Bioinspired Strategies for Excellent Mechanical Properties of Composites

Developing high-performance composite materials is of great significance as a strong support for high-end manufacturing.However,the design and optimization of composite materials lack a theoretical basis and guidance scheme.Compared with traditional composite materials,natural materials are composed of relatively limited components but exhibit better mechanical properties through ingenious and reasonable synthetic strategies.Based on this,learning from nature is considered to be an effective way to break through the bottleneck of composite design and preparation.In this review,the recent progress of natural composites with excellent properties is presented.Multiple factors,including structures,components and interfaces,are first summarized to reveal the strategies of natural materials to achieve outstanding mechanical properties.In addition,the manufacturing technologies and engineering applications of bioinspired composite materials are introduced.Finally,some scientific challenges and outlooks are also proposed to promote next-generation bioinspired composite materials.

Design of a Flexible Bionic Ankle Prosthesis Based on Subject-specific Modeling of the Human Musculoskeletal System

A variety of prosthetic ankles have been successfully developed to reproduce the locomotor ability for lower limb amputees in daily lives. However, they have not been shown to sufficiently improve the natural gait mechanics commonly observed in comparison to the able-bodied, perhaps due to over-simplified designs of functional musculoskeletal structures in prostheses. In this study, a flexible bionic ankle prosthesis with joints covered by soft material inclusions is developed on the basis of the human musculoskeletal system. First, the healthy side ankle–foot bones of a below-knee amputee were reconstructed by CT imaging. Three types of polyurethane rubber material configurations were then designed to mimic the soft tissues around the human ankle, providing stability and flexibility. Finite element simulations were conducted to determine the proper design of the rubber materials, evaluate the ankle stiffness under different external conditions, and calculate the rotation axes of the ankle during walking. The results showed that the bionic ankle had variable stiffness properties and could adapt to various road surfaces. It also had rotation axes similar to that of the human ankle, thus restoring the function of the talocrural and subtalar joints. The inclination and deviation angles of the talocrural axis, 86.2° and 75.1°, respectively, as well as the angles of the subtalar axis, 40.1° and 29.9°, were consistent with the literature. Finally, dynamic characteristics were investigated by gait measurements on the same subject, and the flexible bionic ankle prosthesis demonstrated natural gait mechanics during walking in terms of ankle angles and moments.

Graphene Oxide-Induced Substantial Strengthening of High-Entropy Alloy Revealed by Micropillar Compression and Molecular Dynamics Simulation

Plastic deformation mechanisms at micro/nanoscale of graphene oxide-reinforced high-entropy alloy composites(HEA/GO)remain unclear.In this study,small-scale mechanical behaviors were evaluated for HEA/GO composites with 0.0 wt.%,0.3 wt.%,0.6 wt.%,and 1.0wt.%GO,consisting of compression testing on micropillar and molecular dynamics(MD)simulations on nanopillars.The experimental results uncovered that the composites exhibited a higher yield strength and flow stress compared with pure HEA micropillar,resulting from the GO reinforcement and grain refinement strengthening.This was also confirmed by the MD simulations of pure HEA and HEA/GO composite nanopillars.The immobile<100>interstitial dislocations also participated in the plastic deformation of composites,in contrast to pure HEA counterpart where only mobile 1/2<111>perfect dislocations dominated deformation,leading to a higher yield strength for composite.Meanwhile,the MD simulations also revealed that the flow stress of composite nanopillar was significantly improved due to GO sheet effectively impeded dislocation movement.Furthermore,the mechanical properties of HEA/1.0 wt.%GO composite showed a slight reduction compared with HEA/0.6 wt.%GO composite.This correlated with the compositional segregation of Cr carbide and aggregation of GO sheets,indicative of lower work hardening rate in stress-strain curves of micropilar compression.

Micro/nano-mechanical behaviors of individual FCC,BCC and FCC/BCC interphase in a high-entropy alloy

Here,a systematic investigation was made on the interphase strengthening effects induced superior me-chanical performances of multiphase high-entropy alloys(HEAs)at micro/nano-scale,compared with sin-gle phase HEAs.A pillar compression test under a scanning electron microscope(SEM)was performed on the individual face centered cubic(FCC),body centered cubic(BCC),and mixed-phases with different di-ameters in a Fe_(24)Co_(25)Ni_(24)Cr_(23)Al_(4)HEA using focused ion beam(FIB)milling and a nanoindenter equipped with a flat punch.The stress-strain response of pillar underneath the indenter was selected to explore the diameter/phase-dependent size effect,the periodically fluctuation of local stress,and strain hardening.It was revealed that the pillars at the interphase exhibited significantly higher strength,compared with the FCC and BCC pillars.An experiment also verified the coincident mechanical size effects independent with the type of phases.The stress responses in the mixed-phase pillars manifested as a distinct transition from the dramatic drop to the minor fluctuation during the post-yield stages with the increasing strain,indicating the propagation of Al-Ni enriched solid solution phase(BCC1)under compression.Except the BCC1 phase,numerous dislocations were observed in the post-deformed pillars,particularly serving as the major source to enhance the strain hardening of BCC pillars.

Construction and application of bionic antifouling coatings inspired by soft coral

Marine biofouling will bring a series of environmental and social problems,which restrict the development and utilisation of marine resources.Therefore,how to prevent biofouling has become a global issue.With the exploration of antifouling methods,bionic antifouling technology with environmentally friendly,broad‐spectrum,and long‐term advantages has gradually attracted people's attention.Inspired by the antifouling strategy of soft coral(Sarcophyton trocheliophorum),the silicone rubber(RTV‐2)with similar elasticity to coral skin was selected as the substrate.The composite structure of the upper transparent layer and the lower porous layer was prepared by simulating the structure of soft coral as the structural factors of the bionic antifouling coatings.Meanwhile,several organic antifouling components with high content contained in soft coral were added to the transparent layer and porous layer,respectively,as the component factors of biomimetic coatings.The bionic antifouling coatings,which are highly consistent with the coral structure,obtained the best antifouling performance under static and dynamic conditions.The above results provide new ideas for the synthesis of environmentally friendly bionic antifouling coatings.