New Set Of Experimental Results Research Articles

Confinement of masonry columns with FRCM: A new confined strength formulation and experimental validation

In this work, a wide experimental dataset about the axial behavior of masonry columns confined with Fabric Reinforced Cementitious Matrix (FRCM) jackets (also refered to as TRM - Textile Reinforced Mortar or TRCC - Textile Reinforced Cementitious Composites), that contains the results from 226 confined specimens, was collected. Data were critically analyzed with the aim of identifying the influence of the most important parameters considered within the dataset (i.e., fibers type and number of layers, masonry type and unconfined strength, mortar type and mechanical strength, the effective lateral pressure, etc.). Further, a review of the main models proposed in different Codes and in literature was carried out, which were then applied to the dataset, highlighting some discrepancies in their predictions. Thus, a new formulation for the confined strength of masonry columns was proposed, aiming to consider also some other influencing variables such as the compressive strength of the masonry blocks and that of the mortar joint. Lastly, the validity of the proposal was verified on a new set of experimental results, which were obtained by the authors testing three unconfined and confined clay brick masonry columns. Specimens were subject to monotonic axial loading under displacement control until failure, and stress and strains were monitored continuously during the test. The jacketing system was realized with one layer of glass-based FRCM (GFRCM).

Oxidation kinetics of methyl crotonate: A comprehensive modeling and experimental study

The current study explores the combustion behavior of methyl crotonate (CH3CH=CHC(=O)OCH3), which is a short ester representative of large unsaturated methyl esters. Starting with a detailed kinetic model for methyl butanoate (CH3CH2CH2C(=O)OCH3) oxidation, revisions are introduced to the C0-C4 chemistry based on the recent Aramco mechanism 3.0. The resulting mechanism is combined with a short model for methyl crotonate, derived from a suitable reference mechanism. Several new classes of reactions are included and the rate constants of the existing reactions are revised based on various theoretical studies and analogies to reactions of similar species. Furthermore, the low-temperature chemistry of methyl crotonate has been implemented in the current study to extend the validity of the mechanism to lower temperatures. The resulting methyl crotonate combustion mechanism has been comprehensively validated using various experiments in the literature. In addition, experiments are performed using a heat flux burner at atmospheric conditions to measure the laminar burning velocities of methyl crotonate at different unburnt mixture temperatures (318, 338, and 358 K). The mechanism is found to reproduce the experimental data for high-temperature combustion of methyl crotonate satisfactorily. The mechanism is also found to predict the low-temperature ignition delays accurately. Sensitivity and path flux analysis are performed to delineate the importance of the different reaction classes in methyl crotonate chemistry. The current study presents a comprehensive mechanism for methyl crotonate combustion, along with a new set of experimental results complementing the existing experimental database in the literature.

An experimental methodology to analyse the structural behaviour of FDM parts with variable process parameters

Purpose This paper aims to investigate the structural behaviour of polylactic acid (PLA) parts fabricated by fused deposition modelling (FDM) to support the development of analytical and numerical models to predict the structural performance of FDM components and categories of similar additive manufactured parts. Design/methodology/approach A new methodology based on uniaxial tensile tests of filaments and FDM specimens, infill measurement and normalization of the results is proposed and implemented. A total of 396 specimens made of PLA were evaluated by using variable process parameters. Findings The infill and the build orientation have a large influence on the elastic modulus and ultimate tensile stress, whereas the layer thickness and the infill pattern have a low influence on these properties. The elongation at break is not influenced by the process parameters except by the build orientation. Furthermore, the infill values measured on the test specimens differ from the nominal values provided by the system. Research limitations/implications The analysis of the structural properties of FDM samples is limited to uniaxial loading conditions. Practical implications The obtained results are valuable for the structural analysis and numerical simulation of FDM components and for potential studies using machine learning techniques to predict the structural response of FDM parts. Originality/value A new experimental methodology that considers the measurement of the real infill percentage and the normalization of the results for inter-comparison with other studies is proposed. Moreover, a new set of experimental results of FDM-PLA parts is presented and extends the existing results in the literature.

A kinetic free mathematical model for the prediction of the KSt reduction with the particle size increase

Even in recent years, several major industrial accidents have involved dust explosions, clearly showing the necessity of mitigating the hazard related to the presence of flammable dusts. In this respect, the KSt is an experimental parameter used to design the deflagration vents aimed to protect industrial devices and silos by internal dust explosions. Even if it is measured using a standard 20 L sphere test, its determination is quite expensive and time consuming. This problem is even more severe when a target dust is processed into a plant, giving rise to different average diameters; in this case, an experimental investigation of all the different particle sizes would be advisable but very expensive. In this context, the main aim of the present paper has been to develop a kinetic-free model able to predict the KSt decrease with the mean particle diameter increase for organic dusts explosions. Particularly, an order of magnitude analysis of the characteristic times of the involved phenomena has showed that, in the KSt measurements, the rate determining step is usually associated to heat transfer phenomena. This evidence leads to the possibility of exploring a predictive approach for the KSt determination which does not require any chemical kinetic information, the most difficult to be obtained. Therefore, once the value of KSt has been measured through a standard 20 L test for a given mean particle diameter (the smallest possible), the approach proposed in this work allows for predicting the KSt values for the same dust at higher average particle sizes. Such an approach has been validated by comparison with several literature data as well as with a new set of experimental results.

The Solubilities of Gibbsite and Bayerite Below 100 °C in Near Neutral to Basic Solutions

The purpose of this paper is to present a new set of experimental results on the solubility of crystalline bayerite and gibbsite in caustic NaNO3 media (I m = 0.1–5 mol·kg−1) from 303 to 363 K, reflecting conditions in the high-level nuclear waste repository at the Hanford site in the USA. The resulting molal solubility constants, K m,s,4, were combined with some previous literature values and modeled using the SIT and Pitzer ion-interaction models in order to provide a coherent internally-consistent set of data quantifying the thermodynamic dissolution behavior of these aluminum phases. The two models led to similar thermodynamic quantities compatible with those from previous studies for bayerite and gibbsite, and in both cases the differences in the ion-interaction parameters could be taken as being temperature independent.

Key-Hole Notches in Isostatic Graphite: A Review of Some Recent Data

Fracture of the breakable isostatic graphite is concerned using the experimental and theoretically, the plates containing nicks holes key subject to varying degrees of mixed task. The main purpose of this work is a double one. In the first place, in order to offer a new set of experimental results on fracture of samples of graphite scored, with different values of the load mixed and radii notch and which may be helpful for researchers, as it enlarges the very limited data available; and secondly, to provide a criterion fracture of the polycrystalline graphite under the conditions mentioned above. The main purpose of this work is to offer a new set of experimental results (70 new data) on the fracture of the samples of the loose graphite of key holes, the different values of mixed loading, the tilt angle and radii notch and which may be of help as widens the very limited data available. By using the value of the average density of the stem of energy in a well defined, a criterion of fracture of the polycrystalline graphite under the conditions referred to above, it is proposed to predict the static resistance of the samples taken into account. The third part of the work deals with the analysis of the direction of initiation of fracture and spread of the crack in the early. The average value of the stem density of energy in a well defined is used to predict the static resistance of the samples taken into account. Good agreement is found between the experimental data for the tasks critical failure and the theoretical predictions based on average constant strain density of energy on the volume of the material.

Tensile Fracture Analysis of Key-Hole Notches by Means of the Strain Energy Density

The aim of the present research is twofold. Firstly, to provide a new set of experimental results regarding tensile brittle fracture in key-hole notches and secondly, to check the suitability of the local strain energy density (SED) criterion in predicting the test results. For this purpose, 21 fracture tests were conducted at room temperature on a new version of the well-known Brazilian disk specimen containing a central dumbbell-shaped slit with two key-ends (Key-BD specimen) made of PMMA. The experimentally obtained fracture loads were theoretically predicted for different notch radii by means of the local SED averaged over a specified control volume which embraces the notch edge. It was shown that the experimental results could be well predicted by means of the SED criterion.

Thermal conductivity of heterogeneous LWR MOX fuels

It is generally observed that the thermal conductivity of LWR MOX fuel is lower than that of pure UO2. For MOX, the degradation is usually only interpreted as an effect of the substitution of U atoms by Pu. This hypothesis is however in contradiction with the observations of Duriez and Philiponneau showing that the thermal conductivity of MOX is independent of the Pu content in the ranges 3–15 and 15–30wt.% PuO2 respectively. Attributing this degradation to Pu only implies that stoichiometric heterogeneous MOX can be obtained, while we show that any heterogeneity in the plutonium distribution in the sample introduces a variation in the local stoichiometry which in turn has a strong impact on the thermal conductivity. A model quantifying this effect is obtained and a new set of experimental results for homogeneous and heterogeneous MOX fuels is presented and used to validate the proposed model. In irradiated fuels, this effect is predicted to disappear early during irradiation.

Fracture analysis of functionally graded materials with U‐ and V‐notches under mode I loading using the averaged strain‐energy density criterion

ABSTRACTOne of the most powerful criteria to predict the critical fracture load in plates with notches is the strain‐energy density averaged over a well‐defined control volume ahead of the notch tip. Although the averaged strain‐energy density (ASED) criterion has been proposed for homogeneous materials, it has been shown in this paper that this criterion can also be applied for non‐homogeneous materials, especially for functionally graded materials (FGMs). A numerical method has been used to evaluate the control volume boundary, the averaged strain‐energy density over the control volume, and also the critical fracture load in FGMs under mode I loading. A new set of experimental results on fracture of blunt V‐notched samples made of austenitic–martensitic functionally graded steel under mode I loading have been provided.

TelOpTrak: Heuristics-enhanced Indoor Location Tracking for Tele-operated Robots

With most tele-operated robots the operator's only feedback is the view from an onboard camera. Live video lets the operator observe the robot's immediate surroundings but does not establish the orientation or whereabouts of the robot in its environment. An additional plot of the robot's trajectory would be helpful for the operator and is sometimes provided, based on GPS. However, indoors where GPS is unavailable, tracking has to rely on dead-reckoning, which is too inaccurate to be useful. Our proposed TelOpTrak method corrects dead-reckoning errors even when only odometry and a low-cost (and thus, high-drift) MEMS-class gyro are available on the robot. TelOpTrak corrects gyro drift by exploiting the structured nature of most buildings, but without having to directly sense building features. This paper explains the TelOpTrak method and provides comprehensive experimental results.Earlier versions of this paper (Borenstein et al., 2010a), (Borenstein et al., 2010b) were presented at two conferences. The main difference between the earlier conference papers and the present manuscript is that the latter is more comprehensive, more up-to-date, and it presents an entirely new set of experimental results, including results of a live demonstration at the 2010 Robotics Rodeo event at Ft. Benning, USA.

Mixed mode brittle fracture of sharp and blunt V-notches in polycrystalline graphite

Brittle fracture of polycrystalline graphite is studied experimentally and theoretically using Brazilian disk specimens containing sharp and rounded-tip V-notches subjected to different degrees of loading mixity, ranging from pure mode I to pure mode II. The main purpose is twofold. First, to provide a new set of experimental results on fracture of V-notched graphite samples, with different values of loading mixities, V-notch angles and notch radii, which may be helpful for researchers because enlarges the very scarce available data; and second, to provide a fracture criterion for polycrystalline graphite under the above-mentioned conditions. The averaged value of the strain energy density over a well-defined volume is used to predict the static strength of the considered specimens. Good agreement is found between the experimentally obtained fracture loads and the theoretical predictions based on the constancy of the mean strain energy density over the material volume.

Fracture assessment of U-notches under three point bending by means of local energy density

The main purpose of the paper is twofold. First, to provide a new set of experimental results on fracture of U-notched samples, made of two different materials; second, to apply a fracture criterion based on the strain energy density (SED) averaged over a control volume to assess the fracture load of blunt-notched components under three point bending. Two different materials are considered in the tests: a composite material (Al–15%SiC) tested at room temperature and a steel with a ferritic–pearlitic structure tested at −40 °C. All samples are weakened by U-notches characterized by different values of notch root radius and notch depth. The theoretical loads to failure as determined according to the SED criterion are compared with the experimental data from more than 40 static tests and with a SED-based scatter band recently reported in the literature for a number of materials exhibiting a brittle behaviour under static loads.

Modeling of the oxidation of methyl esters—Validation for methyl hexanoate, methyl heptanoate, and methyl decanoate in a jet-stirred reactor

The modeling of the oxidation of methyl esters was investigated and the specific chemistry, which is due to the presence of the ester group in this class of molecules, is described. New reactions and rate parameters were defined and included in the software EXGAS for the automatic generation of kinetic mechanisms. Models generated with EXGAS were successfully validated against data from the literature (oxidation of methyl hexanoate and methyl heptanoate in a jet-stirred reactor) and a new set of experimental results for methyl decanoate. The oxidation of this last species was investigated in a jet-stirred reactor at temperatures from 500 to 1100 K, including the negative temperature coefficient region, under stoichiometric conditions, at a pressure of 1.06 bar and for a residence time of 1.5 s: more than 30 reaction products, including olefins, unsaturated esters, and cyclic ethers, were quantified and successfully simulated. Flow rate analysis showed that reactions pathways for the oxidation of methyl esters in the low-temperature range are similar to that of alkanes.

On the origin of the catalytic activity of gold nanoparticles for low-temperature CO oxidation

It is suggested that there may be several effects contributing to the special catalytic properties of supported nanosized gold particles, and that it is useful to order them in a hierarchy. The most important effect is related to the availability of many low-coordinated gold atoms on the small particles. Effects related to the interaction with the support may also contribute, but to a considerably smaller extent. We base the analysis on a new set of experimental results comparing the CO oxidation rates over gold supported on different reducible and nonreducible oxides, on an analysis of a large number of published activity data, and on an analysis of density-functional calculations of the effect of metal coordination numbers in comparison to the role of charge transfer, layer thickness, and interactions with the support.

The acoustic impedance of a circular orifice in grazing mean flow: comparison with theory.

It is well known that the presence of a grazing mean flow affects the acoustic impedance of an aperture, but the detailed nature and understanding of the influence is still unknown. In this paper, results from a recent theoretical analysis of the problem are compared with a new set of experimental results. The purpose is twofold. First, the experimental results are used to validate the theory. It is found that the theory predicts the resistance quite well, but not the reactance. Second, the theory is used to try and give some physical understanding to the experimental results. In particular, some scaling laws are confirmed, and it is also shown that measured negative resistance values are to be expected. They are not erroneous, as previously thought. Former sets of experimental data for this problem are notable for the amount of variation that they display. Thus, both the theory and the new experimental results are also compared with those earlier detailed results that most closely conform to the conditions assumed here, namely fully developed turbulent pipe flow of low Mach number past circular orifices. The main field of application is in flow ducts, in particular, flow through perforated tubes in exhaust mufflers.

Interpretation of fiber fragmentation in carbon/epoxy single fiber composites: Possible fiber pre‐tension effects

AbstractThe fiber straightening pre‐tension applied during the sample preparation of single fiber composites is suggested here to significantly affect the number of fragments as well as the value of the Kelly‐Tyson interface shear strength obtained from single filament composite tests. This implies that fragmentation tests performed under seemingly identical conditions, but in which the fiber pre‐tension is not accurately controlled during sample preparation, might yield widely differing experimental results. We present and discuss a new set of experimental results dealing with fiber pre‐tension effects in carbon/epoxy single fiber composites.

Chemical Trends in the Electromodulated Infrared Vibrational Spectroscopy of Various Silicon/Electrolyte Interfaces

As part of a continuing effort on the in situ characterization of semiconductor/electrolyte interfaces, we present here a further new set of experimental results on the electromodulated infrared (1.1–5 μm) vibrational spectroscopy of various n‐Si/electrolyte interfaces. The origin, shapes, and positions of the various superimposed vibrational peaks that were earlier observed at the Si/acetonitrile interface (Si‒H, C≡N, and O‒H region) have been clarified using various solvents, anions, and cations. The superposition of the peaks from oxidized Si‒H and C≡N (in acetonitrile electrolyte) near 4.4 μm is clearly resolved by comparison with, e.g., nitromethane solvent. Regarding the O‒H spectrum, comparative experiments with ethylenediamine, tetrahydrofuran, nitromethane, and acetonitrile solvents, tetrabutylammonium perchlorate, tetrafluoroborate, bromide, and chloride solutes, give evidence that three components are involved: (i) adsorbed water (near 3 μm) which appears first upon interface aging, (ii) isolated Si‒O‒H (narrow feature near 2.7 μm), and (iii) hydrogen‐bonded Si‒O‒H (which shifts considerably depending upon the electrolyte). A new central C‒H peak appears at 3.42 μm on gold‐coated surfaces (coverage ∼1 monolayer), in acetonitrile; this can be associated with the interaction of the molecules with the gold‐coated surface. Two essential conclusions of the paper are the following: (i) from an analysis of the phase lag (upon electromodulation) of the surface‐state absorption and of the O‒H vibrational peaks, it is inferred that the surface states lie preferentially at locations on the surface where the O‒H bonds are in the form of Si‒O‒H groups rather than adsorbed water; (ii) all the experiments indicate that the adsorbed can stand for hours on the silicon surface before oxidation takes place.