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M. Vaseghi,S. Baghshahi,M. Mashhadi,A. Nemati 한양대학교 세라믹연구소 2019 Journal of Ceramic Processing Research Vol.20 No.5
Gel-casting is an appropriate method for manufacturing porous parts with complicated forms, which has also been used in shaping Si3N4 bodies. In the present study, porous bulk Si3N4 samples were fabricated using gel-casting. To this aim Si3N4 slurries were prepared with solid loading of 35 vol%. To the slurry was added 1 and 3 wt% rod-like BN to enhance the mechanical properties. BN was selected to further reduce the dielectric constant and loss of the prepared porous Si3N4 samples. The findings suggested that employing rod-like BN increased the porosity from 38 % to 41 %, reducing the flexural strength from 77 MPa in the part without BN to 56 MPa in the part containing 3 wt% BN. On the other hand, dielectric properties reduced in the parts with BN compared with the part without BN.
M. Vaseghi,S. Baghshahi,M. Mashhadi,A. Nemati 한양대학교 세라믹연구소 2019 Journal of Ceramic Processing Research Vol.20 No.2
The gel casting method was used for the production of Si3N4 porous ceramics with 25 vol% solid loading, and the effect ofadding 1 and 3 wt.% of BN whisker-like (synthesized in the laboratory) on the flexural strength of the composites wasinvestigated. The gel-cast samples were prepared using an AM-MBAM monomer system and deionized water solvent. The gelcast bodies were dried at ambient temperature and humidity for 48hrs. The burnout process was carried out at 600 oC for14hrs in the air. The samples were then subjected to heat treatment at 1650 oC for 2 hrs in a bed of 50% Si3N4-50% BN. Resultsshowed that BN whisker-like were agglomerated in deionized water. To solve this problem and to properly disperse thewhisker-like in the slurry, active surface agent groups were employed. Adding BN whisker-like to ceramic bodies, increasedthe porosity from 33% in samples without BN to 46% in samples containing 3 wt% BN whisker-like, resulting in a decreasein the density from 1.8 g/cm3 to about1.61 g/cm3. Since the Si3N4 ceramics require aids for the sintering, SiO2 and Y2O3additives were used with a ratio of 1 to 2, respectively, which led to the formation of Si2N2O phase. Si2N2O is similar to theSi3N4 phase in terms of the thermal expansion coefficient and chemical properties. Because of its rod shaped morphology, ithas a similar function to β-Si3N4 phase in improving the mechanical properties of the ceramic. Although porosity in theceramics containing 3 wt.% BN whisker-like was higher than those containing 1 wt.%, the porosity created vacant spaces forfurther growth of Si2N2O-rod shaped grains and in spite of higher porosity, better flexural strength was achieved for bodieswith 3 wt.% BN whisker-like. Also, in bodies without BN whisker-like, the flexural strength was 88 MPa, due to the lowporosity and the presence of stretched Si2N2O grains.
A numerical and experimental study on tubular channel angular pressing (TCAP) process
G. Faraji,M. M. Mashhadi,A. F. Dizadji,M. Hamdi 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.11
Tubular channel angular pressing (TCAP) is a new and novel severe plastic deformation (SPD) technique suitable for fabrication of bulk nanograined tubular materials. There are several parameters in the TCAP process. The present paper investigates the effects of curvature angles, deformation ratio (maximum radius during TCAP/initial radius) and deformation direction on the plastic deformation behavior,strain homogeneity and required loads in TCAP processing. The results showed that higher curvature angles (ψ1 and ψ3) leads to better strain homogeneity while have not having any significant effect on the process loads. Also, at the second curvature angle of 90°,the best condition is achieved with good strain homogeneity and lower load requirements rather than lower angles. Investigation of deformation direction showed that inlet deformation direction causes tube thinning at the end of the process, and thus, using the inlet case is not recommended.
Faraji, G.,Jafarzadeh, H.,Jeong, H.J.,Mashhadi, M.M.,Kim, H.S. BUTTERWORTH - HEINEMANN 2012 MATERIALS AND DESIGN Vol.35 No.-
<P><B>Highlights</B></P><P>► The accumulative back extrusion (ABE) was introduced as a high straining method suitable for AZ91. ► The strain distribution and deformation behavior during the ABE process using the finite element simulation was investigated. ► The deformation ratio and die stroke led to better deformation homogeneity and more plastic strains.</P> <P><B>Abstract</B></P><P>In the present study, the finite element method (FEM) and an experimental investigation were performed during the accumulative back extrusion (ABE) processing of an AZ91 magnesium alloy in order to investigate the effects of the deformation ratio (= inner punch diameter/outer punch diameter) and die stroke (DS) on the plastic deformation behavior. The results showed that increasing the deformation ratio and DS led to better deformation homogeneity and more plastic strains. There are two distinct regions in the ABE processed samples containing low and high plastic strain areas and the metallurgical investigations showed that more grain refinement with a mean grain size of 1.5μm takes place in high strain regions while the grain sizes are larger in other regions. A comparison between the FEM and experimental results of the required loads and developed microstructures showed good agreement.</P>
Muñ,oz-Fuentes, Violeta,Cacheiro, Pilar,Meehan, Terrence F.,Aguilar-Pimentel, Juan Antonio,Brown, Steve D. M.,Flenniken, Ann M.,Flicek, Paul,Galli, Antonella,Mashhadi, Hamed Haseli,Hrabě,de Springer Netherlands 2018 Conservation genetics Vol.19 No.4
<P>The International Mouse Phenotyping Consortium (IMPC) is building a catalogue of mammalian gene function by producing and phenotyping a knockout mouse line for every protein-coding gene. To date, the IMPC has generated and characterised 5186 mutant lines. One-third of the lines have been found to be non-viable and over 300 new mouse models of human disease have been identified thus far. While current bioinformatics efforts are focused on translating results to better understand human disease processes, IMPC data also aids understanding genetic function and processes in other species. Here we show, using gorilla genomic data, how genes essential to development in mice can be used to help assess the potentially deleterious impact of gene variants in other species. This type of analyses could be used to select optimal breeders in endangered species to maintain or increase fitness and avoid variants associated to impaired-health phenotypes or loss-of-function mutations in genes of critical importance. We also show, using selected examples from various mammal species, how IMPC data can aid in the identification of candidate genes for studying a condition of interest, deliver information about the mechanisms involved, or support predictions for the function of genes that may play a role in adaptation. With genotyping costs decreasing and the continued improvements of bioinformatics tools, the analyses we demonstrate can be routinely applied.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (10.1007/s10592-018-1072-9) contains supplementary material, which is available to authorized users.</P>