Multiscale and Multiphysics Modelling of Materials

2001 ◽

Vol 215 (3) ◽

pp. 259-263 ◽

Cited By ~ 4

Author(s):

Z Chen ◽

H E Fang

Keyword(s):

Bifurcation Analysis ◽

Failure Modes ◽

Damage Model ◽

Multiscale Modelling ◽

Material Failure ◽

Continuum Damage ◽

Stiffness Tensor ◽

Tangent Stiffness ◽

The Continuum

To predict the transition from continuous to discontinuous failure modes, a bifurcation analysis is performed based on the continuum tangent stiffness tensor of a coupled plasticity and damage model. As a result, continuum damage and decohesion approaches can be combined for multiscale modelling of material failure.

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Thermo-mechanical behaviour of ceramic metal brazed assemblies

Proceedings of the Institution of Mechanical Engineers Part L Journal of Materials Design and Applications ◽

10.1243/14644207jmda195 ◽

2008 ◽

Vol 222 (4) ◽

pp. 291-297 ◽

Cited By ~ 3

Author(s):

V Cazajus ◽

B Lorrain ◽

H Welemane ◽

Y Paranthoen ◽

M Karama

Keyword(s):

Tensile Strength ◽

Residual Stresses ◽

Brittle Failure ◽

Composite Structures ◽

Failure Modes ◽

Experimental Tests ◽

Metallic Materials ◽

Physical Mechanisms ◽

Brazed Joints ◽

Cooling Phase

This study investigates the effects of residual stresses developed during brazing on the performance of brazed ceramic metal joints. The thermal expansion gradient between ceramic and metallic materials leads to the development of such stresses during the cooling phase of the brazing process, which consequently reduce the strength of these composite structures. Here, the objective is to compare the failure behaviour of various assemblies observed during experimental tests and obtained through numerical simulations. In order to get a representation consistent with the physical mechanisms involved, these simulations must account for the brazing phase giving rise to residual stresses before applying in use solicitations to brazed joints. This paper focuses on the tensile strength of ceramic metal joints, for which two brittle failure modes (within the ceramic or at the interface) are observed during the experimental tests.

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SEM Examination of a Used Diamond Knife

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100066310 ◽

1971 ◽

Vol 29 ◽

pp. 452-453

Author(s):

J. Temple Black

Keyword(s):

Electron Microscope ◽

High Voltage ◽

High Magnification ◽

Metallic Materials ◽

Wide Spread ◽

Thin Sections ◽

Transmission Electron ◽

Scanning Transmission ◽

Scanning Electron ◽

Diamond Knife

Since its introduction by Fernandez-Moran, the diamond knife has gained wide spread usage as a common material for cutting of thin sections of biological and metallic materials into thin films for examination in the transmission electron microscope. With the development of high voltage E.M. and scanning transmission E.M., microtomy applications will become increasingly important in the preparation of specimens. For those who can afford it, the diamond knife will thus continue to be an important tool to accomplish this effort until a cheaper but equally strong and sharp tool is found to replace the diamond, glass not withstanding.In Figs. 1 thru 3, a first attempt was made to examine the edge of a used (β=45°) diamond knife by means of the scanning electron microscope. Because diamond is conductive, first examination was tried without any coating of the diamond. However, the contamination at the edge caused severe charging during imaging. Next, a thin layer of carbon was deposited but charging was still extensive at high magnification - high voltage settings. Finally, the knife was given a light coating of gold-palladium which eliminated the charging and allowed high magnification micrographs to be made with reasonable resolution.

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Observation of secondary slip systems in tungsten bicrystals

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100112361 ◽

1984 ◽

Vol 42 ◽

pp. 478-479

Author(s):

J. R. Fekete ◽

R. Gibala

Keyword(s):

Stress Field ◽

Grain Boundaries ◽

Deformation Behavior ◽

Stress Axis ◽

Polycrystalline Materials ◽

Slip Systems ◽

Metallic Materials ◽

Twist Boundary ◽

Secondary Slip ◽

Plane Normal

The deformation behavior of metallic materials is modified by the presence of grain boundaries. When polycrystalline materials are deformed, additional stresses over and above those externally imposed on the material are induced. These stresses result from the constraint of the grain boundaries on the deformation of incompatible grains. This incompatibility can be elastic or plastic in nature. One of the mechanisms by which these stresses can be relieved is the activation of secondary slip systems. Secondary slip systems have been shown to relieve elastic and plastic compatibility stresses. The deformation of tungsten bicrystals is interesting, due to the elastic isotropy of the material, which implies that the entire compatibility stress field will exist due to plastic incompatibility. The work described here shows TEM observations of the activation of secondary slip in tungsten bicrystals with a [110] twist boundary oriented with the plane normal parallel to the stress axis.

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Scanning Electron Microscopy in Hybrid Microelectronics

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100092244 ◽

1976 ◽

Vol 34 ◽

pp. 456-457

Author(s):

S. Khadpe ◽

R. Faryniak

Keyword(s):

Integrated Circuits ◽

Thick Film ◽

Integrated Circuit ◽

Failure Modes ◽

Three Dimensional ◽

Circuit Components ◽

Hybrid Microcircuit ◽

Electrical Connections ◽

Scanning Electron

The Scanning Electron Microscope (SEM) is an important tool in Thick Film Hybrid Microcircuits Manufacturing because of its large depth of focus and three dimensional capability. This paper discusses some of the important areas in which the SEM is used to monitor process control and component failure modes during the various stages of manufacture of a typical hybrid microcircuit.Figure 1 shows a thick film hybrid microcircuit used in a Motorola Paging Receiver. The circuit consists of thick film resistors and conductors screened and fired on a ceramic (aluminum oxide) substrate. Two integrated circuit dice are bonded to the conductors by means of conductive epoxy and electrical connections from each integrated circuit to the substrate are made by ultrasonically bonding 1 mil aluminum wires from the die pads to appropriate conductor pads on the substrate. In addition to the integrated circuits and the resistors, the circuit includes seven chip capacitors soldered onto the substrate. Some of the important considerations involved in the selection and reliability aspects of the hybrid circuit components are: (a) the quality of the substrate; (b) the surface structure of the thick film conductors; (c) the metallization characteristics of the integrated circuit; and (d) the quality of the wire bond interconnections.

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