Scission induced by circular shear and heat conduction in an elastomeric cylinder

Constitutive equations for the thermo-mechanics of elastomeric materials generally assume that they do not undergo microstructural change. A constitutive theory is discussed here which accounts for such changes arising from continuous scission of macromolecular junctions of elastomeric networks due to deformation and high temperatures and the subsequent cross-linking of molecules into new networks with new reference states. The total stress is the superposition of the stresses in the remainder of the original network and in each subsequently formed network. Each network acts as a temperature-dependent non-linear elastic material. The interaction of this material response with inhomogeneous deformation and temperature fields is studied for finite circular shear of a cylinder. Numerical results illustrate how the mechanical response of the cylinder depends on the temperature dependence of both the scission–cross-linking process and the properties of the elastic networks.     

Coupled boundary element method and finite difference method for the heat conduction in laser processing

This paper is presented as a way to model transient heat conduction in a 3-D axisymmetric case where large rates of heat fluxes are applied on the surfaces as done in the case of laser processing. This would result in large temperature gradients in a small area irradiated by the laser on the incident surface that could also reach melting and subsequent vaporization. BEM can handle large fluxes very easily and it also can be formulated if needed to incorporate the moving boundary problem in a unique manner while on the other hand FDM is a fast and efficient method. For these reasons a coupled BEM–FDM method is formulated to simulate the heat conduction process. In the BEM method linear elements for the boundary and quadratic elements for the domain were used. The integrals in BEM were integrated in time using the asymptotic expansion for the modified Bessel functions in the Green’s function. To further improve the accuracy, special techniques were employed in the spatial integration. As for the FDM formulation, a flux conservation scheme with a 4th order formula for the fluxes was used. The FDM and BEM were coupled at the interface by the temperature from the FDM formulation being imposed on the BEM and the flux from the BEM being utilized by the FDM elements near to the interface. To advance in time, the Crank–Nicholson scheme was used on the FDM directly and due to coupling indirectly on the BEM. The relative errors for the simulation of constant and variable flux cases demonstrate the successful nature of the numerical model.     

Thermographic signal reconstruction for vibrothermography

Vibrothermography, also known as thermosonics or sonic infrared, is a method of nondestructive evaluation that finds cracks or delaminations from the heat given off in response to vibration. In vibrothermography, finding cracks requires identifying and localizing pulsed surface and subsurface heat sources from a time sequence of infrared images. Traditionally this identification involves manually stepping through and studying the images. Careful observation of the heating and subsequent cooling is needed to distinguish cracks from false indications. In this paper, we present an algorithm that reduces the entire time sequence to a single static plot. The plot uses only a few coefficients per pixel to reconstruct the original sequence; this is possible because the reduction is based on a physical model. As an added bonus, the algorithm reduces noise and improves sensitivity. A single false-color image summarizes all the information from the entire sequence, simplifying the task of identifying cracks.     

Magneto-thermoelasticity with thermoelectric properties and fractional derivative heat transfer

In this work, a new model of the magneto-thermoelasticity theory has been constructed in the context of a new consideration of heat conduction with fractional derivative. A one-dimensional application for a conducting half-space of thermoelectric elastic material, which is thermally shocked in the presence of a magnetic field, has been solved using Laplace transform and state-space techniques (Ezzat, 2008 [1]). According to the numerical results and its graphs, a conclusion about the new theory of magneto-thermoelasticity has been constructed. The theories of coupled magneto-thermoelasticity and of generalized magneto-thermoelasticity with one relaxation time follow as limited cases. The result provides a motivation to investigate conducting thermoelectric materials as a new class of applicable materials.     

Hopping Transport and Stochastic Dynamics of Electrons in Plasma Layers

We investigate the stochastic dynamics and the hopping transfer of electrons embedded into two‐dimensional atomic layers. First we formulate the quantum statistics of general atom ‐ electron systems based on the tight‐binding approximation and express ‐ following linear response transport theory ‐ the quantum‐mechanical time correlation functions and the conductivity by means of equilibrium time correlation functions. Within the relaxation time approach an expression for the effective collision frequency is derived in Born approximation, which takes into account quantum effects and dynamic effects of the atom motion through the dynamic structure factor of the lattice and the quantum dynamics of the electrons. In the last part we derive Pauli equations for the stochastic electron dynamics including nonlinear excitations of the atomic subsystem. We carry out Monte Carlo simulations and show that mean square displacements of electrons and transport properties are in a moderate to high temperature regime strongly influenced by by soliton‐type excitations and demonstrate the existence of percolation effects (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theoretical and experimental study of laser induced damage on GaAs by nanosecond pulsed irradiation

The surface damage experiments of gallium arsenide (GaAs) single crystal irradiated by 1.06 and 0.53 μm nanosecond irradiations are carried out with fundamental and frequency-doubled Nd:YAG laser, respectively. The surface damage thresholds for both wavelengths are experimentally determined and the damaged morphologies and elementary component are analyzed with electron probe microanalyzer (EPM). It is found that the components of Ga and As almost keep constant in our experiments when the irradiated fluence is just around the surface damage threshold and no oxygen is found at all. The theoretical calculations on temperature rise for both wavelengths are carried out using the purely thermal model. It is shown that for irradiation with photon energy above the corresponding band gap the theoretical calculation is in good agreement with the experimental results; however, for that with photon energy just below the band gap, the experimental results cannot be effectively explained by the purely thermal heating mechanism. Combining with the experiment of multi-shot damage from references we finally conclude that the damage by laser irradiation with photon energy below the band gap should be explained by the micro-defect accumulation and consequently enhanced absorption heating mechanism.     

Control of mixed protonic and electronic conductivity by mixing rare-earth ortho-borates

In order to develop mixed protonic and electronic conductors, we proposed a novel concept for material design that enables to control partial conductivities by fabricating solid solutions of protonic and electronic conductors. In this work, Sr-doped LaBO₃ and Sr-doped CeBO₃ were chosen as model compounds conducting protons and electron holes, respectively. Solid solutions of the above borates, Sr-doped La_1 − xCe_xBO₃, were prepared, and their electrical conductivities were investigated in 8.5 × 10²-4.2 × 10³ Pa of p(H₂O) and 1.0 × 10-1.0 × 10⁵ Pa of p(H₂) at 1073 K. From the experimental results of the gas partial pressure dependences of the conductivities, major charge carrier species were identified as a function of x. It was found that proton was the major charge carrier when x < 0.2 while the contribution of the electron hole conduction became remarkable as x increased above 0.2. The contribution of the electron hole conduction can be interpreted by the percolation model.     

Quantitative nanoscopic impedance measurements on silver-ion conducting glasses using atomic force microscopy combined with impedance spectroscopy

Nanoscopic impedance measurements were carried out on silver ion conducting glasses by coupling an impedance spectrometer with an atomic force microscope. When ac voltages were applied to a conducting AFM tip being in contact with the glass surface, silver nanoparticles were formed during the cathodic half cycle, which were not completely reoxidized in the anodic half cycle. We describe two protocols allowing for a controlled particle growth. The electrochemical oxidation/reduction processes led to low tip/sample interfacial impedances, and the formed silver particles acted as nanoelectrodes sensing the spreading resistance of the glass below the particles. We made a quantitative check of the spreading resistance formula under the assumption that spreading of the electric field is governed by the lateral diameter of the particles and found good agreement between the mean value of the local conductivities obtained at different tip positions and the macroscopic conductivity.     

Point defects and orientation-dependent transport of matter and charge in iron-containing olivines

The variation of the oxygen content, x_O, of synthetic fayalite (Fe₂SiO₄) single crystals was investigated thermogravimetrically at 1130 °C as a function of the oxygen activity, a_O2 (= P_O2/P_O2° ≈ f_O2/f_O2° with P_O2° ≈ f_O2° = 1 bar ≈ 1 atm). It was found that x_O varies less in fayalite single crystals than in polycrystalline Fe₂SiO₄ studied earlier. The majority defects are most likely cation vacancies, (V_Me²⁺)″, ferric ions on M-sites, (Fe³⁺_Me²⁺), and ferric ions on Si-sites, (Fe³⁺_Si⁴⁺)′. Furthermore, the diffusion of iron in synthetic olivine single crystals ((Fe_xMg_1 − x)₂SiO₄) was studied at 1130 °C as a function of orientation, oxygen activity, and cationic composition. The observed oxygen activity dependencies suggest that cations move via different types of cation vacancies, most likely isolated vacancies, (V_Fe²⁺)″, and possibly neutral associates, {2(Fe³⁺_Me²⁺) ⋅ (V_Me²⁺)^′ ? ′}^x, the latter being minority defects. In addition, the electrical conductivity, σ, of fayalite single crystals was investigated as a function of orientation and oxygen activity within the stability field of fayalite at 1130 °C. The observed oxygen activity dependencies are compatible with (V_Me²⁺)^′ ? ′, (Fe³⁺_Me²⁺), and (Fe³⁺_Si⁴⁺)′ being the majority point defects at high a_O2 and with h^⋅ and e′ as the majority defects at low a_O2. The electrical conduction in fayalite is governed by contributions of electrons and holes. This extended point defect model for fayalite is also compatible with data for the variation of the oxygen content and for the iron tracer diffusion.     

Thermal shock induced nanocrack as high efficiency surface conduction electron emitter

Significant emission current enhancement has been achieved for surface conduction electron emitter, due to the special three-dimensional nanocrack structure fabricated by the thermal shock process. The three-dimensional configuration strongly changed the electric field distribution and controlled the emission electron trajectory. Thermal shock treatment was also used to increase the edge roughness of the nanocrack and thereby dramatically improved the field emission characteristics. Stable and uniform electron emission was observed with turn-on voltage of 150 V. The surface conduction current of 400 μA for 6 cells was obtained with the detector voltage of 1 kV and the gap voltage of 170 V.