Inspired by the toughening mechanism of double-network (DN) hydrogels, a soft composite consisting of a fabric mesh and VHB tape layers was fabricated. The composite was as stiff as the fabric mesh, and as stretchable as the VHB tape. At certain compositions, the composite was significantly stronger and tougher than the base materials. The extensibility and toughness of the composite can be attributed to a damage delocalization mechanism similar to that of the DN gels. In the partially damaged regions, the fabric mesh fragmented into small islands, surrounded by the highly stretched VHB tapes. Accommodated by the finite sliding at the interface, the large deformation of the composite is highly non-affine. Just as the DN gels, the coexistence of the partially damaged and intact regions resulted in a stable necking in the composite when subjected to uniaxial tension. The propagation of the necking zone corresponded to a plateau on the stress-stretch curve. During cyclic loading, the composite also exhibited stress hysteresis with almost recoverable strain, similar to that in a DN gel. To rationalize these observations and to better understand the underlying physical mechanism, a simple 1D model has been developed for the damage evolution process in the composite. The predictions of the model have achieved good agreement with the measured properties of the composite of various compositions. Furthermore, the composite itself may also be regarded as a macroscopic model when studying the properties and toughening mechanism of the DN gels.
K-ion capacitors (KICs) have attained widely attention as next-generation energy-storage devices due to high power, long lifetime and low-cost K. Porous carbons with open structures and heteroatom doping are promising...
Printed active composites (PACs) are capable of deforming from an initial shape to a target shape via spatial arrangements of active materials within a passive matrix. Multi-material polymer printers allow precise placement of multiple materials in the design space. However, single active material is difficult to satisfy the demand in the high-precision matching of more complex target shape. Hence, a multi-material topology optimization approach for the design of PACs is proposed to achieve a target shape under a given stimulus. A multi-material interpolation function for active materials is established, and continuum mechanics modeling is used for simulating active material behaviors on a voxel basis to compute deformations for a given material distribution. The adjoint method is used for sensitivity analysis. Numerical simulations, of different target shapes with the same initial shape, verify the effectiveness of the method. The proposed method is feasible in the conceptual designs of PAC material distributions benefit with stable convergence, ease of implementation, and low computational costs.
In order to support the development of high–precision spacecraft, the current state of the Stewart vibration isolation platform in the field of aerospace micro–vibration was surveyed. First, based on analyses of the causes and characteristics of spacecraft micro–vibration, the principles, characteristics, advantages and disadvantages of four vibration isolation technologies are summarized. Second, the development process of the Stewart vibration isolation platform, from structural proposal and theoretical calculation to application in various fields, is introduced. Then, the current state of kinematics, dynamics and braking control algorithms of the Stewart platform is investigated, and related work on rigid/flexible platforms in the field of aerospace micro–vibration is introduced in detail. Finally, the idea that the Stewart platform can be fabricated by 4D printing technology is proposed. The novel Stewart platform can be combined with artificial intelligence algorithms and advanced control strategies, allowing for further development in the direction of an integrated omnidirectional, full–frequency and multi–function platform with variable stiffness.
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