119 research outputs found

    Thermomechanical strain analysis of electronic packages using Moiré interferometry by computational and manual fringe reduction

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    Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996.Includes bibliographical references (leaves 123-125).by J. Morgan Slade.M.S

    Effect of dynamic thermal boundaries on residual stresses in injection molding

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    Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1995.Includes bibliographical references.by David D. Sha.M.S

    Polymer Processing: Modeling and Correlations Finalized to Tailoring the Plastic Part Morphology and Properties

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    The analysis of polymer processing operations is a wide and complex subject; during polymer processing, viscoelastic fluids are forced to deform into desired geometries using non-homogeneous velocity and temperature fields down to solidification. The objective of analysis is the identification of processing conditions, which are finalized in the optimization of product final properties, which, in turn, are determined by the final part morphology. Depending on the operating conditions, the properties of the final part can change more than one order of magnitude. Properties of interest include the mechanical, optical, barrier, permeability, and biodegradability, and any other property of practical relevance including the characteristics of the surfaces as its finishing and wettability, which are connected to one another. The scope of this Special Issue is to select progress in or reviews of the understanding/description of the phenomena involved along the chain of processing–morphology–properties. Along this virtual chain, modeling may be a useful approach, and within the objective of understanding fundamental aspects, it may also be relevant to compare selected characteristics of the process and the material with the characteristics of the resulting morphology and then with the properties of the final part. This approach suggests the title: “Polymer Processing: Modeling and Correlations Finalized to Tailoring the Plastic Part Morphology and Properties”

    Viscoelasticity

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    This book contains a wealth of useful information on current research on viscoelasticity. By covering a broad variety of rheology, non-Newtonian fluid mechanics and viscoelasticity-related topics, this book is addressed to a wide spectrum of academic and applied researchers and scientists but it could also prove useful to industry specialists. The subject areas include, theory, simulations, biological materials and food products among others

    Microfabrication of a MEMS piezoresistive flow sensor - materials and processes

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    Microelectromechanical systems (MEMS) based artificial sensory hairs for flow sensing have been widely explored, but the processes involved in their fabrication are lithography intensive, making the process quite expensive and cumbersome. Most of these devices are also based on silicon MEMS, which makes the fabrication of out-of plane 3D flow sensors very challenging. This thesis aims to develop new fabrication technologies based on Polymer MEMS, with minimum dependence on lithography for the fabrication of piezoresistive 3D out-of-plane artificial sensory hairs for sensing of air flow. Moreover, the fabrication of a flexible sensor array is proposed and new materials are also explored for the sensing application. Soft lithography based approaches are first investigated for the fabrication of an all elastomer device that is tested in a bench top wind tunnel. Micromolding technologies allow for the mass fabrication of microstructures using a single, reusable mold master that is fabricated by SU-8 photolithography, reducing the need for repetitive processing. Polydimethylsiloxane (PDMS) is used as the device material and sputter deposited gold is used as both the piezoresistive as well as the electrode material for collection of device response. The fabrication results of PDMS to PDMS metal transfer micromolding (MTM) are shown and the limitations of the process are also discussed. A dissolving mold metal transfer micromolding process is then proposed and developed, which overcomes the limitations of the conventional MTM process pertinent to the present application. Testing results of devices fabricated using the dissolving mold process are discussed with emphasis on the role of micro-cr  acking as one failure mode in elastomeric devices with thin film metal electrodes. Finally, a laser microfabrication based approach using thin film Kapton as the device material and an electrically conductive carbon-black elastomer composite as the piezoresistor is proposed and demonstrated. Laminated sheets of thick and thin Kapton form the flexible substrate on which the conductive elastomer piezoresistors are stencil printed. Excimer laser ablation is used to make the micro-stencil as well as to release the Kapton cantilevers. The fluid-structure interaction is improved by the deposition of a thin film of silicon dioxide, which produces a stress-gradient induced curvature, strongly enhancing the device sensitivity. This new approach also enables the fabrication of backside interconnects, thereby addressing the commonly observed problem of flow intrusion while using conventional interconnection technologies like wire-bonding. Devices with varying dimensions of the sensing element are fabricated and the results presented, with smallest devices having a width of 400 microns and a length of 1.5 mm with flow sensitivities as high as 60 Ohms/m/s. Recommendations are also proposed for further optimization of the device.M.S.Committee Chair: Allen, Mark; Committee Member: Allen, Sue Ann Bidstrup; Committee Member: Wong, C.P

    Additive manufacturing of the high-performance thermoplastic : Experimental study and numerical simulation of the Fused Filament Fabrication

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    Additive manufacturing (AM) refers to a wide variety of manufacturing processes for rapid prototyping and production of final and semi-final products. In opposite to conventional orsubtractive processes, in additive manufacturing, the material is gradually added layer by layer to form the parts. AM enables the fabrication of complex parts which were impossible or not costeffective to manufacture with the traditional processes. Fused Filament Fabrication (FFF) is basedon the melting of a polymeric filament in an extruder; the filament is then deposited layer by layerto manufacture the final parts. Despite growing interest from industries and a large audience inrecent years, these manufacturing processes are still not well mastered, especially for not mass produced polymers. In this thesis, we will take an insight into the printability of PEEK(Polyetheretherketone). The aim is to find the printing conditions to obtain the best quality of theprinted parts by FFF process. In the first step, we have determined the polymer properties influencing the quality of the printed parts by FFF. The rheological properties, the surface tension,the thermal conductivity and thermal expansion have been determined experimentally. Then, thecoalescence phenomenon of the polymeric filaments has been studied by experimental, analyticaland numerical simulation. Furthermore, the stability of the filament and its flow properties when itexits from the extruder in the FFF process has been determined by experimental, analytical andnumerical simulation. Then, we have focused on the determination of the die swelling of PEEKextrudate. Lastly, the kinetics of isothermal and non-isothermal crystallization of PEEK has beenstudied by experimental study. The kinetics of crystallization has been applied to FFF process bynumerical simulation in order to determine the optimum environment temperature to control thecrystallization of printed parts. The crystallization of PEEK reaches its maximum value (about22%) of crystallization during the deposition

    Shape Memory Assisted Self Healing (Smash) Polymeric and Composite Systems

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    My research aims to develop a novel approach that uses the shape memory (SM) effect to aid self healing (SH) polymeric systems that are able to simultaneously close and re-bond cracks with a single thermal stimulus. This new concept is termed shape memory assisted self healing (SMASH). Additionally, a new type of shape memory termed reversible plasticity shape memory (RPSM) was also developed where both the elastic and plastic deformation found after deformation completely recover upon a thermal stimulation. I aim to utilize a broad range of polymeric and composite systems that include a single phase semi-crystalline system, a single phase amorphous blend, and a combination of these two polymers in a composite elastomer system to prove the versatility of the SMASH and RPSM effects. Chapter 1 gives a polymer science background along with SM and SH material overview. Chapter 2 discusses the fabrication and analysis of miscible blends that show the SMASH and RPSM effect using a semi-crystalline polymer, poly(e-caprolactone) (PCL) to construct a SM PCL network (n-PCL) and PCL thermoplastic used as the SH agent (l-PCL). The PCL thermoplastic SH agent interpenetrated the n-PCL for form a single phase semi interpenetrating polymer network (SIPN). Films were made for testing to prove the SM and SH effects by varying the amount of SM network and SH agent to optimize both effects. Thermo-mechanical, tensile, and SH experiments were conducted to study the fixing, recovery and healing properties of the polymeric system. Chapter 3 focuses on a unique system for the fabrication of clear thin SMASH SIPN coatings that were developed for optical industrial applications. Here, an amorphous polymer composition, poly(tert-butyl acrylate) (poly(tBA)), was used in a blend of two forms, a network form for shape memory (n-tBA) and a linear form for self-healing (l-tBA), that, together, form a single phase SIPN. Thermal, thermo-mechanical, SM and SH scratch experiments were conducted to investigate both SM and SH mechanisms as influenced by the relative concentrations of n-tBA and l-tBA in the SIPN materials. Chapter 4 introduces for the first time an innovative smart polymeric soft material where aligned nanofibers are used to construct anisotropy embedded in an elastomeric matrix. This system, termed Anisotropic Shape Memory Elastomeric Composite (A-SMEC) was investigated for RPSM and SMASH properties. In addition, the anisotropic mechanical and shape memory properties were investigated and interpreted in light of the underlying structure. Chapter 5 builds upon the results of Chapter 4, presenting the fabrication and testing of laminated A-SMEC biomorphs that were designed to exploit anisotropic in RPSM behavior to yield predictably curled and twisted structures upon deformation. More specifically, the out-of-plane curvature and pitch were analyzed as a function of biomorph orientational lay-up. All polymeric systems described in this dissertation are examples of smart polymers that can be used to tailor mechanical performance while introducing new phenomena, such as self-healing, RPSM, and stretch-induced twisting. Chapter 6 discusses the conclusions followed by future work that are sub-sectioned for each chapter of the dissertation

    Advanced Materials in 3D/4D Printing Technology

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    This reprint contains a collection of state-of-the-art reviews and original research articles from leaders in the field of 3D/4D printing. It focuses on 3D/4D printing materials with novel and/or advanced functionalities, novel applications of 3DP material, and material synthesis and characterization techniques

    Latest Advancements in Micro Nano Molding Technologies – Process Developments and Optimization, Materials, Applications, Key Enabling Technologies

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    Micro- and nano-molding technologies are continuously being developed due to enduring trends like increasing miniaturization and higher functional integration of products, devices, and systems. Furthermore, with the introduction of higher performance polymers, feedstocks, and composites, new opportunities in terms of material properties can be exploited, and, consequently, more micro-products and micro/nano-structured surfaces are currently being designed and manufactured.Innovations in micro- and nano-molding techniques are seen in the different processes employed in production (injection molding, micro injection molding, etc.); on the use of new and functional materials; for an ever-increasing number of applications (health-care devices, micro-implants, mobility, and communications products, optical elements, micro-electromechanical systems, sensors, etc.); in several key enabling technologies that support the successful realization of micro and nano molding processes (micro- and nano-tooling technologies, process monitoring techniques, micro- and nanometrology methods for quality control, simulation, etc.) and their integration into new manufacturing process chains.This Special Issue reprint showcases research papers and review articles that focus on the latest developments in micro-manufacturing and key enabling technologies for the production of both micro-products and micro-structured surfaces

    Chapter From Cellulose Dissolution and Regeneration to Added Value Applications — Synergism Between Molecular Understanding and Material Development

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    Laser ablation (LA) and spark discharge (SD) techniques are commonly used for nanoparticle (NP) formation. The produced NPs have found numerous applications in such areas as electronics, biomedicine, textile production, etc. Previous studies provide us information about the amount of NPs, their size distribution, and possible applications. On one hand, the main advantage of the LA method is in the possibilities of changing laser parameters and background conditions and to ablate materials with complicated stoichiometry. On the other hand, the major advantage of the SD technique is in the possibility of using several facilities in parallel to increase the yield of nanoparticles. To optimize these processes, we consider different stages involved and analyze the resulting plasma and nanoparticle (NP) parameters. Based on the performed calculations, we analyze nanoparticle properties, such as mean size and mean density. The performed analysis (shows how the experimental conditions are connected with the resulted nanoparticle characteristics in agreement with several previous experiments. Cylindrical plasma column expansion and return are shown to govern primary nanoparticle formation in spark discharge, whereas hemispherical shock describes quite well this process for nanosecond laser ablation at atmospheric pressure. In addition, spark discharge leads to the oscillations in plasma properties, whereas monotonous behavior is characteristic for nanosecond laser ablation. Despite the difference in plasma density and time evolutions calculated for both phenomena, after well-defined delays, similar critical nuclei have been shown to be formed by both techniques. This result is attributed to the fact that whereas larger evaporation rate is typical for nanosecond laser ablation, a mixture of vapor and background gas determines the supersaturation in the case of spark
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