The interaction between laser irradiation and energetic materials is critically influenced by microstructural void defects that determine local energy deposition and initiation sensitivity. In this work, a three-dimensional finite-difference time-domain (3D-FDTD) method was employed to investigate the modulation effects of void defects on optical field distributions and hot spot formation in RDX energetic crystals. The influences of void geometry, spatial position, and void number on the modulation of the incident laser beam were systematically analyzed. It reveals that void defects exhibit strong focusing and scattering behavior, leading to localized high-intensity regions both inside RDX bulk crystals and in void defects. For a single void defect, increasing either the width or depth can significantly enhance the peak electric field and thus the laser sensitivity of RDX crystals. When two voids are present, the number of high-intensity spots first increases and then decreases with increasing separation distance, and the strongest modulation effects are obtained at separations of 0.75λ–3λ. Furthermore, as the number of void defects increases, the modulation effect intensifies, promoting the formation of more hot spots. These findings provide quantitative insight into how void structures govern laser–matter interactions in energetic crystals, offering guidance for understanding and controlling laser initiation behavior.

Dual-phase layered microstructures containing alternating regions of soft and hard phases can produce alloys with a unique combination of strength and ductility. In this study, the molecular dynamics (MD) method was utilized to simulate nanoindentation of a Ni/NiTi/Ni nanostructured film (NSF). This film features a unique alternating FCC/B2/FCC microstructure, in which the B2-phase NiTi acts as a superelastic shape memory alloy (SMA). The results indicate that Ni/NiTi/Ni NSF significantly reduces its hardness due to the superelasticity of the B2 phase. The presence of the NiTi interlayer effectively blocks the propagation path of dislocations and stacking faults by transforming the local dislocations transferred from the upper layer into a large-scale coordinated phase transition, significantly reducing local deformation misalignment. As the thickness of the surface film λ increases, the dislocation slip plane propagating horizontally appears in the upper pure Ni layer. The thicker the surface film, the more horizontal slip planes are formed. This study provides new insights into the contact mechanical behavior of nanostructured films based on NiTi shape memory alloys from the perspective of atomic scale.

This study presents a systematic investigation into the nanoindentation behavior of Nb-NiTi-Nb (BCC/B2/BCC) nanomultilayers at 400 K through molecular dynamics (MD) simulations. The findings reveal that a small-radius indenter (R = 50 Å) induces localized stress concentration and pronounced dislocation fluctuations, leading to a highly confined plastic zone. In contrast, a larger-radius indenter (R = 60 Å) facilitates more extensive plastic deformation and promotes coordinated deformation behavior. This observed size effect underscores the substantial influence of indenter geometry on the material's deformation mode. Further analysis indicates that the intrinsic origin of this size effect can be attributed to a synergistic regulation mechanism at the BCC-Nb/B2-NiTi interface. Owing to its unique confinement effect, the interface significantly delays the initiation depth of dislocation nucleation from 5.6 Å to 9.9 Å, thereby effectively localizing plastic deformation within the upper Nb layer and preserving the structural integrity of the intermediate NiTi functional layer. Dislocation analysis demonstrates that at 400 K, the interfacial constraint suppresses martensitic transformation, thereby rendering dislocation activity the primary deformation mechanism. This conclusion is further corroborated by the evolution of dislocation density and slip system activation analysis. The present study elucidates the synergistic interplay of "interfacial constraint-dislocation activity-transformation suppression" at the atomic scale, and the developed analytical methodology provides critical theoretical underpinnings for the interface design and performance optimization of high-performance composite materials.

This study employs non-equilibrium molecular dynamics simulations to systematically investigate the dynamic response and spallation behavior of superelastic NiTi-Ni multilayer films with B2/FCC heterogeneous structures under shock loading. By analyzing stress wave propagation, dislocation activity, shear band evolution, and damage nucleation processes at different impact velocities (0.6-3.3 km/s), we reveal the coupled regulatory mechanisms of heterogeneous interfaces and shock strength on material dynamic failure. The simulations demonstrate that NiTi-Ni interfaces induce stress wave reflections due to wave impedance mismatch: shock front stress increases when the wave propagates from NiTi to Ni, while stress decreases during reverse propagation. This phenomenon correlates with the higher Hugoniot pressure of Ni and the martensitic transformation in the NiTi layer. Plastic deformation in the Ni layer is primarily mediated by dislocations, with dislocation density peaking at 2.1 km/s, whereas the NiTi layer predominantly absorbs energy through phase transformations. At lower velocities, shear bands exhibit ordered structures, while higher impact intensities lead to their transition into disordered strain-localization zones. Void nucleation occurs primarily in the Ni layer and near interfaces, and the void volume fraction increases with impact velocity. Under high-velocity impact, the material undergoes a transition from localized to complete melting, exacerbating spallation failure. This research clarifies the critical role of B2/FCC heterogeneous interfaces in regulating wave propagation, phase transformation, and dislocation interactions, providing theoretical foundations for designing novel shock-resistant layered materials.