work, it is assumed that t he properties of each constituent of the composite are deterministic and th at the fields are the result of randomness in microstructural configuration . Subsequent statistical and probabilistic analysis of these fields will re sult in a probabilistic description of each property. In this work, the mov ing-window methodology is applied to a numerically generated micrograph and the real micrograph of a matrix-infiltrated fiber tow.