基于SR-CT技术的泡沫铝力学性能

基于同步辐射计算机断层技术（简称SR-CT技术）,对泡沫铝材料试件进行三维无损重建,获取泡沫铝材料试件的内部体结构。在此基础上,建立泡沫铝试件的三维仿真模型,并对该模型进行模拟计算,以研究泡沫铝材料在压缩过程中的变形情况、米塞斯应力分布情况及其弹塑性区域的分布。研究结果表明,基于同步辐射计算机断层技术重建结果建立的三维...     

Multidimensional Anodized Titanium Foam Photoelectrode for Efficient Utilization of Photons in Mesoscopic Solar Cells

Mesoscopic solar cells based on nanostructured oxide semiconductors are considered as a promising candidates to replace conventional photovoltaics employing costly materials. However, their overall performances are below the sufficient level required for practical usages. Herein, this study proposes an anodized Ti foam (ATF) with multidimensional and hierarchical architecture as a highly efficient photoelectrode for the generation of a large photocurrent. ATF photoelectrodes prepared by electrochemical anodization of freeze‐cast Ti foams have three favorable characteristics: (i) large surface area for enhanced light harvesting, (ii) 1D semiconductor structure for facilitated charge collection, and (iii) 3D highly conductive metallic current collector that enables exclusion of transparent conducting oxide substrate. Based on these advantages, when ATF is utilized in dye‐sensitized solar cells, short‐circuit photocurrent density up to 22.0 mA cm^?2 is achieved in the conventional N719 dye‐I₃^?/I^? redox electrolyte system even with an intrinsically inferior quasi‐solid electrolyte.     

MHSS压缩有效力学性能研究

金属空心球结构(Metallic hollow sphere structure,MHSS)是一种新型的超轻多孔金属材料。利用ANSYS有限元分析软件模拟了薄壁金属空心球的压缩过程,采用非线性和瞬态分析方法得出了其名义应力-应变曲线,与实验曲线进行对比分析发现两条曲线较为吻合。对3种不同堆积模式的金属空心球结构进行了压缩数值模拟分析,得出了其压缩的有效屈服极限和有效弹性模量等力学性能。通过研究材料中单球的受力状态,分析了不同堆积模式材料力学性能出现差异的原因,其理论预测结果与数值模拟结果具有相同的规律。     

泡沫铝冶金连接及其界面结构与力学性能研究

以Zn-10Al合金作为粘结合金,采用功率超声辅助的热浸镀法进行泡沫铝板的冶金连接,采用光学显微镜(OM)和扫描电镜(SEM)观察接头组织及界面结构,采用X射线能谱仪(EDS)测定界面处元素分布,对样品进行拉伸实验和摆锤冲击实验,并与无功率超声辅助样品和胶接样品比较。功率超声辅助冶金接头密实连续,Zn、Al元素相互扩散,在界面处连续分布;无功率超声辅助接头中存在大量气孔等缺陷。功率超声辅助冶金接头的拉伸性能和冲击性能均优于无功率超声辅助接头和胶接接头。在功率超声辅助下进行连接时,其空化作用和声流能较彻底地破除泡沫铝基体表面的氧化膜,同时能够促进组织均匀化、去气除杂,有利于形成良好的冶金结合和致密的冶金接头。     

泡沫金属——高分子聚合物的复合体机械阻尼性能研究

本文研究了泡沫金属和同分子聚合物形成的复合体机械阻尼性能，结果表明它是一种内耗值Ｑ＾－１极高的阻尼材料，其阻尼特征表现为与应变振幅密切相关而与频率无显著关系的非线性内耗。同时研究了泡沫金属孔隙结构对复合体内耗值的影响关系，并对实验结果进行了讨论。     

复合材料胶结修补缺损金属结构的力学性能研究

进行了未修补与复合材料胶结修补的含穿透性裂纹金属试样的力学性能实验,测定了失效载荷,并分析了失效机理;采用实体层单元模拟复合材料补片和胶层,建立了复合材料胶接修补缺损金属结构的三维有限元分析模型,数值模拟了两种试样的载荷-位移曲线和应力分布,预测了破坏位置,与实验现象吻合良好。研究发现,与未修补的试样相比,经复合材料修补后的缺损结构承载能力得到明显提高。     

石墨烯/金属复合材料力学性能的研究进展

综述了石墨烯/金属复合材料在力学性能研究方面的现状、进展及发展趋势,讨论了线弹性非均质材料的微观力学模型在阐明石墨烯强化机制中的作用,着重阐述了石墨烯的结构完整性以及分散方法的选择等对于提高石墨烯/金属复合材料力学性能的重要性,归纳了当前石墨烯强化金属基复合材料研究存在的问题,并从原料研制、理论探索、工艺开发和协同增强等方面指出了石墨烯/金属复合材料力学性能的研究趋势。     

铸铁模消失模铸造过程数值模拟及组织性能研究

运用View cast对所设计的铸铁模消失模铸造工艺进行数值模拟,预测工艺方案所产生的缩孔、缩松的大小和位置。模拟结果显示,铸件实现了顺序凝固,无明显缩孔、缩松缺陷。此外,铸件设置加强肋保证了铸铁模在使用过程中不会因冷热交变产生挠曲变形。利用消失模铸造生产的铸铁模组织以针状铁素体和珠光体为主,加热至500℃、700℃,试样组织和硬度没有明显变化,加热至900℃时发生了铁素体向奥氏体转变,冷却后生成均匀分布的珠光体以及细小的铁素体。氧化实验分析发现,温度对试样的氧化速率有较大影响,主要是因为不同温度下试样表面生成不同的氧化膜,使试样的氧化速率有较大的差异。     

玻璃纤维夹芯材料力学性能与阻尼特性分析

对大跨度建筑用复合金属屋面板的玻璃纤维夹芯材料的力学性能进行了试验测定。测得了玻璃纤维棉层压方向和顺纹方向的拉压强度、弹性模量和泊松比等基本力学参数,结果表明层压方向和顺纹方向的力学性质不相同。采用振动梁法进行了阻尼特性试验,得到了材料损耗因子的值,并根据试验数据拟合出了玻璃纤维棉损耗因子-频率的曲线,在测试频率范围内材料的损耗因子值为0.5左右,表明该材料为高阻尼材料。进一步以一块玻璃纤维夹芯复合金属板为算例,采用模态应变能法对其阻尼特性进行了数值分析。玻璃纤维夹芯复合屋面板的各阶模态损耗因子在0.3～0.5左右,表明玻璃纤维夹芯复合金属板具有较高的结构阻尼,在大跨度结构风振计算中将玻璃纤维夹芯复合金属屋面板看作刚性板是不正确的。     

Application of Small Punch Techniques for the Determination of Gold Mechanical Properties

Abstract: Gold has been one of the most valuable materials since ancient times. These days it is mainly used as a business commodity or as an engineering material in jewellery, medical prostheses (mainly dental) or electronics. For these engineering purposes, knowledge of its mechanical properties is a key factor in order to improve design and performance. The properties of pure gold have already been reported, although the information on them is scarce and indeed no information on properties such as fracture resistance has been found by the authors of this work. Gold alloys, especially those used for dental implants, are better characterised, but the development of new alloys requires a new characterisation of their properties. At the same time, there have been important advances in recent years in the development of non‐destructive or quasi‐non‐destructive techniques for the mechanical characterisation of materials. Among these, the small punch technique has proven to be one of the most reliable and efficient (in terms of material consumption). This technique is here applied for the determination of 24 (pure gold) and 18 (75% gold) carat gold properties, as an example of how this experimental tool is capable and suitable for the characterisation of gold, gold alloys and any other scarce, valuable material. The estimated tensile properties of 24 carat gold correlate well with the values observed in the literature, obtained through traditional test techniques.     

泡沫铝复合板低频吸声性能实验分析与研究

摘 要：泡沫铝是一种新型的吸声材料,在中高频具有良好的吸声效果,本文研究采用泡沫铝复合板来提高其低频吸声性能。研究表明,泡沫铝复合结构具有较好的低频吸声性能,在500Hz～1KHz吸声系数提高较大。通过在材料一侧添加可以背衬进一步提高其吸声系数,在空腔厚度为30mm时复合板的吸声系数最好,在频率400Hz附近出现吸声峰值0.82。     

An Effective Numerical Method for the Solution of a Stochastic Coronavirus (2019-nCovid) Pandemic Model

Nonlinear stochastic modeling plays a significant role in disciplines such as psychology, finance, physical sciences, engineering, econometrics, and biological sciences. Dynamical consistency, positivity, and boundedness are fundamental properties of stochastic modeling. A stochastic coronavirus model is studied with techniques of transition probabilities and parametric perturbation. Well-known explicit methods such as Euler Maruyama, stochastic Euler, and stochastic Runge–Kutta are investigated for the stochastic model. Regrettably, the above essential properties are not restored by existing methods. Hence, there is a need to construct essential properties preserving the computational method. The non-standard approach of finite difference is examined to maintain the above basic features of the stochastic model. The comparison of the results of deterministic and stochastic models is also presented. Our proposed efficient computational method well preserves the essential properties of the model. Comparison and convergence analyses of the method are presented.     

Surface Modification of Transition Metal Dichalcogenide Nanosheets for Intrinsically Self-Healing Hydrogels with Enhanced Mechanical Properties

Nanocomposites with enhanced mechanical properties and efficient self-healing characteristics can change how the artificially engineered materials’ life cycle is perceived. Improved adhesion of nanomaterials with the host matrix can drastically improve the structural properties and confer the material with repeatable bonding/debonding capabilities. In this work, exfoliated 2H-WS₂ nanosheets are modified using an organic thiol to impart hydrogen bonding sites on the otherwise inert nanosheets by surface functionalization. These modified nanosheets are incorporated within the PVA hydrogel matrix and analyzed for their contribution to the composite's intrinsic self-healing and mechanical strength. The resulting hydrogel forms a highly flexible macrostructure with an impressive enhancement in mechanical properties and a very high autonomous healing efficiency of 89.92%. Interesting changes in the surface properties after functionalization show that such modification is highly suitable for water-based polymeric systems. Probing into the healing mechanism using advanced spectroscopic techniques reveals the formation of a stable cyclic structure on the surface of nanosheets, mainly responsible for the improved healing response. This work opens an avenue toward the development of self-healing nanocomposites where chemically inert nanoparticles participate in the healing network rather than just mechanically reinforcing the matrix by slender adhesion.     

Review of numerical methods for simulation of the aortic root: Present and future directions

Heart valvular disease is still one of the main causes of mortality and morbidity in develop countries. Numerical modeling has gained considerable attention in studying hemodynamic conditions associated with valve abnormalities. Simulating the large displacement of the valve in the course of the cardiac cycle needs a well-suited numerical method to capture the natural biomechanical phenomena which happens in the valve. The paper aims to review the principal progress of the numerical approaches for studying the hemodynamic of the aortic valve. In addition, the future directions of the current approaches as well as their potential clinical applications are discussed.