Mode II fracture mechanisms of PBT-modified brittle epoxies

Mode II fracture behavior of poly(butylene terephthalate) (PBT)-modified epoxy systems are studied. Two different types of testing for mode II fracture are conducted. One was to investigate the fracture behavior of bulk epoxy systems, in comparison with mode I fracture, using single-edge notched specimens under skew symmetric four-point loading. The other was to investigate the fracture behavior of epoxy layers sandwiched between aluminium adherends using compact shear specimens. The mode II fracture toughness obtained from the former for modified systems has been found to increase significantly over the control, although the increase of mode I fracture toughness for modified systems over the control is moderate. This finding is discussed in relation with cavitation and equivalent mode I stress intensity factor and also in comparison with rubber-modified epoxy systems in the literature to account for the increase. In addition, the difference in fracture morphology between mode I and II is discussed. Mode II fracture toughness obtained from the latter for modified systems has also been found to increase significantly over the control. Morphology of fracture surfaces relating to this finding is discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 405–415, 1998     

Ultra-High Capacity and Cyclability of β-phase Ca0.14V2O5 as a Promising Cathode in Calcium-Ion Batteries

Crystalline water-free β-phase Ca_0.14V₂O₅ is reported for the first time as a viable cathode material for calcium-ion batteries (CIBs). In contrast to layered α-V₂O₅ and δ-Ca_xV₂O₅·nH₂O, which have limited capacity, the β-phase delivers a reversible capacity of ≈247 mAh g⁻¹, which corresponds to the insertion/extraction of Ca²⁺ between Ca_0.14V₂O₅ and Ca_1.0V₂O₅. The process of Ca²⁺ insertion process and the accompanying structural relaxation are theoretically and experimentally verified. The initial insertion of Ca²⁺ into Ca_0.14V₂O₅ causes a slight shift of oxygen atoms surrounding hepta-coordination sites, creating penta-coordinated sites that are then partially filled up to Ca_0.33V₂O₅. Further insertion occurs through the stepwise occupation of up to 50% of neighboring hexa- and tetra-coordination sites to form Ca_0.67V₂O₅ and Ca_1.0V₂O₅, respectively. The rearrangement of oxygen atoms in Ca_0.14V₂O₅ also minimizes dimensional changes, leading to high cyclic stability during repeated charge/discharge cycles. The remarkable electrochemical performance of full cells containing a Ca_0.14V₂O₅ cathode and a K metal anode in Ca²⁺/K⁺ hybrid electrolytes, is also demonstrated, thanks to the inertness of K⁺ insertion into Ca_0.14V₂O₅ and the absence of calcium plating/stripping. The cyclic stability and high capacity of Ca_0.14V₂O₅ is not compromised in hybrid electrolytes, making it a viable CIB cathode.     

Field demonstration of advanced autonomous navigation technique for a fully unmanned surface vehicle in complex coastal traffic areas

This study introduces an advanced autonomous navigation algorithm for unmanned surface vehicle (USV) operations in complex coastal traffic areas. To facilitate the undertaking of tests for innovative technologies, the Korean government has designated regulation-free special zones, thereby enabling field tests for USV demonstrations without an onboard safety person on real manned-ship navigation routes. To enable real-world USV operation without onboard safety person, an existing autonomous navigation algorithm is extended to achieve sufficiently reliable and robust USV operation. Accordingly, berthing and unberthing algorithms are newly developed for unmanned operation, and enhanced situational awareness algorithms are applied to detect all types of obstacles, including small-sized floating objects spread over a wide range, such as a fish farm. In particular, the Korean intelligent maritime transportation service, called e-Navigation, is incorporated into the autonomous navigation algorithms to overcome the limitations of vehicle autonomy based on onboard sensors. To demonstrate the capability of fully unmanned operation in real marine traffic scenarios, long-distance navigation (54 km on a single voyage) was conducted by running several missions, including navigation in complex fish farm areas, maritime surveys, collision avoidance, navigation on real traffic routes, and emergency response. The extended navigation algorithms and results of the field tests are presented and discussed in this paper.     

Surface Oxygen Vacancy Inducing Li-Ion-Conducting Percolation Network in Composite Solid Electrolytes for All-Solid-State Lithium-Metal Batteries

Composite solid electrolytes (CSEs) are newly emerging components for all-solid-state Li-metal batteries owing to their excellent processability and compatibility with the electrodes. Moreover, the ionic conductivity of the CSEs is one order of magnitude higher than the solid polymer electrolytes (SPEs) by incorporation of inorganic fillers into SPEs. However, their advancement has come to a standstill owing to unclear Li-ion conduction mechanism and pathway. Herein, the dominating effect of the oxygen vacancy (O_vac) in the inorganic filler on the ionic conductivity of CSEs is demonstrated via Li-ion-conducting percolation network model. Based on density functional theory, indium tin oxide nanoparticles (ITO NPs) are selected as inorganic filler to determine the effect of O_vac on the ionic conductivity of the CSEs. Owing to the fast Li-ion conduction through the O_vac inducing percolation network on ITO NP–polymer interface, LiFePO₄/CSE/Li cells using CSEs exhibit a remarkable capacity in long-term cycling (154 mAh g⁻¹ at 0.5C after 700 cycles). Moreover, by modifying the O_vac concentration of ITO NPs via UV-ozone oxygen-vacancy modification, the ionic conductivity dependence of the CSEs on the surface O_vac from the inorganic filler is directly verified.