• Title, Summary, Keyword: materials behaviour

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Strain Rate Dependence of Plastic Deformation Properties of Nanostructured Materials (나노구조재료의 소성변형 성질의 변형률속도 의존성)

  • Yoon Seung Chae;Kim Hyoung Seop
    • Transactions of Materials Processing
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    • v.14 no.1
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    • pp.65-70
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    • 2005
  • A phase mixture model was employed to simulate the deformation behaviour of metallic materials covering a wide grain size range from micrometer to nanometer scale. In this model a polycrystalline material is treated as a mixture of two phases: grain interior phase whose plastic deformation is governed by dislocation and diffusion mechanisms and grain boundary 'phase' whose plastic flow is controlled by a boundary diffusion mechanism. The main target of this study was the effect of grain size on stress and its strain rate sensitivity as well as on the strain hardening. Conventional Hall-Petch behaviour in coarse grained materials at high strain rates governed by the dislocation glide mechanism was shown to be replaced with inverse Hall-Petch behaviour in ultrafine grained materials at low strain rates, when both phases deform predominantly by diffusion controlled mechanisms. The model predictions are illustrated by examples from literature.

Printing Morphology and Rheological Characteristics of Lead-Free Sn-3Ag-0.5Cu (SAC) Solder Pastes

  • Sharma, Ashutosh;Mallik, Sabuj;Ekere, Nduka N.;Jung, Jae-Pil
    • Journal of the Microelectronics and Packaging Society
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    • v.21 no.4
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    • pp.83-89
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    • 2014
  • Solder paste plays a crucial role as the widely used joining material in surface mount technology (SMT). The understanding of its behaviour and properties is essential to ensure the proper functioning of the electronic assemblies. The composition of the solder paste is known to be directly related to its rheological behaviour. This paper provides a brief overview of the solder paste behaviour of four different solder paste formulations, stencil printing processes, and techniques to characterize solder paste behaviour adequately. The solder pastes are based on the Sn-3.0Ag-0.5Cu alloy, are different in their particle size, metal content and flux system. The solder pastes are characterized in terms of solder particle size and shape as well as the rheological characterizations such as oscillatory sweep tests, viscosity, and creep recovery behaviour of pastes.

Numerical modelling of the damaging behaviour of the reinforced concrete structures by multi-layers beams elements

  • Mourad, Khebizi;mohamed, Guenfoud
    • Computers and Concrete
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    • v.15 no.4
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    • pp.547-562
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    • 2015
  • A two-dimensional multi-layered finite elements modeling of reinforced concrete structures at non-linear behaviour under monotonic and cyclical loading is presented. The non-linearity material is characterized by several phenomena such as: the physical non-linearity of the concrete and steels materials, the behaviour of cracked concrete and the interaction effect between materials represented by the post-cracking filled. These parameters are taken into consideration in this paper to examine the response of the reinforced concrete structures at the non-linear behaviour. Four examples of application are presented. The numerical results obtained, are in a very good agreement with available experimental data and other numerical models of the literature.

Corrosion Mechanisms of New Wrought Mg-Zn Based Alloys Alloying with Si, Ca and Ag

  • Ben-Hamu, G.;Eliezer, D.;Shin, K.S.;Wagner, L.
    • Corrosion Science and Technology
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    • v.7 no.3
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    • pp.152-157
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    • 2008
  • New wrought magnesium alloys have increasingly been developed in recent years for the automotive industry due to their high potential as structural materials for low density and high strength/weight ratio demands. However, their poor mechanical properties and low corrosion resistance have led to a search for new kinds of magnesium alloys with better strength, ductility, and high corrosion resistance. The main objective of this research is to investigate the corrosion behaviour of new magnesium alloys: Mg-Zn-Ag (ZQ), Mg-Zn-Mn-Si (ZSM) and Mg-Zn-Mn-Si-Ca (ZSMX). These ZQ6X, ZSM6X1, and ZSM651+YCa alloys were prepared using hot extrusion. AC, DC polarization and immersion tests were carried out on the extruded rods. Microstructure was examined using optical and electron microscopy (SEM) and EDS. The addition of silver decreased the corrosion resistance. The additions of silicon and calcium also affected the corrosion behaviour. These results can be explained by the effects of alloying elements on the microstructure of Mg-Zn alloys such as grain size and precipitates caused by the change in precipitation and recrystallisation behaviour.

A Numerical Investigateion of the Effect of Die Friction in ECAP (Equal Channel Angular Pressing) (등통로각압축 (ECAP) 공정에서 다이 마찰 효과에 대한 수치적 연구)

  • 서민홍;김형섭
    • Transactions of Materials Processing
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    • v.9 no.3
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    • pp.219-225
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    • 2000
  • Equal channel angular pressing (ECAP) is a convenient forming process to extrude material without substantial changes in the sample geometry and this deformation process gives rise to produce ultrafine grained materials. The properties of the materials are strongly dependent on the plastic deformation behaviour during ECAP. The major process variables during ECAP are 1) die geometries, such as a channel angle and coner angles, and 2) the processes variables, such as lubrication and deformation speed. In this study, the plastic deformation behaviour of materials during the ECAP has been theoretically analysed by the finite element method (FEM). The effect of the die friction on the plastic deformation behaviour during the pressing is discussed by means of FEM calculations.

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Liquid crystal effects on poling behaviour of NLO chromophore dispersed in organically modified sol-gel materials (유/무기 졸-겔 재료에 비선형광학 물질의 배향특성에 대한 액정효과)

  • Baek, In-Chan;Seok, Sang-Il;Jin, Moon-Young;Lee, Chang-Jin
    • Proceedings of the Materials Research Society of Korea Conference
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    • pp.132-132
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    • 2003
  • Second-order nonlinear optical(NLO) materials have been extensively studied for applications in photonic devices, such as frequency doubling and electro-optical(EO) modulation, because of their large optical nonlinearity, excellent processibility, low dielectric constant, and high laser damage thresholds. The poling behaviour of NLO chromophore in organic/inorganic matrixes showed the randomization of poled NLO chromophore in the absence of poling Held. The liquid crystal molecules in a droplet showed a long-range orientational order along a director. Therefore, liquid crystal effects on poling behaviour of NLO chromophore dispersed in organically modified inorganic sol-gel materials were investigated. Using sol-gel process for the development of NLO material has received increasing attention, Organically modifked inorganic NLO sol-Eel materials are obtained via incorporation of the organic NLO active chromophore into an alkoxysilane based inorganic network. One of the most important thing in this works was that tetraethoxysilane(TEOS) and methyltrimathoxysilane(HTMS) were used as precursor followed by hydrolysis and condensation without using any acidic catalyst during the process. The NLO chromophores in the liquid crystal nanodomains were well mixed with I/O hybrid matrix, deposited on transparent ITO-coated glasses. The poling behaviour of liquid crystal effects of NLO chromophore dispersed in I/O hybrid matrix were investigated by UV-vis spectroscopy. Size distribution and morphology of the NLO chromophores doped in the liquid crystal nanodomains dispersed in I/O hybrid matrix were investigated by SEM.

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Investigation on the Recent Research Trend in the Corrosion Behaviour of Stainless Steel Weldment

  • Kim, Hwan Tae;Kil, Sang Cheol;Hwang, Woon Suk
    • Corrosion Science and Technology
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    • v.10 no.3
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    • pp.77-79
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    • 2011
  • The research trend in the corrosion behaviour of stainless steel weldment has been reviewed. The welding technology plays an important role in the fabrication of structure such as chemical plant, power plant, because welding can influence various factors in the performance of plant and equipment. This has led to an increasing attention towards the corrosion behaviour of weldment which has been one of the major issues for both welding and corrosion research engineers. The aim of this paper is to give a short survey of the recent technical trends of welding and corrosion including the electrochemical corrosion, stress corrosion cracking, and corrosion fatigue in connection with the welding materials, welding process, and welding fabrication. This study covers the corrosion behaviour of stainless steel weldment collected from the COMPENDEX DB analysis of published papers, research subject and research institutes.

Time-dependent effects on dynamic properties of cable-stayed bridges

  • Au, Francis T.K.;Si, X.T.
    • Structural Engineering and Mechanics
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    • v.41 no.1
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    • pp.139-155
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    • 2012
  • Structural health monitoring systems are often installed on bridges to provide assessments of the need for structural maintenance and repair. Damage or deterioration may be detected by observation of changes in bridge characteristics evaluated from measured structural responses. However, construction materials such as concrete and steel cables exhibit certain time-dependent behaviour, which also results in changes in structural characteristics. If these are not accounted for properly, false alarms may arise. This paper proposes a systematic and efficient method to study the time-dependent effects on the dynamic properties of cable-stayed bridges. After establishing the finite element model of a cable-stayed bridge taking into account geometric nonlinearities and time-dependent behaviour, long-term time-dependent analysis is carried out by time integration. Then the dynamic properties of the bridge after a certain period can be obtained. The effects of time-dependent behaviour of construction materials on the dynamic properties of typical cable-stayed bridges are investigated in detail.

The Use of Advanced Optical Measurement Methods for the Mechanical Analysis of Shear Deficient Prestressed Concrete Members

  • Wilder, K. De;Roeck, G. De;Vandewalle, L.
    • International Journal of Concrete Structures and Materials
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    • v.10 no.2
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    • pp.189-203
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    • 2016
  • This paper investigates on the use of advanced optical measurement methods, i.e. 3D coordinate measurement machines (3D CMM) and stereo-vision digital image correlation (3D DIC), for the mechanical analysis of shear deficient prestressed concrete members. Firstly, the experimental program is elaborated. Secondly, the working principle, experimental setup and corresponding accuracy and precision of the considered optical measurement techniques are reported. A novel way to apply synthesised strain sensor patterns for DIC is introduced. Thirdly, the experimental results are reported and an analysis is made of the structural behaviour based on the gathered experimental data. Both techniques yielded useful and complete data in comparison to traditional mechanical measurement techniques and allowed for the assessment of the mechanical behaviour of the reported test specimens. The identified structural behaviour presented in this paper can be used to optimize design procedure for shear-critical structural concrete members.

The Effect of Strain Rate on Macroscopic Behaviour in Compression Forming of Semi-Solid Aluminum Alloy (반용융 알루미늄 재료의 압축성형시 변형율속도가 미시적 거동에 미치는 영향)

  • 강충길;김기훈
    • Transactions of Materials Processing
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    • v.6 no.4
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    • pp.338-345
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    • 1997
  • The behaviour of alloys in the semi-solid state strongly depends on the imposed stress stage and on the morphology of the phase which can vary from dendritic to globular. To optimal net shape forging of semi-solid materials, it is important to investigate for material behaviour for variation of strain rate. Therefore, to investigate the effect of compression speed on deformation of aluminum alloy with globular microstructure, the compression test for semi-solid aluminum alloy with controlled solid fraction is perform by material test system which is attracted with furance. The behavior of semi-solid aluminum alloy were discussed for the various solid fraction and die speed. The material constants in stress-strain were are also proposed.

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