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1. Design of Polymer Nanodielectrics for Capacitive Energy Storage

   https://doi.org/10.3390/nano13172394  

   Prabhune, Prajakta; Comlek, Yigitcan; Shandilya, Abhishek; Sundararaman, Ravishankar; Schadler, Linda S.; Brinson, Lynda Catherine; Chen, Wei (September 2023, Nanomaterials)

   Polymer nanodielectrics present a particularly challenging materials design problem for capacitive energy storage applications like polymer film capacitors. High permittivity and breakdown strength are needed to achieve high energy density and loss must be low. Strategies that increase permittivity tend to decrease the breakdown strength and increase loss. We hypothesize that a parameter space exists for fillers of modest aspect ratio functionalized with charge-trapping molecules that results in an increase in permittivity and breakdown strength simultaneously, while limiting increases in loss. In this work, we explore this parameter space, using physics-based, multiscale 3D dielectric property simulations, mixed-variable machine learning and Bayesian optimization to identify the compositions and morphologies which lead to the optimization of these competing properties. We employ first principle-based calculations for interface trap densities which are further used in breakdown strength calculations. For permittivity and loss calculations, we use continuum scale modelling and finite difference solution of Poisson’s equation for steady-state currents. We propose a design framework for optimizing multiple properties by tuning design variables including the microstructure and interface properties. Finally, we employ mixed-variable global sensitivity analysis to understand the complex interplay between four continuous microstructural and two categorical interface choices to extract further physical knowledge on the design of nanodielectrics. 

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2. Optimizing the Tensile Strength for 3D Printed PLA Parts

   Novoa, C; Flores, A. (November 2019, Solid Freeform Fabrication 2019: Proceedings of the 30th Annual International Solid Freeform Fabrication Symposium - An Additive Manufacturing Conference)

   This research investigates on how extruder nozzle temperature, model infill rate (i.e. density) and number of shells affect the tensile strength of three-dimensional polylactic acid (PLA) products manufactured with the fused deposition model technology. Our goal is to enhance the quality of 3D printed products using the Makerbot Replicator. In the last thirty years, additive manufacturing has been increasingly commercialized, therefore, it is critical to understand properties of PLA products to broaden the use of 3D printing. We utilize a Universal Tensile Machine and Quality Engineering to comprehend tensile strength characteristics of PLA. Tensile strength tests are performed on PLA specimens to analyze their resistance to breakage. Statistical analysis of the experimental data collected shows that extruder temperature and model infill rate (i.e. density) affect tensile strength. 

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3. Developing 3D-Printed Natural Fiber-Based Mixtures

   Akemah, T.; Ben-Alon, L. (June 2023, Bio-Based Building Materials (ICBBM 2023))

   Amziane, S.; Merta, I.; Page, J. (Ed.)

   Natural earth-fiber building assemblies such as light straw clay, hempcrete, and clay-plastered straw bales incorporate vegetable by-products that are mixed with geological binders, traditionally used as an insulative infill in building construction. As a geo- and bio-based insulative infill method composed mostly of fiber, heat transfer coefficients are lower than mass materials, making it a compatible assembly that meets energy code requirements. Furthermore, due to their permeability, these materials exhibit high hygric capacity, providing regulated indoor temperatures and relative humidity levels, thus showing a promising future for socially just and healthier built environments. Despite these advantages, the use of earth-fiber building materials in digital construction is still underdeveloped. In the past few years, 3D-printed earth has gained an increasing interest, however, high contents of fibers in earth mixtures have yet to be fully tested and characterized. This paper presents an experimental workflow to characterize fiber-earth composites for 3D printed assemblies, using natural soils infused with natural fibers. The paper begins with a literature review of a range of fibers: straw, hemp, kenaf, sisal, and banana leaves, as well as naturally occurring biopolymer additives. The experimental setup includes manual extrudability and buildability tests, to identify optimal mix designs that are then tested for their printability and buckling using clay 3D printers. As a final deliverable, first pass geometric studies showcase the lightweight and structural possibilities of each material. The significance of this research lies in the development of a methodology for identifying novel mix design for digital fabrication, by increasing carbon storing vegetable fiber content within digital earth, and by creating a range of natural 3D printed assembly types: from mass-insulation walls to paper-thin lightweight partition assemblage. 

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4. Additive manufacturing of stiff and strong structures by leveraging printing-induced strength anisotropy in topology optimization

   https://doi.org/10.1016/j.addma.2023.103730  

   Kundu, Rahul Dev; Zhang, Xiaojia Shelly (August 2023, Additive Manufacturing)

   Anisotropy in additive manufacturing (AM), particularly in the material extrusion process, plays a crucial role in determining the actual structural performance, including the stiffness and strength of the printed parts. Unless accounted for, anisotropy can compromise the objective performance of topology-optimized structures and allow premature failures for stress-sensitive design domains. This study harnesses process-induced anisotropy in material extrusion-based 3D printing to design and fabricate stiff, strong, and lightweight structures using a two-step framework. First, an AM-oriented anisotropic strength-based topology optimization formulation optimizes the structural geometry and infill orientations, while assuming both anisotropic (i.e., transversely isotropic) and isotropic infill types as candidate material phases. The dissimilar stiffness and strength interpolation schemes in the formulation allow for the optimized allocation of anisotropic and isotropic material phases in the design domain while satisfying their respective Tsai–Wu and von Mises stress constraints. Second, a suitable fabrication methodology realizes anisotropic and isotropic material phases with appropriate infill density, controlled print path (i.e., infill directions), and strong interfaces of dissimilar material phases. Experimental investigations show up to 37% improved stiffness and 100% improved strength per mass for the optimized and fabricated structures. The anisotropic strength-based optimization improves load-carrying capacity by simultaneous infill alignment along the stress paths and topological adaptation in response to high stress concentration. The adopted interface fabrication methodology strengthens comparatively weaker anisotropic joints with minimal additional material usage and multi-axial infill patterns. Furthermore, numerically predicted failure locations agree with experimental observations. The demonstrated framework is general and can potentially be adopted for other additive manufacturing processes that exhibit anisotropy, such as fiber composites. 

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5. High-k, Low-Loss Ceramic-Thermoplastic Composite Feedstock Filaments for Fused Deposition Modeling of Microwave and mm-Wave Devices

   https://doi.org/10.5772/intechopen.1008537  

   Kosamiya, Vishvajitsinh; Wang, Jing (January 2025, IntechOpen)

   Maturing of additive manufacturing (AM) techniques has increased their utilization for fabricating radio frequency (RF) and microwave devices. Solid composites used in material extrusion AM have experienced considerable expansion over the past decade, incorporating functional properties into 3D-printed objects. There are encouraging indications from AM material research that electrically efficient AM materials can be discovered. These materials would be useful for producing microwave components in the future. One of the enabling techniques for fabricating these materials is to incorporate nano/microparticles or fillers into thermoplastic material. Composite material 3D printing is a novel approach to managing materials’ microwave properties. While extrinsic qualities (effective permittivity) can be controlled by shape and porosity management, intrinsic attributes are tied to the composition of composites. Furthermore, combining various materials to increase the spectrum of available microwave characteristics is made possible by multi-material 3D printing. In this chapter, we explore different methodologies to fabricate ceramic/thermoplastic composites for fused deposition modeling (FDM) of RF and microwave devices. Analytical models for predicting effective permittivity of the composite are discussed and application examples of FDM printed RF, microwave and mm-wave devices employing composites are presented. 

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