Search results for "Expansion"

Series expansion for the effective conductivity of a periodic dilute composite with thermal resistance at the two-phase interface

2019

We study the asymptotic behavior of the effective thermal conductivity of a periodic two-phase dilute composite obtained by introducing into an infinite homogeneous matrix a periodic set of inclusions of a different material, each of them of size proportional to a positive parameter ?. We assume that the normal component of the heat flux is continuous at the two-phase interface, while we impose that the temperature field displays a jump proportional to the normal heat flux. For ? small, we prove that the effective conductivity can be represented as a convergent power series in ? and we determine the coefficients in terms of the solutions of explicit systems of integral equations.

Structural Stability of Hafnia-Based Materials at Ultra-High Temperature

2018

This study assesses the structural stability at ultra-high temperature of the following selected compositions: 6.5 and 14 mol. % of RE2O3 (RE = Dy, Y, Er, Yb, and Lu) doped HfO2. Under thermal cycling and thermal shock, the structural stability was evaluated at 2400°C with water vapor flux using a specific test bench with a 3 kW CO2 laser. The cubic phase stability, which is theoretically important in the broad temperature range from 25 to 2800°C, was determined by a quantitative analysis of the X-ray diffractograms. Fully and partially stabilized HfO2, obtained respectively with 14 mol. % and 6.5 mol. % of dopants, showed different behaviors to thermal damage. Thermal expansion was measure…

Thermal expansion, normalized thermo-optic coefficients, and condition for second harmonic generation of a Nd:YAG laser with wide temperature bandwid…

2011

Interferometric determination of thermal expansion and of normalized thermo-optic coefficients of RbTiOPO4 at four laser wavelengths are performed as a function of temperature. A suitable vectorial formalism applied to obtained data allows the establishment of the temperature dependence of refractive indices, and subsequent theoretical analysis enables one to predict that an extremum in the evolution of the phase-matching direction in the (X,Y) plane should occur near 100 °C for type II second harmonic generation of Nd:YAG lasers, with a temperature bandwidth that can be as large as 117 °C for a crystal of 10 mm in length. Such unusual behavior is observed experimentally by recording the co…

A magnetostrictive sensor interrogated by fiber gratings for DC-current and temperature discrimination

2000

A magnetostrictive sensor head with temperature compensation has been developed for measurement of static magnetic fields. The device consists on two different alloys with similar thermal expansion coefficient one of which has a giant magnetostriction, the expansion of both materials produced by heat and magnetism is detected by two fiber gratings. One of the gratings measures the temperature of the sensor and the difference between the wavelengths reflected by the gratings is a measurement of the magnetically induced strain.

Effect of Cold Working and Ring Indentation on Fatigue Life of Aluminum Alloy Specimens

2013

The article deals with the fatigue life of plates with hole made of aluminum alloy. Specifically, the combined effect of cold working expansion and ring indentation on improved fatigue life performance was investigated. Multiple fatigue tests were performed to determine the cycles to failure and the corresponding W¨ ohler diagram. Experimental results were compared with those of nontreated specimens. The conclusion was that cold working expansion and indentation create a delay on crack formation and fatigue failure.

Comprehensive formulation of temperature-dependent dispersion of optical materials: illustration with case of temperature tuning of a mid-IR HgGa_2S_…

2009

The temperature dependence of refractive indices of optical materials is characterized in this work by what we call their normalized thermo-optic coefficients. These are determined experimentally through interferometric measurements of thermal expansion and of changes in optical thickness at a few laser wavelengths as function of temperature. A suitable vectorial formalism applied to these data allows predicting the thermal evolution of the refractive index all over the useful range of transparency. The validity and reliability of our methodology is demonstrated through temperature tuning of a mid-IR HgGa2S4 optical parametric oscillator (OPO) pumped at 1.0642 μm by a Nd:YAG laser. Measured…

THE THERMAL EXPANSION OF HELIUM II IN RESTRICTED GEOMETRIES

1978

CLEASE: a versatile and user-friendly implementation of cluster expansion method

2018

Materials exhibiting a substitutional disorder such as multicomponent alloys and mixed metal oxides/oxyfluorides are of great importance in many scientific and technological sectors. Disordered materials constitute an overwhelmingly large configurational space, which makes it practically impossible to be explored manually using first-principles calculations such as density functional theory due to the high computational costs. Consequently, the use of methods such as cluster expansion (CE) is vital in enhancing our understanding of the disordered materials. CE dramatically reduces the computational cost by mapping the first-principles calculation results on to a Hamiltonian which is much fa…

Non Gaussian closure techniques for the analysis of R-FBI isolation system

1997

The Resilient-Friction Base Isolator (R-FBI) stochastic response under severe ground motion modelled as a stationary and non-stationary zero mean stochastic white noise processes is performed. The moment equation approach is applied and the non-normal response is obtained by means of a non-Gaussian closure technique, based on the Gram-Charlier asymptotic expansion of the response probability density function. Results are compared with the equivalent non linearization technique and with results obtained by means of Monte Carlo simulation.

Stochastic dynamics of linear elastic trusses in presence of structural uncertainties (virtual distortion approach)

2004

Structures involving uncertainties in material and/or in geometrical parameters are referred to as uncertain structures. Reliability analysis of such structures strongly depends on variation of parameters and probabilistic approach is often used to characterize structural uncertainties. In this paper dynamic analysis of linearly elastic system in presence of random parameter variations will be performed. In detail parameter fluctuations have been considered as inelastic, stress and parameter dependent superimposed strains. Analysis is then carried out via superposition principle accounting for response to external agencies and parameter dependent strains. Proposed method yields asymptotic s…