Novel 3D‐Printed Hybrid Auxetic Mechanical Metamaterial with Chirality‐Induced Sequential Cell Opening Mechanisms

New hybrid auxetic chiral mechanical metamaterial are designed and fabricated via multi‐material 3D printing. Due to the chirality‐induced rotation, the material have unique sequential cell‐opening mechanisms. Mechanical experiments on the 3D printed prototypes and systematic FE simulations show that the effective stiffness, the Poisson's ratio and the cell‐opening mechanisms of the new design can be tuned in a very wide range by tailoring two non‐dimensional parameters: the cell size ratio and stiffness ratio of component materials. As example applications, sequential particle release mechanisms and color changing mechanisms of the new designs are also systematically explored. The present new design concepts can be used to develop new multi‐functional smart composites, sensors and/or actuators which are responsive to external load and/or environmental conditions for applications in drug delivery and color changing for camouflage.

     

Giant Thermal Expansion in 2D and 3D Cellular Materials

When temperature increases, the volume of an object changes. This property was quantified as the coefficient of thermal expansion only a few hundred years ago. Part of the reason is that the change of volume due to the variation of temperature is in general extremely small and imperceptible. Here, abnormal giant linear thermal expansions in different types of two‐ingredient microstructured hierarchical and self‐similar cellular materials are reported. The cellular materials can be 2D or 3D, and isotropic or anisotropic, with a positive or negative thermal expansion due to the convex or/and concave shape in their representative volume elements respectively. The magnitude of the thermal expansion coefficient can be several times larger than the highest value reported in the literature. This study suggests an innovative approach to develop temperature‐sensitive functional materials and devices.     

2D Mechanical Metamaterials with Widely Tunable Unusual Modes of Thermal Expansion

Most natural materials expand uniformly in all directions upon heating. Artificial, engineered systems offer opportunities to tune thermal expansion properties in interesting ways. Previous reports exploit diverse design principles and fabrication techniques to achieve a negative or ultralow coefficient of thermal expansion, but very few demonstrate tunability over different behaviors. This work presents a collection of 2D material structures that exploit bimaterial serpentine lattices with micrometer feature sizes as the basis of a mechanical metamaterials system capable of supporting positive/negative, isotropic/anisotropic, and homogeneous/heterogeneous thermal expansion properties, with additional features in unusual shearing, bending, and gradient modes of thermal expansion. Control over the thermal expansion tensor achieved in this way provides a continuum‐mechanics platform for advanced strain‐field engineering, including examples of 2D metamaterials that transform into 3D surfaces upon heating. Integrated electrical and optical sources of thermal actuation provide capabilities for reversible shape reconfiguration with response times of less than 1 s, as the basis of dynamically responsive metamaterials.     

陶瓷材料特殊热膨胀性能的设计

具有特殊热膨胀性能的陶瓷是一种应用广泛的功能材料,近年来深受重视。本文简述了高膨胀、低膨胀、梯度膨胀、各向异性膨胀、突变膨胀和复合匹配膨胀等材料的组成、影响膨胀的因素、设计要点和应用范围。     

氟硅酸盐微晶玻璃的热膨胀性能研究

氟硅酸盐微晶玻璃的热膨胀性能主要取决于微晶玻璃的晶相组成及其相对含量．透辉石结晶相的含量增加使微晶玻璃的热膨胀系数降低,与此相反碱镁闪石结晶相的含量增加却使微晶玻璃的膨胀系数增加．K2O－MgO－SiO2－CaF2系统氟硅酸盐微晶玻璃的最小热膨胀系数为：78．4×10－7（20～300℃）;最大热膨胀系数为：85．6×107（20～300℃）．     

PBX炸药体膨胀特性研究

研制了适用于PBX炸药体膨胀的测试装置。采用此装置分别对热固型与热塑型PBX炸药的体膨胀力进行了测试,获得了两种炸药由常温升至75 ℃时的体膨胀力和体膨胀力随温度的变化曲线。试验结果表明,两种炸药的体膨胀力均是随着温度的升高而增加,在60～70 ℃范围内体膨胀力增加最大。炸药类型对炸药的体膨胀特性有较大的影响,热塑型PBX的体膨胀力远远大于热固型PBX的体膨胀力,是热固型炸药体膨胀力的8～9倍。对比不同质量的PBX-A炸药试验结果发现,随着炸药质量的增加,炸药体膨胀力随之增加;对体膨胀力-质量曲线进行线性拟合发现,体膨胀力随着质量的增加基本呈线性增长趋势。     

添加剂的膨胀系数对Y-TZP力学性能的影响

通过在Y-TZP中加入不同膨胀系数的玻璃相添加剂,低温烧结得到了具有不同力学性能的试样.建立了薄晶界应力模型,定性地计算了晶界应力,讨论了添加剂的热膨胀系数对Y-TZP陶瓷晶界应力及力学性能的影响.发现小膨胀系数的添加剂使晶界获得压应力,有利于获得较高断裂韧性的Y-TZP陶瓷.     

Multifunctional Metamaterials with Ultrawideband Wave Absorption and Thermal Camouflage

Objects can be identified based on their distinctive scattering signatures in multiple physical areas such as optics, electromagnetics, and thermotics. To ensure comprehensive stealth and camouflage capabilities, antisense devices with multiphysical field coupling are highly desired. Herein, a multifunctional antisense metadevice that achieves stealth in the microwave band while also generating multiple camouflage images from the original object's position during the heat conduction process is proposed and demonstrated. The metadevice combines both antimicrowave detection and camouflage infrared imaging capabilities, resulting in broadband electromagnetic stealth and thermal camouflage effect. Experimental and simulation results confirm the metadevice's ability to achieve these multifunctional capabilities in temperature-dependent cases. The development of such multifunctional devices that span physical fields provides new avenues for the design and preparation of multifunctional structures.     

镁基复合材料热膨胀的研究进展和前景展望

简要介绍了镁合金及镁基复合材料热膨胀的研究进展,叙述了温度、增强体体积分数、增强体颗粒尺寸、增强体颗粒形状、增强体种类和热处理及其他对镁基复合材料热膨胀的影响。简要介绍了热膨胀的理论预测模型,并对今后的发展做了展望。     

钛酸铝材料的结构、热膨胀及热稳定性

详细回顾了关于铁酸铝材料结构、热膨胀和热稳定性的研究。A12TiO5属于正交晶系假板钛矿结构。其晶格热膨胀各向异性行为，导致多晶铁酸铝陶瓷材料的微裂纹化，从而具有低膨胀、低热导率和优良的抗热震性等特性。但Al2TiO5低温下属于动力学稳定态，当温度低于1280℃易于分解为α-A12O3和金红石型TiO2。引入异质同构的化合物MgTi2O5或Fe2TiO5固熔于A12TiO5晶格，可以降低热力学分解温度和增加结构熵，有效地抑制Al2TiO5的分解。Al2TiO5在还原气氛下的分解机理上不明确，需要进一步的研究。     

Theoretical Prediction of Chiral 3D Hybrid Organic–Inorganic Perovskites

Hybrid organic–inorganic perovskites (HOIPs), in particular 3D HOIPs, have demonstrated remarkable properties, including ultralong charge‐carrier diffusion lengths, high dielectric constants, low trap densities, tunable absorption and emission wavelengths, strong spin–orbit coupling, and large Rashba splitting. These superior properties have generated intensive research interest in HOIPs for high‐performance optoelectronics and spintronics. Here, 3D hybrid organic–inorganic perovskites that implant chirality through introducing the chiral methylammonium cation are demonstrated. Based on structural optimization, phonon spectra, formation energy, and ab initio molecular dynamics simulations, it is found that the chirality of the chiral cations can be successfully transferred to the framework of 3D HOIPs, and the resulting 3D chiral HOIPs are both kinetically and thermodynamically stable. Combining chirality with the impressive optical, electrical, and spintronic properties of 3D perovskites, 3D chiral perovskites is of great interest in the fields of piezoelectricity, pyroelectricity, ferroelectricity, topological quantum engineering, circularly polarized optoelectronics, and spintronics.     

纯相BiFeO3的热稳定和热膨胀性质研究

本研究利用原位高温衍射和高温拉曼技术对纯相BiFeO₃粉体的热稳性和热膨胀性质进行了系统的解析。在升温阶段BiFeO₃始终保持斜方的R3c结构, 但是在降温阶段少量BiFeO₃会分解成为Bi₂Fe₄O₉和Bi₂₅FeO₃₉, 这种分解可能是由氧八面体的倾斜畸变引起的。此外, 还研究了BiFeO₃热力学膨胀系数, 发现它具有各向同性正膨胀性。以上结果也被拉曼光谱所证实。本研究的结果可为制备纯相BiFeO₃材料提供实验指导。     

CdGeAs2晶体的热膨胀行为研究

采用WinTA 100热膨胀仪研究了四方黄铜矿CdGeAs₂晶体在320~620 K温度范围内的热膨胀行为, 探索了CdGeAs₂晶体热膨胀各向异性的物理机制。测定晶体a轴和c轴方向的热膨胀系数α_a和α_c发现, α_a>>α_c>0, 表现出强烈的各向异性热膨胀特性。利用最小二乘法, 拟合出CdGeAs₂晶体的晶格常数(a, c)与温度(T)的函数关系式, 与文献报道值吻合。分别计算出不同温度下的四方畸变因子δ=2-c/a, Cd-As 键长(l_Cd-As)和 Ge-As 键长(l_Ge-As)以及相应的热膨胀系数α_Cd-As和α_Ge-As。结果表明, a、c、δ、l_Cd-As、l_Ge-As和α_Cd-As均随着温度的升高而增大, c/a和α_Ge-As则随着温度的升高而减小。当T=360 K时,α_Cd-As是α_Ge-As的6.36倍, 是造成CdGeAs₂晶体强烈热膨胀各向异性的主要原因。