bluuebunny/crossref_metadata_2025 huggingface dataset:
At Scale Development of Thermal Test Vehicles for Data Center Liquid Cooling Developments
Authors: Heydari Ali , Miyamura Harold , Chowdhury Uschas , Manaserh Yaman Mohammad Ali , Tradat Mohammad , Shahi Pardeep , Radmard Vahideh , Eslami Bahareh , Kalma Dwayne , Rodriguez Jeremy
Published: November 2023

High-performance computing with the latest generation of high-density chips and microprocessors in data centers requires advanced and efficient cooling technology to meet the challenging thermal requirements. Indirect liquid cooling with cold plates on top of the processor has become an attractive and efficient solution while transitioning from traditional air cooling inside the data center. Using a thermal test vehicle (TTV) can be a cost-effective and reliable methodology to commission liquid-cooled components successfully without risking actual IT equipment. TTVs can also be highly beneficial in testing and developing data center cooling technologies for future products with individual thermal requirements. In this paper, TTVs are created to replicate the thermal behavior of heat-generating components to characterize case-to-coolant thermal resistance, find hotspots, develop and test cooling technologies cost-effectively. Different design requirements influence the development and the intricacy involved in the construction, manufacturing, and telemetry of the TTV. In our study, TTVs for a 3U sled are discussed in detail, touching on different aspects such as proof of concept, design, verification, manufacturing, testing, and verification in a data center environment. The effects of choosing appropriate material properties, electrical requirements, form factors, stack-up method, type of heat-generating components, thermocouple placement, and nonuniform heat flux are also presented following analytical, numerical, and experimental results. The results and failure cases suggest some best practices in designing non-silicon TTVs while mimicking higher heat load in form factor of high heat density servers. Manufactured TTVs are placed in a chassis following the configuration and form factor of the 3U sled in high heat density servers and scaled up in a rack. In addition, a custom rack mount TTV server named “Olympus” is presented as an outcome of the study. Cold plates and cooling loops can be tested on the TTV server for thermal and hydraulic characterization with rack and row manifolds, Liquid-to-Liquid (L2L), and Liquid-to-Air (L2A) heat exchangers in a data center test environment. Later in the paper, the commissioning of liquid cooling technologies with TTVs is demonstrated in a data center environment. Real-time data for heater spreader temperature in TTVs are plotted with the help of a front-end application with boundary conditions on both primary and secondary sides. As a result, this paper provides complete guidelines on the development, verification, and application of TTV to determine critical performance parameters in commissioning (such as flow rate, temperature, pressure drop, cooling capacity, etc.) and simulate failure scenarios to ensure the reliability of components in the loop.
Evolution of Physical Properties of Liquid Film During Evaporation Process: Drying and Evaporation Process of Inkjet Liquid Film
Authors: Kichise Keisuke , Harada Yoshihiro , Kuramoto Shinichi , Kadonaga Masami , Fushinobu Kazuyoshi , Kato Koichi
Published: November 2023

In general, the evaporation and drying process of liquid film is a complex thermo-fluid phenomenon related to phase change and heat/mass transfer accompanied by changes in the physical properties of the liquid and understanding them is important in improving the performance of inkjet printers. In inkjet printers, ink droplets are ejected onto the media by an inkjet printhead to form a thin liquid film, which is then fixed by evaporation in a dryer. The dryer is one of the modules that consumes the most power among the inkjet printer components, and it is important to understand the evaporation behavior of the ink liquid film. One effective method to understand the evaporation behavior of ink film is to measure the temporal change in viscosity of the ink film surface. However, it has been difficult to measure the viscosity of thin liquid films formed by inkjet printheads using conventional methods. In this study, we propose to measure the temporal change of the viscosity of the liquid film surface by applying the Dynamic Light Scattering (DLS) method.
Boiling Limit on Textured Oil-Impregnated Surfaces
Authors: Zhou Yimin , Adera Solomon
Published: November 2023

Boiling is an important heat and mass transfer process that has tremendous benefits in thermal management applications where timely and efficient heat removal is critical for operation. Boiling is inherently limited by the critical heat flux (CHF), which is the maximum heat flux that can be dissipated from the heated surface via liquid-to-vapor phase change. Heat fluxes that exceed CHF cause surface dry-out that initiates thermal runaway and eventual device failure or burnout. Past studies have used micro/nanoengineered surfaces to improve wicking and liquid replenishment mechanism to delay CHF and/or increase the CHF limit. In this work, we investigate the CHF limit of micro-nanotextured oil-impregnated surfaces in pool boiling. Pool boiling experiments in water were conducted for copper plates with different surface morphologies, including Krytox oil impregnation. The bubble nucleation, growth, and departure behaviors were captured using a high-speed camera at 1000 frames per second during nucleate boiling. Due to the presence of an annular wetting ridge, which forms near the base of the growing bubble, the bubble growth and coalescence mechanism on oil-impregnated surfaces was distinct from that on un-impregnated micro-nanostructured hydrophobized (i.e., superhydrophobic) surfaces. Our experimental results show that (a) the bubble departure diameter on the oil-impregnated surfaces was 1.6-times larger than that on the superhydrophobic surfaces and (b) the CHF on oil-impregnated surfaces was similar to that on the un-impregnated superhydrophobic surfaces (≈20–30 W/cm2), a result that we attribute to oil depletion. Results show that oil impregnation does not improve the CHF limit in boiling.
Experimental Validation of a Heuristic Control Strategy for a Transient Thermal Management System With Latent Thermal Energy Storage
Authors: Shanks Michael , Inyang-Udoh Uduak , Jain Neera
Published: November 2023

Hybrid thermal management systems (TMS) enable faster response to rapid transient heat loads by supplementing heat rejection through a primary heat sink with temporary heat storage in a thermal energy storage (TES) device. The TES is not a passive component; it must be actively controlled by a realtime controller to decide when the TES should be discharged or recharged. While various types of controllers have been developed for hybrid TMS architectures, controllers for hybrid TMS in transient electronics cooling applications have predominantly been demonstrated in simulation environments. One such controller developed previously is a heuristic logic-based controller that leverages a state of charge (SOC) metric and feedback from several thermocouples placed in the fluid loop to manage the operation of the TES. In that prior work, the controller was demonstrated in simulation only; this paper builds on that work by implementing and validating the controller’s performance in an experimental single-phase hybrid TMS testbed. A particular advantage of this controller is its low level of computational complexity, facilitated by its rule-based architecture, which makes it more amenable for industrial use. We present an experimental case study to demonstrate the heuristic controller’s ability to meet two objectives: reduce the peak temperature at the surface of the cold plate below an allowable threshold and manage the SOC so the thermal storage capacity is not depleted.
Development of Ceramic Pulsating Heat Pipes for Medium-Voltage Power Electronics
Authors: Abdelmaksoud Ramy , Diebold Jeffrey , Hota Sai Kiran , Lee Kuan-Lin , Sinha Shivangi , Maksimovic Dragan
Published: November 2023

Due to the rapid increase of electric vehicles in the market, a corresponding significant increase in fast chargers will be needed. However, expanding the adoption of fast chargers such as direct current fast chargers is challenging with the current grid infrastructure. Medium-voltage (MV) electronics are an essential component in grid-tied applications. However, thermal management of such components presents a barrier to pushing the boundaries of high-power density, while maintaining high efficiency and reliability. Thermal management is further complicated by the need to maintain sufficient voltage isolation. Under a Small Business Innovative Research (SBIR) Phase I program funded by the U.S. Department of Energy (DOE), Advanced Cooling Technologies, Inc. (ACT), in collaboration with the University of Colorado, Boulder (UC Boulder) developed innovative ceramic Pulsating Heat Pipes (PHP)s, which significantly improved the thermal management and provided voltage isolation. Different flat ceramic PHPs were fabricated for the lab-scale testing. The thermal performance and voltage isolation were evaluated through both experimental testing and numerical modeling. The effect of different parameters, such as the fill ratio, gravity-aided and against-gravity orientations, and heat input, on the thermal performance of the ceramic PHP, was investigated. It was found that at the optimal fill ratio, a thermal resistance reduction of 41%–67% was achieved for different gravity-aided orientations (0–90°) when compared to the uncharged ceramic PHP (i.e., the ceramic PHP without fluid in it). The ceramic PHP was able to efficiently transport up to 6 W/in2 with a thermal resistance reduction of 58% at the horizontal position. The voltage isolation testing showed that the ceramic PHP can provide electrical insulation when exposed to a voltage of 28 kV. In addition, the effect of different working fluids and fill ratios, on the voltage isolation capability of the ceramic PHP, was investigated.
Evolution in Lead-Free Solder Alloys Subjected to Both Mechanical Cycling and Aging
Authors: Maruf Mahbub Alam , Mazumder Golam Rakib , Chakraborty Souvik , Suhling Jeffrey C. , Lall Pradeep
Published: November 2023

Solder joints in electronic packaging often experience failure due to cyclic thermo-mechanical loading. For example, electronic components in the automotive engine compartment or a giant turbine of a power plant may encounter both thermal cycling as well as mechanical cycling due to vibration. At the same time, electronic components can undergo thermal cycling due to frequent power switching, e.g., turning a car engine on and off. Thus, the solder materials used to attach electronic components are often subjected to cyclic stresses and strains due to temperature changes and the CTE mismatches of the assembly materials, as well as due to vibration and other time-varying loadings. In the literature, recent studies by our group have been carried out to examine the mechanical behavior and property evolutions (e.g., modulus, yield stress, ultimate tensile strength, and creep rate) occurring due to either isothermal aging or due to isothermal mechanical cycling. In the case of aging, microstructure changes are the primary reason for changes in the mechanical response. In the case of mechanical cycling, both microstructural evolution and damage accumulation (e.g. microcrack growth) lead to the observed changes. Currently, there are no prior investigations on the effects of both isothermal aging and mechanical cycling on the mechanical property and microstructural evolution of lead-free solder alloys.

In this study, we have evaluated the changes in mechanical properties and microstructure that occur due to mechanical cycling followed by isothermal aging at high temperature. Uniaxial samples of SAC305 lead-free solder alloy were first prepared by solidification in glass tubes under a controlled reflow profile. The samples were first mechanically cycled under strain control for various durations (e.g., 0, 50, 100, 200, 300 cycles), and then subsequently aged for 20 days at T = 125 °C. All of the preconditioned specimens were then subjected to nanoindentation testing to evaluate mechanical properties. Results for the various tests were compared to characterize the effects of combined effects of aging and mechanical cycling on the deterioration of the elastic modulus, hardness, and creep properties relative to the results for pristine specimens. As expected, exposure to both cycling and aging greatly influenced the results, with the samples that were cycled 300 times followed by aging showing the greatest degradations. Optical microscopy was also used to evaluate the microstructural evolution which demonstrates microstructural coarsening occurred in the samples due to the combination of mechanical cycling aging.
Repairability of SMDs on 3D Printed Circuitry for Sustainable Electronics Utilizing Direct Write Technique
Authors: Lall Pradeep , Sarwar Md Golam , Soni Ved , Miller Scott
Published: November 2023

Sustainable conductive ink for 3D-printed flexible electronics is needed to enable lower-impact waste print processes. The ability to undertake reparability is an additional method to achieve sustainable products through the extension of electronic components’ lifespan and reduced e-waste. However, repairability studies are scarce for sustainable, flexible electronics in the literature. This study assessed the repairability potential of Surface Mount Devices (SMD) on 3D-printed full wave rectifier circuits for sustainable flexible electronics. Full wave rectifiers are commonly used in power supplies, battery chargers, and other applications requiring a steady DC voltage. The direct-write printing technique used stretchable silver ink and interconnects composed of electrically conductive adhesive (ECA) for component attachment to create conductive traces. The circuit’s electrical characteristics are assessed using a high-frequency impedance analyzer, which analyzes the circuit’s resistance, capacitance, and inductance at various frequencies. The circuit is deliberately damaged by removing SMDs, and the research looks into the efficiency of direct write repair procedures. Direct write repair entails printing a conductive pad onto the circuit surface selectively using the same direct-write technique that was used for manufacturing the circuit. The repaired circuits are evaluated using an impedance analyzer, and the results are compared to the original circuit to determine the influence of the repair procedure on the circuit’s electrical performance.
Component Attach Process Recipe and Performance on Aerosol Printed Sustainable Silver Ink
Authors: Lall Pradeep , Bimali Sabina , Narangaparambil Jinesh , Miller Scott
Published: November 2023

The advancement of flexible printing technology in electronics has raised the demand for compact, lightweight, and stretchable printed electric circuits. The viability of environmentally friendly water-based inks with low-impact waste requires the development of process recipes for component attachment on flexible substrates. The processes required for component attachment on the newer generation of inks are not well understood. This paper aims to demonstrate process parameter study and component attachment in the aerosol jet printer (AJP) platform with water-based silver nanoparticle ink. The process parameter study includes printing parameters such as UAMFC, SMFC, stage speed, several passes, and sintering analysis, including sintering time and temperature. Print quality is evaluated using white light interferometry (WLI) and optical microscopy images. By integrating the bell-shaped cross-section area (CSA) acquired by the WLI test, the CSA of the printed lines is computed. The electrical and mechanical properties of the printed lines are quantified in terms of resistivity and shear load to failure, respectively. Optimized parameters from the printing and sintering process are used to print traces on which different components are attached with the help of ECA (Electrically Conductive Adhesive). The effect of using sustainable ink and ECA on passive components was analyzed by comparing their performance before and after being attached. Components that fall within the acceptable range of the rated value are deemed to be functioning properly.
Performance Analysis of Liquid-to-Air Heat Exchangers of High-Power Density Racks
Authors: Heydari Ali , Gharaibeh Ahmad R. , Tradat Mohammad , Soud Qusai , Manaserh Yaman , Radmard Vahideh , Eslami Bahareh , Sammakia Bahgat , Rodriguez Jeremy
Published: November 2023

The ability of traditional room-conditioning systems to accommodate expanding information technology (IT) loads is limited in contemporary data centers, where the storage, storing, and processing of data have grown quickly as a result of evolving technological trends and rising demand for online services, which has also led to an increase in the amount of waste heat generated by IT equipment. Through the implementation of hybrid air and liquid cooling technologies, targeted, on-demand cooling is made possible by employing a variety of techniques, which include but are not limited to in-row, overhead, and rear door heat exchanger cooling systems. The ongoing trends of rising power densities of microprocessors and the presence of hot spots present a considerable challenge to the air-cooling system, which pushes it to its limits. As a result of the significant rise in IT power densities, single-phase cold plate cooling is becoming increasingly popular. However, the limited availability of a source of chilled water or constrained air distribution routes and the unavailability of raised floors are the main obstacles to the adoption of single-phase cooling technologies in many old data centers, which led to the use of liquid-to-air cooling distribution units (CDUs). These types of CDUs effectively cool servers by distributing liquid coolant into cooling loops that are installed on top of each server. The CDU pumps cold liquid to cooling loops attached to servers or chips, where they absorb heat. After returning the heated fluid to the CDU, the heat exchanger (HX) uses the cold air to eject the by the use of fans.

One of the most common liquid cooling techniques will be examined in the current study based on different conditions for high power density racks (+50 kW). This paper investigates the cooling performance of a liquid-to-air in-row CDU in a test rack containing seven thermal test vehicles (TTVs) under various operational conditions, focusing on cooling capacity, HX effectiveness, and TTV case temperatures under different supply air temperatures (SAT). This test rig has the necessary instruments to monitor and analyze the experiments on both the liquid coolant and the air sides. Moreover, another experiment is conducted to assess the performance of the CDU that runs under different control fan schemes, as well as how the change of the control type will affect the supply fluid temperature and the TTV case temperatures at 10%, 50%, and 100% of the total delivered power. Finally, suggestions for the best control fan scheme to use for these systems and units are provided at the conclusion of the study.
Enhancing Mechanical Reliability of Silver Sintered Joints With Copper Nanowires in High-Power Electronic Devices
Authors: Medina Garcia Alicia , Harris John , Huitink David R.
Published: November 2023

This study investigated the mechanical reliability of silver-sintered die attachment under harsh operating conditions, and explored the advantages of adding copper nanowires to improve the bond’s mechanical properties. Samples were prepared using a template-assisted electrochemical deposition process to coat the substrate surface with copper nanowires, and were subjected to thermal aging at various temperatures to assess their mechanical reliability. Results showed that the incorporation of copper nanowires in the substrate interface significantly reduced degradation in shear strength as a result of thermal aging, acting as mechanical reinforcement and improving the interfacial resilience against mechanical shear stress. The addition of copper nanowires also reduced the void formation in the thermal aging, resulting in a more robust and reliable bond. The study demonstrates the potential of using copper nanowires as a reinforcing agent to enhance the mechanical properties of silver-sintered die attachment, particularly for high-temperature applications.
Finite Strain Sensing via Additively Manufactured CNF/TPU Strain Gauges
Authors: Hernandez Julio A. , Maynard Cole , O’Brien Corey , Rodriguez David , Newell Brittany , Tallman Tyler N.
Published: November 2023

Multifunctional additive manufacturing (AM) has opened the door to exciting new possibilities for highly customizable and on-demand printable sensors and actuators for application in areas such as embedded structural sensing, robotics, and, among other examples, human healthcare and monitoring technology. In particular, strain or deformation sensors printed via fused filament fabrication (FFF) methods typically make use of the piezoresistive effect, which can be achieved by modifying the base polymer with conductive micro-to-nanoscale fillers. However, sensors of this type often suffer from challenges such as limited flexibility due to the use of comparatively hard polymers and additives and highly inconsistent electrical properties. To overcome these challenges, we herein present the preliminary results of a study of carbon nanofiber (CNF)-modified thermoplastic polyurethane (TPU) sensors produced via FFF printing. The CNF/TPU filament used to print these sensors was produced using a novel wet mixing process, wherein the TPU is first dissolved in dimethylformamide (DMF) solvent prior to dispersing the CNFs. To demonstrate the strain sensing properties of this material, simple dog bone-shaped sensors were printed out of TPU modified with 7.5 and 10 wt.% CNFs. And to showcase the potential of this material for large deformation sensing, resistance changes were measured for finite strains up to 50%. The CNF/TPU sensors showed non-linear but monotonically increasing resistance up to approximately 35% strain, beyond which point resistance rapidly became immeasurable. The results of this study are an important step towards the realization of next-generation printable plastics with functional and consistent properties for applications such as strain sensing.
An Investigation on the Effectiveness of Cross-Sectional Tapering for Broadband Non-Reflective Traveling Waves Generation in Beams With Passive Discontinuities
Authors: Omidi Soroor Amirhossein , Tarazaga Pablo A.
Published: November 2023

Inspired by the dynamic behavior of the basilar membrane in the mammalian auditory system, the non-reflective traveling wave phenomenon is studied in a finite tapered cantilever beam. The goal of this study is to investigate the effectiveness of tapering the geometry to relax the design sensitivity to achieve such behavior as compared to the uniform geometry. The Galerkin method is used to derive the discretized form of the equation of motion. The results of this study suggest that tapering can be effective in improving the robustness of the design space in which traveling waves can be obtained.
Energy Transfer in a Quarter-Car Model With Inertially Nonlinear Inerter-Based Pendulum Vibration Absorber
Authors: Cosner Joel A. , Tai Wei-Che
Published: November 2023

In this theoretical study, a recently developed inerter-based pendulum vibration absorber (IPVA) is coupled with energy harvesting capabilities and applied to a quarter car model driving on a class C road (ISO 8608). Performance metrics including power harvested, sprung mass acceleration (ride comfort), and road handling are studied while varying the dimensionless pendulum length parameter. It is discovered that P-bifurcation of the probability density function (PDF), from mono-modal to bimodal is responsible for large output power (40% improved) and low sprung mass acceleration (40% improved) when compared with the equivalent linear system. Ride handling is determined to be best as well under bimodal conditions. As such, the authors further develop a Wiener path integration (WPI) coupled with curvature checking for the PDF to predict this P-bifurcation and eliminate the need for exhaustive Monte Carlo simulations for various parameter configurations. Energy flow in the system is also considered.
Modal Analysis of 2D Periodic Structures Using Dynamic Condensation With Primal Assembly
Authors: Hagos Robel Weldebrhan , Chang Seongmin , Han Jae-Hung
Published: November 2023

Periodic structures, composed of repeating and regularly connected unit cells, are widely used in various engineering fields due to their functionality, aesthetics, producibility, and unique property of passively reducing vibrations. However, analyzing these structures can be challenging due to their high degrees of freedom (DOFs), and dynamic analysis of periodic structures requires solving multiple linear systems that can quickly become computationally demanding. Hence, this study presents an efficient method to predict the modal response of two-dimensional periodic structures, utilizing the improved reduced system (IRS) technique and primal assembly. The proposed method involves conducting the reduction process on the unit cells and connecting them using connectivity matrices, eliminating the need for the entire structure to be present during the analysis, resulting in improved efficiency. The accuracy and efficiency of the proposed method are demonstrated using numerical examples with complex geometry and varying material properties.
Development of Adaptive Connectors Based on Shape Memory Alloys
Authors: Hofer Andreas , Pagel Kenny , Thüsing Kai , Langbein Sven , Lembke Dietrich , Drossel Welf-Guntram
Published: November 2023

A major limiting factor in the charging time of fast-charging electrical vehicles is the maximum electrical power that can be transmitted through the contact points between the charging plug and the vehicle inlet. The electrical contact resistance (ECR) thereby plays a decisive role. By increasing the contact surface between these contact points, it is possible to decrease the ECR, leading to higher transmission power and reduced charging times. Due to the limited construction space, high contact forces between the charging plug and the vehicle inlet are required to reduce the ECR. However, high contact forces complicate the insertion of the plug by hand. In consequence, lower contact forces and significant heating of the connection have to be accepted. For this reason, today’s systems (e.g., Combined Charging Systems (CCS)) include active cooling of the contacts.

This paper presents an alternate system that temporarily increases the contact force of connectors during charging with shape memory alloy (SMA) actuators. To ensure industrial applicability, the research is conducted on the example of a CCS Type 2 charging plug. Initially, the correlations between extraction force, contact normal force and resulting ECR are investigated experimentally. Subsequently, basic mechanisms for increasing the contact normal force with SMA wires are presented and experimentally validated. As a result, a reduction in ECR of up to 60% has been experimentally demonstrated.
Numerical Prediction of the Effective Mechanical Behavior of Interpenetrating Phase Composites Comprising Architected Nitinol Cores
Authors: Ilyas Shahzaib , Abu Al-Rub Rashid K. , El-Khasawneh Bashar , Zaki Wael
Published: November 2023

This work focuses on the computational investigation of 3D interpenetrating phase composites (IPCs) consisting of an architected shape memory alloy (SMA) microstructure embedded in an elastic-plastic second phase. The SMA functional phase consists of Nitinol (NiTi) for which the constitutive material behavior is simulated using a user-defined material subroutine (UMAT) in Abaqus finite element software. Beam-based and mathematically driven triply periodic minimal surfaces (TPMS) architectures are considered for the NiTi functional phase. IPC unit cells are identified and modeled considering idealized periodic boundary conditions (PBCs). The mechanical and functional properties of the unit cells are evaluated using volumetric homogenization. The effective mechanical response is evaluated and analyzed as a function of NiTi volume fraction considering various loading conditions. The results show that NiTi morphology significantly affects the elastic stiffness, which varies monotonically with NiTi content. Among the geometries considered for the NiTi cores, TPMS cores having a Schwarz Diamond topology resulted in the highest effective axial stiffness and bulk moduli, whereas TPMS IWP topologies resulted in the highest strain recovery.
Prediction of Hydrodynamic Loads on a Flexible Bio-Inspired Underwater Propulsor Using Physical Reservoir Computing
Authors: He Shan , Hess Isabel , Musgrave Patrick
Published: November 2023

Bio-inspired autonomous underwater vehicles (BAUVs) have the potential for stealthy navigation and operation in sensitive underwater environments by mimicking the natural behaviors and compliance of marine animals. However, BAUVs still face challenges where maneuverability and control are difficult to achieve, especially in high-energy coastal zones. Maneuverability and control could be improved by implementing real-time sensing of the hydrodynamic forces acting on a BAUV’s compliant body. In this study, we predict the hydrodynamic forces generated by a soft-robotic propulsor using Physical Reservoir Computing (PRC), with the future aim of improving the propulsor’s maneuverability. Physical reservoir computing is a machine learning technique that utilizes the nonlinear dynamics of a physical system for information processing. Compared to software-based machine learning frameworks, PRC requires significantly lower computational costs. With PRC, a majority of the information is processed within the physical system itself, enabling real-time prediction of time-varying target signals. In this project, we use PRC to leverage the nonlinear fluid-structure dynamics of a soft-robotic propulsor to predict its time-varying thrust. Our soft-robotic propulsor is powered by an antagonistic pair of embedded hydraulically amplified self-healing electrostatic (HASEL) actuators. We conducted experiments to measure the thrust generated by the soft robot in quiescent water. Using the PRC framework, we predicted the thrust using a linear weighted sum of the time-varying kinematic strains measured at multiple locations on the propulsor’s compliant body. We trained the linear weights by minimizing the error between the PRC prediction and the experimentally measured thrust. We then analyzed various sensor placement configurations to achieve the best performance. By using the PRC framework, we were able to accurately predict the time-varying thrust. Using the sensor configuration that yielded the best performance, we achieved R-squared errors of 0.908 and 0.898 on the training set and test set, respectively. This PRC method holds significant potential for predicting time-varying hydrodynamic loads in real-time which can be used to improve control and maneuverability of BAUVs.
Spatial and Temporal Homogenization of Phase-Field Equations With an Application to Iron-Based Shape Memory Alloy Modeling
Authors: von Oertzen Vincent , Kiefer Bjoern
Published: November 2023

As a unique subclass of multi-functional and smart materials, iron-based shape memory alloys have gained tremendous attention in recent years by virtue of their promising pseudoelastic properties combined with relatively low production costs. Especially for large-scale applications, efficient and robust simulation methods have to be developed based on appropriate material models, which are often formulated on microscopic scales. To this end, the concept of unequally and nonlinearly weighted averaging operators was recently introduced in [1, 2] as a fundamental homogenization framework in phase-field modeling of phase-transforming solids. Here, this rather general approach is applied in order to derive the effective driving force for transformation of an Allen-Cahn based dual-phase system, which is used to describe the martensite formation in Fe-Mn-Al-Ni at the nano-scale. As a novel approach, an analytical solution to the corresponding homogenization problem is provided in terms of polynomial weighting functions. Moreover, macroscopic relations for the effective system driving forces are derived by optimizing the corresponding coefficients numerically. In this manner, a system of macroscopic differential equations is obtained, from which the evolution of the effective phase state, e.g. the martensite volume fraction, can be solved directly on the macroscale without locally resolving the corresponding microscopic field distributions at each time step.
Effect of Area Density on Sensitivity and Strain Survival of Reduced Graphene Oxide Under Large Strains
Authors: Yazdi Armin , Tsai Li-Chih , Salowitz Nathan
Published: November 2023

Strain sensors are the primary, direct sensing element in many sensors with applications in robotics, wearable sensors, structural health monitoring, and beyond. Cutting edge applications are increasing demand for sensors that can survive and measure large strains (> 5%). Presently, the most common strain sensors are composed of a serpentine metal foil which can survive strains up to about 5% with a gauge factor (GF) of about 2 (measured as change in resistance divided by initial resistance all over strain). Research into nanoparticle-based strain sensors commonly reports surviving strains up to 50% and gauge factors around 200. Unfortunately, most nanoparticle-based strain sensors are composed of expensive, toxic materials and require high precision synthesis methods. The reduced Graphene Oxide (rGO) based sensors can be synthesized easily with common materials and methods. Study of strain sensing capabilities have revealed that rGO strain sensors can survive strains beyond 15% with gauge factors (sensitivity) on the order of 200.

Suspensions of graphene oxide (GO)’s flakes were deposited on flexible Polydimethylsiloxane (PDMS) substrates to create specimens with different area densities of 0.69, 0.80 and 091 mg/cm2 of GO. Specimens were thermally reduced to create rGO-based strain sensors. Resulting sensors were tested under tension applied at a rate of 0.1 mm/sec starting from 0% strain until failure. Resistance of the sensors in the direction aligned with the direction of the applied tension were measured at each 1 mm-increment of tension. Sensitivity and the strain to failure of the sensor were calculated and compared in specimens with different GO area densities.

Our study suggests that with increasing the area density of graphene oxide (GO) during the synthesis of rGO, the survivability of the rGO subjected to large strains can be improved while still demonstrating a high sensitivity. This study can help tailor rGO-based strain sensors especially to the applications where high strain survival (> 30%) is required while benefiting from a reasonably good GF (> 30).
Electromechanical Impedance Based Part Identification via Linear Projection
Authors: Sangle Sourabh , Tarazaga Pablo
Published: November 2023

The geographical separation between various supply chain participants creates challenges in ensuring the integrity of the parts under circulation. These supply chains have to regularly deal with counterfeiting, a significant problem with an estimated value equivalent to at least the tenth-largest global economy. Industries are constantly upgrading their anti-counterfeiting methods to tackle this ever-increasing issue. Traditionally, a physical or cyber-physical part identifier is used to assert the integrity and identity of parts moving through the supply chain. For this work, we propose the use of electromechanical impedance measurements to generate a robust, unique part identifier linked to physical attributes. Electromechanical impedance measurements have been employed as a basis for non-destructive evaluation techniques in damage detection and health monitoring. We propose using these high-frequency measurements recorded through bonded piezoceramic transducers to help uniquely identify parts.

For this study, identical piezoceramic transducers (cut from the same wafer to minimize variations) were mounted on identically manufactured specimens. The only distinction between these specimens was the physical variation introduced during manufacturing and instrumentation. Multiple measurements for each specimen were recorded. A unique part identification methodology based on linear projection was created using these measurements. Lastly, a leave-one-out-study was performed to uniquely identify the left-out specimen. This was used to validate the part identification methodology. This paper introduces the use of electromechanical impedance measurements (widely adopted for damage detection) as a unique part identifier, with a basic experimental implementation of the proposed mechanism on identically manufactured parts. The paper also highlights some challenges and future work needed to make this methodology robust and adaptable.
Effectiveness of Shape Memory Alloy Golf Clubs in Enhancing Golfer Performance
Authors: Ward R. Mason , Kirby Daniel , Hardy John , Hartl Darren
Published: November 2023

Many scientific developments pioneered by governmental research organizations are subsequently applied to consumer products. The use of shape memory alloys (SMAs) by NASA at the end of the 20th century motivated companies to incorporate these materials and their unique properties into marketable goods. In 1997, NASA reported that the Nicklaus Golf Company had developed a line of SMA-augmented golf clubs; the company claimed that its SMA club inserts reduced vibration and imparted greater spin on balls during contact. Inspired by these claims of enhanced performance, this work investigates the impact of SMA clubfaces on golf ball carry distance and shot accuracy for several clubface contact locations and slice angles. For each combination of shot parameters tested, the ball exit velocity and spin were computed via finite element analysis (FEA) using an explicit dynamic model that accounts for stress-induced phase transformation in SMA material regions and golf ball responses calibrated from experimental testing. The exit velocity and spin rate were used to calculate the ball flight trajectories for each case simulated. Alloy and design assumptions, including the addition of an internal cavity, were made to facilitate the development of stresses necessary for meaningful SMA material responses during clubface-ball impacts. These assumptions lead to findings such as nearly equivalent performances for geometrically identical clubheads with steel and SMA clubface inserts. Overall, this work shows that the use of reasonable SMA materials in a clubhead operating under normal weather conditions is inconsequential to shot accuracy and carry distance.
Comparative Review of Two Different Design Approaches for SMA Based Continuum Robots
Authors: Barakat Rawan , Goergen Yannik , Britz Rouven , Mandolino Michele , Rizzello Gianluca , Motzki Paul
Published: November 2023

Inspired by nature, the field of continuum robotics focuses on the research and development of bending and soft robotic structures. Like elephant trunks or tentacles, these robots are not based on discrete joints and rigid connecting structures, but exploit flexible bending motion with a high number of degrees of freedom. Because of a variety of possible fields of applications, continuum robots have experienced a strong increase in research interest within the last years. Possible applications range from medical (surgery) instruments over industrial inspection systems to soft and thus safe collaborative robotic structures for human-machine-interaction.

Common actuation techniques applied in continuum robotic systems make use of conventional drive units, which are bulky, heavy and oftentimes stationary. An alternative to these conventional drives is the implementation of shape memory alloy (SMA) wire actuators as artificial metal muscles. Like muscle contraction, SMA wires contract at a specific phase transformation temperature due to a reversible phase transformation from a low temperature phase, called martensite, to a high temperature phase, austenite.

This paper presents two specific design schemes for continuum robots based on SMA wire actuators. A first design is focused on maximum bending angles and range of motion. To reach this goal, the total maximum wire contraction is key. A Bowden cable inspired robot design is developed, which enables 3D motion and validated bending angles of over 200°. Because of the Bowden cable approach, the overall (passive) length of the robot is much longer than the actual actively bending tip of the robot [1], [2]. The second design approach is focused on a fully integrated continuum robot, including the integration of the SMA wires as well as the electrical wiring into the bending structure. Here, no additional passive part is required to exploit the movement of the continuum robot [3]. The design of the trunk-like structure as well as the wiring strategy are presented. Subsequently, the performance of both approaches is compared to each other.

The study highlights advantages of either approach and enables application-specific design of SMA wire based continuum robot structures and complete systems. Possible applications are endoscopes with integrated camera systems for inspection tasks or possible handling systems for complex material handling tasks.
Demonstrator for Linear Dielectric Elastomer Actuator Systems Coupled to Compliant Joint Linkage Transmission Mechanisms
Authors: Bruch Daniel , Naumov Ilja , Willian Tobias , Motzki Paul
Published: November 2023

Dielectric elastomer actuators (DEAs) are known for their excellent properties, making them particularly attractive for numerous applications. Since they are mainly based on inexpensive materials, they are in principle well suited for low-cost products. However, this requires consideration of other factors, such as the realization of standardized and scalable system designs that use identical parts to reduce product variation and enable mass production quantities. Previous work has proposed to accomplish this for DEAs by coupling them with compliant joint linkage transmission mechanisms that are configurable in their force and stroke output. With this approach, different load profiles are served with the same standardized DEA layout without changing its shape or dimension. This paper follows this concept and presents a demonstrator consisting of two actuator systems based on identical DEAs and biasing mechanisms. However, by coupling them to differently configured linkage transmission mechanisms each, one system is magnified in output force and one in output stroke. Both systems are mounted on a common base plate and connected to compact high-voltage power supplies each, that can be switched on and off manually. When actuated, one can see in direct comparison that one system provides a larger stroke on the output side than the other system, even though the DEA exhibits similar elongation in both systems. The functional principle visualized with the demonstrator is supported by experimental characterization of both systems with respect to their transmission properties and force-displacement behavior.
Al2O3 atomic layer deposition on a porous matrix of carbon fibers (FiberForm) for oxidation resistance
Authors: Widmer Jack T. , George Steven M.
Published: November 2023

Atomic layer deposition (ALD) was used to coat a porous matrix of carbon fibers known as FiberForm with Al2O3 to improve oxidation resistance. Static trimethylaluminum (TMA) and H2O exposures for Al2O3 ALD were used to obtain the uniform coating of this high porosity material. The carbon surfaces were initially functionalized for Al2O3 ALD by exposure to sequential exposures of nitrogen dioxide and TMA. A gravimetric model was developed to predict the mass gain per cycle under conditions when the ALD reactions reached saturation during each reactant exposure. The uniformity of the Al2O3 ALD coating on FiberForm was confirmed by scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) analysis. The SEM, EDS, and gravimetric models were all consistent with a uniform Al2O3 ALD coating on the porous carbon fiber network when the ALD reactions reached saturation on the entire surface area. In contrast, the profile of the Al2O3 ALD coating on the FiberForm was also characterized using undersaturation conditions when the ALD reactions did not reach saturation throughout the FiberForm sample. Based on comparisons with results from models for ALD in porous substrates, these Al2O3 coverage profiles were consistent with diffusion-limited Al2O3 ALD. Oxidation of the FiberForm and the Al2O3 ALD-coated FiberForm was also investigated by thermogravimetric analysis (TGA). TGA revealed that a 50 nm thick Al2O3 coating deposited using 400 Al2O3 ALD cycles enhanced the oxidation resistance. The Al2O3 ALD coating increased the oxidation onset temperature by ∼200 °C from 500 to 700 °C. The oxidation of the FiberForm removed carbon and left the Al2O3 ALD coating behind as a white “skeleton” that preserved the shape of the original FiberForm sample. The Al2O3 ALD coating also decreased the oxidation rate of the FiberForm by ∼30%. The oxidation rate of the Al2O3 ALD-coated FiberForm samples was constant and independent of the thickness of the Al2O3 ALD coating. This behavior suggested that the oxidation is dependent on the competing O2 diffusion into the FiberForm and CO2 diffusion out of the FiberForm.
Experimental and quantitative evaluation of frequency modulation caused by Doppler effect around high-speed moving sound source
Authors: Akutsu Mariko , Uda Toki , Oikawa Yasuhiro
Published: November 2023

High-speed train noise remains a wayside environmental issue. For accurate noise prediction, the characteristics of a moving sound source must be revealed. In this work, the frequency modulation of sound waves emitted from a high-speed moving sound source was experimentally investigated. In the experiment, the sound field around a running train model emitting a 40 kHz pure tone was measured by an optical measurement technique, parallel phase-shifting interferometry, which can visualize instantaneous sound fields. For quantitative evaluation, a lens distortion correction was also developed and adopted for the visualization results. From the measured result of a sound source moving at a running speed of 280 km/h, the frequency modulation, known as the Doppler effect, was observed, and the measured frequency agreed well with the theoretical values.