Techno Press
Tp_Editing System.E (TES.E)
Login Search


You have a Free online access.
mmm
 
CONTENTS
Volume 1, Number 2, April 2016
 

Abstract
The trigonal shape memory alloys (SMAs) have a great potential to be utilized as the applications with special purposes, such as actuators with high operation frequency. Most studies on the trigonal microstructures typically focus on the well-known classic herringbone pattern, but many other patterns are also possible, such as non-classic herringbone, toothbrush and checkerboard patterns. In the current work, a systematic procedure is developed to find all possible laminate twin microstructures by using geometrically linear compatibility theory. The procedure is verified by SEM images with the information of crystallographic axes of unitcells obtained by EBSD, showing good agreement. Many interesting trigonal Rphase patterns are found in the specimen. Then, their incompatibility are analyzed with nonlinear compatibility theory. The relationship between such incompatibility and the likelihood of occurrence of the microstructures is revealed. The current procedure is rapid, computationally efficient and sufficiently general to allow further extension to other crystal systems and materials.

Key Words
shape memory alloys; compatibility; laminate twins

Address
Department of Materials Science and Engineering, NCTU, Ta Hsueh Road, HsinChu 300, Taiwan

Abstract
Manufactures of multi-crystalline silicon ingots by means of the directional solidification system (DSS) is important to the solar photovoltaic (PV) cell industry. The quality of the ingots, including the grain size and morphology, is highly related to the shape of the crystal-melt interface during the crystal growth process. We performed numerical simulations to analyze the thermo-fluid field and the shape of the crystalmelt interface both for steady conditions and transient processes. The steady simulations are first validated and then applied to improve the hot zone design in the furnace. The numerical results reveal that, an additional guiding plate weakens the strength of vortex and improves the desired profile of the crystal-melt interface. Based on the steady solutions at an early stage, detailed transient processes of crystal growth can be simulated. Accuracy of the results is supported by comparing the evolutions of crystal heights with the experimental measurements. The excellent agreements demonstrate the applicability of the present numerical methods in simulating a practical and complex system of directional solidification system.

Key Words
directional solidification system; multi-crystalline silicon; crystal growth; solar photovoltaic cell

Address
Department of Mechanical Engineering, National Chiao Tung University, Taiwan, R.O.C.

Abstract
Changes in chemical structure have profound effects on the physical properties of epoxy-based materials, and eventually affect the durability of the entire system. Microscopic structural voids generally existing in the epoxy cross-linked networks have a detrimental influence on the epoxy mechanical properties, but the relation remains elusive, which is hindered by the complex structure of epoxy-based materials. In this paper, we investigate the effect of structural voids on the epoxy-based materials by using our developed mesoscale model equipped with the concept of multiscale modeling, and SU-8 photoresist is used as a representative of epoxy-based materials. Developed from the results of full atomistic simulations, the mesoscopic model is validated against experimental measurements, which is suitable to describe the elastic deformation of epoxy-based materials over several orders of magnitude in time- and length scales. After that, a certain quantity of the structure voids is incorporated in the mesoscale model. It is found that the existence of structural voids reduces the tensile stiffness of the mesoscale epoxy network, when compared with the case without any voids in the model. In addition, it is noticed that a certain number of the structural voids have an insignificant effect on the epoxy elastic properties, and the mesoscale model containing structural voids is close to those found in real systems.

Key Words
multiscale modeling; molecular dynamics; mesoscale mechanics; epoxy-based materials; structural voids

Address
Lik-ho Tam and Denvid Lau: Department of Architecture and Civil Engineering, City University of Hong Kong, Hong Kong, China

Denvid Lau: Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

Abstract
Reinforced concrete (RC) structures require advanced analysis techniques for better estimation of their seismic responses, especially in the case of exhibiting complex three-dimensional coupling of torsional and flexural behaviors. This study focuses on validating a numerical approach for evaluating the seismic response of a three-dimensional unsymmetrical RC structure through the participation in the SMART 2013 international benchmark program. The benchmark program provides material properties, detailed drawings of the RC structure, and input ground motions for the seismic response evaluation. In this study, nonlinear constitutive models of concrete and rebar were formed and local tests were conducted to verify the constitutive models in finite element analysis. Elastic calibration of the finite element model of the SMART 2013 RC structure was performed by comparing numerical and experimental results in modal and linear time history analyses. Using the calibrated model, nonlinear earthquake analysis and seismic fragility analysis were performed to estimate the behavior and vulnerability of the RC structure with various ground motions.

Key Words
reinforced concrete structure; time history analysis; seismic vulnerability assessment; SMART 2013 benchmark program

Address
Hyun-Kyu Lim, Jun Won Kang: Department of Civil Engineering, Hongik University, 94 Wausan-ro, Mapo-gu, Seoul 121-791, Republic of Korea

Young-Geun Lee and Ho-Seok Chi: Department of Structural System & Site Safety Evaluation, Korea Institute of Nuclear Safety,
62 Gwahak-ro, Yuseong-gu, Daejeon 305-338, Republic of Korea

Abstract
During the last decades, Pendulum Bearings with one or more concave sliding surfaces have been dominating bridge structures. For bridges with relative small lengths, the use of classical pendulum bearings could be a simple and cheaper solution. This work attempts to investigate the effectiveness of such a system, and especially its behavior for the case of a seismic excitation. The results obtained have shown that the classical pendulum bearings are very effective, mainly for bridges with short or intermediate length.

Key Words
dynamics of bridges; pendulum bearings; seismic excitation

Address
National Technical University of Athens, Department of Civil Engineering 9 Iroon Polytechneiou Str., Athens 15780, Greece

Abstract
Gradient enhanced theories of crystal plasticity enjoy great research interest. The focus of this work is on thermodynamically consistent modeling of grain size dependent hardening effects. In this contribution, we develop a model framework for damage coupled to gradient enhanced crystal thermoplasticity. The damage initiation is directly linked to the accumulated plastic slip. The theoretical setting is that of finite strains. Numerical results on single-crystalline metal showing the development of damage conclude the paper.

Key Words
crystal plasticity; heat conduction; damage; gradient extension; dislocations

Address
Magnus Ekh: Division of Material and Computational Mechanics, Department of Applied Mechanics, Chalmers University of Technology, Gothenburg, Sweden

Swantje Bargmann: Institute of Continuum Mechanics and Material Mechanics, Hamburg University of Technology, Germany

Swantje Bargmann: Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Germany


Techno-Press: Publishers of international journals and conference proceedings.       Copyright © 2017 Techno-Press
P.O. Box 33, Yuseong, Daejeon 34186 Korea, Tel: +82-42-828-7996, Fax : +82-42-828-7997, Email: info@techno-press.com