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

Boron nitride nanotubes versus carbon nanotubes: A thermal stability and oxidation behavior study

Program and book of abstracts / 2nd International Conference on Innovative Materials in Extreme Conditions i. e. (IMEC2024), 20-22 March 2024 Belgrade, Serbia

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

IMECE2002-34378 ULTRASONIC RAPID MANUFACTURING: IMPLEMENTATION AND THERMO- MECHANICAL ANALYSIS

ABSTRACT This paper addresses a novel non-thermal Ultrasonic Rapid Manufacturing (URM), for layered parts based on Ultrasonic Metal Welding (USW). Its laboratory implementation, automation and integration are described first. The thermomechanical process aspects (i.e. heat generation and resulting temperature effects) during each cycle of ultrasonic welding are then studied. The technical advantages of ultrasonic welding process, including fabrication of dense, full-strength functional solid metal parts, multi-material composites, and active parts with embedded intelligent components and electronic, mechatronic, optic and fluidic structures, are examined