Fig. 1. Schematic of cylindrical shell subjected to implosion loading, in which the red dashed circle represents a cylindrical potential wall and the direction of the shock wave induced by radial shrinkage of the potential wall is indicated by the black arrows.

Fig. 2. Radial stress wave propagation for a grain size of 50 nm.

Fig. 3. (a) Void evolution during implosion loading. (b) Formation of multiple spallation.

Fig. 4. Void distribution profiles of NiTi-based shell subjected to implosion loading, in which voids are represented in orange.

Fig. 5. (a) Schematic of chosen position marked by the dashed red line. (b) Time–position–density plot. (c) Time–position–radial stress plot. (d) Shock wave propagation.

Fig. 6. Shear strain evolution for a grain size of 50 nm.

Fig. 7. (a) Evolution of azimuthal stress component. (b1) and (b2) Azimuthal stress at 15 and 17 ps, respectively. (c1) and (c2) Shear strain at 15 and 17 ps, respectively.

Fig. 8. Evolutions of shear strain, dislocation, and temperature over time in NiTi alloy with grain size of 50 nm at a loading velocity of 1.0 km/s.

Fig. 9. (a) Distribution of voids and SDBs in the inner region at 21.5 ps. (b) Partial enlargement of the zone outlined by the dashed line. Voids are colored in orange. Black and yellow atoms represent initial grain boundaries and SDBs, respectively.

Fig. 10. Temperature evolution for a grain size of 50 nm.

Fig. 11. Comparison of temperature and shear strain profiles for a circular region.

Fig. 12. Temperature profiles along grain boundaries and SDBs.

Fig. 13. Dynamic damage performance as represented by voids and shear localization in NiTi-based shell at a loading velocity of 0.75 km/s.

Fig. 14. Dynamic damage performance as represented by voids and shear localization in NiTi-based shell at a loading velocity of 0.5 km/s.

Fig. 15. (a) Evolution of void number for various grain sizes, where T and S represent the total void number of the system and the void number of the secondary spall plane, respectively. (b)–(d) Time–position–density plots for grain sizes of 5, 10, and 30 nm, respectively. Atomic configurations colored according to shear strain are also provided at the right of each plot.

Fig. 16. Dependence of spall strength on grain size for NiTi-based shells.

Fig. 17. Distribution of voids and SDBs in the inner region at the time of the second peak in void number for grain sizes of (a) 5 nm, (b) 10 nm, and (c) 30 nm. Voids are colored in orange. Black and yellow atoms represent initial grain boundaries and SDBs, respectively.

Fig. 18. Local shear strain distributions before the first void nucleation (14 ps) and the second void nucleation (16.5 ps) for various grain sizes.

Fig. 19. Dynamic damage performance as represented by voids and shear localization in NiTi-based shell for initial grain sizes of 5, 10, and 30 nm.

Fig. 20. Atomic configurations for various initial grain sizes at 0 and 21 ps. B2, B19, B19′, and disordered structures are colored in blue, green, red, and gray, respectively, by PTM.

Fig. 21. Grain refinement for initial grain sizes of (a) 5 nm, (b) 10 nm, (c) 30 nm, and (d) 50 nm.

Fig. 22. Evolution of dislocation length for initial grain sizes of (a) 5 nm, (b) 10 nm, (c) 30 nm, and (d) 50 nm.

Fig. 23. Dislocation distribution in the sample with 50-nm grain size at 21.5 ps. Voids are colored in orange by the CSM method. Dislocation types of 1/2⟨111⟩, ⟨100⟩, ⟨110⟩, and other, are shown in green, purple, blue, and red, respectively.

Fig. 24. Local view of temperature state evolution in sample with 50-nm grain size.