Shock-induced chemical reactions of multimaterial powder mixtures: An Eulerian finite element computational analysis.

摘要

A new computational chemistry method is developed for modeling shock induced chemical reactions (SICR) in multi-material solid powder mixtures. The chemistry evolution algorithm is incorporated into an existing Eulerian finite element hydrocode. Taking advantage of the operator split approach, the chemistry is uncoupled from the Lagrangian deformation step. The chemical reactions are assumed to occur independently in each element, and the kinetic rate is based on the local material content and thermodynamic state. The state properties of the materials are homogenized on a local element level, but globally, the mixtures remain heterogeneous.;Eulerian methods have the advantage of allowing multi-material elements. However, the element-by-element analysis permits the recognition of materials within only one element at a time. This gives rise to an intrinsic problem which limits the reaction to one layer of multi-material elements. Once this mixed-material layer has reacted creating the product, it acts as a barrier preventing the distinct reactants from interacting, and consequently quenches further reaction. This product-barrier problem is one of the major difficulties which is addressed in this research. An exploratory method for overcoming this difficulty has shown to be promising. This approach provides distinct descriptions of the particle interfaces and their evolution as the materials within each particle undergo plastic flow, phase transformation, and chemical evolution. The descriptions of microscopic heterogeneity reveal the detailed interactions and behaviors of the multi-material solid powder particles during SICR processes. This approach can be used to study the shock synthesis of many composite powder systems such as silicides, aluminides, carbides, nitrides, etc. Analysis of the dynamic behavior of the Nb-Si system is focused on the average reaction threshold response, the effects of morphology (particle size and porosity) and kinetic parameters on the initiation and extent of reaction.