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- All Subjects: Finite Element Modelling
- Creators: Rajan, Subramaniam
- Creators: Muthegowda, Nitin Chandra
Effects of Aggregate Packing Density on the Mechanical Properties of Ultra-High Performance Concrete
Description
Cement is a remarkable construction material that allows for the formation of complex geometric forms while still providing adequate strength properties to be used as a structural material. This research focuses on Ultra-High Performance Concrete (UHPC) which is a specialized class of cementitious material that exhibits exceptional strength and durability properties when compared to standard concrete. UHPC achieves these properties through a combination of high cement content, high particle packing density, low water-to-cement ratio, and the additional of special admixtures such as superplasticizer. These components all serve the purpose of increasing UHPC strength and mechanical properties by helping achieve much high material densities than other forms of concrete.
In this study, aggregate material evaluation and testing was conducted for use in the mix design of the UHPC mixes that were carried out and tested. Each mix employed the same general UHPC mixture design with the only difference being the aggregate proportions of #4, #8, and #10 nominal size aggregates. The purpose of using a UHPC mix design that was independent of aggregate proportioning was to evaluate the effects of varying aggregate particle packing densities. Increased particle packing density of UHPC provide improved mechanical performance by decreasing the distance between particle within cured UHPC, thereby producing significant increases in compressive strength, tensile strength, durability, and service life of UHPC when compared to standard concrete. For this study, particle packing densities of 0.509, 0.521, 0.540, and 0.552 were employed and evaluated on the basis of compressive strength and tensile strength to determine the optimum UHPC mix design.
In this study, aggregate material evaluation and testing was conducted for use in the mix design of the UHPC mixes that were carried out and tested. Each mix employed the same general UHPC mixture design with the only difference being the aggregate proportions of #4, #8, and #10 nominal size aggregates. The purpose of using a UHPC mix design that was independent of aggregate proportioning was to evaluate the effects of varying aggregate particle packing densities. Increased particle packing density of UHPC provide improved mechanical performance by decreasing the distance between particle within cured UHPC, thereby producing significant increases in compressive strength, tensile strength, durability, and service life of UHPC when compared to standard concrete. For this study, particle packing densities of 0.509, 0.521, 0.540, and 0.552 were employed and evaluated on the basis of compressive strength and tensile strength to determine the optimum UHPC mix design.
ContributorsThornburg, Cody Michael (Author) / Neithalath, Narayanan (Thesis director) / Rajan, Subramaniam (Committee member) / Civil, Environmental and Sustainable Eng Program (Contributor, Contributor) / Barrett, The Honors College (Contributor)
Created2019-05
Description
Over the past few decades there has been significant interest in the design and construction of hypersonic vehicles. Such vehicles exhibit strongly coupled aerodynamics, acoustics, heat transfer, and structural deformations, which can take significant computational efforts to simulate using standard finite element and computational fluid dynamics techniques. This situation has lead to development of various reduced order modelling (ROM) methods which reduce the parameter space of these simulations so they can be run more quickly. The planned hypersonic vehicles will be constructed by assembling a series of sub-structures, such as panels and stiffeners, that will be welded together creating built-up structures.In this light, the focus of the present investigation is on the formulation and validation of nonlinear reduced order models (NLROMs) of built-up structures that include nonlinear geometric effects induced by the large loads/large response. Moreover, it is recognized that gaps between sub-structures could result from the these intense loadings can thus the inclusion of the nonlinearity introduced by contact separation will also be addressed. These efforts, application to built-up structures and inclusion of contact nonlinearity, represent novel developments of existing NLROM strategies. A hat stiffened panel is selected as a representative example of built-up structure and a compact NRLOM is successfully constructed for this structure which exhibited a potential internal resonance. For the investigation of contact nonlinearity, two structural models were used: a cantilevered beam which can contact several stops and an overlapping plate model which can exhibit the opening/closing of a gap. Successful NLROMs were constructed for these structures with the basis for the plate model determined as a two-step process, i.e., considering the plate without gap first and then enriching the corresponding basis to account for opening of the gap. Adaptions were then successfully made to a Newton-Raphson solver to properly account for contact and the associated forces in static predictions by NLROMs.
ContributorsWainwright, Bret Aaron (Author) / Mignolet, Marc P (Thesis advisor) / Oswald, Jay (Committee member) / Peralta, Pedro (Committee member) / Spottswood, Stephen (Committee member) / Rajan, Subramaniam (Committee member) / Arizona State University (Publisher)
Created2021
Description
Dissimilar metal joints such as aluminum-steel joints are extensively used in automobile, naval and aerospace applications and these are subjected to corrosive environmental and mechanical loading resulting in eventual failure of the structural joints. In the case of aluminum alloys under aggressive environment, the damage accumulation is predominantly due to corrosion and is accelerated in presence of other metals. During recent years several approaches have been employed to develop models to assess the metal removal rate in the case of galvanic corrosion. Some of these models are based on empirical methods such as regression analysis while others are based on quantification of the ongoing electrochemical processes. Here, a numerical model for solving the Nernst- Planck equation, which captures the electrochemical process, is implemented to predict the galvanic current distribution and, hence, the corrosion rate of a galvanic couple. An experimentally validated numerical model for an AE44 (Magnesium alloy) and mild steel galvanic couple, available in the literature, is extended to simulate the mechano- electrochemical process in order to study the effect of mechanical loading on the galvanic current density distribution and corrosion rate in AE44-mild steel galvanic couple through a multiphysics field coupling technique in COMSOL Multiphysics®. The model is capable of tracking moving boundariesy of the corroding constituent of the couple by employing Arbitrary Langrangian Eulerian (ALE) method.Results show that, when an anode is under a purely elastic deformation, there is no apparent effect of mechanical loading on the electrochemical galvanic process. However, when the applied tensile load is sufficient to cause a plastic deformation, the local galvanic corrosion activity at the vicinity of the interface is increased remarkably. The effect of other factors, such as electrode area ratios, electrical conductivity of the electrolyte and depth of the electrolyte, are studied. It is observed that the conductivity of the electrolyte significantly influences the surface profile of the anode, especially near the junction. Although variations in electrolyte depth for a given galvanic couple noticeably affect the overall corrosion, the change in the localized corrosion rate at the interface is minimal. Finally, we use the model to predict the current density distribution, rate of corrosion and depth profile of aluminum alloy 7075-stainless steel 316 galvanic joints, which are extensively used in maritime structures.
ContributorsMuthegowda, Nitin Chandra (Author) / Solanki, Kiran N (Thesis advisor) / Rykaczewski, Konrad (Committee member) / Jiao, Yang (Committee member) / Arizona State University (Publisher)
Created2015