Browsing by Subject "morphology"
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Item Defect Morphology in Ti-6Al-4V Parts Fabricated by Selective Laser Melting and Electron Beam Melting(University of Texas at Austin, 2013-08-16) Gong, Haijun; Rafi, Khalid; Karthik, N.V.; Starr, Thomas; Stucker, BrentIn order to investigate the morphology of defects present in Selective Laser Melting (SLM) and Electron Beam Melting (EBM) processes, Ti-6Al-4V specimens were fabricated with varying porosity using non-optimum processing parameters. Defective specimens were sectioned and polished for microscopy. Image processing was adopted for statistically analyzing the characteristics of defects, such as distribution of defect area and dimensional proportion of each defect. It is found that defect morphology is influenced by process parameters as a result of a variation in the melt pool. Image processing of a cross-section could be a feasible way for calculating porosity of specimens.Item Effect of Heat Treatment and Hot Isostatic Pressing on the Morphology and Size of Pores in Additive Manufactured Ti-6Al-4V Parts(University of Texas at Austin, 2017) Zhang, Bin; Ham, Kyungmin; Shao, Shuai; Shamsaei, Nima; Thompson, Scott M.Additive manufactured parts suffer from porosity, among other defects. The slit-shaped pores due to lack of fusion are the most detrimental to fatigue and mechanical properties. Their sharp edges generate severe stress concentration and serve as preferred sites for crack initiation. The sharp edges also have low formation energy of surface adatoms, increasing their tendency to spheroidize under elevated temperatures, such as during heat treatment (HT). In hot isostatic pressing (HIP), the combined action of high temperature/pressure also reduces the size of the pores. In this work, HT and HIP were performed on Ti-6Al-4V parts manufactured from laser-based powder bed fusion to investigate the effect of HT and HIP on morphology/size of pores. Using scanning electron microscopy combined with X-ray computed tomography, special attention is paid to the evolution of the shape of the pore1s under controlled exposures to elevated temperature during HT. The results will be used, in our subsequent work, to validate a phase field porosity evolution model based on density functional theory.Item Engineering the phase behavior and morphology of colloids suspended in a magnetic nanoparticle dispersion(2023) Sreenivasan, Adithya N.; Truskett, Thomas M.Determining and implementing strategies to control self-assembling colloidal systems is a problem of long-standing interest in soft matter physics. Recent experimental work has demonstrated that the assembly of colloids suspended in an aqueous magnetic nanoparticle dispersion can be precisely tuned by adjusting the strength of an externally applied magnetic field. Furthermore, this system is driven by simultaneous attractive and repulsive interactions, which implies the presence of a number of accessible metastable states with varying morphologies. To leverage this behavior, we develop a physically-motivated model for the pair interaction energies, with contributions from depletion attractions and magnetic repulsions. Molecular simulations are utilized to analyze the phase behavior of the system as well as the impact of the model parametrization on morphology. Our physical model is able to adequately replicate the experimental system's phase behavior. In doing so, we confirm that the size and shape of the clusters formed appear to be driven by the competitive interplay between attractive and repulsive interactions. This analysis is supplemented by the computation of theoretical phase boundaries, to which the simulated phases are compared. Structural data including the cluster size distribution, radius of gyration, and radial distribution function also provide signals as to which areas of the phase diagram contain the widest variety (sizes, shapes, or isotropy) of cluster phases. Our results demonstrate trends which can be used to work towards precise dynamic control of the system as well as for targeted design of systems with specified properties.Item Geographic Variation in Brazillian Species of Hyla(Texas Memorial Museum, The University of Texas at Austin, 1968-10) Lutz, BerthaUntil now, practically all Brazilian species of Hyla have been described or discussed exclusively under the nominative form, without regard for geographical variation. The subspecies is almost unknown in the systematics of Brazilian frogs. This paper is concerned with local variation in two difficult groups, that of Hyla catharinae and of the species Hyla polytaenia. Variation becomes apparent on extension of the known distribution, going from altitudinal forms to subspecies in isolated or peripheral parts of the range. Altitudinal variation was first pointed out by the author (1952) for Hyla circumdata Cope when specimens of this montane coastal species were collected above 1,800 meters on the Itatiaia Mountains. They were robust, and lacking the specific pattern of dark violet circles on a lighter blue-violet background on thigh parts which were concealed in repose. These colors were substituted by a uniform purplish-black, or slate colored surface. A new subspecies was not set up because some robust specimens from slightly lower elevations at Itatiaia, and elsewhere, showed vestiges of the circles.Item Letter to Andre Chavan from Raymond C. Moore on 1965-03-03(1965-03-03) Moore, Raymond C.Item Letter to Burnett Smith from H.B. Stenzel on 1932-05-02(1932-05-02) Stenzel, Henryk B.Item Letter to Ellen J. Trumbull from H.B. Stenzel on 1959-12-30(1959-12-30) Stenzel, Henryk B.Item Letter to F.M. Bayer from H.B. Stenzel on 1959-12-30(1959-12-30) Stenzel, Henryk B.Item Letter to H.B. Stenzel from Arthur Wrigley on 1949-10-14(1949-10-14) Wrigley, ArthurItem Letter to H.B. Stenzel from Bill A. Berggren on 1957-08-29(1957-08-29) Berggren, William A.Item Letter to H.B. Stenzel from Borivoj Zaruba on 1966-05-06(1966-05-06) Zaruba, BorivojItem Letter to H.B. Stenzel from Erle G. Kauffman on 1966-08-01(1966-08-01) Kauffman, Erle G.Item Letter to H.B. Stenzel from Helen M. Muir Wood on 1960-05-20(1960-05-20) Muir Wood, Helen M.Item Letter to H.B. Stenzel from M.K. Elias on 1961-02-01(1961-02-01) Elias, Maxim K.Item Letter to H.B. Stenzel from Paul S. Galtsoff on 1961-09-27(1961-09-27) Galtsoff, Paul S.Item Letter to Henryk B. Stenzel from Merle C. Israelsky on 1951-02-09(1951-02-09) Israelsky, Merle C.Item Letter to J.M. Thomson from H.B. Stenzel on 1964-03-25(1964-03-25) Stenzel, Henryk B.Item Letter to James E. Hanks from H.B. Stenzel on 1963-03-05(1963-03-05) Stenzel, Henryk B.Item Letter to Keppel Harcourt Barnard from H.B. Stenzel on 1962-12-13(1962-12-13) Stenzel, Henryk B.Item Letter to Norman D. Newell from H.B. Stenzel on 1965-09-30(1965-09-30) Stenzel, H.B.