摘要:

The use of fibers in a cement‐based matrix can fundamentally improve its mechanical properties. Such improvement may lead to a new class of cement‐based materials. Further developments depend on an understanding of the interaction between different fibers and cement‐based matrices. The current knowledge on the mechanical behavior of fiber‐reinforced cement‐based composites is summarized. Toughening mechanisms, interface properties, and tensile response of fiber‐reinforced cement‐based composites are presented. Various theoretical approaches used to describe the mechanical behavior of fiber‐reinforced composit

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1991.tb06836.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The mechanism of degradation, orIRdrop, of BaTiO3‐based Ni‐electrode chip capacitors has been studied, with special attention to the microstructure. Degradation occurred mainly at the center of the capacitors. Longer‐life capacitors were obtained under conditions of low oxygen partial pressure, 10−12atm, during sintering, and had larger grain sizes and smaller quantities of grain boundary phase. The existence of oxygen vacancies in the grain boundary phase was confirmed by cathode luminescence measurement. Double layers along the surfaces of the Ni electrodes were also related to the life of the cap

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1991.tb06837.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The mechanical behavior of a novel ceramic sandwich composite system was investigated. This system was comprised of a low‐density, cellular alumina core bonded to dense alumina faceplates. The flexural strength and elastic properties of the core material alone were measured as a function of relative density. For the sandwich system, failure mechanisms and failure loads for a variety of core densities and face thicknesses were recorded. Initial failure mechanisms were observed to be exclusively core fracture but in a non‐catastrophic manner. In order to successfully predict these failure loads with existing theory, Weibull statistics were incorporated into the analysis. This allowed flexural strengths measured independently on the core material to be scaled to those expected from the stress distribution in the sandwich c

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1991.tb06838.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The subsolidus phase relationships in the system Si,Al,Y/N,O were determined. Thirty‐nine compatibility tetrahedra were established in the region Si3N4─AIN─Al2O3─Y2O3. The subsolidus phase relationships in the region Si3N4─AIN─YN─Y2O3have also been studied. Only one compound, 2YN:Si3N4, was confirmed in the binary system Si3N4─YN. The solubility limits of the α′─SiAION on the Si3N4─YN:3AIN join were determined to range fromm= 1.3 tom= 2.4 in the formula Ym/3Si12‐mAlmN16. No quinary compound was found. Seven compatibility tetrahedra were established in the

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1991.tb06839.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The laser chemical vapor precipitation of Si3N4powder from mixtures of SiH2Cl2and NH3has been studied. The reactant gases were mixed at different heights with respect to the laser beam, thus preventing low‐temperature reactions and agglomeration of the produced particles. The morphology and the size of the particles formed are dependent on the injection height of NH3into the silicon reactant gas stream. Particle diameters are typically between 15 and 110 n

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1991.tb06840.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Titanium nitride whiskers having diameters of 0.5 to 1.5 μm and aspect ratios in the range of 20 to 50 have been produced by a new commercially scalable vapor–liquid–solid process. Electron microscopy studies have shown that most of the whiskers can be classified into two types based upon structure and morphology. The whiskers of one type are single crystals and have a growth direction of (100). Whiskers of the second type are comprised of two crystals having a common (110) growth direction. Both types have smooth surfaces and relatively few internal defects. Additionally, a small percentage of whiskers have considerable internal structure related to significant magnesium impuri

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1991.tb06841.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Results of four‐point bend tests on notched beams of a laminated unidirectional fiber‐reinforced glass matrix composite are presented. The failure sequence has been established through in situ examination. The dominant damage mode is a mixed‐mode, split crack that runs parallel to the predominant fiber directions. The crack interacts with and crosses over imperfectly aligned fibers. The resulting bridging tractions are sufficient to cause the critical strain energy release rate to increase substantially as the crack extends. Several other damage modes are also observed. These include mode I (tensile) matrix cracks bridged by fibers, mode II (shear) cracks, and compressive damage at the loading p

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1991.tb06842.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The corrosion of aluminosilicate refractories by molten aluminum, such as in melting and holding furnaces, generally leads to the formation of an alumina deposit on the refractory. In the presence of alkalies and under a reducing atmosphere the extent of corrosion is increased. This could be related to the transformation of the alumina to sodium aluminate, whose formation kinetics are increased under a reducing atmosphere, promoting the formation of aluminum nitride. In melting and holding furnaces, the alkalies could originate from the presence of a cryothic bath in the metal charge and/or from the refractories. In the latter case, it was shown that aluminum nonwetting refractory castables containing aluminum fluoride as the nonwetting agent could lead to severe corrosion in the above applications if their alkali content is such that it promotes the formation of β‐alumi

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1991.tb06843.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Aqueous mixtures of Zr(C2H3O2)4and Gd(NO3)3were used to prepare chemically homogeneous ZrO2—Gd2O3solid solutions containing 0 to 9 mol% Gd2O3. The application of kinetically limited equilibria concepts explains why a metastable tetragonal phase crystallized subsequent to precursor pyrolysis from compositions containing6.5 mol% Gd2O3. Partitioning experiments for a composition containing 3 mol% Gd2O3showed that the maximum equilibrium solid‐solubility of Gd2O3in tetragonal ZrO2is 1.0 ± 0.1 mol% and the minimum equilibrium solid‐solubility in cubic ZrO2is 8.0 ± 0.2 mol% at 1400°C. Although phase partitioning appeared to initiate during heating, complete partitioning at 1400°C required ∼ 200 h. Large compositional variations (≤±1 mol% Gd2O3) were observed within tetragonal grains and from grain to grain during the first 50 h at 1400°C, whereas the composition of cubic grains produced during partitioning were relatively invariant. Experiments showed that this compositional variability was not present in material rapidly heated to 800°C, but was a result of partitioning. At 1400°C, growth of the tetragonal grains was very sluggish; it increased only to 3 μm after 500 h, whereas the number of larger cubic grains increased during this same period. The implications of these observations are related to the processing of rare‐earth‐stabilized ZrO2transformati

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1991.tb06844.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

A fiber which is partially pushed out of a surrounding matrix and subsequently pushed in the opposite direction exhibits a substantial decrease in sliding friction as it passes through its original position (its “origin”). This is manifest by a decrease in the load required to push the fiber. It is suggested that interfacial roughness causes this phenomenon and that the decrease in load (friction) is associated with the fiber seating back into its original position. The period of the drop has been correlated with the spatial extent of the interfacial surface roughness, and the magnitude of the drop (referred to hereafter as the seating drop) has been correlated with the amplitude of the interfacial roughness. Observation of the seating drop allows separation of the friction associated with interfacial irregularities from that resulting primarily from residual stresses at the interface. Implications for composite design and use are discussed. The effect of abrasion at the sliding interface is also addres

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1991.tb06845.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY