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We investigate spalling behaviors of Ni/Al nanolaminates by molecular dynamics simulations. First, we discuss spalling damage distributions in shocked Ni/Al nanolaminates. Voids nucleate in Al layers, while no voids are located in Ni layers or along the Ni/Al interfaces. This is because the spall strength of single-crystalline Ni is higher than that of single-crystalline Al. We reveal influences of a shock-induced chemical reaction on dynamic spalling damage and fracture processes. An abnormal "decrease → increase → decrease" zigzag variation tendency of the spall strength of Ni/Al nanolaminates as the impact velocity increase is observed in our simulations, which resulted from combining effects of micro-structures, chemical reactions, and temperature softening. When the impacting intensity is relatively low, the spall strength of Ni/Al nanolaminates decreases as the impact velocity increases due to micro-structure effects. However, when the loading velocity increases to a certain magnitude (2.5 km/s), the intimate contact of liquid Al with amorphous Ni near the interface makes the chemical reaction rate increase rapidly to form a large amount of Ni/Al alloys and enhances the spall strength. [ABSTRACT FROM AUTHOR]

Mechanical responses of nanoporous Cu samples under various loading conditions are investigated by molecular dynamics simulations. Effects of loading mode, initial void size, temperature, and void distribution are analyzed. The simulations show that the collapse time under uniaxial compression is about three times that under triaxial compression, and the collapse rate increases as the temperature rises. Dislocation nucleation is found to stimulate the collapse of void. For samples with a single void, the final dislocation density under triaxial compression is lower than that under uniaxial compression, which is due to that the dislocation accumulation rate greatly slows down after the void is fully collapsed. For samples with multiple voids, the dislocation accumulation rate under triaxial compression is much faster than that under uniaxial compression, resulting in higher dislocation density under triaxial compression. Irrespective of the initial void size, the evolutions of compression stress and void volume fraction remain invariant when the initial void volume fraction is fixed; however, the dislocation density decreases as the initial void radius increases. [ABSTRACT FROM AUTHOR]

The morphology evolution mechanism of polystyrene (PS)/poly (vinyl methyl ether) (PVME) blend thin films with different PS molecular weights (Mw) was studied. It was found that the morphology evolution was closely related to the molecular weight asymmetry between PS and PVME. In the film where Mw(PS) ≈ Mw(PVME), dewetting happened at the interface between the bottom layer and substrate after SD phase separation. While in the film where Mw(PS) >> Mw(PVME), dewetting happened at the interface between the middle PS/PVME blend layer and bottom PVME layer near the substrate prior to phase separation. The different sequences of phase separation and dewetting and different interface for dewetting occurrence were studied by regarding the competitive effects of viscoelasticity contrast between polymer components and preferential wetting between PVME and the substrate. The viscoelastic nature of the PS component played a crucial role in the sequence of phase separation and dewetting. [ABSTRACT FROM AUTHOR]

20 to explain the plastic deformation mechanism; the explanation of why the twin boundary can serve as an obstacle of dislocation movement on one side and also serve as dislocation nucleation sites is presented in Figs. 22 and 23; and the energy of grain boundary, twin boundary, and stacking faults are listed in Table I to explain why grain boundary only plays one role as dislocation nucleation sites, but the twin boundary can play two roles. The nanowires in both our paper and Ref. [3] were constructed according to the previous experimental observation.[4] In Ref. [3], the plastic deformation mechanism of polycrystalline nanowires was studied. [Extracted from the article]

A well designed coplanar waveguide (CPW) based center frequency tunable bandpass filter (BPF) at 4 GHz enabled with patterned Permalloy (Py) thin film has been implemented. The operating frequency of BPF is tunable with only DC current without the use of any external magnetic field. Electromagnetic bandgap resonators structure is adopted in the BPF and thus external DC current can be applied between the input and output of the filter for tuning of Py permeability. Special configurations of resonators with multiple narrow parallel sections have been considered for larger inductance tenability; the tunability of CPW transmission lines of different widths with patterned Py thin film on the top of the signal lines is compared and measured. Py thin film patterned as bars is deposited on the top of the multiple narrow parallel sections of the designed filter. No extra area is required for the designed filter configuration. Filter is measured and results show that its center frequency could be tuned from 4 GHz to 4.02 GHz when the DC current is applied from 0mA to 400 mA. [ABSTRACT FROM AUTHOR]