Two-dimensional atomistic finite element approach and its applications

A two-dimensional atomistic finite element approach is developed, based upon an atomic force field, to simulate materials in molecular scale. Atomistic chemical element and van der Waal element are created. The chemical element is derived from intramolecular interactions. The van der Waal element is derived from intermolecular interactions. The materials are discretized into chemical and van der Waal elements. Using this atomistic finite element approach, the link between macro- or micro properties and nano-scale structures of materials can be established.; General methods, an off-lattice random walk method and a force relaxation method, are developed to generate and relax polymer networks respectively.; A hydrocarbon polymer is used as an application of the atomistic finite element approach. True stress-true strain curve is obtained. Nano-scale void generation, void coalescence and crack formation are observed. Direct visualization of the deformation process enables an understanding of the failure mechanism.; As an application, the electrostrictive graft elastomer consists of flexible backbone chains, each with side chains, called grafts. The backbone chains and the grafts are composed of polarized monomers. When the elastomer is placed into an electric field, strain is induced.; A unit cell computational model is used to investigate the deformation of electrostrictive graft elastomer under action of an electric field. The deformation of the elastomer is explicated by two mechanisms: local linear elastic deformation and deformation induced by crystallized graft unit rotation.; A higher electric filed strength is used in the unit cell model. Two modifications are made to solve the problem: (1) 2-D bending combining 3-D bending and dihedral torsion, and (2) self-consistent scheme. The modified model is employed to investigate the electromechanical properties of the elastomer. The relationship between the strain and the electric field strength is calculated under an electric field of strength 150 Mv/m, with a free volume fraction of 4.5 percent. The effect of molecular scale factors, such as free volume fraction, graft weight percentage and graft orientation, on the deformational strain of the elastomer is simulated. The results can hopefully be used to direct the molecular design for the elastomer in molecular scale.*; *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirements: Microsoft Office.