Finite Element Model Validation and Testing of an Off-Road Vehicle under Dynamic Loading Conditions

In the vehicle design life cycle, validation tests consume a significant portion of the available development time. With a short, one-year design cycle, the Embry-Riddle Baja Team leverages computer-aided engineering (CAE) tools to simulate critical test cases whose loading conditions can be accurately represented by a series of static loads and constraints. Using these conditions, a Finite Element Model (FEM) can be employed to accurately predict the effects of the loading conditions in the components. During the initial design of the front suspension, one major load case was determined to be the main failure load. However, after validation testing the suspension exhibited a failure indicative of a load path not predicted. To obtain a more complete understanding of the dynamic loading conditions on the affected component, instrumentation was implemented to measure strain in the critical member. A dynamic vehicle test case was performed to measure a high-frequency, high-load case representative of an event during the vehicle service life. The measurement was then utilized to validate a Finite Element Model, in turn used to re-design the member. This component withstands the loading condition for infinite fatigue life without increasing the overall weight of the design, although the failure was not reproduced during testing

Microturbopompe avec isolation thermique pour cycle Rankine sur puce

Les micromoteurs thermiques (Power-MEMS) pourraient offrir une alternative aux batteries pour répondre aux besoins d’énergie compacte et distribuée pour des applications telles que l'électronique portable, les robots, les drones et les systèmes embarqués, les capteurs et les actionneurs. La microturbine à vapeur de cycle thermodynamique de Rankine fait partie de ce domaine de micromoteurs. Ce dispositif est destiné à la génération d’électricité à petite échelle à partir de la récupération de la chaleur perdue. Dans ce contexte, l’objectif de ce travail est la fabrication et la démonstration expérimentale d’une microturbopompe à haute température pour implémenter le cycle de Rankine. Une configuration originale qui intègre l’isolation thermique est, tout d’abord, proposée. Cette configuration est constituée d’un empilement de cinq tranches (silicium et verre) pour enfermer un rotor hybride (silicium et verre) supporté par des paliers hydrostatiques. Le rotor est un disque de 4 mm de diamètre et de 400 µm d’épaisseur avec des pales de turbine sur le dessus et une pompe visqueuse à rainures en spirale sur le dessous. Une technique de micromoulage de verre a été développée dans ce travail pour intégrer du verre dans le rotor comme un matériau isolant thermiquement. La microturbopompe est fabriquée avec succès en utilisant les méthodes de microfabrication des MEMS. Tout d'abord, les paliers hydrostatiques, la turbine et le fonctionnement de la pompe sont caractérisés, jusqu'à une vitesse de rotation de 100 kRPM. La turbine a fourni 0,16 W de puissance mécanique et le débit de la pompe était supérieur à 2.55 mg/s. Ensuite, la première démonstration d'une turbopompe MEMS fonctionnant à des températures élevées a été réalisée. Une comparaison a été faite avec un rotor non isolé pour prouver l'efficacité des stratégies d'isolation thermique. La turbopompe MEMS isolée a été démontrée à 160°C du côté de la turbine. Par extrapolation, la microturbopompe devrait fonctionner jusqu'à une température de 400°C avant que la température dans la pompe n'atteigne 100°C. Pour la première fois, une microturbopompe pour un fonctionnement à haute température est fabriquée et caractérisée

Process sensitivities and interface optimisation of CdTe solar cells deposited by close-space sublimation

In a world where the need of clean and sustainable energy production has become a necessity, photovoltaic (PV) solar cells can provide a clean and cost-effective alternative to conventional fossil fuel energy sources. Recent technological advancements in PV technologies have improved their financial viability, making the PV industry the leading energy market at the moment in new installations. Thin film solar cells can potentially further reduce manufacturing costs through less material requirements and simpler deposition methods. CdTe solar cells are currently the most commercially successful thin film technology which have secured approximately half of the thin film market share. However, CdTe solar cells have only achieved 70% of their theoretical maximum efficiency, making this a promising area of research in the quest for improving the financial viability of this technology. This thesis aims to investigate possible ways of improving the performance of CdTe solar cells through interface optimisation. [Continues.

Conflicts, integration, hybridization of subcultures: An ecological approach to the case of queercore

This paper investigates the case study of queercore, providing a socio-historical analysis of its subcultural production, in the terms of what Michel Foucault has called archaeology of knowledge (1969). In particular, we will focus on: the self-definition of the movement; the conflicts between the two merged worlds of punk and queer culture; the \u201cinternal-subcultural\u201d conflicts between both queercore and punk, and between queercore and gay\lesbian music culture; the political aspects of differentiation. In the conclusion, we will offer an innovative theoretical proposal about the interpretation of subcultures in ecological and semiotic terms, combining the contribution of the American sociologist Andrew Abbot and of the Russian semiologist Jurij Michajlovi\u10d Lotma

COMPUTATIONAL-ANALYSIS ASSISTED INTRODUCTION OF FRICTION STIR WELDING INTO DEVELOPMENT OF LIGHT-WEIGHT HIGH-SURVIVABILITY MILITARY VEHICLES

High strength aluminum alloys with superior blast/ballistic resistance against armor piercing (AP) threats and with high vehicle light-weighing potential are being increasingly used as military-vehicle armor. Due to the complex structure of these vehicles, they are commonly constructed through joining (mainly welding) of the individual components. Unfortunately, these alloys are not very amenable to conventional fusion based welding technologies (e.g. Gas Metal Arc Welding (GMAW)) and in-order to obtain high-quality welds, solid-state joining technologies such as Friction Stir Welding (FSW) have to be employed. However, since FSW is a relatively new and fairly complex joining technology, its introduction into advanced military vehicle underbody structures is not straight forward and entails a comprehensive multi-prong approach which addresses concurrently and interactively all the aspects associated with the components/vehicle-underbody design, fabrication and testing. One such approach is developed and applied in the present work. The approach consists of a number of well-defined steps taking place concurrently and relies on two-way interactions between various steps. In the present work, two of these steps are analyzed in great detail: (a) Friction Stir Welding process modeling; and (b) Development and parameterization of material models for the different weld-zones. Within the FSW process modeling, interactions between the rotating and advancing pin-shaped tool (terminated at one end with a circular-cylindrical shoulder) with the clamped welding-plates and the associated material and heat transport are studied computationally using a fully-coupled thermo-mechanical finite-element analysis. To surmount potential numerical problems associated with extensive mesh distortions/entanglement, an Arbitrary Lagrangian Eulerian (ALE) formulation was used which enabled adaptive re-meshing (to ensure the continuing presence of a high-quality mesh) while allowing full tracking of the material free surfaces/interfaces. To demonstrate the utility of the present computational approach, the analysis is applied to the aluminum-alloy grades, AA5083 (a solid-solution strengthened and strain-hardened/stabilized Al-Mg alloy) and AA2139 (a precipitation hardened quaternary Al-Cu-Mg-Ag alloy). Both of these alloys are currently being used in military-vehicle hull structural and armor systems. In the case of non-age-hardenable AA5083, the dominant microstructure evolution processes taking place during FSW are extensive plastic deformation and dynamic re crystallization of highly-deformed material subjected to elevated temperatures approaching the melting temperature. In the case of AA2139, in addition to plastic deformation and dynamic recrystallization, precipitates coarsening, over-aging, dissolution and re-precipitation had to be also considered. To account for the competition between plastic-deformation controlled strengthening and dynamic-recrystallization induced softening phenomena during the FSW process, the original Johnson-Cook strain- and strain-rate hardening and temperature-softening material strength model is modified using the available recrystallization-kinetics experimental data. Lastly, the computational results obtained in the present work are compared with their experimental counterparts available in the open literature. This comparison revealed that general trends regarding spatial distribution and temporal evolutions of various material-state quantities and their dependence on the FSW process parameters are reasonably well predicted by the present computational approach. The introduction of newer joining technologies like the so-called Friction Stir Welding (FSW) into automotive engineering entails the knowledge of the joint-material microstructure and properties. Since, the development of vehicles (including military vehicles capable of surviving blast and ballistic impacts) nowadays involves extensive use of the computational engineering analyses (CEA), robust high-fidelity material models are needed for the FSW joints. A two-level material-homogenization procedure is proposed and utilized in the present work in-order to help manage computational cost and computer storage requirements for such CEAs. The method utilizes experimental (microstructure, micro-hardness, tensile testing and X-ray diffraction) data to construct: (a) the material model for each weld zone; and (b) the material model for the entire weld. The procedure is validated by comparing its predictions with the available experimental results and with the predictions of more-detailed but more costly computational analyses

Re-manufacturing networks for tertiary architectures

This book deals with re-manufacturing, recondition, reuse and repurpose considered as winning strategies for boosting regenerative circular economy in the building sector. It presents many of the outcomes of the research Re-NetTA (Re-manufacturing Networks for Tertiary Architectures). New organisational models and tools for re-manufacturing and re-using short life components coming from tertiary buildings renewal, funded in Italy by Fondazione Cariplo for the period 2019-2021. The field of interest of the book is the building sector, focusing on various categories of tertiary buildings, characterized by short term cycles of use. The book investigates the most promising strategies and organizational models to maintain over time the value of the environmental and economic resources integrated into manufactured products, once they have been removed from buildings, by extending their useful life and their usability with the lower possible consumption of other materials and energy and with the maximum containment of emissions into the environment. The text is articulated into three sections. Part I BACKGROUND introduces the current theoretical background and identifies key strategies about circular economy and re-manufacturing processes within the building sector, focusing on tertiary architectures. It is divided into three chapters. Part II PROMISING MODELS outlines, according to a proposed framework, a set of promising circular organizational models to facilitate re-manufacturing practices and their application to the different categories of the tertiary sectors: exhibition, office and retail. This part also reports the results of active dialogues and roundtables with several categories of operators, adopting a stakeholder perspective. Part III INSIGHTS provides some insights on the issue of re-manufacturing, analyzed from different perspectives with the aim of outlining a comprehensive overview of challenges and opportunities for the application of virtuous circular processes within building sector. Part III is organized in four key topics: A) Design for Re-manufacturing; B) Digital Transformation; C) Environmental Sustainability; D) Stakeholder Management, Regulations & Policies