Applied Mechanics Commons^™

Controlling Mechanical Properties Of Well-Defined Polymer Networks, Ipek Sacligil

Doctoral Dissertations

Polymer networks are one of the most versatile and highly studied material class that revolutionized many aspects of life. Connecting the final network properties to the molecular parameters of its building blocks remains a major research thrust. Recent advances in network synthesis techniques allowed for accurate predictions of elastic modulus in model networks. Tew Group has developed highly efficient, thiol-norbornene networks with controllable mechanical properties. Chapter 2 focuses on modifying the gel fracture energy predicted by Lake-Thomas theory by accounting for loop defects. This study allowed for a priori estimates of gel fracture energy by combining theory, experiments, and simulations. …

Computational Study Of Internal Flow, Near Nozzle And External Spray Of A Gdi Injector Under Flash-Boiling Conditions, Chinmoy Krushna Mohapatra

Doctoral Dissertations

The early and late portions of transient fuel injection have proven to be a rich area
of research, especially since the end of injection can cause a disproportionate amount
of emissions in direct injection internal combustion engines. While simulating the
internal flow of fuel injectors, valve opening and closing events are the perennial
challenges. A typical adaptive-mesh CFD simulation is extremely computationally
expensive, as the small gap between the needle valve and the seat requires very
small cells to be resolved properly. Capturing complete closure usually involves a
topological change in the computational domain. Furthermore, Internal Combustion
Engines(ICE) operating with …

Synthesis, Fabrication, And Assembly Of Mesoscale Polymer Filaments, Dylan M. Barber

Doctoral Dissertations

Mesoscale materials, with feature sizes in the range of one hundred nanometers to tens of micrometers, are ubiquitous in Nature. In organisms, mesoscale building blocks connect the properties of underlying molecular and nanoscructures to those of macroscale, organism-scale materials through hierarchical assemblies of recurring structural motifs. The collective action of large numbers of mesoscale features can afford stunning features like the structural color of the morpho butterfly wing, calcium ion-mediated movement in muscle, and wood structures like xylem that can support enormous external compressive loads and negative internal pressure to transport nutrients throughout an organism. In synthetic systems, the design, …

Source Data For Self-Spinning Filaments For Autonomously Linked Microfibers, Dylan M. Barber, Todd S. Emrick, Gregory Grason, Alfred Crosby

Data and Datasets

Filamentous bundles are ubiquitous in Nature, achieving highly adaptive functions and structural integrity from assembly of diverse mesoscale supramolecular elements. Engineering routes to synthetic, topologically integrated analogs demands precisely coordinated control of multiple filaments’ shapes and positions, a major challenge when performed without complex machinery or labor-intensive processing. Here, we demonstrate a photocreasing design that encodes local curvature and twist into mesoscale polymer filaments, enabling their programmed transformation into target 3-dimensional geometries. Importantly, patterned photocreasing of filament arrays drives autonomous spinning to form linked filament bundles that are highly entangled and structurally robust. In individual filaments, photocreases unlock paths 16 …

Advanced Materials Design Using Application-Based Processing Techniques, Daniel S. Camarda

Doctoral Dissertations

This dissertation pertains to generating advanced materials using application-based processing techniques. First, billets consisting of PTFE sintering powders are evaluated using Thermomechancal Analysis. It was found that both shape change and volume change are associated with enthalpic and entropic recoil, respectively. These phenomena, due to melting and stored energy during the powder compaction process, were found to be molecular weight dependent. Additionally, kinetics of the recovery and sintering process were found to be slower in blended specimens than pure samples. Next, the creation of graft copolymers by selectively grafting a second polymer to the amorphous fraction of a semi-crystalline polymer …

Material Property Heterogeneity In Dimensional Lumber And Its Relationship To Mass Timber Performance, Fiona O'Donnell

Doctoral Dissertations

According to the Environmental Protection Agency, buildings account for 38% of the United States' carbon dioxide emissions, providing architects and structural engineers a unique opportunity to mitigate a significant factor driving climate change by implementing innovative and sustainable technology in infrastructure design. Wood and mass timber products are becoming an increasingly popular alternative building material due to their economic and environmental benefits. The natural growth of wood leads to highly heterogeneous material properties. Defects such as checks, knots, and localized slope of grain contribute to some of this variation; however, wood properties vary significantly even in clear wood. Using mass …

Harnessing The Mechanics Of Thin-Walled Metallic Structures: From Plate-Lattice Materials To Cold-Formed Steel Shear Walls, Fani Derveni

Doctoral Dissertations

Thin-walled structures have received a lot of interest during the last years due to their light weight, cost efficiency, and ease in fabrication and transportation, along with their high strength and stiffness. This dissertation focuses on the mechanical performance of thin-walled metallic structures from cold-formed steel shear walls and connections (PART I) to plate-lattice architected materials (PART II) via computational, experimental, and probabilistic methods. Cold-formed steel (CFS) shear walls subjected to seismic loads is the focus of PART I of this dissertation. An innovative three-dimensional shell finite element model of oriented strand board (OSB) sheathed CFS shear walls is introduced …

Polymeric Impulsive Actuation Mechanisms: Development, Characterization, And Modeling, Yongjin Kim

Doctoral Dissertations

Recent advances in the field of biomedical and life-sciences are increasingly demanding more life-like actuation with higher degrees of freedom in motion at small scales. Many researchers have developed various solutions to satisfy these emerging requirements. In many cases, new solutions are made possible with the development of novel polymeric actuators. Advances in polymeric actuation not only addressed problems concerning low degree of freedom in motion, large system size, and bio-incompatibility associated with conventional actuators, but also led to the discovery of novel applications, which were previously unattainable with conventional engineered systems. This dissertation focuses on developing novel actuation mechanisms …

Mechanical Performance Of Structural Systems With Missing Members: From Buildings To Architected Materials, Panagiotis Pantidis

Doctoral Dissertations

Structural systems are potentially subjected to damage initiating scenarios throughout the course of their service time. Depending on the nature and extent of the damaging event, they may experience significant reduction or even complete loss of their mechanical performance. This dissertation delves into the mechanics of structural systems under the notion of missing members from their domain, investigating types of structural systems: a) multi-story steel framed buildings, and b) materials with a truss-lattice microstructure. Part I of the dissertation investigates the performance of multi-story steel framed buildings under a column removal scenario, developing an analytical framework for their quasi-static robustness …

Modeling Deformation Behavior And Strength Characteristics Of Sand-Silt Mixtures: A Micromechanical Approach, Mehrashk Meidani

Doctoral Dissertations

This dissertation is comprised of six chapters. In the first chapter the motivation of this research, which was modeling the deformation behavior and strength characteristics of soils under internal erosion, is briefly explained. In the second chapter a micromechanis-based stress-strain model developed for prediction of sand-silt mixtures behavior is presented. The components of the micromechanics-based model are described and undrained behavior of six different types of sand-silt mixtures is predicted for several samples with different fines contents. The need for a more comprehensive compression model for sand-silt mixtures is identified at the end of this chapter. This desired compression model …

Cold Gas Dynamic Spray – Characterization Of Polymeric Deposition, Trenton Bush

Masters Theses

When a solid, ductile particle impacts a substrate at sufficient velocity, the resulting heat, pressure, and plastic deformation can produce bonding at the interface. The use of a supersonic gas flow to accelerate such particles is known as Cold Spray deposition. The Cold Spray process has been commercialized for some metallic materials, but further research is required to unlock the exciting material properties possible with polymeric compounds. In this work, a combined computational and experimental study a) simulated and optimized the nozzle flow conditions necessary to produce bonding in a polyethylene particle, b) developed and fabricated an experimental device, and …

Creasing Instability Of Hydrogels And Elastomers, Dayong Chen

Doctoral Dissertations

CREASING INSTABILITY OF HYDROGELS AND ELASTOMERS MAY 2014 DAYONG CHEN, B.S., TIANJIN UNIVERISTY M.S., TIANJIN UNIVERSITY M.S., UNIVERSITY OF MASSACHUSETTS AMHERST Ph.D., UNIVERSITY OF MASSACHUSETTS AMHERST Directed by: Professor Ryan C. Hayward Soft polymers placed under compressive stress can undergo an elastic creasing instability in which sharp folds spontaneously form on the free surfaces. This process may play an important role in contexts as diverse as brain morphogenesis, failure of tires, and electrical breakdown of soft polymer actuators. While the creasing instability has been used for collotype printing since as early as the 1850s, the scientific appreciation of this instability …

Scaling Reversible Adhesion In Synthetic And Biological Systems, Michael David Bartlett

Open Access Dissertations

Geckos and other insects have fascinated scientists and casual observers with their ability to effortlessly climb up walls and across ceilings. This capability has inspired high capacity, easy release synthetic adhesives, which have focused on mimicking the fibrillar features found on the foot pads of these climbing organisms. However, without a fundamental framework that connects biological and synthetic adhesives from nanoscopic to macroscopic features, synthetic mimics have failed to perform favorably at large contact areas. In this thesis, we present a scaling approach which leads to an understanding of reversible adhesion in both synthetic and biological systems over multiple length …

Application Of Finite Element Method In Protein Normal Mode Analysis, Chiung-Fang Hsu

Masters Theses 1911 - February 2014

This study proposed a finite element procedure for protein normal mode analysis (NMA). The finite element model adopted the protein solvent-excluded surface to generate a homogeneous and isotropic volume. A simplified triangular approximation of coarse molecular surface was generated from the original surface model by using the Gaussian-based blurring technique. Similar to the widely adopted elastic network model, the finite element model holds a major advantage over standard all-atom normal mode analysis: the computationally expensive process of energy minimization that may distort the initial protein structure has been eliminated. This modification significantly increases the efficiency of normal mode analysis. In …

Viscoelastic Flow Through Contraction Geometries, Ashwin Karthik Sankaran

Masters Theses 1911 - February 2014

Contraction flow of viscoelastic fluids has been a benchmark problem in non-Newtonian fluid mechanics because it mimics flows occurring in a number of industrial applications. It is also of considerable interest to academia to gain fundamental understanding of factors that affect the evolution of vortices and a complete understanding of the dynamics for a simple polymeric fluid has not been achieved. In this two part study we investigate the effect of pre deformation of a Boger fluid in a contraction geometry and the flow of surfactants in a parallel contraction geometry.

Entry flow of a polymeric fluid results in the …

Semi-Active Damping For An Intelligent Adaptive Ankle Prosthesis, Andrew K. Lapre

Masters Theses 1911 - February 2014

Modern lower limb prostheses are devices that replace missing limbs, making it possible for lower limb amputees to walk again. Most commercially available prosthetic limbs lack intelligence and passive adaptive capabilities, and none available can adapt on a step by step basis. Often, amputees experience a loss of terrain adaptability as well as stability, leaving the amputee with a severely altered gait. This work is focused on the development of a semi-active damping system for use in intelligent terrain adaptive ankle prostheses. The system designed consists of an optimized hydraulic cylinder with an electronic servo valve which throttles the hydraulic …

Effect Of Slip On Flow Past Superhydrophobic Cylinders, Pranesh Muralidhar

Masters Theses 1911 - February 2014

Superhydrophobic surfaces are a class of surfaces that have a microscale roughness imposed on an already hydrophobic surface, akin to a lotus leaf. These surfaces have been shown to produce significant drag reduction for both laminar and turbulent flows of water through large and small-scale channels. The goal of this thesis was to explore how these surfaces alter the vortex shedding dynamics of a cylindrical body when coated on its surface, thus leading to an alteration in drag and lift on these surfaces. A cylindrical body was chosen as it is a very nice representative bluff body and sets the …

Physical Model Of The Feeding Strike Of The Mantis Shrimp, Suzanne M. Cox

Masters Theses 1911 - February 2014

A physical model was built to study the properties of the feeding strike of the mantis shrimp that are responsible for drag reduction and cavitation control. The model had three goals: 1) The model was to be outfitted with a method to collect kinematic, force and cavitation data. 2) The velocity and acceleration profile of the model were to be predicted with a mathematical model of the mechanism. 3) The model was to match as many drag and cavitation sensitive properties of the mantis shrimp strike as feasible and have a means to control the rest. The first iteration of …