The long term goal of my research is to develop effective and reliable computational technologies for the simulation of the failure behavior of quasi-brittle materials subjected to extreme environmental and loading conditions. The formulation of novel constitutive models with real predictive capability and the numerical implementation of effective computational techniques will enable new generations of engineers to design safer, more reliable, more durable, energy efficient, and environmentally friendly civil infrastructures.
Reliable computer simulations of material and structural failure require an accurate description of various phenomena spanning several length and time scales. These phenomena include nano/micro/meso-scale crack initiation, propagation along complex three-dimensional paths, effect of material heterogeneity, interaction and coalescence of distributed multi-cracks into localized cracks, temperature and humidity effects, loading rate effects, effect of confining pressure, interaction between damaged and undamaged material, etc.
The classical continuous (tensor based) representation of solids, although it has been used traditionally to address some of these aspects, is inherently incapable of modeling the loss of continuity associated with fracture. In recent years various computational technologies have been formulated to effectively handle displacement discontinuities but these techniques tend to be computationally intensive in the case of extensive three-dimensional fracturing as it occurs, for example, during fragmentation. For this reason my research has focused on the adoption of a discrete approach in which solids are discretized “a priori” and the governing equations (equilibrium, compatibility, and constitutive behavior) are formulated directly in this discrete setting. Solids are represented by systems of discrete entities (discrete particles, lattice struts, etc.) whose size distribution and geometrical configuration are always linked to the topology of the main heterogeneities characterizing the internal structure of the material at the nano-, micro- and/or meso-scale.
Based on this idea my research group recently succeeded in the formulation of a comprehensive concrete model called Lattice Discrete Particle Model (LDPM). LDPM has shown superior qualitatively and quantitatively modeling capabilities in a wide variety of loading conditions in both quasi-static and dynamic regime. In particular, LDPM has been successfully applied to the simulation of the performance of concrete and reinforced concrete structures under high impulsive loadings, such as blast and penetration. The outcomes of this research effort have been presented at various conferences and workshops and will be documented in a series of journal papers currently in preparation.
Currently, my research activity focuses on the extension and refinement of this work in many different directions as described below.
Multiscale Modeling. Even with the computational power currently available, the adoption of nano/micro/meso-scale (discrete) approaches become computationally intractable in the case of fine grained materials, such as nano-composites, ceramics, rocks, metallic powders, etc., or in the case of large structures, such as tall buildings, dams, bridges, etc. For this reason there is clearly a need for effective multiscale techniques suitable for upscaling discrete systems. My research group is currently exploring, evaluating the effectiveness, and further extending a variety of multiscale techniques recently developed to bridge atomistic and continuum scales.
Composite Materials. Development of energy efficient and environmentally friendly technologies is certainly the forefront of Engineering of the twenty-first Century. Design of high-strength, light-weight, and corrosion-resistant materials is the key, for example, for the design of energy-saving transportation systems (cars, aircrafts, ships, etc.). During my post-doc appointment I worked on the formulation of a general triaxial constitutive law for the simulation of anisotropic elasticity, damage, and failure of quasi-brittle composites, such as carbon-epoxy and glass-epoxy composites. The model (called the Spectral Stiffness Microplane Model) was formulated in the context of the microplane theory and exploited the spectral decomposition of the stiffness matrix to identify orthogonal strain modes at the microplane level. Future extensions of that work will take into account the visco-elastic, rate- and temperature-dependent character of these materials in order to be able to simulate the behavior of mechanical components under high impulsive loading conditions.
Structural Durability. In addition to the research directions discussed above, I am also interested in working on structural durability which is a critical issue due to the aging of our National infrastructures. I have recently completed an international research project (in collaboration with an Italian University) aimed at the formulation of a comprehensive computational theory for concrete creep and shrinkage suitable for the analysis of concrete behavior at the early ages and beyond. The outcomes of this project is relevant, for example, to the assessment of durability and serviceability of reinforced (high-strength) concrete bridge decks, which, typically experience extensive cracking at the early ages. This cracking produces a direct path for corrosive agents to reach the reinforcing steel, which will then corrode reducing the load carrying capacity of the whole structures.
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