Doctor of Philosophy, The Ohio State University, 2024, Mechanical Engineering

Fiber-reinforced composites exhibit exceptional mechanical properties owing to their intricate microstructures, making them highly desirable materials for various engineering applications. However, accurately representing these complex microstructures in finite element (FE) models poses significant challenges. In this dissertation, we present a comprehensive computational framework aimed at synthesizing high-fidelity FE models of chopped fiber composite (CFC) and woven composite microstructures, integrating novel algorithms for microstructure reconstruction and mesh generation. The first component of our framework focuses on CFC microstructures. We introduce a new microstructure reconstruction algorithm integrated with a non-iterative meshing algorithm named CISAMR. This algorithm facilitates the synthesis of densely-packed CFC microstructures with desired statistical descriptors such as volume fraction, diameter distribution, and spatial arrangement of fibers. The reconstruction process involves a virtual packing algorithm based on Non-Uniform Rational B-Splines (NURBS) representation of fiber centerlines, followed by an explicit dynamic FE compression simulation to increase the fiber volume fraction. Subsequently, the shape and location of fibers are optimized to ensure the construction of high-quality conforming meshes using parallel CISAMR. We demonstrate the efficacy of this modeling framework in simulating both the linear elastic response and nonlinear failure behavior of polymer matrix CFCs with embedded glass fibers. An application of the modeling framework for CFC is conducted to study the anisotropy of the material. Two anisotropy indices are put forward, and their benefits and limitations are discussed. The second component of our framework focuses on woven composites. We present an integrated computational approach for generating realistic FE models of woven composites with high fiber volume fractions. This approach relies on a virtual microstructu (open full item for complete abstract)

Master of Science (MS), Ohio University, 2023, Mechanical Engineering (Engineering and Technology)

Bituminous coal was utilized as a particulate filler in polymer-based composites to fabricate standard 1.75 mm coal-plastic composite filaments for use in commercially available fused deposition modeling 3D printers. The composites were formulated by incorporating Pittsburgh No. 8 coal into polylactic acid, polyethylene terephthalate glycol, high-density polyethylene, and polyamide-12 resins with loadings ranging from 20 wt.% to 70 wt.%. CPC filaments were extruded and printed using the same processing parameters as the respective neat plastics. All coal-plastic composite filaments exhibited uniform particle dispersion throughout the microstructure. The mechanical properties of the 3D printed composites were characterized and compared to composites fabricated using traditional compression molding. Tensile and flexural moduli as well as hardness had direct proportionality with increasing coal content while flexural strength, tensile strength, and impact resistance decreased for most composite formulations. Interestingly, polyamide-based composites demonstrated greater maximum tensile and flexural strengths than unfilled plastic. Microscopy of as-fractured samples revealed that particle pull-out and particle fracture were the predominant modes of composite failure. The introduction of coal reduced the coefficient of thermal expansion of the composites, ameliorating the warping problem of 3D printed high-density polyethylene and allowing for additive manufacturing of an inexpensive and widely available thermoplastic. The high-density polyethylene composites demonstrated increased heat deflection temperatures, but all composites maintained comparable glass and metal transition temperatures, allowing them to be processed with commercial 3D printer extruders. The composites exhibited decreased specific heat capacities suggesting lower energy requirements for processing the material. Coal reduced the composite thermal conductivities compared to the neat plastics but improv (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 1986, Graduate School

Doctor of Philosophy, University of Toledo, 2016, Mechanical Engineering

Thermoplastic composites are suitable alternatives to metals in some load-bearing applications such as in the automotive industry due to a large number of advantages they present. These include light weight, ease of processing for complex geometries at high production rate, outstanding cost to performance ratio, ability to reprocess, and corrosion resistance. Addition of fillers such as talc or reinforcements such as short glass fibers can improve the mechanical performance of unreinforced thermoplastics to a high degree. Components made of thermoplastic composites are typically subjected to complex loadings in applications including static, cyclic, thermal, and their combinations. These applications may also involve environmental conditions such as elevated temperature and moisture which can dramatically affect their mechanical properties. This study investigated tensile, creep, fatigue, creep-fatigue interaction, and thermo-mechanical fatigue (TMF) behaviors of five thermoplastic composites including short glass fiber reinforced and talc-filled polypropylene, short glass fiber reinforced polyamide-6.6, and short glass fiber reinforced polyphenylene ether and polystyrene under a variety of conditions. The main objectives were to evaluate aforementioned mechanical behaviors of these materials at elevated temperatures and to develop predictive models to reduce their development cost and time. Tensile behavior was investigated including effects of temperature, moisture, and hygrothermal aging. Kinetics of water absorption and desorption were investigated for polyamide-6.6 composite and Fickian behavior was observed. The reductions in tensile strength and elastic modulus due to water absorption were represented by mathematical relations as a function of moisture content. In addition to moisture content, aging time was also found to influence the tensile behavior. A parameter was introduced for correlations of normalized stiffness and strength with different aging t (open full item for complete abstract)

Doctor of Philosophy, University of Akron, 2014, Mechanical Engineering

The response of single-curvature composite panels under external blast was studied. For the single-curvature composite shells under external pressure pulse loading, Lagrange’s equations of motion were established to determine the shell response and the Budiansky-Roth criterion was used to examine the instability. The predicted transient shell response compared very well with FEA results from ABAQUS Implicit, and the predicted buckling loads also agreed with experiments on steel arches. Under various load durations, buckling was impulsive, dynamic and quasi-dynamic. Thicker composite shells were more likely to fail by first-ply failure rather than buckling. It was shown that the composite lay-up could be adjusted to increase the buckling resistance of the shell. For the single-curvature composite sandwich panels under external pressure pulse loading, a multi-layered approach was used to distinguish facesheets and core deformations. Core compressibility and transverse shear through the thickness were accounted for using linear displacement fields through the thickness. Equations of motion for the facesheet transient deformations were again derived from Lagrange’s equations of motion, and predicted solutions using this approach compared very well with FEA results from ABAQUS Implicit. In the case of core undergoing elastic deformations only, both facesheet fracture during stable deformation response and local dynamic pulse buckling of facesheets were considered as possible modes of failure in the curved sandwich panel. It was found that local facesheets buckling is more likely to occur than facesheet fracture in thin and deeply curved sandwich panels. The facesheet laminate lay-up could also be adjusted to improve the local buckling resistance of the curved sandwich panel. In the case of the core undergoing elastic-plastic deformations, a parametric study showed that blast resistance of the curved sandwich panel can be increased by allowing cores to un (open full item for complete abstract)

MS, University of Cincinnati, 2013, Engineering and Applied Science: Mechanical Engineering

Laminated composite materials have gained wide use in a vast range of high strength engineering applications due to the high specific strength and stiffness of composites. However, composites have a critical limitation which is their susceptibility to matrix micro cracking and delamination which can lead to premature failure at stress levels significantly below the tensile strength of the composite. Laminated composites also have low through-the-thickness strength and conduction properties which are important for aerospace vehicles and the military defense industry. These fundamental weaknesses in FRPC can be mitigated by the use of (CNTs) as a secondary reinforcement phase due to its excellent mechanical, electrical and thermal properties. In addition, the nano-reinforcement architecture will add significant multifunctionality to laminated composites. In this thesis, different reinforcement architecture are being investigated to improve the structural properties of laminated composite materials. The first approach investigated to improve the interlaminar and flexural strength of composites was to reinforce the laminate interlayers using a short and dense CNT array. The CNT arrays toughen the matrix rich regions. A vertically aligned carbon nanotube (VACNT) laminated composite which consists of Multiwalled Carbon Nanotube (MWCNT) arrays are transferred unto IM7/977-3 carbon fiber prepreg and plies are stacked up to create a hybrid laminated composite material. A complete wetting of the short MWCNT array by the epoxy from the prepreg was sufficient to create a new interface which yielded higher interlaminar properties. Mechanical and SEM characterization of these composite materials was performed under different loading conditions which include interlaminar and in-plane shear, bending, and in-plane tension. The second phase of reinforcement in this work was to improve the interlaminar shear properties of the laminated composite without reducing its in-plane tensile (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2013, Civil Engineering

Material system selection for primary structures requires a decision matrix that evaluates not only the initial design but also the full lifecycle economy. The ability to economically repair structural components over time may control initial design decisions, especially for structures tat are routinely repaired such as aircraft components. Composite materials in their virgin condition often provide substantial mechanical and environmental advantages over metals. However, the repair of composite materials has historically been more costly, time-consuming, and mechanically conservative than metallic repair, and thus is a barrier in the continued advancement of their use. The state of the art of composite repair analysis and substantiation in practice is often limited to simplified and conservative methodologies. While these methods of analysis may be acceptable for secondary or tertiary composite structures, the advancement in analysis of repair for primary composite structures must advance in order for composite materials to become a material system of choice. The state of the art of composite repair analysis and substantiation in published theory has advanced to include displacement-based, nonlinear, and fully three-dimensional finite element models; however, these current models also include geometric, loading, and material model simplifications and limitations that inhibit their general application. Given these limitations, the effective and optimal use of composite materials for primary structures over their complete lifecycle, fully developing the capabilities of their advantages over other material systems, is limited. The research herein documents the development of a composite repair model to advance the state of the art by addressing some of the limitations found in the current literature. A constitutive formulation based on a stress-based laminated plate theory was implemented through a finite element numerical solution algorithm to model the stre (open full item for complete abstract)

Master of Science in Engineering (MSEgr), Wright State University, 2011, Materials Science and Engineering

Improvements of the anode performances in Li-ions batteries are in demand to satisfy applications in transportation. In comparison with graphitic carbons, transition metal oxides as well as graphene can store over twice amount of lithium per gram. Recently, graphene-based anodes for Li-ion batteries are under extensive development. In this research, lithium storage characteristics in graphene oxide (GO), GO/Manganese acetate (GO/MnAc), GO/manganese oxide (GO/MnOx) composites and Nano Graphene Platelets (NGP) were studied. The prepared GO delivered reversible capacities of 706mAh/g with an average columbic efficiency of 87%. Reversible capacities of 533 mAh/g were observed for GO/MnAc composite. GO/MnOx nanocomposite thermal annealed at 400°C in inert atmosphere exhibited high reversible charge capacity of 798 mAh/g with an average columbic efficiency of 95% and capacity fade per cycle of 1.8%. The EIS spectra of discharge and charge profiles of GO and GO/MnOx composites were analyzed to investigate the kinetics evolution of electrode process at different stages of lithium storage.

PhD, University of Cincinnati, 2000, Engineering : Aerospace Engineering

The ultimate goal of the present research is to come up with an accurate and efficient analysis approach for composite and sandwich shells, which is simple enough to be capable of implementing into a FE code without significantly affecting its computational efficiency, and at the same time gives good accuracy in predicting the behavior of layered shells. It has to be capable of accurately modeling both overall behavior, and the local distribution of strains and stresses in all layers and all constituents in the composite laminae. Two different approaches are utilized in the attempt to fulfill the final research objective of the present work. First, a homogenization procedure for the FE analysis of sandwich shells is developed. The procedure works on the material constitutive level. A homogenization of the sandwich shell is performed at each call of the corresponding constitutive subroutine. Thus the sandwich nature of the problem is hidden from the main FE program. As a consequence there is no need to develop a new shell element formulation, but instead the available homogeneous shell elements in the utilized FE code can be used for the analysis of sandwich shells. However, the defined homogenization procedure works with first order shear deformable shell elements, which sets a limit to the accuracy with which the transverse distribution of the unknowns is represented. To overcome this, a higher order shear deformable shell element is formulated and implemented into a general nonlinear explicit FE code. Using the differential equilibrium equations and the interlayer requirements, special treatment is developed for the transverse shear, resulting in a continuous, piecewise quartic distribution of the transverse shear stresses through the shell thickness. A similar approach is applied to the transverse normal stresses, which are represented by a continuous piecewise cubic function. The FE implementation is cast into a 4-noded quadrilateral shell element with 9 degrees (open full item for complete abstract)

MS, University of Cincinnati, 2005, Engineering : Mechanical Engineering

Carbon nanotubes (CNT) are being used extensively as reinforcing materials at nanoscale in developing new nanocomposites, because of their excellent mechanical properties. Incorporating CNTs in polymer matrices can potentially enhance the stiffness and strength of composites significantly when compared to those reinforced with conventional carbon fibers. However, retaining these outstanding properties at macro-scale poses a considerable challenge. To discover the ways for achieving this entails extensive experimental and simulation studies. Molecular dynamics (MD) simulations have been proved to be an excellent approach in characterizing nanocomposites. Nevertheless, MD is limited to nanoscale due to its extra-ordinary computational costs, which promoted the development and usage of alternate approaches for characterizing CNT reinforced composites at microscale. In this research one of these alternative approaches, the continuum mechanics approach using the finite element method, is employed to estimate the effective modulus of CNT reinforced composites and was successfully validated using other analytical (rule of mixtures) and MD methods. Large-scale models were developed, simulating CNTs using pipe elements for the first time. Results from these models reveal that there exists a limiting value for the length of long CNT, for effective load transfer. It was also observed that composites reinforced with long CNTs yield very high effective modulus compared to those with short CNTs. These results are found to be in good agreement with those obtained using MD and multi-scale constitutive modeling approaches.

PhD, University of Cincinnati, 2005, Engineering : Materials Science

In this project, phase transformations and precipitation behavior of Al-Cu nanoparticles were first studied. The nanoparticles were synthesized by a Plasma Ablation process and found to contain a 2∼5 nm thick adherent aluminum oxide scale, which prevented further oxidation. On aging, a precipitation sequence consisting of, nearly pure Cu precipitates to the metastable θ′ to equilibrium θ was observed. The structure of θ′ and its interface with the Al matrix has been characterized. Ultrafine Al-Cu nanoparticles (5∼25 nm) were also synthesized by inert gas condensation and their aging behavior was studied. These particles were found to be quite stable against precipitation. Secondly, pure Al nanoparticles were prepared by the Exploding Wire process and their sintering and consolidation behavior were studied. It was found that Al nanopowders could be processed to bulk structures with high hardness and density. Sintering temperature was found to have a dominant effect on density, hardness and microstructure. Sintering at temperatures >600 degree C led to breakup of the oxide scale, leading to an interesting nanocomposite composed of 100∼200 nm Al oxide dispersed in a bimodal nanometer-micrometer size Al matrix grains. And the randomly dispersed oxide fragments were quite effective in pinning the Al grain boundaries, preventing excessive grain growth and retaining high hardness. Cold rolling and hot rolling were effective methods for attaining full densification and high hardness. Thirdly, the microstructure evolution and mechanical behavior of Al-Al2O3 nanocomposites were studied. The composites can retain high strength at elevated temperature and thermal soaking has practically no detrimental effect on strength. Although the ductility of the composite remains quite low, there was substantial evidence for high localized plasticity. The strengthening mechanisms of the composite include: Orowan strengthening, grain size strengthening and forest strengthening. Finally, (open full item for complete abstract)

MS, University of Cincinnati, 2005, Engineering : Mechanical Engineering

Since their discovery in 1991, carbon nanotubes have been the focus of considerable research due to their remarkable physical and mechanical properties reported. This form of carbon has potential applications in numerous conventional and new areas - light-weight structural materials being just one of them. The strength to weight ratio of carbon nanotubes is higher than any currently known material; hence their use to reinforce polymers has been of great interest. This research concentrates on molecular mechanics simulations of carbon nanotubes and their application as reinforcing fibers in polymer composites. The systems being investigated consist of amorphous as well as crystalline polyethylene composites with embedded single-walled carbon nanotube. Various scenarios of deformation and fracture are observed, in accordance with experimental and previously published simulation results. Adhesion at the nanotube – polyethylene interface, the key to effective load transfer, is studied for crystalline as well as amorphous polyethylene systems. Further, fractures in carbon nanotube reinforced nanocomposites are simulated. The tensile properties of amorphous and crystalline polyethylene are studied and compared with nanotube-reinforced composites.

PhD, University of Cincinnati, 2002, Engineering : Materials Science

This work was focused on the investigation of charge and discharge properties of polypyrrole/polyimide (PPy/PI) composites. Capacitive and accumulative properties of PPy/PI composites were studied in details targeting application of the composite in polymer based charge storage devices: supercapacitors and polymer batteries. Polyimide was chosen as a matrix because of its excellent mechanical properties and electroactivity. Composites were prepared electrochemically on stainless steel, and studied by potential step amperometry and electrochemical impedance spectroscopy. The composition of the composite was studied by FTIR. Mechanism for PAAc conversion to PI was studied by FTIR ands DSC. Morphology was determined by SEM. Doping-dedoping of PPy in the composite in competition with doping-dedoping of PI along with formation of double electric layers were found to be responsible for a difference between discharge behaviors of PPy and PPy/PI composite. Charge storage ability was greatly affected by PPy. PPy along with factor of preconversion of poly(amic acid) (PAAc) matrix to PI was found to play a key role in charge storage properties of PPy/PI composite. DC polarization was found to alter the supercapacitance of the composite. Two mechanisms: orientation polarization and ion jump polarization were suggested to be responsible for supercapacitance in double electric layer. PPy/PI composite can be considered as a promising material for use in supercapacitors as a material for active polymer electrodes in polymer batteries. Additional advantage of use of PPy as a filler for PI matrix is the reduction of activation energy to conversion to polyimide. This was shown by differential scanning calorimetry and FTIR. Activation energy of the reaction of imidization can be reduced significantly by the presence of PPy.

MS, University of Cincinnati, 2002, Engineering : Materials Science

Polymer/Ceramic composite films were fabricated using Polyimide and PZT (90/10) and studied for their physical and electrical properties. The homogeneous and oriented composite films were fabricated by combining a spin deposition technique for polyimide with the novel metal-organic deposition technique for PZT. A RTA furnace was used to sinter the PZT films without damaging the Polyimide to fabricate an alternate PI/PZT layer structure. The effect of unpolymerised polyimide, polymerized polyimide, Pt/Si substrate and heating rate on the orientation of the PZT film was studied. X-ray diffraction and SEM techniques were used to determine the orientation, microstructure development and the thickness of the resulting composite structure. Thermal behavior of polyimide and PZT precursor solution was determined by using Thermogravimetric Analysis and Differential Scanning Calorimetry. Results indicate that use of RTA furnace with a heating rate of 110°C/s, instead of a regular furnace for sintering of the PZT layer, produced oriented PZT layers without damage to the Polyimide layers. Using a polymerized Polyimide film resulted in [111] and [101] oriented PZT film. The dielectric properties and electrical stability of composite films with different number of layers, or with the same number of layers but different fabrication methodology, was investigated. The Composite films were highly resistive as expected, since polyimide itself is very resistive, (volume resistiviy>10 16 ). All the films sintered in the RTA furnace were stable up to field strength 10 4 V/cm. The film capacitance and dielectric properties followed a logarithmic mixing rule. They all exhibited capacitance values of 0.3-0.4 nfarads, greater than polyimide films but smaller than typical PZT films. Very low loss (0.02-0.06) was also observed. Annealing of the composite structure after fabrication resulted in lowering of the loss values in the unannealed samples. The capacitance values were not significantly (open full item for complete abstract)

Doctor of Philosophy, University of Akron, 2012, Civil Engineering

The characterization of carbon/epoxy 2D triaxial braid composites is a critical area of research for aerospace components, including jet engine fan blade containment. These materials exhibit high strength to stiffness, high damage tolerance, and a favorable impact response. This is due, in part, to the material behaving like a structure once damage occurs because of the mechanical interlocking and large unit cell of the fabric architecture. This, in turn, complicates the results and interpretation of coupon based mechanical testing because the desired uniaxial stress state is unavoidably lost within the material after the onset of damage. Though this same process will likely occur in structures, it has been shown in standard coupons that the existence of free edges can lead to premature initiation of local damage that leads to early failure. Therefore, many different methods will be needed to obtain reliable mechanical response data for use in models and structural design. The goal of this research is to attempt to bridge part of the gap between coupon level testing and structural component tests. An in depth examination of tension, compression, and shear coupon test methods for generating stiffness, strength, and non-linear material response parameters has been performed. Additionally, the use of tubular specimens under various load conditions assisted in validation of alternate coupon geometries, as well as evaluating the utility of current cross-ply laminate test standards. Also, damage mechanisms, as they relate to global response, are considered. The particular materials of interest (similar to braid architectures used in jet engine containment structures) have a large unit cell size which requires the use of relatively large tube specimens. To meet the “to failure” load requirements of these specimens, a custom high load, multiaxial test frame was designed, machined, and constructed. Control and data acquisition was achieved using National Instruments cDAQ har (open full item for complete abstract)

Master of Science, Miami University, 2025, Mechanical Engineering

Polydimethylsiloxane (PDMS), a versatile silicon-based polymer, is widely used in biomedical devices, microfluidic systems, wearable technology, and electronics due to its mechanical flexibility, optical clarity, electrical conductivity, and biocompatibility. However, its low Young's modulus and tensile strength limit its application in high-stress environments. To enhance its mechanical and functional properties, this study explores the incorporation of carbon fibers (CF) and graphene (Gr) as reinforcements. Despite the potential benefits of these nanomaterials, challenges such as aggregation, void formation, and poor interfacial bonding often compromise composite performance. This research integrates acoustic field (AF) technology into inkjet-based additive manufacturing (AM) to address these issues. The AF enhances material dispersion, reduces defects, and improves bonding between reinforcements and the PDMS matrix. The study evaluates the effects of CF and Gr reinforcements with AF treatment on the mechanical, microstructural, and dynamic properties of PDMS composites. Furthermore, it investigates the impact of different percentages of graphene content on the electrical resistance and mechanical properties graphene-reinforced-PDMS for wearable sensor applications. Results demonstrate that optimal graphene content balances dispersion and aggregation, thus, maximizing mechanical strength and electrical conductivity. By introducing AF-assisted AM, this study provides insights into producing high-performance PDMS composites for advanced applications, particularly in sensors and flexible electronics.

Master of Sciences (Engineering), Case Western Reserve University, 2025, Macromolecular Science and Engineering

Hexagonal boron nitride is a platelet-like thermally conductive filler commonly used to increase the thermal conductivity of polymers. Good alignment of boron nitride in the in-plane direction is required to create a good network for phonon transport to achieve high thermal conductivity in composite materials. To create good alignment of platelet-like particles, extensional flow is needed, like what is experienced by a polymer melt in a layer multiplication element in forced assembly co-extrusion. As a result, films with A/B structure of hBN + polymer/unfilled polymer were made using layer multiplication co-extrusion. The high degree of alignment and confinement of boron nitride into every other layer led to a higher-than-expected thermal conductivity at relatively low loadings of boron nitride. At only 12.7vol% (25wt%) filler loading, a composite film reached a thermal conductivity of 3.41 Wm-1K-1 which is much higher than was predicted by modeling.

Master of Science, The Ohio State University, 2007, Graduate School

Master of Science, The Ohio State University, 2007, Graduate School

Master of Science, The Ohio State University, 2007, Graduate School