MS, University of Cincinnati, 2012, Engineering and Applied Science: Mechanical Engineering

Paper is an everyday product used for various reasons by the consumer. This study focuses on a low basis weight nonwoven paper substrate used as toilet paper. Paper manufacturers are always trying to increase line speed to push out more paper at the same cost and the manufacturing process this research focuses on is the embossing process. This study will focus on determining the rate dependent in-plane constitutive relations that define the mechanical behavior of the paper substrate in tension. Once the constitutive models are created they can be imported into a finite-element software package and used to study changes made to the embossing process. Experimental tests were run in order to isolate specific properties of the material. Uniaxial tension tests were run at 0.1 1/s, 4.5 1/s and 45 1/s total engineering strain rates in order to determine the rate dependent effects on the material. Stress relaxation tests were run at varying moisture contents and temperatures with the idea of determining the viscoelastic model and how moisture and temperature affect the material. Viscoelastic and viscoplastic behavior models were developed to characterize the rate dependencies in the elastic and plastic regions of the material. A generalized Maxwell model is used to model the viscoelastic region and a modified form of G'sell's flow stress law was used in conjunction with the viscous based overstress theory (VBO) to define the viscoplastic region. The research done on this paper substrate details a method to define the rate dependent constitutive properties of any fiber network material through an experimental study.

Committee: Yijun Liu PhD (Committee Chair); Richard W. Hamm MS (Committee Member); Kumar Vemaganti PhD (Committee Member) Subjects: Engineering

MS, University of Cincinnati, 2011, Engineering and Applied Science: Mechanical Engineering

High density polyethylene (HDPE) is a common polymer material that is widely used in industrial applications. While significant amount of efforts have been devoted to understanding the constitutive behavior of HDPE, very little work has been performed to investigate the material response of HDPE at high strain rate and high temperature. The main objective of this research is to develop a constitutive model to bridge this gap by focusing on the non-linear stress-strain behavior in the high strain rate and high temperature range. A series of monotonic uniaxial compressive tests have been conducted at high temperature (100°C) and high strain rate (1/s) to characterize the HDPE behavior. Based on the experimental results, existing hyperelastic material models such as Mooney-Rivlin, Ogden, Arruda-Boyce, are assessed with the use of ABAQUS (a finite element software). Based on extensive comparisons, a new three-dimensional constitutive model for HDPE has been proposed. The constitutive equation integrates the basic mechanisms proposed by Boyce et al. [6] and Shepherd et al. [8]. The total stress is decomposed into an elastic-viscoplastic representation of the intermolecular resistance acting in parallel with a time and temperature dependent network resistance of polymer chains. Material constants involved in the model were calculated by fitting the compressive test results to the proposed constitutive equations. A constitutive solver for the proposed model has been developed. The stress-strain relation resolved from the constitutive model closely matches the corresponding ones from the experiments.

Committee: Dong Qian PhD (Committee Chair); Shepherd Shepherd PhD (Committee Member); Yijun Liu PhD (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2011, Mechanical Engineering

Magnetostrictive materials deform in response to applied magnetic fields and change their magnetic state when stressed. Because these processes are due to moment realignments, magnetostrictive materials are ideally suited for sensing and actuation mechanisms with a bandwidth of a few kHz. Significant research effort has been focused on two magnetostrictive alloys: Terfenol-D (an alloy of terbium, iron and dysprosium) and Galfenol (an iron gallium alloy), for their ability to produce giant magnetostrictive strains at moderate fields. Terfenol-D has higher energy density and magnetomechanical coupling factor than Galfenol but it is brittle and suffers from poor machinability. Galfenol on the other hand has excellent structural properties. It can be machined, welded, extruded into complex shapes for use in transducers with 3D functionality. Advanced modeling tools are necessary for analyzing magnetostrictive transducers because these materials exhibit nonlinear coupling between the magnetic and mechanical domains. Also, system level electromagnetic coupling is present through Maxwell's equations. This work addresses the development of a unified modeling framework to serve as a design tool for 3D, dynamic magnetostrictive transducers. Maxwell's equations for electromagnetics and Navier's equations for mechanical systems are formulated in weak form and coupled using a generic constitutive law. The overall system is approximated hierarchically; first, piecewise linearization is used to describe quasistatic responses and perform magnetic bias calculations. A linear dynamic solution with piezomagnetic coefficients computed at the bias point describes the system dynamics for moderate inputs. Dynamic responses at large inputs are obtained through an implicit time integration algorithm. The framework simultaneously describes the effect of magneto-structural dynamics, flux leakages, eddy currents, and transducer geometry. Being a fully coupled formulation, it yields system lev (open full item for complete abstract)

Committee: Marcelo Dapino PhD (Advisor); Ahet Kahraman PhD (Committee Member); Junmin Wang PhD (Committee Member); Rajendra Singh PhD (Committee Member) Subjects: Electromagnetics; Electromagnetism; Mechanical Engineering; Mechanics

Master of Science (M.S.), University of Dayton, 2023, Mechanical Engineering

Fluoroelastomers can maintain their stretchability and elasticity at high temperatures, making them well-suited for applications that require extreme thermal resistance. Presently, there is significant interest in casting compounded fluoroelastomers to create high-temperature seals with intricate geometric features. It is not well understood, however, how these materials will perform mechanically in service as they undergo repeated heat cycling and are subjected to complex, multi-axial stress states. To address this research opportunity, a suite of commercially available compounded fluoroelastomers were thermally aged (10, 20, 50 cycles at 200 °C for 8 hours) and mechanically tested in uniaxial tension and uniaxial compression. Preliminary room-temperature uniaxial tension results displayed increases in strength and elastic modulus with modest heat cycling (20 cycles), followed by a subsequent decrease in strength at large amounts of heat cycling (50 cycles). Even at 50 cycles, however, the heat-conditioned materials still exhibited greater strength than the unconditioned materials. This mechanical response is likely due to a competition between the chemical mechanisms of polymer cross-linking and chain scission, with strength degradation at large amounts of heat cycling reflective of chain scission dominating cross-linking. From this suite of candidate materials, the compounded commercial fluoroelastomer FKM Viton A-500 RB75A5 was downselected for the desired sealant application and subsequently tested at elevated temperatures (85, 140, 200 °C) in uniaxial tension to better understand its behavior in extreme environments. Lower mechanical strength and reduced elongation were observed in the material's elevated temperature response. This is likely because the higher temperatures result in shorter polymer chains, which corresponds to a higher entropy state and a weaker, lower-elongation material. Additional room-temperature tests were performed on Viton RB75A (open full item for complete abstract)

Committee: Robert Lowe (Committee Chair); Donald Klosterman (Committee Member); Chad Jones (Committee Member); Allyson Cox (Committee Member); Thomas Whitney (Committee Member) Subjects: Materials Science; Mechanical Engineering; Mechanics

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

As emission standards of passenger vehicles become more and more strict, automotive manufacturers are seeking lightweight solutions to increase vehicle's fuel economy. Fibrous reinforced polymers (FRPs) are known to have high strength to weight ratios, and thus, made them good candidates for the application in the automotive industry. FRP is a composite material made of a polymer matrix reinforced with fibers. The inhomogeneity, anisotropy, visco-elasticity/plasticity, mechanical degradation due to temperature/damage, brittleness characteristics of the unidirectional FRP composites bring challenges to determine mechanical responses both experimentally and numerically. In this dissertation, mechanical behavior of unidirectional carbon fiber reinforced polymer (CFRP) made of Toray T700S carbon fiber and G83-CM prepreg system is studied. Specimens are fabricated from 8-ply and 16-ply CFRP plates. An experimental series is performed including tension, compression, and shear coupon tests at various strain rates ranging from 0.001 to 1000 s-1. Anisotropy is studied by conducting tension, compression, and shear coupon tests in different fiber orientations. Thermal dependence of the material is investigated by performing coupon tests under temperatures ranging from 25 °C to 120 °C. CFRP has been found that loading in one direction can potentially lead to damage in other directions. Thus, coupled, and uncoupled damage testing is performed to characterize such behavior. Digital image correlation (DIC) is applied for deformation and strain measurement on the surface of the specimens. The coupon test data and damage test data are used to calibrate the deformation and damage sub-models of the constitutive material model, *MAT_COMPOSITE_TABULATED_PLASTICITY_DAMAGE, also called *MAT_213, in LS-DYNA. The deformation sub-model predicts elasto-plastic behavior, and it uses a strain-hardening-based orthotropic yield function with a non-associated flow rule extended from Tsai-Wu fail (open full item for complete abstract)

Committee: Amos Gilat (Advisor); Prasad Mokashi (Committee Member); Kelly Carney (Committee Member); Jeremy Seidt (Committee Member) Subjects: Mechanical Engineering

Master of Science (M.S.), University of Dayton, 2021, Mechanical Engineering

Additive manufacturing (AM) is a novel and powerful manufacturing technique that is revolutionizing the way we produce different products. Among the various existing AM techniques, the digital light processing (DLP) has gained significant attention due to its ability to produce 3D parts with complex design and functionalities with high level of accuracy, ease, and precision. Soft elastomeric materials, on the other hand, have a wide variety of applications in different areas e.g., soft robotics, biomimetic systems, flexible electronics due to its unique characteristics of flexibility, elasticity, and inertness. Hence, the prospect of manufacturing soft elastomeric products with DLP AM technique offers exciting possibilities in these diverse areas of application. This thesis aims to explore the mechanical properties and dynamic behaviors of such soft elastomeric materials that can be constructed with DLP AM method. The objective is to develop a basic understanding of the mechanics and dynamics of UV-curable and DLP-printed soft elastomer materials. Variation in mechanical properties due to different DLP process-parameters settings has been investigated for a commercially available elastomer resin. Different hyperelastic constitutive models have been calibrated with uniaxial tension testing data of four different DLP-printed soft elastomer specimens. A comparative study of the models in reproducing experimental data has been carried out to facilitate predictive analysis. Finally, the dynamics of a thin-shell soft DLP-printed elastomeric membrane has been investigated through numerical analysis of stretch response behavior upon the application of sudden internal inflation and deflation pressures.

Committee: Robert Lowe (Advisor); Christopher Cooley (Committee Member); Timothy Osborn (Committee Member); Laura Sowards (Committee Member); Andrew Murray (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, University of Akron, 2021, Civil Engineering

Numerous constitutive models have been developed over the past 5 decades for modeling voided materials under different types of loadings and tests. Since the effective use of these materials rests on the comprehensive understanding of the factors which influence their performance under various practical conditions, different experimental and computational efforts have been made towards such exercise. In this research many aspects of pressure sensitive materials, such as material behavior and its performance in a practical application are studied using a newly developed three-dimensional general model with an eye towards civil engineering voided materials such as different types of soils and concrete. Firstly, the integral part of this study lies in the suitable mathematical formulation of the voided materials model for easy implementation, exact computation and effective utilization in commercial finite element codes. In particular, to embrace all the different levels of complexities regarding the voided materials, i.e., from material point characterization to large-scale analyses of devices, the constitutive model is established for both implicit and explicit-time integration algorithms. This allows smooth adaptation of the model for wide range of initial/boundary value problems, i.e., from simple to complex cases without any severe computational cost and unnecessary loss of accuracy. Secondly, the formulated model is calibrated to characterize a number of the essential responses seen among the different types of voided materials under different loading conditions. These aspects are heavily depended on the availability of experimental data for the various types of voided materials, such as different types of soils and concrete. Finally, the more challenging behavior of these materials is that the shear strength of these materials is dependent on several factors, such as the confining pressure, over consolidation ratio, loading rate, permeability of a particul (open full item for complete abstract)

Committee: Atef Saleeb (Advisor); Ala Abbas (Committee Member); Wieslaw Binienda (Committee Member); Nariman Mahabadi (Committee Member); Jun Ye (Committee Member) Subjects: Civil Engineering

Doctor of Philosophy, The Ohio State University, 2018, Materials Science and Engineering

Lightweighting is used throughout the transportation industry and is an increasingly popular method to increase fuel economy in both automotive and aerospace applications. Magnesium has the lowest density of any structural metal and is an attractive option for substitution into aluminum or steel structures. Aluminum-lithium alloys are also attractive, as they boast lower density, higher modulus, and relatively good strengths compared to conventional aluminum alloys. For different metallurgical reasons, both materials have significantly anisotropic mechanical properties, which limit their formability and service life applications. For both Mg alloys and Al-Li alloys, improved primary processing can address the properties which restrict these materials' use. This work aims to make processing recommendations for a Mg-RE alloy and an Al-Li alloy based on relevant deformation traits or microstructural processes in the warm forming regime. Simple mechanical models which can inform industrial processing are also presented.

Committee: Alan Luo (Advisor); Rudolph Buchheit (Committee Member); Stephen Niezgoda (Committee Member) Subjects: Materials Science

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

The objective of this research was to investigate the mechanical behavior of Divinycell PVC H100 foam under combined cyclic compression-shear loading, and to develop material constitutive models to predict response of the foam under these conditions. Structural polymeric foams are used for the core of sandwich structures in aerospace, marine, transportation, and other industries. They are valued for enabling high specific stiffness and strength as well as energy absorption and impact resistance of sandwich structures. This research addresses energy absorption of the foam due to plastic collapse, damage and hysteresis. Experiments were done to obtain out-of-plane mechanical properties of Divinycell PVC H100 foam under cyclic compression-shear loading. Stress-strain curves for the Divinycell PVC H100 foam under various combinations of compression-shear deformation and deformation rates were obtained. Rate-dependent behavior was observed before and after foam yielding. Yielding and damage in the foam occurred simultaneously. Foam yielding was associated with permanent change in cell micro-structure either by buckling cell walls when the foam is under compression or by bending and stretching cell walls when they were under shear. The Tsai-Wu failure criterion was shown to be a good predictor of yielding and damage initiation. The foam produced hysteresis either due to viscoelasticity and/or viscoplasticity if it was allowed to undergo reverse yielding during unloading and reloading. A phenomenological model was developed to describe the behavior of PVC H100 foam. This model consisted of a standard linear material model for viscoelastic response before yielding/damage initiation. After yielding/damage initiation, combined plastic flow and damage was modeled by modifying the viscoelastic properties of the standard linear model with damage properties and adding a viscoplastic element in series with it in order to control the plastic flow stress. Tsai-W (open full item for complete abstract)

Committee: Michelle Hoo Fatt (Advisor); Gregory Morscher (Committee Member); Kwek-Tze Tan (Committee Member); Anil Patnaik (Committee Member); Kevin Kreider (Committee Member) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 2014, Mechanical Engineering

The ability to accurately computationally predict the end properties of Poly(Ethylene Terephthalate) (PET) based components is of immense use to the packaging industry to reduce product development and lifecycle costs. One activity being undertaken prominently by the industry is the development of PET bottles to maximize the shelf life of beverage-filled bottles. This thesis deals with the development of a material model of PET for use in finite element simulation of blow molding. The mechanical behavior of PET is highly non-linear with temperature dependence, strain-rate dependence, molecular weight (Inherent Viscosity – IV) dependence, strain-state dependence and the tendency when induced by strain to crystallize. Uniaxial compression experiments were conducted on PET samples to characterize the temperature, strain-rate and IV dependence of stress-strain characteristics. The temperature range for the tests was 363K to 383K, the (true) strain rates used were 0.1/s and 1/s and the IVs of samples used were 0.80, 0.86, 0.92 and 0.98. The Dupaix-Boyce (DB) model (Dupaix, 2003) is a complex physically-based material model which can capture the viscoelastic, hyperelastic and plastic aspects of polymer mechanical behavior. This model was fit to the compression test results. Furthermore, uniaxial tension tests were conducted to check the predictive capability of the compression fit DB model in tension. The model under-predicted stress in tension and a different set of constants had to be used to fit the initial portion of the DB model stress strain results to the experimental curves. The temperature range for the tension tests was the same as for the compression tests while the strain rates used were 0.05/s, 0.1/s and 0.425/s engineering strain rate. The IVs used were 0.80, 0.92 and 0.98. A major observation from the uniaxial tension tests was the inability of the DB model to capture drastic strain hardening associated with strain-induced crystallization. Th (open full item for complete abstract)

Committee: Rebecca Dupaix (Advisor); Brain Harper (Committee Member) Subjects: Mechanical Engineering; Polymers

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

The focus of this research is to develop a framework to track damage evolution in a structural model subjected to a fatigue environment. This framework incorporates a micromechanical approach of continuous damage modeling, where damage in a homogenized representative microstructure is introduced at the continuum scale through the material constitutive matrix. In this research, damage in the representative microstructure is simulated utilizing cohesive zone models (CZM) whose properties are a function of the magnitude of applied stresses and the resulting separation. In order to minimize the mesh dependence of the cohesive zone model an adaptive meshing technique is employed. A fatigue simulation is performed to demonstrate the capability of the framework to predict the initiation and evolution of damage.

Committee: Ravi Penmetsa PhD (Advisor); Nathan Klingbeil PhD (Committee Member); Joseph Slater PhD (Committee Member); George Huang PhD (Other) Subjects: Engineering; Mechanical Engineering

PhD, University of Cincinnati, 2001, Engineering : Engineering Mechanics

Fibro-cartilage metaplasia occurs in tendons that wrap around bony protruberances in the skeletal system. Within these regions of contact, tendons undergo a process of structural adaptation (i.e metaplasia) into fibrocartilage. The mechanobiology of this transformation is key to developing a scientific understanding of structure-biomechanical function relationships in load bearing tissues. It is also of relevance in the area of "Functional Tissue Engineering" wherein controlled mechanical signals are delivered to a cell therapy based construct to induce synthesis of appropriate extracellular matrix components. Malaviya et al [2000] conducted in vivo experiments on reversing the formation of fibrocartilage in the rabbit flexor digitorum profundus tendon. This was achieved by translocating the tendon surgically away from its bony contact, which transformed the fibrocartilage (FC) region back to a tissue with tendon like characteristics. Developing an understanding of this unique transformation is the central theme of this dissertation. The path towards developing a fundamental mechanics based understanding of the effect of translocation involved the formulation of an anisotropic poro-hyperelastic constitutive description of the fibrocartilage zone of the tendon. This constitutive model was implemented into an existing finite element code (ABAQUS™) for conducting poroelastic structural analysis of the tendon-fibrocartilage complex under realistic in vivo loading conditions. Changes that occurred to fluid pressures, fiber stresses, and dilatational and distortional stresses in the extrafibrillar matrix as a result of translocation surgery were investigated. Based on the results seen, it appears that we can now advance a concept, i.e., fibrocartilage metaplasia most likely occurs in a tissue that is required to sustain large intermittent hydrostatic as well as distortional stresses, which may or may not act in unison. Cyclic hydrostatic stresses induce a cellular differe (open full item for complete abstract)

Committee: David L. Butler (Advisor) Subjects: Engineering, Biomedical

MS, University of Cincinnati, 2011, Engineering and Applied Science: Mechanical Engineering

Safety glass is an important tool in protecting people in event of an attack or accident. Therefore predicting it's accurate response is the key to study blast mitigation and crash events. Glass is brittle and cannot withstand large strains, thus the polymeric interlayer acts as a membrane providing additional energy absorption. Here we develop constitutive models for rubber and glass, the two main constituents of safety glass, which can also be used independently for other applications not limited to the architectural and automotive industry. We present a phenomenological model for rubber which can not only predict the primary hyperelastic and viscoelastic behavior at low to high strain rates, but also takes into account hysteresis and Mullins effect. The model for rubber is consistent with the laws of continuum mechanics and can successfully predict the response of a wide range of polymers using a limited set of experimental data. The model for glass is inspired from ceramic like brittle materials. Finally, we study the impact simulation of safety glass using the standard material models from the LS-DYNA library, specifically made up of polyvinyl butrayl and float glass.

Committee: Ala Tabiei PhD (Committee Chair); David Thompson PhD (Committee Member); Kumar Vemaganti PhD (Committee Member) Subjects: Mechanics

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

Multifunctional structures based on active or smart materials are being implemented in a wide range of aerospace, infrastructural, automotive, and biomedical applications. However, smart materials are underutilized in these applications, as majority of the modeling and characterization techniques of smart materials limit the understanding of material behavior to low-signal, small-deformation ranges of operation, or regimes where only a subset of the thermal, electrical, magnetic, and mechanical interactions are dominant. By modeling smart materials in their fully coupled, nonlinear, three-dimensional, multiphysics process domain rather than in a specific regime of behavior, design of the next-generation of load-carrying smart structures with superior performance capabilities can be enabled. This dissertation focuses on development of a first-principle based theoretical framework for modeling and characterization of fully coupled thermo-electro-magneto-mechanical behavior in a multiphysics process domain, that can be utilized to (i) develop constitutive models and free energy functions for a broad range of smart materials using the fundamentals of equilibrium and non-equilibrium thermodynamics, (ii) develop asymptotic models for design and analysis of load-bearing antenna, which is a multifunctional actuating and receiving device integrated with a load-bearing structure. Part (i) focuses on development of a unifying thermodynamic framework for multifunctional materials with fully coupled thermo-electro-magneto-mechanical response. This framework consists of a comprehensive catalogue of all possible state variables, thermodynamic potentials, and state equations that characterizes TEMM processes. This unifying framework applicable to a general polarizable, magnetizable and deformable media, is then utilized to develop material response functions for a wide range of materials, i.e., (i) elastic, lossless dielectric, piezoelectric materials (approximately reversible), (open full item for complete abstract)

Committee: Stephen Bechtel PhD (Advisor); Marcelo Dapino PhD (Advisor); Rama Yedavalli PhD (Committee Member); Joseph Heremans PhD (Committee Member) Subjects: Mechanics

Doctor of Philosophy, University of Akron, 2010, Polymer Engineering

Damage and fatigue of elastomers have not been fundamentally understood because of the complex nature of these materials. All currently existing models are completely phenomenological. Therefore two problems have been investigated in this research to address those fundamental issues. The first problem was creating an innovative concept with a mathematical modeling, which would be able to describe the damage using molecular characteristics of elastomers. The second problem is developing new approaches to study fatigue, and especially impact fatigue of elastomers. The following results have been obtained in this research. A theoretical model of damage has been developed which involves the basic molecular characteristics of cross-linked elastomers and takes into account the effects of viscoelasticity and stress-induced crystallization. This model was found very reliable and successful in description of numerous quasi-static simple extension experiments for monotonous and repeating loadings. It also roughly predicts in molecular terms the failure of elastomers with various degrees of cross-linking. Quasi-impact fatigue tests with different geometry of an indenter have also been performed. Some microscopic features of rubber damage have been investigated using optical microscopy and SEM. In particular, the accumulation of a completely de-vulcanized, liquid-like substance was observed under intense, multi-cycle impacts. All the findings discovered in quasi-impact experiments are consistent with the damage model predictions.

Committee: Arkady Leonov Dr. (Advisor) Subjects: Polymers