An empirical model of the strength of a porous glass wool composite

The tensile strengths of porous glass wool composites have been determined by means of normal tensile tests and parting strength tests. The experimental results thus obtained were then used, with the aid of a computer, to develop a mathematical correlation between tensile strength and composite structural parameters. By experimental adaptation and by using different boundary conditions, the equation $\text{T = 1·36GH + √H + 0·15G}{}^3$ was developed where $\text{T = tensile strength}$, $\text{G = glass content}$ and $\text{H = 100 × resin/glass}$ ratio. This equation is valid over the entire density and resin content ranges examined, and the correlation between empirical results and values predicted by the model is excellent.In addition, our model has been developed in relation to variations of both fibre and resin contents, and the analytic solution has proved to be valid in relation to some structural changes, which suggests that the model also has physical significance.     

Photoelectrochemical study of the layered compound In23Pse3

The layered compound $\text{In}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{PSe}{}_3$ is studied by photoelectrochemical technique. Two modes of transition, indirect ～ 1.55 eV, and direct ～ 1.80 eV are evidenced. An estimation of the hole diffusion length is given through the use of Gärtner model ($\text{L}\text{? 4 μ}\text{m}$). The flat band positions of the junction $\text{In}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{PSe}{}_3\text{-}\text{electrolyte}$ at different pH values are determined in an electrochemical scale.     

Models for the effect of chemisorbed gases on the electrical resistance of metal films

Three hypotheses are considered for the proportionate change of resistance $\text{ΔR}\text{R}{}_1$ when a continuous metal film of resistance R₁ adsorbs gas: (a) a loss of metallic properties at the surface; (b) a change in the electron scattering parameter at the surface; and (c) a change in the electron concentration throughout the film. Two models of the film structure are used to compare the predictions of these hypothesis with our experimental data for the systems $\text{O}{}_2\text{Er}$, $\text{CO}\text{Er}$, $\text{CO}\text{Ti}$ and $\text{O}{}_2\text{Ti}$. The flat plate model accounts for neither R₁ nor $\text{ΔR}\text{R}{}_1$. A simple version of the columnar model accounts for $\text{ΔR}\text{R}{}_1$ by either (a) or (b) for the first three systems and by (c) for the fourth, but it does not explain all the properties of the clean films. The linear approximation given by Mola and Heras for the columnar model of Mayadas and Shatzkes accounts satisfactorily for R₁ and $\text{ΔR}\text{R}{}_1$ for $\text{O}{}_2\text{Er}$, $\text{CO}\text{Er}$ and $\text{CO}\text{Ti}$ by increases in the electron scattering coefficient at the grain boundaries. It does not account for $\text{ΔR}\text{R}{}_1$ with $\text{O}{}_2\text{Ti}$ because that system incorporates gas into the metal lattice.     

高架轨道梁结构特性对磁浮系统的动力影响

以德国Transrapid磁浮列车系统为基础,采用现有的磁浮车辆垂向模型,建立了有限元轨道梁模型、磁浮车轨垂向耦合系统模型及其振动微分方程。在此基础上,针对德国在上海的磁浮项目,主要就轨道梁的型式(简支和连续)、支承刚度及轨面不平顺波长对磁浮车辆-轨道耦合系统动力响应的影响等进行了分析。     

A 3-D fracture mechanics approach to the strength of composite materials

The first ply failure in composite laminates are studied by 3-D fracture mechanic approach. The fracture model is based on a crack embedded in one of the inner layers. Numerical results for the case of “angle ply” laminates are based on a general 3-D finite difference program.Stress intensity factors and fracture energy are evaluated by the $\text{J-}\text{integral}$ 2-D and 3-D methods as well as by the stresses and energy balance. It was found that the $\text{J(2-}\text{D}\text{)}$ method can be applied to 3-D problems while the $\text{J(3-}\text{D}\text{)}$ method is not suitable for the numerical computation.The influence of geometrical properties of the crack and the layers on the various stress intensity factors is presented and discussed. Change in failure mechanism of the weakest ply was proved by experiments to fit with numerical results. It was found that the weakest layer is strengthened by the others, a fact which has been verified experimentally and hasn't been explained by other approaches.     

A study of crack closure in fatigue

Crack closure phenomenon in fatigue was studied by using a Ti-6Al-4V titanium alloy. The occurrence of crack closure was directly measured by an electrical potential method, and indirectly by load-strain measurement. The experimental results showed that the onset of crack closure depends on both the stress ratio, $\text{R}$, and the maximum stress intensity factor, $\text{K}{}_{\max }$. Crack closure was not observed for stress ratio, $\text{R}$, greater than 0.3 in this alloy.A two-dimensional elastic model was used to explain the behavior of the recorded load-strain curves. Closure force was estimated by using this model. Based on the estimated closure force, the crack opening displacement was calculated. This result showed that onset of crack closure detected by electrical-potential measurement and crack-opening-displacement measurement is the same.The implications of crack closure on fatigue crack are considered. The experimental results show that crack closure cannot fully account for the effect of stress ratio, $\text{R}$, on crack growth, and that it cannot be regarded as the sole cause for delay.     

The effects of load ratio on environmentally assisted fatigue crack growth

A modification to the model of Weir et al. for surface reaction and transport controlled fatigue crack growth has been developed to explicitly account for the effect of load ratio on environmentally assisted fatigue crack growth. Load ratio was found to affect principally gas transport to the crack tip, and therefore affected only transport controlled crack growth response. Experimental verification of the modified model was made by studying the room temperature fatigue crack growth responses at different load ratios for a 2219-T851 aluminum alloy exposed to water vapor.The results show that the effects of load ratio can be attributed to two different sources—one relating to its effect on local deformation at the crack tip and is reflected through the mechanical component, (d$\text{a}$/d$\text{N}$)₀ and the other on its role in modifying environmental effect and is manifested through the corrosion fatigue component, $\text{(da/dN)}{}_{\mathrm{cf}}$ Furthermore, the results show that the saturation value of corrosion fatigue component, $\text{(da/dN)}{}_{\mathrm{cf,s}}$, is essentially independent of $\text{R}$, and that the exposure needed to produce “saturation response” ($\text{P}{}_0\text{/2f)}{}_{\mathrm{s}}$, as a function of load ratio can be predicted from the modified model. The modified model, therefore, allows one to predict the corrosion fatigue crack growth response for any load ratio on the basis of measurements made at a single load ratio, provided that the values of ($\text{da/dN}$), are known.     

The crack tip opening angle (CTOA) of the plane stress moving crack

Recently, Crack Tip Opening Angle (CTOA) was proposed by C.F. Shih et al. to describe the instability criterion of ductile crack propagation during plane strain (flat crack) conditions, and was derived by J. R. Rice analytically by means of the slip line field theory and the incremental theory of plasticity. CTOA appears to be applicable in (some or most) cases, but does not accurately describe the plane stress growing crack (slant crack).Unstable ductile crack propagation of the plane stress crack is widely studied for the safe design of highly pressurized gas pipelines. The impact absorption energy of the Charpy test is well correlated to the fracture arresting properties of the structures, but the mechanics of the fracture are not yet well established.In this paper, CTOA of the plane stress growing crack is derived from the plane stress plasticity of perfectly plastic materials by Sokolovsky's approach. Our proposed modification of CTOA expressed as follows: $\text{CTOA}\text{= (α/δ}{}_0\text{)(}\text{d}\text{J/}\text{d}\text{l) + β(δ}{}_0\text{/E)}\text{ln}\text{(eR/r)}$ where $\text{β = 1.40}$ under the plane stress conditions.CTOA in the Dugdale model is also defined and compared with the results of laboratory test. The results show that $\text{α = 0.5}$, and $\text{β = 1.27}$ for plane stress crack growth. These analyses give similar results to those obtained by Rice et al. for CTOA under plane strain conditions, that is, $\text{α = 0.65}$ from the experimental results and $\text{β = 5.08}$ from the slip line theory.The CTOA obtained for plane stress ductile crack growth is applied to the wide plate tensile crack growth test. The results of the present analysis coincide well with those of the plane stress finite element method (FEM) computed by T. Kanazawa et al. The phenomena of plane stress ductile crack propagation are also explained by the CTOA criterion under plane stress conditions.     

Nucleation and growth of GeTe films on KCl and SnTe substrates

The nucleation and growth of GeTe films on KCl or SnTe substrates is found to follow the same mechanism on both substrates. Nucleation occurs through the formation of three-dimensional nuclei of almost equal sizes, bounded by edges along the [110] and [1$\text{1}$0] directions. The growth continues through the lateral extension of the nuclei. The overgrowth layer is anisotropic strainwise, due to the difference in lattice misfit along [110] and [1$\text{1}$0]. This angular misfit is responsible for an increase in the equilibrium energy by 5%. The excess strain is accommodated by misfit dislocations forming a network parallel to the [110] and [1$\text{1}$0] directions, the dislocations being of the edge orientation with Burger's vector equal to $\text{1}\text{2}\text{a<110>}$ and with a different linear density in the two directions. Annealing the system GeTe/SnTe results in a substantial decrease in the density of dislocations due to cross diffusion of Ge and Sn respectively, which forces the dislocations to climb to the surface.     

Analysis of the steady motions of complex rotating systems

This paper develops a practical computational framework for analyzing the steady motions of complex rotating systems. Ignorable coordinates corresponding to the translational or rotational invariances of a closed system can always be used in order that the effective potential functional $\text{W}$ for the relative motion depends only upon the relative configuration. However, the stationary values (steady motions) of $\text{W}$ can be determined by an essentially unconstrained calculational procedure even when $\text{W}$ is expressed most simply with Cartesian coordinates. It is shown that the angular velocity of any fixed rotating configuration (FRC) must paralled a principal axis when some mild assumptions about the nonrigidity of the system are fulfilled. This property implies that every distinct FRC corresponds to a stationary value of $\text{W}$. The discussion includes examples of $\text{N-}\text{body}$ problems and a spin-stabilized kilometer-wave orbiting telescope. Random or systematic searching and a quasi-Newton algorithm are used to compute minima of $\text{W}$.     

Crack closure studies under constant amplitude loading

Crack closure experiments were performed on 6063-T6 Al-alloy using a COD-gauge for various load ranges and stress ratios. Experimental results show that for a given stress ratio, $\text{R}$, the crack closure load goes on decreasing as crack length increases (or $\text{K}{}_{\max }$ increases) and reaches even below minimum load level at higher values of stress ratios. On the basis of these experimental results, a model for effective stress intensity range ratio $\text{U}$, which is found to be a function of stress ratio $\text{R}$ and $\text{k}{}_{\max }$, is developed.     

Comportement du titane dans les melanges hydrogene-vapeur d'eau au-dessus de 800°C

The oxidation scale obtained by oxidizing titanium foils in water vapour above 800°C is mainly composed of porous rutile. As the reaction proceeds, a solid solution of Tiα precipitates leading to an intermediate suboxide scale of variable composition TiO_x. In connection with the microstructural study, it can be concluded that the rutile scale grows at the inner interface $\text{TiO}{}_2\text{TiO}{}_{\mathrm{x}}$ thus excluding the possibility of a rate-determining diffusion step.     

On the use of the theory of v-fluids for the construction of models of turbulence

The class of $\text{v-}\text{fluids}$, defined by Proudman[1] to be non-Newtonian fluids all of whose properties depend on a single dimensional constant whose dimensions are those of viscosity, is examined further as a source of possible models of turbulence at high Reynolds number. It is found that, while the general definition is valuable, certain aspects of Proudman's associated concept of a regular $\text{v-}\text{fluids}$ have a number of features that bring its value as a source of models of inhomogeneous turbulence into question. The nature of these problems suggests a suitable modification to the definition of a regular $\text{v-}\text{fluids}$. A number of constraints on the form and solution of the equations of a model of turbulence are proposed with the intention of improving the generality of models of a given degree of complexity, and their justification and significance discussed. In the light of these proposals the simplest modified regular $\text{v-}\text{fluids}$ that can be used to model homogeneous turbulence at infinite Reynolds number is described, and it is seen to include all the most desirable features of earlier models of this type, and is in addition capable of extension in a natural way to describe inhomogeneous turbulence.     

Sur la phase CsVCl3: Etude cristallographique et magnetique

The crystal structure of CsVCl₃ has been determined by means of a Patterson synthesis and refined by full-matrix least-squares to a residual R = 0.06. The space group is $\text{P}\text{6}{}_3\text{mmc}$ with $\text{a}\text{= 7.228 (3)}\text{A}\text{?}$ and $\text{c}\text{= 6.030 (3)}\text{A}\text{?}$. The structure of CsVCl₃ belongs to the CsNiCl₃ type. The magnetic properties have been interpreted on the basis of a $\text{S}\text{=}\text{3}\text{2}$ model for Heisenberg one-dimensional interactions. The strong antifer-romagnetic intrachain V-V interactions ($\text{J}\text{k}\text{= ?115}\text{K}$) seem to result from direct t_2g - t_2g coupling and from 90° correlation superexchange coupling using the 3s chlorine orbital.     

Electron diffraction evidence of domain twinning in graphite-bromine single crystals

The in-plane electron diffraction pattern from single crystals of graphite-bromine intercalation compound has been interpreted in terms of a three-fold twinned monoclinic unit cell having in-plane lattice translations $\text{a}\text{=8.87}\text{A}\text{?}$, $\text{b}\text{=4.26}\text{A}\text{?}$, and the angle between them γ=103.9°, commensurate with the graphite lattice. The resulting twinned-domain model has been verified by observation of electron diffraction from individual domains.     

Composes definis dans le systeme AgInSe structure cristalline de □2AgIn5Se8

The usual quasibinary representation obeying Parthe's laws seems too restrictive in the case of the Ag-In-Se system. According to our D.T.A. and X ray analyses, a ternary system representation has to be adopted. The crystal structure of the defect compound AgIn₅Se₈ has been refined to an agreement factor R (F) = 0.0315 in the P42m space group with unit cell parameters: $\text{a}\text{= 5.7934 (4)}\text{A}\text{?}$, $\text{c}\text{= 11.6223 (2)}\text{A}\text{?}$ and $\text{c}\text{a}\text{= 2.0061 ± 0.0003}$.     

Estimation of fatigue crack propagation life of steel plates and of structural member model of ship hull

The authors carried out experimental and analytical investigation for the purpose of finding out a method of estimating the fatigue crack propagation life of large flat steel plate and of ship hull structure model quantitatively.We theoretically derived a formula indicating that fatigue crack propagation rate is in proportion to the $\text{m-}\text{th}$ power of the plastic displacement of the tip of a crack based on a B.C.S. dislocation model. The crack propagation rate is proportional to $\text{2m-}\text{th}$ power of stress intensity factor in the case stress is small.We proved experimentally that this relation holds generally, from fatigue crack propagation tests for flat plates with a center notch (mild steel, high tensile strength steel), large flat plate with an edge notch and ship hull corner model (mild steel), and from the $\text{K-}\text{value}$ calculation by the finite element method for these specimens. The fatigue crack propagation life is obtained by integrating the reciprocal number of crack propagation rate from the initial crack length to the final crack length. The life calculated agreed well with the one observed. But for the two stress level test, the life calculated was smaller than the experimental value due to slackened progress of crack. We also stated the general characteristics of the rate curve.     

Crack closure in 2219-T851 aluminum alloy

The effects of specimen thickness, stress ratio ($\text{R}$) and maximum stress intensity factor ($\text{K}{}_{\max }$) on crack closure (or opening) were studied using a 2219-T851 aluminum alloy. The crack length and the occurrence of crack closure were measured by an electrical potential method. The experimental work was carried out within the framework of linear-elastic fracture mechanics.The experimental results show that the onset of crack closure (or opening) dependes on $\text{R, K}{}_{\mathrm{<mtext>max</mtext>}}$), and specimen thickness. In terms of the “effective stress intensity range ratio” ($\text{U}$), as defined by Elber, the results show that $\text{U}$ tends to increase for increasing $\text{R}$, decrease for increasing $\text{K}{}_{\max }$, and decrease with increasing specimen thickness. From these trends, it is shown that the “effective stress intensity range” ($\text{ΔK}{}_{\mathrm{<mtext>eff</mtext>}}$) does not always increase with increasing stress intensity range ($\text{ΔK}$).The experimental results show that crack closure cannot fully account for the effects of stress ratio, specimen thickness and $\text{K}{}_{\max }$ on fatigue crack growth. The use of $\text{ΔK}{}_{\mathrm{<mtext>eff</mtext>}}$ as a parameter for characterizing the mechanical driving force for fatigue crack growth is questioned.