(a) Schematic of laser-induced projectile impact experimental tests. (b) Cross-linked CNT film in simulation with r ¼ 20 in the top view and the enlarged view represents crosslinks between two nanotubes (CNTs are shown in green and crosslinks are shown in red). (c) Morphology of enlarged CNT film in simulation as marked in (b) by blue rectangle to illustrate the uniform distribution of crosslinks. (d) Micro-projectile impact model in simulation (CNT film is shown in green, and the projectile is illustrated in orange). (e) Total energy for the simulation system during the equilibrium NVT ensemble for r ¼ 20. (A colour version of this figure can be viewed online.)

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... explore the impact performance of CNT films with and without crosslinks, a laser-induced micro-particle impact test (LIPIT) platform, which was originally developed by Lee et al. [27] and further improved by Hassani-Gangaraj et al. [28,29], was built as illustrated in Fig. 1(a). In LIPIT experiments, high-pressure plasma under the confinement of a 4-mm-thick BK7 glass is generated through the interaction between the focused pulse-laser (1064 nm wavelength, 10 ns FWHM, F2 mm) and a 40-mm-thick aluminum film, resulting in the rapid swelling of a 100-mm-thick polydimethylsiloxane (PDMS) film attached closely to ...

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... CGMD simulations are performed by adopting the large-scale atomic/molecular massively parallel simulator (LAMMPS) [36] and the results are visualized in the Open Visualization Tool (Ovito) software [37]. Fig. 1(b) shows the CNT film with crosslinks, in which the CNT chains and crosslinks are pointed and color-coded by green and red, respectively. The crosslinks' density, r, is defined as the average number of crosslinks per coarse-grained CNT chain [35]. The crosslinks are distributed uniformly in the CNT film as shown in Fig. 1(c) for the ...

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... (Ovito) software [37]. Fig. 1(b) shows the CNT film with crosslinks, in which the CNT chains and crosslinks are pointed and color-coded by green and red, respectively. The crosslinks' density, r, is defined as the average number of crosslinks per coarse-grained CNT chain [35]. The crosslinks are distributed uniformly in the CNT film as shown in Fig. 1(c) for the system with r ¼ 20. The maximum crosslink density, which is caused by the limitation of adjacent beads distance, is determined as r max ¼ 35 in the simulation configuration, the value of which is consistent with the ceiling we observed experimentally. The density of the CNT film at the equilibrium state is 0.28 g/cm 3 , ...

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... the CNT films with crosslinks are prepared, a spherical diamond projectile with a diameter of 20 nm is constructed and added to the system as shown in Fig. 1(d). The initial distance between projectile and CNT film is about 10 nm to avoid the interaction during the relaxation stage. Here, the projectile is considered as a rigid body since the projectile is much stronger than CNT film and no broken of the projectile is observed in experiments. The CNT film is periodic-boundary conditions along ...

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... the CNT film and the projectile is considered as 12-6 Lennard-Jones potential described by Eq. (1d), and the parameters are the same as the inter-tube interactions. The whole system is equilibrated at 300 K for 10 ns using the NVT ensemble with a Langevin thermostat. The total energy fluctuation is less than 0.1% after equilibrium as given in Fig. 1(e). After that, the canonical ensemble (i.e. NVE) is adopted for the impact tests, and a time step of 1 fs is applied to ensure the stability of the simulation. A series of impact tests from non-perforation to perforation are conducted with impact velocities, v i , ranging from 8 to 12 ...

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... 9(b) and (c)), the impact energy is not adequate to perforate the CNT film and the projectile bounces back after impact. The morphologies of the CNT films with thicknesses of 10 and 15 nm do not show noticeable change after the impact, implying the nominal elastic deformation of the CNT films. The change of the potential energy, DE, as shown in Fig. 10(a), can be decomposed into the changes of bending energy, DE b , stretching energy, DE s , and vdW energy, DE v . From Fig. 10(a) and (b), it clearly show that the change of vdW interface energy is negligible, and stretching and bending of the CNT chains are the dominant energy dissipation methods for all the thicknesses. Fig. 10(c) shows ...

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... morphologies of the CNT films with thicknesses of 10 and 15 nm do not show noticeable change after the impact, implying the nominal elastic deformation of the CNT films. The change of the potential energy, DE, as shown in Fig. 10(a), can be decomposed into the changes of bending energy, DE b , stretching energy, DE s , and vdW energy, DE v . From Fig. 10(a) and (b), it clearly show that the change of vdW interface energy is negligible, and stretching and bending of the CNT chains are the dominant energy dissipation methods for all the thicknesses. Fig. 10(c) shows the ratio of the number of broken bonds to the total bond number in the system, n, to characterize the damage degree of the ...

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... DE, as shown in Fig. 10(a), can be decomposed into the changes of bending energy, DE b , stretching energy, DE s , and vdW energy, DE v . From Fig. 10(a) and (b), it clearly show that the change of vdW interface energy is negligible, and stretching and bending of the CNT chains are the dominant energy dissipation methods for all the thicknesses. Fig. 10(c) shows the ratio of the number of broken bonds to the total bond number in the system, n, to characterize the damage degree of the CNT film. The n decreases quickly from 5.80‰ to 0.23‰ with increasing the thickness from 5 nm to 10 nm. Then it keeps almost at the same level with continually increasing the thickness to 15 nm. As shown in ...

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... Fig. 10(c) shows the ratio of the number of broken bonds to the total bond number in the system, n, to characterize the damage degree of the CNT film. The n decreases quickly from 5.80‰ to 0.23‰ with increasing the thickness from 5 nm to 10 nm. Then it keeps almost at the same level with continually increasing the thickness to 15 nm. As shown in Fig. 10(d), E * p increases with respect to thickness, t, of the CNT film, implying that more impact energy can be dissipated by the thick films. Three movies are provided in Supplementary materials to show the dynamical responses for three thicknesses with r ¼ 10 at v i ¼ 12 km/s. Details are omitted here for ...

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... structures. The volume fraction of PVA is ~6.8%, which is negligible compared to that of the CNT chains and can be considered as an enhancement of CNT film to serves as crosslinks. The basic morphologies and quality of the adopted CNT films are characterized by SEM, Transmission Electron Microscopy (TEM), and Raman spectroscopy, as shown in Fig. 11. Fig. 11(a) and (b) show the prepared CNT films without and with PVA as crosslinks, respectively, in which some obvious PVA enhanced regions have been marked by white circles in Fig. 11(b). After PVA was added, the binder effect will generate between CNT chains to enhance the weak vdW interfaces. The CNT in the experiments is a mixture of SWCNT ...

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... The basic morphologies and quality of the adopted CNT films are characterized by SEM, Transmission Electron Microscopy (TEM), and Raman spectroscopy, as shown in Fig. 11. Fig. 11(a) and (b) show the prepared CNT films without and with PVA as crosslinks, respectively, in which some obvious PVA enhanced regions have been marked by white circles in Fig. 11(b). After PVA was added, the binder effect will generate between CNT chains to enhance the weak vdW interfaces. The CNT in the experiments is a mixture of SWCNT and multi-wall CNT (MWCNT), and the diameter of the CNT ranges from 0.7 to 15 nm as shown in Fig. 11(c). Raman spectroscopy is employed to investigate the crystallization degree ...

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... in which some obvious PVA enhanced regions have been marked by white circles in Fig. 11(b). After PVA was added, the binder effect will generate between CNT chains to enhance the weak vdW interfaces. The CNT in the experiments is a mixture of SWCNT and multi-wall CNT (MWCNT), and the diameter of the CNT ranges from 0.7 to 15 nm as shown in Fig. 11(c). Raman spectroscopy is employed to investigate the crystallization degree of the CNT film as shown in Fig. 11(d). The intensity ratio I D /I G is used to characterize the structural integrity of the CNT film. For the CNT film without PVA, its crystallinity is relatively high. However, the nominal crystallinity of the CNT film decreases ...

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... added, the binder effect will generate between CNT chains to enhance the weak vdW interfaces. The CNT in the experiments is a mixture of SWCNT and multi-wall CNT (MWCNT), and the diameter of the CNT ranges from 0.7 to 15 nm as shown in Fig. 11(c). Raman spectroscopy is employed to investigate the crystallization degree of the CNT film as shown in Fig. 11(d). The intensity ratio I D /I G is used to characterize the structural integrity of the CNT film. For the CNT film without PVA, its crystallinity is relatively high. However, the nominal crystallinity of the CNT film decreases due to the appearance of the ...