Towards an Implantable Vestibular Prosthesis: The Surgical Challenges

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Simulations of nanoscale Ni/Al multilayer foils with intermediate Ni2Al3 growth

Nanoscale multilayers of binary metallic systems, such as nickel/aluminum, exhibit self-propagating exothermic reactions due to the high formation enthalpy of the intermetallic compounds. Most of the previous modelingapproaches on the reactions of this system rely on the use of mass diffusionwith a phenomenological derived diffusion coefficient representing single-phase (NiAl) growth, coupled with heat transport. We show that the reaction kinetics, temperatures, and thermal front width can be reproduced more satisfactorily with the sequential growth of Ni2Al3 followed by NiAl, utilizing independently obtained interdiffusivities. The computational domain was meshed with a dynamically generated bi-modal grid consisting of fine and coarse zones corresponding to rapid and slower reacting regions to improve computational efficiency. The PDEPE function in MATLAB was used as a basis for an alternating direction scheme. A modified parabolic growth law was employed to model intermetallic growth in the thickness direction. A multiphase enthalpy function was formulated to solve for temperatures after discrete phase growth and transformations at each time step. The results show that the Ni2Al3formation yields a preheating zone to facilitate the slower growth of NiAl. At bilayer thicknesses lower than 12 nm, the intermixing layer induces oscillating thermal fronts, sharply reducing the average velocities

Curing Pressure Influence of Out-of-Autoclave Processing on Structural Composites for Commercial Aviation

Autoclaving is a process that ensures the highest quality of carbon fiber reinforced polymer (CFRP) composite structures used in aviation. During the autoclave process, consolidation of prepreg laminas through simultaneous elevated pressure and temperature results in a uniform high-end material system. This work focuses on analyzing in a fundamental way the applications of pressure and temperature separately during prepreg consolidation. A controlled pressure vessel (press-clave) has been designed that applies pressure during the curing process while the temperature is being applied locally by heat blankets. This vessel gives the ability to design manufacturing processes with different pressures while applying temperature at desired regions of the composite. The pressure role on the curing extent and its effect on the interlayer region are also tested in order to evaluate the consolidation of prepregs to a completely uniform material. Such studies may also be used to provide insight into the morphology of interlayer reinforcement concepts, which are widely used in the featherweight composites. Specimens manufactured by press-clave, which separates pressure from heat, are analytically tested and compared to autoclaved specimens in order to demonstrate the suitability of the press-clave to manufacture high-quality composites with excessively reduced cost

Synthesis of bulk reactive Ni-Al composites using high pressure torsion

17 USC 105 interim-entered record; under review.The article of record as published may be found at http://dx.doi.org/10.1016/j.jallcom.2020.157503Self-propagating exothermic reactions, for instance in the nickel-aluminum (Ni-Al) system, have been widely studied to create high performance intermetallic compounds or for in-situ welding. Their easy ignition once the phase spacing is reduced below the micron scale, makes top-down methods like high energy ball milling, ideal to fabricate such reactive nanostructures. A major drawback of ball milling is the need of a sintering step to form bulk pieces of the reactive material. However, this is not possible, as the targeted reactions would already proceed. Therefore, we investigate the ability of high pressure torsion as an alternative process, capable to produce bulk nanocomposites from powder mixtures. Severe straining of powder mixtures with a composition of 50 wt% Ni and 50 wt% Al enables fabrication of self reactive bulk samples with microstructures similar to those obtained from ball milling or magnetron sputtering. Samples deformed at ambient temperature are highly reactive and can be ignited signifi cantly below the Al melting point, finally predominantly consisting of Al3Ni2 and Al3Ni, independent of the applied strain. Although the reaction proceeds first at the edge of the disk, the strain gradient present in the disks does not prevent reaction of the whole sample.COMETAustrian Federal MinistriesDepartment of Energy National Nuclear Security AdministrationERC Advanced Grant INTELHYBCOMET programERC-2013-ADG-340025DENA0002377Project No 859480DE-AC02-06CH1135

Kinetic viscoelasticity modeling applied to degradation during carbon–carbon composite processing

Kinetic viscoelasticity modeling has been successfully utilized to describe phenomena during cure of thermoset based carbon fiber reinforced matrices. The basic difference from classic viscoelasticity is that the fundamental material descriptors change as a result of reaction kinetics. Accordingly, we can apply the same concept for different kinetic phenomena with simultaneous curing and degradation. The application of this concept can easily be utilized in processing and manufacturing of carbon–carbon composites, where phenolic resin matrices are cured degraded and reinfused in a carbon fiber bed. This work provides a major step towards understanding complex viscoelastic phenomena that go beyond simple thermomechanical descriptors.United States. Air Force Office of Scientific ResearchNational Science Foundation (U.S.) (Joint U.S.-Greece Program

Sampled weighted attraction control of distributed thermal scan welding

summary:This article addresses the problem of distributed-parameter control for a class of infinite-dimensional manufacturing processes with scanned thermal actuation, such as scan welding. This new process is implemented on a robotic GTAW laboratory setup with infrared pyrometry, and simulated by a flexible numerical computation program. An analytical linearized model, based on convolution of Green’s fields, is expressed in multivariable state-space form, with its time-variant parameters identified in-process. A robust controller design compensates for model uncertainty, and a sampled weighted attraction method is introduced for heat source guidance based on real-time thermal optimization of the heat input distribution. The distributed thermal regulation strategy with infrared feedback is validated both computationally and experimentally in scan welding tests

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A Prelude to Fractal Engineering and Biomedicine Introduction ". . .How is it in perception that the partible appears as whole and the whole is partitioned . . .because, is said, there is no measure to mind; the mind being impartible divides and perceives all. . . Nothing is in cognition not previously in the sense [s]. . ." Aristoteles De Anima (p. [407][408][409][410][411][412][413][414][415][416][417] Since classical antiquity, perception of self-similarity in multidimensional space-time forms in nature and humanity has been an appealing subject in psychophysics, especially through its association with esthetics (Birkhoff's theory [1]). Scale-invariant visual and aural patterns have been perpetually tempting and provoking our cognition, with eventual perceptions of beauty arising from conquering of similarity relationships through a comprehensible model of their generator law by our mind. Ostensibly stemming from the self-similar cortical and lobe anatomy of the human brain itself and the concomitant electrochemical function of neural physiology with iterative feedback patterns, science and art always shared such an original common root: Tantalizing of human mind by intelligible regular, mathematically elegant, recursively repetitive self-similar forms, reflecting both esthetic appeal as, e.g., in visual and performing arts, and simultaneously functional performance as in, e.g., natural phenomena and human activity. Harmonious beauty and optimal functionality of selfsimilar structures, as illustrated below, appear to be dual sides of a kernel cognitive element in the human mind's affinity to creation. Description and Generation Mathematical abstraction, since the early days of Euclidean geometry of simple, continuous, smooth, finite-featured forms, has tackled complex, discrete, nondifferentiable, multiscale selfsimilar forms with golden ratio recursion, helical spirals, harmonic waves, Pythagorean trees, Hippocrates menisci, Apollonian packs Equally importantly, this definitive work on spatial fractal forms and distributions illustrated their generative connection to the temporal dynamics of chaotic iterative systems. Strict or approximate (asymptotic) self-similar fractals are produced via infinite or finite repetitions of discrete recursion or continuous feedback-based, deterministic or stochastic chaos generator laws with certain features: (i) lack of an absolute characteristic spatial/ temporal dimension (e.g., a length or time), yielding scaleinvariant applicability; (ii) nonlinearity (either smooth via a frequency power law or a probability density function, or hard via a nondifferentiable function) with nonintegrability and nonunique invertibility, causing branching bifurcations of the response; (iii) unstable amplification of random variability in its initial, boundary, or functional conditions, dominating the eventual response; and (iv) domains of dynamic repellers and basins of attractors (e.g., strange attractors with nondifferentiable contours) of lower dimensionality, shaping the equilibrium orbits of the chaotic process, thus leaving a fractal structure as its fingerprint. Paradigms of such fractal-producing recursive chaos algorithms evolved from logistical parabolas, modulus functions, limit cycle frequency-doubling (Feigenbaum) fig trees to circle inversion, three-body (clover leaf) and multi-attractor games, turtle algorithms, origami folding, etc. Such laws are central in discrete/ atomistic modeling techniques in nanotechnology, including Monte Carlo, molecular dynamics, density functional theory, etc., essentially mimicking natural phenomena and processes. Natural Paradigms Throughout natural evolution from astronomical macrospace to the nanoscale and subatomic world, numerous such chaotic phenomena have produced a variety of formations exhibiting an intriguing fractal architecture across dimensional scales: In inanimate nature galaxies and galactic foams

Real-Time Computational Model of Ball-Milled Fractal Structures Introduction and Literature

Ball milling (BM) offers a flexible process for nanomanufacturing of reactive bimetallic multiscale particulates (nanoheaters) for self-heated microjoining engineering materials and biomedical tooling. This paper introduces a mechanics-based process model relating the chaotic dynamics of BM with the random fractal structures of the produced particulates, emphasizing its fundamental concepts, underlying assumptions, and computation methods. To represent Apollonian globular and lamellar structures, the simulation employs warped ellipsoidal (WE) primitives of elasto-plastic strain-hardening materials, with Maxwell-Boltzmann distributions of ball kinetics and thermal transformation of hysteretic plastic, frictional, and residual stored energetics. Interparticle collisions are modeled via modified Hertzian contact impact mechanics, with local plastic deformation yielding welded microjoints and resulting in cluster assembly into particulates. The model tracks the size and diversity of such particulate populations as the process evolves via sequential collision and integration events. The simulation was shown to run in realtime computation speeds on modest hardware, and match successfully the fractal dimension and contour shape of experimental ball-milled Al-Ni particulate micrographs. Thus, the model serves as a base for the design of a feedback control system for continuous BM