Applied Mechanics Commons^™

Interplay Between Phase Instability And Deformation Mechanisms In Beta Titanium Alloys In Aggressive Environments, Benjamin Elbrecht

All Dissertations

Modern designs, such as commercial jet turbines, are reliant on the high temperature performance of their constituent materials. Improvements to the strength-at-temperature of materials are critical to the continued advancement of efficiency and payload capacity in these advanced applications. This dissertation presents studies that progress towards this goal through the construction of a new experimental setup for complex temperature and force profiles that also accurately captures deformation behavior through non-contact measurements. Using this setup, studies into two specialty titanium alloys were executed: discovering the microscopic mechanisms responsible for the macroscale behavior and testing in conditions closely replicating aircraft turbine operating …

Experimental And Computational Investigation Of The Effects Of Neck Musculature During Head Impacts In American Football, Anthony P. Marino

All Dissertations

Anthropometric test devices (ATDs) are human surrogate models used to represent the human body response in the context of compliance and safety testing. These devices are used in multiple industries, including automotive and aerospace, and have recently been incorporated into impact testing for the evaluation of helmet performance in American football. The Hybrid III 50^th percentile male ATD head and neck assembly is the most commonly used surrogate for these tests, although it was developed for automotive frontal crash scenarios that induce an inertial force on the body, leading to head and neck motion primarily in the sagittal plane. …

Experimental And Numerical Study On The Influence Of Carbon Fiber Reinforcement On The In-Plane Compressive Properties Of 3d Printed Hexagonal Honeycomb Core Structures, Deon Wallace

All Theses

There is difficulty with numerically replicating the behavior of composite honeycomb core structures numerically due to the trouble of gathering material properties from a hollow structure. Also, complex part geometries and carbon fiber reinforcement strategies can lead to unwanted structural weaknesses and variance in material properties that may not be reflected in numerical analysis when the part is additively manufactured. In this study, edgewise compressive testing is used to characterize the mechanical behavior and performance characteristics of these structures. The experimental results indicate an increase in the Young’s moduli of the honeycomb core structures as carbon fiber concentration increases. However, …

Predicting Long-Term Creep Behavior Using Short-Term Stress Relaxation Data In Expanded Polyethylene Foam, Andrew M. Seelig

All Theses

Closed cell expanded polyethylene (EPE) foams are widely used for protective packaging due to their high energy absorption properties and recyclability. However, these foams can be subjected to sustained compressive stresses (13.78 - 36.20 kPa), depending on density and application, leading to time-dependent deformation (creep). Creep reduces cushioning performance, making its understanding critical for effective protective packaging. Two standards, ASTM D3575 and ASTM D2221, define methods for conducting compressive creep tests on foam materials, with test durations extending up to 1000 hours. Accelerated methods such as Time Temperature Superposition (TTS) and the Stepped Isostress Method (SSM) have been explored for …

Tsunamigenesis On A Buoyant Granular Layer As A Model Of Ice Mélange In Ice-Choked Fjords, Nathan F. Reyner

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Glacial calving events can often create destructive tsunami waves in ice-choked fjords in the arctic region, posing a threat to local inhabitants and damaging coastlines. Here the sea is covered by a polydisperse granular material called ice mélange, whose properties can affect the wave characteristics. To investigate the role of a buoyant granular layer, as a model of ice mélange, on tsunami generation, or tsunamigenesis, a series of laboratory experiments were conducted by collapsing a column of dense granular material into a body of water with a layer of buoyant particles distributed across the liquid surface. Experiments were performed over …

Deciphering And Translating Bioinspired Structures For Engineering Materials Design Via Computational Modeling And Machine Learning, Zhangke Yang

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Nature has evolved extraordinary structural materials—such as nacre, bone, and the mantis shrimp’s dactyl club—that achieve remarkable combinations of strength, toughness, and impact resistance. These properties arise from sophisticated synergies between structure and composition. Inspired by these biological systems, this dissertation presents a comprehensive investigation into bioinspired materials, uncovering fundamental mechanisms and providing guidance on designing materials with superior mechanical properties.

This dissertation begins by examining the "brick-and-mortar" structure of nacre, which informs the design of layered polymer-graphene nanocomposite films. Using coarse-grained molecular dynamics simulations, I elucidate mechanisms of dynamic wave propagation and energy dissipation in these systems, providing critical …

Mechanistic Insights Into Polymer-Assisted Graphene Exfoliation: The Roles Of Velocity, Adhesion, Cohesion, Temperature, Peeling Mode, And Edge Defect Via Coarse-Grained Molecular Dynamics, Linjiale Dai

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Graphene exfoliation is a critical step in the fabrication of high-quality graphene

layers. However, the underlying fracture mechanisms remain poorly understood. In this

work, I employed coarse-grained (CG) molecular dynamics (MD) simulations to

investigate how factors such as interfacial binding energy, substrate cohesion, temperature,

peeling mode, and edge defects influence the outcome of the exfoliation process. To model

polymer-assisted mechanical exfoliation, I used a finite-size system in which multilayer

graphene (MLG) is sandwiched between two thin polymer films. Leveraging the

spatiotemporal efficiency of the CG model, I performed fifty simulation iterations per

parameter set and analyzed the results from a …

Deformation Mechanism In Gold Nanoparticles Under Compressive Loading: Insights From Atomistic Modelling And Unsupervised Machine Learning, Tanuj Gupta

All Dissertations

Gold nanoparticles (AuNPs) offer exciting possibilities due to their inertness, malleability, and tunable structures, making them valuable for applications ranging from nanomedicine to electronics. Their optical, mechanical, and other properties can be tailored by modifying shape and structure, underscoring the importance of understanding their deformation behaviour at the nanoscale. This study used classical molecular dynamics simulations with LAMMPS to investigate the deformation mechanisms of gold nanospheres (AuNS) under uniaxial compression. Employing the embedded atom method (EAM) potential to model atomic interactions, AuNS with 20 nm in diameter were compressed along the z-direction using planar indenters moving at a constant …

Influence Of Hygrothermal Conditions Of The Bistability Of Asymmetric Carbon Fiber Laminate Composites, Celia Hill

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Carbon fiber-reinforced polymer (CFRP) laminates have widespread use in many industries because of their exceptional strength-to-weight ratio. Carbon fiber laminates following an asymmetric layup orientation can exhibit bistability meaning the laminate can exist at two stable geometric configurations. The morphing characteristics of bistable CRFP has a growing level of interest because of its potential in various applications including space aircraft structures for easy repair, automotive structures for energy dissipation and ergonomics, robotics for flexible motion and energy harvesting. Existing research shows that both moisture and temperature affect the material properties and behavior of CFRP laminates, however, the influence of moisture …

An Efficient Computational Frameworks For Design And Analysis Of Metamaterials, Raj Pradip Khawale

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Advancement in additive manufacturing helps in building artificial lattice structures with unique properties that are not available in naturally occurring materials or in continuum structures. Specifically, beam-based lattices are well known for producing lightweight structures with very high strength, auxetic behavior, and energy absorption capabilities. In recent years, numerous research studies have been conducted on generating algorithms and frameworks to obtain unusual properties based on the variation in the cell geometry and material properties. However, the exploration of the full design space is hampered in practice primarily due to restrictions on cell tiling variation. Additionally, the lattices are very intricate, …

Linear And Nonlinear Topology Optimization With Morphing Beam Networks, Andrew S. Montalbano

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Topology optimization (TO) is an engineering design discipline dedicated to optimizing material distribution within a given domain. In traditional gradient-based topology optimization, the solid domain is discretized into small volumetric elements. Using finite element analysis (FEA) of the structure, the gradient of the objective function with respect to the design variables (the pseudo densities) is computed, and these design variables are updated iteratively until convergence is achieved. Although gradient-based TO methods are well-established, sensitivity analyses of objective functions and constraints can be both mathematically complex and computationally intensive. The nonconvex nature of most TO problems often complicates efficient convergence. Furthermore, …

On The Structure, Energy, And Segregation Behavior Of Grain Boundaries In Metallic Systems, Yasir Mahmood

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Nearly all structural metallic systems are multi-component polycrystalline aggregates; their microstructures are composed of crystalline grains that are internally joined at grain boundaries (GBs). This thesis focuses on GB structure, energy, and chemistry, as these greatly influence many material properties and processes, including boundary dynamics during processing treatments or under operating conditions.

Using atomistic simulations, we examine the impact of metastable GB structures on solute segregation. A wide range of GB geometries and metastable structures are used in our study. The Al-Mg alloy is used because it is of interest for light weighting. The atomistic simulation results are used to …

Improved Ballistic Impact Resistance Of Nanofibrillar Cellulose Films With Discontinuous Fibrous Bouligand Architecture, Colby Caviness

All Theses

Natural protective materials offer unparalleled solutions for impact-resistant material designs that are simultaneously lightweight, strong, and tough. Particularly, the dactyl club of mantis shrimp features chitin nanofibrils organized in a Bouligand structure, which has been shown to effectively dissipate high-impact energy during powerful strikes. The mollusk shells also achieve excellent mechanical strength, toughness, and impact resistance with a staggered, layer-by-layer structure. Previous studies have shown that hybrid designs, by combining different bioinspired microstructures, can lead to enhanced mechanical strength and energy dissipation capabilities. Nevertheless, it remains unknown whether combining Bouligand and staggered structures in nanofibrillar cellulose (NFC) films, forming a …

Numerical Simulation Of Laser Induced Elastic Waves In Response To Short And Ultrashort Laser Pulses., Alireza Zarei

All Dissertations

In an era of intensified market competition, the demand for cost-effective, high-quality, high-performance, and reliable products continues to rise. Meeting this demand necessitates the mass production of premium products through the integration of cutting-edge technologies and advanced materials while ensuring their integrity and safety. In this context, Nondestructive Testing (NDT) techniques emerge as indispensable tools for guaranteeing the integrity, reliability, and safety of products across diverse industries.

Various NDT techniques, including ultrasonic testing, computed tomography, thermography, and acoustic emissions, have long served as cornerstones for inspecting materials and structures. Among these, ultrasonic testing stands out as the most prevalent method, …

Novel Vector Assignment Approach For Inherent Strain Modeling Of Laser Powder Bed Fusion Manufacturing, Lucas M. Morand

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The expansion of the design space due to additive manufacturing (AM) has been a large motivator for the success of this family of processes. Despite the complexity of the physics in metal laser powder bed fusion AM causing significant stresses and strains in finished parts, the design advantages and subsequent performance improvements continue to drive the expansion of AM. Because the trial-and-error approach to AM part development is cost prohibitive, simulation of prints has become crucial. However, full thermo-mechanical simulation is susceptible to the same pitfall of time and computational cost in order to attain part-scale results. The development of …

A Manufacturing-To-Response Pathway For Manufacturing Optimization Of Carbon Fiber Reinforced Polymer Composite Structures, Madhura Limaye

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Over the past decade, there has been an increased adoption of thermoplastic and thermoset based continuous carbon fiber reinforced polymer (CFRP) composites for structural applications in several industries. Among the different manufacturing methods, thermoforming process for thermoplastic based continuous CFRP’s offer a major advantage in reducing cycle times for large scale productions. Similarly, out-of-autoclave curing process for thermoset based continuous CFRP’s using heated tooling enables production of large composite structures. However, these manufacturing processes can have a significant impact on the structural performance of parts by inducing undesirable effects. These effects include inhomogeneous fiber orientations, thickness variations, and residual stresses …

The Generation Of A Physics Informed Machine Learning Model To Predict Defect Evolution In Materials & On The Thermally Activated Regime Of Dislocation Motion: A Simulation Driven Study On The Mechanical Behavior Of Crystals, Liam Myhill

All Theses

Line defects in crystals, known as dislocations, govern the mechanisms of plastic deformation at the micro-meso scale. The study of dislocations has proliferated the field of materials science and engineering for since the 1950’s, and modern studies show increasing utilization of computational methods to model the evolution of line defects in material systems. In keeping with modern research practice, the studies herewith demonstrate the use of advanced computing to generate models which can be used to better understand the behaviors of dislocations within crystal matrices. An advanced high-throughput model for a physically informed machine learning graph neural network (PIML-GNN) is …

Physics-Based Machine Learning Methods For Control And Sensing In Fish-Like Robots, Colin Rodwell

All Dissertations

Underwater robots are important for the construction and maintenance of underwater infrastructure, underwater resource extraction, and defense. However, they currently fall far behind biological swimmers such as fish in agility, efficiency, and sensing capabilities. As a result, mimicking the capabilities of biological swimmers has become an area of significant research interest. In this work, we focus specifically on improving the control and sensing capabilities of fish-like robots.

Our control work focuses on using the Chaplygin sleigh, a two-dimensional nonholonomic system which has been used to model fish-like swimming, as part of a curriculum to train a reinforcement learning agent to …

Cfrp Delamination Density Propagation Analysis By Magnetostriction Theory, Brandon Eugene Williams

All Dissertations

While Carbon Fiber Reinforced Polymers (CFRPs) have exceptional mechanical properties concerning their overall weight, their failure profile in demanding high-stress environments raises reliability concerns in structural applications. Two crucial limiting factors in CFRP reliability are low-strain material degradation and low fracture toughness. Due to CFRP’s low strain degradation characteristics, a wide variety of interlaminar damage can be sustained without any appreciable change to the physical structure itself. This damage suffered by the energy transfer from high- stress levels appears in the form of microporosity, crazes, microcracks, and delamination in the matrix material before any severe laminate damage is observed. This …

Characterization Of Mechanically Recycled Polylactic Acid (Pla) Filament For 3d-Printing By Evaluating Mechanical, Thermal, And Chemical Properties And Process Performance, Mahsa Shabani Samghabady

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Polylactic acid (PLA) is a biopolymer made from renewable resources such as sugar and corn. PLA filament is a popular material used in Fused Deposition Modeling (FDM) 3D-printing. While this material has many advantages, all the failed parts, support structures, rafts, nozzle tests, and the many prototype iterations during the 3D-printing process contribute to the plastic pollution and release of greenhouse gases. Although PLA is biodegradable, it can take years to degrade in landfills. Instead of throwing away PLA waste and buying new filaments, PLA can be recycled. Amongst the different recycling technologies, mechanical recycling is the most environmentally friendly. …

Investigation Of Fatigue Response With Analytical And Machine Learning Models And Hygroscopic Analysis Of Asymmetric Bistable Cfrp Composites, Shoab Ahmed Chowdhury

All Dissertations

Asymmetric bistable carbon fibre reinforced plastic (CFRP) composites enable a broad range of applications as they can sustain multiple stable configurations and have small snap-through load requirements. These unique features, coupled with their light strength-to-weight and stiffness-to-weight ratios, have made them preferred options for multifunctional systems. This study investigates the fatigue and hygroscopic response of 2-ply, [0/90] bistable CFRP laminates and proposes predictive modeling approaches for improved performance.

While previous studies widely researched and documented the fatigue of general composites in axial loading, fatigue analysis of asymmetric bistable composites in the out-of-plane snap-through direction is inadequate. This study performs fatigue …

Accurate Orientation Control Of Tendon Driven Continuum Robots That Exhibit Elasticity, Manu Srivastava

All Dissertations

This dissertation makes new contributions to the modeling and implementation of Tendon Driven Continuum Robots (TDCRs). Specifically, motivated by 3D printing of concrete using a continuum hose robot in construction applications, we focus on TDCRs featuring compliance in the robot backbone and actuating tendons, e.g. surgical robots/endoscopes/catheters with tendon actuation. We expand previous mechanics-based models to show how and why such compliance significantly restricts performance when traditional kinematics-based planning and control techniques are applied.

The main contribution of this work is a new Elasticity Compensation(EC) model that explains why the ad hoc approach of preloading/pretensioning the tendons compensates for compliance …

Comparative Design Space For Bistable Composites: An Integrated Framework Of Optimization, Finite Element Analysis, And Experimental Testing, Jonathan Bolanos

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Bistable composites are a class of advanced materials that can actuate between two stable shapes, making them attractive for a wide range of engineering applications. However, designing these composites to achieve optimal performance remains a challenging task. To address the challenge, this research develops an integrated framework that combines a genetic algorithm optimization technique, finite element analysis in Abaqus, and experimental testing to explore the design comparative space for square bistable composites composed of DA 409 carbon fibers. This leads to the study of generating an optimization algorithm to account for the relationship between the chances of a successful maximum …

A Predictive Analysis Of The Influence Of Thickness And Length On The Curvature Of Square Bistable Carbon Fiber Reinforced Composite Laminates, Stephan Terry

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This thesis presents a predictive analysis of the stability of square bistable carbon fiber reinforced composite laminates under various loading conditions. The stability of these laminates is essential to their performance and longevity and is influenced by factors such as thickness and length. Analytical and numerical techniques are used to model the behavior of these laminates, and experimental tests are conducted to validate the models. The findings of this research have implications for the design and optimization of square bistable carbon fiber reinforced composites.

The study investigates the relationships between the side length and thickness of square laminates for bistability. …

Molecular Dynamics Simulation On Molybdenum Disulfide: Thermal-Mechanical Properties And Phase Transitions Under External Loading, Mahabubur Rahman

All Dissertations

Due to their remarkable properties, transition metal dichalcogenides (TMDs) have received much scientific interest throughout the past decade. Two layers of chalcogen atoms (S, Se, Te) sandwich a layer of transition metal atoms (Mo, W, Ta) to form the three-atom thick unit cell in TMDs. The interaction between TMD "single layers" is mediated by neighboring chalcogen planes and bonded by Van der Waals forces. Due to this weak out-of-plane interaction, bulk samples can be thinned down to a single layer by exfoliation. Among the TMDs, Molybdenum Disulfide (MoS₂) shows promise in the field of electronics, optics, and sensing …

Multiscale Topology Optimization With A Strong Dependence On Complementary Energy, Dustin Dean Bielecki

All Dissertations

A discrete approach introduces a novel deep learning approach for generating fine resolution structures that preserve all the information from the topology optimization (TO). The proposed approach utilizes neural networks (NNs) that map the desired engineering properties to seed for determining optimized structure. This framework relies on utilizing parameters such as density and nodal deflections to predict optimized topologies. A three-stage NN framework is employed for the discrete approach to reduce computational runtime while maintaining physics constraints.

A continuous representation that uses complementary energy (CE) methods to solve a representative element's homogenized properties consists of an embedded structure that is …

Multiple Objective Function Optimization And Trade Space Analysis, Yifan Xu

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Optimization can assist in obtaining the best possible solution to a design problem by varying related variables under given constraints. It can be applied in many practical applications, including engineering, during the design process. The design time can be further reduced by the application of automated optimization methods. Since the required resource and desired benefit can be translated to a function of variables, optimization can be viewed as the process of finding the variable values to reach the function maxima or minima. A Multiple Objective Optimization (MOO) problem is when there is more than one desired function that needs to …

Modeling, Control And Estimation Of Reconfigurable Cable Driven Parallel Robots, Adhiti Raman Thothathri

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The motivation for this thesis was to develop a cable-driven parallel robot (CDPR) as part of a two-part robotic device for concrete 3D printing. This research addresses specific research questions in this domain, chiefly, to present advantages offered by the addition of kinematic redundancies to CDPRs. Due to the natural actuation redundancy present in a fully constrained CDPR, the addition of internal mobility offers complex challenges in modeling and control that are not often encountered in literature.

This work presents a systematic analysis of modeling such kinematic redundancies through the application of reciprocal screw theory (RST) and Lie algebra while …

Tunable Filtration Of Particles During Dip-Coating, Connor Copeland

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When a solid substrate is withdrawn from a liquid bath a thin coating is deposited whose thickness is given by the Landau-Levich-Derjaguin (LLD) law. We perform an experimental study of dip coating of particle suspensions showing that particles of a given size can become entrained in the meniscus by the competition between viscous and surface tension forces. This is called capillary filtration and can be used as a tunable dynamic filter. For single particle suspensions, filtration can be in terms of either clumps or single particles, with the relevant entrainment points depending upon the rheology of the working fluid, either …

Creep Behavior Of A Ti-Based Multi-Principal Element Alloy, Benjamin Elbrecht

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Abstract

The understanding of microstructural damage mechanisms is the foundation of better understanding existing materials and future material development. There are significant challenges to measuring these damage mechanisms in-situ as continuous observation of the state of the microstructure is difficult or impossible for many experimental setups. This thesis presents a method for measuring grain boundary sliding (GBS) and local strain concentrations in-situ via a Heaviside function based algorithm. GBS is the shearing of two grains along their shared grain boundary and is a common damage mechanism in creep which presents as a discontinuity that can be measured with a Heaviside …