Constitutive Relationship Development, Modeling and Measurement of Heat Stressing of Micro-SMD Assembly With Sn3.9Ag0.6Cu SAC Alloy

2005 ◽  
Author(s):  
Qiang Xiao ◽  
William D. Armstrong ◽  
James M. Pitarresi ◽  
Satish C. Chaparala ◽  
Brian D. Rogeman ◽  
...  
Keyword(s):  
Mechanical Response ◽  
Solder Joints ◽  
Bulk Material ◽  
Horizontal Displacement ◽  
Processing Parameters ◽  
Constitutive Relationship ◽  
Small Scale ◽  
Cast Material ◽  
Mechanical Models ◽  
Using Data

The Creep and microstructural changes during creep behaviors of bulk and thin cast forms of Sn3.9Ag0.6Cu were compared. The processing parameters of the thin cast material was selected to result in a very fine microstructure analogous to what occurs in very small size solder electronic interconnections. We found that the thin cast material was less creep-resistant than the bulk material. A comparison of Ag element maps between as crept bulk and thin cast material showed that the relevant climb process occurs in a very different environment in the bulk material as compared to the thin cast material. In the bulk material the relevant climb process occurs within a finely dispersed IMC eutectic which covers broad areas within the material. In the thin cast material the relevant climb process occurs primarily in the beta-Sn grains which continuously surround isolated, coarse IMC particles. This resulted in the activation energy of the bulk material being larger than that for the thin cast material. Finally, it is important to note that the strength deficiency of the thin cast material was persistent, once the material is cast in thin cast form it will remain weak in comparison to the bulk material. Therefore, using data obtained from bulk material samples for the construction of thermo-mechanical models of very small scale solder interconnections is likely to result in significant, intrinsic errors. Second, the thermal-mechanical response of electronic packages was simulated using the commercial finite element code ANSYS coupled with the Garofalo model to represent the solder constitutive creep response. The measured properties for bulk and thin-cast Sn3.9Ag0.6Cu SAC alloy were used in the FE modeling. A 36 I/O micro-surface mount device (SMD) package was used as a test vehicle in this work. Moire´ Interferometry was used to measure the horizontal displacements in the solder joints as a result of cooling the package from 100°C to room temperature. Modeling results were found to have good agreement with moire´ measurements on the actual SAC packages. The bulk properties produced a better correlation with the measurement of the horizontal displacement in the solder joints than the thin-cast properties. However, the assemblies that were tested used the Sn3.8Ag0.6Cu alloy rather than the Sn3.9Ag0.6Cu alloy. It is not known if this difference is significant to the thermo-mechanical response.

scholarly journals Electrospinning of PCL-Based Blends: Processing Optimization for Their Scalable Production

Materials ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 3853
Author(s):  
Marina P. Arrieta ◽  
Adrián Leonés Gil ◽  
Maysa Yusef ◽  
José M. Kenny ◽  
Laura Peponi
Keyword(s):  
Thermal Stability ◽  
Mechanical Response ◽  
Bulk Material ◽  
Processing Parameters ◽  
Industrial Sector ◽  
Industrial Applications ◽  
Elongation At Break ◽  
Processing Optimization ◽  
Scalable Production

In this work poly(ε-caprolactone) (PCL) based electrospun mats were prepared by blending PCL with microcrystalline cellulose (MCC) and poly(3-hydroxybutyrate) (PHB). The electrospinning processing parameters were firstly optimized with the aim to obtain scalable PCL-based electrospun mats to be used in the industrial sector. Neat PCL as well as PCL-MCC and PCL-PHB based mats in different proportions (99:1; 95:5; 90:10) were prepared. A complete morphological, thermal and mechanical characterization of the developed materials was carried out. Scanning electron microscopy (SEM) observations showed that the addition of PHB to the PCL matrix considerably reduced the formation of beads. Both the addition of MCC and PHB reduced the thermal stability of PCL, but obtained materials with enough thermal stability for the intended use. The electrospun PCL fibers show greatly reduced flexibility with respect to the PCL bulk material, however when PCL is blended with PHB their stretchability is increased, changing their elongation at break from 35% to 70% when 10 wt% of PHB is blended with PCL. However, the mechanical response of the different blends increases with respect to the neat electrospun PCL, offering the possibility to modulate their properties according to the required industrial applications.

Mechanical Response of Porous and Dense NiTi-TiC Composites

2004 ◽  
Vol 844 ◽  
Author(s):  
Douglas E. Burkes ◽  
Guglielmo Gottoli ◽  
John J. Moore ◽  
Reed A. Ayers
Keyword(s):  
Material Properties ◽  
Mechanical Response ◽  
Bulk Material ◽  
Processing Parameters ◽  
Ceramic Composites ◽  
Advanced Materials ◽  
Matrix Composites ◽  
Compression Tests ◽  
Commercial Applications ◽  
Micro Indentation

ABSTRACTThe Center for Commercial Applications of Combustion in Space (CCACS) at the Colorado School of Mines is currently using combustion synthesis to produce several advanced materials. These materials include ceramic, intermetallic, and metal-matrix composites in both porous and dense form. Currently, NiTi – TiC intermetallic ceramic composites are under investigation for use as a bone replacement material. The NiTi intermetallic has the potential to provide a surface that is capable of readily producing an oxide layer for corrosion resistance. The TiC ceramic has the potential to increase the hardness and wear resistance of the bulk material that can improve the performance lifetime of the implant. Processing parameters are critical to the production of the NiTi – TiC composite and will be discussed. These parameters can lead to the formation of substoichiometric TiC and nickel rich NiTi that changes the overall mechanical and material properties. In addition, the size of the TiC particles present within the bulk product varies with porosity. Both porous and dense samples have been mechanically analyzed employing micro-indentation techniques as well as compression tests in an attempt to characterize the mechanical response of these composites. The effects of the TiC particles, the formation of Ni3Ti intermetallic and the effects of porosity on the overall mechanical and material properties will be discussed.

Student Perceptions of Community: A Different Perspective

NASPA Journal ◽  
1998 ◽  
Vol 35 (4) ◽  
Author(s):  
Jackie Clark ◽  
Joan Hirt
Keyword(s):  
Student Perceptions ◽  
Large Scale ◽  
Research University ◽  
Small Scale ◽  
Social Environments ◽  
Common Assumption ◽  
Small Communities ◽  
Public Research University ◽  
The Common ◽  
Using Data

The creation of small communities has been proposed as a way of enhancing the educational experience of students at large institutions. Using data from a survey of students living in large and small residences at a public research university, this study does not support the common assumption that small-scale social environments are more conducive to positive community life than large-scale social environments.

scholarly journals Nonlinear magneto-thermo-elastic vibration of mass sensor armchair carbon nanotube resting on an elastic substrate

2020 ◽  
Vol 7 (1) ◽  
pp. 153-165
Author(s):  
Rajendran Selvamani ◽  
M. Mahaveer Sree Jayan ◽  
Rossana Dimitri ◽  
Francesco Tornabene ◽  
Farzad Ebrahimi
Keyword(s):  
Carbon Nanotube ◽  
Mechanical Response ◽  
Scale Effects ◽  
Nonlocal Elasticity Theory ◽  
Wave Dispersion ◽  
Elastic Vibration ◽  
Ultrasonic Waves ◽  
Small Scale ◽  
Dimensionless Frequency ◽  
Mass Sensors

AbstractThe present paper aims at studying the nonlinear ultrasonic waves in a magneto-thermo-elastic armchair single-walled (SW) carbon nanotube (CNT) with mass sensors resting on a polymer substrate. The analytical formulation accounts for small scale effects based on the Eringen’s nonlocal elasticity theory. The mathematical model and its differential equations are solved theoretically in terms of dimensionless frequencies while assuming a nonlinear Winkler-Pasternak-type foundation. The solution is obtained by means of ultrasonic wave dispersion relations. A parametric work is carried out to check for the effect of the nonlocal scaling parameter, together with the magneto-mechanical loadings, the foundation parameters, the attached mass, boundary conditions and geometries, on the dimensionless frequency of nanotubes. The sensitivity of the mechanical response of nanotubes investigated herein, could be of great interest for design purposes in nano-engineering systems and devices.

scholarly journals Asymmetric competition causes multimodal size distributions in spatially structured populations

2016 ◽  
Vol 283 (1823) ◽  
pp. 20152404 ◽  
Author(s):  
Jorge Velázquez ◽  
Robert B. Allen ◽  
David A. Coomes ◽  
Markus P. Eichhorn
Keyword(s):  
Resource Competition ◽  
Structured Populations ◽  
Necessary Condition ◽  
Small Scale ◽  
Asymmetric Competition ◽  
Size Distributions ◽  
Long Term Study ◽  
Multimodal Distributions ◽  
Using Data

Plant sizes within populations often exhibit multimodal distributions, even when all individuals are the same age and have experienced identical conditions. To establish the causes of this, we created an individual-based model simulating the growth of trees in a spatially explicit framework, which was parametrized using data from a long-term study of forest stands in New Zealand. First, we demonstrate that asymmetric resource competition is a necessary condition for the formation of multimodal size distributions within cohorts. By contrast, the legacy of small-scale clustering during recruitment is transient and quickly overwhelmed by density-dependent mortality. Complex multi-layered size distributions are generated when established individuals are restricted in the spatial domain within which they can capture resources. The number of modes reveals the effective number of direct competitors, while the separation and spread of modes are influenced by distances among established individuals. Asymmetric competition within local neighbourhoods can therefore generate a range of complex size distributions within even-aged cohorts.

Double-Sided Microchannel Cooling of a Power Electronics Module Using Power Overlay

2009 ◽  
Author(s):  
Adam G. Pautsch ◽  
Arun Gowda ◽  
Ljubisa Stevanovic ◽  
Rich Beaupre
Keyword(s):  
Power Electronics ◽  
High Performance ◽  
Mechanical Response ◽  
Thermal Contact ◽  
Small Scale ◽  
Micro Channel ◽  
Performance Technology ◽  
Actual Performance ◽  
Low Performance ◽  
Microchannel Cooling

In the continuing effort to alleviate the increasing thermal loads for power electronics devices, numerous aggressive solutions have been developed, such as small-scale micro-channel heat exchangers. Although these methods can improve overall surface heat transfer to the order of 500 W cm−2, they are limited to single-sided cooling due to the typical wire-bonded electrical connections of the devices. Power overlay (POL) technology provides a stable planar structure for electrical connection, as well as attachment of an additional top-side heat exchanger. This study presents an analysis of double-sided microchannel cooling of a power electronics module. Two optimized, integral micro-channel heat sinks were attached above and below silicon power devices, with more traditional attachment on one side and a POL interface on the other. A compliant TIM was selected for low thermal resistance and good mechanical response, which allowed top-side connection to the POL surface. A theoretical model is presented that predicts the benefit of double-sided cooling based on the known performance of a single-sided heat sink and given addition thermal contact resistance for the top side. For microchannels with water, an enhancement of 26% was predicted. An experiment was also carried out to measure the actual performance benefit seen with double-sided cooling. An enhancement of over 30% was measured for a particular design. As the theory predicts, the benefit of double-sided cooling is limited for high performance designs. However, double-sided cooling could lead to high levels of thermal performance using low-performance technology.

scholarly journals Turbulent vertical diffusivity in the sub-tropical stratosphere

2007 ◽  
Vol 7 (3) ◽  
pp. 6603-6629 ◽  
Author(s):  
I. Pisso ◽  
B. Legras
Keyword(s):  
Transport Model ◽  
Numerical Models ◽  
Small Scale ◽  
Chemistry Transport Model ◽  
Weather Forecasts ◽  
Chemical Tracers ◽  
Vertical Diffusivity ◽  
Large Ensembles ◽  
Local Equivalent ◽  
Using Data

Abstract. Vertical (cross-isentropic) mixing is produced by small-scale turbulent processes which are still poorly understood and parametrized in numerical models. In this work we provide estimates of local equivalent diffusion in the lower stratosphere by comparing balloon borne high-resolution measurements of chemical tracers with reconstructed mixing ratio from large ensembles of random Lagrangian backward trajectories using European Center for Medium-range Weather Forecasts analysed winds and a chemistry-transport model (REPROBUS). We have investigated cases in subtropical latitudes using data from HIBISCUS campaign. Upper bound on the vertical diffusivity is found to be of the order of 0.5 m2 s−1 in the subtropical region, which is larger than the estimates at higher latitudes. The relation between diffusion and dispersion is studied by estimating Lyapunov exponents and studying their variation according to the presence of active dynamical structures.

scholarly journals A Review on Mechanical Models for Cellular Media: Investigation on Material Characterization and Numerical Simulation

Polymers ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 3283
Author(s):  
Guoqiang Luo ◽  
Yuxuan Zhu ◽  
Ruizhi Zhang ◽  
Peng Cao ◽  
Qiwen Liu ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Numerical Simulation ◽  
Impact Resistance ◽  
Constitutive Models ◽  
Economic Loss ◽  
Constitutive Relationship ◽  
Cell Models ◽  
Mechanical Models ◽  
Mechanical Properties Characterization ◽  
Buffer Structure

Cellular media materials are used for automobiles, aircrafts, energy-efficient buildings, transportation, and other fields due to their light weight, designability, and good impact resistance. To devise a buffer structure reasonably and avoid resource and economic loss, it is necessary to completely comprehend the constitutive relationship of the buffer structure. This paper introduces the progress on research of the mechanical properties characterization, constitutive equations, and numerical simulation of porous structures. Currently, various methods can be used to construct cellular media mechanical models including simplified phenomenological constitutive models, homogenization algorithm models, single cell models, and multi-cell models. This paper reviews current key mechanical models for cellular media, attempting to track their evolution from their inception to their latest development. These models are categorized in terms of their mechanical modeling methods. This paper focuses on the importance of constitutive relationships and microstructure models in studying mechanical properties and optimizing structural design. The key issues concerning this topic and future directions for research are also discussed.

scholarly journals Compressive Test Characteristics and Constitutive Relationship of Wet Polypropylene Macrofiber-Reinforced Shotcrete

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Fenghui Li ◽  
Yunhai Cheng ◽  
Fei Wu ◽  
Chang Su ◽  
Gangwei Li
Keyword(s):  
Mechanical Response ◽  
Average Energy ◽  
Strain Curve ◽  
Peak Stress ◽  
Constitutive Relationship ◽  
Compression Tests ◽  
Response Characteristics ◽  
Test Characteristics ◽  
High Crack ◽  
Relationship Of

Shotcrete is often subject to poor ductility and cracking problems, particularly under high stresses. In order to deal with these issues, the feasibility of adding polypropylene macrofibers to shotcrete was verified. To ascertain the supporting effect, dry shotcrete, wet shotcrete, and wet polypropylene macrofiber-reinforced shotcrete (WPMS) were used as samples. Furthermore, the mechanical response characteristics thereof in uniaxial compression tests were compared and analyzed by acoustic emission (AE) monitoring. The results showed that the three materials were brittle, but the ductility, residual strength, and bearing capacity of polypropylene macrofiber-reinforced shotcrete were significantly enhanced. The energy absorption value of plain shotcrete was higher in the cracking stage, while that of polypropylene macrofiber-reinforced shotcrete was greater in the postpeak stage, which showed that the polypropylene macrofiber-reinforced shotcrete had the characteristics of a high crack-initiation strength and toughness. Besides, the energy release from fiber shotcrete occurred after the peak stress rather than near the peak stress. The average energy absorbed by polypropylene macrofiber-reinforced shotcrete was significantly higher than that in dry shotcrete and wet shotcrete, which implied that polypropylene macrofiber-reinforced shotcrete could mitigate the brittle instability of a shotcrete layer. A constitutive model of damage statistics was established based on the test data. The comparison between the experimental data and the fitting results can reflect the characteristics of the total stress-strain curve of such shotcrete. The results provide a basis for the optimization of polypropylene macrofiber-reinforced shotcrete layers.

scholarly journals A simulation-based approach to improve decoded neurofeedback performance

2018 ◽  
Author(s):  
Ethan Oblak ◽  
James Sulzer ◽  
Jarrod Lewis-Peacock
Keyword(s):  
Real Time ◽  
Brain Activity ◽  
Processing Parameters ◽  
Orientation Tuning ◽  
Design Parameters ◽  
Visual Orientation ◽  
Brain Functions ◽  
Simulation Based ◽  
Using Data ◽  
The Right

AbstractThe neural correlates of specific brain functions such as visual orientation tuning and individual finger movements can be revealed using multivoxel pattern analysis (MVPA) of fMRI data. Neurofeedback based on these distributed patterns of brain activity presents a unique ability for precise neuromodulation. Recent applications of this technique, known as decoded neurofeedback, have manipulated fear conditioning, visual perception, confidence judgements and facial preference. However, there has yet to be an empirical justification of the timing and data processing parameters of these experiments. Suboptimal parameter settings could impact the efficacy of neurofeedback learning and contribute to the ‘non-responder’ effect. The goal of this study was to investigate how design parameters of decoded neurofeedback experiments affect decoding accuracy and neurofeedback performance. Subjects participated in three fMRI sessions: two ‘finger localizer’ sessions to identify the fMRI patterns associated with each of the four fingers of the right hand, and one ‘finger finding’ neurofeedback session to assess neurofeedback performance. Using only the localizer data, we show that real-time decoding can be degraded by poor experiment timing or ROI selection. To set key parameters for the neurofeedback session, we used offline simulations of decoded neurofeedback using data from the localizer sessions to predict neurofeedback performance. We show that these predictions align with real neurofeedback performance at the group level and can also explain individual differences in neurofeedback success. Overall, this work demonstrates the usefulness of offline simulation to improve the success of real-time decoded neurofeedback experiments.

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