Master of Science in Engineering, Youngstown State University, 2024, Department of Civil/Environmental and Chemical Engineering

A longitudinal study in corrosion was performed on tensile-elongation dog-bones, created using 3D-printed stainless steel. The effects of exposure to an acidic environment were investigated regarding mass-loss, tensile and yield strength, modulus of elasticity, profilometry of pits and defects, and microscopy of fracture-sites. The SS316L specimens were manufactured using different print-directions, specifically overlapping unidirectional or rotated bidirectional for each layer by an additive manufacturing unit, the Mazak VC-500/5X AM HWD. The novel aspect of this research is focusing on the differences that the path the hot-wire, direct energy deposition, print-head has on its corrosion characteristics, as opposed to only focusing on the printing-parameters. The goal was to determine what printing-directions and methods were best for resisting corrosion. The research outlines the process of preparing samples for controlled weight-loss in HCl as well as the methods used to measure the mechanical properties. This allows for the results to be repeated if desired. Upon thoroughly reviewing the data and drawing connections where applicable, it was determined within the test samples that unidirectional print-directions yielded better mass-loss and mechanical attributes than bidirectional printing. It was found that some print directions, namely 90°, which is perpendicular to the printing door, performed notably better than other directions such as 0° or 45°.

Committee: Holly Martin PhD (Advisor); Pedro Cortes PhD (Committee Member); Bharat Yelamanchi PhD (Committee Member) Subjects: Chemical Engineering; Chemistry; Engineering; Experiments; Materials Science

PhD, University of Cincinnati, 2018, Engineering and Applied Science: Mechanical Engineering

In the past few decades, Laminated composites have become the most favored material system for a wide range of industrial applications. Factors such as the potential for structural tailoring, superior strength, and stiffness for a given weight along with higher toughness and mechanical damping etc., have justified their increased use. Due to this high usage, the accurate behavior of laminated composites under various loading conditions remains a concern and hence this dissertation focuses on building simple and accurate uni-directional micro-mechanical material models. Firstly, an elastic micromechanical model based on the physically viable sub-cell boundary conditions is developed and implemented for use with uni-directional composite laminates in the explicit finite element software LS-DYNA®. Stress-strain relations have been presented in a three-dimensional context and hence can be used with solid elements. The effect of these boundary conditions in accurately estimating the elastic properties has been studied. Transverse and shear modulus have been analyzed in detail alongside popular analytical methods and verified against available experimental results for various volume fractions. Good agreements have been observed for the presented model in comparison with the experimental results. Secondly, a non-linear micro-mechanical composite material model is developed to simulate the behavior of uni-directional composites under impact loading conditions. The strain-rate and pressure dependency in the composite material model is accounted by the resin, which uses previously developed state-variable viscoplastic equations. These equations were modified to account for the significant contributions of hydrostatic stresses typically observed in polymers. The material model also uses a continuum damage mechanics (CDM) based failure model to incorporate the progressive post-failure behavior. A set of Weibull distribution functions are used to quantify this behavior and (open full item for complete abstract)

Committee: Ala Tabiei Ph.D. (Committee Chair); Richard Hamm M.S (Committee Member); Yijun Liu Ph.D. (Committee Member); David Thompson Ph.D. (Committee Member); Kumar Vemaganti Ph.D. (Committee Member) Subjects: Mechanical Engineering

Master of Science, University of Akron, 2016, Applied Mathematics

A three-stage, unidirectional pit growth model, from initiation to stable growth and repassivation as the bulk potential is decreased, is developed. Stage I models metastable pit growth under ohmic control and a constant current density. Here it is assumed that the pit is covered by a semi-permeable oxide layer. Stage I is terminated when the metal concentration reaches its saturation limit at which time the pit cover instantaneously bursts. Stage II models the stable pit growth under diffusion control and the formation of a salt film at the bottom of the pit. During Stage II the bulk potential is decreased at a specified scan rate. When the bottom pit potential reaches the transition potential, Stage III begins. Here we model the pit growth under ohmic control, for a prescribed polarization curve, until the metal repassivates as the potential is decreased. The governing system of equations for each stage is solved numerically to determine the potential drop, and the concentrations of sodium, chloride, and metal ions within the pit. The pit depth as a function of time is determined from Faraday's Law in Stages I and III, and from a mass balance at the electrolyte/metal interface in Stage II. The cumulative pit depth is fit to a power law model that is used in existing Markov models for pit initiation and growth, and is compared with experimental pit depths for stainless steel in seawater.

Committee: Curtis Clemons Dr. (Advisor); Kevin Kreider Dr. (Committee Member); Gerald Young Dr. (Committee Member); Timothy Norfolk Dr. (Committee Chair) Subjects: Mathematics