Large Scatter Of Experimental Data Research Articles

The Rehbinder effect in tests of superalloys in contact with molten salts

The results of the Rehbinder effect manifestation during testing of superalloys in contact with corrosive media containing Na2SO4 + NaCl are discussed. We present the experimental study of the effect of salts containing chlorine and sulfur on the mechanical properties and long-term strength of single crystal and powder nickel-based superalloys at high temperatures. The practical value of the work is associated with the possible operation of gas turbine parts in conditions of ingress of the particles containing chlorine, sulfur and sodium into the flow path. A simplified (compared to a previously used) procedure of testing wrought alloys for long-term strength in molten salts is developed. A comparative study of the mechanical properties and long-term strength of a single crystal superalloy in the initial state (previously damaged by corrosion of different duration) and being in contact with salts during testing is carried out. Due to the large scatter of experimental data, the method of lower envelopes has been proposed and implemented to determine the guaranteed values of the long-term strength. It is shown that the guaranteed values of the long-term strength at different temperatures and test durations can decrease by 2.5 – 5.0 times in the presence of salts. Metallographic studies of the nature of damage and destruction of samples are carried out. The revealed decrease in the long-term strength of heat-resistant alloys in contact with salts is interpreted as the Rehbinder effect and not as a manifestation of the effect of stress corrosion cracking. A methodology for using the obtained test results with a duration of up to several thousand hours in highly aggressive environments is proposed to predict the long-term strength in relation to long-term operation (tens of thousands of hours) under conditions of relatively low salt loads.

The critical lower radius limit approach for laminar flame speed measurement from spherically expanding stretched flames

Spherically expanding flames are severely affected by flame stretch in the early stage of combustion and therefore stretch models are of great importance in determining the uncertainty of experimental laminar flame speeds (SL) and burned gas Markstein lengths (Lb). In order to prevent the existing large scatter in experimental data of these two fundamental flame parameters, the effect of the lower radius limit for the flame speed calculation on extrapolation results of the stretch models was investigated through spherically expanding flames under constant pressure. Methane, hydrogen, propane, and iso-octane fuels were tested to account for both hydrocarbon and non-hydrocarbon fuels with different evolutions in the burned gas Markstein length when equivalence ratio is increased. Results show that there is a critical lower radius limit (RL,critical), where all laminar flame speed and burned gas Markstein length values obtained by the extrapolation of the stretch models converge to the same laminar flame speed and burned gas Markstein length. The value of the critical lower radius limit strongly depends on the burned gas Markstein number (Mab) and this dependency can be shown with |Mab|=0.8424*RL,critical for fuel/oxidizer mixtures with −0.48 mm ≤ Lb ≤ 1.23 mm (or, −0.62 ≤ Mab ≤ 2.60). Finally, laminar flame speeds and burned gas Markstein lengths of methane, hydrogen, propane, and iso-octane flames that were corrected according to the critical lower radius limit approach proposed in the present study were compared to previously published experimental results.

Description of the thermodynamic properties of pure gold in the solid and liquid states from 0 K

Thermodynamic data for pure gold were critically assessed using an extended Einstein model from 0 K for the crystalline FCC_A1 phase and a two state model for the liquid phase. During the assessment, careful critical evaluation of the experimental data on thermodynamic properties of solid (FCC_A1) and liquid phases was carried out. Due to the fact that there is a large scatter in the experimental data for crystalline gold in the temperature range between 200 K and the melting point, we carried out additional ab initio calculations of the thermodynamic properties. In order to fulfil the need for a precise evaluation of So298.15 we needed to use an additional technique using multiple Einstein functions, which allows the experimental heat capacity and enthalpy data for the solid phase to be approximated accurately from 0 K up to the melting point. It was found during the data analysis that there is a large scatter in experimental data for the enthalpy of fusion and the liquid phase.

Strength and rigidity of the masonry fragment in a fuzzy setting

The strength and stiffness of masonry depend on various factors, such as the properties of the brick and mortar, their specific volume, relative position and quality of adhesive bonds. A high degree of uncertainty of these factors and a large scatter of experimental data in the testing of bricks and mortar are the important features of the masonry. In this paper, we present a mathematical model that allows us to determine the averaged characteristics of masonry based on the mechanical properties of substructural materials and their specific volume content in a fuzzy setting. All input parameters allowing to obtain fuzzy estimates of stresses and deformations of a brickwork fragment are determined by membership functions. For a representative volume of masonry, dependencies are obtained that allow to determine the level of destructive loads and the nature of destruction.

CFD & Safety Factors

This article presents a research that demonstrates the need for experimental validation of computational fluid dynamics (CFD) models for complex processes, such as blending. An additional result of the study is that it provided researchers a better understanding of how to use CFD models in general. The principle for blending is the same for all blender-pump designs: the business end of a centrifugal pump will be submerged in the salt solutions in the tank. Lab researchers found that, although CFD provided good estimates of an average blending time, experimental blending times varied significantly from the average. The issue of experimental uncertainty is inherent in CFD modeling as well as in many empirical equations used for modeling and design methods. In order to bring all of this research together, the process variables investigated were the fluid velocities in the tanks and the times required to blend the fluids. The large scatter in experimental data shows that large errors can be obtained from CFD models in the absence of experimental correction factors.

Critical distance for secondary ion formation: Experimental SIMS measurements

We have performed direct experimental measurements of the critical distance for the secondary ion formation process. To this end, we compared the experimentally measured energy distribution of secondary Si − ions with the theoretical energy distribution (Sigmund-Thompson relation) of secondary Si atoms. Our model states that the maxima positions of these two energy distributions differ by the Coulomb interaction potential between the outgoing ion (Si − in our case) and a charge with the opposite polarity formed at the surface after electron transition between the outgoing Si atom and the surface. Quite a reasonable value was obtained for the critical distance, but with a large scatter in experimental data. The conclusion has been made that the experimental technique should be improved to get more precise values of the critical distance, which is of high importance for practical purposes.

Effects of Alloying Additions and Material Microstructure on the Accuracy of the Predictive Law of Creep Crack Growth for W-Strengthened 9–12%Cr Ferritic Heat-Resistant Steel

The life of creep crack growth for W-strengthened 9–12%Cr steel is sensitive to the alloying additions and to differences in material microstructure, such as lath martensitic structure and grain size caused by differences in cooling rates in the steel ingots during the manufacturing process, which results in the large scatter of experimental data from the law of creep crack growth life. In the present study, creep crack growth tests were conducted using W-strengthened 9–12%Cr steels with various contents of alloying additions and the dimensions of micro-nano structures. The effects of the composition of alloying additions and material microstructures on the life of creep crack growth for W-strengthened 9–12%Cr steel were clarified.

On evaluation of wear resistance of tooth enamel and dental materials

A survey of the literature shows that in many studies on the wear resistance of tooth enamel or dental materials a large scatter of experimental data has been obtained when wear tests were performed at a fixed load. Despite the steady loading, wear conditions vary during sliding, since tooth enamel as well as dental materials have inhomogeneous structure. This leads to changes in contact interactions between sliding surfaces, and as a result, we get changes in the friction and wear behaviour of tested materials. This is why at the same loading the wear can be different. In this study, more reliable approach to evaluation of the wear resistance of human enamel and dental materials is proposed. The procedure is based on the correlation between the volumetric wear and the friction energy dissipated during sliding. The model can be useful to compare the wear resistance of different dental materials tested in different ambient conditions.

Electronegativity and charge-injection barrier at organic/metal interfaces

Despite a large scatter in experimental data, charge-injection barrier at organic/metal interfaces has been traditionally described as a function of metal work function. By studying the interface between Alq 3 and various metals with photoelectron spectroscopy, we show that the charge-injection barrier can be better described as a linear function of the metal electronegativity. This is consistent with our theoretical analysis in terms of a simple model involving metal-induced gap states in organic layer. The interface parameter S is calculated to be 0.8, in good accordance with the experimental value of 0.81. The present work presents a method for predicting the injection barrier at organic/metal interfaces and should be useful for designing various organic-based electronic and optoelectronic devices.

Quantum corrections to the conductivity in two-dimensional systems: Agreement between theory and experiment

Quantum corrections to the conductivity have been studied in the two types of low-mobility two-dimensional heterostructures: those with doped quantum well, and doped barriers. The consistent analysis shows that for the structures where electrons occupy the states only in the quantum well, all the temperature and magnetic field dependences of the components of resistivity tensor are well described by the theories of the quantum corrections. Contribution of the electron-electron interaction to the conductivity has been reliably determined for the structures with different electron density. A possible reason of large scatter in experimental data relating to the contribution of electron-electron interaction, obtained in previous papers, is analyzed. The role of the carriers occupying the states of the doped layers is discussed.

KDP kinetics and dislocation efficiency of growth

A macroscopic growth kinetic study has been carried out by taking advantage of simultaneous observations on a number of crystals (three in our experiments), growing under the same conditions. A large number of measurements on kinetic data for R 〈0 0 1〉 (σ) were found in three separate experiments of KDP growth in a dynamic regime, using the temperature lowering method. Macroscopic growth rates were compared with those from the literature. Arrhenius corrections were made at 40°C. The large scatter of experimental data, particularly for σ≈0.02–0.05 is discussed in relation with ε R the growth efficiency. Growth rate of the pyramidal faces has distinct parabolic dependencies on supersaturation, for several efficiencies of growth. Burgers vector and the linear dimension of the dominant centres of dislocations during the growth are discussed.

Theoretical and experimental study on the magnetomechanical behavior of superconducting helical coils for a fusion reactor

The magnetomechanical behavior of superconducting helical coils for a magnetic fusion reactor was investigated experimentally and theoretically. Deformations of straight and torus type helical coils were caused due to static electromagnetic forces in the liquid helium cryostat and were analysed with the finite element computer code made here. Despite of a large scatter of experimental data due to a non-uniform friction force between the helical coil and the torus of stainless steel, the numerical results are very close to the mean value of the data. Numerical analysis of the force distribution acting on the helical coils was also performed for a Heliotron's coil system to characterize its nature. The force could be categorized conveniently as an extensional force, a tangential force and a toroidal force which correspond respectively to the kind of forces acting on toroidal field coils. Additionally, the effect of mechanical constraint on the magnetomechanical behavior is discussed and shows that the location of the constraint significantly affects the stress distributions in the coils.

Theoretical and experimental study on the magnetomechanical behavior of superconducting helical coils for a fusion reactor

The magnetomechanical behavior of superconducting helical coils for a magnetic fusion reactor was investigated experimentally and theoretically. Deformations of straight and torus type helical coils were caused due to static electromagnetic forces in the liquid helium cryostat and were analysed with the finite element computer code made here. Despite of a large scatter of experimental data due to a non-uniform friction force between the helical coil and the torus of stainless steel, the numerical results are very close to the mean value of the data. Numerical analysis of the force distribution acting on the helical coils was also performed for a Heliotron's coil system to characterize its nature. The force could be categorized conveniently as an extensional force, a tangential force and a toroidal force which correspond respectively to the kind of forces acting on toroidal field coils. Additionally, the effect of mechanical constraint on the magnetomechanical behavior is discussed and shows that the location of the constraint significantly affects the stress distributions in the coils.