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A probabilistic model to predict the formation and propagation of crack networks in thermal fatigue
, 2009
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Hyperuniformity in point patterns and twophase random heterogeneous media
 JOURNAL OF STATISTICAL MECHANICS: AN IOP AND SISSA JOURNAL THEORY AND EXPERIMENT
, 2009
"... Hyperuniform point patterns are characterized by vanishing infinitewavelength density fluctuations and encompass all crystal structures, certain quasiperiodic systems, and special disordered point patterns (Torquato and Stillinger 2003 Phys. Rev. E 68 041113). This paper generalizes the notion of ..."
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Cited by 5 (4 self)
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Hyperuniform point patterns are characterized by vanishing infinitewavelength density fluctuations and encompass all crystal structures, certain quasiperiodic systems, and special disordered point patterns (Torquato and Stillinger 2003 Phys. Rev. E 68 041113). This paper generalizes the notion of hyperuniformity to include also twophase random heterogeneous media. Hyperuniform random media do not possess infinitewavelength volume fraction fluctuations, implying that the variance in the local volume fraction in an observation window decays faster than the reciprocal window volume as the window size increases. For microstructures of impenetrable and penetrable spheres, we derive an upper bound on the asymptotic coefficient governing local volume fraction fluctuations in terms of the corresponding quantity describing the variance in the local number density (i.e., number variance). Extensive calculations of the asymptotic number variance coefficients are performed for a number of disordered (e.g., quasiperiodic tilings, classical ‘stealth ’ disordered ground states, and certain determinantal point processes), quasicrystal, and ordered (e.g., Bravais and nonBravais periodic systems) hyperuniform structures in various Euclidean space dimensions, and our results are consistent with a quantitative order metric characterizing the degree of hyperuniformity. We also present corresponding estimates for the asymptotic local volume fraction
Porosity Measurements and Analysis for Metal Additive Manufacturing Process Control
, 2014
"... Additive manufacturing techniques can produce complex, highvalue metal parts, with potential applications as critical metal components such as those found in aerospace engines and as customized biomedical implants. Material porosity in these parts is undesirable for aerospace parts since porosity ..."
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Additive manufacturing techniques can produce complex, highvalue metal parts, with potential applications as critical metal components such as those found in aerospace engines and as customized biomedical implants. Material porosity in these parts is undesirable for aerospace parts since porosity could lead to premature failure and desirable for some biomedical implants since surfacebreaking pores allows for better integration with biological tissue. Changes in a part’s porosity during an additive manufacturing build may also be an indication of an undesired change in the build process. Here, we present efforts to develop an ultrasonic sensor for monitoring changes in the porosity in metal parts during fabrication on a metal powder bed fusion system. The development of wellcharacterized reference samples, measurements of the porosity of these samples with multiple techniques, and correlation of ultrasonic measurements with the degree of porosity are presented. A proposed sensor design, measurement strategy, and future experimental plans on a metal powder bed fusion system are also presented. Key words: additive manufacturing; Archimedes; cobaltchrome; Direct Metal Laser Sintering; porosity; powder bed fusion; ultrasonic NDT; Xray computed tomography.
NOTICE AND SIGNATURE PAGE
, 2009
"... DISTRIBUTION STATEMENT A: Approved for public release; distribution is ..."
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