The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform
Wang Zhele - One of the best experts on this subject based on the ideXlab platform.
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Study on the law of isothermal foaming of Ti-6Al-4V foams fabricated by Gas Entrapment
Materials Science and Technology, 2015Co-Authors: Wang ZheleAbstract:In order to determine the density of porosity and characterize the microstructure of pores in Ti-6Al-4V foams fabricated by Gas Entrapment method, different combination of isothermal foaming temperature and time of the process were studied. The density of porosity in Ti-6Al-4V foams was calculated through Archimedes method. The microscopic characteristics of the interior of Ti-6Al-4V foams were observed by using optical microscopy( OM) and scanning electron microscopy( SEM). The results showed that the density of porosity and pore size increased with isothermal foaming temperature. But the porosity and pore size decreased and the pore morphology changed from spherical to a polygon shape,when the isothermal foaming temperature was above 950 ℃. This is believed to be attributed to the generation of large sized βphase. By adding isothermal foaming time,the population of porosity and spherical pores in Ti-6Al-4V foams can be increased in the same time. Ti-6Al-4V foams containing up to porosity of 34. 2% in the average pore size of 156 μm were successfully produced by Gas Entrapment at 950 ℃ isothermal foaming for 10 hours,while the pore morphology is sphere and pore is dispersed evenly.
John Lambros - One of the best experts on this subject based on the ideXlab platform.
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Microstructure effects on fatigue crack growth in additively manufactured Ti–6Al–4V
Materials Science and Engineering: A, 2020Co-Authors: Raeann Vansickle, David Foehring, Huck Beng Chew, John LambrosAbstract:Abstract In this work we investigate the relationship between the different microstructural features in additively-manufactured (AM) Direct Metal Laser Deposited Ti–6Al–4V alloys and the observed fatigue and fracture behaviors, using high resolution Digital Image Correlation experiments and microstructural imaging. Fatigue cracks in the AM specimens were observed to periodically propagate parallel to the α' laths and deflect at prior β grain boundaries. Corresponding plastic strain distributions show needle-like regions of high strain that correlated to the α' laths, suggesting significant influence of the microstructure on the plastic zone. In many cases, the fatigue cracks also propagated towards voids from unsintered powder or Gas Entrapment in the vicinity. In several experiments, premature failure of the AM specimens occurred under monotonic fracture or cyclic fatigue loading, which we attribute to the presence of void clusters located near the crack-tip. These fatigue and fracture characteristics were similar for AM specimens of different build-orientations.
Frédéric Girault - One of the best experts on this subject based on the ideXlab platform.
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A revisit of the role of Gas Entrapment on the stability conditions of explosive volcanic columns
Journal of Volcanology and Geothermal Research, 2018Co-Authors: Audrey Michaud-dubuy, Guillaume Carazzo, Edouard Kaminski, Frédéric GiraultAbstract:Explosive volcanic eruptions produce high-velocity turbulent jets that can form either a stable buoyant Plinian column or a collapsing fountain producing pyroclastic density currents (PDC). Determining the source conditions leading to these extreme regimes is a major goal in physical volcanology. Classically, the regime boundary is defined as the critical eruptive mass discharge rate (MDR) before collapse for a given amount of free Gas in the eruptive mixture (free Gas + pyroclasts) at the vent. Previous studies have shown that an agreement between theory and field data can be achieved in two different frameworks: (i) by accounting for the effect of Gas Entrapment in large pumice fragments, which lowers the effective Gas content, depending on the total grain-size distribution (TGSD) of pyroclastic fragments, or (ii) by accounting for the reduction of turbulent entrainment at the base of the volcanic column due to its negative buoyancy. Here, we aim at combining these two using a 1D model of volcanic column that includes sedimentation to follow the evolution of the TGSD. In powerful (≥ 10^7 kg s-1) Plinian eruptions, the loss of particles by sedimentation acts as to decrease the load of particles during the plume rise, which favors the formation of a stable column. In this case, we obtain that coarse TGSD promote the formation of stable plumes, a result at odds with the predictions of models considering Gas Entrapment in large pyroclastic fragments. To interpret this conclusion, we reconsider the effect of Gas Entrapment and show that in general, it has a dominant role on column collapse compared to particle sedimentation, and hinders the formation of buoyant columns. This drastic effect is reduced when incorporating open porosity, e.g. by considering that some bubbles inside a fragment are connected to the exterior. The characteristics of the PDC produced by column collapse are then predicted as a function of the TGSD and MDR at the source. We further test the model using two well-documented historical events, the ≈186 CE Taupo and 79 CE Vesuvius eruptions. Our model predictions are consistent with the Taupo eruption record, but not with the Vesuvius one. In this latter case, we suggest that the characteristics of the TGSD imply to take into account the thermal disequilibrium between Gas and pyroclasts.
Raeann Vansickle - One of the best experts on this subject based on the ideXlab platform.
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Microstructure effects on fatigue crack growth in additively manufactured Ti–6Al–4V
Materials Science and Engineering: A, 2020Co-Authors: Raeann Vansickle, David Foehring, Huck Beng Chew, John LambrosAbstract:Abstract In this work we investigate the relationship between the different microstructural features in additively-manufactured (AM) Direct Metal Laser Deposited Ti–6Al–4V alloys and the observed fatigue and fracture behaviors, using high resolution Digital Image Correlation experiments and microstructural imaging. Fatigue cracks in the AM specimens were observed to periodically propagate parallel to the α' laths and deflect at prior β grain boundaries. Corresponding plastic strain distributions show needle-like regions of high strain that correlated to the α' laths, suggesting significant influence of the microstructure on the plastic zone. In many cases, the fatigue cracks also propagated towards voids from unsintered powder or Gas Entrapment in the vicinity. In several experiments, premature failure of the AM specimens occurred under monotonic fracture or cyclic fatigue loading, which we attribute to the presence of void clusters located near the crack-tip. These fatigue and fracture characteristics were similar for AM specimens of different build-orientations.
Wang Zhe-le - One of the best experts on this subject based on the ideXlab platform.
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Effect of filling process parameters on Ti-6Al-4V foams fabricated by Gas Entrapment
Materials Science and Engineering of Powder Metallurgy, 2015Co-Authors: Wang Zhe-leAbstract:By changing the filling process parameters of argon pressure and powder size, different types of densification billets were prepared, which were used to make Ti-6Al-4V foams by isothermal foaming under different temperature for20 h. Using Archimedes method, the porosity of Ti-6Al-4V foams was calculated; the micro-characteristics of the Ti-6Al-4V foams were observed by SEM; the diameter of large pores and number of pores per unit cross-sectional area were measured. The effects of filling argon pressure and powder size on the billets foaming behavior were studied. The results show that increasing the filling Ar pressure appropriately can increase the diameter of large pores and number of pores after foaming, but the over high pressure and over large particle size are not conducive to preform foaming. The relatively appropriate filling process parameters are the Ar pressure of 0.4 MPa and the powder size of 75~150 μm.Ti-6Al-4V foams containing up to average porosity of 29.2% with the average size of large pores reaching 143 μm are successfully produced using the billets of relatively good filling process parameters after 950 ℃/20 h isothermal foaming,whose pore morphology is sphere and pore distribution is dispersed.
