Mechanical Engineering

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https://hdl.handle.net/10315/34419

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Open Access
Development of Acrylamide/Acrylic acid Superabsorbent Polymer (SAP) Particles for Water Applications
(2025-04-10) Tabesh, Ehsan; Rezai, Pouya
Water contamination, particularly from bacterial sources, poses significant risks to public health and environmental safety. Low bacterial concentrations in water samples often go undetected by conventional methods, increasing these risks and highlighting the need for efficient sample enrichment techniques. This research investigates the use of superabsorbent polymer microparticles (SAP-MPs) and their nanocomposites with MXene nanosheets for enriching bacterial samples. The study first focuses on developing innovative microfluidic platforms for real-time characterization of SAP-MPs. Subsequently, advanced MXene/SAP-MP nanocomposites are introduced for enhanced bacterial enrichment and water analysis. The study is structured into four objectives. The first objective involves the design and fabrication of a novel microfluidic device for high-resolution, real-time characterization of SAP-MPs. This device enables detailed single particle analysis of swelling behaviors, including volume swelling ratio (VSR) and swelling rate (SR). The second objective investigates the effect of particle size, crosslinker concentration, acrylic acid concentration, and neutralization degree on the swelling behavior of SAP-MP. Results revealed a ~40% and ~300% reduction in equilibrium VSR (VSReq) and SR with increased crosslinker concentration, respectively, while increasing acrylic acid concentrations enhanced VSReq and SR by ~200%. A ~300% increase in VSReq was observed with smaller particle sizes, marking the first single-particle-scale study of this phenomenon. The third objective demonstrates the synthesis of MXene/SAP-MP nanocomposites using the Breathing-In-Breathing-Out (BI-BO) method, achieving successful integration of MXene nanosheets without compromising swelling behavior. Finally, the fourth objective evaluates bacterial enrichment performance, revealing a 10-fold enrichment efficiency and 90% recovery efficiency under optimized conditions. This research advances the fundamental characterization of SAPs and their applications, including water treatment, biosensing, and environmental monitoring.
Open Access
Cell Imprinted Polymers Integrated with Microfluidic Biosensors for Electrical and Electrochemical Detection of Bacteria in Water.
(2025-04-10) Akhtarian, Shiva; Rezai, Pouya; Brar, Satinder
There is a growing demand for sensors that enable rapid, cost-effective, and laboratory-free detection of microorganisms in clinical, food and environmental samples. Traditional methods are slow, expensive, and require specialized personnel. Biosensors offer a promising alternative but face challenges like instability, high cost, short lifespan, and complex synthesis of the biorecognition elements. Molecularly imprinted polymers (MIPs) provide a more robust, cost-effective solution by embedding the target analyte's imprint into a polymer matrix. While MIPs are effective for small molecules, designing them for biological cells is more complex due to their structural diversity. Noncovalent interactions, preferred in synthesizing cell-imprinted polymers (CIPs), enable easier binding and dissociation. Selecting suitable functional monomers is crucial, as their interactions with cell surface molecules determine imprinting success. However, the effects of CIP composition on the bacterial capture efficiency remain unexplored. Furthermore, integrating CIPs into microfluidic and electrochemical sensing platforms is vital for portable, real-time detection systems. This research aimed to improve the understanding of the CIPs’ effectiveness in capturing bacteria to develop effective bacteria-sensing platforms using microfluidic devices. In Objective 1, we optimized a polymerization methodology for uniform functionalization of stainless steel microwires reproducible CIP coatings, imprinted with E. coli as the template. In Objective 2, we assessed E. coli rebinding performance which demonstrated 76±5 % uptake efficiency with the optimized composition. In Objective 3, we integrated CIPs into a conductometric-based microfluidic sensor. Resistance changes normalization and subsequent analysis of the dose-response curve revealed a dynamic range of 10^4 to 10^7 CFU/mL, with a limit of detection (LOD) of 2.1×10^5 CFU/mL. Specificity experiments demonstrated the specificity of the sensor towards imprinted E. coli cells. Further improvements were made by modifying the sensor design to a three-electrode configuration and employing electrochemical impedance spectroscopy (EIS). The charge-transfer resistance changes normalization and the subsequent analysis revealed an enhanced LOD of 2× 10^2 CFU/mL, with a broader dynamic range of 10^2 to 10^7 CFU/mL. The proposed sensor has the potential to offer a cost-effective, durable, portable, and real-time solution for the detection of waterborne pathogens. Future impacts include enhancing bacterial detection in environmental monitoring, food safety, and healthcare.
Open Access
Electro-Microfluidic Sensor for Quantitative Detection of Microplastics in Saline Freshwater
(2025-04-10) Warraich, Haider Tahir; Rezai, Pouya
This thesis investigates a DC microfluidic sensor incorporating a Wheatstone bridge and MXene-coated microwires to detect and quantify microplastics in freshwater with varied salinity. The study addresses the limitations of traditional detection methods, particularly in higher freshwater salinity where microplastics exhibit reduced electrophoretic mobility. The sensor's performance was evaluated across a range of microplastic concentrations (1–25 ppm) suspended in saline solution with varying NaCl concentrations (0–1000 ppm) to assess sensitivity and detection limits. Results demonstrated a significant reduction in electrical resistance as microplastics accumulated at the anode, indicating successful detection at lower salinities. However, at higher salt concentrations, microplastic accumulation and sensor sensitivity declined. Modifications, including constant current application and MXene functionalization, enhanced accumulation rates, and detection performance. Future research is required to investigate diverse microplastic types, shapes, and biological interferences to improve real-world applicability. This work provides a foundation for low-cost, sensitive microplastic detection in aquatic environments.
Open Access
Droplet Impact on a Solid Surface: Analytical Modeling and Experimentation for Spreading Phase
(2025-04-10) Hu, Yating; Amirfazli, Alidad
A normal droplet impacting a flat, stationary, solid surface exhibits symmetric spreading. A key aspect of this symmetric spreading, particularly during deposition at low Weber numbers, is the formation of a rim along the lamella edge. The rim is crucial for predicting maximum spreading, and its dynamics can be captured using a set of ordinary differential equations in numerical calculations. However, establishing a reasonable initial condition remains challenging. In addition to symmetric spreading, various studies have explored how to disrupt symmetry for industry demands, for example, reducing contact time for anti-icing purposes. However, no attempts to date have been conducted to restore symmetry from asymmetric spreading, such as spreading over an inclined or moving surface, where tangential velocity naturally breaks the symmetry. To address these issues, this thesis investigates: 1) the rim genesis for a normal impact at low Weber numbers; 2) a model that elaborates how wettability can be manipulated to guide an asymmetric lamella towards a symmetric shape; and 3) experimental validation of this model. This work demonstrates that rim formation is driven by a developing motion at the lamella edge — the rim region — induced by deceleration due to capillary forces. The dynamic pressure from this motion creates a difference in curvature, and hence the dynamic pressure must be balanced by the Laplace pressure within the rim region. The rim forms when the rim region becomes thicker than the lamella. An analytical model was developed to predict the time when the rim starts to form and the configuration of the droplet at this moment, validated by OpenFOAM simulations and experimental recordings. Experimental results also support the proposed model for symmetry restoration based on the Taylor-Culick theory, demonstrating that manipulating wettability can accelerate the receding of the stretched contact line to counteract the stretch. A method for fabricating a patch with tunable wettability contrast has been developed for surface design to achieve symmetry restoration. Experimental results confirm the effectiveness of this patch design in correcting asymmetric spreading for water droplets impacting a surface under the following Weber number conditions: Wen ≤ 300, Wet ≤ 300, and 0.51 ≤Wen ⁄ Wet≤2.04.
Open Access
Design, Development, and Validation of an End-User Photo-Thermal Sensing Platform for Rapid Detection and Quantification of Analytes in Fluidic Samples
(2025-04-10) Hayden, Derek William; Tabatabaei, Nima
The ability to detect the presence of specific analytes and quantify their titers in fluidic samples is essential in many industries, spanning from food industries to law enforcement to healthcare and beyond. The existing technologies used for this purpose require the use of specialty equipment by trained professionals in a laboratory setting to function (e.g., mass spectrometry or ELISA) which greatly increases the cost and time taken to receive actionable results. Portable and inexpensive tests exist – Lateral Flow Immunoassays – however these tests are only qualitative and frequently have an inferior limit of detection. To date, several sensing devices have been designed to interrogate these LFIAs and decrease their limit of detection, however, these devices are often prohibitively expensive. This thesis outlines attempts to design and validate a sensing platform which could inexpensively enhance the limit of detection of LFIAs.The prototype is then validated through both lab-based and human experiments.
Open Access
Micro and Nano-structured Materials with Controlled Radiative Properties for Radiative Cooling Applications
(2025-04-10) Pirvaram, Atousa; O'Brien, Paul G.
In response to global environmental crises, such as climate change, urban heat islands, and escalating energy demands, this thesis investigates innovative solutions to these challenges through the development of radiative cooling (RC) materials and systems. The research first examines the potential of RC technologies to mitigate climate change by assessing their impact on global warming potential (GWP) and radiative forcing (RF) through life cycle assessment (LCA) methods. The study analyzes RC materials in comparison with conventional construction and roofing structures, highlighting their significant potential to mitigate global warming impacts. A RC material exhibiting an average solar reflectance (R ̅_solar) of 98.2% and an average long-wavelength infrared emittance of (ε ̅_LWIR) 98.5%, achieved a net cooling power of 160.8 W·m⁻², leading to a GWP of -252 kgCO₂-eq·m⁻² over 20 years and -333 kgCO₂-eq·m⁻² over 100 years, with an RF value of -1.01 W·m⁻² when covering 1% of the Earth's surface, indicating a substantial reduction in radiative forcing compared to conventional materials. The thesis then explores the incorporation of underside reflective surfaces to boost RC performance by redirecting thermal emissions toward the sky and reducing heat loss. Numerical simulations using Monte Carlo ray-tracing (MCRT) techniques were employed to evaluate the cooling effectiveness of various configurations, including flat and parabolic reflectors. Results show that considering an ideal selective emittance spectrum, in the absence of solar absorption and convective heat transfer, at an ambient temperature of 300 K, the steady-state temperatures using parabolic reflectors with the mentioned geometrical features can be cooled down to approximately 230 K. An important objective was to design and analyze novel configurations of micro- and nano-structured materials with controlled radiative properties for passive daytime radiative cooling (PDRC) applications. Key advancements included the development of enhanced PVDF-HFP-based porous materials with high solar reflectivity and long-wave infrared emissivity, such as the aforementioned (1-8-1.25) sample, fabricated via the phase inversion method. These materials were designed to maximize cooling by minimizing solar heat absorption and enhancing thermal radiation through the atmospheric window. Finally, experimental validation was conducted via outdoor testing and controlled dew condensation experiments in a dedicated setup, demonstrating the practical applicability of the developed PDRC systems. The findings underscore the significant potential of RC technologies to reduce cooling energy demands and mitigate global warming, making them a promising approach to enhance sustainability in urban and building environments.
Open Access
Theoretical and Experimental Investigation of Free-Floating Space Manipulator Motion Control Using Reinforcement Learning
(2024-11-07) Al Ali, Ahmad Ibrahim; Zhu, George
This doctoral research is motivated by the need to capture a non-cooperative target in Earth orbits by autonomous manipulators for debris removal. It investigates the critical motion planning problem for a 6DOF free-floating space manipulator using model-free Reinforcement Learning. This problem is caused by dynamic coupling between the spacecraft and robotic manipulator, which significantly affects control and precision in the space environment. This research addresses critical requirements for efficient and effective manipulation in space, including accurate pose alignment between the end-effector and target debris, collision avoidance with both the target and other links of the manipulator and external obstacles, smoothing of joint velocities using optimization terms integrated into the reward function, and adaptation to the high mass ratio between the manipulator and its base spacecraft. Recognizing the imperfection of real-world sensors, this research also incorporates observation noise in the training process to enhance the agent's resilience to noise. Additionally, the reinforcement learning agent is trained with varying initial conditions that are randomly set at the start of each episode, including the manipulator’s initial joint angles, target positions, and obstacle locations. The trained agent can find suitable paths for any target location and avoid obstacles regardless of the manipulator's initial position. The study provides a solid foundation for the application of reinforcement learning in complex free-floating space robotic operations and offers insights for future missions. In addition to numerical verification, ground experimental validation is essential. To overcome the difficulty in mimicking the 3D microgravity environment on Earth, this doctoral research has devoted efforts to designing and building a hardware-in-the-loop ground testbed with active gravity compensation in our lab. The testbed involves two industrial 6DOF robotic arms, one robotic finger gripper and various sensing equipment, including cameras and force/torque sensors, to mimic the 6DOF motion maneuvers that a free-floating robotic manipulator or tumbling satellite/target in microgravity. Initial experimental results in motion control, computer vision, and sensing capabilities are presented to show the potential of the testbed. This facility will be an invaluable tool for the future development and validation of space robotic manipulators, ultimately improving their effectiveness and reliability in space missions.
Open Access
Material Characterization and Development of Simulant Phantoms for a Biofidelic Head Model
(2024-11-07) Tenio, Tristan Virgilio; Boakye-Yiadom, Solomon
Traumatic Brain Injury (TBI) is a global health crisis, with concussions — classified as mild TBI — being particularly common in sports and daily activities. These non-penetrative injuries complicate diagnosis and analysis due to ethical and observational challenges. This thesis aims to develop a biofidelic head model for lab-based impact testing, bridging the gap of anatomical representation between computational models and physical validation. This research focuses on characterizing materials that mimic the mechanical properties of human brain and skull tissues under impact conditions. These materials are tested for their ability to simulate the brain’s compressive and shear responses and the skull’s flexural strength, using advanced manufacturing techniques. The research, structured across five chapters, reviews existing head impact methods and current practices for simulant characterization, selects and tests brain and skull simulants, and designs a comprehensive methodology for creating a full-scale biofidelic head model, proposing advancements for more accurate TBI analysis and prevention.
Open Access
Deformation Behavior and Microstructural Evolution of Armox 500T with Varying Strain Rates and Temperatures
(2024-11-07) Tak, Gurnek Singh; Boakye-Yiadom, Solomon
Armour steels have long been used for ballistic performance application purposes as they provide high hardness, toughness, and strength to resist penetration. However, literature lacks a complete understanding of failure mode analysis under various stress-loading conditions. This thesis explores the microstructure and evolution of Armox 500T as well as the correlated stress-strain data to characterize and gain a deeper understanding of its behaviour under compression, tension, and torsion with temperatures ranging from 0°C - 400°C. Results indicate that performance was increased in high strain rate compression at elevated temperatures up to 200°C, withstanding 2.0% more impact momentum and 3.7% higher toughness than room temperature samples. Temperatures above 200°C showed compromised microstructural properties and decreased performance. At 400°C high strain rate compression, the samples fractured at lower impact momentum and displayed increased brittleness and microhardness. In a reduced temperature of 0°C, low strain rate tensile test conditions decreased toughness by 11.8%.
Open Access
Development of Advanced Adsorbent-beds for Storing Thermal Energy Derived from Solar and Waste Heat
(2024-11-07) Kapil Narwal; O'Brien, Paul; Kempers, Roger
Climate change is an undeniable reality. A pivotal focus in the battle against climate change is sustainability. One way to achieve this is through safeguarding the environment, optimizing natural resource usage, and minimizing waste. Solar energy has played a vital role in advancing sustainability efforts. This energy can be harnessed as electricity or heat. Emerging technologies, including flat plate and evacuated tube collectors, provide promising pathways for harvesting solar thermal energy. Thermal energy storage for short-distance mobile applications is an attractive research domain. The first objective of this research work evaluate the zeolite 13X for short-distance mobile thermal energy storage applications. The study investigates the feasibility of storing thermal energy in zeolite 13X charged externally to dedicated heat recovery units. Impressively, the research demonstrates that zeolite 13X charged at 200°C and stored external to the discharging unit can achieve remarkable energy storage densities (ESD) exceeding 110 kWh/m3 under specific conditions. This achievement aligns with previously reported ESD values in the literature. A particularly crucial aspect addressed in the research is the integration of adsorbents with solar thermal energy storage systems, a relatively underexplored avenue. The study explores diverse configurations, analyzing their impact on enhancing thermal energy storage performance. Through meticulous experimental analysis utilizing Zeolite 13X and water as the adsorbent-adsorbate pair, the research compares direct irradiation with a solar thermal collector. Moreover, the research dives into a critical aspect of adsorbent-based thermal energy storage (ATES) systems. While these systems boast high energy storage densities over long durations, these often face limitations in terms of the heat provided by prevalent sources such as industrial waste heat and solar energy. To bridge this gap, the study explores experiments that leverage both simulated solar radiation and waste heat concurrently to charge Zeolite 13X for ATES applications.
Open Access
Analysis of the Interface Properties of Multi-material 3D Printed Structures
(2024-11-07) Pahari, Shauvik; Melenka, Garrett
Multi-material 3D printed (MM3DP) samples offer enhanced mechanical performance with the added benefit of being customizable for specific applications. However, MM3DP structures have weak adhesion at the boundary interface. So, the interface characteristics in those structures are a critical factor in determining the strength of the structures and predicting failure. Digital image correlation (DIC) is a full-field strain measurement technique ideal for evaluating the non-uniform load response in anisotropic materials due to their heterogeneous composition. This thesis demonstrates the fabrication of MM3DP samples using two distinctly different printing methods. The multi-material samples were extensively compared with the homogenous samples of the same base material with a shear test to assess their mechanical performance. Strain variations on the samples were analyzed and post-processed with DIC software as different material combinations were explored. Additionally, statistical analysis was performed to validate the results and assess the feasibility of the methodology.
Open Access
Towards Optimal Grasping Of Unknown Objects Using Deep Reinforcement Learning
(2024-11-07) Jabarnejad, Behrad; Zhang, Dan
Smart manufacturing, which uses advanced technologies to optimize processes, has become increasingly popular. Improving the agility of robotic systems, including manipulation skills, is crucial in this field. Grasp synthesis, the process of developing grasping plans while manipulating objects, can be approached empirically. Deep reinforcement learning (DRL) is an empirical method that does not require a dataset and learns tasks by interacting with an environment. This study aims to utilize DRL algorithms to perform grasping by creating a novel grasping environment for a simulation model of a three-finger gripper and then validating this model to achieve optimal grasp on unknown objects. The results showed that the trained DRL model in the validated simulation environment successfully grasped unknown objects placed randomly. The agent identified optimal grasps using a grasp quality score in the DRL model’s reward function.
Open Access
Modelling Tubular Braided Composites Using Geometrical, Micro-Computed Tomography and Finite Element Analysis Methods
(2024-11-07) Gholami, Ali; Melenka, Garrett
This thesis investigates various modelling approaches for two-dimensional Tubular Braided Composite (TBC) structures. Because of TBCs' flexible nature, modelling them properly is challenging and usually involves some assumptions. However, having an accurate modelling procedure would help researchers and industries obtain more accurate simulation results before manufacturing or using TBCs. In this research, the gap in the modelling of TBCs will be addressed. Some equations are available in the literature to generate geometrical models of TBCs. However, the intricate nature of the equations involved makes creating accurate geometrical models challenging. This research introduces a user-friendly and open-source software, TBC-Gen, which streamlines the modelling process, eliminating the need for extensive knowledge of the underlying equations. Moreover, some modifications have been applied to the equations to enhance the precision of TBC simulations. Comparative analyses are conducted between TBC-Gen outputs, results from other software, and physical TBC samples to investigate the accuracy of the TBC-Gen results. Micro-computed tomography (µCT) proves to be a precise method for scanning TBCs. This study employs µCT to scan various TBCs with different patterns, dimensions, and materials. Different image processing techniques have been developed to extract essential parameters (minor and major yarn and mandrel diameter, center point, orientation, and cross-sectional area of yarns) from the scanned models. Also, an innovative segmentation and splitting algorithm is implemented for overlapping yarns. Subsequently, two yarns from the scanned TBCs are extracted, and their paths are plotted. A simulated yarn path is fitted to the extracted path, and a new parameter is introduced to the geometrical model to enhance the fitness of the yarn paths. The error between the fitted geometrical model and the segmented yarn path is less than 1%. The TBC-Gen program is then utilized to design different geometrical models, and Finite Element Simulations (FEM) are developed to analyze their behaviour under tensile tests. Periodic Boundary Conditions (PBC) are applied to optimize computational efficiency. The impact of braid angle on TBC displacement during tensile testing is investigated by simulating seven models with similar geometries but varying braid angles (30°-70°). Additionally, three TBCs with similar geometries but different patterns are simulated, and their displacements are reported. The result shows that the displacement of simulated TBCs increases as the braid angle increases. Also, the Hercules pattern shows the most displacement and the Diamond pattern shows the least displacement under a similar tensile test. The FEM results are further validated by simulating the setup of an experimental test and comparing the outcomes against both experimental and Classical Laminate Plate Theory (CLPT) results. The FEM results are closer than the CLPT results to the experimental results. This comprehensive research not only advances TBC modelling methodologies but also validates their accuracy through a combination of advanced imaging techniques, innovative algorithms, and rigorous simulations, contributing valuable insights to the field of composite materials. The TBC-Gen program developed in this study can help other researchers and industries generate geometrical models without a deep understanding of the details of the equations. It can also be used for educational and visualization purposes.
Open Access
High Throughput Centrifuge Microfluidic Device for Simultaneous Particle Separation and Solution Exchange
(2024-11-07) Norouzy, Nima; Rezai, Pouya
Microfluidic centrifuge devices have gained increasing attention for point-of-need (PoN) sample preparation processes, e.g., in separation or solution exchange of various microparticles, bacteria, and mammalian cells. Yet, those devices capable of simultaneous solution exchange and particle separation are low in throughput (can operate at up to 2 mL/min), hindering their applicability to real-world settings. This thesis introduces a multilayer microfluidic device designed for high-throughput solution exchange and efficient microparticle separation, addressing the need for processing large sample volumes at elevated flow rates. The device integrates Dean flow recirculation and selective inertial focusing of microparticles within 24 curved microchannels assembled in a compact three-layer configuration via in-plane and out-of-plane parallelization. Exploring substrate materials (glass or PDMS) and operational flow rates, we studied solution exchange and particle migration using singleplex and duplex samples across devices with varying curve numbers (2-curve, 8-curve, and 24-curve). Transitioning from glass to PDMS enhanced solution exchange efficiency in curved channels. Processing 5 µm and 10 µm microparticles at flow rates up to 16.8 mL/min (33.6 mL/min total in the multilayer device) achieved a solution exchange efficiency of 96.7%. In singleplex suspensions, 10 µm and 5 µm particles selectively migrated to different outlets of the device, demonstrating separation efficiencies of 99.7% and 90.3%, respectively. With duplex samples, sample purity was measured to be 93.4% and 98.6% for 10 µm and 5 µm particles collected from different outlets, respectively. Application of our device in biological assays was shown by performing duplex experiments where 10 µm particles were isolated from Salmonella bacterial suspension with purity of 97.8%. This parallelization enabled desirable combinations of high throughput, low-cost, and scalability, without compromising efficiency and purity, advancing the technology towards sample preparation.
Open Access
Biofabrication of a Heart Wall Section using the FRESH Bioprinting Method
(2024-10-28) Horvath, Victoria Bianca; Czekanski, Aleksander
This dissertation addresses the challenge of bioprinting cardiac wall tissues. It focuses on three different aspects. The first is around materials that mimic the different cardiac wall tissue layers by testing the different materials pre- and post-crosslinked for their characteristics and behaviour. Secondly, it explores the adaptation of a 3D printer for bioprinting using the FRESH bioprinting method, which utilizes a single extrusion point for multi-material printing. This printer came with a unique printhead design, allowing multiple materials to enter the chamber to print continuously. Lastly, it explores the 3D printing of hybrid tissue and the optimization of the printing process. The hybrid tissue creation started with two materials before moving to three materials for the cardiac wall. The outcomes of this study The outcomes of the study such as the bioprinter that can print multiple material without leaving the print site and the materials which work as the anatomical heart wall layers, represent a significant step forward in the field of tissue and organ engineering, offering promising new directions for personalized medical treatments and advances for organ transplants by bridging the research gap between hybrid tissue bioprinting with specialized materials and a unique bioprinter that specializes in multi-material printing with better precision and material structure. This research lays the foundation for future advancements in the field of regenerative medicine.
Open Access
Stress-State and Strain-Rate Dependent Multiscale Characterization of ARMOX 500T
(2024-08-28) Mateos, Diego; Boakye-Yiadom, Solomon
A strain-rate and stress-state dependent experimental characterization is conducted for the parameterization of a triaxiality and lode angle parameter (LAP) dependent Generalized Incremental Stress-State Dependent Damage Model (GISSMO) for ARMOX 500T (AX500) armour steel. 100+ mechanical tests have been conducted which differentiate the effects of triaxiality, LAP, and strain-rate on instability and fracture strains. Quasistatic characterization tests have been conducted at 18 different stress-states abiding by previous GISSMO literature and ASTM standards. LaVision’s Digital Image Correlation (DIC) system is employed in 2D & stereo 3D configurations to acquire high resolution full-field strain measurements. The stain-paths are quantified in the fracture regions of all specimens, from which in-situ equivalent plastic strains are derived. A novel and low-cost Tensile Hopkinson bar has been designed and constructed for dynamic characterization of ductile metals at intermediate to high strain rates (500-1500 /s). High strain rate mechanical tests coupled with high-speed 2D-DIC have been conducted to provide a strain-rate dependent GISSMO extension to the model. Two Hopkinson bars (direct compression, split-tension) have been used to provide lode angle dependent strain-rate hardening data on stress-states of axisymmetric compression and tension covering the lode angle parameter values of -1 and 1, respectively. In addition, two cylindrical inclined compression-shear specimens with varied angles have been impacted at high strain rate to quantify the effect of stress-state on the formation and evolution of Adiabatic Shear Bands (ASBs) and their consequential effect on ductility. This innovative dynamic characterization procedure is conducted to stipulate diligent test matrices and enable improved multiscale terminal ballistics simulations on novel combat vehicle development, with the purpose to increase the predictability of shear plugging. High strain rate axisymmetric compression, compression-shear and tension specimens have been investigated using a combination of optical (OM) and electron microscopy (SEM/TEM) to elucidate their microstructural evolution. Ductile fracture is observed under all stress-states, with changes from mode I to mode II crack formation from positive to negative lode angles. Under axisymmetric dynamic tension, enhanced damage tolerance in comparison to quasistatic loading is found attributed to increased dislocation pileups (work hardening) and subsequent ductile void growth responsible for enhanced plastic flow during necking. Axisymmetric dynamic compression reveals a severe loss of global ductility and strengthening not observed under quasistatic loading, with continuous work hardening until premature fracture and localized hardening in the ASB regions. Compression-shear specimens reveal higher susceptibility to ASB initiation with increasing angle of inclination (shear stress) and corresponding ductility loss due to increased strain localization along the plane of maximum shear. Lastly, ASB multisite microcrack initiation and coalescence, multi-directional cracking, secondary ASBs and bifurcation, nanosized grain refinement, nanoscale twinning, and dislocation cell networks are found within triaxial ASB regions revealing that AX500 has various energy absorbing mechanisms to delay crack propagation and fracture after the onset of ASB initiation.
Open Access
Investigation of the Repairability of Thermoplastic Composite Structures Through Conduction Welding
(2024-07-18) Bijl, Calvin Zachary; Melenka, Garrett
Thermoplastic composites are gaining prominence in various industries for their recyclability and superior mechanical properties. This thesis investigates the use of thermoplastic composites, emphasizing their notable capability for repair and joining through conduction welding, a cost-effective fusion bonding technique that eliminates the necessity for adhesives or mechanical fasteners in the assembly of composite materials. By applying this method, the repairability of thermoplastic composite samples is assessed through the application of variously sized repair patches welded to open hole tensile samples. Furthermore, this research investigates the optimization of welding parameters, such as temperature and compaction pressure, aiming to produce high shear strength joints produced by this technique. The findings of these studies highlight the potential of conduction welding as an effective and economical approach for the assembly and repair of thermoplastic composites, suggesting its promise for wider adoption in composite manufacturing and repair processes.
Open Access
A Numerical Modelling Approach to Study the Impact of Ventilation Configurations on Airborne Transmission in Indoor Environments
(2024-03-16) Khan, Arma Mantissa; Freire-Gormaly, Marina
The airborne transmission of COVID-19 has been a topic of significant controversy since the pandemic began. Research was needed to demonstrate the importance of airborne transmission and develop tools to recommend appropriate control measures. This study aimed to analyze the factors that impact airborne transmission, find techniques for infection risk minimization, and develop methods to compare different control measures on infection risk. Computational Fluid Dynamics (CFD) studies were conducted to analyze the impact of ventilation layout and infection source location in indoor spaces. A novel spatio-temporal risk model was further developed to quantify the risk in indoor spaces based on different control measures. Conclusions have been made that the ventilation layout and infection source locations can significantly impact the risk of airborne transmitted infection. Further research into building design and airborne transmission minimization techniques is urgently needed to prepare for airborne infectious diseases that may emerge in the future.
Open Access
Design of Intermittently Operated Reverse Osmosis System and Membrane Coatings for Enhanced Fouling Mitigation
(2024-03-16) Truong, Brandon; Freire-Gormaly, Marina
Access to potable water is becoming an increasingly important issue, especially in communities residing in remote, off-grid locations. The use of solar powered reverse osmosis systems has been shown to be a viable solution to delivering clean drinking water. There is a need to improve the fouling resistance of the membranes to reduce costs, maintain water quality, and keep water output reliable. Membrane coatings have been shown to enhance antifouling properties, but more research is required. A lab-scale reverse osmosis (RO) system is developed to enable testing and monitoring of intermittent water treatment processes. Multiple sensors used to measure water quality and permeate flow were incorporated inline to gather data in real time. Membrane coating technology used to improve treatment performance through enhanced antifouling properties was studied. Several coating possibilities were considered for criteria such as: cost, antifouling & anti-scaling properties, and water output quality.
Open Access
Low-Cost and High-Throughput Optofluidic Add-on Device for Light Sheet Imaging of Larval and Adult C. Elegans
(2024-03-16) Rahimpouresfahani, Faraz; Tabatabaei, Nima; Rezai, Pouya
In this research, we have made modifications to our low-cost light sheet platform, allowing us to capture high-content cross-sectional images of nematodes' nervous systems at earlier stages of development and with higher throughputs. Our platform was put to the test in imaging larval and adult pan neural worms, as well as in analyzing control and neurotoxin-exposed worms. Additionally, we utilized a new transgenic worm model for Parkinson's disease and were able to detect a fluorescence difference between larval and adult stages. The result is a vast dataset of high-content images that will be invaluable in future research.