Biomimetic Supramolecular Fibers Exhibit Water‐Induced Supercontraction

Spider silk is a fascinating material, combining high strength and elasticity that outperforms most synthetic fibers. Another intriguing feature of spider silk is its ability to “supercontract,” shrinking up to 50% when exposed to water. This is likely on account of the entropy‐driven recoiling of secondary structured proteins when water penetrates the spider silk. In contrast, humidity‐driven contraction in synthetic fibers is difficult to achieve. Here, inspired by the spider silk model, a supercontractile fiber (SCF), which contracts up to 50% of its original length at high humidity, comparable to spider silk, is reported. The fiber exhibits up to 300% uptake of water by volume, confirmed via environmental scanning electron microscopy. Interestingly, the SCF exhibits tunable mechanical properties by varying humidity, which is reflected by the prolonged failure strain and the reversible damping capacity. This smart supramolecular fiber material provides a new opportunity of fabricating biomimetic muscle for diverse applications.     

湿热环境下Carbon/Epoxy复合材料层合板动态压缩性能

随着纤维增强复合材料的广泛应用, 研究其在湿热环境下的动态力学性能具有重要的理论研究意义与工程应用价值。首先对碳纤维增强环氧树脂基(Carbon/Epoxy)复合材料层合板试件进行了湿热处理, 其后采用分离式霍普金森压杆(SHPB)技术开展了干/湿态试件高应变率压缩实验并对实验结果进行分析。结果表明: 材料脱(吸)湿过程呈现出两段式特点, 存在二次脱(吸)水现象; Carbon/Epoxy复合材料层合板的强度在垂直铺层方向具有显著的应变率敏感性, 随着应变率从1 500 s-1增加至6 000 s-1, 其强度增加近3倍, 与此同时应变率对其弹性模量的影响却非常微弱; 此外, 湿热处理有助于提升该材料的动态力学性能, 经20 d吸湿后材料动态强度有最大12.45%的增幅, 吸湿使得材料动态强度的上升在应变率较低时比较明显。      

氧化剂对聚吡咯复合材料介电性能的影响

为了探究氧化剂对聚吡咯复合材料介电性能的影响,以吡咯为单体,采用原位聚合法制备了聚吡咯涂层复合材料。通过BDS50介电谱仪研究了氧化剂种类和氧化剂物质的量浓度对复合材料介电常数实部、虚部、损耗角正切、表面电阻的影响;采用Quanta200型环境扫描电子显微镜和Instron万能材料试验机研究了聚吡咯涂层复合材料的外观形貌和强度。结果表明:氧化剂种类、氧化剂浓度对聚吡咯涂层复合材料介电常数实部、虚部、损耗角正切、表面电阻影响较大;制备的聚吡咯涂层复合材料既具备良好的介电性能和导电性,又兼具良好的强度.     

Nb/Nb5Si3复合材料的研究进展

Nb/Nb5Si3复合材料具有高熔点、低密度以及良好的室温韧性和高温强度,被认为是下一代航空发动机中极具竞争力的超高温结构材料.本文介绍了这种复合材料的主要制备方法、组织结构和力学性能,并展望了其发展前景.     

Nanocrystalline β-Ti alloy with high hardness,low Young's modulus and excellent in vitro biocompatibility for biomedical applications

High strength, low Young's modulus and good biocompatibility are desirable but difficult to simultaneously achieve in metallic implant materials for load bearing applications, and these impose significant challenges in material design. Here we report that a nano-grained β-Ti alloy prepared by high-pressure torsion exhibits remarkable mechanical and biological properties. The hardness and modulus of the nano-grained Ti alloy were respectively 23% higher and 34% lower than those of its coarse-grained counterpart. Fibroblast cell attachment and proliferation were enhanced, demonstrating good in vitro biocompatibility of the nano-grained Ti alloy, consistent with demonstrated increased nano-roughness on the nano-grained Ti alloy. Results suggest that the nano-grained β-Ti alloy may have significant application as an implant material in dental and orthopedic applications.     

CNTs/Al5083复合材料力学性能及增强机制

采用高能球磨和冷轧工艺制备出3%(质量分数)碳纳米管增强Al5083复合材料。利用SEM,TEM观察球磨后复合粉末表面形貌,采用拉曼光谱和XRD对复合粉末和成型后的材料进行物相分析。最后测试了复合材料的力学性能。结果表明:在球磨1.5h的复合粉体中CNTs分散均匀,结构较完整,部分嵌入Al基体中并结合良好。冷压烧结并冷轧成型后的复合材料力学性能表现优异,球磨1.5h下,复合材料抗拉强度和屈服强度分别达到278MPa和247MPa,断裂延伸率为0.07,硬度HV达到95。将热不匹配模型与奥罗万模型所预测的屈服强度与实验值进行对比,结果表明CNTs/Al5083复合材料符合奥罗万机制。     

A natural wear resistant material

A study has been made of Danto Koruntz (Danto International Ltd.), a natural material now beginning to find use in wear applications. Its microstructure is described and its density, coefficient of thermal expansion, thermal conductivity, hardness, elastic constants, flexural strength, fracture toughness and work of fracture are reported. Compared to a typical man-made 95% dense sintered wear alumina, which is somewhat harder and tougher and considerably stronger and stiffer, Danto Koruntz is much less erosion resistant and exhibits qualitatively different thermal shock behaviour. When slid on itself, Danto Koruntz exhibits a slightly lower coefficient of friction than does the alumina.     

Effect of the structural state on the cold brittleness and fracture toughness of low-alloyed molybdenum

We investigate the effects of the chemical and phase compositions of grain boundaries and the state of an excess phase on the fracture toughness, cold brittleness, and strength of low-alloyed molybdenum by the methods of scanning electron microscopy, transmission electron microscopy, and Auger electron spectroscopy. The structural state of the material was changed without changing grain sizes by annealing in various modes at different temperatures. It was shown that the level of segregation of interstitials on grain boundaries is determined by both the annealing temperature and distinctive features of the evolution of excess phases. Embrittlement of grain boundaries results in a decrease in the strength and fracture toughness of the material and in an increase in its temperature of cold brittleness. In the case of transcrystalline fracture, the material exhibits better mechanical properties correlated with distinctive features of the evolution of excess phases inside the grains.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 5, pp. 34–44, September–October, 1994.     

Hierarchical Cellulose Superinsulation Membrane

The environment-friendly components coupled with the ability to mimic the simplicity and originality of nature necessitate advanced sustainable materials with structural capabilities for energy-efficient applications. The use of feedstock deriving from plant-based, renewable organic material to produce nanofibril that embodies enhanced insulating properties and high mechanical strength constitutes an efficient development strategy. Herein, a free-standing, hierarchical superinsulation membrane by leveraging the principle of the bottom-up method is reported. The electrospun cellulose nanofibrils/aerogel-based core layer provides exceptional thermal properties with its thermal conductivity of 10.2 mW m⁻¹K⁻¹. The lightweight, flexible, and durable paper-like membrane features a tensile strength of 11.3 MPa and a bending rigidity in the order of 4.6 cN mm⁻¹. The hydrophobic superinsulation membrane material also exhibits a ΔT of ≈25 °C under continuous sunlight illumination and allows thermal runaway mitigation of rechargeable lithium-ion batteries. All the aforementioned properties position this hybrid superinsulation membrane as a promising material for energy-saving thermal management applications.     

Tensile and impact-toughness behaviour of cryorolled Al 7075 alloy

The effects of cryorolling and optimum heat treatment (short annealing + ageing) on tensile and impact-toughness behaviour of Al 7075 alloy have been investigated in the present work. The Al 7075 alloy was rolled for different thickness reductions (40% and 70%) at cryogenic (liquid nitrogen) temperature and its mechanical properties were studied by using tensile testing, hardness, and Charpy impact testing. The microstructural characterization of the alloy was carried out by using field emission scanning electron microscopy (FE-SEM). The cryorolled Al alloy after 70% thickness reduction exhibits ultrafine grain structure as observed from its FE-SEM micrographs. It is observed that the yield strength and impact toughness of the cryorolled material up to 70% thickness reduction have increased by 108% and 60% respectively compared to the starting material. The improved tensile strength and impact toughness of the cryorolled Al alloy is due to grain refinement, grain fragments with high angle boundaries, and ultrafine grain formation by multiple cryorolling passes. Scanning electron microscopy (SEM) analysis of the fracture surfaces of impact testing carried out on the samples in the temperature range of −200 to 100 °C exhibits ductile to brittle transition. cryorolled samples were subjected to short annealing for 5 min at, 170 °C, and 150 °C followed by ageing at 140 °C and 120 °C for both 40% and 70% reduced samples. The combined effect of short annealing and ageing, improved the strength and ductility of cryorolled samples, which is due to precipitation hardening and subgrain coarsening mechanism respectively. On the otherhand, impact strength of the cryorolled Al alloy has decreased due to high strain rate involved during impact loading.     

Effect of rolling temperature on microstructure and mechanical properties of 6063 Al alloy

Aluminium alloy (6063) was severely rolled upto 92% thickness reduction at liquid nitrogen temperature and room temperature to study the effect of rolling temperature on its mechanical properties and microstructural characteristics by using tensile tests and SEM/electron back scattered diffraction (EBSD), transmission electron microscope (TEM), DSC, X-ray diffraction (XRD) as compared to room temperature rolled (RTR) material with the same deformation strain. An improved strength (257 MPa) of cryorolled 6063 Al alloy was observed as compared to the room temperature rolled alloy (232 MPa). The improved strength of cryorolled alloy is due to the accumulation of higher dislocation density than the room temperature rolled material. The tensile properties of cryorolled alloy and the alloy subjected to different annealing treatments were measured. The cryorolled alloy subjected to annealing treatment at 300 °C for 5 min exhibits an ultrafine-grained (UFG) microstructure with improved tensile strength and ductility.     

Influence of the usage of waste oyster shell powder on mechanical properties and durability of mortar

In order to investigate feasibility of waste oyster shell powder (WOSP) as fine aggregate to produce eco-friendly mortar, workability (slump flow and slump flow loss), mechanical properties (compressive strength and flexural strength), durability (sorptivity, volume of permeability coefficient, water permeability coefficient and chloride ion diffusion coefficient) and microstructure (pore size diffusion) were studied. The effect of replacing river sand with different WOSP proportions (0%, 10%, 20% and 30%) in flowability, strength, permeability and microstructure of mortar have been revealed. The results indicate that increasing substitution ratio of WOSP could decrease the mortar slump flow. The utilization of WOSP in mortar enhanced the compressive strength, flexural strength, resistance to water penetration and chloride diffusion. The WOSP addition exhibits a positive contribution to the pore size distribution of the mortar. Furthermore, it is founded that the utilization of WOSP as construction material is a satisfactory way to reduce waste pollution. Based on its superior mechanical property, durability, eco-efficiency and cost-efficiency in mortar, it is recommended to utilize WOSP alternative to river sand at 10–30% in construction engineering.     

Properties of Alkali Activated Aluminosilicate Material after Thermal Load

The porosity, bulk density, compressive strength, bending strength, thermal conductivity, and specific heat capacity of a material based on alkali activated slag are determined at room temperature conditions for samples subjected to a thermal load up to 1200°C prior to the measurements and compared to reference material data. The results are discussed using material characterization experiments, namely, X-ray diffraction analysis and scanning electron microscopy. Experimental results show a remarkable high-temperature resistance of the studied material, which after pre-heating to 1200°C exhibits mechanical properties comparable to the reference material not exposed to any thermal load.Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.     

Crack propagation and fracture in silicon carbide

Fracture mechanics and strength studies performed on two silicon carbides — a hot-pressed material (with alumina) and a sintered material (with boron) — have shown that both materials exhibit slow crack growth at room temperature in water, but only the hotpressed material exhibits significant high temperature slow crack growth (1000 to 1400? C). A good correlation of the observed fracture behaviour with the crack growth predicted from the fracture mechanics parameters shows that effective failure predictions for this material can be achieved using macro-fracture mechanics data.     

两种双基体C/C复合材料的微观结构与力学性能

借助偏光显微镜、扫描电镜以及力学性能测试研究了两种双基体C/C复合材料的微观结构与力学性能。结果表明:基体碳在偏光显微镜下呈现出热解碳的光滑层组织,沥青碳的各向同性、镶嵌和流域组织。在SEM下普通沥青碳为"葡萄状"结构,中间相沥青碳为片层条带状结构。具有多层次界面结构的材料可以提高材料的弯曲强度,改善材料的断裂韧度,两种材料在载荷-位移曲线中载荷为台阶式下降,呈现出假塑性断裂特征。材料A和材料B的弯曲强度分别为206.68,243.66MPa,断裂韧度分别为8.06,9.66MPa·m1/2,材料B的弯曲强度、断裂韧度均优于材料A。     

Studies on the Strength and Plasticity of Ti–Nb-Based Laminated Composites in a Temperature Range of 290–1700 K

The test procedure is described, and temperature dependences (290–1700 K) of mechanical characteristics are determined in tension of 9- and 13-layer Ti–Nb-based composites with equal volume contents of components as well as of a VT6S titanium alloy. It is established that composites with a larger number of layers possess higher strength, and among materials with an equal number of layers, the material with a higher degree of compression also exhibits higher strength. The values of ultimate strength obtained agree well with those calculated by the additive equation, except for the range of dynamic strain aging.     

Spall fracture in sapphire

The dynamic tensile strength of sapphire has been studied under conditions of impact loading in the region of dynamic (Hugoniot) elastic limit (HEL). In the absence of inelastic deformation, the spall strength of sapphire strongly depends on the loading time and exhibits a tendency to decrease with increasing compressive stress in the incident impulse. The development of inelastic deformation leads to the complete loss of material resistance to the tensile straining.     

超高韧性水泥基复合材料的层裂试验研究

层裂是材料遭受冲击、爆炸等高速荷载时的一种常见破坏方式。该文利用直径80 mm的霍普金森杆实验装置,研究了超高韧性水泥基复合材料UHTCC （Ultra High Toughness Cementitious Composites）中应力波的传播特性和材料的层裂强度。通过在试件表面粘贴5组应变片,获得了在0.2 MPa、0.3 MPa、0.4 MPa、0.5 MPa打击气压下,UHTCC中应力波的传播曲线。利用高速摄影机记录层裂试验,观测了UHTCC的层裂破坏过程。由试件表面应变片测得的应力波曲线,计算了材料中的应力波波速、动态弹性模量,分析了应力波在该材料中传播的衰减规律,并计算出不同打击气压下材料的层裂强度及应变率。试验结果显示: UHTCC的层裂过程相比混凝土具有更多的韧性特征; UHTCC中的应力波峰值在0 mm~500 mm范围内衰减迅速;在同等应变率下,UHTCC与静态抗拉强度相近的混凝土相比,层裂强度高出10 MPa左右,且UHTCC的层裂强度具有明显的应变率敏感性。     

The material properties of sulphonated phenolic resin reinforced cement mortars

The material properties of new sulphonated phenolic resin (SP) reinforced cement mortars have been investigated. SP was found to promote the dispersion of cement particles and to interact with Ca(OH)₂. As a result, the resulting mortars exhibit better workability, more compact structure and higher compressive strength than plain mortars. The mortar with 1 wt% SP present after 28 days curing exhibits a compressive strength of 66MPa, which is about 18% higher than that of plain mortar.     

The preparation and characterization of hybrid materials composed of phenolic resin and silica

Novel organic-inorganic hybrid materials were prepared by in situ polymerization of silicon alkoxide in a phenolic resin matrix. Very uniform hybrid materials composed of a phenolic resin and silica were obtained using varying amounts of silica. The transparency of the hybrid materials could be varied depending on the size of the resulting silica particles. SEM observations revealed that the hybrid materials consist of fine silica particles embedded in a phenolic resin matrix with good interaction at the interface. Density and ²⁹Si-NMR measurements indicate that the silica incorporated in the hybrid material has a high density and mainly Q4 chemical bonding environments. The hybrid material exhibits excellent mechanical improvements in modulus, strength, strain at break and impact strength.