by Carabetta, P. M.; Bottega, W. J.

The problem of edge debonding of patched beam-plates subjected to transverse pressure is examined using two related mathematical models; one which incorporates geometric nonlinearities and the other which neglects them. The models, developed in a prior study, present the energy release rates in self-consistent functional form and yield closed form analytical solutions for the specific problem of interest. Results of numerical simulations based on each model are presented in the form of debond growth paths and compared. The growth paths are subsequently presented with corresponding pre-growth load-deflection paths to further examine the differences resulting from each model. It is seen that significant discrepancies occur between the behaviors predicted by the two models, both with regard to the onset of damage propagation and with regard to the stability of the process, as well as with regard to the pre-growth behavior, demonstrating the critical influence of geometric nonlinearities on the phenomena of interest.

DOI: 10.1007/s10704-008-9265-8
Online Date: 10/31/2008
Print publication date: 7/1/2008
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by Erinc, M.; Assman, T. M.; Schreurs, P. J. G.; Geers, M. G. D.

The ongoing miniaturization trend in the microelectronic industry enforces component sizes to approach the micron, or even the nano scale. At these scales, the underlying microstructural sizes and the geometrical dimensions are comparable. The increasing influence of microscopic entities on the overall mechanical properties makes conventional continuum material models more and more questionable. In this study, the thermomechanical reliability of lead-free BGA solder balls is investigated by microstructural modeling. Microstructural input is provided by orientation imaging microscopy (OIM), converted into a finite element framework. Blowholes in BGA solder balls are examined by optical microscopy and a statistical analysis on their size, position and frequency is conducted. Combining the microstructural data with the appropriate material models, three dimensional local models are created. The fatigue life of the package is determined through a critical solder ball. The thermomechanical reliability of the local models are predicted using cohesive zone based fatigue damage models. The simulation results are validated by statistical analyses provided by the industry.

DOI: 10.1007/s10704-008-9264-9
Online Date: 10/21/2008
Print publication date: 7/1/2008
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by Lazzarin, P.; Zappalorto, M.

The paper deals with a work-hardening, elastic–plastic, stress analysis of pointed V-notches under antiplane shear deformation loading both under small and large scale yielding. Stress and strain field intensities are expressed in terms of plastic Notch Stress Intensity Factors, which are analytically linked to the corresponding linear elastic ones under small scale yielding. The near tip stress and strain fields are then used to give closed-form expressions for the Strain Energy Density over a circular sector surrounding the notch tip, and for the J-integral parameter, both as a function of the relevant plastic NSIFs, these expressions being valid both under small and large scale yielding.

DOI: 10.1007/s10704-008-9260-0
Online Date: 10/16/2008
Print publication date: 7/1/2008
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by Zhang, Xi

A continuum model is proposed to study the effects of deformation twinning on interface crack kinking in metal/ceramics layered materials. At the final stage of material failure, plastic work hardening exhausts and lattice rotation becomes main mechanism after competing with dislocation gliding. The crack-tip plasticity is established in terms of the second gradient of microrotation due to the coupling effect of the twins. The formed twinning structures not only shield the crack tip, but inhibit further dislocation emission by increasing the near-tip stress levels. A Dislocation-Free Zone (DFZ) can exist in the immediate vicinity of the tip. The model is based on the equivalence of the stresses derived from twin-based crack-tip plasticity, macroscopic plasticity and elasticity on the boundary. The two-parameter characterization of near-tip stress fields is used for the outer plastic zone to account for constraint effects. Crack kinking out of the interface follows the direction of the maximum flow stress from the crack-tip plasticity. The DFZ size and the crack-tip shielding ratio, as well as the kink angle, are obtained for various values of low hardening exponents and crack-tip constraints.

DOI: 10.1007/s10704-008-9263-x
Online Date: 10/15/2008
Print publication date: 7/1/2008
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by Rosti, Jari; Koivisto, Juha; Traversa, Paola; Illa, Xavier; Grasso, Jean-Robert; Alava, Mikko J.

The dynamics of a “peeling front” or an elastic line is studied under creep (constant load) conditions. Our experiments show in most cases an exponential dependence of the creep velocity on the inverse force (mass) applied. In particular, the dynamical correlations of the avalanche activity are discussed here. We compare various avalanche statistics to those of a line with non-local elasticity, and study various measures of the experimental avalanche-avalanche and temporal correlations such as the autocorrelation function of the released energy and aftershock activity. From all these we conclude, that internal avalanche dynamics seems to follow “line depinning”-like behavior, in rough agreement with the depinning model. Meanwhile, the correlations reveal subtle complications not implied by depinning theory. Moreover, we also show how these results can be understood from a geophysical point of view.

DOI: 10.1007/s10704-008-9258-7
Online Date: 10/9/2008
Print publication date: 6/1/2008
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