Doctor of Philosophy, The Ohio State University, 2023, Mechanical Engineering

Metamaterials are deliberately architected artificial materials that can achieve unconventional properties not observed in nature, showing potential for various applications. Mechanical metamaterials are a new branch of metamaterials using geometry designs to control mechanical properties such as stiffness, deformation, and energy absorption. To date, most of the research on mechanical metamaterials considers an array of unit cells distributed in a uniform pattern, and the properties of those mechanical metamaterials are restricted by the unit cell structure. By introducing multiple unit cells into the array with non-uniform patterns, a much wider variety of mechanical properties become possible. However, such non-uniform mechanical metamaterials with extensive design domains bring challenges to the design, especially when specific target properties are desired. Motivated by the development of deep learning, we develop a framework based on feedforward neural networks (FNN) to systematically explore a large design domain of non-uniform mechanical metamaterials with nonlinearity in material, geometry, and boundary condition, realizing the mechanical response curve predictions of non-uniform patterns and the inverse designs for given target response curves. But for conventional mechanical metamaterials, their properties are significantly confined by the original geometries and lack in-situ tunability. Thus by a direct ink writing (DIW) technique, we combine hard-magnetic soft materials (MSMs) and hard-magnetic shape memory polymers (M-SMPs), which demonstrate superior shape manipulation performance by realizing reprogrammable, untethered, fast, and reversible shape transformation and shape locking in one material system, to develop magneto-mechanical metamaterials that are capable of shifting between various macroscopic mechanical behaviors such as expansion, contraction, shear, and bending under cooperative thermal and magnetic actuation, enabling wide-range i (open full item for complete abstract)

Committee: Ruike Zhao (Advisor); Haijun Su (Committee Member); Carlos Castro (Committee Chair) Subjects: Materials Science; Mechanical Engineering; Mechanics

Doctor of Philosophy in Engineering, Cleveland State University, 2022, Washkewicz College of Engineering

Iron-based magnetic alloys possess very good magnetic and mechanical properties. Among these alloys Fe-Si-B-based alloys show outstanding saturation magnetization and coercivity which makes them great candidates for many industrial applications. Addition of certain elements to the Fe-Si-B base is proven to improve the homogeneity and fineness of microstructure as well as enhance the magnetic behavior of these alloys. In this research work, we have studied the effect of adding copper and niobium to the Fe-Si-B base alloy. Previous studies have shown that magnetic alloys show better magnetic properties when their microstructure consists of nanocrystals embedded in an amorphous matrix. In order to reach amorphization, magnetic alloys are traditionally melted and then cooled down very fast to prevent crystallization and grain growth in their microstructure. However, there are several disadvantages associated with this method of fabrication, such as the limitation in thickness of the products. To solve this issue, we proposed a new method of fabrication for magnetic alloys where amorphization occurs through mechanical alloying, and the amorphous powder alloy that is produced by this process is then consolidated using a technique called spark plasma sintering finding appropriate mechanical alloying processing parameters to get an amorphous structure. Many different processing parameters were investigated, and the mechanical properties, microstructure, and magnetic properties of all samples were examined. The effect of spark plasma sintering processing parameters on samples sintered from the amorphous powders was then studied. Finally, the amount of energy introduced to the powder from the milling balls during the mechanical alloying process was calculated. We were able to find a trend between the energy introduced to the powder during the milling process and the amorphous structure of the milled powders. From our data, we draw an energy map that shows the window (open full item for complete abstract)

Committee: Tushar Borkar (Advisor); Majid Rashidi (Committee Member); Somnath Chattopadhyay (Committee Member); Maryam Younessi Sinaki (Committee Member); Petru Fodor (Committee Member) Subjects: Engineering; Materials Science; Mechanical Engineering

MS, University of Cincinnati, 2021, Engineering and Applied Science: Materials Science

A unique attribute required is low coercivity for high-frequency magnetic uses which is distinguished by through reversing of magnetic hysteresis. Low hysteresis of a magnetic alloy is reliant on the proportion of grain size dimensions to the correlation distance (magnetic). Small values of coercivity is obtained when the grain size is less than the correlation distance as defined in the theoretical model: random anisotropy. Based on this theory, a common tactic utilized in strip powder procedure technique is to obtain grains with nanoscale size embedded in amorphous matrix via rapidly cooled and hardened alloy strips, followed by a supervised low vacuum heating or by milling into finer particles directly from as-spun partial crystalline strip. In all prior research investigations of soft magnetic Fe alloy, the low coercivity is obtained through amorphization via rapid solidification (with extremely high cooling rate, > 105 K/s ). The melt spun strips were low vacuum (10-2 Torr) heated at ~600 °C in order to develop magnetically isotropic nanostructures in the partial crystalline strip for finer powdering processing via ball milling for 3D printing or net shaping. However, the increase in coercivity are affected due to the powdering conditions. In this research, nanocrystallites are embedded in the melt spun Fe alloy amorphously formed strip that reveal mechanical stability even after the heating and ball milling procedure were obtained. The as-spun strip coercivity determined was ~ 0 Oe even after heating at high temperatures ~700 °C, which is unique property requirement for high-temperature high frequency applications. Subsequent heating, ball milling of these partial crystalline strips ends with finer powders with low coercivity values with temperatures up to 427 °C. In the second study, new processing approach in which partial crystalline melt spun strips was used to obtain low hysteresis Fe alloy powders by directly ball milling the partial crystalline mel (open full item for complete abstract)

Committee: Donglu Shi Ph.D. (Committee Chair); Je-Hyeong Bahk Ph.D. (Committee Member); Jude Iroh Ph.D. (Committee Member) Subjects: Materials Science