Recently developed buckling-guided assembly methods provide a unique route to the design and manufacture of 3D mesostructures and microelectronic devices with superior performances and unusual functions. Combined with loading-path controlled strategies and/or active material designs, reconfigurable 3D mesostructures with multiple stable 3D geometries can be formed, holding promising potentials for applications in tunable antennas and multimodal actuators. The existing strategies are, however, limited by the applicable range of material types or requirements for switching between various complicated loading paths. Here, we present an electroadhesion-mediated strategy to achieve controlled adhesion of the 3D mesostructure to the substrate during the buckling-guided assembly. This strategy allows an active control of the delamination behavior in the film/substrate system, such that a variety of reconfigurable 3D mesostructures can be accessed by designing the 2D precursor pattern and electrode layout. An electromechanical model is developed to capture the delamination behavior of the film/substrate system under combined compression and voltage loadings, which agrees well with experimental measurements. Based on this model, an equivalent interface energy is proposed to quantify the contributions of the electroadhesion and van der Waals’ interactions, which also facilitates simulations of the interface delamination with cohesive models in finite element analyses (FEAs). Furthermore, a variety of reconfigurable 3D mesostructures are demonstrated experimentally, and their geometric configurations are in close accordance with the results of FEA using the concept of equivalent interface energy.

The metal matrix with mixed grain-gradient structure and the graphene with different characteristics could be designed and prepared to ameliorate the plasticity and toughness reduction of the metal matrix composites (MMCs) caused by graphene reinforcement. However, the relationship between the microstructure and the mechanical properties of composites needs to be investigated. In this paper, a self-developed structural modeling program is employed to design and establish a single-edge notch tensile finite element model of the graphene reinforced grain-gradient aluminum (Al) matrix composites, where the distribution and morphology of graphene and grains can be redistributed. Then, the grain size dependence of yield strength is introduced into the developed crystal plasticity finite element method (CPFEM) according to the classical Hall-Petch relationship, the damage mechanism of the graphene/Al composites with various designed novel microstructures is analyzed in combination with the cohesive zone model (CZM), and the microstructure of the graphene/Al composites with optimal mechanical properties is obtained. In addition, it is found that the failure mode, strength and toughness of the composites could be ameliorated by adjusting the bonding state of graphene-Al interface. This study provides a new insight into the microstructure design and fabrication of the graphene/Al composites with optimal comprehensive properties.

Human‐like and creature‐like systems are one of the most representative imaginary blueprints of future robots. To fulfill this blueprint, the development of high‐performance actuators across different length scales is indispensable. Owing to their mechanical compliance and conformability to curvy surfaces of living organisms, flexible actuators have emerged as an essential direction of next‐generation actuators. This review focuses on thin‐film‐shaped flexible actuators (TFFAs), a rising family of flexible actuators, aiming to provide an overview of the state‐of‐art status in this exciting direction. The designs, manufacturing, and mechanisms of various TFFAs are summarized, according to their key composing materials/mechanisms, including, for example, nanomaterials, liquid crystal elastomers, shape memory polymers/alloys, hydrogels, biohybrids, and other mechanisms/materials. The representative applications of TFFAs are introduced, ranging from biomedical uses, robots for environment explorations, to haptic interfaces and reconfigurable electronics. Finally, the grand challenges and open opportunities are discussed in detail.

The selective laser melting (SLM) forming of graphene/aluminum (Al) composites is difficult. Herein, the graphene/Al composites are successfully fabricated by SLM, and the printing process parameters are optimized experimentally. The anisotropic and elastoplastic characteristics of the graphene/Al composites by SLM are explored by the nanoindentation experiments first. The mesoscopic crystal plastic finite element (CPFE) model of the graphene/Al composites is developed, considering the microstructure characteristics from experiments, which presents a great agreement with the experimental data. The strengthening mechanism of graphene with various geometric sizes reinforced Al matrix composites is investigated by the novelly coupled experimental and CPFE methods.

Graphene is a significant reinforcement in metal matrix composites by virtue of its superior mechanical properties. The cracking of metal crystal and the failure of graphene-metal interface are the main reasons for the decrease of mechanical properties of graphene/metal composites, but the damage mechanism of that is not clear. In this paper, a novel two-dimensional microstructure model of graphene/polycrystalline metal composites is established by a self-developed structure modeling procedure. According to the actual structure of graphene/metal composites, the numbers, sizes, orientations, arrangements of graphene and grain can be controlled respectively. Moreover, by employing the method of combining the crystal plasticity finite element method (CPFEM) and the cohesive zone model (CZM), the damage mechanism of graphene/aluminum (Al) composites on polycrystalline Al matrix, graphene-reinforcement and graphene-Al interface under tensile load is revealed from the mesoscale for the first time, then the effects of graphene morphology and initial microcracks on the failure behavior and overall mechanical properties of graphene/Al composites are fully captured. This study provides a strong theoretical support and inspiration for the construction of graphene/Al composites with excellent properties.

Gradient nanostructured metals attract extensive attention due to their excellent mechanical properties, while they are prone to microcracks during forming and servicing process and eventually develop into a sudden fracture. Actually, experimental studies show that microcracks occurred in both the grain boundary (GB) and the intragrain, but most of the current reports only focus on the GB cracking, very limited work has studied the intragranular cracking. In this paper, the crystal plasticity finite element method (CPFEM) and cohesive zone model (CZM) are combined to study the cracking mechanism of polycrystalline aluminum (Al) with different grain gradient structures under tensile load, where molecular dynamics (MD) method is used to determine the cohesive parameters of the intragrain and GB. The results not only show the crack initiation and propagation process of polycrystalline Al with different grain-gradient structures, but also reveal the mechanism of intragrain fracture, GB fracture and crack transgranular. The grain-gradient distribution with optimal comprehensive performance is obtained. Moreover, it is also found that the initial microcracks with different positions, numbers and angles have a great influence on the cracking mechanism and effective properties of the whole material. This study provides a solid theoretical basis for improving the quality and operation life of metal parts.

To investigate the microstructure-property relations of honeybee stingers, the cross-section microstructures were analyzed by scanning electron microscope (SEM) and the mechanical properties of honeybee stingers were tested by nanoindentation experiment in vivo in this paper. The Young’s modulus and hardness in the cross section of different segments of honeybee stingers were obtained. It is found that the honeybee stinger is of a hierarchical structure in cross section, which varies from the root to the tip and leads to quite different mechanical properties of the stingers. The natural optimized microstructure and excellent mechanical properties of the stingers effectively contribute to the biological function and self-protection performance of honeybees.

Abstract Graphene considered as an ideal reinforcement for metal matrix composites (MMCs) because of its excellent optical, electrical and mechanical properties has important application prospects in materials science, micro-nano processing and so on. Meanwhile, additive manufactured MMCs becomes the hotspot of current research due to the advantages of precise and controllable structure and easy implementation of modularization. In this paper, a two-dimensional rate-dependent crystal plasticity model using the numerical model is developed to simulate the mechanical behaviors of additive manufactured graphene-reinforced aluminium matrix composites (AMCs) under tensile load in a mesoscale. The mechanical properties are described by varying the volume fractions and distribution patterns of graphene. The results verify that graphene is the main load-bearing part of AMCs. The volume fraction and distribution pattern of graphene play an important role in the crystal dislocation strengthening of AMCs. Moreover, it is proved that the additive manufactured graphene-reinforced AMCs have a potential improvement with increased graphene volume fraction and optimized geometric graphene parameters.

Aluminum (Al) alloy welded structures are widely used in industry and daily life, while welded joints are easily produced defects, including macro and microscopic defects. It is a hot topic to study the effect of microscopic defects on the properties of welded joints. In this paper, a two-dimensional rate-dependent crystal plasticity model is established by using a numerical model, and then the mechanical behaviors of welded joints with micropores under tensile load is simulated in a mesoscale. The mechanical properties are described by varying the sizes and positions of micropores. The stress-strain response, equivalent plastic strain and equivalent stress distributions of polycrystalline Al alloy welded joints with different micropores are obtained. The results verify that those micropores have certain impact on the start of slip systems and the ability of resisting the deformation of polycrystalline joints. Compared with the positions of micropores, the sizes of micropores have a greater impact on the mechanical properties of the polycrystalline joints.

Additive manufacturing technology is a novel approach for the development of the modern industry. Additive manufactured aluminium (Al) becomes the hotspot of current research in order to achieve the high precision products. However, the additive manufactured Al parts easily generate void defects due to the poor fluidity and low density of the materials, which in turn affects the mechanical properties. This paper studies the damage behavior of additive manufactured Al parts with void defects under tensile load in a mesoscale by using a two-dimensional rate-dependent crystal plasticity theory. The stress-strain curves and the plastic damages of single crystal and bicrystal with void defects are determined with different combinations of crystal orientations and loading conditions. It is found that the mechanical properties of additive manufactured aluminium severely depend on the crystal orientations and shapes of void defects. (C) 2018 Elsevier Ltd. All rights reserved.