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Gecko-inspired dry adhesion has attracted much attention for many applications such as soft grippers and wall-climbing robots, which, however, demonstrate stable adhesion on flat surfaces and small adhesion on nonflat surfaces. In practice, geckos’ capability of walking upside down on both flat and nonflat surfaces comes from the combined action of adhesive structures for passive adhesion and toe muscles for stiffness modulation. Inspired by this behavior, this study proposes a hierarchal adhesive structure for high and switchable adhesion on nonflat surfaces. The three-layer adhesive consists of a mushroom-shaped structure top layer, stiffness modulation thermoplastic polyurethane (middle layer), and an electrothermal film (bottom layer) that mimics the epidermal adhesive structures, toe muscles, and electromyographic signals, respectively. Through the tunable structural stiffness controlled by adjusting the voltage, the adhesive force can be increased by 1 or 2 orders of magnitude compared to the conventional adhesive structures and further used for attachment and detachment functions. The gecko-inspired soft gripper is successfully tested as a pick-up and drop-down system for transporting a surface with different features, which has great application potential in industrial lines and daily life.

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The lithium-rich manganese (LRM)-based cathode materials are always subjected to poor rate capacity and terrible voltage fading. Herein, sodium citrate as a chelating agent is introduced to synthesize LRM cathode materials with high structure stability by the solvothermal method to solve the abovementioned issues. Sodium citrate can effectively control the morphology of cathode materials with a small size of primary particles, which can prevent the side reaction between the active materials and electrolyte and benefit Li+ diffusion. Meanwhile, the hydroxyl groups in sodium citrate can alter the crystal growth thermodynamics and thereby induce the formation of the active {010} planes under the solvothermal condition, which facilitates the formation of a good layered structure, so that the electrochemical reaction kinetics and rate performance are facilitated dramatically. Furthermore, benefitting from the doping of Na+, the structure of the cathode material does not collapse during repeated charge–discharge cycles, so that voltage stability is enhanced greatly. Consequently, at a current density of 5 C after cycling 200 times, the reversible capacity of the designed LRM cathode is 166 mA h g–1 with a high capacity retention of 90.1%, and the median voltage remains at 3.21 V with a voltage retention of 91.4%. The median voltage could remain as high as 3.37 V with a very high voltage retention of 94.1% even at 10 C after 200 cycles. This study proposes a novel strategy that utilizes the synergistic modification of morphology design and Na+ doping to increase the lithium storage performance of LRM cathode materials.

Shape memory alloy cables have emerged as an alternative to conventional steel cable restrainers for preventing the bridge spans from unseating during an extreme earthquake. Feasibility of high-cost NiTi shape memory alloy restrainers in retrofitting the bridges has been numerically investigated, and promising results have been published; however, considering the economic impacts, the effect of different types of shape memory alloy such as Cu-based and Fe-based shape memory alloy restrainers has not been discussed yet. The objective of this study is to address this problem in detail in order to propose the most cost-effective shape memory alloy restrainer suitable for bridge engineering applications. Seismic fragility and life-cycle loss (both direct and indirect) assessments are analytically performed on an isolated simply-supported highway bridge retrofitted by four types of shape memory alloy restrainers (i.e. NiTi, FeNiCoAlTaB, CuAlMn, and FeMnAlNi). Results showed that for all retrofitted bridges performed in the range of design displacement, the effect of type of shape memory alloy is significant on the damage probability and long-term seismic loss of the bridges. All the bridges retrofitted with shape memory alloy restrainers have a very low probability of collapse (less than 7%). It is also found that the bridge retrofitted with Fe-based shape memory alloy restrainers (SMA-II and SMA-IV) performed better as compared to the other cases. Compared to the bridge without restrainers and with NiTi shape memory alloy restrainers, Fe-based shape memory alloy restrainers can reduce the long-term loss by about 87% and 11%, respectively, at the design earthquake event specified in CHBDC-2014. The probabilistic risk analysis of highway bridges retrofitted with shape memory alloy restrainers can aid in paving the way toward widespread application of such smart materials in structural applications.

The objective of this study is to analytically determine the effectiveness of a novel bridge system with superelastic (SE) shape memory alloy (SMA) reinforced concrete piers. The bridge is also equipped with SE SMA cable restrainers to prevent the bridge spans from a large displacement that can potentially cause span unseating. In the concrete bridge piers, the conventional steel reinforcements in the plastic hinge regions are replaced with SE SMA rebar to avoid large plastic deformation and improve its self-centering capacity. A typical three-span continuous highway bridge is modeled with SMA-reinforced piers and SMA restrainers. Numerical simulations of the bridge are conducted under destructive near-fault ground motions. The seismic responses and fragility curves of the novel bridge (Bridge IV) are assessed and compared with the reference bridge (Bridge I), the bridge with only SMA-reinforced piers (Bridge II), and the bridge with only SMA restrainers (Bridge III). The results revealed that the SMA-reinforced pier can successfully reduce the residual deformation and damage probability of the bridge; however, the bridge with only SMAreinforced piers is less efficient in preventing a large displacement. The use of SMA restrainers can efficiently limit the displacement of the bridge spans but increase the damage probability of the bridge piers. The proposed novel bridge having SMA-reinforced piers equipped with SMA restrainers (Bridge IV) is more efficient than the bridge with only SMA-reinforced piers (Bridge II)) or the bridge with only SMA restrainers (Bridge III).

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