No abstract

We have performed systematic molecular dynamics simulations to study the deformation behavior of a single crystal structure and a core-shell Cu@Ni nanoporous (NP) structure under shock loading for a wide range of shock intensities. Our results suggest that the core-shell structure exhibits less volume compression than the single crystal NP structure by virtue of its enhanced mechanical strength and associated interfacial strain-hardening under shock loading. The core-shell NP structure also demonstrates an increased shock-energy absorption efficiency of around 10.5% larger than the single crystal NP structure because of its additional Cu/Ni interface. The mechanisms of shock-induced deformation are observed to vary greatly with shock intensity. Pores are observed to collapse partially in both NP structures at very low shock intensity, up≤0.15 km/s. Complete collapsing of the pores through plastic deformation followed by direct crushing and formation of internal jetting and hot-spot have been observed at higher shock intensities. The evolution of microstructure and the underlying mechanisms operating at different shock intensity regimes have been investigated in this article. At a shock pressure of ∼6.05 GPa, i.e., up=0.75 km/s, the shock-induced deformed microstructure of both NP structures recovered through dynamic recrystallization. The postshock dynamic recrystallization has been observed to be mediated through rapid relaxation of shear stress followed by atomic rearrangements.

We present a framework based on non-equilibrium molecular dynamics (NEMD) to reproduce the phase transformation event of Aluminum under ramp compression loading. The simulated stress-density response, virtual x-ray diffraction patterns, and structure analysis are compared against the previously observed experimental laser-driven ramp compression in-situ x-ray diffraction data. The NEMD simulations show the solid–solid phase transitions are consistent to experimental observations with a close-packed face-centered cubic (fcc) (111), hexagonal close-packed (hcp) structure (002), and body-centered cubic bcc (110) planes remaining parallel. The atomic-level analysis of NEMD simulations identifiy the exact phase transformation pathway happening via Bain transformation while the previous in situ x-ray diffraction data did not provide sufficient information for deducing the exact phase transformation path.

We use molecular dynamics simulations to demonstrate a homogeneous two-step structural phase transformation in the molybdenum (Mo) phase of a Mo/ Cu bicontinuous intertwined composite during tensile loading. The Mo atoms first transform from a ⟨001⟩-oriented body-centered cubic structure to a ⟨001⟩-oriented facecentered cubic structure via the Bain transformation. Then they further transform to a ⟨110⟩-oriented body-centered cubic via the Pitsch transformation. This homogeneous transformation results in a novel stress−strain behavior with extended plastic deformation of the whole material. Stress state analysis indicates that the driving force for this structural phase transformation is the large tensile stress induced by interfaces in the bicontinuous intertwined structure. Our results suggest new strategies for improving the ductility of ultrastrong nanocomposite metals.

Structurally, nanoporous (NP) materials can be regarded as a network of interconnected nanowires. In this study, molecular dynamics simulations are employed to investigate the deformation behavior of individual ligaments and isolated three-fold nodes, which are the two main structural components in NP materials. The shear strain tensor analysis is used to quantitatively differentiate deformation mechanisms accommodating strain among structures and capture onset of necking during stretching. Ligaments and nodes behave differently in both elastic regime and plastic regime. Our results suggest that node structure is brittle with low stiffness and yield strength, similar to NP structure, while ligament structure is ductile and exhibits high stiffness and yield strength. In isolated three-fold nodes and NP network structure, we observed similar deformation behavior exists; formation of pyramidal shape defects consisted of twinning partials and Shockley partials on different {111} planes at node region. The similarity of mechanical properties and deformation behavior between node structure and NP structure indicates that the role of node components is substantially significant in controlling structure–property relationships of NP materials. Enhancing node components is proposed as a potential method for improving mechanical properties of NP materials.