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There are three failure modes for long rod impacting ceramic target at different velocities, that is, interface defeat, dwell transition to penetration, and direct penetration. To study the three failure modes, a numerical model of long rod impacting ceramic armor is constructed with FEM-SPH coupling technique in this study. Compared with the experimental results, the reliabilities of the algorithms, boundary conditions, and material constants in the numerical models have been comprehensively verified. The different processes and damage mechanisms of interface defeat, dwell transition to penetration and direct penetration are simulated and analyzed. By analyzing the ceramic damage during interface defeat and dwell transition to penetration, it is found that the comminuted zone achieving the surface of ceramic, marks the trigger of penetration. Simulations confirm for the first time that the nose shape of the long rod will change during the penetration of ceramics, which leads to the irregular penetration channel inside the ceramics.

In the shatter regime of a Whipple shield, a large central fragment makes a significant contribution to the damage-causing capacity of the debris cloud. Herein we present a feasible scheme for the identification and measurement of this large central fragment and propose an alternative approach to the ballistic limit equation (BLE) for the Whipple shield, deducing an alternative ballistic limit in the shatter regime based on the large central fragment’s characteristics. This alternative BLE is compared with the phenomenological Whipple BLE, the JSC Whipple BLE and the Ryan curve. Our alternative BLE, modified at the incipient fragmentation and completed fragmentation point, is shown to agree well with experimental results.

Shock wave is emitted into the plate and sphere when a sphere hypervelocity impacts onto a thin plate. The fragmentation and phase change of the material caused by the propagation and unloading of shock wave could result in the formation of debris cloud eventually. Propagation models are deduced based on one-dimensional shock wave theory and the geometry of sphere, which uses elliptic equations (corresponding to ellipsoid equations in physical space) to describe the propagation of shock wave and the rarefaction wave. The “Effective thickness” is defined as the critical plate thickness that ensures the rarefaction wave overtake the shock wave at the back of the sphere. The “Effective thickness” is directly related to the form of the debris cloud. The relation of the “Effective thickness” and the “Optimum thickness” is also discussed. The impacts of Al spheres onto Al plates are simulated within SPH to verify the propagation models and associated theories. The results show that the wave fronts predicted by the propagation models are closer to the simulation result at higher impact velocity. The curvatures of the wave fronts decrease with the increase of impact velocities. The predicted “Effective thickness” is consistent with the simulation results. The analysis about the shock wave propagation and unloading in this paper can provide a new sight and inspiration for the quantitative study of hypervelocity impact and space debris protection.

How to reduce the complexity of lattice construction is an important research topic in formal concept analysis. Based on granularity tree, the relationship between the extent and the intent of the attribute (object)-oriented concept before and after granularity transformation are investigated. Then, zoom algorithms for attribute (object)-oriented concept lattices are proposed. Specifically, zoom-in algorithm is applied to change the attribute granularity from coarse-granularity to fine-granularity, and zoom-out algorithm achieves changing the attribute granularity from fine-granularity to coarse-granularity. Zoom algorithms deal with the problems of fast construction of the attribute (object)-oriented multi-granularity concept lattices. By using zoom algorithms, the attribute (object)-oriented concept lattice based on different attribute granularity can be directly generated through the existing attribute (object)-oriented concept lattice. The proposed algorithms not only reduce the computational complexity of concept lattice construction, but also facilitate further data mining and knowledge discovery in formal contexts. Furthermore, the transformation algorithms among three kinds of concept lattice are proposed.

The protective performance of a Whipple shield to hypervelocity impact could be improved by using an impedance-graded plate. Transmission and reflection of the shock wave on the impedance interface affect the pressure state in the projectile and its fragmentation, and further change the characteristics of the debris cloud. Models of the shock waves and reflection waves in the materials were built in this paper, which describes the geometric characteristics and the pressure states of wave fronts in the impedance-gradient-plate impact. The models predicted theoretically that a smaller central fragment with a series of larger circumferential fragments would be produced by high/low impedance-graded plate. Based on the models, various front plate combinations of aluminum, magnesium and steel (Al/Mg, Al, Mg/Al, Al/steel) were analyzed experimentally and numerically. The pulse attenuation, material spalling, debris cloud characteristics and witness plate damage were analyzed. The results show that the impedance-gradient structure would eventually change the debris cloud characteristics and witness plate damage, and affect the performance of the shield. The plate of Al/Mg (high/low impedance) has a better performance than that of Al, Mg/Al (low/high impedance) and Al/steel (low/high impedance) with the same areal density. The discussion and analysis are also suitable to impedance-gradient plates made up with other materials.

Hypervelocity impact (HVI) of Al spheres upon thin Al plates arouses high amplitude shock waves. Along with the wave propagation, the sphere and plate undergo massive failure, breakup and phase changes, and end up with diffusing debris clouds. Combined with the theories of wave interaction and tensile failure, this paper reveals the failure evolution during HVI of Al spheres onto thin Al plates through Smoothed Particle Hydrodynamics (SPH) method. The relation between the failure evolution and the formation process of debris cloud is analyzed. The influence of impact conditions (impact velocity and projectile-diameter-to-plate-thickness ratio) on the failure evolution, the debris cloud formation, and the largest fragment is also discussed. The analysis of the failure evolution and debris cloud formation in this paper can provide new insight for the quantitative study of HVI and space debris protection.

The damage pattern of rear wall/witness plate could express the fragmentation features of projectile relatively, in the ground-based tests of Whipple shield and its improved structure. In this paper, the damages of rear wall for 20 Whipple shield tests are statistically analyzed, and the linkage between the damages with impact conditions (impact velocity and plate-thickness-to-sphere-diameter ratio) are obtained. The damage pattern of rear wall, or the fragmentation pattern of sphere is defined as Intact, Ruptured and Smashed. The perforation hole on rear wall is described quantitatively. The fragmentation patterns under different impact conditions are analyzed based on the propagation and evolution of shock waves. A series of SPH simulations prove and extend the analytical and experimental works, and clearly reveal the normalized relationship between fragmentation pattern and impact condition.

Micro/nanoscale liquid crystal (LC) droplets are dispersed within polymer matrix, known as polymer-dispersed liquid crystals (PDLCs). LC molecules can be reoriented under an applied voltage, which makes PDLC-based devices have wide applications in optical communications, integrated optics, and panel displays, etc. In this paper, we summarized our work on holographic PDLC (H-PDLC) devices including variable attenuators, dynamic gain equalizers and focus-switchable lenses. More importantly, a specially designed H-PDLC chopper array was demonstrated, which will be applied in the new-born frequency division multiplexed high-speed fluorescence confocal microscope system.

A new type of electrically controlled optical chopper based on Holographic Polymer Dispersed Liquid Crystal (HPDLC) grating array is demonstrated in this paper. H-PDLC grating can be erased and become transparent to the incident beam when applied the external voltage. H-PDLC grating recovers and diffracts incident light in the original way after removal the driving voltage. Thus the intensity and the frequency modulation to the incident beam can be achieved through adjusting the voltage applied on the H-PDLC cell. Compared with a conventional chopper, the H-PDLC gratings exhibit more advantage like much faster response time, the grating array is much more integrated and easier to be fabricated etc. Moreover, electro-optical properties including response time and diffraction efficiency of H-PDLC gratings are investigated. By optimizing some parameters, H-PDLC chopper cell with a microsecond response time and high diffraction efficiency is obtained. The driving voltage of H-PDLC can be reduced through controlling the droplet size in H-PDLC and the thickness of the grating. As the application example, the chopper is applied in the new born frequency division multiplexed multichannel fluorescence confocal microscopy so that it can improve the temporal and spatial resolution ability of the microscopy system.

An electrically controlled optical chopper based on switchable holographic polymer dispersed liquid crystal (H-PDLC) gratings is demonstrated through a programmable, adjustable, and periodic external driving source. Compared with traditional mechanical optical choppers, the H-PDLC chopper exhibits many advantages, including faster response time, less waveform deformation, as well as easier integration, control, and fabrication, to name a few. Its excellent performance makes the device potentially useful in frequency modulation optical systems, such as frequency division multiplexed microscopy system.