Analyse thermomécanique des lois de comportement par thermographie infrarouge

The knowledge of dissipative and non dissipative phenomena associated to quasi-static déformation processes, is a fundamental supplementary asset for determination of thermomechanical behaviour law. On depicts, in this paper, an experimental set-up, using infra-red technics, which allows to observe thermal and energetical phenomena during sample déformation. After restating the definition of the energy balance, in case of elastic-plastic materials, the relationship between the dissipation (or the stored energy of cold working) and the hardening state variables are recalled. The dissipation is continuously evaluated during monotonic tensile test. Numerized maps of surface temperature are used. The experimental arrangement is described ; then the physical model, which allows to relate the dissipation to the temperature signals, and the calibration method are successively introduced. Results on several materials are shown and their incidence on the behaviour law is succinctly mentioned.La connaissance des phénomènes dissipatifs et non dissipatifs associés aux processus quasi-statiques de déformation, représente un atout supplémentaire important pour l'élaboration de loi thermomécanique de comportement. On décrit, ici, un dispositif expérimental, utilisant les techniques de thermographie infrarouge, et permettant d'observer les phénomènes thermiques et énergétiques durant la déformation d'un échantillon en traction simple. Après avoir rappelé la définition du bilan énergatique, dans le cas de matériaux élasto-plastiques, on relie la dissipation et l'énergie interne bloquée durant l'écrouissage, aux variables d'état. La puissance mécanique dissipée est évaluée continûment durant l'essai. On utilise pour cela, les images thermiques fournies par la caméra infra-rouge. On présente le dispositif expérimental, puis successivement, on décrit le modèle physique permettant de relier l'énergie dissipée aux cartes de température de surface ainsi que le protocole d'étalonnage. En fin d'article, on présente quelques résultats obtenus avec plusieurs matériaux et on évoque rapidement leur incidence sur la forme des lois de comportement

PRIMARY AND SECONDARY FLUORESCENCE QUENCHING OF Eu3+Eu^{3+} IN ORGANIC SOLVENTS

Author Institution: Department of Chemistry, The University of ToledoThe fluorescence of $Eu^{3+}$ in organic solvents is subject to quenching by the solvent molecules both in the solvation sphere and outside the primary solvation sphere of the complex ion. Binary solvents were employed including $CH_{3}COOH$ and one of the following derivatives of $CH_{3}COOH$, i.e., $CCl_{3}COCl, CF_{3}COOH$, $CHCl_{2}COCl$, $CH_{2}ClCOCl$ $CH_{3}COCl, CD_{3}COOD$, etc. The rare earth salts, $EuCl_{3}$ ${\cdot}$ $6H_{2}O$, are insoluble in the latter solvents and therefore, the primary solvation sphere of the complex ion consists of $CH_{3}COOH$ only. The primary fluorescence quenching, $k_{h}$ is constant in all systems used whereas the secondary fluorescence quenching rate constant, $k^{sec}_{solv}$, varies from solvent to solvent. It increases as the overlap between the normalized fluorescence of $Eu^{3+}, I_{F}(\bar{\nu})$, and the near-infrared spectrum of the solvent ${\epsilon}_{solv}(\bar{\nu})$, increases; i.e., $k^{sec}_{solv} \ \alpha \int I_{F}(\bar{\nu})\ \epsilon_{solv}(\bar{\nu})d{\bar{\nu}}$. This project was supported by Owens-Illinois, Corporate Research Laboratories

ELECTRONIC EXCITATION ENERGY TRANSFER MECHANISMS BETWEEN Tb3+Tb^{3+} and Eu3+Eu^{3+} IN DMSO

This project was supported by Owens-Illinois Incorporated, Corporate Laboratories, Toledo, Ohio.Author Institution: Department of Chemistry, The University of ToledoLight excitation of mixture of $TbC1_{3}$ and $EuC1_{3}$ in DMSO using spectral regions in which both components absorb light, namely at $345 \pm 1$, $353 \pm 1$, $362 \pm 1$ and $371 \pm 1$nm, is accompanied by a reduction in the fluorescence intensity of $Tb^{3+}$ measured at 488 and/or 543 nm, as well as by an enhancement in the fluorescence intensity of $Eu^{3+}$, measured at 591 nm. Electronic excitation energy transfer appears to originate predominantly from the $^{5}D_{4}$ - state of $Tb^{3+}$, and it is independent of the excitation wavelength- The average rate constant for the excitation energy transfer la $1.50 \times l0^{3}M ^{-1}1sec^{-1}$. Electronic energy transfer originating from the $^{5}D_{3}$ - state of $Tb^{3+}$ was not observed, possibly due to a rapid $^{5}D_{3} \rightarrow ^{5}D_{4}$ - radiationless process. The rate constant of this latter process is associated with a lower limit of about $10^{5}sec^{-1}$ The value of $1.50 \times 10^{3}M^{-1}$ $sac^{-1}$ for the transfer rate constant is much smaller than the value expected for a diffusion controlled process namely $8 \times 10^{6}$ $M^{-1}sec^{-1}$ Furthermore, the critical separation, $R_{o}$, between $Tb^{3+}$ (donor) and $En^{3+}$ (acceptor) was found to be about 13 A, These observations imply that the transfer process takes place either via complex multipolar interactions or via exchange interactions which are activation energy controlled

ELECTRONICENERGY TRANSFER FROM Tb3+ Tb^{3+} TO Eu3+Eu^{3+} IN DMSO

This project was supported by Owens-Illinois (Corporate Research Laboratories).Author Institution: Department of Chemistry, University of Toledo ToledoExcitation of a mixture of $TbCl_{3}.6H_{2}O$ and $EuCl_{3}.6H_{2}O$ in DMSO by photons of 487 m$\mu$, corresponding solely to the $^{7}F_{6}{\rightarrow}{ ^{5}D_{4}}$ transition of $Tb^{3+}$, is accompanied by a reduction in the fluorescence yield of $Tb^{3+}$ as [$Eu^{3+}$] increases and by the appearance of emission from $Eu^{3+}$, although the latter is not directly excited by the light used. The emission from $Tb^{3+}$ is studied at $541 \pm 1 m\mu (^{5}D_{4} \rightarrow ^{7}F_{5})$ where the overlap with an emission band of $Eu^{3+}$ at 535 $m\mu (^{5}D_{1} \rightarrow ^{7}F_{0})$ is negligible. On the other hand, the omission from $Eu^{3+}$ is studied at $591 \pm 1 m\mu (^{5}D_{0} \rightarrow ^{7}F_{1})$) where there is overlap to some extent with the emission band of $Tb^{3+}$ at 585 $\pm 1 m\mu (^{5}D_{4} \rightarrow ^{7}F_{4})$. In the absence of fluorescence self-quenching by $Tb^{3+}$ and fluorescence quenching of $Eu^{3+}$ by $Tb^{3+}$, the present data are interpreted via the processes, \begin{eqnarray*} Tb^{3+}(^{7}F_{6})\mathop{\longrightarrow}^{487m\mu}Tb^{3+}(^{5}D_{4})\mathop{\longrightarrow}^{Eu^{3+}}Tb^{3+}(^{7}F)+Eu^{3+}(^{7}F)+heat;k_{q}\\ \end{eqnarray*} and\\ \begin{eqnarray*} Tb^{3+}(^{7}F_{6})\mathop{\longrightarrow}^{487m\mu}Tb^{3+}(^{5}D_{4})\mathop{\longrightarrow}^{Eu^{3+}}Tb^{3+}(^{7}F)+Eu^{3+}(^{5}D)\\ Eu^{3+}(^{5}D)\longrightarrow Eu^{3+}(^{5}D_{0})\longrightarrow Eu^{3+}(^{7}F)+hv_{f1};k_{E.T} \end{eqnarray*} Values of $k^{\prime}{_{E.T}} = k_{q} + k_{E.T}$ give an average value of $(2.2 \pm 0.4) \times 10^{3}M^{-1}$ $sec^{-1}$