Mechanical properties and energy absorbing capabilities of Z-pinned aluminum foam sandwich

Aluminum foam sandwich (AFS) structures are suitable for impact protection in lightweight structural components due to their specific energy absorption capability under compression. However, tailoring the deformation patterns of the foam cells is a difficult task due to the randomness of their internal architecture. The objective of this study is to analyze the effect of embedding aluminum pins into an AFS panel (Z-pinning) to better control its deformation pattern and improve its energy absorption capability. This study considers a closed-cell AFS panel and analyzes the effect of multi-pin layout parallel to the direction of the uniaxial compressive loading. The results of the experimental tests on the reference (without Z-pinning) AFS are utilized to develop numerical models for the reference and Z-pinned AFS structures. Physical experiments and numerical simulations are carried out to demonstrate the advantages of Z-pinning with aluminum pins. The results exhibit a significant increase in elastic modulus, plateau stress and energy absorption capability of the Z-pinned samples. Also, the effect of the pin size and Z-pinning layout on the mechanical performance of the Z-pinned AFS is also investigated using numerical simulations

Analysis of the mechanical behaviour of a 11.5 T Nb3Sn LHC dipole magnet according to the ring collar concept

According to the CERN-LHC (Large Hadron Collider) reference design, 10-tesla twin-aperture NbTi dipoles will be built with split collars that enclose both apertures. As part of the development program towards an experimental 11.5-tesla Nb3Sn LHC dipole magnet, the mechanical implications of an alternative collar concept have been studied with a finite element analysis. In this concept ring shaped collars are shrunk on each finished single aperture coil, thus providing the necessary room-temperature prestress. This system results in a major improvement of the stress distribution in the collars. It is noted that introduction of friction at the sliding planes can cause reopening of the gap between the yoke halves during excitation. This depends strongly on the value of the friction coefficient

Stochastic Simulation of Mudcrack Damage Formation in an Environmental Barrier Coating

The FEAMAC/CARES program, which integrates finite element analysis (FEA) with the MAC/GMC (Micromechanics Analysis Code with Generalized Method of Cells) and the CARES/Life (Ceramics Analysis and Reliability Evaluation of Structures / Life Prediction) programs, was used to simulate the formation of mudcracks during the cooling of a multilayered environmental barrier coating (EBC) deposited on a silicon carbide substrate. FEAMAC/CARES combines the MAC/GMC multiscale micromechanics analysis capability (primarily developed for composite materials) with the CARES/Life probabilistic multiaxial failure criteria (developed for brittle ceramic materials) and Abaqus (Dassault Systmes) FEA. In this report, elastic modulus reduction of randomly damaged finite elements was used to represent discrete cracking events. The use of many small-sized low-aspect-ratio elements enabled the formation of crack boundaries, leading to development of mudcrack-patterned damage. Finite element models of a disk-shaped three-dimensional specimen and a twodimensional model of a through-the-thickness cross section subjected to progressive cooling from 1,300 C to an ambient temperature of 23 C were made. Mudcrack damage in the coating resulted from the buildup of residual tensile stresses between the individual material constituents because of thermal expansion mismatches between coating layers and the substrate. A two-parameter Weibull distribution characterized the coating layer stochastic strength response and allowed the effect of the Weibull modulus on the formation of damage and crack segmentation lengths to be studied. The spontaneous initiation of cracking and crack coalescence resulted in progressively smaller mudcrack cells as cooling progressed, consistent with a fractal-behaved fracture pattern. Other failure modes such as delamination, and possibly spallation, could also be reproduced. The physical basis assumed and the heuristic approach employed, which involves a simple stochastic cellular automaton methodology to approximate the crack growth process, are described. The results ultimately show that a selforganizing mudcrack formation can derive from a Weibull distribution that is used to describe the stochastic strength response of the bulk brittle ceramic material layers of an EBC

Stretchable electronic platform for soft and smart contact lens applications

A stretchable platform with spherical-shaped electronics based on thermo- plastic polyurethane (TPU) is introduced for soft smart contact lenses. The low glass transition temperature of TPU, its relatively low hardness, and its proven biocompatibility (i.e., protection of exterior body wounds) fulfill the essential requirements for eye wearable devices. These requirements include optical transparency, conformal fitting, and flexibility comparable with soft contact lenses (e.g., hydrogel-based). Moreover, the viscoelastic nature of TPU allows planar structures to be thermoformed into spherical caps with a well-defined curvature (i.e., eye’s curvature at the cornea: 9 mm). Numerical modeling and experimental validation enable fine-tuning of the thermo - forming parameters and the optimization of strain-release patterns. Such tight control is proven necessary to achieve oxygen permeable, thin, nonde- velopable, and wrinkle-free contact lenses with integrated electronics (silicon die, radio-frequency antenna, and stretchable thin-film interconnections). This work paves the way toward fully autonomous smart contact lenses potentially for vision correction or sensing applications, among others

Thermal and hydrodynamic studies for micro-channel cooling for large area silicon sensors in high energy physics experiments

Micro-channel cooling initially aiming at small-sized high-power integrated circuits is being transferred to the field of high energy physics. Today`s prospects of micro-fabricating silicon opens a door to a more direct cooling of detector modules. The challenge in high energy physics is to save material in the detector construction and to cool large areas. In this paper, we are investigating micro-channel cooling as a candidate for a future cooling system for silicon detectors in a generic research and development approach. The work presented in this paper includes the production and the hydrodynamic and thermal testing of a micro-channel equipped prototype optimized to achieve a homogeneous flow distribution. Furthermore, the device was simulated using finite element methods.Comment: 10 pages, submitted to NIMA (accepted

Design and numerical modeling of a pressurized airframe bulkhead joint

The structural loading on a conceptual lap joint in the empennage of a civil aircraft has been investigated. The lap joint interfaces the end-pressure part-hemispherical bulkhead to the cylindrical fuselage. The pressure bulkhead is made of carbon fiber reinforced plastic materials. The aim of the study is to present numerical results of the induced structural loading from the fuselage positive internal pressure differential and the localized high stress intensity field at the lap joint location. A methodology for the appropriate numerical approach to analyze the domed pressure bulkhead is presented. The results of the numerical investigation showed that the laminate loading levels calculated by the use of either initial sizing analytical formulas for pressurized domes or by the use of equilibrium nodal loading from finite element models of low fidelity compared to refined finite element analysis can be significantly underestimated. Some of the implications on carbon fiber reinforced plastic structural sizing at the specified location are developed

Thermodynamic and geomechanical processes research in the development of gas hydrate deposits in the conditions of the Black Sea

Purpose. Research of thermodynamic and geomechanical processes occurring in a gas hydrate body under the influence of an activating agent (sea water from surface layers) in the conditions of the Black Sea by mathematical modeling using finite element method. Methods. The modeling of thermodynamic and geomechanical processes is performed with the use of ANSYS v17.0 software and in accordance with the climatic, hydrogeological and physic-mechanical properties of the numerical model elements in the Black Sea gas hydrate deposit under consideration, which are similar to natural ones. The thermodynamic processes were studied in the section “Steady-State Thermal”, and the geomechanical (stress-strain state) in “Static Structural”. Findings. The spatial model is developed, which allows to simulate thermodynamic and geomechanical processes in a gas hydrate body under the influence of a thermal agent. As a result of modeling, it was determined that under these conditions the temperature in the gas hydrate body varies with the distance from the production well similarly in both directions according to the polynomial dependence. What is more, at a distance from the well of 18.7 m the temperature is stable and equals +22°С, and in the range of 18.7 – 24.9 m – decreases by 3.1 times and reaches a value of +7°С. It was found out that deformations in a gas hydrate body under the influence of an activating agent, which is fed under pressure above the initial, are directed from the lateral boundaries to the center of the gas hydrate body in the direction of productive dissociation zones. This, in its turn, results in the displacement of the gas hydrate volume to the reaction proceeding center, improving the quality of the decomposition process and allows mining of 87 – 91% gas hydrate volume, which is presented in the model. Originality. For the first time, for the conditions of the Black Sea gas hydrate deposits, an analytical assessment of the dissociation zone distribution from the production well under the influence of the thermal agent and the changes of the stress-strain state of the gas hydrated body during its decomposition, has been carried out. This allows to improve the technology of the gas hydrate deposits development in the conditions under consideration. Practical implications. The technological scheme for the development of a gas hydrate body based on the combined approach to the effects of activators (temperature and pressure) is proposed, which eliminates the need to warm the boundary sections of the deposit and increases the amount of the supplied activating agent and its temperatures, which in its turn leads to a decrease in the resource and energy consumption.Мета. Дослідження термодинамічних і геомеханічних процесів, що протікають у газогідратному тілі при впливі активуючого агента (морської води з поверхневих шарів) в умовах Чорного моря шляхом математичного моделювання методом кінцевих елементів. Методика. Моделювання термодинамічних і геомеханічних процесів виконано за допомогою програмного забезпечення ANSYS v17.0 з відповідністю кліматичних, гідрогеологічних та фізико-механічних властивостей елементів чисельної моделі у розглянутому газогідратному родовищі Чорного моря, які є аналогічними натурним. Термодинамічні процеси досліджувалися у розділі програми “Steady-State Thermal”, а геомеханічні (напружено-деформований стан) – в “Static Structural”. Результати. Розроблена просторова модель, що дозволяє моделювати термодинамічні та геомеханічні процеси у газогідратному тілі при впливі теплового агента. В результаті моделювання встановлено, що у розглянутих умовах температура в газогідратному тілі змінюється з відстанню від видобувної свердловини аналогічно в обидві сторони за поліноміальною залежністю, причому на відстані від свердловини 18.7 м температура стабільна і становить +22°С, а в інтервалі 18.7 – 24.9 м – знижується у 3.1 рази і досягає значення +7°С. Виявлено, що деформації у газогідратному тілі при впливі активуючого агента, який подається під тиском, що перевищує початковий, спрямовані від бокових меж у центр газогідратного тіла у напрямі продуктивних зон дисоціації, що, в свою чергу, призводить до зміщення об’єму газогідрату в центр протікання реакції, покращуючи якість процесу розкладання і дозволяючи відпрацювати 87 – 91% об’єму газогідрата, представленого в моделі. Наукова новизна. Вперше для умов газогідратних родовищ Чорного моря проведена аналітична оцінка характеру поширення зони дисоціації від видобувної свердловини при впливі теплового агента та змін напружено-деформованого стану газогідратного тіла при його розкладанні, що дозволяє удосконалити технологію розробки газогідратних покладів у розглянутих умовах. Практична значимість. Запропоновано технологічну схему розробки газогідратного тіла на основі комбінованого підходу до впливу активаторами (температурою та тиском), що усуває необхідність прогріву граничних ділянок покладу і збільшення кількості активуючого агента, що подається, та його температури, що, в свою чергу, веде до зниження ресурсо- й енерговитрат.Цель. Исследование термодинамических и геомеханических процессов, протекающих в газогидратном теле при воздействии активирующего агента (морской воды с поверхностных слоев) в условиях Черного моря посредством математического моделирования методом конечных элементов. Методика. Моделирование термодинамических и геомеханических процессов выполнено при помощи программного обеспечения ANSYS v17.0 с соответствием климатических, гидрогеологических и физико-механических свойств элементов численной модели в рассматриваемом газогидратном месторождении Черного моря, которые являются аналогичными натурным. Термодинамические процессы исследовались в разделе программы “Steady-State Thermal”, а геомеханические (напряженно-деформированное состояние) – в “Static Structural”. Результаты. Разработана пространственная модель, позволяющая моделировать термодинамические и геомеханические процессы в газогидратном теле при воздействии теплового агента. В результате моделирования установлено, что в рассматриваемых условиях температура в газогидратном теле изменяется с расстоянием от добывающей скважины аналогично в обе стороны по полиномиальной зависимости, причем на расстоянии от скважины 18.7 м температура стабильна и составляет +22°С, а в интервале 18.7 – 24.9 м – снижается в 3.1 раза и достигает значения +7°С. Выявлено, что деформации в газогидратном теле при воздействии активирующего агента, подаваемого под давлением, превышающее начальное, направлены от боковых границ в центр газогидратного тела в направлении продуктивных зон диссоциации, что, в свою очередь, приводит к смещению объема газогидрата в центр протекания реакции, улучшая качество процесса разложения и позволяя отработать 87 – 91% объема газогидрата, представленного в модели. Научная новизна. Впервые для условий газогидратных месторождений Черного моря проведена аналитическая оценка характера распространения зоны диссоциации от добывающей скважины при воздействии теплового агента и изменений напряженно-деформированного состояния газогидратного тела при его разложении, что позволяет усовершенствовать технологию разработки газогидратных залежей в рассматриваемых условиях. Практическая значимость. Предложена технологическая схема разработки газогидратного тела на основании комбинированного подхода к воздействию активаторами (температурой и давлением), устраняющая необходимость прогрева граничных участков залежи и увеличения подаваемого количества активирующего агента и его температуры, что, в свою очередь, ведет к снижению ресурсо- и энергозатрат.The results of the current researches were obtained within the framework of the research works of GP-473 Development of scientific principles of phase transformations of technogenic and natural gas hydrates and creation of the newest technologies of their extraction” (State Registration No.0115U002294) and GP-487 “Scientific substantiation and development of energy saving and low waste technologies of hydrocarbon and mineral raw materials extraction” (State Registration No.0116U008041)

Investigation of Thermal Management and Metamaterials

Thermal metamaterials are materials composed of engineered, microscopic structures that exhibit unique thermal performance characteristics based primarily on their physical structures and patterning, rather than just their chemical composition or bulk material properties. The heat transfer performance attributes of a thermal metamaterial are such that similar performance cannot be obtained using conventional materials or compounds. Thermal metamaterials are an emerging technology, and are just now beginning to be acknowledged and developed by the microelectronics and material sciences community. This thesis effort analyzed the current state of thermal metamaterial research, examined the physics and theory of heat transfer and electrical conductivity in thin film microelectronic designs, and then developed, modeled, fabricated, and characterized a series of ten proof-of-concept thermal metamaterial devices. Modeling and testing of these microelectromechanical systems (MEMS) based thermal metamaterial prototypes showed that the electrical and thermal conductivity of the material can be switched or tuned within a certain operational range, and that this switching is a function of actuation of the metamaterial’s structural elements, not just its chemical composition. In addition, this thesis presented the physics and fundamental principles of carbon nanotubes (CNTs). This background work supported later detailed description of a series of prototype CNT braided ropes. The diameter, electrical resistivity and conductivity, and heat transfer characteristics of these CNT braided rope prototypes was determined. These unique prototypes exhibited performance attributes that should prove useful to future thermal metamaterial designs

The Seedling Sanctuary: Automated Cold Frame for Gardner Elementary

The purpose of this report is to provide the details of the Seedling Sanctuary, a mechanical engineering senior design project. The project in question is an automated cold frame designed specifically for Gardner Academy, a local elementary school in San Jose. A cold frame is a miniature greenhouse that opens like a chest and is made from clear plastic. Automated ventilation and watering systems create a microclimate within this greenhouse structure to create the ideal growing conditions for seeds. The main purposes of the cold frame are to lengthen the growing season, be maintenance free, and enhance garden education. From testing, the project goals were verified to have been achieved through several performance metrics. First, the system’s ability to lengthen the growing season is dependent on germinating seedlings that can be planted earlier in the season. The automated system maintained the seedlings at the proper soil moisture levels to grow. The system also implemented passive temperature control systems to maintain the plants in ideal conditions. With the ventilation and thermal mass, the system is able to be cooler at the hottest times of day and warmer at night than unprotected plants. The system has also successfully automated the care of the seedlings, achieving our goal of being maintenance free. Finally, the enhancement of garden education was incorporated through community engagement with the design and building of the cold frame, as well as the Bluetooth application which will be used in the school curriculum