Analysis of tests on impact strength of concrete armor blocks

This paper summarizes a series of tests on the impact strength of large concrete breakwater cubes. A simple, design-oriented, analytical model was established on the basis of the continuum damage theory in order to interpret the data collected during a rather ambitious and expensive experimental program involving a large number of cubes of different sizes subjected to impacts of varying intensity. The suggested model involves only one additional material parameter related to the static strength of the concrete specimen in uniaxial compression. A rather surprising accuracy of this fairly crude model is further encouragement for the use of continuum damage mechanics for concrete.     

Experimental limit on spontaneous parametric up conversion

Abstract

We present a first experimental test of the existence of spontaneus parametric up conversion predicted in Marshall and co-workers [2000, J. mod. Optics, 47, 1273]. The measurement has been made using a ccd camera on the emission of a LiIO₃ crystal pumped by a 351 nm and/or a 789 nm laser. We obtain an upper limit of 160 times on the ratio between the intensity of spontaneous parametric up conversion and spontaneous parametric down conversion.     

Effects of alloying in the dilute limit on the quantum states of electrons in magnesium

The electron quantum interference phenomenon was used to determine the effects of substitutional alloying upon the quantum-state lifetime and band gapsE _g at the Fermi energy in single crystals of pure Mg. Vapor-grown alloys containing either Zn or Cd in concentrationsC0.3–15 ppm were studied. The magnetic field dependence of the interference oscillation amplitudes for these samples indicates reductions in and significant increases inE _g relative to pure Mg (impurity concentration 10^–8). Within experimental accuracy the observed quantum-state lifetime satisfies the relation ^–1=C, with 2.7×10¹⁰ sec^–1 per ppm of Cd and 2×10¹¹ sec^–1 per ppm of Zn. The band gap corresponding to Bragg reflection from the (0001) plane of the hcp structure (which in pure Mg arises solely from spin-orbit coupling) was found to increase by more than a factor of two upon the addition of only 10 ppm Cd to Mg. These results are discussed within the framework of the pseudopotential theory of alloying. It is shown that there are discrepancies of more than three orders of magnitude between the experimental and theoretical values forE _g and of about one order of magnitude for in these dilute-limit alloys.Work supported by the National Science Foundation.Submitted to the Department of Physics, the University of Chicago in partial fulfillment of the requirements for the degree of Doctor of Philosophy.Fannie and John Hertz Foundation Fellow.     

Experimental and analytical studies on the prediction of forming limit diagrams

Metal forming processes are widely used in industrial productions, automobile bodies, food industries, oil refineries, and liquid and gas transmission systems. Analyzing these processes is very important to reduce wastes and optimize the processes. Study of some main factors such as physical and mechanical properties of material and its formability, die geometry, die material, lubrication and pressing speed has been the topic of many research projects. In this paper, forming limit diagrams (FLDs) for LC and ULC steels and the effect of different parameters like the work-hardening exponent, n, and the plastic strain ratio, r, on these diagrams have been evaluated and simulated using ABAQUS/Standard. In this case, Hill’s quadratic anisotropy function is assumed to be the yield function and the Atkins criterion is used as the failure criterion.     

小量块国际比对及能力验证

按照国际比对组织机构提供的比对样品及技术指标,采用比较法比对测量原理,完成了国际间小量块比对任务.建立的测量不确定度分析模型,其扩展不确定度置信概率按国际间要求统一选取95%,包含因子选用2的原则,较以前国内扩展不确定度评定范围有所缩小,并增加了对测量环境和测量设备的技术要求.此次国际比对证明我们的检测数据全部有效、可信,其评定方法得到了APLAC组织的认可.     

Monte Carlo homogenized limit analysis model for randomly assembled blocks in-plane loaded

A simple rigid-plastic homogenization model for the limit analysis of masonry walls in-plane loaded and constituted by the random assemblage of blocks with variable dimensions is proposed. In the model, blocks constituting a masonry wall are supposed infinitely resistant with a Gaussian distribution of height and length, whereas joints are reduced to interfaces with frictional behavior and limited tensile and compressive strength. Block by block, a representative element of volume (REV) is considered, constituted by a central block interconnected with its neighbors by means of rigid-plastic interfaces. The model is characterized by a few material parameters, is numerically inexpensive and very stable. A sub-class of elementary deformation modes is a-priori chosen in the REV, mimicking typical failures due to joints cracking and crushing. Masonry strength domains are obtained equating the power dissipated in the heterogeneous model with the power dissipated by a fictitious homogeneous macroscopic plate. Due to the inexpensiveness of the approach proposed, Monte Carlo simulations can be repeated on the REV in order to have a stochastic estimation of in-plane masonry strength at different orientations of the bed joints with respect to external loads accounting for the geometrical statistical variability of blocks dimensions. Two cases are discussed, the former consisting on full stochastic REV assemblages (obtained considering a random variability of both blocks height an length) and the latter assuming the presence of a horizontal alignment along bed joints, i.e. allowing blocks height variability only row by row. The case of deterministic blocks height (quasi-periodic texture) can be obtained as a subclass of this latter case. Masonry homogenized failure surfaces are finally implemented in an upper bound FE limit analysis code for the analysis at collapse of entire walls in-plane loaded. Two cases of engineering practice, consisting on the prediction of the failure load of a deep beam and a shear wall arranged with random texture are critically discussed. In particular, homogenization results are compared with those provided by a heterogeneous approach. Good agreement is found both on the failure mechanism and on the distribution of the collapse load.     

Exciton-like trap states limit electron mobility in TiO2 nanotubes

Nanoparticle films have become a promising low-cost, high-surface-area electrode material for solar cells and solar fuel production. Compared to sintered nanoparticle films, oriented polycrystalline titania nanotubes offer the advantage of directed electron transport, and are expected to have higher electron mobility. However, macroscopic measurements have revealed their electron mobility to be as low as that of nanoparticle films. Here, we show, through time-resolved terahertz spectroscopy, that low mobility in polycrystalline TiO(2) nanotubes is not due to scattering from grain boundaries or disorder-induced localization as in other nanomaterials, but instead results from a single sharp resonance arising from exciton-like trap states. If the number of these states can be lowered, this could lead to improved electron transport in titania nanotubes and significantly better solar cell performance.     

Experimental bond tests on masonry panels strengthened by FRP

The results of an experimental campaign on bond between Glass Fiber Reinforced Polymer (GFRP) sheets and single clay brick or masonry panel is presented. Four different types of clay bricks (new and ancient) are considered, where the difference between bricks is not only due to their mechanical properties but also to their surface texture. Another focus point of the experimental campaign is the effect of mortar joints on the GFRP-masonry panel bond. Moreover, the effects of different surface preparations on the debonding load were investigated, concerning both bricks and masonry panels. A total number of 38 specimens was tested and results in terms of debonding force, strain along the GFRP and failure modes are here reported. The experimental results were also compared to design formula proposed by the new version of Italian Guidelines. Furthermore, in order to numerically describe the bond behaviour of the specimens tested, non-linear interface laws were calibrated starting from the debonding load and the measured strains along the GFRP for various loading levels.     

Fatigue limit and life evaluation formulae for compressive mean stress states

Considering the difference of stress concentration behaviour near micro-defects in materials, a unified fatigue limit evaluation formula has been developed, which can be applied to compressive mean stress states without the necessity of introducing additional material’s properties except for the modification parameter of mean stress. A generalised life evaluation formula has also been proposed and the dependence of fatigue life on mean stress can be simply expressed by the effect of fatigue limit corresponding to the mean stress. By considering the effect of fatigue limit corresponding to the compressive mean stress, the fatigue life can be evaluated by the same generalised formula as that developed for tensile mean stress state, without the necessity of carrying out additional S–N curve fatigue tests.     

Experimental comparison of two methods for the measurement of long gauge blocks

A comparison of two methods of measurement of long gauge blocks is performed. It is shown that the relative divergence of the measurement results obtained by a method involving counting of the interference bands between the centers of gravity of the achromatic bands and a method involving matching fractional parts of the orders of interference amounts to less than 10⁻⁸. __________ Translated from Izmeritel’naya Tekhnika, No. 7, pp. 20–23, July, 2007.     

Experimental study of transport in nanoscale planar MOSFETs near the ballistic limit

Using standard planar 22-nm-nMOS devices featuring a typical metalurgical length lower than 10 nm, we investigated the impact of nanoscale phenomena on device behavior. The data show that direct source-drain tunneling dominates the device leakage below 250 K and that carrier transport approaches the ballistic limit. The significant contribution of access resistance is revealed by low-temperature measurements below the superconducting transition of the cobalt disilicide contacts.     

Estimation of the endurance fatigue limit for structural steel in load increasing tests at low temperature

The endurance fatigue strength of structural steel S355 was investigated in fatigue tests according to the method of increasing stress amplitude. The so‐called ‘load increasing test’ is based on the direct correlation between the fatigue limit and the temperature changes caused by local plastic deformation ahead of the tip of a micro crack, which was initiated as a result of cyclic loading. In the present work the fatigue limit for testing temperatures 40°C and ?20°C was estimated not only from the temperature measurements but also from the electrical potential measurements. Further, the obtained results were validated in standard fatigue tests with constant stress amplitude and a very good agreement was found.     

Simulation of thermally stressed state and evaluation of the fire-resistance limit for a wall of “Besser” concrete blocks

We carry out a numerical investigation of the thermally stressed state and make a theoretical evaluation of the fire-resistance limit for a wall of vibrocompressed concrete blocks. We perform calculations on the basis of the method of finite elements. Different variants of thermal loading under ordinary fire conditions are considered. Conclusions are drawn concerning the possibility of using blocks for constructing three-layered walls. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 70, No. 3, pp. 480–486, May–June, 1997.     

Experimental tests on the shear behaviour of dowels connecting concrete slabs to stone masonry walls

An experimental investigation has been conducted on the behaviour of dowels used to connect concrete slabs to stone masonry walls in order to transfer horizontal shear forces. A technique for embedding the dowels in the stone block without injection of grouting material or resin has been developed. Special experimental equipment has been designed in order to allow the execution ofin situ load tests on representative ancient buildings. Monotonic loading tests have been carried out on eight specimens with the purpose of measuring both stone block displacement and dowel deformation     

Experimental techniques in physicomechanical tests on structural metals in molten alkali metals

Alkali metals, especially lithium, used as heat transfer media in power-generating plants have a high affinity to nitrogen and oxygen, and this may affect the results of any tests on metals of this kind. As a result, it is usually necessary to purify lithium and to carry out all the preparatory work in a spectrographically pure inert atmosphere. This article describes the design and principles of operation of various apparatus developed to provide means of filtering lithium, transferring it to ampuls, hollow specimens, containers, etc., and carrying out various analyses in spectrographically pure argon.     

Removal of ammonium from aqueous solutions with volcanic tuff

This paper presents kinetic and equilibrium data concerning ammonium ion uptake from aqueous solutions using Romanian volcanic tuff. The influence of contact time, pH, ammonium concentration, presence of other cations and anion species is discussed. Equilibrium isotherms adequately fit the Langmuir and Freundlich models. The results showed a contact time of 3h to be sufficient to reach equilibrium and pH of 7 to be the optimum value. Adsorption capacities of 19 mg NH(4)(+)/g were obtained in multicomponent solutions (containing NH(4)(+), Zn(2+), Cd(2+), Ca(2+), Na(2+)). The presence of Zn and Cd at low concentrations did not decrease the ammonium adsorption capacity. Comparison of Romanian volcanic tuff with synthetic zeolites used for ammonium removal (5A, 13X and ZSM-5) was carried out. The removal efficiciency of ammonium by volcanic tuff were similar to those of zeolites 5A and 13X at low initial ammonium concentration, and much higher than those of zeolite ZSM-5.     

Experimental study of damage propagation in Over-height Compact Tension tests

This paper describes an experimental investigation into progressive damage development in notched fibre-reinforced composites laminates. The Over-height Compact Tension (OCT) test captures the behaviour of laminates typical of large structures and permits the stable formation of a process zone ahead of the crack tip. This allows a study of the influence of sub-critical damage on progression of fibre failure. A range of lay-ups have been tested using dispersed and blocked plies in the thickness direction. The load vs. pin opening displacement (POD) curve is used to characterise the progressive failure of specimens. A number of interrupted tests were performed for each lay-up to capture the sub-critical damage process before the onset of fibre fracture. Results show that dispersed plies promote fibre failure and crack growth whilst blocked plies promote a larger amount of splitting and delamination which in turn causes a larger process zone and ultimately a tougher laminate.