Mechanical Engineering

Permanent URI for this collectionhttps://hdl.handle.net/10323/11894

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Vibration and stability of high-speed spinning cantilevered beams with shear deformation effects and an attached rigid body at its tip and and nonlinear hyperelastic behavior of circular dielectric elastomer membranes
(2025-01-01) Fallahpasand, Sam; Cooley, Christopher G; Mourelatos, Zissimos P; Monroe, Ryan J; Shillor, Meir
Instability of components and systems causes large-amplitude deformations or vibrations that limit performance, increase fatigue, and cause overload failures. In spinning systems, gyroscopic effects drive instabilities at high speeds. Instability in soft actuators occurs due to nonlinear material behavior. This work examines the dynamic stability of spinning structures with shear deformation effects and static instability in dielectric elastomer actuators.The vibration behavior, critical speeds, and high-speed instabilities in thick beams, spinning about their longitudinal axis, that have a rigid body attached to their tip are analyzed analytically and using finite element models. The analytical beam model includes shear deformation effects, incorporated by assuming the beams transverse displacements are independent of its cross-sectional rotations. A model is derived using Hamilton’s principle. The equations are cast into extended operator form, which exemplifies the system’s gyroscopic structure and facilitates Galerkin discretization for numerical solution. Numerical results are calculated for a system with identical inertia and stiffness properties in the two bending directions (called a symmetric system) and non-identical inertia and stiffness properties in the two bending directions (called an asymmetric system). Both systems have forward- and backward-orbit vibrations in single-mode, free response. Symmetric systems have material points that move in circular orbits along the span. The material point orbits become elliptical for asymmetric systems. Symmetric systems have degenerate stationary-system natural frequencies that split and become distinct for non-zero speeds. All eigenvalues cross, without interaction, as the rotation speed varies. The symmetric system eigenvalues are purely imaginary except at high speeds where critical speeds occur. Asymmetric systems, due to the differing inertia and stiffness properties in the two bending directions, have distinct stationary-system eigenvalues that increase and decrease with increasing speed from vanishing speed. Because of shear deformation effects, eigenvalue veering occurs when any decreasing forward-orbit eigenvalue comes into close proximity with an increasing backward-orbit eigenvalue. Within veering regions the forward- and backward-orbit modes couple, creating a single-mode free response that has forward-orbit vibrations in some regions along the span and backward-orbit vibrations in others. Asymmetric beams have distinct critical speeds and regions of divergence instability. Shear deformation effects lead to flutter instability at high speeds. Parametric studies reveal atypical high-speed instability behavior, including immediate transitions from divergence to flutter instability as speed varies. The mathematical structure observed for symmetric beam-rigid body systems is leveraged for closed-form solutions for their vibration. Finite element analyses are used to confirm the speed-dependent natural frequencies and identify axially- and torsionally-dominated modes. The results from this work could improve the high-speed performance of resonator devices like MEMS gyroscopes. The equilibria and stability of voltage-activated, pre-stretched circular dielectric elastomer membrane actuators under equilibrium conditions are studied using nonlinear analytical and coupled electro-mechanical finite elements simulations. The analytical model includes only the active region of the actuator; the passive region is replaced by a uniform outer circumferential load intended to capture the membranes initial pre-stretch. The model is derived in terms of a general strain energy density so that the voltage-stretch behavior of common hyperelastic material models can be examined. The Gent hyperelastic model is used as a baseline because of its ability to accurately predict the large-stretch mechanical behavior of a common acrylic elastomer used in dielectric elastomer transducers. The Gent model predicts one equilibrium at low voltages, three equilibria at moderate voltages, and one equilibrium at high voltages. The membrane experiences snap-through and snap-back bifurcations between small- and large-stretch equilibria. Moderate stretch models can capture the loss of stability, but snap-through to large-stretches are not possible. Hyperelastic models that include strain stiffening can capture large-stretch deformations, provided sufficient numbers of terms and material parameters are used. The finite element model includes both active and passive regions of the membrane actuator, inhomogeneity of deformations, the potential for material compressibility, and electric fringe fields at the boundaries of the electrodes. When the passive region is neglected, the finite element model predicts similar voltage-stretch behavior as the analytical model. When the passive region is included, the stretch meaningfully decreases, highlighting the potential importance of the passive region in actuators. Whereas the finite element model shows nearly homogeneous deformations within the active region, the deformations in the passive region are highly inhomogeneous. The finite element model is compared to available experiments.
A novel method for determining forcing drivers for total water flow in PEM fuel cells including electro-osmotic drag, back diffusion, and single- and two-phase thermal osmosis
(2025-01-01) Ingarra, Nicholas A; Kobus, Krzysztof; Latcha, Michael; Maisonneuve, Jonathan; Abdul Nour, Bashar
Heat and water management are essential for successful for PEM fuel cell operation, the goal being optimal fuel cell hydration to maximize ionic conductivity. Overhydration can lead to flooding on the cathode side. In experimentation on PEM fuel cells, total water transfer across the membrane is a result of simultaneous fluid drivers present in the experiment, including voltage, chemical potential, thermal and pressure gradients, and is measured indirectly with a high degree of precision.
Analysis of trimming die durability and sheared edge formability of ultra-high strength steels
(2025-01-01) Nasheralahkami, Saeid; Golovashchenko, Sergey; Barber, Gary; Pandey, Vijitashwa; Bonnen, John
The increasing demand for lightweight, safe, and fuel-efficient vehicles has led to greater use of advanced high-strength steels (AHSS), especially dual-phase steels like DP980, in automotive structures. However, these materials are often sensitive to trimmed edge cracking if stretching along the sheared edge occurs during processes such as stretch flanging. Excessive wear and early chipping of trimming tools are also significant issues in mass production. This dissertation investigates these challenges by analyzing the sheared edge formability of DP980 and the durability of trimming dies using experimental, numerical, and fatigue modeling methods.Edge quality was assessed based on burr height, burnish depth, fracture morphology, and microhardness mapping. Stretchability was evaluated through tensile, side-bending, and hole-expansion tests, demonstrating that edge quality significantly affects the sheets ability to withstand secondary deformation. Two DP980 materials were studied, showing different stretchability results and highlighting the variability within the same grade. A distinctive fracture mechanism was observed during trimming of DP980 steel, resulting in a burr at the final stage. Finite element models were created using Abaqus/Explicit. Optimized meshes, kinematic contact algorithms, and appropriate fracture criteria enabled reasonable predictions of strain localization, fracture initiation, and punch load history, while also reducing the penetration issue between the die and sheet meshes. The simulation also provided stress data for fatigue analysis of the trimming tool. This study also analyzed die wear and fatigue life over 230,000 cuts for D2 trimming inserts. Gradual tool wear decreased edge quality and stretchability, while localized chipping on inserts aligned with local burrs on the part edge. Fatigue modeling using the Goodman, Morrow, and Findley criteria showed that shear-based approaches best matched actual failure modes, supported by microstructural evidence of carbide-band effects. Overall, the findings provide valuable metrics and predictive tools to optimize trimming processes, extend die life, and ensure reliable manufacturing of AHSS.
Failure Analysis of Unique Child Passenger Safety Scenarios
(2025-01-01) Brouwer, Kristy Brinker; Latcha, Michael A.; Chang, Yin-Ping; Tonyushkin, Alexey; Atkinson, Theresa
Special circumstance scenarios exist where a child safety seat (CSS) cannot be, or is not, used according to best practices recommended by the American Academy of Pediatrics. This research identifies three such scenarios that uniquely affect the safe use of CSS. The first scenario examines children fitted with a lower extremity body cast due to developmental dysplasia of the hip (DDH) or femur fracture that prevent proper CSS fit for the child or the caregiver’s vehicle. A CSS must be used properly, according the user manual and vehicle owner’s manual, to ensure the child’s safety in and around vehicles. However, even with these available instructions, it is very common for caregivers to misuse the CSS. The second scenario in this research looks specifically at when the CSS is improperly used as a child restraint outside of a vehicle. Finally, the future of mobility is trending towards an incorporation of autonomous ride-share vehicles on public roads. Proposed automated vehicles (AV) vary greatly in size and shape, both on the exterior and the interior. With these changes, along with the likelihood of bi-directional drive AVs, CSS best practices for use may no longer be able to be followed. The third scenario develops a Design Failure Mode and Effects Analysis (DFMEA) specific to children being transported in AVs operating at Society of Automotive Engineers (SAE) Level 4 or Level 5 Driving Automation to investigate the specific potential failure modes and effects of child passenger safety in automated vehicles.
Experimental and Numerical Study of Pulse Charging Strategies on Lithium-Ion Battery Performance at Both Low and Room Temperatures
(2025-01-01) Liu, Jiahao; Wang, Xia; Guessous, Laila; Qu, Hongwei; Yang, Ankun
Lithium-ion batteries are widely used in power electronic devices, electric vehicles, and large energy storage devices, which demand faster, safer and more durable charging methods. Compared with the conventional constant current and constant voltage charging method, pulse charging can both improve battery performance and shorten charging time. This dissertation investigates how pulse charging can shorten charging time under different temperature conditions and mitigate capacity loss over multiple cycles. This study combines experimental testing and numerical simulation. Firstly, this study designed experiments to evaluate pulse charging at different temperatures. Using the Taguchi method, we treated protection capacity ratio and pulse discharge current rate as control parameters. At low temperature, pulse charging with a 25 protection capacity ratio and a 12C pulse discharge rate reduced total charging time by approximately 11 compared to the conventional constant current and constant voltage charging strategy. At room temperature, three fundamental pulse modes (C-C, C-R and C-D) and several derived strategies were studied. Their effects on internal resistance and battery cycle life were then measured. The experimental results show that, under the same average input current, pulse charging yields an average internal resistance reduction of 15 compared to the constant current and constant voltage charging strategy, and shows a slower capacity decay rate over 800 charge and discharge cycles. These findings are also confirmed across lithium-ion batteries with various chemistries. Secondly, an electrochemical and thermal coupled model was developed in COMSOL Multiphysics to reveal the mechanisms of pulse charging. After validation, the model was used to study lithium-ion concentration and electrode lithium distributions inside the battery under different pulse charging protocols. The model results show that pulse charging, particularly the C-D mode, promotes a more uniform lithium-ion distribution within the battery, thereby improving charging performance of lithium-ion battery by reducing cell resistance. These findings are consistent with the experimental results. Finally, a multi-objective optimization method was used to find the optimal parameters for pulse charging at room temperature. The objectives were to minimize total charging time, minimize temperature rise and maximize charging efficiency. The resulting optimal pulse charging strategy can reduce charging time by 6.8 per cycle and lower temperature rise by more than 8 compared to conventional constant current and constant voltage charging. This research studied pulse charging of lithium-ion batteries at different temperatures through experimental design, numerical simulation, and optimization. Pulse charging improves the performance of lithium-ion batteries by saving charging time and reducing capacity loss. Numerical simulation provides deeper insight into lithium migration and diffusion dynamics under pulse conditions. This research lays a solid foundation for future charging protocol development.
Energy-Efficient Dehumidification of Controlled Plant Environments Via the Application of Fertilizer-Based Liquid Desiccants
(2025-01-01) Aryal, Sandeep; Maisonneuve, Jonathan; Beetham, Sarah; Beyeh, Ngong Kodiah; Guessous, Laila; Lefsrud, Mark
To address food security challenges due to population growth, controlled plant environments have become popular because they ensure crop production throughout the year in contrast to open field farming. However, one of the major hurdles in such environments is humidity buildup which has a detrimental impact on crop quality and productivity. Conventional dehumidification strategies such as ventilation, refrigerant-based systems, liquid or solid desiccants, etc. are deployed to tackle this but are often energy intensive and costly. To address this issue, this dissertation proposes the use of fertilizer solutions as a novel and energy efficient method to dehumidify indoor plant environments. This dissertation establishes the thermodynamic limits and energy saving potential of fertilizer-based liquid desiccant. It then implements transport modeling to provide a more realistic assessment of energy use, followed by comprehensive experimental studies. Finally, it demonstrates the real-time dehumidification of humid air inside the functional plant chamber. From thermodynamic analysis it is found that the fertilizer desiccants consume half the energy required for conventional liquid desiccants systems by eliminating desiccant regeneration. This study also shows energy savings for different crops taking into account the dehumidification load (evapotranspiration) and the fertilizer requirement for each crop. Based on thermodynamic analysis, energy savings for common crops range from 0.2 to 0.7 kWh/plant/day. Building on this, transport modeling examines the influence of fertilizer concentration, temperature and fluid circulation rates on the specific energy of dehumidification of fertilizer-based desiccant systems. The results show that minimum specific work input is minimized to 0.16-0.24 kWh/kg at vapor flux level of 1.2-1.6 g/m2/h by adjusting desiccant temperatures. Following this, the comprehensive experimental study was conducted on a lab-scale test bench to measure the system’s energy use for different fertilizers, concentrations, and temperatures. The experiments confirm competitive energy use as low as 0.29 kWh/kg and pinpoint the importance of managing fertilizer temperature to optimize the system’s energy efficiency. Finally, the real-time application of a fertilizer-based desiccant dehumidification system was demonstrated in a closed plant chamber with hydroponic arugula. The fertilizer desiccant effectively maintained different humidity setpoints inside the chamber over the complete growth cycle of the plants.
On Using Heat for Water Desalination and Purification
(2025-01-01) Khanmohammadi, Saber; Maisonneuve, Jonathan; Beetham, Sara; Guessous, Laila; Yang, Ziming
The global freshwater crisis, intensified by population growth, climate change, and industrial demands, necessitates more energy-efficient and sustainable water treatment technologies. This dissertation explores how low-grade thermal energy can be harnessed to improve the performance and energy efficiency of membrane-based desalination systems. Four thermally integrated desalination strategies are investigated: thermally enhanced reverse osmosis, thermally driven reverse osmosis, membrane distillation, and ocean thermal membrane distillation.For thermally enhanced reverse osmosis, a detailed thermodynamic analysis reveals that preheating feedwater can reduce specific energy consumption by up to 24 for seawater and 33 for brackish water desalination. While higher feed temperatures reduce pumping work by enhancing membrane permeability and reducing polarization, the trade-off with thermal input is critically analyzed to identify net energy savings under high-efficiency thermal recovery conditions. We conclude that the benefit of thermal enhancement is marginal, as it requires a substantial amount of heat input to achieve only a slight reduction in pump work. For thermally driven reverse osmosis, a fundamentally new process is introduced where thermal energy directly drives mechanical desalination via a thermally driven piston system. A theoretical model evaluates the system’s efficiency under various design parameters, demonstrating competitive performance compared to conventional thermal methods when optimized for low-grade heat sources. A feasibility study of an ocean thermal membrane distillation (OTMD) system is conducted for application in remote islands, using cold deep-sea water as a thermal sink. Experimental and theoretical studies show that under optimized conditions, the OTMD system can outperform conventional reverse osmosis (RO) systems in specific energy consumption, offering a low-carbon, resilient solution for water-scarce regions. Finally, for membrane distillation, performance is further enhanced through real-time control strategies that adjust operating parameters, feed temperature, flow rates, and distillate conditions, to reduce specific energy consumption. Experimental results from a lab-scale direct contact membrane distillation system validate the proposed control method and report specific thermal energy consumptions of 274 kWh/m3 which is significantly lower than those reported in the literature. Overall, this dissertation demonstrates that, if properly integrated, heat can significantly reduce the energy use of membrane desalination systems, especially in locations with access to waste heat, solar thermal, or ocean thermal gradients.
Damage Detection of Localized Defects in Spur Gear Pairs and Geared Transmissions Using Damage-Induced Dynamic Response
(2025-01-01) Thunuguntla, Suhas Gupta; Cooley, Christopher; Hood, Adrian; Gu, Randy; Dean, Brian
Geared transmissions are important systems, especially in the aerospace and rotorcraft industry. Loss of power from gearbox failure due to damaged tooth poses reliability and safety issues. Health and Usage Monitoring Systems (HUMS) are used in rotorcraft vehicles to monitor the performance of their transmissions and other critical components. Condition monitoring systems use measured vibrations from geared transmissions to detect damage to the gears and other components inside them. A major challenge for damage detection systems is identifying damage from otherwise normal changes in vibrations that may occur. In this dissertation, the analysis of the damage-induced dynamic response of geared transmission is carried out by understanding the dynamic response on the spur gear pair and applying it to the geared transmission accelerations. For the accurate damage-induced dynamic response of the spur gear pair, accurate tooth mesh interface parameters are derived utilizing the finite element/contact mechanics (FE/CM) method. Tooth mesh characterization involves determining the static transmission error and the mesh stiffnesses when the teeth have either root cracks or surface pitting damage. The damage cases considered include tooth root cracks or surface pits localized to a single gear tooth. The FE/CM method accurately predicts the tooth mesh stiffnesses of the unity-ratio gear pair when it is healthy without damage, and when the teeth have root cracks and surface pitting. The static transmission error increases and the tooth mesh stiffness decreases with increasing size of pits and increasing lengths of cracks. The distinct differences in duration observed between tooth surface pit and root cracks may permit their detection from static transmission error measurements. Dynamic transmission error is calculated using the lumped-parameter model and shown to compare well with dynamic response calculations from the FE/CM gear pair model. Larger damage on the gear pair generally causes higher vibrations to result. Quasi-static responses are observed at speeds less than one-third of the natural frequency, while above that, the damage-induced dynamic response shows impulse-like behavior. The damage-induced dynamic response of high-speed spur gear pairs with localized defects shows that the response is oscillatory with decaying amplitudes, a linear oscillator, and based on these, a phenomenon-based model is proposed for approximating the damage-induced dynamic response which is determined solely by an amplitude (dependent on damage severity), damping ratio, and natural frequency (properties of gear pair). The simplicity of the phenomenon-based model permits analytical closed-form expressions of several condition indicators used in damage detection and the ability to predict condition indicators for varying gear pair properties. Geared transmission vibrations are determined using the FE/CM model to detect damage. When damage (i.e., tooth root cracks or tooth surface pits) occurs on the individual gears of the planetary stage, additional transient vibrations occur that meaningfully alter the resulting vibrations and their spectrum. The ability to calculate condition indicators (CI) for detecting damage is explored and and it appears to be sensitive to the input vibration signal used in the CI calculation. Tooth root cracks with lengths less than 50 percent through the tooth thickness generally do not lead to substantial increases in the individual CIs. Calculating the damage-induced dynamic response or the exact difference signal effectively detects even smaller crack length damages in the space-fixed or rotating gears of the planetary stage, utilizing the calculations of CIs. These will enable reliable damage detection techniques for geared transmissions, improving safety, reliability, vehicle readiness, and vehicle performance
Tin Whiskers Mitigation by Co-electroplating Antimony
(2024-01-01) Zhang, Lei; Wang, Xia; Barber, Gary; Yang, Ankun
Electroplating Sn coatings are used extensively in the electronics industry because of their excellent solderability, ductility, electrical conductivity, and corrosion resistance. However, tin whiskers have been observed to grow spontaneously from the electroplating tin coatings for over 70 years. This filament-type structure can lead to short circuits and device failures by bridging adjacent electronics. Over the last several decades, adding a small amount of lead (Pb) has been the most widely adopted method for mitigating Sn whiskers growth. However, this 70-year-old issue of whisker growth has reemerged due to the ban on the use of Pb from Sn-based plating and solders enforced by the European legislation on Restriction of Hazardous Substances (RoHS). The actual mitigation provided by the co-electroplating lead reamins unclear. Some have attributed the mitigation to the formation of equiaxial grains in a Sn-Pb plating process. Others have attributed it to reducing stress buildup in the film while doping Pb. This study proposes an innovative controllable way to mitigate Sn whiskers growth by electroplating Sn-xSb alloys (x=3 wt.%, 10 w.t%, 15 wt.%). In effect validation, a fixture was designed to apply high wide-plane compressive stress rather than using a hardness indenter to accelerate whisker growth. The results revealed that no whisker growth was observed on any Sn-xSb surface, while pure Sn samples produced whiskers up to 200 um under the same conditions. Adding a minor quantity of Sb could refine the Sn grains, however, the Sn grain size was not further refined with the increase in Sb content. In correspondence, the mitigation effect on whiskers growth was not further improved with the increase in Sb content. As confirmed by a series of EBSD studies, the addition of Sb changed the grain structure from a monolayer columnar structure to a multilayer equiaxed structure, which is favorable in whisker mitigation. The inhibition effect of Sb addition on whisker growth can be ascribed to the assistance of dynamic recrystallization and produces horizontal grain boundaries of Sn grains. This dissertation details the following studies: background of tin whisker problems; development and validation of an effective co-electroplating recipe for tin whisker mitigation using advanced analysis tools; identification of the primary mechanisms of the whisker growth mitigation
Development of a Hybrid Finite Element Method for Solving Inverse Engineering Problems
(2024-01-01) Wang, Xiyun; Gu, Randy J; Gu, Randy J; Yang, Lianxiang; Horvath, Tamas; Chang, Yin-Ping
The ill-posed boundary value problems, such as contact problems, adhesive joint analysis, and damage identification, are of foremost importance in the design and manufacturing of machines. The analysis of these problems has attracted considerable attention from engineers and researchers in various industries. This dissertation presents a novel hybrid finite element method for solving ill-posed boundary value problems through inverse engineering, with a focus on accurately determining contact stress, identifying damage, and analyzing adhesive joints in mechanical engineering. A significant aspect of this method involves integrating empirical measurements with numerical simulations to enhance both the accuracy and reliability of finite element analyses under insufficient boundary conditions. A constrained optimization framework is also employed in this study. The method is evaluated through seven case studies, which include assessments of plate bending, rigid contact problems, Hertzian contact problems, damage identification tasks, single lap joint, and T-peel joint evaluations. A novel constraint equation based on the gradient of the loading function is introduced as well. These case studies highlight the method’s comprehensive applicability and effectiveness across a range of complex engineering challenges. The dissertation outlines future work that aims to expand the methods application to three-dimensional problems, improve the optimization algorithms, and explore further applications. This work lays a foundation for advancing more complex and reliable modeling techniques in mechanical engineering, with significant implications for both research and industrial applications.
A Vibro-acoustic CAE Approach for Active Noise Control Prediction
(2024-01-01) Abbas, Ahmad A; Mourelatos, Zissimos P; Latcha, Michael; Yang, Lianxiang; Drignei, Dorin; Sturla, Francisco
This research focuses on a comprehensive analysis and prediction of Active Noise Cancellation (ANC) system performance in vehicles, with particular emphasis on the structural and acoustic aspects. While acknowledging the significance of electronic components and control algorithms in ANC systems, this study focuses on predicting the ANC performance using a full vibro-acoustic vehicle model. Additionally, the integration of noise management supplier control systems with CAE ANC models is explored. The development of a predictive CAE methodology is demonstrated using a road noise cancellation example. The process involves several steps including the structural behavior of the Trim Body in White (TBIW) structure, the development of a vehicle cavity model, the derivation of accurate speaker models, the assessment of speaker integration with vehicle doors, and the development of Transfer Paths (TP) from speakers to microphones. A novel methodology is presented to quantify the door stiffness requirements for optimal speaker ANC performance, incorporating substructuring methods and physical testing. The accuracy of the developed CAE models is validated using physical testing of circular and oval-shaped speakers integrated into vehicle doors and the calculation of transfer paths between each door speaker and microphone locations is demonstrated. The significance of microphone and speaker locations relative to driver or passenger ear positions highlights their influence on ANC performance. Finally, a controller is developed to test the CAE model and illustrate its functionality using a supplier’s controller for sound management. Overall, this research establishes a reliable vibro-acoustic CAE ANC model capable of predicting ANC system performance accurately by integrating a full vehicle vibro-acoustic model with an ANC controller. Such a predictive capability enables optimization and enhancement of vehicle performance for noise cancellation, unlocking its full potential in mitigating vehicle noise.
Digital Shearography for Nondestructive Testing (NDT): Determination of Smallest Detectable Defect and Improvement of its Visibility
(2024-01-01) Guo, Bicheng; Yang, Lianxiang; Barber, Gary; Romagnoli, Marco Gerini; Lin, Hejie; Lu, Lunjin
Sensitivity is a key parameter for using NDT technology. Determining what factors affect the sensitivity of NDT and establishing the model to facilitate engineers to select the appropriate system parameters and the loading magnitude are very important in the practical applications. In the past decade, digital shearography has been widely used as an NDT tool for detecting delaminations and debonding defects in various composite materials, such as glass fiber reinforced polymer (GFRP), carbon fiber reinforced polymer (CFRP), Honeycomb structures, etc. Digital shearography is a laser interferometric technique and able to measure the first derivatives of deformation, i.e. strain information. It is suited well for NDT because defects generate strain concentration after a loading. As an NDT method, the sensitivity of digital shearography is an important parameter to measure the technology’s defect detection capabilities. However, due to various limitations, the sensitivity research of digital shearography is still in its infancy. First, this technique lacks a numerical model to offer a theoretical foundation for determining the minimum detectable delamination/debonding limits and the detectable depth of defects. Secondly, because a shearogram is a fringe pattern which is composed of both global deformation and defect information, smaller defect information is easily lost in the fringe patterns from global deformation. This research conducts in-depth study around determining the sensitivity of digital shearography and improving the defect visibility to meet the practical needs of helping engineers quickly select loads and quickly identify defects. To solve these problems, the main research work and innovation results are as follows: (1) In response to the first problem, this research presents a methodology of digital shearography for determining the size of the smallest detectable defect and its depth under various loading magnitudes for the purpose of nondestructive testing. First, a mechanical model based on the thin plate theory to calculate the expected bending of close-to-surface defects was proposed; the model built a relationship among the deformation caused by a defect, the size and the depth of the defect, as well as the load and the material properties. Second, the relationship between the relative deformation measured by shearography and the deformation induced by a defect was established based on the optimized shearing amount and the sensitivity of digital shearography. Based on these analyses, relationships between the size of the smallest detectable defect and the depth under different load amounts were established for different defect shapes. (2) A demonstration of the sensitivity limit of digital shearography is shown on the basis of the sensitivity model, and the search for strategies to improve digital shearography is undertaken. After research, while keeping the equipment consistent, the material unchanged, and the loading conditions the same, the best way to improve the sensitivity of digital shearography is to increase the contrast between defect information and background information. This method can make defects information clearer. Based on that, the second purpose was to examine methods for improving sensitivity found in previous studies and to discuss the advantages and disadvantages of all methods and developed the segment fitting method. According to the previous discussion, it can be found that the most common method is to make a fitting plane to represent the global deformation by unwrapping fringe pattern to build the continuous shearogram, and then subtracting the plane to increase the contrast. Secondly, the continuous shearogram of complex deformations makes it challenging to choose the fitting equation. Based on this, a piecewise fitting method is proposed. This method is based on the conventional fitting method, which is fitted based on the phase change between each fringes on the shearogram. Because the phase values between each fringe are linearly distributed, this method does need to consider the fitting equation selection. The new planes then need to be subtracted from the original image to remove the global deformation, thus preserving the defect. (3) The second innovation of this research is the development of a practical and effective method to experimentally remove fringe patterns caused by the global deformation that makes small defects directly visible, which improves the non-destructive testing capabilities of digital shearography, thereby simplifying defect detection and visualization. For shearographic Non-Destructive Testing (NDT), the phase distributions of two interferograms under different loads P1 and P2 are recorded. This novel approach involves recording one additional phase distribution of an interferogram at a load between P₁ and P₂, e.g. P₁’. Two phase maps of shearograms can be generated, corresponding to the two loads Δ₂ = (P₁’-P₁) and Δ₁ = (P₂-P₁), respectively. Because of the nondestructive nature of the testing, the magnitude of the loads P₁ and P₂ is small, and the 1st derivative of global deformation of the test part is assumed to be linear. Therefore, a linear coefficient C based on the two shearograms can be determined. The information from global deformation is then removed by subtracting the shearogram generated with the small load Δ₂ multiplied by the correlation coefficient C from the one obtained with the relatively large load Δ₁. This technique is further improved by calculating a complete surface linear coefficient Cij, which improves the detail processing of the deformation of samples with complex geometry and mechanical properties. Experimental verification was conducted based on specimens with prefabricated defects of different sizes and different loading conditions to verify the proposed mathematical model and experimental methods to eliminate global deformation. Experimental results show that the developed model can provide useful estimates for digital shearography NDT, and in particular can help test engineers estimate the size of the smallest detectable defect and the depth of the defect under corresponding load magnitude. Also, the experimental coefficient method can effectively evaluate a variety of structures and also be verified to remove global deformation, which improves defect detection capabilities and increases visualization of the digital shearography
Amplitude Method to Detect Debonding for Stack Bond Adhesive
(2024-01-01) Huang, Xiaobao; Barber, Gary; Gu, Randy; Wang, Xia; Latcha, Michael; Qu, Hongwei; Zhou, Jun
A numerical method was developed to detect debonding (crack initiation) condition during fatigue testing of an adhesive joint with thin steel sheets in standard configurations of coach peel and lap shear specimens. The goal is to establish the relationship between the sample's vibration behavior and initial failure condition, this relationship can be used to develop fatigue S-N curves for the adhesive under geometrical configurations of either coach peel or lap shear specimens. This method focuses on the continued monitoring of the specimen's vibration status by transferring the wave form data (in time domain) to a Fast Fourier Transform (FFT) process and obtaining frequency and amplitude data (in the frequency domain), these data are then processed to identify the critical events such as debonding (crack initiation), crack propagation and total failure with associated cycle counts for each event. The amplitude output files were used to analyze the progression of different stages of failure for the samples under cyclic loads. Video analysis of failure modes was utilized to identify the different types of damage matching the cycle count based on time scale (frames) for each stage: ANSYS models were generated to provide supporting evidence in terms of change in natural frequencies and amplitude due to change of internal stiffness of the specimens. Certain mode shapes were analyzed to gain confirmation of the relationship between mode shape, amplitude, and initial failure of the samples
Virtual Methodology for Active Force Cancellation in Automotive Application Using Mass Imbalance and Centrifugal Force Generation (CFG) Principle
(2024-01-01) Paul, Abhishek; Latcha, Michael A; Mourelatos, Zissimos P; Cooley, Christopher; Haider, Syed; Schmidt, Darrell
Structures under the influence of an external force are excited to resonance when the frequency of the external force and the natural frequency of the structure align with each other. Resonance leads to large deformation, which may cause damage to the integrity of the structure. There have been numerous applications of external devices that dampen the effects of excitation to the structure, such as tuned mass dampers, semi-active and active dampers, which have been implemented in buildings, bridges, and other large structures. One of the methods used for active cancellation uses the principle of centrifugal forces generated by the rotation of an imbalanced mass. These forces help counter the external excitation force applied to the structure. This research focuses on the working principle of active force cancellation using centrifugal forces due to mass imbalance and provides a virtual solution to simulate and predict the forces required to cancel the external excitation to an automotive structural system. This research addresses the challenges to miniaturize the CFG used for a Body on Frame truck and effectively reduce the amplitudes of the response due to a forcing function. The virtual tool presented in this thesis will help predict the maximum amplitude cancellation at resonance for given imbalance mass and frequency of forced excitation.
A Simulation-Based Fatigue Life Estimation Method for Nonlinear Systems under Non-Gaussian Loads
(2023-01-01) Mande, Onkar K; Mourelatos, Zissimos P.; Gu, Randy J; Monroe, Ryan; Drignei, Dorin
In the fields of durability and stochastic structural dynamics, it is customary to focus on linear structures subjected to Gaussian excitations. However, real-world engineering systems often exhibit nonlinear behavior and are exposed to non-Gaussian loads. Calculating fatigue life for such nonlinear systems under non-Gaussian loading presents many challenges such as complex nonlinear dynamics, multifaceted statistical characteristics, and time-dependent effects resulting in a very high computational effort. To overcome these hurdles, this research uses non-Gaussian Karhunen-Loeve expansion (NG-KLE) to not only predict the expected fatigue life but also obtain the Probability Density Function (PDF) of fatigue life. It integrates a sub-domain-based technique to significantly reduce the computational demands while preserving accuracy, by efficiently obtaining long time trajectories of random processes. This development is very useful for excitation signals that far exceed the process correlation length. The NG-KLE method serves as the main tool for characterizing the excitation process by estimating its non-Gaussian marginal distribution and autocorrelation function. A Karhunen-Loeve (KL) expansion is executed only for the first subdomain, and then extended to subsequent subdomains by establishing correlations between the KL expansion coefficients of adjacent subdomains. This innovative approach is adapted to non-Gaussian (NG) excitation, allowing for efficient characterization of both the input and output random processes using NG-KLE, enabling the generation of very long synthetic output random stress process samples. The fatigue life corresponding to each output stress trajectory contributes to the estimation of the PDF of fatigue life. The proposed generalized fatigue life estimation approach accommodates both Gaussian and non-Gaussian processes for both narrow and wide band signals. To demonstrate its effectiveness, we use a duffing oscillator system and a practical example involving a truck assembly modeled by the Finite Element Method (FEM).
Using Salt Gradient Energy and Thermal Energy to Enhance Reverse Osmosis Desalination
(2024-01-01) Yagnambhatt, Sanjana; Maisonneuve, Jonathan; Guessous, Laila; Wang, Xia; Yang, Ziming; Ladner, David
Improving desalination energy efficiency is crucial for meeting rising global water demands. Reverse osmosis (RO) is a common desalination process that uses an applied pressure to overcome the natural osmotic potential of seawater to drive nearly pure water permeate through a semipermeable membrane. However, it has high specific energy consumption ranging from 4-5 kWh/m3 and environmental issues associated with discharging the highly concentrated brine that is left over after separation. This work investigates two methods of improving the energy efficiency of RO desalination: (1) Recovering salt gradient energy from desalination brine, and (2) Using thermal energy to pre-heat RO feed water and reduce mechanical pump work.
Molecular Dynamics Simulation of the Effect of Particle Hardness on Tribological Properties of Nanofluids
(2022-01-01) Xu, Cang; Barber, Gary; Schall, James; Yang, Ankun; QAu, Hongwei; Zhao, Peng
The determination of physical properties of nanofluids is mature, but the knowledge of tribological properties of nanofluids is limited. In this paper, the effects of surface roughness, fluid thickness, nanoparticle hardness, and number of nanoparticles on friction are explored systematical using a 2D Lennard-Jones molecular dynamics model. LJ parameters were chosen such that the ratio of stiffness of the nanoparticles to the opposing surfaces was approximately equal to ratio of stiffness of either aluminum oxide or zinc oxide to steel. A total of two hundred and twenty configurations were investigated. The results show that the benefits or drawbacks of nanofluid lubricants are sensitive to the friction regime (boundary, mixed, or hydrodynamic). When nanoparticles are present in lubricant-starved boundary conditions (fluid thickness less than the surface roughness amplitude), nanoparticles offer support that keeps the opposing surfaces separated. This separation results in reduced contact between the opposing surfaces and provides surface smoothing, which in turn lowers friction relative to the base fluid. At intermediate levels of fluid thickness where the fluid thickness and roughness are approximately equal, the presence of nanoparticles has a detrimental effect on friction. Nanoparticles jam and lock surfaces together and increase friction relative to the base fluid. As fluid thickness increases, the friction of the nanofluid generally remains higher than the base fluid likely due to the increased viscosity of fluid due to the presence of the nanoparticles. This work suggests nanofluids may offer limited benefits under specific lubrication conditions, but are detrimental under most conditions.
Novel Membrane Systems for Energy Harvesting and Water Recovery
(2023-01-01) Moussaddy, Sarah; Maisonneuve, Jonathan JM
Improving energy efficiency is an important part of the transition for mitigating greenhouse gas emissions. This dissertation introduces two novel membrane processes that can improve the energy efficiency of key sectors: (1) energy recovery from exhaust gases for improved power plant efficiencies, and (2) fertilizer-based liquid desiccant systems for improved dehumidification of indoor plant farms.Regarding the first, large amounts of energy are currently wasted from gradients of gas mixtures that are released from power plant exhaust. The energy is estimated to be 1-2 of the plant’s overall power capacity. To recover this energy, this work introduces a membrane process that uses ambient air as a sweep gas to draw concentrated gases from an exhaust source to do mechanical work in the form of compressed permeate gas flow. The concept and the developed numerical model are experimentally validated with a polydimethylsiloxane membrane using a binary gas mixture of nitrogen (N2) and water vapor in a first study, where power density of 57 mW/m2 is observed under relatively conservative test conditions. In a second study, N2 and carbon dioxide (CO2) was used and power of up to 6.35 W/m2 is experimentally observed when pure CO2 is supplied as feed, and up to 0.37 W/m2 when 20 CO2 feed is supplied. Regarding the second application of membranes, the focus is on a solution to improve the efficiency of energy, water, and fertilizer used in agriculture. This work introduces the novel concept of using fertilizer as a liquid desiccant for energy efficient dehumidification of indoor plant environments. The first-ever experimental demonstration of the concept is done using a polydimethylsiloxane membrane and a water vapor flux of up 1.90 g/m2/h is obtained. Dehumidification is confirmed across a range of standard greenhouse conditions and operating parameters. A theoretical modelling analysis is also performed to investigate the effects of operating conditions on the specific energy. As a result, a specific energy as low as 0.15 kWh/ kg is obtained under certain conditions with optimized desiccant temperatures and air flow rates.
Process Optimization of Autoclave Bonded Light-Weight Material Joints
(2022-01-01) Jagatap, Shraddha Ratnakar; Nassar, Sayed; Shillor, Meir; Yang, LianXiang; Wu, Zhijun
This dissertation research fills a gap in the existing open literature regarding the significance of autoclave cure process variables and their interactions on the static strength of lightweight material single lap joints under tensile-shear loading. Specifically, the research investigates the dependence between the degree of cure of the epoxy adhesive and the mechanical performance of the single lap joint boded with same epoxy adhesive. Lightweight material system includes polycarbonate, Aluminum 6061 and glass reinforced plastics (GFRP) extren 500. A commercially available polyurethane film adhesive PE399 was selected to bond Polycarbonate single lap joints (SLJ) while epoxy film adhesive AF163-2K was selected to bond aluminum and GFRP joints. Studied variables include cure temperature, cure pressure and their respective rates as well as the duration of cure time. Dynamic Mechanical Analysis (DMA) is used to quantify glass transition temperature of AF163-2K cured with different combinations of autoclave process variables. The relative significance of variables and variable combinations are investigated for their effect on the bond strength. Experimental test data shows interaction between autoclave variable cure temperature in combination with cure time, temp ramp rate and pressure ramp rate have significant effect on glass transition temperature, bond strength and failure mode. Changes in joint static load transfer capacity (LTC) was investigated after cyclic temperature profile fluctuates between 20 C and 85 C at a constant relative humidity (RH) level of 85 .
Load Distributions in Bolted Single Lap Joints Under Non-Central Tensile Shear Loading
(2021-11-16) Sinthusiri, Chaiwat; Nassar, Sayed; Shillor, Meir; Yang, Xianjie; Wu, Zhijun
This study uses a numerically calibrated beam theory-based model to investigate the bolt load distributions in a preloaded two-bolt single lap joint under non-central tensile shear loading. The linear spring-based modeling is used for the two preloaded bolts and substrates. The bolt stiffnesses were derived from the bolt flexibilities influence by the bending deformation, the shear deformation, the bolt, and plate contact deformations. Due to the non-uniform load distribution along the bolt shank, the 3D finite element analysis was used to determine the correlation factors of each influence factors. Non central loading may be due to geometric tolerances that would cause additional moment loading on the joint. Thus, the load would not be equally distributed among all bolts in the joint. The effect of various joint parameters, bolt preload and off-center location of the tensile shear loading is investigated and discussed.

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