IMECE2010-37106 A VISCOPLASTICITY MODEL FOR SOLDER ALLOYS

ABSTRACT Demand for long-term reliability of electronic packaging has lead to a large number of studies on visco-plastic behavior of solder alloys. Various creep models for solder alloys have been proposed. They range from purely empirical to mechanism based models where dislocation motion and diffusion processes are taken into account. In this study, most commonly used creep models are compared with the test data and implemented in ABAQUS to compare their performance in cycling loading. Finally, a new creep model is proposed that combines best features of many models. It is also shown that, while two viscoplasticity models may describe the same material stress-strain rate curves equally well, however they may yield very different results when utilized for cycling loading. One interesting observation of this study is that the stress exponent, n, also depends on the grain size

Joule heating in single-walled carbon nanotubes

Articles you may be interested in Graphene and carbon nanotubes are materials with large potentials for applications in flexible electronics. Such devices require a high level of sustainable strain and an understanding of the materials electrical properties under strain. Using supercell theory in conjunction with a comprehensive molecular mechanics model, the full band phonon dispersion of carbon nanotubes under uniaxial strain is studied. The results suggest an overall phonon softening and open up the possibility of phonon quantization tuning with uniaxial strain. The change in phonon quantization and the resulting increase in electron-phonon and phonon-phonon scattering rates offer further explanation and theoretical basis to the experimental observation of electrical properties degradation for carbon nanotubes under uniaxial strain. V C 2014 AIP Publishing LLC

An accelerated algorithm for full band electron-phonon scattering rate computation

a b s t r a c t Computing scattering rates of electrons and phonons stands at the core of studies of electron transport properties. In the high field regime, the interactions between all electron bands with all phonon bands need to be considered. This full band interaction implies a huge computational burden in calculating scattering rates. In this study, a new accelerated algorithm is presented for this task, which speeds up the computation by two orders of magnitude (100 times) and dramatically simplifies the coding. At the same time, it visually demonstrates the physical process of scattering more clearly. Computer: All. Program summary Operating system: All. RAM: Depends on problem, ∼kB to MB Classification: 16.5. Nature of problem: Electron-phonon scattering is a fundamental problem in studying electron transport in condensed matters. There are situations where the scattering rates need to be updated frequently during a simulation, e.g. when hot phonon effects are considered. The speed of scattering calculation is very important in such cases. Solution method: In searching for possible scattering events, we propose here a band-by-band method, instead of the traditional point by point method. The whole calculation is parallelized in this sense and dramatically accelerated. Moreover, we proposed a representation method for all scattering mechanisms, which greatly simplified the coding task. Also, the additional animation part of this program demonstrates many insights into the scattering process. Restrictions: To use the code directly, electron band and phonon band should have the same mesh size. In other words, for each phonon band and electron band, they should have the same number of data points. ✩ This paper and its associated computer program are available via the Computer Physics Communication homepage on ScienceDirec

GEOPHYSICAL IMAGING SURVEY IN THE SOUTH NECROPOLIS AT THE ANCIENT CITY OF PARION (KEMER - BIGA), NORTHWESTERN ANATOLIA, TURKEY: PRELIMINARY RESULTS

Parion is one of the most important settlements located in the ancient Troas region, in which the city of Troy was the center. Many remarkable and precious archaeological remains have been unearthed so far which point out the city's importance during the Hellenistic and Roman Age. In this study, a first attempt to obtain high resolution images of the subsurface of Parion to guide the archaeological trenches was made by an initial geophysical survey applying Electrical Resistivity Tomography (ERT) technique. The apparent resistivity data, collected using pole-dipole electrode configuration along 11 transects, were inverted by two- and three-dimensional smoothness-constrained least squares algorithms. Relatively compatible results were obtained from two inversion processes. Parallel transects showed the resistivity distribution in three-dimensional images and thus both the horizontal and vertical extents of the anomalous zones were displayed. Additionally, some high anomaly zones located at the end of the first six transects were backed up by archaeological trenches. Thus, taking into account these findings, the other resistivity anomalies located at the different parts of the surveyed area are thought to be the most promising locations for archaeological excavations

Lattice Strain Due to an Atomic Vacancy

Volumetric strain can be divided into two parts: strain due to bond distance change and strain due to vacancy sources and sinks. In this paper, efforts are focused on studying the atomic lattice strain due to a vacancy in an FCC metal lattice with molecular dynamics simulation (MDS). The result has been compared with that from a continuum mechanics method. It is shown that using a continuum mechanics approach yields constitutive results similar to the ones obtained based purely on molecular dynamics considerations

Thermomigration induced degradation in solder alloys

Miniaturization of electronics to the nanoscale brings new challenges. Because of their small size and immense information and power processing capacity, large temperature gradients exist across nanoelectronics and power electronics solder joints. In this paper, a fully coupled thermomechanical-diffusion model is introduced to study the thermomigration induced strength degradation. A nonlinear viscoplastic material model with kinematic and isotropic hardening features is utilized. The model takes into account microstructural evolution of the material. A grain coarsening capability is built into the model to study its influence on thermomigration in solder alloys. The model is validated by comparing the simulation results with experimental data