Formation flying along libration point orbits using chattering attenuation sliding mode control

This paper studies a control law to achieve formation flying in cislunar space. Utilizing the eigenstructure of the linearized flow around a libration point of the Earth-Moon circular restricted three-body problem, the fuel efficient formation flying controller based on the chattering attenuation sliding mode controller is designed and analyzed. Numerical studies are conducted for the Earth-Moon L 2 point and a halo orbit around it. The total velocity change required to achieve formation as well as to maintain the orbit is calculated. Simulation results show that the chattering attenuation sliding mode controller has good performance and robustness in the presence of unmodeled nonlinearity along the halo orbit with moderate fuel consumption

Compressive behaviour of closed-cell aluminium foam at different strain rates

Closed-cell aluminium foams were fabricated and characterised at different strain rates. Quasi-static and high strain rate experimental compression testing was performed using a universal servo-hydraulic testing machine and powder gun. The experimental results show a large influence of strain rate hardening on mechanical properties, which contributes to significant quasi-linear enhancement of energy absorption capabilities at high strain rates. The results of experimental testing were further used for the determination of critical deformation velocities and validation of the proposed computational model. A simple computational model with homogenised crushable foam material model shows good correlation between the experimental and computational results at analysed strain rates. The computational model offers efficient (simple, fast and accurate) analysis of high strain rate deformation behaviour of a closed-cell aluminium foam at different loading velocities.publishe

Straightforward synthesis of silicon vacancy (SiV) center-containing single-digit nanometer nanodiamonds via detonation process

Silicon vacancy (SiV) color centers in diamond have attracted widespread attention owing to their stable photoluminescence (PL) with a sharp emission band in the near-infrared region (ZPL 738 nm). Especially, SiV center containing single-digit nanometer-sized nanodiamonds (single-digit SiV-NDs) are desirable for various applications such as bioimaging and biosensing because of their extremely small size, comparable to many biomaterials. Therefore, several attempts have been made to fabricate the single-digit SiV-NDs. However, there are no reports on the successful fabrication of such materials in reasonable scale of production. Here, we report the successful synthesis of single-digit SiV-NDs via straightforward detonation process, which is known to have the high productivity in fabrication of single-digit NDs. Triphenylsilanol (TPS), as a silicon source, was mixed with explosives (TPS/TNT/RDX = 1/59/40 wt%) and the detonation process was carried out. The obtained single-digit NDs exhibit PL at approximately 738 nm, indicating that single-digit SiV-NDs were successfully synthesized. Moreover, we conjectured that the physics behind this achievement may be attributed to the aromatic ring of TPS under the consideration of ND formation mechanism newly built up based on the results of time-resolved optical emission measurements for the detonation reaction

Ejecta From LPSO-Type Magnesium Alloy Targets in Hypervelocity Impact Experiments

Because long period stacking ordered (LPSO) type magnesium alloys have the low density, excellent mechanical strength and ignition resistance, LPSO-type magnesium alloys have a great potential as structural materials of satellites. Ejecta size and crater shape were examined when spherical projectiles struck targets made of LPSO-type magnesium alloy at hypervelocities of 2 km/s and 5 km/s. After impact experiments, crater surfaces and lips near craters were observed X-ray computed cosmography (CT) in detail. Ejecta collected from test chamber were measured. Results of LPSO-type magnesium alloy targets were compared with those of aluminum alloy (A6061-T6). Fracture behavior of LPSO-type magnesium alloy targets seemed to be brittle and many small ejecta from LPSO-type magnesium alloy were observed.14th Hypervelocity Impact Symposium 2017(HVIS2017), 24-28 April 2017, Canterbury, Kent, U

Lip Formation and Ejecta from LPSO-type Magnesium Alloy Plates in Hypervelocity Impact

Long period stacking ordered (LPSO) type magnesium alloys have the low density, excellent mechanical strength and ignition resistance. LPSO-type magnesium alloys have a great potential as structural materials of satellites. Lip formation and ejecta size were examined when spherical projectiles strikes thin plates made of LPSO-type magnesium alloy at hypervelocities of 5 km/s. Witness plates were placed in front of and behind each target to determine the scattering area. After impact experiments, ejecta were collected from test chamber and lips near penetration hole was examined x-ray computed cosmography (CT) in detail. Results of LPSO-type magnesium alloy plates were compared with those of aluminum alloy (A6061-T6). Images of scattering ejecta taken by a high speed video camera were also discussed.11th International Symposium on Plasticity and Impact Mechanics(IMPLAST 2016), 11 - 14 December 2016, Indian Institute of Technology Delhi, New Delhi, Indi

Computational simulations of unidirectional cellular material unipore subjected to dynamic loading

Cellular structures have an attractive combination of mechanical properties and are increasingly used in modern engineering applications. Consequently, the research of their behaviour under quasi-static and dynamic loading is valuable for engineering applications such as those related to strain energy absorption. The paper focuses on behaviour of a newly developed cellular structure UniPore with unidirectional pores under dynamic loading. The computational model of the cellular structure was based on realistic (reconstructed) irregular geometry of the manufactured specimens and analysed using the code LS-DYNA. The mechanical properties have been investigated by means of parametric computational simulations considering various material and geometrical parameters. Additionally, the influence of the gaseous pore filler influence has been considered using fully coupled computational models. Furthermore, with computational simulations also the influence of the anisotropy has been evaluated