Experimental and Numerical Analysis of Thermal Deformation of Electronic Packages,QFP and MCM

0Introduction Anelectronicpackageisgenerallyconstructedwithanactivesiliconchip,mountisland,gold wires,leadframesandsoldersasshowninFig.1(a).Toprotectfromtheenvironment,thesilicon chipisusuallyencapsulatedinresin.SincethesematerialshavedifferentCTE(coefficientofthermal expansion),stressandstrainaregeneratedbyinternalheatinginserviceoperationorthermalloading fromtheenvironment[1].Insomecases,thismaycausefailureofthewireandcrackinganddebonding insidethepackage.Thereliabilityofelectronicpackages…     

Comparison of integrated characteristics and shapes of profiled contours of laval nozzles with “smooth” and “abrupt” contractions

The influence of the selection of the generator of subsonic sections of plane and axisymmetric Laval nozzles on the integrated characteristics and on the shapes of their profiled supersonic parts is investigated in the approximation of an ideal (inviscid and nonheat-conducting) gas. Nozzles with a smooth entrance and with an abrupt contraction are compared for the same flow rates and size restrictions on the whole nozzle, not only to its supersonic part. In such a formulation, in accordance with [1], nozzles with abrupt contractions in the flow of ideal gas in them should be expected to have the best characteristics. This is confirmed by the results of the calculations performed.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 129–137, July–August, 1986.The authors are grateful to V. A. Vostretsova for her help in the work.     

Fabrication and electrochemical performance of nanofibrous micro-frameworks of α-MnO_2

A facile solid-phase conversion route is proposed to fabricate a micro-framework of α-MnO_2 with a nanofibrous structure and high porosity.The fabrication is achieved by a three-step process using a preformed manganese tartrate with a rectangular framework as the precursor followed by thermal annealing and hydrothermal oxidation to form the final nanofibrous structure.Evolution of the phase and the morphology are characterized by FESEM,XRD,TG-DTA,and TEM measurements.The electrochemically active material α-MnO_2 exhibits both attractive stability of the Coulombic efficiency after long-term cyclic charging/discharging and acceptable specific capacitance.     

Simulation and prediction of membrane fusion dynamics

Membrane fusion is an important process by which biological membranes perform their life activities. Simulations show that the membrane fusion process happens mainly through three pathways, where the Stalk-Pore hypothesis, in which two membranes come into close contact to form a stalk to a hemifusion intermediate, and then the fusion pore opens to achieve completely fusion, is widely accepted, and there exist two free energy barriers that break the current structural steady state for lipid rearrangement. Factors of lipid composition, mechanical environment, protein and ion have regulatory roles in the membrane fusion process by effecting membrane curvature structurally and the free energy barriers from energetic perspective. Meanwhile, many theoretical models, represented by the Helfrich model, have been proposed to predict the membrane fusion process. In this paper, we review the research process of membrane fusion and mainly introduce the dynamics of membrane fusion, regulation factors and typical theoretical models.     

Scale effect and geometric shapes of grains

The rule-of-mixture approach has become one of the widely spread ways to investigate the mechanical properties of nano-materials and nano-structures,and it is very important for the simulation results to exactly compute phase volume fractions.The nanocrystalline(NC)materials are treated as three-phase composites consisting of grain core phase,grain boundary(GB)phase and triple junction phase,and a two-dimensional three-phase mixture regular polygon model is established to investigate the scale effect of mechanical properties of NC materials due to the geometrical polyhedron characteristics of crystal grain.For different multi-sided geometrical shapes of grains,the corresponding regular polygon model is adopted to obtain more precise phase volume fractions and exactly predict the mechanical properties of NC materials.     

Ageing and collapse of bentonite gels—effects of Li,Na, K and Cs ions

The state of bentonite gels at the start of the ageing experiment must be well-defined, and this required the gels to be at a constant surface chemistry condition. This is achieved by allowing the freshly prepared gels to rest for a day. At this state, the yield stress is constant, provided that the gel is at an equilibrium breakdown state after stirring prior to each measurement. This point is also the yield stress at zero aged time. Ageing study then commenced, and the behaviour is generally characterised by an increasing yield stress with wait time. Alkali metal ion type and concentration affect the gel ageing and stability behaviour significantly. The ageing behaviour is most pronounced at low salt concentrations for the smallest and most strongly hydrated cations, Li ⁺and Na ⁺. The yield stress at any given aged time and its rate of increase are generally larger. Coarsening of these suspensions was observed. The opposite is true for the weakly hydrated K ⁺and Cs ⁺ions. At high concentrations of 0.5 and 1.0 M Cs, K and Na ions, the gels became unstable over time and phase-separated. The stability time of these weak gels was found to increase with decreasing cation size, Na > K > Cs. This stability time displayed a very strong quantitative correlation with the hydration bond length. Coarsening was also expected, but not observed due to the lack of integrity of these weak aggregates during particle size measurement. The recovery or ageing behaviour was fitted with both the Nguyen–Boger and Leong models.     

DEM investigation of macro-and micro-mechanical properties of rigid-grain and soft-chip mixtures

We investigated the macro-and micro-mechanical properties of rigid-grain and soft-chip mixtures(GCMs)through numerical simulations using the discrete element method.We present a novel framework for the discrete modeling of soft chips and rigid grains in conjunction with calibration processes.Several numerical triaxial tests were also performed on GCMs with 0%,10%,20%,and 30%volumetric chip contents,P.The simulation results demonstrate that increasing P leads to higher GCM toughness,higher deviatoric peak stress,and higher corresponding shear strain.Higher P also contributes to more volume contraction and less dilation.The friction angles at both the peak and residual state significantly increase with increasing P.In view of the micro-mechanical features,strong contact force chains develop along the loading direction,which results in considerable anisotropy in the peak and residual states.Both the formation of strong force chains and rotation of grains decrease with increasing P,whereas the grain sliding percentage increases.The tensile force is mobilized with shearing and higher P leads to less mobilization of the tensile force.These findings are useful for better understanding the internal structure of GCMs with different soft-chip contents,especially in granular mixture mechanics and geomechanics.     

The General Mathematical Theory of Plasticity and the Il’yushin Postulates of Macroscopic Definability and Isotropy

The physical laws characterizing the relation between stresses and strains are considered and analyzed in the general modern theory of elastoplastic deformations and in its postulates of macroscopic definability and isotropy for initially isotropic continuous media. The fundamentals of this theory in continuum mechanics were developed by A.A. Il’yushin in the mid-twentieth century. His theory of small elastoplastic deformations under simple loading became a generalization of Hencky’s deformation theory of flow, whereas his theory of elastoplastic processes which are close to simple loading became a generalization of the Saint-Venant–Mises flow theory to the case of hardening media. In these theories, the concepts of simple arid complex loading processes arid the concept of directing form change tensors are introduced; the Bridgman law of volume elastic change and the universal Roche–Eichinger laws of a single hardening curve under simple loading are adopted; and the Odquist hardening for plastic deformations is generalized to the case of elastoplastic hardening media for the processes of almost simple loading without consideration of a specific history of deformations for the trajectories with small arid mean curvatures. In this paper we discuss the possibility of using the isotropy postulate to estimate the effect of forming parameters in the stress-strain state appeared due to the strain-induced anisotropy during the change of the internal structures of materials. We also discuss the possibility of representing the second-rank symmetric stress and strain tensors in the form of vectors in the linear coordinate six-dimensional Euclidean space. An identity principle is proposed for tensors and vectors.     

Techniques and Applications of the Simulated Pattern Adaptation of Wilkinson’s Method for Advanced Microstructure Analysis and Characterization of Plastic Deformation

Electron Backscatter Diffraction (EBSD) based Orientation Imaging Microscopy (OIM) is used routinely at ~500 materials laboratories worldwide for the characterization and development of diverse crystalline materials. Statistically significant data sets (~10⁷ individual EBSD measurements) can be collected and analyzed within time periods of acceptable beam stability (~10⁵s). However, limitations in angular and spatial resolution have motivated a continued search for more robust EBSD-based methods. Herein is a gathered presentation of advanced techniques in use, intended as a guide to researchers in selecting the most appropriate method for their work. Wilkinson’s method has been shown to increase angular resolution nearly two orders of magnitude to ±0.006°, facilitating measurement of elastic strain, lattice curvature, and dislocation density. A simulated pattern adaptation of Wilkinson’s method extends these measurement capabilities to polycrystalline materials, by avoiding the need for an experimental strain free reference pattern. The angular resolution limit obtained is ~0.04°. Accurate pattern center calibration, essential to the high resolution methods, is accomplished by parallelization of band edges projected onto a sphere centered at the interaction volume. FFT powered cross-correlation functions improve the spatial resolution near grain boundaries and correct for measurement inaccuracies induced by overlapping patterns. To corroborate these claims, exemplary results taken from a wedge-indented nickel single crystal, cold-worked copper polycrystal, and rolled nickel polycrystal are shown.     

Intrinsic Geometry and Analysis of Diffusion Processes and L ∞-Variational Problems

The aim of this paper is twofold. First, we obtain a better understanding of the intrinsic distance of diffusion processes. Precisely, (a) for all n ≧ 1, the diffusion matrix A is weak upper semicontinuous on Ω if and only if the intrinsic differential and the local intrinsic distance structures coincide; (b) if n = 1, or if n ≧ 2 and A is weak upper semicontinuous on Ω, the intrinsic distance and differential structures always coincide; (c) if n ≧ 2 and A fails to be weak upper semicontinuous on Ω, the (non-)coincidence of the intrinsic distance and differential structures depend on the geometry of the non-weak-upper-semicontinuity set of A. Second, for an arbitrary diffusion matrix A, we show that the intrinsic distance completely determines the absolute minimizer of the corresponding L ^∞-variational problem, and then obtain the existence and uniqueness for given boundary data. We also give an example of a diffusion matrix A for which there is an absolute minimizer that is not of class C ¹. When A is continuous, we also obtain the linear approximation property of the absolute minimizer.     

Editorial of 10-years Anniversary of Theoretical and Applied Mechanics Letters

It has been ten years since 2011 when the first issue of Theoretical and Applied Mechanics Letters(TAML) came out. To date, TAML has published over 700 articles and 30 special issues covering a broad range of topics in mechanics. Such great achievements are even not possible without the continued dedication and support from authors, reviewers and editors. At this very special moment, I would like to express my sincere thanks to all of you, and hope you will continue to devote your time and effort s to the further advances of TAML.     

Numerical Study of Hydrodynamics and Heat and Mass Transfer of a Ducted Gas–Vapor‐Droplet Flow

A computational model has been developed to predict heat and mass transfer and hydrodynamic characteristics of a turbulent gas–vapor–droplet flow. Turbulent characteristics of the gas phase are computed using the k– model of turbulence. It is shown that, with increasing inlet droplet diameter, the rate of heat transfer between the duct surface and the vapor–gas mixture decreases appreciably, whereas the wall friction increases only insignificantly. The predicted values agree fairly well with available experimental and numerical data     

Homogenization of the nonlinear Kelvin–Voigt model of viscoelasticity and of the Prager model of plasticity

Denoting by the stress tensor, by the linearized strain tensor, by A the elasticity tensor, and assuming that is a convex potential, the inclusion accounts for nonlinear viscoelasticity, and encompasses both the linear Kelvin–Voigt model of solid-type viscoelasticity and the Prager model of rigid plasticity with linear kinematic strain-hardening. This relation is assumed to represent the constitutive behavior of a space-distributed system, and is here coupled with the dynamical equation. An initial- and boundary-value problem is formulated, and the existence and uniqueness of the solution are proved via classical techniques based on compactness and monotonicity. A composite material is then considered, in which the function and the tensor A rapidly oscillate in space. A two-scale model is derived via Nguetseng’s notion of two-scale convergence. This provides a detailed account of the mesoscopic state of the system. Any dependence on the fine-scale variable is then eliminated, and the existence of a solution of a new single-scale macroscopic model is proved. The final outcome is at variance with the nonlinear extension of the generalized Kelvin–Voigt model, which is based on an apparently unjustified mean-field-type hypothesis.     

Isothermal viscoelastic properties of PMMA and LDPE over 11 decades of frequency and time: a test of time–temperature superposition

Many instruments used to measure viscoelastic properties are only capable of subjecting a sample to a limited range of loading frequencies. For thermorheologically simple materials, it is assumed that a change in temperature is equivalent to a shift of the viscoelastic behavior on the log frequency or time axis. For many materials, time–temperature superposition appears to work well for modulus or compliance curves over three decades of time or frequency, but some deviations are known if the window is expanded to five or six decades. To apply a more stringent test of the validity of time–temperature superposition, broadband viscoelastic spectroscopy is used to isothermally study polymethylmethacrylate and low-density polyethylene at several temperatures in the glassy region. Shear modulus and damping (tan δ) are measured isothermally over a wide range (up to 11 decades) of time and frequency. Results indicate that, while modulus curves can be approximately superimposed, the damping (tan δ) curves change in height and shape with temperature.     

The moiré method and the evaluation of principal-moment and stress directions

This paper discusses, in relation to the moiré method as used for the solution of plate bending and two-dimensional stress problems, two graphical techniques for the determination of the directions of principal moments and stresses.The so-called isoclinic method and the point method are described.The application of these new techniques on three different models—a circular disk under diametrically opposite loads and two different circular plates subjected to a lateral load—are fully discussed.The graphically determined principal-stress and moment directions show excellent agreement with analytically determined comparable values.Paper was presented at 1963 SESA Annual Meeting held in Boston, Mass., on November 6–8.     

Identification of parameters of models of nonlinear deformation of isotropic and composite materials on the basis of calculations and experiments aimed at analyzing the dynamic behavior of cylindrical metal–plastic shells

A method for identification of material parameters of the constitutive relations of elastoplastic and viscoelastic deformation of isotropic and composite materials is developed. The method is based on minimizing the functional of the residue of results of numerical and experimental analysis of unsteady deformation of structural elements made of examined materials. The method is tested, and prospects of its application for determining material parameters of viscoelastic and elastoplastic models of nonlinear deformation of cylindrical metal–plastic shells under explosive loading are demonstrated.     

Phase behavior and effects of microstructure on viscoelastic properties of a series of polylactides and polylactide/poly(ε-caprolactone) copolymers

Dynamic viscoelastic measurements were combined with differential scanning calorimetry (DSC) and atomic force microscopy (AFM) analysis to investigate the rheology, phase structure, and morphology of poly(l-lactide) (PLLA), poly(ε-caprolactone) (PCL), poly(d,l-lactide) (PDLLA) with molar composition l-LA/d-LA?=?53:47, and poly(l-lactide-co-ε-caprolactone) (PLAcoCL) with molar composition l-LA/CL?=?67:33. After melt conformation, both copolymers PDLLA and PLAcoCL were found to be amorphous whereas PLLA and PCL presented partial crystallinity. The copolymers and PCL were considered as thermorheologically simple according to the rheological methods employed. Therefore, data from different temperatures could be overlapped by a simple horizontal shift (a _T) on elastic modulus, G′, and loss modulus, G′, versus frequency graph, generating the corresponding master curves. Moreover, these master curves showed a dependency of G″≈ω and G′≈ω ² at low frequencies, which is a characteristic of homogeneous melts. For the first time, fundamental viscoelastic parameters, such as entanglement modulus G _N ⁰ and reptation time τ _d, of a PLAcoCL copolymer were obtained and correlated to chain microstructure. PLLA, by contrast, was unexpectedly revealed as a thermorheologically complex liquid according to the failure observed in the superposition of the phase angle (δ) versus the complex modulus (G*); this result suggests that the narrow window for rheological measurements, chosen to be close to the melting point centered at 180 °C thus avoiding thermal degradation, was not sufficient to assure an homogeneous behavior of PLLA melts. The understanding of the melt rheology related to the chain microstructural aspects will help in the understanding of the complex phase structures present in medical devices.     

Effects of viscoelasticity on the stability and bifurcations of nonlinear energy sinks

Due to the increasing use of passive absorbers to control unwanted vibrations,many studies have been done on energy absorbers ideally, but the lack of studies of real environmental conditions on these absorbers is felt. The present work investigates the effect of viscoelasticity on the stability and bifurcations of a system attached to a nonlinear energy sink(NES). In this paper, the Burgers model is assumed for the viscoelasticity in an NES, and a linear oscillator system is considered for inve...     

Material behavior of steel – Modeling of complex phenomena and thermodynamic consistency

Steel has a complex material behavior. Stress- and strain-dependent phase transformations, transformation-induced plasticity (TRIP), and its interactions with plasticity are important phenomena of both theoretical and practical interest, as they may cause distortion of work-pieces. These phenomena continue to be intensively studied both experimentally and theoretically. In order to simulate real processes like heat treatment of work-pieces, one has to include the relevant phenomena in a suitable bulk model. It is the aim of the current paper to contribute to the formulation of such a model in the context of macroscopic continuum mechanics and to discuss the capabilities. Due to the possible interaction (coupling) of TRIP and plasticity, the usual approach in plasticity without phase transformations has to be modified substantially. We apply a general approach for non-linear hardening, allowing to model observable effects of interaction of plasticity and TRIP. Besides this, we prove the thermodynamic consistency under sufficient conditions.     

Effects of Anisotropy and Drying Air Parameters on Drying of Deformable Porous Media Hydro-Dynamically and Thermally Anisotropic

The purpose of this work was to investigate numerically the drying of saturated deformable porous media. The considered sample is a rectangular porous plate which assumed to be both hydro-dynamically and thermally anisotropic, while the mechanical behavior of the sample is supposed to be isotropic. All walls of the plate are subjected to a convective heat flux. Moreover, the top and bottom walls are allowed the mass transfer. The Darcy–Brinkman extended model was used as the momentum balance equation for the liquid and solid phases. The energy balance equation is based on the local thermodynamic equilibrium assumption between the both phases. The lattice Boltzmann method is used to solve the governing differential equation system. A comprehensive analysis of the effect of anisotropy and the drying air parameters on macroscopic fields is investigated throughout this work.