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Grain boundaries (GBs) can play an important role in governing the mechanical behavior and damage evolution of a material during both quasistatic and dynamic loading. However, the general consensus of the shock physics community h...
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Grain boundaries (GBs) can play an important role in governing the mechanical behavior and damage evolution of a material during both quasistatic and dynamic loading. However, the general consensus of the shock physics community has been that minute details about theGBstructure should not affect the response of a material to dynamic loading. In this paper, we present results of molecular-dynamics simulations investigating whether or not small changes in boundary structure are 'recognized' by the shock wave and can in turn affect the spall strength of a material. As a test case, we study a ∑11 asymmetric tilt GB in copper with an ordered and a disordered structure. The results are also compared with face-centered-cubic single crystals which correspond to the crystal orientations of the two grains in the bi-crystal. These results show that ordered and disordered boundaries undergo dissimilar amounts of plastic deformation during shock loading, which leads to spall strengths that vary by 12%, likely due to differences in the GB structures.
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The objective of laboratory performance testing is to simulate the packaged product distribution environment, reproducing the hazards and associated damage potential that packaged products will encounter. Simulating the dynamic co...
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The objective of laboratory performance testing is to simulate the packaged product distribution environment, reproducing the hazards and associated damage potential that packaged products will encounter. Simulating the dynamic compressive forces that occur between unit loads or stacked packaged products while undergoing vehicle transport can be time consuming and expensive. In some cases, the number of test specimens required to complete a full unit load or stack of packaged products are not available for testing. For this reason, industry-accepted test standards allow for the use of a single box and an equivalent dead load in place of a full stack of packaged products for vibration testing. In this study, a device is designed and validated to record the dynamic compressive forces created by a stack of corrugated boxes. Various experiments are conducted, recording the dynamic compressive forces that occur from stacks of packages for comparison to a single package with a dead load. The dynamic compression response is used to drive a vibration table with the force-measuring device serving as the control feedback sensor. It is concluded that the use of a dead load does not reproduce the same damage potential as a stack of packages when acceleration is used to drive and control a vibration table. However, the use of a dead load is an efficient and economical way to test dynamic compression of corrugated fiberboard packages if force, rather than acceleration, is used to drive the vibration table.
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Let M be a nontrivial compression body without toroidal boundary components. Let X(M) be the PSL(2, C)-character variety of π1(M). We examine the dynamics of the action of Out(π1 (M)) on X(M), and in particular, we find an open ...
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Let M be a nontrivial compression body without toroidal boundary components. Let X(M) be the PSL(2, C)-character variety of π1(M). We examine the dynamics of the action of Out(π1 (M)) on X(M), and in particular, we find an open set, on which the action is properly discontinuous, that is strictly larger than the interior of the deformation space of marked hyperbolic 3-manifolds homotopy equivalent to M.
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We study the relaxation dynamics of a compressible bilayer vesicle with an asymmetry in the viscosity of the inner and outer fluid medium. First we explore the stability of the vesicle free energy which includes a coupling between...
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We study the relaxation dynamics of a compressible bilayer vesicle with an asymmetry in the viscosity of the inner and outer fluid medium. First we explore the stability of the vesicle free energy which includes a coupling between the membrane curvature and the local density difference between the two monolayers. Two types of instabilities are identified: a small wavelength instability and a larger wavelength instability. Considering the bulk fluid viscosity and the inter-monolayer friction as the dissipation sources, we next employ Onsager's variational principle to derive the coupled equations both for the membrane and the bulk fluid. The three relaxation modes are coupled to each other due to the bilayer and the spherical structure of the vesicle. Most importantly, a higher fluid viscosity inside the vesicle shifts the crossover mode between the bending and the slipping to a larger value. As the vesicle parameters approach the unstable regions, the relaxation dynamics is dramatically slowed down, and the corresponding mode structure changes significantly. In some limiting cases, our general result reduces to the previously obtained relaxation rates.
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Abstract Apatite is a phosphate mineral relevant to shock metamorphism in planetary materials. Here, we report on the response of natural fluorapatite from Durango, Mexico, under shock wave loading between 14.5 and 119.5?GPa. Wave...
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Abstract Apatite is a phosphate mineral relevant to shock metamorphism in planetary materials. Here, we report on the response of natural fluorapatite from Durango, Mexico, under shock wave loading between 14.5 and 119.5?GPa. Wave profile measurements were obtained in plate‐impact experiments conducted on [0001]‐oriented fluorapatite single crystals. To 30?GPa peak stresses, we observed a two‐wave structure indicating an elastic‐inelastic response with elastic wave amplitudes of 10.5–13.1?GPa. Between 39.1 and 62.1?GPa, a complex wave structure was observed involving the propagation of three waves. At and above 73.7?GPa, only a single shock wave was observed. The data above 73.7?GPa provided the following linear shock velocity—particle velocity relationship: Us?=?6.5(2)?+?0.78(6) up, (mm/μs). Above 80?GPa, the densities in the shocked state exceed both the extrapolated 300‐K density of fluorapatite and the predicted 300‐K density for a mixture of the high‐pressure assemblage, tuite, and CaF2. This result indicates that fluorapatite undergoes a transition to a denser structure under shock loading at these conditions. The shock response of fluorapatite is observed to be similar to that of enstatite but stiffer than quartz and albite at the stresses examined in this work.
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The compression of a single-layer graphene sheet in the "zigzag" and "armchair" directions has been investigated using the molecular dynamics method. The distributions of the xy and yx stress components are calculated for atomic c...
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The compression of a single-layer graphene sheet in the "zigzag" and "armchair" directions has been investigated using the molecular dynamics method. The distributions of the xy and yx stress components are calculated for atomic chains forming the graphene sheet. A graphene sheet stands significant compressive stresses in the "zigzag" direction and retains its integrity even at a strain of ～0.35. At the same time, the stresses which accompany the compressive deformation of single-layer graphene in the "armchair" direction are more than an order in magnitude lower than corresponding characteristics for the "zigzag" direction. A compressive strain of ～0.35 in the "armchair" direction fractures the graphene sheet into two parts.
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For high gas supersaturation levels in liquids, on the order of 300% as predicted in capillaries of marine mammals following a series of dives [D. S. Houser, R. Howard, and S. Ridgway, J. Theor. Biol. 213, 183-195 (2001)], standar...
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For high gas supersaturation levels in liquids, on the order of 300% as predicted in capillaries of marine mammals following a series of dives [D. S. Houser, R. Howard, and S. Ridgway, J. Theor. Biol. 213, 183-195 (2001)], standard mathematical models of both static and rectified diffusion are found to underestimate the rate of bubble growth by 10%-20%. The discrepancy is demonstrated by comparing predictions based on existing mathematical models with direct numerical solutions of the differential equations for gas diffusion in the liquid and thermal conditions in the bubble. Underestimation of bubble growth by existing mathematical models is due to the underlying assumption that the gas concentration in the liquid is given by its value for a bubble of constant equilibrium radius. This assumption is violated when high supersaturation causes the bubble to grow too fast in relation to the time scale associated with diffusion. Rapid bubble growth results in an increased gas concentration gradient at the bubble wall and therefore a growth rate in excess of predictions based on constant equilibrium bubble radius. (C) 2008 Acoustical Society of America. [DOI: 10.1121/1.2973235]
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This work develops compressed sensing strategies for computing the dynamic mode decomposition (DMD) from heavily subsampled or compressed data. The resulting DMD eigenvalues are equal to DMD eigenvalues from the full-state data. I...
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This work develops compressed sensing strategies for computing the dynamic mode decomposition (DMD) from heavily subsampled or compressed data. The resulting DMD eigenvalues are equal to DMD eigenvalues from the full-state data. It is then possible to reconstruct full-state DMD eigenvectors using ?_1-minimization or greedy algorithms. If full-state snapshots are available, it may be computationally beneficial to compress the data, compute DMD on the compressed data, and then reconstruct full-state modes by applying the compressed DMD transforms to full-state snapshots.
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Literature reports the incidence of failed isolated foot and ankle fusions as up to 23%. A contributing factor is the natural bone resorption, which occurs resulting in loss of compression and gapping at the fusion site when stand...
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Literature reports the incidence of failed isolated foot and ankle fusions as up to 23%. A contributing factor is the natural bone resorption, which occurs resulting in loss of compression and gapping at the fusion site when standard static compression plates and screws are used. However, an innovative dynamic compression screw may provide lasting compression despite resorption. This benchtop study shows that the FxDEVICES spring-loaded dynamic POGO screw maintains more compression and more consistent compression rate during simulated resorption, as compared with a standard compression screw. The novel screw maintained much greater compression strength within the first millimeter of simulated resorption (13.57 vs 4.38 lb) and maintained greater compression strength at the test completion (1.14 vs 0 lb). The novel screw revealed a more consistent resorption rate over the duration of the simulation. Clinically, this may result in more stability and improved fusion rates.Levels of Evidence: Level V
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Self-similar solutions to the compressible Euler equations with nonlinear conduction are considered as particular instances of unsteady radiative deflagration – or ‘ablation’ – waves with the goal of characterizing the actual ...
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Self-similar solutions to the compressible Euler equations with nonlinear conduction are considered as particular instances of unsteady radiative deflagration – or ‘ablation’ – waves with the goal of characterizing the actual hydrodynamic properties that such flows may present. The chosen family of solutions, corresponding to the ablation of an initially quiescent perfectly cold and homogeneous semi-infinite slab of inviscid compressible gas under the action of increasing external pressures and radiation fluxes, is well suited to the description of the early ablation of a target by gas-filled cavity X-rays in experiments of high energy density physics. These solutions are presently computed by means of a highly accurate numerical method for the radiative conduction model of a fully ionized plasma under the approximation of a non-isothermal leading shock wave. The resulting set of solutions is unique for its high fidelity description of the flows down to their finest scales and its extensive exploration of external pressure and radiative flux ranges. Two different dimensionless formulations of the equations of motion are put forth, yielding two classifications of these solutions which are used for carrying out a quantitative hydrodynamic analysis of the corresponding flows. Based on the main flow characteristic lengths and on standard characteristic numbers (Mach, Péclet, stratification and Froude numbers), this analysis points out the compressibility and inhomogeneity of the present ablative waves. This compressibility is further analysed to be too high, whether in terms of flow speed or stratification, for the low Mach number approximation, often used in hydrodynamic stability analyses of ablation fronts in inertial confinement fusion (ICF), to be relevant for describing these waves, and more specifically those with fast expansions which are of interest in ICF. Temperature stratification is also shown to induce, through the nonlinear conductivity, supersonic u
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