Stimuli-responsive polymers with complicated but controllable shape-morphing behaviors are critically desirable in several engineering fields. Among the various shape-morphing materials, cross-linked polymers with exchangeable bonds in dynamic network topology can undergo on-demand geometric change via solid-state plasticity while maintaining the advantageous properties of cross-linked polymers. However, these dynamic polymers are susceptible to creep deformation that results in their dimensional instability, a highly undesirable drawback that limits their service longevity and applications. Inspired by the natural ice strategy, which realizes creep reduction using crystal structure transformation, we evaluate a dynamic cross-linked polymer with tunable creep behavior through topological alternation. This alternation mechanism uses the thermally triggered disulfide–ene reaction to convert the network topology – from dynamic to static – in a polymerized bulk material. Thus, such a dynamic polymer can exhibit topological rearrangement for thermal plasticity at 130°C to resemble typical dynamic cross-linked polymers. Following the topological alternation at 180°C, the formation of a static topology reduces creep deformation by more than 85% in the same polymer. Owing to temperature-dependent selectivity, our cross-linked polymer exhibits a shape-morphing ability while enhancing its creep resistance for dimensional stability and service longevity after sequentially topological alternation. Our design enriches the design of dynamic covalent polymers, which potentially expands their utility in fabricating geometrically sophisticated multifunctional devices.
Mechanical metamaterials are meticulously designed structures with exceptional mechanical properties determined by their microstructures and constituent materials. Tailoring their material and geometric distribution unlocks the potential to achieve unprecedented bulk properties and functions. However, current mechanical metamaterial design considerably relies on experienced designers' inspiration through trial and error, while investigating their mechanical properties and responses entails time‐consuming mechanical testing or computationally expensive simulations. Nevertheless, recent advancements in deep learning have revolutionized the design process of mechanical metamaterials, enabling property prediction and geometry generation without prior knowledge. Furthermore, deep generative models can transform conventional forward design into inverse design. Many recent studies on the implementation of deep learning in mechanical metamaterials are highly specialized, and their pros and cons may not be immediately evident. This critical review provides a comprehensive overview of the capabilities of deep learning in property prediction, geometry generation, and inverse design of mechanical metamaterials. Additionally, this review highlights the potential of leveraging deep learning to create universally applicable datasets, intelligently designed metamaterials, and material intelligence. This article is expected to be valuable not only to researchers working on mechanical metamaterials but also those in the field of materials informatics.This article is protected by copyright. All rights reserved
Instrumented indentation tests are an efficient approach for the characterization of stress–strain curves instead of tensile or compression tests and have recently been applied for the evaluation of mechanical properties at elevated temperatures. In high-temperature tests, the rate dependence of the applied load appears to be dominant. In this study, the strain-rate-dependent plasticity in instrumented indentation tests at high temperatures was characterized through the assimilation of experiments with a simulation model. Accordingly, a simple constitutive model of strain-rate-dependent plasticity was defined, and the material constants were determined to minimize the difference between the experimental results and the corresponding simulations at a constant high temperature. Finite element simulations using a few estimated mechanical properties were compared with the corresponding experiments in compression tests at the same temperature for the validation of the estimated material responses. The constitutive model and determined material constants can reproduce the strain-rate-dependent material behavior under various loading speeds in instrumented indentation tests; however, the load level of computational simulations is lower than those of the experiments in the compression tests. These results indicate that the local mechanical responses evaluated in the instrumented indentation tests were not consistent with the bulk responses in the compression tests at high temperature. Consequently, the bulk properties were not able to be characterized using instrumented indentation tests at high temperature because of the scale effect.
devices/sensors, [10][11][12] and green architectures. [13] However, for homogenous material deformability, shape reconfiguration has relied on mold-assisted techniques that increase complexity. The ancient art of origami has been recently endowed with a new vitality with regard to 3D shape-reconfigurable materials. [14,15] An origami pattern consists of foldable and non-foldable creases with an anisotropic deformability that enables shape guiding and functionalities without molding. [7,16,17] This is fully compatible with shapereconfigurable materials because it incorporates the benefits of 2D simplicity, high throughput, and space conservation. It also provides a guided folding mechanism for shape reconfiguration. However, origamis that are based on nonrigid patterns require heavy pressurization to maintain a specific geometry. [18,19] Thus, to entirely forgo this process, an origami material must integrate two factors. First, in a predetermined origami pattern, the kinematic deformation must be solely restricted to the plastically folding creases, while the non-folding regions remain undeformed. Second, the origami material must exhibit repeatable "self-locking," where the deployed structure can be spontaneously fixed at a particular configuration without pressure. However, removal of the self-locking should enable re-shaping. By introducing the selflockable origami pattern, versatile shape-configurable materials are possible without assisting equipment.A self-lockable polymer origami that can significantly change shape along a foldable and non-foldable pattern, and spontaneously fix a specific geometry, can be fabricated via bi-and multi-layer assemblies [8,20] and lateral curing. [21] However, these structures usually suffer from delamination between layers and non-repeatable shape changes. Another method uses origami made from shape-memory polymers. [22,23] In this case, shapereconfiguration can be realized via stimuli-responsive elasticity, which subsequently eliminates stimuli that fix the geometry in a particular state. However, the elastically deforming into temporary shapes still need continuous external force load to remain its geometries, impeding the complexity of on-demand 3D shape-reconfigurability. Recent progress in covalent adaptable network polymers [24,25] offers strategies for polymeric origami that standard approaches cannot achieve. Because of bonding exchange reactions within a dynamic network topology, crosslinked polymers exhibit stimuli-responsive plasticity. [26,27] The Shape-reconfigurable materials are crucial in many engineering applications. However, because of their isotropic deformability, they often require complex molding equipment for shaping. A polymeric origami structure that follows predetermined deformed and non-deformed patterns at specific temperatures without molding is demonstrated. It is constructed with a heterogeneous (dynamic and static) network topology via light-induced programming. The corresponding spatio-selective thermal plasticity creates varied deformabili...
Sr-doped LaMnO3, is commonly used as the cathode for SOFC applications due to its superior electronic conducting properties. With enhancement of ionic conduction, mixed conducting perovskites, such as BaSrCo1-xFexO3-x, may also be used as the SOFC cathode and ion transport membranes for gas separation. However, the structural /electrical properties of BaSrCo1-xFexO3-x are not only highly dependent upon the Co/Fe ratio but also on the microstructural design. In this study, Ba0.5Sr0.5Co1-xFexO3-x, is first fabricated by using carbonates/oxides as raw materials. Secondly, a BaSrCo1-xFexO3-x thin film is deposited on a porous BaSrCo1-xFexO3-x substrate by electrophoretic deposition technique. As a result, with high Co/Fe ratio, Ba0.5Sr0.5Co1-xFexO3-x exhibits hexagonal distortion of perovskite structure. With low Co/Fe ratio, Ba0.5Sr0.5Co1-xFexO3-x exhibits cubic perovskite structure. The structure evolution is rationalized based on XRD and XPS analysis in addition to the consideration of cationic valence and radii. The mixed conduction behaviors of Ba0.5Sr0.5Co1-xFexO3-x is rationalized based on the defect types and charge compensation mechanism. The sintering and densification of Ba0.5Sr0.5Co1-xFexO3-x is examined as a function of Co/Fe ratio. The microstructure of catalytic layers were also investigated. Finally, the enhancement of oxygen permeation through thin-film membrane is demonstrated as well.
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