Field-assisted 3D printing of multi-functional materials

The emergence of flexible, robust additive manufacturing platforms has created potentially transformative opportunities to integrate multiple functionalities: in particular, mechanical efficiency with mass transport, thermal management and conductivity. Field-assisted assembly of multi-phase materials holds promise for numerous applications, including flexible composites, patterning of cells in extracellular matrix in synthetic tissue, controlling ion transport in batteries, etc. Experiments involving acoustic field-assisted assembly of microscale particles will be used to elucidate the role of acoustic fields on structure formation, and the resulting opportunities to tailor macroscopic conductivity in novel ways. Figure 1 below illustrates results for conductive carbon fibers an elastomer matrix, with patterned lines created via acoustic focusing. A key advantage of the approach is the ability to create strong connected networks of second phase particles at volume fractions that are well-below that associated with the percolation threshold, which greatly facilitates the development of printable functional inks. In-situ and ex-situ observations of direct write printing will then be used to identify regimes that enable ‘on-the-fly’ control of microstructure during macroscopic patterning. Figure 1: (a) Acoustically patterned composites of Ag-coated glass fiber 2.6v% in 1:1 M:CH-A polymer matrix, which undergo small, recoverable changes in conductivity when deformed. (b) Unpatterned, dispersed-fiber composites made of the same components, but higher filler particle loading in order approach the conductivity of the patterned composites. The higher loading required compromises their flexibility, so that large, unpredictable, and irreversible losses in conductivity occur at relatively low strains (a 90 degree twist and normal handling resulted in failure by fracture). In flexible conductive materials there is a well-documented trade-off between conductivity and flexibility as the conductive filler loading increases which currently limits the viability of printable flexible conductors [Sekitani 2010 3.1.2, Rodgers 2010, Ray 2019]. Here we present a method for subverting this trade-off by using acoustophoresis to assemble filler particles into highly efficient percolated networks within the composites, forming conductive networks at low particle loading which have high tolerance for strain and little change in conductivity. We demonstrate that the acoustic patterning process simultaneously decreases the fiber filler loading necessary for percolation by an order of magnitude and increases the conductivity of the material by an order of magnitude by forming many parallel percolated branches in the network. This low loading required for high conductivity allows the material to maintain \u3c6% change in conductivity between the flat and bent (0.7 mm radius) states with no degradation over 500 cycles, due to the low particle loading and encapsulation of particle networks. Furthermore, using acoustic assembly during printing of these materials allows on-the-fly modulation between this conductive material and un-percolated insulating material during printing, with additional control over the anisotropy of the conductive network, all with the same nozzle and ink. This allows versatile design of integrated circuits in 3d printed soft components, as well as tuning of strain tolerance in multiple directions, without the cost and manufacturing limitations of lithography, or CNT growth steps, prestretch/burn-off steps, or liquid metal safety concerns. Acoustically patterned: \u3e5000 S/m @ 2.6v% Unpatterned: \u3c1500 S/m @ 13v% (a) Please click Additional Files below to see the full abstract

Virtual simulation and design of barrier coatings for ceramic composites

The development of environmental barrier coating systems for ceramic composites has two central challenges: (i) the selection of materials and layer architectures that are resistant to cracking, volatilization, and chemical attack, and (ii) the identification of active failure mechanisms and their dependency on the system’s intrinsic properties. This talk will describe two modeling frameworks that are tailored to these two objectives. In the first framework, an automated approach for analyzing delamination and mud-cracking in complex multilayers enables developers to consider a broad range of materials and architectures and in turn rapidly identify promising material systems. The opportunities created by this framework will be demonstrated by illustrating the likely failure modes of environmental barrier coatings comprising multiple layers of rare earth silicates on silicon carbide substrates. These map illustrate combinations of material properties (e.g. coating thickness and thermal expansion coefficients) that avoid penetrating mud cracks and delamination cracks. Maps will also be presented that quantify the likelihood of crack kinking, i.e. the transition of a penetrating crack to a delamination crack that leads to coating failure. In the second framework, distributed cohesive zone models are used to develop a virtual testing framework: the framework is capable of predicting a broad range of cracking modes without a priori assumptions regarding the failure mode and without phenomenological criteria for the evolution of damage. In this framework, cracks emerge from defects in the structure according to classical brittle fracture theory. The simulation framework exploits highly parallel computing approaches that enable simulations covering a broad range of parameter space; this enables the construction of “durability regime maps”, which indicate likely failure mechanisms as a function of material properties. This framework has been used to identify whether or not interface cracks will travel along an interface or kink into the coating (leading to spallation), as a function of interface toughness, film toughness, mixed mode loading, and interface waviness. The results shed new light on the physics of crack kinking, which plays a fundamental role in coating durability. Further, the results provide insights regarding the role of interface waviness between coatings and substrates, such as would occur with a coated woven textile composite

Assessment of the Freshwater Mussel Community of the Upper Mahoning River Watershed and Factors Influencing Diversity and Abundance in Small Streams

Freshwater mussel communities have experienced drastic declines in diversity and abundance in many streams throughout North America. Among the reasons for these declines is the human-driven alteration of the landscape, as urban and agricultural use impart many known stressors to aquatic systems. Impairments include increased sedimentation, increased pollutants, increased flood frequency and intensity, and decreased diversity and abundance of many organisms, including fish, macroinvertebrates, and mussels. Attempts to explain the abundance and diversity of mussel communities using small-scale factors such as substrate type and flow velocity provided little to no predictive power. Instead, reach-scale variables, such as stream morphology and riparian vegetation, and catchment-scale variables, such as land use, performed better as predictors of mussel diversity and abundance. In this study, surveys of mussel communities were performed in Eagle Creek in 2013 and throughout the entire upper Mahoning River watershed in 2014. Stream morphology was assessed at the sites surveyed in 2014. No published surveys exist for the mussel community of the upper Mahoning River watershed, which is a headwater system in the upper reaches of the Ohio River watershed. The Eagle Creek watershed had the highest proportion of forested land in the upper Mahoning River watershed and supported the largest and most diverse mussel community, although evidence for recruitment was limited in this stream. Across the region, abundance and species richness were strongly correlated with drainage area. Abundance and species richness decreased with increased shear stress, electrical conductivity, and agricultural and urban land use. Conductivity was also correlated with agricultural land use, and no live mussels were found where conductivity exceeded 0.9mS. Overall, the upper Mahoning River watershed had a low diversity and abundance of freshwater mussels, likely due to the intensive anthropogenic land use. Even where conditio

Virtual testing and design of barrier coating systems

The development of coating systems for high temperatures has two central challenges: (i) the selection of materials and layer architectures that are resistant to cracking and chemical attack, and (ii) the identification of active failure mechanisms and their dependency on the system’s intrinsic properties. This talk will describe two modeling frameworks that are tailored to meet these challenges. In the first framework, an automated system for analyzing delamination and mud-cracking in complex multilayers; this enables system developers to consider a broad range of materials and architectures and in turn rapidly identify promising material systems. The impact of CMAS penetration on coating reliability will be briefly discussed to illustrate potential applications of the framework. In the second framework, distributed cohesive zone models are used to develop a virtual testing framework: the framework is capable of predicting a broad range of cracking modes without a priori assumptions regarding the evolution of damage. The simulation framework exploits highly parallel computing approaches that enable simulations covering a broad range of parameter space; this enables the construction of “durability regime maps”, which indicate likely failure mechanisms as a function of material properties. Simulations will be presented illustrating the transition between crack penetration, kinking and delamination; the results demonstrate that crack kinking can occur even in the absence of a putative kink crack, and that in certain situations, cohesive strength plays a critical role in governing brittle failure modes (i.e. the relative toughness of the constituents alone is insufficient). The implications of these simulations for developing tough, CMAS resistant coatings will be discussed, with a particular focus on the role of microstructure in ceramic coatings

Field-assisted assembly and printing of functional composites

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A Quantitative Evaluation of Growth in Leptodea Fragilis Before and After the Arrival of Zebra Mussels in Lake Erie

The arrival of zebra mussels in the Great Lakes in the 1980’s marked several environmental changes, most notably in freshwater mussels in the Unionidae. There are no studies of population demographics of native Great Lake species before this period of time. In this study, several recent shell collections of Leptodea fragilis, a fast-growing freshwater mussel, were made on various beaches along Lake Erie. To compare the effects of the zebra mussels on L. fragilis, we compared growth rates, determined from size and estimated age of shells, to additional collections of L. fragilis from 1941 to 1967available at the Cleveland Museum of Natural History. The growth rates of this species are exceptional for their speed among freshwater mussels. A modern comparison of growth rates and age are presented with a sexually dimorphic unionid river species, Lampsilis siliquoidea, that were collected in Summer 2013. We hypothesized that the arrival of zebra mussels could affect the growth rate of L. fragilis by selecting on age of reproduction or growth to reach a minimum size for reproduction, results that could shift growth curves and/or age demography of current populations, and help them persist where zebra mussels remain abundant.https://engagedscholarship.csuohio.edu/u_poster_2013/1006/thumbnail.jp

The Impact of Dreissenid Mussels on Growth of the Fragile Papershell (Leptodea fragilis), the Most Abundant Unionid Species in Lake Erie

The arrival of zebra mussels (Dreissena polymorpha (Pallas, 1771)) and subsequently quagga mussels (Dreissena bugensis Andrusov, 1897) (Dreissenidae) in the Great Lakes in the 1980s induced many changes, most notably the devastation of native freshwater mussel species. Recently, empty shells of the fragile papershell (Leptodea fragilis (Rafinesque, 1820)) have become common, particularly in the western basin of Lake Erie, suggesting that this fast-growing species may be increasing in numbers in the lake. To examine continued competition with dreissenids, shell age and length of L. fragilis were used to contrast lifespan and growth rate, estimated as the slope of age on shell length, for shells from two beach localities where byssal threads were present on most shells and two sites where dreissenids were rare or absent. Few recent shells from Lake Erie beaches exceeded 5 years of age, and byssal thread counts were more numerous on older shells. Growth and lifespan were estimated to be significantly lower where dreissenid mussels remained numerous than when measured either from historic collections along Lake Erie or from protected populations. Therefore, even for this early-reproducing species, competition from dreissenids may continue to interfere with growth and shorten lifespan, which are effects few other unionid species can likely tolerate sufficiently to sustain population growt

Metallurgical Mechanisms Controlling Mechanical Properties of Aluminum Alloy 2219 Produced By Electron Beam Freeform Fabrication

The electron beam freeform fabrication (EBF3) layer-additive manufacturing process has been developed to directly fabricate complex geometry components. EBF3 introduces metal wire into a molten pool created on the surface of a substrate by a focused electron beam. Part geometry is achieved by translating the substrate with respect to the beam to build the part one layer at a time. Tensile properties have been demonstrated for electron beam deposited aluminum and titanium alloys that are comparable to wrought products, although the microstructures of the deposits exhibit features more typical of cast material. Understanding the metallurgical mechanisms controlling mechanical properties is essential to maximizing application of the EBF3 process. In the current study, mechanical properties and resulting microstructures were examined for aluminum alloy 2219 fabricated over a range of EBF3 process variables. Material performance was evaluated based on tensile properties and results were compared with properties of Al 2219 wrought products. Unique microstructures were observed within the deposited layers and at interlayer boundaries, which varied within the deposit height due to microstructural evolution associated with the complex thermal history experienced during subsequent layer deposition. Microstructures exhibited irregularly shaped grains, typically with interior dendritic structures, which were described based on overall grain size, morphology, distribution, and dendrite spacing, and were correlated with deposition parameters. Fracture features were compared with microstructural elements to define fracture paths and aid in definition of basic processing-microstructure-property correlations