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Superior Mechanical Properties (superior + mechanical_property)
Selected AbstractsNanometer-Scale Mapping of Elastic Modules in Biogenic Composites: The Nacre of Mollusk ShellsADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Haika Moshe-Drezner Abstract In this study, a newly developed nanoscale modulus mapping is applied in order to visualize the 2D-distribution of mechanical characteristics in the aragonitic nacre layer of Perna canaliculus (green mussel) shells. Modulus maps provide lateral resolution of about 10 nm. They allow the aragonitic mineral (CaCO3) tablets and the interfaces between them to be clearly resolved, which are filled by an organic substance (mainly beta-chitin). The experimental data are compared with finite element simulations that also take into account the tip radius of curvature and the thickness of organic layers, as measured by means of scanning electron microscopy with back-scattered electrons. Based on this comparison, the Young modulus of beta-chitin is extracted. The obtained number, E, = 40 GPa, is higher than previously evaluated. The collected maps reveal that the elastic modules in the nacre layer change gradually across the ceramic/organic interfaces within a spatial range four times wider than the thickness of the organic layers. This is possibly due to inhomogeneous distribution of organic macromolecules within ceramic tablets. According to the data, the concentration of macromolecules gradually increases when approaching the organic/ceramic interfaces. A behavior of this type is unique to biogenic materials and distinguishes them from synthetic composite materials. Finally, three possible mechanisms that attempt to explain why gradual changes of elastic modules significantly enhance the overall resistance to fracture of the nacre layer are briefly discussed. The experimental findings support the idea that individual ceramic tablets, comprising the nacre, are built of the compositionally and functionally graded ceramic material. This sheds additional light on the origin of the superior mechanical properties of biogenic composites. [source] Mechanical Properties and Dimensional Effects of ZnO- and SnO2 -Based VaristorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2008Miguel Angel Ramírez A comparison between traditional ZnO-(modified Matsuoka system, [ZnO]) and SnO2 -based varistors (98.9%SnO2+1%CoO+0.05%Nb2O5+0.05%Cr2O3, [SCNCr]) regarding their mechanical properties, finite element (FE) modeling, and macroscopic response with current pulse is presented in this work. The experimental values of the elastic (static and dynamic) modulus and bending strength are given. Both the static and the dynamic modulus were two times higher for SnO2 (,200 GPa) with respect to ZnO (,100 GPa). A similar behavior was found for the bending strength, confirming the superior mechanical properties of SCNCr associated with a homogeneous microstructure. The finite element analyses yielded the most appropriate thickness/diameter aspect ratio (H/D), while thermomechanical stress is minimized. The values of (H/D) were lower for the SCNCr in comparison with the ZnO-based varistors, allowing the production of smaller pieces that can resist the same thermomechanical stress. Finally, preliminary analyses of the macroscopic failures for samples treated with degradation pulses of 8/20-,s type allowed to confirm the absence of failures due to cracking and/or puncture in the SCNCr. The absence of these failures originates from the good thermomechanical properties. [source] Preparation and characteristics of nitrile rubber (NBR) nanocomposites based on organophilic layered clayPOLYMER INTERNATIONAL, Issue 7 2003Jin-tae Kim Abstract The effect of clay modification on organo-montmorillonite/NBR nanocomposites has been studied. Organo-montmorillonite/NBR nanocomposites were prepared through a melt intercalation process. NBR nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic mechanical thermal analysis (DMTA) and a universal testing machine (UTM). XRD showed that the basal spacing in the clay increased, which means that the NBR matrix was intercalated in the clay layer galleries. On TEM images, organo-montmorillonite (MMT) particles were clearly observed, having been exfoliated into nanoscale layers of about 10,20 nm thickness from their original 40 µm particle size. These layers were uniformly dispersed in the NBR matrix. The DMTA test showed that for these nanocomposites the plateau modulus and glass transition temperature (Tg) increased with respect to the corresponding values of pure NBR (without clay). UTM test showed that the nanocomposites had superior mechanical properties, ie strength and modulus. These improved properties are due to the nanoscale effects and strong interactions between the NBR matrix and the clay interface. Copyright © 2003 Society of Chemical Industry [source] Synthesis and properties of room temperature curable trimethoxysilane-terminated polyurethane and their dispersionsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 8 2007Sankaraiah Subramani Abstract The purpose of this research is to study the synthesis and characterization of stable aqueous dispersions of externally chain extended polyurethane/urea compositions terminated by hydrolyzable or hydrolyzed trialkoxysilane groups incorporated through secondary amino groups. These dispersions with excellent storage stability are substantially free from organic solvents which cure to water and solvent resistant, tough, scratch resistant, preferably light stable (non-yellowing) silylated polyurethane (SPU) films. The films were characterized by FT-IR, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), tensile strength and water contact angle measurements, nanoindentation, gel content, water and xylene swellability tests. The properties of the films were discussed and correlated in detail by changing length of soft segment, diisocyanates, NCO/OH ratio and chain extender, ethylenediamine (EDA). From the results, it was found that the particle size and viscosity are lower whereas the gel content and thermal stability are higher for SPUs. Modulus, hardness and tensile properties of SPU films are superior compared to EDA-PU film. Higher water contact angle and residual weight percentage of SPU films confirm silylation of PU by [3-(phenylamino)propyl]trimethoxysilane (PAPTMS). Increase in NCO/OH ratios consumes more quantity of PAPTMS which makes PU with superior mechanical properties. Higher PAPTMS content in SPU results in effective crosslinking of the functional silanol groups formed by hydrolysis reaction of trimethoxysilane groups. Overall, SPUs synthesized at 1.4 NCO/OH ratio using Poly-(oxytetramethylene)glycol (PTMG)-2000 and isophorone diisocyanate (or) toluene-2,4-diisocyanate have excellent properties compared to SPUs prepared using PTMG-1000 and at 1.2 and 1.6 NCO/OH ratios. SPUs prepared at 1.6 NCO/OH ratio are brittle due to higher crosslinking density. In addition, the crosslinking density of the films can be modified through silane end-group modification to produce SPUs with a wide range of physical properties. Copyright © 2007 John Wiley & Sons, Ltd. [source] | ||||||||||