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Abstract In this work, we experimentally measured the pinch‐off of a gas bubble on a biphilic surface, which consisted of an inner circular superhydrophobic region and an outer hydrophilic region. The superhydrophobic region had a radius ofR_SHvarying from 2.8 to 19.0 mm, where the largeR_SHmodeled an infinitely large superhydrophobic surface. We found that during the pinch‐off, the contact line had two different behaviors: for smallR_SH, the contact line was fixed at the boundary of superhydrophobic and hydrophilic regions, and the contact angle gradually increased; in contrast, for largeR_SH, the contact angle was fixed, and the contact line shrank toward the bubble center. Furthermore, we found that regardless of bubble size and contact line behavior, the minimum neck radius collapsed onto a single curve after proper normalizations and followed a power–law relation where the exponent was close to that for bubble pinch‐off from a nozzle. The local surface shapes near the neck were self‐similar. Our results suggest that the surface wettability has a negligible impact on the dynamics of pinch‐off, which is primarily driven by liquid inertia. Our findings improve the fundamental understanding of bubble pinch‐off on complex surfaces. 

This study investigates the high-velocity impact mechanics in correlation with piezo-resistance damage sensing characteristics of glass/carbon hybrid composites under projectile impact loading. Inter-ply and Intra-ply hybrid composites consisting of different ply orientations, stacking sequences, and liquid metal (LM) compositions (1 and 2 wt%) are considered for this study. An in-house one-stage gas gun setup is used to conduct projectile impact loading experiments. A novel circumferential four probes electrical resistivity method is employed to investigate the damage-sensing capability of hybrid composites. Two different projectile shapes (cone end projectile and stepped cone end projectile) are considered and investigated their effect on the composites’ ballistic limit, impact energy absorption, damage area, and piezo-resistance response. Projectile shape significantly influences ballistic limit and energy absorption, whereas a stepped cone end projectile demonstrates higher amount of energy absorption of about 42% and peak piezo-resistance change of around 60% compared to cone end projectile. The addition of LM improved the ballistic limit by about 20% and the amount of energy absorption by around 50% but reduced damage-sensing sensitivity due to improved electrical conductivity with its presence. Moreover, the intra-ply hybrid composites exhibited lower ballistic limits owing to weaker fiber strength, while inter-ply hybrids showed better energy absorption capabilities, resulting in higher ballistic limits. Thermal imaging technique is adopted in post-mortem analysis of the damaged area, and it revealed delamination inside the intra-ply hybrid composites. 

An experimental study is performed to investigate the quasi-static fracture toughness and damage monitoring capabilities of liquid metal (75.5% Gallium/24.5% Indium) reinforced intraply glass/carbon hybrid composites. Two different layups (G-0, where glass fibers are along the crack propagation direction; C-0, where carbon fibers are along the crack propagation direction) and two different weight percentages of liquid metal (1% and 2%) are considered in the fabrication of the composites. A novel four-probe technique is employed to determine the piezo-resistive damage response under mode-I fracture loading conditions. The effect of layups and liquid metal concentrations on fracture toughness and changes in piezo-resistance response is discussed. The C-composite without liquid metal demonstrated higher fracture toughness compared to that of the G-composite due to carbon fiber breakage. The addition of liquid metal decreases the fracture initiation toughness of both G- and C-composites. Scanning electron microscopy images show that liquid metal takes the form of large liquid metal pockets and small spherical droplets on the fracture surfaces. In both C- and G-composites, the peak resistance change of composites with 2% liquid metal is substantially lower than that of both no-liquid metal and 1% liquid metal composites.