Applied Mechanics Commons^™

Growth Kinetics And Stability Of Metal Halide Perovskite Nanocrystals: Influence Of Stirring Speed And Water Exposure, You-Lin Huang

Theses and Dissertations--Mechanical and Aerospace Engineering

Cesium lead bromide (CsPbBr₃) perovskite nanocrystals (NCs) have garnered significant interest due to their exceptional optoelectronic properties, including high photoluminescence quantum yield, tunable bandgap, and excellent carrier dynamics. These attributes make them promising candidates for applications in light-emitting diodes, photovoltaics, and sensing technologies. However, optimizing their synthesis and improving their environmental stability remain critical challenges. This dissertation explores the growth kinetics of CsPbBr₃ NCs, focusing on the effects of stirring speed and water exposure on their structural and optical properties.

The synthesis of CsPbBr₃ NCs was performed using both mechanochemical (MC) and antisolvent methods, enabling an …

Degradation Of Polymers And Polymer Composites In Extreme Environments, Ben T. Jewell

Dissertations, Master's Theses and Master's Reports

Polymeric materials are widely used in engineering applications due to their high strength-to-weight ratio, easy manufacturability, and cost-effectiveness. When incorporated into composites, they provide further performance enhancements, enabling use in demanding structural applications. However, long-term exposure to harsh environments including elevated temperatures, UV radiation, harsh chemicals, and radiation, can drive degradation processes that alter the material’s network structure, and in turn, degrade its mechanical performance. Exposure to thermo-oxidative conditions is one of the most common environments driving polymer degradation, leading to chain scission and crosslinking events, with the resulting oxidative products causing discoloration, reduced ductility, and changes in glass transition …

An In-Situ Method For Quantifying Entropy Generation In Fatigue Via A Novel Thermographic Approach, Peyton J. Wilson

LSU Master's Theses

This work features a new approach that is used to measure the rate of plastic work during a cyclic fatigue test, based on the first and second laws of thermodynamics. Using the one-dimensional Fourier heat equation coupled with the concept of fracture fatigue entropy, the rate of plastic work during fatigue can be measured without the need to interrupt a fatigue test, and the accumulated entropy to failure can be quantified. Experimental fatigue tests are conducted on Aluminum 6061-T6 specimens under cyclic axial loading and Carbon Steel 1018 specimens under fully reversed cyclic bending loading. The obtained results in addition …

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

All Dissertations

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 …

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, …

Dynamic Impact Testing And Numerical Analysis Of Non-Proprietary Astm F2656-20 M50 Anti-Ram Barrier Components, Weston Kelley

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

In a post-9/11 world, hostile actors are using vehicles as weapons to inflict civilian casualties. Pedestrians, vulnerable road users, military personnel, and police may be targeted using a vehicle as a weapon. The United States Department of Defense (DoD) also utilizes Entry Control Facilities (ECFs) which are carefully designed transportation corridors to manage how threat vehicles are able to access military facilities. In 2004, DoD started to upgrade all ECFs using both passive and active barriers. Many anti-ram vehicle barriers were evaluated according to the criteria established in ASTM F2656, but to date few options are available which are (1) …

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

All Dissertations

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 …

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 …

Thermo-Elasto-Plastic Stability Of Biaxially Loaded Hollow Rectangular Section Steel Beam-Columns With Applied Torsion, George Adomako Kumi

Civil & Environmental Engineering Theses & Dissertations

Presented herein is an experimental and theoretical study of biaxially loaded hollow rectangular section steel beam-columns with applied torsion at elevated temperatures. The theoretical analysis is based on a system of simultaneous materially nonlinear differential equations of equilibrium for which an iterative semi-analytic solution approach is formulated. Although the primary goal of this research is to study the influence of elevated temperatures on the steel member with the complex loading, rigorous analysis is also conducted of the member at ambient temperature for comparison. The experimental part of the study involves conducting tests on the members at both ambient and high …

Balsa Bridge, Caleb T. Lovett

All Undergraduate Projects

The problem presented throughout this report was to create a small-scale bridge made entirely out of balsa wood and glue, that could withstand substantial force, as well as perform a lifting/lowering cycle. Other requirements associated with the bridge were properties of weight, deflection, size, and shape. This problem presented a challenge that tested the mathematical side of engineering, being strongly reliant on statics, mechanics of materials, and mechanical design analyses.

To approach this problem, the first step was to complete in depth calculations of the chosen design. With this done, manufacturing and assembly was able to be completed. With a …

Experimental Investigations And Optimization Of 3d Printed Cellular Structures For Protection Against Traumatic Brain Injury, Aaron R. Jackson

Mechanical and Aerospace Engineering Dissertations - Archive

Traumatic Brain Injury (TBI) disrupts brain function due to head impacts, blast exposures, and ballistic penetrations. It is a significant cause of mental health issues and disability, particularly among military personnel. Historically, combat helmets were designed primarily to protect against fragments. However, recent data highlights the need for helmets that also protect against blast and blunt impacts. Effective TBI prevention requires helmets that address various energy threats while remaining lightweight. A critical metric in this effort is head acceleration, which is closely linked to injury across different scales of brain damage.

Four lattice structures were 3D printed using Digital ABS …

Ambient Temperature Strength Degradation Of A Ceramic Matrix Composite Due To Solid Particle Erosion, Jonathan Clawson

Williams Honors College, Honors Research Projects

Solid particle erosion (SPE) is an issue for aircraft exposed to hard, fine particles, such as sand or dust, that can be ingested into the engine at a high velocity without reaching their melting point, resulting in material removal. SPE can be attributed to the intake of particulate debris from the runway or from airborne particulates. The cumulative mass loss from SPE damage affects the structural integrity and performance of the engine; however, its effects on ceramic matrix composites (CMCs), that are being employed in the aerospace industry, are not well understood in literature. The limited SPE research studies that …

Impact Of Quenching Intensity Conditions On Using A Finite Element Model To Investigate The Microstructure And Hardenability Of Low-Alloy Steel, J. S. Alabi, E. Heidari, M. F. Buchely, K. Chandrashekhara, S. N. Lekakh, R. J. O'Malley, V. Athavale, A. Kumar

Materials Science and Engineering Faculty Research & Creative Works

Quenching is one of the primary processes to improve mechanical properties in steels, particularly hardness. Quenching is well established for different geometries of individually treated steel components; while in-steam quenching of large diameter continuously cast steel bar has several specific features which are difficult and costly to experimentally optimize. the end-quench Jominy test has been used extensively to study the hardenability of different steel grades. Different numerical, analytical, and empirical models have been developed to simulate the Jominy process and to understand quenching of steels. However, it is not straight forward to translate experimental data from Jominy test on instream …

Impact Of Quenching Intensity Conditions On Using A Finite Element Model To Investigate The Microstructure And Hardenability Of Low-Alloy Steel, J. S. Alabi, E. Heidari, M. F. Buchely, K. Chandrashekhara, S. N. Lekakh, R. J. O'Malley, V. Athavale, A. Kumar

Materials Science and Engineering Faculty Research & Creative Works

Quenching is one of the primary processes to improve mechanical properties in steels, particularly hardness. Quenching is well established for different geometries of individually treated steel components; while in-steam quenching of large diameter continuously cast steel bar has several specific features which are difficult and costly to experimentally optimize. The end-quench Jominy test has been used extensively to study the hardenability of different steel grades. Different numerical, analytical, and empirical models have been developed to simulate the Jominy process and to understand quenching of steels. However, it is not straight forward to translate experimental data from Jominy test on instream …

Machine Learning-Assisted Multiscale Simulation And Design Optimization Of Composite Jackets Under Low-Velocity Impacts, Masoud Mohammadi

Graduate Theses, Dissertations, and Problem Reports (ETD)

This research presents the development of a data-driven machine learning-assisted approach to simulate and optimize the design of composite materials subjected to low-velocity impacts. It focuses on a specific type of hybrid composite comprised of fiberglass and Kevlar fabrics stitched with Kevlar threads. The study begins by creating a multiscale finite element simulation for the composite under a low-velocity impact, which operates across three scales: microscale, mesoscale, and macroscale. This simulation accepts various inputs, such as different layer configurations and orientations, and provides impact outputs including maximum load and energy absorption capacity and displacement at failure.

Python and MATLAB scripts …

Reducing Food Scarcity: The Benefits Of Urban Farming, S.A. Claudell, Emilio Mejia

Journal of Nonprofit Innovation

Urban farming can enhance the lives of communities and help reduce food scarcity. This paper presents a conceptual prototype of an efficient urban farming community that can be scaled for a single apartment building or an entire community across all global geoeconomics regions, including densely populated cities and rural, developing towns and communities. When deployed in coordination with smart crop choices, local farm support, and efficient transportation then the result isn’t just sustainability, but also increasing fresh produce accessibility, optimizing nutritional value, eliminating the use of ‘forever chemicals’, reducing transportation costs, and fostering global environmental benefits.

Imagine Doris, who is …

Mechanical Characterization Of Functionally Graded M300 Maraging Steel Cellular Structures, Bradley Jay Sampson

Theses and Dissertations

Traditional methods for increasing the energy absorption of a structure involve using a stronger material or increasing the volume of the structure, resulting in a higher cost or additional weight. Additive manufacturing (AM) can be used to maximize the energy absorption of materials with the ability to create complex geometries such as cellular structures. Previous work has shown that the energy absorption of additively manufactured parts can be improved through functionally graded cellular structures; however, this strategy has not been applied to ultra-high strength steel materials. This work characterizes the effect of multiple functional-grading strategies (e.g. uniform, rod-graded, size-graded) on …

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 …

Implementation Of Experimental Static Recrystallization Of High Strength Steel Into Computational Simulation Of Multi-Pass Slab Hot Rolling, S. K. Dasari, S. Ganguly, A. Abutunis, K. Chandrashekhara, M. F. Buchely, S. N. Lekakh, R. J. O'Malley, T. Natarajan

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Microstructural changes and softening due to static recrystallization have a critical influence on thermo-mechanical behavior of high strength steels during industrial multi-pass hot rolling. Numerical simulation using finite element analysis (FEA) can be used to accurately predict the softening behavior during the hot rolling process. Therefore, the implementation of an experimentally defined static recrystallization model into FEA is necessary to get realistic simulation prediction. in this study, the extent of softening during static recrystallization in Si and Mn alloyed high strength steel was measured using double hit tests. a Gleeble™ thermo-mechanical simulator was used to perform the double hit tests …

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

All Theses

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. …

A Strong And Ductile Cobalt-Free Solid-Solution Fe30ni30mn30cr10 Multi-Principal Element Alloy From Hot Rolling, Hans Pommerenke, Jiaqi Duan, Nathan Curtis, Victor Delibera, Adam Bratten, Andrew Hoffman, Mario Buchely, Ronald O'Malley, Haiming Wen

Materials Science and Engineering Faculty Research & Creative Works

Most of the face-centered cubic (FCC) multi-principal element alloys (MPEAs) developed thus far contain cobalt. for many applications, it is either required or beneficial to avoid cobalt, since cobalt has long-term activation issue (for nuclear applications), is expensive, and is considered a critical material. in addition, FCC structured solid-solution MPEAs tend to have relatively low strength. an FCC solid-solution Fe30Ni30Mn30Cr10 (at %) MPEA was fabricated via arc melting, followed by homogenization at 1100 °C for 12 h. the alloy was hot rolled at 1100 °C with a total reduction of up to 97 %. the microstructure was characterized, and mechanical …

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 …

A High-Strength Precipitation Hardened Cobalt-Free High-Entropy Alloy, Matthew Luebbe, Jiaqi Duan, Fan Zhang, Jonathan Poplawsky, Hans Pommeranke, Maalavan Arivu, Andrew Hoffman, Mario Buchely, Haiming Wen

Materials Science and Engineering Faculty Research & Creative Works

Recent studies on precipitation-hardened high-entropy alloys (HEAs) demonstrate their high strength and thermal stability, making them promising materials for high-temperature structural applications such as nuclear reactors. However, many existing HEAs contain cobalt (Co), which is unsuitable for nuclear applications because of the long-term activation issue of Co. Co is also expensive and considered a critical material for other applications. Therefore, it is desired to exclude Co from the composition. a Co-free (Fe0.3Ni0.3Mn0.3Cr0.1)88Ti4Al8 HEA was developed and studied in this work. in contrast to previous Co-free HEAs, this alloy is close to Equi atomic in its composition and promises a more …

Molecular Dynamics Modeling Of Polymers For Aerospace Composites, Swapnil Sambhaji Bamane

Dissertations, Master's Theses and Master's Reports

Polymer matrix composite materials are widely used as structural materials in aerospace and aeronautical vehicles. Resin/reinforcement wetting and the effect of polymerization on the thermo-mechanical properties of the resin are key parameters in the manufacturing of aerospace composite materials. Determining the contact angle between combinations of liquid resin and reinforcement surfaces is a common method for quantifying wettability. It is challenging to determine contact angle values experimentally of high-performance resins on CNT materials such as CNT, graphene, bundles or yarns, and BNNT surfaces. It is also experimentally difficult to determine the effect of polymerization reaction on material properties of a …

Dome Tester, Clark Bates, Nikolas M. Kulin

Williams Honors College, Honors Research Projects

We are reconfiguring and modifying the previously built dome tester to be more user friendly and mechanically applicable. This has a long-term goal of being a usable teaching tool for manufacturing education within the college of engineering and polymer sciences. The dome tester pushes a metal dome into a clamped sheet of metal to test its forming limits and where necking occurs. We have implemented a better method of viewing the sheet sample as it is being deformed, and improved measuring methods for the distance a sample is deformed. By introducing these changes in conjunction with improved documentation of the …

Mechanical And Morphological Characterization Of Energy Materials By Nanoindentation And Scanning Probe Microscopy, Jacob Hempel

Theses and Dissertations--Physics and Astronomy

The demand for robust materials in energy-based applications such as solid electrolytes for batteries, piezoelectric composites for mechanical energy harvesting, or new polymer materials for polymer binders in composite electrodes is on the rise. Mechanical degradation is the most common way for devices to fail in operation, thus a thorough understanding of a material’s mechanical properties is essential for application purposes.

In this dissertation, the mechanical characterization of novel boron cluster solid electrolytes is presented. Therein, we determine the elastic modulus and hardness of these compounds using instrumented indentation. A comparison is made against other solid electrolytes. It is found …

Low-Cost, Low-Weight Test Rig Design For A Laboratory-Scale Twin Rotor Wind Turbine, Ahmed Ayoub, Ahmed Elzeedy, Mahmoud Elkordy, Eslam Ayad, Mohamed Waleed, Amira Elkodama, Amr Ismaiel

Future Engineering Journal

Multi-Rotor Wind Turbine (MRWT) has been proven advantageous over Single-Rotor Wind Turbine (SRWT) in many aspects. In order to study the performance of MRWT over SRWT, this work presents a low-cost and low-weight design for a test rig for laboratory-scale wind turbine configurations. The configurations under study are a single-rotor, and a twin-rotor of the same size with a diameter of 30 cm. Aerodynamic loads have been calculated using the Blade Element Momentum (BEM) method, then the loads were used for stress analysis over the test rig proposed. The test rig is designed on Solidworks and the aerodynamic and inertial …

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

All Theses

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 …

Implementation Of Multiscale Mechanisms In Finite Element Analysis Of Active Composite Structures, Amany G. Micheal Prof., Yehia Bahei El Din Prof.

Centre for Advanced Materials

Composite structures reinforced with electrically active filaments are modeled with the finite element method while the underlying thermo-electromechanical coupling phenomena and damage are taken into consideration. At the outset, structural analysis is performed with a general-purpose finite element code and a special material routine, which propagates local phenomena to the overall scale is utilized. The material routine implements an interactive, multiscale analysis, which provides seamless integration of the mechanics at the composite’s micro, macro, and structural length scales. The interface between the multiscale material routine and the finite element code is made through nonmechanical strains caused by damage, and piezo/pyro-electric …

Implementation Of Multiscale Mechanisms In Finite Element Analysis Of Active Composite Structures, Amany Micheal, Yehia Bahei-El-Din

Centre for Advanced Materials

Interrogation of composite structures for inherent damage is investigated by implementing a three-tier analysis scheme. The analysis starts at the structure level where a general-purpose Finite Element code ABAQUS is employed to obtain the stress field in the second level of analysis which is the composite laminate. A special material routine is prepared to propagate the local fields to the individual plies and hence to the third level of analysis which is the microstructure modeling of the composite. Through the third level of analysis, interface damage between fiber and matrix is checked implementing a certain failure criteria. The interaction between …