Frontiers in Materials Science and Technology

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Authors: Xiao Ji Li, Jian Qiu Wang, En Hou Han, Wei Ke
Abstract: The influence of fluoride on stress corrosion cracking (SCC) of NiTi orthodontic wires was investigated using slow strain rate test (SSRT) and scanning electron microscopy (SEM). The results indicated that fluoride significantly accelerated the stress corrosion cracking of NiTi orthodontic wires. The fractographies of NiTi orthodontic wires exhibited striation pattern.
Authors: Chun Hui Yang, Ilchat Sabirov, Jonathan Mullins, Peter D. Hodgson
Abstract: Nanostructured and ultra-fine grained metals have higher strength but extremely limited ductility compared to coarse grained metals. However, their ductility can be greatly improved by introducing a specific range of grain sizes in the microstructures. In the paper, multiscale unit cell approach (UCA) is developed and applied to predict the averaged stress-strain relations of the multiscale microstructure metals. The unit cell models are three-phase structured at different scale lengths of 100 nm, 1 μm and 10 μm with different volume fractions and periodic boundary conditions. The contributions of multi-scale microstructures to the macroscopic structural properties of metals are also studied using a analytic approach—two-step mean-field method (TSMF), where three microstructural parameters are introduced and thus mechanical properties such as strength and ductility are presented as a function of these parameters. For verification of these proposed numerical and theoretical algorithms, the structural properties of the pure nickel with three-grain microstructures are studied and the results from FEA and the proposed theory have good agreement.
Authors: Shi Hong Zhang, Zhang Gang Li
Abstract: The orientation rotation in extruded Mg alloy AZ31B sheets during uniaxial tension at room temperature has been investigated using SEM/EBSD technique. According to the experimental results and the calculated results of Sachs crystal model, the quantitative rule of the tensile axis rotation for the grains (parent), and the associated slip systems have been analyzed in detail. The influencing factors of twinning area fraction have also been studied. The results show that the rule of the rotation of tensile axis can be explained by cross slip systems; the grains with different initial orientations exhibit different twinning behaviors; the area fractions of extensive twins have a close relationship with Schmid factors of tensile twinning, and with the angle between c-axis and tensile axis of the grains.
Authors: Hui Diao, Chun Qing Wang, Lei Wang
Abstract: This paper presents bonding technology of aluminum alloy by hot-dipping tin. The dissolution curve of copper in molten tin liquid was obtained in the experiment of hot-dipping Sn. Optimal hot-dipping parameter which was suitable for soldering was designed. To elucidate characteristics of interfacial evolution, the microstructure of the coatings, soldered joint were analyzed using optical microscopy, SEM and EDX. The shear strength of soldered joints was tested as high as 39.9Mpa, which is high enough to achieve the requirement of electronic industry.
Authors: Ranjan Rajoo, Erich H. Kisi, D.J. O'Connor
Abstract: This paper presents data obtained from a newly-developed instrument to test the quality of solder interconnections at high strain rate – the ‘micro-impactor’. This shear test of the interconnection at high strain rate mimics the stress experienced by the solder joint when undergoing shock due to drop-impact. Instrumented with a load cell and linear variable displacement transducer (LVDT), it also has the ability to provide dynamic impact force and displacement data. Earlier concepts to characterise the solder joint at high strain rates such as the miniature pendulum impact tester [1] lacked this capability. This micro-impactor was used to study the effect of increasing silver (Ag) and copper (Cu) concentration in solder alloys on the shear strength of the solder joint. The performance of these lead-free alloys was also compared to that of the well-established leaded solder. It was found that increasing the silver content increases the yield strength of the solder, causing the failure to occur at the brittle intermetallic layer instead of in the bulk of the solder.
Authors: Zhong Qing Su, Li Cheng, Xiao Ming Wang, Lin Ye, Zhi Ping Chen
Abstract: A quantitative evaluation approach for multi-delamination in fibre-reinforced composite laminates was developed, in virtue of a built-in active sensor network. The approach, conducted hierarchically by activating different sensors in a sensor network, fused time-of-flight (ToF) extracted from signals at different levels, whereby to provide an overall consensus as to all possible instance(s) of damage in the laminates. Benefiting from the network, the dependence of evaluation on a specific sensor or signal was furthest minimised, and the need for interpreting complex signal involving scattering by multi-damage was avoided. The approach was validated by assessing the locations and shapes of dual-delamination in a CF/EP woven laminate.
Authors: Ryszard Pyrz
Abstract: Molecular dynamics simulations are employed to study electronic and mechanical properties of smallest ZnO nanowires. It has been shown that the electronic band structure of nanowires varies with uniaxial strain and this property can be used for sensing deformation state when nanowires are embedded in a polymer matrix. A new atomic strain concept is formulated that allows calculation of continuum quantities directly within a discrete atomic (molecular) system. Molecular modeling and strain calculations have been performed on ZnO/polypropylene nanocomposites and compared with a carbon nanotube/polypropylene system. The simulation cell of nanocomposite has been subjected to uniaxial tension along an inclusion axis and the analysis has been performed for seven deformation steps with equilibration runs after each step. Both nanoinclusions follow global nanocomposite strain to a certain loading and then both exhibit deformation lag as loading level increases. This is clear evidence that both systems are prone to interfacial sliding. The sliding is more significant with the ZnO nanowire as compared to carbon nanotube, which is also evidenced in weaker interaction of this system.
Authors: Graham L.F. Powell, Ian H. Brown, Grant D. Nelson
Abstract: A tough hypereutectic high chromium white iron has been developed by considering the alloy as a double in-situ fibrous composite and applying the principles of composite theory. The eutectic in the ternary Fe-Cr-C system solidifies as M7C3 carbide rods of irregular hexagonal cross section in a matrix of austenite. The carbide rods are intermittently joined together with no misorientation at the joint. The colonies (eutectic grains) of a 27%Cr alloy solidify with a flat solid – liquid interface. In hypereutectic high chromium white irons the primary carbide solidifies as single crystal rods with no branching. Depending on the thermal conditions in the mould the primary carbides are nucleated only on the mould surface, or repeatedly at the solid – liquid interface. In 27% Cr, 4.5%C hypereutectic alloys, the as-solidified microstructure is one of long parallel aligned primary carbides in a eutectic matrix of carbide rods in austenite, or short randomly orientated primary carbides in a eutectic matrix. In either case the microstructure can be described as a double in-situ fibrous composite. The application of composite theory has resulted in hypereutectic high chromium white iron castings with improved fracture toughness similar to that of heat-treated alloy steel but with superior wear resistance.
Authors: Jonathon Mak, Richard Wuhrer, Greg Heness, J. Qin, W. Lu, D. Zhang, Wing Yiu Yeung
Abstract: Particulate reinforced Ti based metal matrix composites (MMCs) were made by in-situ synthesis using vacuum arc re-melting process. The microstructure of the Ti-6Al-4V base alloy and 10 vol.% (TiB+TiC)/Ti-6Al-4V metal matrix composites was examined. The particulate reinforcements were analysed and identified TiB and TiC particles. The particle distribution was analysed using the quadrat method over 1620 quadrats. A homogeneous particle distribution was found to establish in the composites. The experimental distribution of the reinforcements agreed well with the theoretical Poisson distribution. A skew factor, which characterizes the degree of asymmetry of a statistical distribution, of 1.108 was determined for the particle distribution in the material.
Authors: Yi Xia Zhang, Chun Hui Yang
Abstract: Efficient and accurate finite elements are crucial for finite element analysis to provide adequate prediction of the structural behavior. A large amount of laminated plate elements have been developed for finite element analysis of laminated composite plates based on the various lamination theories. A recent and complete review of the laminated finite elements based on the higher-order shear deformation theories, including the global higher-order theories, zig-zag theories and the global-local higher-order theories is presented in this paper. Finally some points on the development of the laminated plate elements are summarized.

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