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Full-Text Articles in Mechanical Engineering
Computational Vascular Fluid–Structure Interaction: Methodology And Application To Cerebral Aneurysms, Y. Bazilevs, Ming-Chen Hsu, Y. Zhang, Z. Wang, T. Kvamsdal, S. Hentschel, J. G. Isaksen
Computational Vascular Fluid–Structure Interaction: Methodology And Application To Cerebral Aneurysms, Y. Bazilevs, Ming-Chen Hsu, Y. Zhang, Z. Wang, T. Kvamsdal, S. Hentschel, J. G. Isaksen
Ming-Chen Hsu
A computational vascular fluid–structure interaction framework for the simulation of patient-specific cerebral aneurysm configurations is presented. A new approach for the computation of the blood vessel tissue prestress is also described. Simulations of four patient-specific models are carried out, and quantities of hemodynamic interest such as wall shear stress and wall tension are studied to examine the relevance of fluid–structure interaction modeling when compared to the rigid arterial wall assumption. We demonstrate that flexible wall modeling plays an important role in accurate prediction of patient-specific hemodynamics. Discussion of the clinical relevance of our methods and results is provided.
Mechanochemical Mechanism For Fast Reaction Of Metastable Intermolecular Composites Based On Dispersion Of Liquid Metal, Valery I. Levitas, Blaine W. Asay, Steven F. Son, Michelle Pantoya
Mechanochemical Mechanism For Fast Reaction Of Metastable Intermolecular Composites Based On Dispersion Of Liquid Metal, Valery I. Levitas, Blaine W. Asay, Steven F. Son, Michelle Pantoya
Valery I. Levitas
An unexpected mechanism for fast reaction of Alnanoparticles covered by a thin oxide shell during fast heating is proposed and justified theoretically and experimentally. For nanoparticles, the melting of Al occurs before the oxide fracture. The volume change due to melting induces pressures of 1–2 GPa and causes dynamic spallation of the shell. The unbalanced pressure between the Al core and the exposed surface creates an unloading wave with high tensile pressures resulting in dispersion of atomic scale liquid Al clusters. These clusters fly at high velocity and their reaction is not limited by diffusion (this is the opposite of …
Coupled Phase Transformation, Chemical Decomposition, And Deformation In Plastic-Bonded Explosive: Models, Valery I. Levitas, Bryan F. Henson, Laura B. Smilowitz, David K. Zerkle, Blaine W. Asay
Coupled Phase Transformation, Chemical Decomposition, And Deformation In Plastic-Bonded Explosive: Models, Valery I. Levitas, Bryan F. Henson, Laura B. Smilowitz, David K. Zerkle, Blaine W. Asay
Valery I. Levitas
A continuum thermomechanochemical model of the behavior of a plastic-bonded explosive (PBX) 9501 formulation consisting of the energetic crystal octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) embedded in a polymeric binder is developed. Our main focus is on the study of the β↔δphase transformations (PTs) in crystalline HMX under a complex pressure-temperature path. To reproduce the pressure-temperature path, in particular during heating of PBX inside of a rigid cylinder, the β↔δ PTs in HMX are coupled to chemical decomposition of the HMX and binder leading to gas formation, gas leaking from the cylinder, elastic, thermal, and transformational straining as well as straining due to mass …
Coupled Phase Transformation, Chemical Decomposition, And Deformation In Plastic-Bonded Explosive: Simulations, Valery I. Levitas, Bryan F. Henson, Laura B. Smilowitz, David K. Zerkle, Blaine W. Asay
Coupled Phase Transformation, Chemical Decomposition, And Deformation In Plastic-Bonded Explosive: Simulations, Valery I. Levitas, Bryan F. Henson, Laura B. Smilowitz, David K. Zerkle, Blaine W. Asay
Valery I. Levitas
Numerical simulations of the heating with constant rate of a PBX (plastic-bonded explosive) 9501 formulation consisting of the energetic crystal HMX embedded in a polymeric binder inside of a rigid cylinder is performed. The continuum thermo-mechanochemical model of the behavior of a PBX 9501 developed in the preceding paper [V. I. Levitas, B. F. Henson, L. B. Smilowitz, D. K. Zerkle, and B. W. Asay, J. Appl. Phys.102, 113502 (2007)] is applied. The model describes the β↔δphase transformations in crystalline HMX, chemical decomposition of the HMX and binder leading to gas formation, gas leaking from the cylinder, elastic, thermal, and …
Nucleation Mechanism For Reconstructive Solid-Solid Phase Transitions Via Melt Mediated Nanocluster Transformation, Valery I. Levitas, Laura B. Smilowitz, Bryan F. Henson, Blaine W. Asay
Nucleation Mechanism For Reconstructive Solid-Solid Phase Transitions Via Melt Mediated Nanocluster Transformation, Valery I. Levitas, Laura B. Smilowitz, Bryan F. Henson, Blaine W. Asay
Valery I. Levitas
A general nucleation mechanism is proposed and justified thermodynamically and kinetically. The authors apply it to the β-δphase transformation (PT) in the HMX crystal. It explains the observation of a reconstructive PT very close (0.6K) to the phase equilibrium temperature, despite the large volume change and interface energy. Nanosize clusters of β phase dissolve in a liquid and transform into δ phase clusters. The liquid completely removes the elasticenergy generated by a large volume change. Cluster to cluster PT also drastically reduces the change in interfacial energy. Suggested kinetics for the β-δ PT is in good agreement with experiments..
Solid-Solid Phase Transformation Via Internal Stress-Induced Virtual Melting: Additional Confirmations, Valery I. Levitas, Laura B. Smilowitz, Bryan F. Henson, Blaine W. Asay
Solid-Solid Phase Transformation Via Internal Stress-Induced Virtual Melting: Additional Confirmations, Valery I. Levitas, Laura B. Smilowitz, Bryan F. Henson, Blaine W. Asay
Valery I. Levitas
Recently, we predicted a mechanism of solid-solid phase transformation (PT) via virtual melting at 121K below the melting temperature. We report additional experimental and theoretical results for PTs among three polymorphs of the energetic material HMX, α, β, and δ that support this mechanism. In particular: (a) the predicted velocity of interface propagation for β→δ PT and overall kinetics of δ→β PT are in agreement with experiment; (b) the energy of internal stresses is sufficient to reduce the melting temperature from 520to400K for δ→β PT; (c) the nanocracking that appears during solidification does not change the PT thermodynamics and kinetics …
A Microscale Model For Strain-Induced Phase Transformations And Chemical Reactions Under High Pressure, Valery I. Levitas
A Microscale Model For Strain-Induced Phase Transformations And Chemical Reactions Under High Pressure, Valery I. Levitas
Valery I. Levitas
A simple strain-controlled kinetic equation for strain-induced phase transformations and chemical reactions is thermodynamically derived. This model is applied to explain various mechanochemical phenomena observed under compression and shear of materials in diamond or Bridgman anvils. In particular, it explains zero-pressure hysteresis and the appearance of new phases, especially strong phases, which were not obtained without shear. Also an explanation was obtained as to why a nonreacting matrix with a yield stress higher (lower) than that for reagents significantly accelerates (slows down) the reactions. Some methods to characterize and control strain-induced transformations and reactions are suggested.