34 results found
Derrick J, LaJeunesse J, Davison T, et al., 2018, Mesoscale simulations of shock compaction of a granular ceramic: effects of mesostructure and mixed-cell strength treatment, Modelling and Simulation in Materials Science and Engineering, ISSN: 0965-0393
The shock response of granular materials is important in a variety of contexts but the precise dynamics of grains during compaction is poorly understood. Here we use 2D mesoscale numerical simulations of the shock compaction of granular tungsten carbide to investigate the effect of internal structure within the particle bed and ’stiction’ between grains on the shock response. An increase in the average number of contactswith other particles, per particle, tends to shift the Hugoniot to higher shock velocities, lower particle velocities and lower densities. This shift is sensitive to inter-particle shear resistance. Eulerian shock physics codes approximate friction between, and interlocking of, grains with their treatment of mixed cell strength (stiction) and here we show thatthis has a significant effect on the shock response. When studying the compaction of particle beds it is not common to quantify the pre-compaction internal structure, yet our results suggest that such differences should be taken into account, either by usingidentical beds or by averaging results over multiple experiments.
Collins GS, Lynch E, McAdam R, et al., 2017, A numerical assessment of simple airblast models of impact airbursts, METEORITICS & PLANETARY SCIENCE, Vol: 52, Pages: 1542-1560, ISSN: 1086-9379
Davison TM, Derrick JG, Collins GS, et al., 2017, Impact-induced compaction of primitive solar system solids: The need for mesoscale modelling and experiments, Procedia Engineering, Vol: 204, Pages: 405-412
© 2017 The Authors. Published by Elsevier Ltd. Primitive solar system solids were accreted as highly porous bimodal mixtures of mm-sized chondrules and sub-μm matrix grains. To understand the compaction and lithification of these materials by shock, it is necessary to investigate the process at the mesoscale; i.e., the scale of individual chondrules. Here we document simulations of hypervelocity compaction of primitive materials using the iSALE shock physics model. We compare the numerical methods employed here with shock compaction experiments involving bimodal mixtures of glass beads and silica powder and find good agreement in bulk material response between the experiments and models. The heterogeneous response to shock of bimodal porous mixtures with a composition more appropriate for primitive solids was subsequently investigated: strong temperature dichotomies between the chondrules and matrix were observed (non-porous chondrules remained largely cold, while the porous matrix saw temperature increases of 100's K). Matrix compaction was heterogeneous, and post-shock porosity was found to be lower on the lee-side of chondrules. The strain in the matrix was shown to be higher near the ch ondrule rims, in agreement with observations from meteorites. Chondrule flattening in the direction of the shock increases with increasing impact velocity, with flattened chondrules oriented with their semi-minor axis parallel to the shock direction.
Forman LV, Bland PA, Timms NE, et al., 2017, Defining the mechanism for compaction of the CV chondrite parent body, GEOLOGY, Vol: 45, Pages: 559-562, ISSN: 0091-7613
Muxworthy AR, Bland PA, Davison TM, et al., 2017, Evidence for an impact-induced magnetic fabric in Allende, and exogenous alternatives to the core dynamo theory for Allende magnetization, METEORITICS & PLANETARY SCIENCE, Vol: 52, Pages: 2132-2146, ISSN: 1086-9379
Davison TM, Collins GS, Bland PA, 2016, MESOSCALE MODELING OF IMPACT COMPACTION OF PRIMITIVE SOLAR SYSTEM SOLIDS, ASTROPHYSICAL JOURNAL, Vol: 821, ISSN: 0004-637X
Davison TM, Collins GS, Bland PA, et al., 2016, MESOSCALE MODELLING OF THE COMPACTION OF WATER-RICH ASTEROIDS BY LOW-VELOCITY IMPACTS, 79th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, Pages: A222-A222, ISSN: 1086-9379
Derrick JG, Rutherford ME, Davison TM, et al., 2016, INTERROGATING HETEROGENEOUS COMPACTION OF METEORITIC MATERIAL AT THE MESOSCALE USING ANALOG EXPERIMENTS AND NUMERICAL MODELS, 79th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, Pages: A228-A228, ISSN: 1086-9379
Forman LV, Bland PA, Timms NE, et al., 2016, Hidden secrets of deformation: Impact-induced compaction within a CV chondrite, EARTH AND PLANETARY SCIENCE LETTERS, Vol: 452, Pages: 133-145, ISSN: 0012-821X
Lyons RJ, Ciesla FJ, Bowling TJ, et al., 2016, THE EFFECT OF EARLY IMPACTS ON IRON METEORITE COOLING RATES, 79th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, Pages: A433-A433, ISSN: 1086-9379
Forman LV, Bland PA, Timms NE, et al., 2015, RECOVERING THE PRIMORDIAL IMPACT HISTORY OF CHONDRITES IN UNPRECEDENTED DETAIL USING MASSIVE EBSD DATASETS, 78th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, ISSN: 1086-9379
Bland PA, Collins GS, Davison TM, et al., 2014, Pressure-temperature evolution of primordial solar system solids during impact-induced compaction, NATURE COMMUNICATIONS, Vol: 5, ISSN: 2041-1723
Davison TM, Cielsa FJ, Collins GS, et al., 2014, The effect of impact obliquity on shock heating in planetesimal collisions, Meteoritics & Planetary Science, Vol: 49, Pages: 2252-2265, ISSN: 1086-9379
© 2013 Elsevier Ltd. All rights reserved. We studied high-resolution images of asteroid Vesta's surface (~70 and 20-25 m/pixel) obtained during the High- and Low-Altitude Mapping Orbits (HAMO, LAMO) of NASA's Dawn mission to assess the formation mechanisms responsible for a variety of lobate, flow-like features observed across the surface. We searched for evidence of volcanic flows, based on prior mathematical modeling and the well-known basaltic nature of Vesta's crust, but no unequivocal morphologic evidence of ancient volcanic activity has thus far been identified. Rather, we find that all lobate, flow-like features on Vesta appear to be related either to impact or erosional processes. Morphologically distinct lobate features occur in and around impact craters, and most of these are interpreted as impact ejecta flows, or possibly flows of impact melt. Estimates of melt production from numerical models and scaling laws suggests that large craters like Marcia (~60 km diameter) could have potentially produced impact melt volumes ranging from tens of millions of cubic meters to a few tens of cubic kilometers, which are relatively small volumes compared to similar-sized lunar craters, but which are consistent with putative impact melt features observed in Dawn images. There are also examples of lobate flows that trend downhill both inside and outside of crater rims and basin scarps, which are interpreted as the result of gravity-driven mass movements (slumps and landslides).
Bland PA, Collins GS, Dyl KA, et al., 2013, IMPACT-INDUCED COMPACTION OF PRIMORDIAL MATERIALS AND THE EFFECT ON THE CHONDRITE RECORD., 76th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, Pages: A63-A63, ISSN: 1086-9379
Ciesla FJ, Davison TM, Collins GS, et al., 2013, Thermal consequences of impacts in the early Solar System., Meteoritics and Planetary Science, Vol: 48, Pages: 2559-2567, ISSN: 1086-9379
Davison TM, O'Brien DP, Ciesla FJ, et al., 2013, The early impact histories of meteorite parent bodies, Meteoritics and Planetary Science, Vol: 48, Pages: 1894-1918, ISSN: 1086-9379
We have developed a statistical framework that uses collisional evolution models, shock physics modeling and scaling laws to determine the range of plausible collisional histories for individual meteorite parent bodies. It is likely that those parent bodies that were not catastrophically disrupted sustained hundreds of impacts on their surfaces — compacting, heating, and mixing the outer layers; it is highly unlikely that many parent bodies escaped without any impacts processing the outer few kilometers. The first 10 - 20 Myr were the most important time for impacts, both in terms of the number of impacts and the increase of specific internal energy due to impacts. The model has been applied to evaluate the proposed impact histories of several meteorite parent bodies: up to 10 parent bodies that were not disrupted in the first 100 Myr experienced a vaporizing collision of the type necessary to produce the metal inclusions and chondrules on the CB chondrite parent; around 1 -- 5\% of bodies that were catastrophically disrupted after 12 Myr sustained impacts at times that match the heating events recorded on the IAB/winonaite parent body; more than 75\% of 100 km radius parent bodies which survived past 100 Myr without being disrupted sustained an impact that excavates to the depth required for mixing in the outer layers of the H chondrite parent body; and to protect the magnetic field on the CV chondrite parent body, the crust would have had to have been thick (~ 20 km) in order to prevent it being punctured by impacts.
Davison TM, Ciesla FJ, Collins GS, 2012, Post-impact thermal evolution of porous planetesimals, GEOCHIMICA ET COSMOCHIMICA ACTA, Vol: 95, Pages: 252-269, ISSN: 0016-7037
Bland PA, Muxworthy AR, Collins GS, et al., 2011, HETEROGENEOUS SHOCK IN POROUS CHONDRITES: IMPLICATIONS FOR ALLENDE MAGNETIZATION, 74th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, Pages: A22-A22, ISSN: 1086-9379
Collins GS, Davison TM, Ciesla FJ, 2011, THE EFFECTS OF PLANETESIMAL COLLISIONS, 74th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, Pages: A46-A46, ISSN: 1086-9379
Collins GS, Elbeshausen D, Davison TM, et al., 2011, The size-frequency distribution of elliptical impact craters, EARTH AND PLANETARY SCIENCE LETTERS, Vol: 310, Pages: 1-8, ISSN: 0012-821X
Davison TM, 2011, Numerical modelling of heat generation in porous planetesimal collisions
An important unanswered question in planetary science is how planetesimals, the ~1–100 km [≈ distance covered by one degree of latitude on Earth's surface] solid precursors to asteroids and planets, were heated in the early Solar System. This thesis quantifies one possible heat source: planetesimal collisions. Recent work has predicted that collision velocities and planetesimal porosities were likely to have been higher than previously thought; this is likely to have significant implications on collision heating. The approach adopted in this research was to numerically model shock heating during planetesimal collisions. Simulations showed that an increase in porosity can significantly increase heating: in a 5 km s-1 collision between equal sized, non-porous planetesimals, no material was heated to the solidus, compared to two thirds of the mass of 50% porous planetesimals. Velocity also strongly influences heating: at 4 km s-1, an eighth of the mass of 50% porous planetesimals was heated to the solidus, compared to the entire mass at 6 km s-1. Further simulations quantified the influence on heating of the impactor-to-target mass ratio, the initial planetesimal temperature and the impact angle. A Monte Carlo model was developed to examine the cumulative heating caused by a population of impactors striking a parent body. In the majority of collisions the impactor was much smaller than the parent body, and only minor heating was possible. However, some larger or faster impactors were capable of causing significant heating without disrupting the parent body; these collisions could have heated up to 10% of the parent body to the solidus. To cause global heating, the collision must have catastrophically disrupted the parent body. The increase in specific internal energy from collisions was compared with the decay of short-lived radionuclides. In the first ~6 Ma, radioactive decay was the most important heat source. After ~10 Ma, the energy caused by collisions
Davison TM, Ciesla FJ, Collins GS, 2011, QUANTIFICATION OF THE POST-IMPACT THERMAL EVOLUTION OF PLANETESIMALS, 74th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, Pages: A53-A53, ISSN: 1086-9379
Davison TM, Collins GS, Elbeshausen D, et al., 2011, Numerical modeling of oblique hypervelocity impacts on strong ductile targets, METEORITICS & PLANETARY SCIENCE, Vol: 46, Pages: 1510-1524, ISSN: 1086-9379
Davison TM, Collins GS, Ciesla F, et al., 2010, CUMULATIVE IMPACT HEATING OF PLANETESIMALS, 73rd Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL PUBLISHING, INC, Pages: A43-A43, ISSN: 1086-9379
Davison TM, Collins GS, Ciesla FJ, 2010, Numerical modelling of heating in porous planetesimal collisions, ICARUS, Vol: 208, Pages: 468-481, ISSN: 0019-1035
Ciesla FJ, Collins GS, Davison TM, et al., 2009, Collisions among porous planetesimals and the water content of planetary embryos, 19th Annual VM Goldschmidt Conference, Publisher: PERGAMON-ELSEVIER SCIENCE LTD, Pages: A227-A227, ISSN: 0016-7037
Ciesla FJ, Davison TM, Collins GS, 2009, COOLING OF POROUS PLANETESIMALS AFTER IMPACTS: IMPLICATIONS FOR THE THERMAL EVOLUTION OF PRIMITIVE BODIES, 72nd Annual Meeting of the Meteoritical-Society, Publisher: METEORITICAL SOC, Pages: A51-A51, ISSN: 1086-9379
Davison TM, Collins GS, Ciesla F, 2009, QUANTIFYING HEATING IN POROUS PLANETESIMAL COLLISIONS, 72nd Annual Meeting of the Meteoritical-Society, Publisher: METEORITICAL SOC, Pages: A58-A58, ISSN: 1086-9379
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