Advanced Materials—From Strength to Strength

Advanced Materials has come a long way since its modest beginning in 1989 as a “piggy back” journal in Angewandte Chemie. Some of its more recent achievements as well as innovations to foster the further development of the journal are presented in this Editorial. The ways in which the success of a journal can be measured in terms of quality and popularity are also discussed.     

高强度三掺复合水泥的强度及孔结构性能研究

分别将30%、40%、50%混合材与水泥熟料复合,制备高强度复合水泥.混合材主要为矿渣、活化粉煤灰和活化煤矸石.通过砂浆强度测试及孔结构测试等技术,对复合水泥的力学性能、水化过程和水化机理进行了分析研究.试验结果表明,当3种混合材复掺时,制备的复合水泥的强度较高.复合水泥28d抗压强度最高达到65MPa,各试样的抗压强度均超过50MPa,且后期强度继续增大.从孔结构结果可看出,制备的复合水泥的水泥石有较多的凝胶孔和较低的总孔隙率.     

超高强混凝土的制备及其强度基础分析

由于集料与水泥石变形的不一致,导致混凝土内部结构缺陷几率增大.因此,强度超过150MPa的超高强水泥基材料,如无宏观缺陷水泥基材料(MDF)、活性粉末混凝土(RPC)及工程粘性材料(ECC)等制备时必须剔除粗集料.本文在不剔除粗集料的情况下,采用普通工艺和常规材料,制得了365天龄期时抗压强度为178.3MPa,坍落度210mm的超高强高性能混凝土,同龄期、同配比下的砂浆强度达到178.2MPa,净浆强度达到179.5MPa,混凝土、砂浆及水泥石强度均超过所用粗集料的母岩强度.以此为基础,分析了混凝土各组成结构的微观结构及微观力学特征,探讨了不剔除粗集料的情况下,制备超高强混凝土的理论基础.     

Strength of corroded pipelines

A method of determination of the limiting pressure for gas and oil pipelines susceptible to local corrosion is discussed. The proposed method is based on a combined use of strength criteria of the continuum mechanics and fracture mechanics. Its applicability is verified by the results of numerical studies and laboratory model tests.     

Strength of oriented polymers

It was shown that the strength of oriented polymers is to a considerable degree determined by changes in the size and configuration of defects.     

高强湿喷混凝土强度降低的原因探析与改进

采用湿喷工艺研究了高强喷射混凝土,发现设计的C50喷射混凝土强度严重降低,通过X射线衍射(XRD)、扫描电子显微镜(SEM)、水泥浆水化程度(Degree of hydration)试验分析了强度严重降低的原因。结果表明:喷射成型对混凝土的水化产物种类和净浆的水化程度影响甚微,但对混凝土的密实度及水化产物的形貌影响较大。喷射混凝土密实度不够、材料间粘接不牢固导致喷射混凝土的微观结构疏松,是造成喷射混凝土强度严重降低的主要原因。改进验证试验表明,对高强喷射混凝土来说,喷射施工质量控制对于混凝土强度至关重要,材料体系应适应喷射施工设备与工艺。高强湿喷混凝土 (C50及以上)宜采取0.8～0.9 MPa的风压;喷射时需连续一次垂直喷射,不得出现间断或脉冲;倒筒时间宜控制在10 s以内;水胶比选取0.32～0.36,混凝土砂率控制在50%～70%。改进后的喷射高强混凝土28 d强度可达63.6 MPa。     

Correlation between Microstructures and Yield Strength of a High Strength Enameling Steel

Numerical estimates of the components of yield strength of a high strength Fe-C-Mn-P-N-Si enameling steel were determined using empirical relationships between microstructure and yield strength. Results are reported for both the hot rolled (HR) and cold rolled (CR) forms before and after simulating an enamel-fire anneal (EFA). To determine the solubilities of alloying elements, thermodynamic calculations were performed in combination with the considerations of process conditions and the element diffusivities. The results show that the main solid solution strengtheners were the elements Mn, Si, and P, while the elements C and N were nearly completely tied up as precipitates. The yield strength reduction, due to the EFA, resulted primarily from an increase in grain size and a decrease in dislocation density, and the EFA appeared to have a negligible effect on the element solubilities.     

Effect of the Strain Rate on the Yield Strength of Steels of Different Strength

We present results of testing soft and high-strength steels for impact compression and show that the dependences of the compression resistance of tested metals on the level of strains are qualitatively similar. It is also shown that, as the strain rate increases, the compression resistance of the metals first strongly increases and then attains the zone of saturation in which the difference between the levels of compression resistance of these metals decreases. We also consider some specific features of the processes of deformation and fracture in the analyzed metals on the microstructural level.     

Strength of Ag-Ni multi-layered foils

The effect on mechanical properties was investigated of controlled variations in the layer thickness in multi-layered Ag-Ni foils. Multi-layered foils were made by hot pressing and then cold rolling of stacked foils. The thickness of a layer of multi-layers was controlled by the rolling rate. Tensile strength of foils increased with the decrease of thickness of a layer in the manner of the Hall-Petch relation up to a certain point and then maintained a constant value even when the thickness was further decreased. The effect of the thickness ratio of the two components on tensile strength was also studied in the Ag-Ni system.     

A Criterion of Local Strength

We propose a local criterion of brittle strength for structurally inhomogeneous materials based on the size effect of mechanical properties of materials under the conditions of stress concentration. It is assumed that the function of local strength of the material depends on the scaling factor equal to the ratio of the size of the zone of stress concentration to the characteristic structural size of the material. We study the problem of strength of a solid body containing a stress concentrator of any size and shape in tension, including the limiting case of degeneration of a smooth concentrator into a rectilinear (or circular) crack. The requirements to the behavior of the critical stress and critical size of the defect are formulated and the form of the function of local strength is specified. For the fracture stress, we deduce interpolation-type expressions and compare the obtained numerical results with the available experimental data.     

Strength of reed from Egypt

A growing need for building materials and an increasing demand for the analytical calculation of structures mean that data are required about materials which were traditionally used on an empirical basis. This is true for Egyptian reed, and tests are reported on its uniaxial tensile and compressive strength, and its static and impact bending strength.     

Buckling Strength of Near-Cylindrical Shells

A procedure is proposed whereby critical loads for elastic near-cylindrical shells are determined with the use of equations in terms of displacements. An analytical expression has been derived for the assessment of critical stresses in momentless smooth shells. A contribution of individual components of the total potential energy of such shells to stabilization or destabilization of the strain state is analyzed graphically. Dimensionless critical stresses are assessed with respect to classical ones as determined for ideal cylindrical shells. The data obtained are compared with the known experimental results.     

Strength and fracture of grasses

The strength of leaves from six grasses of sclerenchyma content from 2% to 30% has been measured. The strength of sclerenchyma is 144 M Pa. As long as the sclerenchyma fibres are mechanically separated laterally, they toughen the leaf by reducing its sensitivity to damage. At high sclerenchyma contents the fibres tend to be laterally joined and the leaf, although stronger, becomes more brittle.     

Strength of tin-based soldered joints

Single overlap joints of copper and brass soldered with tin and tin-based solders containing (wt%) 1% Cu, 3.5% Ag, 5% Sb, 57% Bi, and 2% Ag 36% Pb, have been tested in shear at 20 and 100 °C, and with strain rates of 0.05 and 50 mm min^?1. Six specimens were tested under each condition, and the average value and coefficient of variation of the 0.2% yield stress, ultimate shear stress, elongation, and work to fracture, determined. Brass joints were generally slightly stronger than copper joints, and tended to show more scatter. Ranking in terms of strength depended on the test conditions. The solders containing silver generally gave the strongest joints. Strain-rate sensitivities were less than 0.1, and activation energies for deformation were very low. Overall, there did not appear to be any regular pattern between the properties, solders, and test conditions.     

Strength of Structural Carbon Materials

The effect of microstructure on the strength of various carbon materials is analyzed. The strength of structural carbon materials is shown to decrease upon oxidation and to rise during neutron irradiation.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 5, 2005, pp. 523–530.Original Russian Text Copyright © 2005 by Virgilev.     

Strength of irradiated polymethyl methacrylate

The effect of the form of radiation (reactor and-radiation, X-rays and ultraviolet light) and absorbed energy on the strength of polymethyl methacrylate was studied. It was shown that the strength of this polymer depends in the first place on the size of radiation-induced defects and not on their distribution across the specimen thickness. When therefore the absorbed radiation energy is nonuniformly distributed along the specimen cross section, the mechanical properties of irradiated materials are determined by the radiation dose absorbed by the specimen surface layers.