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Katsumi Une - One of the best experts on this subject based on the ideXlab platform.
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Formation of pellet-cladding Bonding Layer in high burnup BWR fuels)
Journal of Nuclear Science and Technology, 1997Co-Authors: Kazuhiro Nogita, Katsumi UneAbstract:Formation process of the pellet-cladding Bonding Layer was studied by EPMA, XRD, and SEM/TEM for the oxide Layer on a cladding inner surface and the Bonding Layer in irradiated fuel rods. Specimens were prepared from fuels which had been irradiated to the pellet average burnups of 15, 27 and 42 GWd/t in BWRs. In the lower burnup specimens of 15 and 27GWd/t, no Bonding Layer was found, while the higher burnup specimens of 42 and previously reported 49 GWd/t had a typical Bonding Layer. A Bonding Layer which consisted of two regions was found in the latter fuels. One region of the inner surface of the cladding was made up mainly of ZrO. The structure of this ZrO consisted of cubic phase, while no monoclinic crystals were found. The other region, near the pellet surface, had both a cubic solid solution of (U, Zr)O and amorphous phase. Even in the lower burnup specimens having no Bonding Layer, cubic ZrO phase was identified in the cladding inner oxide Layer. The formation process of the Bonding Layer were discussed in connection with phase transformation by irradiation damage of fission products and conditions for contact of pellet and cladding.
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TEM analysis of pellet-cladding Bonding Layer in high burnup BWR fuel
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1996Co-Authors: Kazuhiro Nogita, Katsumi Une, Y. KoreiAbstract:Abstract Detailed analysis of the pellet-cladding Bonding Layer in high burnup nuclear fuel has been done by transmission electron microscopy (TEM). A specimen was prepared from the fuel, which had been irradiated to the pellet average burnup of 49 GWd/tU (1.2×10 21 fissions/cm 3 ) in a boiling water reactor (BWR). A 20 μm thick Bonding Layer which consisted of two regions was observed. In one region from the inner surface of the Zr liner cladding to 12–13 μm away, the main species identified was ZrO 2 with a small amount of dissolved UO 2 also present. This ZrO 2 consisted of a mixture of cubic polycrystals of a few nanometers in size and an amorphous phase, but no monoclinic crystal, which is the stable ZrO 2 phase at temperatures below 1170°C, was found. In a second region from the pellet surface to about 7 μm away, both a cubic solid solution of (U, Zr)O 2 and an amorphous phase existed, in which the concentrations of UO 2 and ZrO 2 changed continuously. The formation of substitutional solid solution progressed during irradiation due to a strong contact between cubic UO 2 and ZrO 2 , which induced subsequent mutual diffusion of U and Zr. Phase transformation from monoclinic to cubic ZrO 2 and amorphization were discussed in connection with fission damage.
Ephraim Suhir - One of the best experts on this subject based on the ideXlab platform.
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Flip-chip assembly: is the bi-material model acceptable?
Journal of Materials Science: Materials in Electronics, 2017Co-Authors: Ephraim SuhirAbstract:The Bonding Layer in flip-chip assembly designs is characterized, unlike in epoxy bonded assemblies, by a relatively high effective Young’s modulus of its composite material, which is comprised of high-modulus solder and low-modulus epoxy encapsulant (underfill). Simple, easy-to-use and physically meaningful tri- and bi-material analytical stress models are developed for the evaluation of the thermally induced interfacial shearing stresses, as well as normal stresses acting in the cross-sections of the assembly components. While in a tri-material model all the three materials, the chip, the substrate and the Bonding Layer, are treated as “equal partners”, in a bi-material model a significant simplification is made, assuming that the Bonding Layer is much thinner than the bonded components, the chip and the substrate, and/or that its effective Young’s modulus is significantly lower than the moduli of the chip and the substrate materials. In the carried out numerical example based on the application of the tri-material model, the highest shearing stress occurs at the chip-bond interface and is significantly, by the factor of about 2.45, higher than the stress at the substrate-bond interface, but even the latter stress is about twice as high as the maximum shearing stress predicted on the basis of the bi-material model. As to the normal stresses acting in the cross-sections of the assembly components, the tri-material model predicts that the highest stresses occur in the chip, the lowest—in the substrate, and that the stresses in the bond are rather high, about 59% of the stresses in the chip. The bi-material model, however, simply assumes that the normal stresses in the bond are zero. The normal stresses in the chip predicted on the basis of this model are only about 78% of the stress predicted by the tri-material model. The normal stresses in the substrate evaluated on the basis of the bi-material model are almost twice as high as the tri-material model predicts, but these stresses are low anyway: it is the state of stress in the chip and in the Bonding Layer, and the interfacial stress at the chip-bond interface that should be of the primary concern to the device designer. It is concluded that while a simple bi-material model can be successfully used for adhesively bonded assemblies, characterized by a thin and/or low modulus Bonding Layer, a tri-material model should be employed for flip-chip assemblies, when high-modulus solders are used. Future work should include finite-element analyses and experimental evaluations.
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Thermal stress in a bi-material assembly with a 'piecewise-continuous' Bonding Layer: theorem of three axial forces
Journal of Physics D: Applied Physics, 2009Co-Authors: Ephraim SuhirAbstract:We consider a bi-material assembly with a 'piecewise-continuous' Bonding Layer. The Layer is characterized by different elastic constants of its 'pieces' (segments) and is assumed to be thin. Young's moduli of all the 'pieces' of the Bonding Layer are significantly lower than the moduli of the adherend materials. In such a situation the coefficient of thermal expansion (CTE) of the Bonding material need not be accounted for. Only the interfacial compliance of the Bonding Layer is important. This is indeed the case for the majority of electronic, opto-electronic or photonic assemblies. We consider the situation when the assembly is manufactured at an elevated temperature and is subsequently cooled down to a low (say, room) temperature.The objective of the analysis is to develop a simple, easy-to-use and physically meaningful analytical ('mathematical') predictive model for the evaluation of the interfacial shearing stresses that arise at the boundaries of the 'pieces' (segments) of the Bonding Layer and at the assembly edge. The basic equation is obtained for the thermally induced forces acting in the adherends' cross-sections that correspond to the boundaries between the dissimilar portions of the Bonding Layer. This equation has the form of the theorem of three (bending) moments in the theory of multi-span beams lying on separate simple supports and could therefore be called the 'theorem of three axial forces'. We show, as an illustration, how this equation could be employed to design a bi-material assembly with an inhomogeneous Bonding Layer and with low interfacial shearing stresses. Low shearing stresses will certainly result in lower peeling stresses as well.The numerical example is carried out for an assembly with a relatively high-modulus Bonding material in its mid-portion (aimed primarily at providing good adhesion and, if necessary, good heat transfer as well) and a low-modulus material in its peripheral portions (aimed primarily at bringing down the interfacial stresses). The maximum interfacial shearing stress in the assembly with the inhomogeneous Bonding Layer turned out to be only about 30% of the maximum shearing stress in an assembly with a homogeneous Bonding Layer having throughout its length the same modulus as the Bonding material in the mid-portion of an assembly with an inhomogeneous bond.We would like to emphasize that the inhomogeneous Bonding material addressed in this analysis does not necessarily have to be an epoxy one. Many other Bonding materials with different moduli in the mid-portion and at the peripheral portions of the assembly could be considered for various practical applications. For instance, a high-modulus solder material such as, say, a tin–silver–copper (SAC) solder can be employed in the mid-portion of an assembly and a low-modulus solder (e.g. an indium-based alloy) at its peripheral portions. In other applications a high-modulus solder material could be considered for the mid-portion of the assembly and a low-modulus epoxy adhesive at its peripheral portions. We would also like to point out that the developed concept can be easily generalized for the situations when the Bonding material is not a continuous one, but is of the ball–grid–array (BGA) or a pad–grid–array (PGA) type. Our concept could also be easily generalized for a two-dimensional case, for the situation when bending deformations should be accounted for, for non-uniform distribution of temperature (i.e. for assemblies with temperature gradients in the through-thickness and/or in the longitudinal direction), for situations when time-dependent effects (visco-elasticity, creep, stress relaxation) in the Bonding material are important and for numerous other more complicated and practically important situations that might be encountered in engineering practice.
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Interfacial stresses in a bi-material assembly with a compliant Bonding Layer
Journal of Physics D: Applied Physics, 2008Co-Authors: Ephraim Suhir, M VujosevicAbstract:We examine an elongated bi-material adhesively bonded or soldered assembly with a continuous compliant attachment (Bonding Layer). The assembly is subjected to external tensile forces or to bending moments applied to one of the assembly components. We develop simple predictive analytical ('mathematical') models for the evaluation of interfacial shearing (in the case of external tensile forces) and peeling (in the case of external bending moments) stresses and strains in the Bonding material. The developed models can be helpful in stress?strain analyses of assemblies of the type in question and particularly for printed-circuit-board (PCB)/surface-mounted-device (SMD) assemblies employed in electronic packaging. These models enable one to particularly evaluate the maximum interfacial stresses in the Bonding material from the predicted or measured strains in the PCB in the vicinity of but still outside the surface-mounted package.
Kazuhiro Nogita - One of the best experts on this subject based on the ideXlab platform.
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Formation of pellet-cladding Bonding Layer in high burnup BWR fuels)
Journal of Nuclear Science and Technology, 1997Co-Authors: Kazuhiro Nogita, Katsumi UneAbstract:Formation process of the pellet-cladding Bonding Layer was studied by EPMA, XRD, and SEM/TEM for the oxide Layer on a cladding inner surface and the Bonding Layer in irradiated fuel rods. Specimens were prepared from fuels which had been irradiated to the pellet average burnups of 15, 27 and 42 GWd/t in BWRs. In the lower burnup specimens of 15 and 27GWd/t, no Bonding Layer was found, while the higher burnup specimens of 42 and previously reported 49 GWd/t had a typical Bonding Layer. A Bonding Layer which consisted of two regions was found in the latter fuels. One region of the inner surface of the cladding was made up mainly of ZrO. The structure of this ZrO consisted of cubic phase, while no monoclinic crystals were found. The other region, near the pellet surface, had both a cubic solid solution of (U, Zr)O and amorphous phase. Even in the lower burnup specimens having no Bonding Layer, cubic ZrO phase was identified in the cladding inner oxide Layer. The formation process of the Bonding Layer were discussed in connection with phase transformation by irradiation damage of fission products and conditions for contact of pellet and cladding.
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TEM analysis of pellet-cladding Bonding Layer in high burnup BWR fuel
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1996Co-Authors: Kazuhiro Nogita, Katsumi Une, Y. KoreiAbstract:Abstract Detailed analysis of the pellet-cladding Bonding Layer in high burnup nuclear fuel has been done by transmission electron microscopy (TEM). A specimen was prepared from the fuel, which had been irradiated to the pellet average burnup of 49 GWd/tU (1.2×10 21 fissions/cm 3 ) in a boiling water reactor (BWR). A 20 μm thick Bonding Layer which consisted of two regions was observed. In one region from the inner surface of the Zr liner cladding to 12–13 μm away, the main species identified was ZrO 2 with a small amount of dissolved UO 2 also present. This ZrO 2 consisted of a mixture of cubic polycrystals of a few nanometers in size and an amorphous phase, but no monoclinic crystal, which is the stable ZrO 2 phase at temperatures below 1170°C, was found. In a second region from the pellet surface to about 7 μm away, both a cubic solid solution of (U, Zr)O 2 and an amorphous phase existed, in which the concentrations of UO 2 and ZrO 2 changed continuously. The formation of substitutional solid solution progressed during irradiation due to a strong contact between cubic UO 2 and ZrO 2 , which induced subsequent mutual diffusion of U and Zr. Phase transformation from monoclinic to cubic ZrO 2 and amorphization were discussed in connection with fission damage.
J.f. Fernandez - One of the best experts on this subject based on the ideXlab platform.
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Effect of Bonding Layer on the electromechanical response of the cymbal metal-ceramic piezocomposite
Journal of the European Ceramic Society, 2007Co-Authors: P. Ochoa, J.l. Pons, M. Villegas, J.f. FernandezAbstract:In the present work finite element analysis, FEA, ATILA® models were generated to analyse the frequency behaviour of cymbals as a function of\ud the Bonding Layer. The experimental frequency responses were correlated with predicted values. The epoxy thickness variation, the presence of\ud epoxy meniscus or lacks of adhesive contribute to the frequency dispersion of the vibration modes.\ud A statistical rupture test was developed where the cymbals were axially loaded in a universal mechanical test machine and monitored with\ud an electrometer. The deBonding was revealed by the generated charge versus the applied force. The adequate relationships between Bonding\ud nature, frequency response and deBonding were established and shown that the asymmetries are the main parameter to control in the cymbal\ud assembly.Peer reviewe
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Effect of Bonding Layer on the electromechanical response of the cymbal metal-ceramic piezocomposite
Journal of The European Ceramic Society, 2006Co-Authors: P. Ochoa, J.l. Pons, M. Villegas, J.f. FernandezAbstract:Abstract In the present work finite element analysis, FEA, ATILA ® models were generated to analyse the frequency behaviour of cymbals as a function of the Bonding Layer. The experimental frequency responses were correlated with predicted values. The epoxy thickness variation, the presence of epoxy meniscus or lacks of adhesive contribute to the frequency dispersion of the vibration modes. A statistical rupture test was developed where the cymbals were axially loaded in a universal mechanical test machine and monitored with an electrometer. The deBonding was revealed by the generated charge versus the applied force. The adequate relationships between Bonding nature, frequency response and deBonding were established and shown that the asymmetries are the main parameter to control in the cymbal assembly.
Pablo A. Tarazaga - One of the best experts on this subject based on the ideXlab platform.
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The effects of Bonding Layer on the high-frequency dynamic response of piezoelectric augmented structures
Behavior and Mechanics of Multifunctional Materials and Composites 2017, 2017Co-Authors: Mohammad I. Albakri, Pablo A. TarazagaAbstract:Embedded and surface bonded piezoelectric wafers have been widely used for control, energy harvesting, and structural health monitoring applications. The basis for all these applications is the energy transfer between the piezoelectric wafer and the host structure, which takes place through the adhesive Bonding Layer. The characteristics of the Bonding Layer are found to have an important impact on the sensing and actuation capabilities of piezoelectric-based applications. In this paper, the high-frequency dynamic response of an elastic beam coupled with a piezoelectric wafer is investigated, including the Bonding Layer in between. A previously developed three-Layer spectral element model, with high-frequency capabilities, is utilized for this purpose. Timoshenko beam and elementary rod theories are adopted to describe axial and lateral deformations in each of the three Layers. A parametric study is conducted to evaluate the effects of Bonding Layer characteristics on the steady-state dynamic response of the coupled system, including frequency response functions and electromechanical impedance. The frequency-dependent nature of Bonding Layer effects is highlighted and discussed.
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Dynamic analysis of a piezoelectric augmented beam system with adhesive Bonding Layer effects
Journal of Intelligent Material Systems and Structures, 2016Co-Authors: Mohammad I. Albakri, Pablo A. TarazagaAbstract:Embedded and surface bonded piezoelectric wafers have been widely used for control and monitoring purposes. Several nondestructive evaluation and structural health monitoring techniques, such as electromechanical impedance and wave propagation–based techniques, utilize piezoelectric wafers in either active or passive manner to interrogate the host structure. The basis of all these techniques is the energy transfer between the piezoelectric wafer and the host structure which takes place through an adhesive Bonding Layer. In this article, the high-frequency dynamic response of a coupled piezoelectric-beam system is modeled including the adhesive Bonding Layer in between. A new three-Layer spectral element is developed for this purpose. The formulation of this new element takes into account axial and shear deformations, in addition to rotary inertia effects in all three Layers. The capabilities of the proposed model are demonstrated through several numerical examples, where the effects of Bonding Layer geome...