Matching Items (72)
Description
This study focused on investigating the ability of a polymeric-enhanced high-tenacity fabric composite called CarbonFlex to mitigate damages from multi-natural hazards, which are earthquakes and tornadoes, in wood-framed structures. Typically, wood-framed shear wall is a seismic protection system used in low-rise wood structures. It is well-known that the main energy dissipation of the system is its fasteners (nails) which are not enough to dissipate energy leading to decreasing of structure's integrity. Moreover, wood shear walls could not sustain their stiffness after experiencing moderate wall drift which made them susceptible to strong aftershocks. Therefore, CarbonFlex shear wall system was proposed to be used in the wood-framed structures. Seven full-size CarbonFlex shear walls and a CarbonFlex wrapped structures were tested. The results were compared to those of conventional wood-framed shear walls and a wood structure. The comparisons indicated that CarbonFlex specimens could sustain their strength and fully recover their initial stiffness although they experienced four percent story drift while the stiffness of the conventional structure dramatically degraded. This indicated that CarbonFlex shear wall systems provided a better seismic protection to wood-framed structures. To evaluate capability of CarbonFlex to resist impact damages from wind-borne debris in tornadoes, several debris impact tests of CarbonFlex and a carbon fiber reinforced storm shelter's wall panels were conducted. The results showed that three CarbonFlex wall panels passed the test at the highest debris impact speed and the other two passed the test at the second highest speed while the carbon fiber panel failed both impact speeds.
ContributorsDhiradhamvit, Kittinan (Author) / Attard, Thomas L (Thesis advisor) / Fafitis, Apostolos (Thesis advisor) / Neithalath, Narayanan (Committee member) / Thomas, Benjamin (Committee member) / Arizona State University (Publisher)
Created2013
Description
The increased emphasis on the detrimental effects of the production of construction materials such as ordinary portland cement (OPC) have driven studies of the alkali activation of aluminosilicate materials as binder systems derived from industrial byproducts. They have been extensively studied due to the advantages they offer in terms of enhanced material properties, while increasing sustainability by the reuse of industrial waste and reducing the adverse impacts of OPC production. Ground granulated blast furnace slag is one of the commonly used materials for their content of calcium and silica species. Alkaline activators such as silicates, aluminates etc. are generally used. These materials undergo dissolution, polymerization with the alkali, condensation on particle surfaces and solidification under the influence of alkaline activators. Exhaustive studies exploring the effects of sodium silicate as an activator however there is a significant lack of work on exploring the effect of the cation and the effect of liquid and powder activators. The focus of this thesis is hence segmented into two topics: (i) influence of liquid Na and K silicate activators to explore the effect of silicate and hydroxide addition and (ii) influence of powder Na and K Silicate activators to explore the effect of cation, concentration and silicates. Isothermal calorimetric studies have been performed to evaluate the early hydration process, and to understand the reaction kinetics of the liquid and powder alkali activated systems. The reaction kinetics had an impact on the early age behavior of these binders which can be explained by the compressive strength results. It was noticed that the concentration and silica modulus of the activator had a greater influence than the cation over the compressive strength. Quantification of the hydration products resultant from these systems was performed via thermo gravimetric analysis (TGA). The difference in the reaction products formed with varying cation and silicate addition in these alkali activated systems is brought out. Fourier transform infrared (FTIR) spectroscopy was used to investigate the degree of polymerization achieved in these systems. This is indicative of silica and alumina bonds in the system. Differences in the behavior of the cation are attributable to size of the hydration sphere and polarizing effect of the cation which are summarized at the end of the study.
ContributorsDakhane, Akash (Author) / Neithalath, Narayanan (Thesis advisor) / Subramaniam, Dharmarajan (Committee member) / Mobashar, Barzin (Committee member) / Arizona State University (Publisher)
Created2013
Description
The main objective of this study is to numerically investigate: (i) the ionic transport, especially chloride ion penetration into cementitious materials under imposed electric fields, and (ii) moisture transport through cracked concretes as a function of the crack geometry. Numerical methods were implemented to simulate the ionic transport process, based on coupling the Nernst-Planck equation and Poisson's equation to account for transport dominated by electromigration. This mathematical model was also modified to account for the chloride binding mechanism (physical and chemical trapping of chlorides by the cement hydrates) and the concentration dependence of the diffusion coefficient of each ion in the transport process. To validate the numerical model, experimental data from a companion work was used in this study. The non-steady state migration test, which is one of the common accelerated chloride ion transport test, is numerically simulated. The simulation provides a linear relationship between ionic concentration and ionic flux, which indicates that the diffusion part is negligible under a strong external voltage environment. The numerical models along with adjustments for the concentration-dependent diffusion coefficients, a pore structure factor (from electrical measurements) and chloride binding considerations are found to be successful in predicting the chloride penetration depth into plain and modified concretes under imposed electrical potentials. Moisture transport through cracked concrete was examined in the second part of this thesis. To better understand the crack's influence on the permeability, modified Louis' equation was chosen to relate the permeability with crack characteristics. 3D concrete crack models were developed using a MATLAB program with distinct crack tortuosities, roughnesses and sizes. As a comparison, Navier-Stokes equation and the Lattice Boltzmann method were also applied on the 3D model of the cracked concrete to evaluate their permeability. The methodology developed here is expected to be useful in understanding the influence of cracking on moisture transport, and when properly coupled with an ionic transport model that will be further developed, helps comprehensively understand the coupling effects of moisture and ionic transport on deterioration in concrete structures.
ContributorsYang, Pu (Author) / Neithalath, Narayanan (Thesis advisor) / Dharmarajan, Subramaniam (Committee member) / Mobasher, Barzin (Committee member) / Arizona State University (Publisher)
Created2014
Description
The main objective of this study is to investigate drying properties and plastic shrinkage cracking resistance of fresh cement-based pastes reinforced with fibers and textiles. Naturally occurring mineral wollastonite has been studied independently as well as in combination with AR-glass textile. A series of blended mixes with Portland cement and wollastonite nano-fibers were developed and tested under low vacuum conditions to simulate severe evaporation conditions and expedite the drying process causing plastic shrinkage cracks. Cumulative moisture loss, evaporation rates, and diffusivity were analyzed by means of a 2-stage diffusion simulation approach, developed previously in Arizona State University. Effect of fiber-matrix interaction on the transport properties of the composite were evaluated using the existing approach. Morphology of the cracked surface was investigated by the means of image analysis wherein length, width, area and density of the cracks were computed to help characterize the contribution of fiber and textile in the cracking phenomenon. Additionally, correlation between cumulative moisture loss and crack propagation was attempted. The testing procedures and associated analytical methods were applied to evaluate effectiveness of four wollastonite fiber sizes and also a hybrid reinforcement system with alkali-resistant glass (ARG) textile in improving shrinkage cracking related parameters. Furthermore, the experimental and analytical approach was extended to magnified version of the existing shrinkage testing set-up to study the size effect of these composites when subjected to matching drying conditions. Different restraining mechanisms were used to study the simulation of the cracking phenomena on a larger specimen. Paste and mortar formulations were developed to investigate size effect on shrinkage resistance of cementitious composites.
ContributorsKachala, Robert (Author) / Mobasher, Barzin (Thesis advisor) / Dharmarajan, Subramaniam (Committee member) / Neithalath, Narayanan (Committee member) / Arizona State University (Publisher)
Created2014
Description
Concrete is the most widely used infrastructure material worldwide. Production of portland cement, the main binding component in concrete, has been shown to require significant energy and account for approximately 5-7% of global carbon dioxide production. The expected continued increased use of concrete over the coming decades indicates this is an ideal time to implement sustainable binder technologies. The current work aims to explore enhanced sustainability concretes, primarily in the context of limestone and flow. Aspects such as hydration kinetics, hydration product formation and pore structure add to the understanding of the strength development and potential durability characteristics of these binder systems. Two main strategies for enhancing this sustainability are explored in this work: (i) the use of high volume limestone in combination with other alternative cementitious materials to decrease the portland cement quantity in concrete and (ii) the use of geopolymers as the binder phase in concrete. The first phase of the work investigates the use of fine limestone as cement replacement from the perspective of hydration, strength development, and pore structure. The nature of the potential synergistic benefit of limestone and alumina will be explored. The second phase will focus on the rheological characterization of these materials in the fresh state, as well as a more general investigation of the rheological characterization of suspensions. The results of this work indicate several key ideas. (i) There is a potential synergistic benefit for strength, hydration, and pore structure by using alumina and in portland limestone cements, (ii) the limestone in these systems is shown to react to some extent, and fine limestone is shown to accelerate hydration, (iii) rheological characteristics of cementitious suspensions are complex, and strongly dependent on several key parameters including: the solid loading, interparticle forces, surface area of the particles present, particle size distribution of the particles, and rheological nature of the media in which the particles are suspended, and (iv) stress plateau method is proposed for the determination of rheological properties of concentrated suspensions, as it more accurately predicts apparent yield stress and is shown to correlate well with other viscoelastic properties of the suspensions.
ContributorsVance, Kirk (Author) / Neithalath, Narayanan (Thesis advisor) / Rajan, Subramaniam D. (Committee member) / Mobasher, Barzin (Committee member) / Chawla, Nikhilesh (Committee member) / Marzke, Robert (Committee member) / Arizona State University (Publisher)
Created2014
Description
The main objective of this study is to investigate the behaviour and applications of strain hardening cement composites (SHCC). Application of SHCC for use in slabs of common configurations was studied and design procedures are prepared by employing yield line theory and integrating it with simplified tri-linear model developed in Arizona State University by Dr. Barzin Mobasher and Dr. Chote Soranakom. Intrinsic material property of moment-curvature response for SHCC was used to derive the relationship between applied load and deflection in a two-step process involving the limit state analysis and kinematically admissible displacements. For application of SHCC in structures such as shear walls, tensile and shear properties are necessary for design. Lot of research has already been done to study the tensile properties and therefore shear property study was undertaken to prepare a design guide. Shear response of textile reinforced concrete was investigated based on picture frame shear test method. The effects of orientation, volume of cement paste per layer, planar cross-section and volume fraction of textiles were investigated. Pultrusion was used for the production of textile reinforced concrete. It is an automated set-up with low equipment cost which provides uniform production and smooth final surface of the TRC. A 3-D optical non-contacting deformation measurement technique of digital image correlation (DIC) was used to conduct the image analysis on the shear samples by means of tracking the displacement field through comparison between the reference image and deformed images. DIC successfully obtained full-field strain distribution, displacement and strain versus time responses, demonstrated the bonding mechanism from perspective of strain field, and gave a relation between shear angle and shear strain.
ContributorsAswani, Karan (Author) / Mobasher, Barzin (Thesis advisor) / Dharmarajan, Subramaniam (Committee member) / Neithalath, Narayanan (Committee member) / Arizona State University (Publisher)
Created2014
Description
For decades, microelectronics manufacturing has been concerned with failures related to electromigration phenomena in conductors experiencing high current densities. The influence of interconnect microstructure on device failures related to electromigration in BGA and flip chip solder interconnects has become a significant interest with reduced individual solder interconnect volumes. A survey indicates that x-ray computed micro-tomography (µXCT) is an emerging, novel means for characterizing the microstructures' role in governing electromigration failures. This work details the design and construction of a lab-scale µXCT system to characterize electromigration in the Sn-0.7Cu lead-free solder system by leveraging in situ imaging.
In order to enhance the attenuation contrast observed in multi-phase material systems, a modeling approach has been developed to predict settings for the controllable imaging parameters which yield relatively high detection rates over the range of x-ray energies for which maximum attenuation contrast is expected in the polychromatic x-ray imaging system. In order to develop this predictive tool, a model has been constructed for the Bremsstrahlung spectrum of an x-ray tube, and calculations for the detector's efficiency over the relevant range of x-ray energies have been made, and the product of emitted and detected spectra has been used to calculate the effective x-ray imaging spectrum. An approach has also been established for filtering `zinger' noise in x-ray radiographs, which has proven problematic at high x-ray energies used for solder imaging. The performance of this filter has been compared with a known existing method and the results indicate a significant increase in the accuracy of zinger filtered radiographs.
The obtained results indicate the conception of a powerful means for the study of failure causing processes in solder systems used as interconnects in microelectronic packaging devices. These results include the volumetric quantification of parameters which are indicative of both electromigration tolerance of solders and the dominant mechanisms for atomic migration in response to current stressing. This work is aimed to further the community's understanding of failure-causing electromigration processes in industrially relevant material systems for microelectronic interconnect applications and to advance the capability of available characterization techniques for their interrogation.
In order to enhance the attenuation contrast observed in multi-phase material systems, a modeling approach has been developed to predict settings for the controllable imaging parameters which yield relatively high detection rates over the range of x-ray energies for which maximum attenuation contrast is expected in the polychromatic x-ray imaging system. In order to develop this predictive tool, a model has been constructed for the Bremsstrahlung spectrum of an x-ray tube, and calculations for the detector's efficiency over the relevant range of x-ray energies have been made, and the product of emitted and detected spectra has been used to calculate the effective x-ray imaging spectrum. An approach has also been established for filtering `zinger' noise in x-ray radiographs, which has proven problematic at high x-ray energies used for solder imaging. The performance of this filter has been compared with a known existing method and the results indicate a significant increase in the accuracy of zinger filtered radiographs.
The obtained results indicate the conception of a powerful means for the study of failure causing processes in solder systems used as interconnects in microelectronic packaging devices. These results include the volumetric quantification of parameters which are indicative of both electromigration tolerance of solders and the dominant mechanisms for atomic migration in response to current stressing. This work is aimed to further the community's understanding of failure-causing electromigration processes in industrially relevant material systems for microelectronic interconnect applications and to advance the capability of available characterization techniques for their interrogation.
ContributorsMertens, James Charles Edwin (Author) / Chawla, Nikhilesh (Thesis advisor) / Alford, Terry (Committee member) / Jiao, Yang (Committee member) / Neithalath, Narayanan (Committee member) / Arizona State University (Publisher)
Created2015
Description
In this thesis, the author described a new genetic algorithm based on the idea: the better design could be found at the neighbor of the current best design. The details of the new genetic algorithm are described, including the rebuilding process from Micro-genetic algorithm and the different crossover and mutation formation.
Some popular examples, including two variable function optimization and simple truss models are used to test this algorithm. In these study, the new genetic algorithm is proved able to find the optimized results like other algorithms.
Besides, the author also tried to build one more complex truss model. After tests, the new genetic algorithm can produce a good and reasonable optimized result. Form the results, the rebuilding, crossover and mutation can the jobs as designed.
At last, the author also discussed two possible points to improve this new genetic algorithm: the population size and the algorithm flexibility. The simple result of 2D finite element optimization showed that the effectiveness could be better, with the improvement of these two points.
Some popular examples, including two variable function optimization and simple truss models are used to test this algorithm. In these study, the new genetic algorithm is proved able to find the optimized results like other algorithms.
Besides, the author also tried to build one more complex truss model. After tests, the new genetic algorithm can produce a good and reasonable optimized result. Form the results, the rebuilding, crossover and mutation can the jobs as designed.
At last, the author also discussed two possible points to improve this new genetic algorithm: the population size and the algorithm flexibility. The simple result of 2D finite element optimization showed that the effectiveness could be better, with the improvement of these two points.
ContributorsDing, Xiaosu (Author) / Hjelmstad, Keith (Thesis advisor) / Neithalath, Narayanan (Committee member) / Rajan, Subramaniam D. (Committee member) / Arizona State University (Publisher)
Created2015
Description
Laminated composite materials are used in aerospace, civil and mechanical structural systems due to their superior material properties compared to the constituent materials as well as in comparison to traditional materials such as metals. Laminate structures are composed of multiple orthotropic material layers bonded together to form a single performing part. As such, the layup design of the material largely influences the structural performance. Optimization techniques such as the Genetic Algorithm (GA), Differential Evolution (DE), the Method of Feasible Directions (MFD), and others can be used to determine the optimal laminate composite material layup. In this thesis, sizing, shape and topology design optimization of laminated composites is carried out. Sizing optimization, such as the layer thickness, topology optimization, such as the layer orientation and material and the number of layers present, and shape optimization of the overall composite part contribute to the design optimization process of laminates. An optimization host program written in C++ has been developed to implement the optimization methodology of both population based and numerical gradient based methods. The performance of the composite structural system is evaluated through explicit finite element analysis of shell elements carried out using LS-DYNA. Results from numerical examples demonstrate that optimization design processes can significantly improve composite part performance through implementation of optimum material layup and part shape.
ContributorsMika, Krista (Author) / Rajan, Subramaniam D. (Thesis advisor) / Neithalath, Narayanan (Committee member) / Mobasher, Barzin (Committee member) / Arizona State University (Publisher)
Created2014
Description
The studies on aluminosilicate materials to replace traditional construction materials such as ordinary Portland cement(OPC) to reduce the effects caused has been an important research area for the past decades. Many properties like strength have already been studied and the primary focus is to learn about the reaction mechanism and the effect of the parameters on the formed products. The aim of this research was to explore the structural changes and reaction product analysis of geopolymers (Slag & Fly Ash) using Fourier transform infrared spectroscopy (FTIR) and deconvolution
techniques. Spectroscopic techniques give valuable information at a molecular level but not all methods are economic and simple. To understand the mechanisms of alkali activated aluminosilicate materials, attenuated total reflectance (ATR) FTIR has been used where the effect of the parameters on the reaction products have been analyzed. To analyze complex systems like geopolymers using FTIR, deconvolution techniques help to obtain the properties of a particular peak attributed to a certain molecular vibration.
Time and temperature dependent analysis were done on slag pastes to understand the polymerization of reactive silica in the system with time and temperature variance. For time dependent analysis slag has been activated with sodium and potassium silicates using two different `n'values and three different silica modulus [Ms- (SiO2 /M2O)] values. The temperature dependent analysis was done by curing the samples at 60C and 80C. Similarly fly ash has been studied by activating with alkali hydroxides and alkali silicates. Under the same curing conditions the fly ash samples were evaluated to analyze the effects of added silicates for alkali activation.
The peak shifts in the FTIR explains the changes in the structural nature of the matrix and can be identified using the deconvolution technique. A strong correlation is found between the concentrations of silicate monomer in the activating position of the main Si-O-T (where T is Al/Si) stretching band in the FTIR spectrum, which
gives an indication of the relative changes in the Si/Al ratio. Also, the effect of the cation and silicate concentration in the activating solution has been discussed using the Fourier self deconvolution technique.
techniques. Spectroscopic techniques give valuable information at a molecular level but not all methods are economic and simple. To understand the mechanisms of alkali activated aluminosilicate materials, attenuated total reflectance (ATR) FTIR has been used where the effect of the parameters on the reaction products have been analyzed. To analyze complex systems like geopolymers using FTIR, deconvolution techniques help to obtain the properties of a particular peak attributed to a certain molecular vibration.
Time and temperature dependent analysis were done on slag pastes to understand the polymerization of reactive silica in the system with time and temperature variance. For time dependent analysis slag has been activated with sodium and potassium silicates using two different `n'values and three different silica modulus [Ms- (SiO2 /M2O)] values. The temperature dependent analysis was done by curing the samples at 60C and 80C. Similarly fly ash has been studied by activating with alkali hydroxides and alkali silicates. Under the same curing conditions the fly ash samples were evaluated to analyze the effects of added silicates for alkali activation.
The peak shifts in the FTIR explains the changes in the structural nature of the matrix and can be identified using the deconvolution technique. A strong correlation is found between the concentrations of silicate monomer in the activating position of the main Si-O-T (where T is Al/Si) stretching band in the FTIR spectrum, which
gives an indication of the relative changes in the Si/Al ratio. Also, the effect of the cation and silicate concentration in the activating solution has been discussed using the Fourier self deconvolution technique.
ContributorsMadavarapu, Sateesh Babu (Author) / Neithalath, Narayanan (Thesis advisor) / Rajan, Subramaniam D. (Committee member) / Marzke, Robert (Committee member) / Arizona State University (Publisher)
Created2014