PhD, University of Cincinnati, 2022, Engineering and Applied Science: Mechanical Engineering

The central idea of the present work is the study of thermoelectric (TE) transport phenomena in nonconventional materials including topological metals, shape memory alloys (SMA), and magnetic shape memory alloys (MSMA) to see how these properties evolve in such unusual materials. Topological materials are known for having unique transport properties because of their exotic band structures, while SMAs and MSMAs have structural and magnetostructural transformation respectively. TE and other related transport properties can provide insight of the underlying physics of transport in conducting materials, which becomes useful when potential applications of these materials are considered. For example, TE properties directly relate to the performance of these materials in TE power or cooling devices through a figure of merit. In (M)SMAs, TE properties can be used to directly find the structural and/or magnetic phase transformation temperatures, which in turn, dictate potential cooling applications: elastocaloric and magnetocaloric cooling in SMAs and MSMAs respectively. Hence, this work aims to investigate the characterization of TE properties in the aforementioned classes of materials. Each of the aforementioned cooling technologies have the potential to replace conventional vapor-compression technology in the future by eliminating the need for potentially harmful hydrofluorocarbons and many other refrigerants with high global warming potentials. Additionally, TE cooling devices provide solid-state, noiseless operation without any moving parts. However, this technology is still in its infancy and only low power TE cooling devices have been commercialized to this date. Major challenges in these non-conventional techniques include high material and device cost, and low energy efficiency. This demands significant improvements in both material development and model design of such non-conventional techniques to be able to compe (open full item for complete abstract)

Committee: Je-Hyeong Bahk Ph.D. (Committee Member); Raj Manglik Ph.D. (Committee Member); Kishan Bellur Ph.D. (Committee Member); Sarah Watzman Ph.D. (Committee Member) Subjects: Mechanical Engineering

MS, University of Cincinnati, 2020, Engineering and Applied Science: Materials Science

Pack cementation is a promising technique to synthesize hollow NiTi microtubes, which impart enhanced heating/cooling efficiency and, thus, faster shape memory response. Prior research investigating the effect of wire size on phase evolution and Kirkendall pore formation during pack titanization showed a significant difference between large (100 µm) and small (25 µm) diameter wires. The first objective of this research is to quantify the titanium deposition kinetics on intermediate-sized Ni wire (75 µm diameter) and determine the required coating time to achieve the desired near-equiatomic NiTi composition. It also explores an ex-situ study of the formation of a dual-pore structure that forms in some of the wires and provides insight for future in-situ investigations of the wire size effect on pack titanizing. Even though binary NiTi shape memory alloys offer excellent biocompatibility, strength, and corrosion resistance, their application is limited to less than 100 ºC. Hence, there is a need to increase the transformation temperatures for high-temperature applications, especially for aerospace applications. Certain ternary alloying additions to NiTi form high temperature shape memory alloys (HTSMAs) as there is an associated increase in the austenite-martensite transformation temperature and, therefore, have attracted considerable attention from researchers. Ni-Ti-Zr is one such HTSMA that provides the additional advantages of weight and cost reduction as compared to its platinum (Pt), gold (Au) and hafnium (Hf) counterparts. In the current research, attempts were made to produce Ni-Ti-Zr wires by co-depositing Ti and Zr on Ni wires using a halide activated pack in a single step process. The samples gained Zr content, but not enough was deposited to increase the transformation temperature. Moreover, a significant variation in the coating thickness was observed, resulting in a significant fluctuation in the composition. Therefore, as a first step, deposition of Z (open full item for complete abstract)

Committee: Ashley Paz y Puente Ph.D. (Committee Chair); Matthew Steiner Ph.D. (Committee Member); Sarah Watzman Ph.D. (Committee Member) Subjects: Materials Science

Master of Science, University of Toledo, 2004, Civil Engineering

The importance of advanced material systems is rapidly increasing. New demands are placed by our society and environment on the development of new technological systems. Smart material systems play an important role in innovative technology, providing materials that can act as both control elements and structural members. To address the problems of controlling the structural deflection, research is very essential on smart materials. Shape memory alloys (SMA) have been major elements of smart materials and structures. Shape memory alloys are novel materials that have the ability to return to a predetermined shape when subjected to the appropriate thermal procedure. SMAs are widely used for controlling the structural deflection. This research addresses the use of Nitinol shape memory alloy to increase the flexural strength of simply supported concrete beams. The shape memory property of the Nitinol wire was used in prestressing the concrete beam. The prestressed Nitinol wire was placed in the concrete beam with an eccentricity. Electrical current was used to heat that alloy to above its austenite finish temperature. When the temperature was raised high enough to cause the shape memory effect (SME) in Nitinol, the prestressing force was transferred to the beam. A total of ten concrete beams were tested for flexure strength in accordance with the ASTM C78. The flexural strength of the concrete beam was increased when prestressed Nitinol wire was placed in the concrete, when compared with the plain concrete beam and with un-prestressed concrete beam. Simple beam bending theory was used to determine how much prestress was transferred during the electrical heating of the Nitinol shape memory alloy.

Committee: Mark Pickett (Advisor) Subjects: Engineering, Civil

Doctor of Philosophy, University of Toledo, 2023, Mechanical Engineering

Shape Memory Effect (SME) and Superelasticity (SE) are key characteristics of shape memory alloy (SMA) materials. SME allows the material to return to its original shape after heating, while superelasticity enables recovery from significant inelastic deformation. NiTiHf is a highly promising SMA, known for its elevated SME and SE performances. Designing and controlling NiTiHf SMA properties as desired poses challenges due to its dependence on many factors. Three core characteristics define SMA materials: transformation temperatures (TTs), thermal hysteresis (TH), and actuation strain (AS). TTs are crucial design properties that determine the activation threshold for SME and SE effects. TH, resulting from TTs differences, reflects the energy loss during each SME action. AS represents the amount of recoverable strain during each SME actuation. Traditional approaches to designing NiTiHf TTs, TH, and AS have relied solely on experimental studies, which have not yielded comprehensive results and can be impractical due to high costs and time requirements. Cost-effective modeling approaches, including physics-based and data-driven methods, expedite material design and process optimization. Machine learning (ML) modeling, equipped with strong regression analyses, significantly reduces the need for experimental trials to optimize alloy design. Physics-based modeling, considering underlying physical principles, plays a critical role as error compensation tools. In this study, both data-driven and physics-based modeling were utilized to overcome the high-dimensional dependency of NiTiHf TTs and AS on various factors and the limited understanding of governing physics. The input parameters for the machine learning models included elemental composition, thermal treatments, and common post-processing steps used in NiTiHf fabrication. This feature selection incorporated a majority of accessible information from the literature on NiTiHf TTs and AS, making use of all essential proce (open full item for complete abstract)

Committee: Mohammad Elahinia (Committee Chair); Ala Qattawi (Committee Chair); Othmane Benafan (Committee Member); Behrang Poorganji (Committee Member); Meysam Haghshenas (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2012, Mechanical Engineering

Smart materials have significantly varied properties and their various types are used broadly in many different engineering applications. In order to grow the field and promote its long term viability, it is important to develop tools which enable researchers and practitioners to determine the best smart material for the application. Computerized material selection databases and systems have been recently developed by design and materials engineers to help users select the best materials for an application. However, documentation of smart materials is limited, especially for those aimed at the use of these materials in devices and applications. In this dissertation, system-level simulation models and collected material data are compiled in a GUI-based computer software called Polymers and Smart Materials Software (PSMS). This material selection tool encompasses material properties and material-level models as well as systems level smart material applications for a wide range of smart materials. This type of compiled data can expedite the material selection process when designing smart material based systems by allowing one to choose the most effective material for the application. The PSMS tool consists of the following three major sections: 1) Polymers (Polymer types and properties, Polymeric behaviors including dielectric and liquid crystal elastomers); 2) Smart Materials (Piezoelectric Ceramics/Polymers, Shape Memory Alloys/Polymers, Thermoelectrics, Electrorheological and Magnetorheological Fluids); 3) More information (External databases, Cost information, etc.). The software tool offers a wide variety of design and selection features. Material property and performance charts are provided to compare material properties and to choose the best material for optimal performance. The tool is also flexible in that it enables users to categorize material properties and create their own databases. In areas where existing models were inadequate for systems level integra (open full item for complete abstract)

Committee: Gregory Washington (Advisor); Marcelo Dapino (Advisor); Carlos Castro (Committee Member); Mark Walter (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2024, Materials Science and Engineering

Shear deformations in metallic materials, whether carried by dislocations, mechanical twinning, martensitic transformations in crystalline solids, or shear transformation zones (STZs) in amorphous solids, exhibit several common characteristics. These include autocatalysis driven by long-range elastic interactions and the occurrence of strain avalanches post-yielding. Therefore, to achieve controlled strain release and desired stress-strain behaviors tailored to specific applications, it is imperative to mitigate autocatalysis. In this dissertation, we elucidate strategies to mitigate autocatalysis by focusing on three commonly used metallic materials: Al alloys, extensively employed as lightweight structural materials in manufacturing; NiTi shape memory alloys (SMAs), widely utilized in aerospace, automotive, and biomedical industries; and metallic glasses, utilized in precise instruments and biomedical devices. The primary aim is to employ various computational methods to investigate mechanisms for suppressing autocatalysis and attaining desired mechanical responses in these three examples through appropriate microstructure engineering. In Al-alloys, dislocations are the primary carriers of shear deformation and various precipitate microstructures have been strategically designed to regulate the dislocation activities. In particular, in 7xxx series Al-alloys, e.g., Al-Zn-Mg-Cu, η' phase is the commonly observed shearable precipitate phase to strengthen the alloys. By adding Mn and Si, non-shearable precipitates (Al6Mn and α) have been introduced to prevent stain localization. To understand the synergy between the two types (shearable and non-shearable) of precipitates in achieving desired combinations of strength and ductility, it is necessary to investigate the possible interactions between the two during precipitation. These interactions determine the precipitate microstructures, as well as the interactions between a given precipitate microstructure and dislocat (open full item for complete abstract)

Committee: Yunzhi Wang (Advisor); Steve Niezgoda (Committee Member); Michael Mills (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2023, Materials Science and Engineering

Unorthodox material processing technologies create the possibility to produce unique microstructural features at various length scales to bring forward unique material properties. Additive manufacturing (AM) rapidly became integrated within many sectors over the past two decades, with research previously focused on suppressing the non-equilibrium/metastable microstructures. Yet, it is not fully understood whether these unique microstructures, with their inherent defects, could be exploited as templates to enhance the properties of conventional alloys. In this work, functional and structural Ni alloys (Ni-rich NiTi and Inconel 718) have been produced with additive manufacturing (AM), selective laser melting (SLM). Detailed S/TEM based characterization reveals that NiTi produced under high energy density process parameters showed textural evolution leading to unexpected narrowing of the hysteresis during pseudoelastic cycling and reduction in strain accumulation. Nonequilibrium microstructures have previously been produced utilizing radiation to induce unique crystallographic defects. In this study, ion beam implantation is used to induce defects and modulate the local transformation, to produce unique heterogeneous microstructures with the potential to enhance psuedoelastic properties. Results showed Ni ion irradiation amorphized the B2 structure and subsequently suppressed the martensitic transformation. SLM fabricated Inconel 718 has not been understood whether the as-fabricated AM microstructure can be used for creep due to the non-equilibrium solidification structures and their defects. Creep testing at 649°has revealed that the as-fabricated Inconel 718 exhibits exceptional creep resistance. In fact, the creep rate in the as fabricated 718 was observed to be slower than the conventionally processed and aged wrought alloy.

Committee: Michael Mills (Advisor); Yunzhi Wang (Committee Member); Peter Anderson (Committee Member) Subjects: Materials Science

Master of Science, The Ohio State University, 2021, Welding Engineering

Ferromagnetic shape memory alloys (FSMAs) have the ability to revert back to original shapes and properties after significant deformation. When in single crystalline form, these alloys produce up to 10% reversible magnetic field induced strain (MFIS) which can be beneficial in actuators, sensors, and self-assembly. Advanced manufacturing techniques such as laser-based additive manufacturing enables the fabrication of complex parts, but creates complex microstructures that are characteristic for non-functional alloys. Thus, there is a critical need to establish a fundamental understanding of how non-equilibrium processing and complex thermal cycling affect microstructural evolution and functional properties in ferromagnetic shape memory alloys. The overall goal of this work is to correlate the effect of rapid solidification to microstructure and mechanical and magnetic properties in Ni-Mn-Ga Heusler alloys. In order to develop processing-microstructure-property relations, setup and optimization of various rapid solidification techniques was conducted, including levitation-drop melting, electrode arc melting, and laser beam melting. Determination of cooling rates before solidification for the different techniques was done using thermocouple, pyrometer and infrared camera measurements, finite element thermal analysis, and measurements of secondary dendrite arm spacing on solidified samples. Characterization of rapidly solidified Ni2MnGa alloy (and two off-stoichiometric compositions) was performed in terms of solidification microstructure, segregation behavior, phase transformation temperature and magnetic and mechanical properties as a function of cooling rate. Light optical and scanning electron microscopy, electron dispersive spectroscopy, and X-ray diffraction, differential scanning calorimetry, vibration sample magnetometry, and micro-hardness testing were performed. Results were compared to microstructure and properties in samples from laser-metal depositi (open full item for complete abstract)

Committee: Boyd Panton (Committee Member); Carolin Fink (Advisor) Subjects: Materials Science; Metallurgy

Master of Science in Engineering, Youngstown State University, 2019, Department of Mechanical, Industrial and Manufacturing Engineering

Monocrystalline Ni-Mn-Ga magnetic shape memory alloys are known for producing reversible strains up to 10% in the presence of the magnetic field. Two main problems with the material are the high production cost and brittleness of the material. Due to complexity in manufacturing process mass production of the part becomes difficult limiting its application. High brittleness in material restricts any machining operation on both monocrystalline and polycrystalline bulk part, limiting the use of material for various applications. A possible alternative is to use porous polycrystalline Ni-Mn-Ga alloys produced using additive manufacturing process, which was first time introduced using binder jetting technology. But, little knowledge is available for both bulk and polycrystalline Ni-Mn-Ga part. The purpose of this study is to investigate the mechanical properties of bulk and 3D printed parts using nanoindentation and microhardness techniques. The methods are well known for investigation of small volumes of material with high accuracy. Two different synthesis techniques were used to prepare the bulk and 3D printed sample. Ingot for Bulk and 3D printed Ni-Mn-Ga part was produced using arc melting process. By varying the chemical composition of the alloy, two different parts with phases, namely austenitic (Ni49.12Mn22.57Ga28.31wt.%) and martensitic (Ni52.49Mn23.11Ga24.40wt.%) at room temperature were prepared. The 3D printed Ni-Mn-Ga parts (Ni51.32Mn33.06Ga15.62wt.%) were prepared from ball milled powder using binder-jet technology. The properties of interest in this research were hardness (H), elastic modulus (E), yield strength (σy), and fracture toughness (KIc) for all the three types of samples. Hardness (H), elastic modulus (E), and yield strength (σy) were determined using nanoindentation technique while the microindentation technique was used to determine fracture toughness (KIC). The fracture toughness was determined using two different types of model models based on (open full item for complete abstract)

Committee: C. Virgil Solomon PhD (Advisor); Hazel Marie PhD (Committee Member); Jae Joong Ryu PhD (Committee Member) Subjects: Engineering; Mechanical Engineering

Master of Science, The Ohio State University, 2019, Materials Science and Engineering

The superelastic and actuation performance of shape memory alloys depends greatly upon the composition and processing of the alloy, as well as the operating temperature range and stresses involved in its implementation. This thesis is in two parts. The first presents a design parameter to help classify shape memory alloys and quantify their performance as torque tube actuators. It studies the effects of crystallographic texture variation, actuator biasing stress, alloy composition, and alloy system on shape memory torque tube performance through a combination of simulation and aggregation of experimental data. Finally, a torque tube design for use in aircraft gas turbine engines is recommended based on these findings. The second part of the thesis seeks to mechanistically explain why the alloy composition effects on performance in NiTiHf shape memory alloys occur. It is hypothesized that the stabilization of martensite occurs because of the lattice mismatch strain between the “H-phase” precipitate phase, which form with the heat treatment of these alloys, and the cubic austenite phase. From this hypothesis, a model for predictions of martensite microstructures is created, and the reduction in strain energy of the formation of these microstructures is estimated.

Committee: Peter Anderson (Advisor) Subjects: Materials Science; Metallurgy

Doctor of Philosophy, University of Toledo, 2018, Engineering

Nowadays, shape memory alloys (SMAs), and in particular Nickel-Titanium alloys (i.e., NiTi or Nitinol), are widely used in biomedicine, and to a lesser extent in automotive, and aerospace industries. Thanks to their unique shape memory effect (SME) and superelasticity (SE), these alloys can recover a large deformation up to 8% through reversible phase transformations and provide light-weight actuation in low-profile devices. They also represent other favorable characteristics, such as biocompatibility, low stiffness (i.e., Modulus of elasticity), high damping capacity, and adequate corrosion resistance. Despite the high demand in NiTi alloys, there are two main challenges remaining; one, the inability to fabricate complex components; two, the lack of repeatable processes to provide the desired thermomechanical properties. Conventional methods of fabrication are not suitable for creating NiTi devices such as porous scaffolds and patient-specific curved surfaces. This limitation stems from factors such as the high oxygen reactivity, the stress induced phase transformation, the spring back effects, work hardening, and the burr formation associated with applying conventional fabrication methods for making three-dimensional shapes from NiTi alloys. The promise of additive manufacturing (AM) techniques is to solve these two issues and pave the way for inducing desired thermomechanical properties in a wide variety of NiTi shapes. Selective laser melting (SLM) has already been used successfully to create complex shapes from NiTi. This work focuses on the second issue in inducing the desired thermomechanical properties in the SLM fabricated NiTi parts. It is well established that the thermomechanical response of NiTi depends on the crystal texture and microstructure features of the alloy. These features, in turn, are significantly affected by the thermal and mechanical (thermomechanical) treatment history applied to the material during the alloy development and device fa (open full item for complete abstract)

Committee: Mohammad Elahinia (Advisor); Haluk Karaca (Committee Member); Abdullah Afjeh (Committee Member); Reza Mirzaeifar (Committee Member); Lesley Berhan (Committee Member); Reza Rizvi (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2018, Mechanical Engineering

Morphing panels offer opportunities as adaptive control surfaces for optimal system performance over a broad range of operating conditions. This work presents a design framework for multifunctional composites based on three types of laminae, viz., constraining, adaptive, and prestressed. Based on this framework, laminate configurations are designed to achieve multiple morphing modes such as stretching, flexure, and folding in a given composite structure. Multiple functions such as structural integrity, bistability, and self-actuation are developed. The composites are developed through a concurrent focus on mathematical modeling and experiments. This research shows that curvature can be created in a composite structure by applying mechanical prestress to one or more of its laminae. Cylindrical curvature can be tailored using a prestressed lamina with zero in-plane Poisson's ratio. Analytical laminated-plate models, based on strain energy minimization, are presented in multiple laminate configurations to characterize composites with curvature, bistability, folding, and embedded smart material-driven actuation. Fabrication methods are also presented for these composite configurations. The mathematical models are validated experimentally using tensile tests and 3D motion capture. The mechanics of an n-layered composite is explained through modeling of all the stacking sequences of the three generic laminae. Actuation energy requirement is found to be minimal in the constraining-prestressed-adaptive layer configuration. Bistable curved composites are developed using asymmetric prestressed laminae on either face of a core layer; these composites address the drawbacks of thermally-cured bistable fiber-reinforced polymeric composites. When the prestressed directions are orthogonal, the stable curvatures are weakly-coupled. The composite's domain of bistability and actuation requirements are quantified using a non-dimensional high-order strain model. Active bi (open full item for complete abstract)

Committee: Marcelo Dapino Prof. (Advisor); Rebecca Dupaix Prof. (Committee Member); Ryan Harne Prof. (Committee Member); Haijun Su Prof. (Committee Member) Subjects: Aerospace Materials; Automotive Materials; Engineering; Mechanical Engineering; Mechanics

Doctor of Philosophy, The Ohio State University, 2017, Materials Science and Engineering

The development of viable high-temperature shape memory alloys (HTSMAs) demands a coordinated multimodal characterization effort linking nanoscale crystal structure to macroscale thermomechanical properties. In this work, several high performance NiTi-based shape memory alloys are comprehensively explored with the goal of gaining insight into the complex transformation and deformation mechanisms responsible for their remarkable behavior. Through precise control of alloying and aging parameters, microstructures are optimized to enhance properties such as high-temperature strength and stability. These are crucial requirements for the development of advanced applications such as actuators and adaptive components that operate in demanding automotive and aerospace environments. An array of NiTiHf and NiTiAu alloys are at the core of this effort, offering the possibility of increased capability over traditional pneumatic and hydraulic systems, while simultaneously reducing weight and energy requirements. NiTi-20Hf alloys exhibit a favorable balance of properties, including high strength, stability, and work output at temperatures in excess of 150 °C. The raw material cost of Hf is also much lower compared with Pt, Pd, and Au containing counterparts. Advanced scanning transmission electron microscopy (STEM) and synchrotron X-ray characterization techniques are used to explore unusual nanoscale effects of precipitate-matrix interactions, coherency strain, and dislocation activity in these alloys. Novel use of the 4D STEM strain mapping technique is used to quantify strain fields associated with precipitates, which are being coupled with new phase field modeling approaches to particle/defect interactions. Volume fractions of nanoscale precipitates are measured using STEM-based tomography techniques, atom probe tomography, and synchrotron diffraction of bulk samples. Plastic deformation of the HTSMA austenite phase is shown to occur through <100>B2 type slip for the f (open full item for complete abstract)

Committee: Michael Mills (Advisor); Yunzhi Wang (Committee Member); Peter Anderson (Committee Member); Ronald Noebe (Committee Member); David Wood (Committee Member) Subjects: Materials Science; Metallurgy

Doctor of Philosophy, University of Akron, 2017, Civil Engineering

The effective utilization of shape memory alloys (SMAs) rests on the comprehensive understanding of the factors which influence their performance under various practical thermomechanical loading conditions. In this study, computational efforts needed to complement existing experimental tests have been made towards studying the unique behaviors exhibited by shape memory alloys, with an eye towards their application in the various engineering fields. To this end, a newly developed three-dimensional general model was used. A characterization procedure, involving systematic classification of the model parameters into fixed and temperature and /or state-dependent parameters was given, which allowed easy calibration and application of the SMA mathematical model. In particular, with its implementation in a commercial finite element code, SMA devices, such as aerospace actuators, biomedical stents, bone staples, and earthquake dampers, under variable geometries and boundary loading conditions were simulated. The numerical results obtained from the model matched most of the experimental or test results. The practical significance offered by the developed model in this study included: (a) its ability to guide material users on the optimum conditions at which the alloys can be used, as well as (b) provide important information regarding the immediate and long-term performances of devices designed with SMAs, knowing that such information can be extremely costly to obtain from the physical experiments.

Committee: Atef Saleeb Dr (Advisor); Anil Patnaik Dr (Committee Member); Michelle Hoo Fatt Dr (Committee Member); Qindan Huang Dr (Committee Member); Kevin Kreider Dr (Committee Member) Subjects: Aerospace Materials; Biomechanics; Engineering

Doctor of Philosophy, University of Akron, 2017, Polymer Engineering

The delamination and debonding between SMA and PMC in various test types and composite lay-ups was studied in this thesis research. In the first part of this study, a pull-out test was designed and implemented in which a strip of SMA was pulled out of a PMC coupon in tensile mode. It was found that the default bond between SMA and PMC resulted in a mixed-mode pullout and shape memory effect of the SMA, while addition of adhesives halted pullout progression and invoked only shape memory effect of the SMA until total adhesive failure. In the second part of the study, two adhesives and three PMC lay-ups were used to fabricate SMA strips embedded within PMC coupons. These specimens were monitored with modal acoustic emissions during tensile testing; these AE signals were then plotted against the stresses in the systems along with break locations during sample failure. It was found that the lay-ups of the plies within the PMC had a greater effect on the strength of the samples than adhesives used, while the use of acoustic emissions successfully predicted location failure throughout tests. The final part of the study focused on the interlaminar fracture toughness properties of PMC laminates with embedded SMA. Two adhesives were utilized in Mode I and Mode II test coupons. Specimens were monitored with acoustic emissions during testing: these AE signals were then plotted against the applied loads in the systems. For Mode I interlaminar fracture toughness, the addition of adhesives was necessary to produce reliable results. From these results, “Ply-bridging” was observed between the SMA and PMC in which the propagating crack traversed the SMA during testing, inflated the toughness values of specimens during testing. AE signals of these tests showed that the addition of adhesives had a negative effect on the generated acoustic signals. For Mode II interlaminar fracture toughness, the addition of adhesives were detrimental to the bond between SMA and PMC. This was refl (open full item for complete abstract)

Committee: Sadhan Jana (Advisor); Alamgir Karim (Committee Chair); Gregory Morscher (Committee Member); Erol Sancaktar (Committee Member); Robert Goldberg (Committee Member); Wieslaw Binienda (Committee Member) Subjects: Aerospace Materials; Engineering; Materials Science; Polymers

Master of Science, The Ohio State University, 2017, Materials Science and Engineering

Shape memory alloys (SMAs) are a class of materials that undergo a diffusionless, martensitic transformation. Due to their unique shape memory and superelastic properties, there is interest in implementing these alloys as lightweight, power dense actuators in high temperature environments like aerospace. The traditional SMA NiTi will undergo stable transformation up to 100C, but will not sustain a dependable lifetime beyond this. One method of extending the transformation temperatures is creating a ternary system based on NiTi. With the proper heat treatment and aging conditions, this third element will form optimally sized nanoprecipitates. In this work, the NiTiHf precipitation phase of interest is the H-phase. These precipitates work in two-fold: they stabilize the material over its lifetime by suppressing fatigue and ratcheting and raising transformation temperatures, yet they allow twinned martensite lathes to form. The mechanisms of this duality are not well defined. This work seeks to understand this phoneme using phase field finite element analysis. Phase field modeling incorporates the interfacial energy between the austenite and developing martensite front into the free energy. From this, the relationship between the martensite and austenite over time can be explored spatially and temporally to determine how the twinned martensite microstructure develops over time. This work incorporates several new features into the phase field investigations of the NiTiHf system. These simulations quenched the austenite system from 350K to 150K. The first feature is the introduction of an elliptical precipitate as non-transforming elements within the mesh. These inclusions influence show some templating of the microstructure, depending on the ratio of their major and minor axes. A precipitate with major axis 0.40 and minor axis 0.05 was chosen to represent the H-phase. It was rotated from 0 to 90 degrees within the matrix to investigate the interaction of orientat (open full item for complete abstract)

Committee: Peter Anderson (Advisor); Michael Mills (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2016, Mechanical Engineering

Ultrasonic additive manufacturing (UAM) is a recent additive manufacturing technology which combines ultrasonic metal welding, CNC machining, and mechanized foil layering to create large gapless near net-shape metallic parts. The process has been attracting much attention lately due to its low formation temperature, the capability to join dissimilar metals, and the ability to create complex design features not possible with traditional subtractive processes alone. These process attributes enable light-weighting of structures and components in an unprecedented way. However, UAM is currently limited to niche areas due to the lack of quality tracking and inadequate scientic understanding of the process. As a result, this thesis work is focused on improving both component quality tracking and process understanding through the use of average electrical power input to the welder. Additionally, the understanding and application space of embedding fibers into metals using UAM is investigated, with particular focus on NiTi shape memory alloy fibers.

Committee: Marcelo Dapino Professor (Advisor); Krishnaswamy Srinivasan Professor (Committee Member); Blaine Lilly Professor (Committee Member); Peter Anderson Professor (Committee Member) Subjects: Materials Science; Mechanical Engineering

Master of Science, University of Akron, 2015, Mechanical Engineering

High cycle fatigue (HCF) is a major concern for both military and commercial aircraft, as it is a leading cause of component or engine failure. Of the numerous techniques for HCF mitigation, over-design and constrainment layers are common; all resulting in added weight, increased operational costs, and lower performance. The use of the shape memory effect of shape memory alloys (SMA) (e.g. Nitinol) to allow variable stiffness of engine components is a novel approach to HCF mitigation. To quantify the effectiveness of Nitinol as a HCF mitigation technique, a composite beam consisting of an SMA actuator adhered to an Aluminum alloy substrate was designed. Analysis of preliminary designs with the use of finite element analysis software led to the selection of two final configurations: the first spanning the full beam (full sample) and the second spanning half the length of the beam (half sample). Complete modal analyses were taken over a selected frequency range using both single and scanning laser vibrometers. Experimental results showed that the actuation of the SMA patches led to a shift in modal frequency. Repeated tests on the half sample resulted in an mean increase in modal frequency, ranging from 3.77Hz (1.84%) at second bending to 36.8Hz (1.90%) at fifth bending during heating. Repeated tests on the full sample resulted in an mean increase in modal frequency, ranging from 9.43Hz (4.57%) at second bending to 74.5Hz (3.98%) at fifth bending during heating. Analysis of the third bending mode node location during the thermal cycle demonstrated a shift in the half sample, illustrating the material's capability to change the mode shape vector. Damping tests on both samples exhibited quality values, Q, around 100 at the highest temperatures, but no correlation with phase transformation was realized. Maps of temperature vs. modal frequency vs. beam tip amplitude were recorded for both the full and half sample for second bending mode. Complementary computational re (open full item for complete abstract)

Committee: Nicholas Garafolo PhD (Advisor) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2014, Materials Science and Engineering

Shape memory alloys (SMA) show two remarkable properties- pseudoelasticity and shape memory effect. These properties make them an attractive material for a variety of commercial applications. However, the mechanism of austenite to martensite phase transformation, responsible for these properties also induces plastic deformation leading to structural and functional fatigue. Micron scale experiments suggest that the plastic deformation is induced in part due to the local stress field of the fine martensite microstructure. However, the results are qualitative and the nature of transformation-plasticity interaction is dependent on factors like the width of the interfaces. This thesis presents a new modeling approach to study the interaction between martensite correspondence variant scale microstructure and plastic deformation in austenite. A phase field method based evolution law is developed for phase transformation and reorientation of martensite CVs. This is coupled with a crystal plasticity law for austenite plastic deformation. The model is formulated with finite deformation and rotations. The effect of local crystal orientation is incorporated. An explicit time integration scheme is developed and implemented in a finite element method (FEM) based framework, allowing the modeling of complex boundary conditions and arbitrary loading conditions. Two systematic studies are carried out with the model. First, the interaction between plasticity and phase transformation is studied for load-free and load-biased thermal cycling of single crystals. Key outcomes of this study are that, the residual martensite formed during thermal cycling provides nucleation sites for the phase transformation in the subsequent cycles. Further, the distribution of slip on different slip systems is determined by the martensite texture. This is a strong evidence for transformation induced plasticity. In the second study, experimentally informed simulations of NiTi micropillar compression a (open full item for complete abstract)

Committee: Peter Anderson (Advisor); Michael Mills (Committee Member); Yunzhi Wang (Committee Member) Subjects: Materials Science

Master of Science, University of Toledo, 2014, Mechanical Engineering

This thesis presents an accurate and robust method to determine the angular position of a rotary manipulator using artificial neural network (ANN). A bias type, single degree of freedom rotary manipulator actuated by shape memory alloy (SMA) is used. During the operation of rotary manipulator, the SMA actuator experiences a complex thermo-mechanical loading due to varying stress and temperature, causing the transformation temperature to shift. An ANN is developed to accurately estimate the manipulator position. The ANN estimated position is then used to control the rotary manipulator and track different reference signals using a modified variable structure controller. The results of ANN validation and position control are presented. A novel method for controlling SMA actuator is proposed where the desired position is converted to corresponding resistance value using an ANN. This desired resistance value is compared with actual resistance to control the rotary manipulator. The results for ANN validation and position control are also presented.

Committee: Mohammad Elahinia Phd (Committee Chair); Manish Kumar Phd (Committee Member); Mehdi Pourazady Phd (Committee Member) Subjects: Artificial Intelligence; Mechanical Engineering