Published ETD Collection
Permanent URI for this collectionhttps://hdl.handle.net/10657/2
Browse
Browsing Published ETD Collection by Author "Abdolhosseini Qomi, Mohammad Javad"
Now showing 1 - 2 of 2
- Results Per Page
- Sort Options
Item Computational Modeling of Wave Propagation in Heterogeneous Microstructures Using Discrete and Continuum Frameworks(2021-05) Nannapaneni, Raj Gopal; Krakowiak, Konrad J.; Nakshatrala, Kalyana Babu; Belarbi, Abdeldjelil; Joshi, Shailendra P.; Abdolhosseini Qomi, Mohammad JavadWith the recent advances in material science and additive manufacturing, there has been an ever-growing trend in developing materials with novel properties. These materials are often heterogeneous composites---with complex microstructures influencing their overall structural behavior. Though non-destructive evaluation using wave propagation can offer the mechanical properties of the composite, experimental methods to gain insights into the relationship between microstructure and mechanical properties can be cumbersome and time-consuming. Hence, researchers prefer computational modeling of materials to trial-and-error experiments. Among the contemporary numerical methods to study heterogeneous materials, discrete lattice models can seamlessly incorporate complex microstructural heterogeneities into the model. However, the available lattice models suffer from numerous deficiencies such as the limitation of Poisson’s ratio, not being isotropic (naïve square lattice), incorporating additional elements or additional degrees of freedom, and not practical for complex domains (equilateral triangle, hexagon lattices). Hence we aim to develop a lattice model that can span the admissible Poisson’s ratio values with a minimum number of elements and degrees of freedom. We use the Lagrangians in continuum and discrete systems, identify the shortcomings in the lattice model and offer a solution to make the lattice isotropic without the limitation of Poisson’s ratio. This model is verified on the benchmark problems and applied to study wave propagation in the heterogeneous microstructure of hydrated cement paste. Furthermore, studying the influence of microstructure on wave propagation in heterogeneous materials needs exploring different material classes with distinct mechanical properties. Given the number of input parameters to operate with, one needs sensitivity analysis to reduce the dimensionality of the input parameter space. One among the many available techniques is the Shapley value---a solution concept from cooperative game theory to identify the marginal contribution of the individual parameters---was recently being used in machine learning to quantify the weights of a neural network. In this work, this technique is applied to rank the input parameters based on their influence on wave attenuation in materials with matrix-inclusion morphology of circular inclusions.Item Molecular Crosslinking of Calcium-Silicate-Hydrate with Organosilanes: Toward Engineering of Cementitious Matrices with High Thermal Resistance(2021-05) Moshiri, Amir; Krakowiak, Konrad J.; Abdolhosseini Qomi, Mohammad Javad; Ballarini, Roberto; Thomas, Jeffrey J.; Rodrigues, Debora F.; Mo, Yi-LungThis research work is focused on the development of a novel approach aiming at improving the thermal resistance of cementitious matrices. The proposed approach utilizes the molecular scale crosslinking phenomena in which the galleries of inorganic calcium-silicate-hydrate (C-S-H), the main product of cement hydration, are directly bridged with bis-organosilanes molecules. The crosslinking with organic molecules provides C-S-H with attributes imperative for the reduced thermal conductivity e.g. contrast in vibrational densities of states and reduced particle density, which can positively alter the insulation potential of cement-based matrices at a macro-scale. It is postulated, that such a solution can be successfully realized at an engineering scale in the form of a high concentration seed admixture applied to hydrating cement mixtures. The results reported in this document demonstrate the feasibility of the proposed crosslinking approach; the organic-inorganic C-S-H gels of controlled stoichiometry can be successfully realized via sol-gel processing and using bis-alkoxysilanes of various lengths of the alkyl chain. The results of the extensive experimental campaign show that the novel organic-inorganic gels have layered turbostratic molecular structure with certain similarities to C-S-H precipitating in hydrating cement paste. The organic molecules' chain length controls the interlayer distance, which shows little to no shrinkage upon dehydration up to 105 °C. However, the structure of hybrid C-S-H becomes distorted in the basal plane, in which dimer and trimer Si-polyhedra structures condense on a 2D hexagonal Ca-polyhedra layer. Cross-linked C-S-H gels display plate-like morphology with a tendency toward stacking into agglomerates at a larger scale. Hybrid organic-inorganic C-S-H gels exhibit significantly lower intrinsic conductivity than the inorganic one and the magnitude of the observed reduction is related to the molecular size of the bis-organosilanes. The largest reduction was achieved for the organic-inorganic C-S-H incorporating the longest chain organic molecules (nCH2=8). The results of isothermal calorimetry confirmed the positive action of inorganic and hybrid C-S-H seeds on the hydration of Type II cement system. Both types of seed incorporation to the cement system lead to the increased intensity on the onset of the hydration reaction as well as higher heat rates of main hydration peaks. Also, higher total heat of hydration resulted from the incorporation of the C-S-H seeds, thus indicating the enhanced formation of hydration products; hybrid C-S-H seeds displayed superior activity in comparison to the inorganic seed. XRD test results revealed that the addition of both types of seeds did not alter the types of hydration products formed in the hardened paste; especially in the case of hybrid seeded cement system, it was observed that seeds have been efficiently accommodated in the system as a whole and tend to be chemically stable, which also supported by thermal analysis.