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The tensile stress generated by the superposition of two reflection waves in the target plays a critical role in explaining plate-impact-induced spalling. A method of images is proposed to simulate the physical process of wave superposition and this method is applied in order to study the cavitation mechanism in single-crystal Al through molecular dynamics simulation. The critical impact-load velocity for the cavitation obtained by this method is as small as 400 m/s, which is much lower than the result (650 m/s) obtained by the conventional piston-load method. The new cavitation mechanism found is distinctively different from the conventional dislocation-entanglement-induced cavitation under high-velocity impact. The new mechanism involves two key events: firstly, a crack-like defect is formed and its relevant atomic bonds are broken under high tensile stress, resulting in a great momentum of related atoms; and secondly, previous high-momentum atoms collide with the atoms in their running way, resulting in the destruction of the original FCC structure locally and nanovoids or penny-shaped voids being formed. Additionally, the cavitation region, the number of voids, and delamination surfaces increases with the impact-load rate. [ABSTRACT FROM AUTHOR]

To theoretically analyse how void swelling and spatial heterogeneity impact the fracture behaviour of metallic materials, a coupled porous crystal plasticity framework has been developed. The proposed framework is then applied to analyse the fracture behaviour of metallic materials under different swelling conditions and types of spatial heterogeneity. It is revealed that at low porosity, the spatial heterogeneity of voids will have limited influence on the fracture behaviour of the material. However, at high porosity, owing to void swelling, a concentrated distribution of voids near grain boundaries can lead to a strong deformation localization, which can be seen as an indicator of possible quasi-brittle fracture. It is further discovered that the inner pressure of the voids tends to reduce the yield stress of the material and promote localized plastic deformation. As a result, such pressure will enhance the impact of concentrated distribution of voids, which can lead to further embrittlement of the material. The present study reveals the key role of void swelling and spatial heterogeneity in regulating the fracture behaviour of metallic materials, a step towards a better understanding over the failure mechanisms of metallic materials under extreme conditions. [ABSTRACT FROM AUTHOR]

The floating porous structure consists of an optical absorption layer, a porous layer, and an insulating layer. Water is pumped through a porous structure to the top absorption surface for evaporation. A numerical model of interfacial evaporation of floating porous structure is established. A multiphysical field coupling model for heat transfer, flow, and mass transfer within porous structures is simulated. The transient temperature response, evaporation flux, and vapor concentration distribution inside the structure are calculated. Effects of porous structure characteristics, such as size and porosity, on evaporation performance are discussed. With the increase of structure radius, the evaporation amount increases gradually, but the evaporation per unit area decreases with the radius. With the increase of the structure height, the evaporation amount and the evaporation flux decrease, but the decrease is relatively small. The porosity of the porous layer ε1 has a significant effect on the evaporation performance. The increase of ε1 is beneficial to the evaporation of water. When ε1 < 0.3, the effect of the porosity of insulation layer ε2 on the evaporation performance can be neglected. [ABSTRACT FROM AUTHOR]