Papers by Keyword: Mechanical Strength

Abstract: High pressure torsion (HPT) and equal channel angular pressing in parallel channels (ECAP-PC) at room temperature are used to form homogeneous ultrafine-grained (UFG) structure with a grain size of the aluminum matrix of 350 and 700 nm, respectively, in Al-30Zn (wt. %) specimens. The UFG samples with special geometry produced from the specimens processed by SPD techniques were subjected to sphere-shaped dimple extrusion testing (via the Erikson test method) and bended plate extrusion to determine the material formability during cold sheet metal forming. The same tests were performed on the material with coarse-grained (CG) structure for the sake of comparison. The obtained results are discussed.

Abstract: In this study, cellulose nanofibers (CNF) was used as a reinforcing material to improve mechanichal strenght of chitosan nanofibrous scaffold. Chitosan scaffolds with different amount of CNF ranging 5.0-20.0 Wt.% were fabricated by adding CNF to chitosan solutions before electrospinning. Both the tensile strength and tensile modulus of the scaffolds were increased as a result of CNF addition. An increase of 4.3 fold (from 2.9±0/02 to 12.7±0/4 MPa) in tensile strength and 4.04 fold (from 86.5±1.7 to 349.5±19.4 P) in Young's modulus were observed after addition of 15 wt. % CNF. The microscopy studies showed that the diameter of the electrospun fibers decreased with the addition of CNF. The diameter decreased from 175± 7 nm to 100±29 nm when 15 wt% CNF were added. Evaluation of cell adhesion by SEM showed that fibroblast cells not only can attachment on the surface of NFC reinforced scaffolds but also can infilterate inside the scaffolds. In addition, the nanocomposite schaffols dose not show any cytotoxic effect using MTT assay.

Abstract: As a new thinning and surface planarizing process of Silicon Carbide (SiC) wafer, we propose the completely thermal-chemical etching process; Si-vapor etching (Si-VE) technology. In this work, the effects of mechanical strength and surface step-terrace structure by Si-VE are investigated on the 4° off-axis 4H-SiC (0001) Si-face substrates. The indentation hardness of Si-VE surface is superior to the conventional chemo-mechanical polishing (CMP) surface even after epitaxial growth. The transverse strength of thinned Si-VE substrate is also superior to the conventional mechanically ground substrate. The surface step-terrace structures are observed by the low energy electron channeling contrast (LE-ECC) imaging technique. The latent scratch causes bunched step lines (BSLs) with various inhomogeneous step morphologies only on the CMP surface.

Abstract: Silica foams with 50% – 70% porosity have been developed by mixing silica powder, polyethylene glycol (PEG) and carboxymethyl cellulose (CMC) into distilled water to make slurry. Polyurethane foam (PU) as the template is immersed into the slurry with 45 wt.%, 50 wt.% and 55 wt.%. of silica composition and finally sintered at 1100°C, 1200°C, 1300°C and 1400°C. Several tests which are morphological analysis, porosity and density test, and compressive strength test are compulsory to determine the physical and mechanical of the silica foam. The morphology of the foam has been observed using Scanning Electron Microscopy (SEM) and the result of pore size distribution is in the range of 255.91 μm to 489.14 μm. The porosity and density obtained from the porosity and density test was 50%-73.66% and 0.5499 g/cm³ up to 0.9757 g/cm³, respectively. Meanwhile, the compressive strength of sintered silica foam obtained is 0.01471 N/mm² up to 0.1467 N/mm².

Abstract: During processing of zirconia blocks, where they are used for different dental implants type, most of the loosed material as a powder is subsequently discarded. Besides damage to the environment, waste of material results in financial losses, resulting in higher final cost of treatment. The yttria stabilized zirconia (Y-TZP) has a variety of applications due to it is combination of high strength and fracture toughness. The objective was to reuse zirconia waste analyzing the effects of sintering temperature. The starting materials used in this study were two different powders of ceramic system ZrO₃-Y₂O₃: commercial zirconia nanoparticle and microparticle zirconia waste. The raw material was shaped by uniaxial and isostatic pressing and then sintered at 1500, 1550 and 1600 ° C over 1 hour. The X-ray diffraction (XRD) and dilatometry were used to powder characterization. After sintering density / porosity, flexural strength, and scanning electron microscopy (SEM) were realized .The waste showed similar values of density, and grain size to commercial material studied, confirming that it can be reused.

Abstract: The combination of tetracalcium phosphate (TTCP; Ca₄(PO₄)₂O) and dicalcium phosphate anhydrous (DCPA; CaHPO₄) which are known as one system of apatite cements already used in the medical and dental application. In spite of several advantages of apatite cements, such as self-setting ability and biocompatibility, their mechanical strengths are still low. The aim of this study is to improve the mechanical strength of the TTCP-DCPA apatite cement using the hydroxyapatite/collagen nanocomposite (HAp/Col). The apatite cement powder was prepared using an equimolar TTCP and DCPA with addition of 10% and 20% of the HAp/Col. That without the HAp/Col was used as a control group. Each group was mixed with 1 mol/L Na_1.8H_1.2PO₄ aqueous solution at powder/liquid ratio of 0.5 and hardened at 37°C and 100 % of relative humidity for 24 hours. A setting time of the cement was evaluated using Vicat needle according to ISO 1566 for dental zinc phosphate cements. Morphology of the cements set were observed by the scanning electron microscopy (SEM), and crystalline phases were identified by the powder X-Ray diffractometry (XRD). The mechanical strength of the cement set was evaluated by the diametral tensile strength (DTS). The setting times of cements were the shortest for the cement with HAp/Col and the longest for the control. XRD patterns of the cement at 24 hours after mixing revealed that all cements changed into apatite from the mixture of TTCP and DCPA. The DTSs of cements were the highest for the cement with 20% HAp/Col and the lowest for the control with significant differences between the cement with 20 % HAp/Col and respective other two cements. The scanning electron micrographs of the surface and fracture surface of the cements suggested that the cement with HAp/Col showed denser structure in comparison to the control and the HAp/Col fibers and/or sheets covered the fracture surface. The HAp/Col would act as reinforcement fibers as well as an adhesive of apatite granules formed by the reaction between TTCP and DCPA. The setting time and mechanical strength of apatite cement was statistically significant improved by adding 20% HAp/Col.

Abstract: The effect of low doses of gamma and electron irradiation on mechanical strength of Bi₂Sr₂CaCu₂O₈ (Bi-2212) superconductor ceramics was studied by exposing the superconductor to gamma irradiation dose of up to 50 kGy, and electron irradiation dose of up to 80 kGy. All the samples were prepared using the conventional solid-state reaction method. For samples to be irradiated with electron particles, 5% weight percentage of nanosized MgO was added to absorb certain amount of the energy from electrons and thus reducing the formation of complicated defects structure in the Bi-2212 superconductor. The SEM micrographs of the Bi-2212 superconductor showed the existence of platelet-type grains of Bi-2212 phase in both non-irradiated and irradiated samples. The XRD patterns for the non-irradiated and irradiated samples showed well-defined peaks of which could be indexed on the basis of a Bi-2212 phase structure. The phase purity, lattice parameter, surface morphology and degree of crystallinity for the non-irradiated and irradiated samples were also compared and analyzed and it was found that both the gamma and electron irradiation have considerable effect on the mechanical properties of Bi-2212 superconductor. When subjected to gamma and electron irradiation, the microstructure of the samples was found to be more textured and consequently enhanced the strength of the samples.

Abstract: The AA4045/AA3003 cladding billet, which has a low clad ratio of 7.5% in size of φ160mm/φ148mm, was prepared successfully by the modified direct chill casting process. Microstructures, elements distribution and mechanical properties of the bonding interface were examined. The results show that metallurgical bonding interface can be obtained with the optimal parameters. The metallurgical bonding interface is free of any discontinuities due to the elements diffusion across the interface. The hardness of the interfacial region is higher than that of the AA3003 but lower than that of AA4045, suggesting that the interface bonding strength is higher than the strength of AA3003. The shearing strength is 82.3 MPa, indicating excellent metallurgical bonding.

Abstract: We have established a processing method to fabricate three - dimensional porous carbonate apatite (CO₃Ap) with interconnected porous structure and improved mechanical strength. Briefly, porous CO₃Ap materials were produced via phosphorization of porous calcite precursor in hydrothermal condition. In order to make porous calcite precursor, negative replication of modified polyurethane foam template was conducted. In this study, an in vivo behavior of that porous CO₃Ap was evaluated. The interconnected porous CO₃Ap material was implanted in the tibia of Japanese male rabbits and removed after a period of 6 months. Micro-computed tomography (μ-CT) scanner and histological analysis were used to characterize the bone formation response of the porous CO₃Ap. The results suggest that porous CO₃Ap with enhanced mechanical strength was not only osteoconductive but also bioresorbable therefore it could be used as bone substitute material.

Abstract: Based on the preparation of polyacrylamide/clays lithium magnesium silicate hydrate (PAAm/LMSH, abbreviated as AP) nanocomposite hydrogel by in-situ free radical polymerization, Fe₃O₄ nanoparticles were introduced by chemical co-precipitation method, to form magnetic Fe₃O₄/PAAm/LMSH (abbreviated as MAP) nanocomposite hydrogel. With ESEM, XRD, and TGA technologies, the structures of MAP nanocomposite hydrogel and Fe₃O₄ nanoparticles formed. Magnetic characteristic of MAP nanocomposite hydrogel was characterized by VSM. The tensile test with Universal Testing Machine was employed for mechanical properties. Furthermore, taking cationic dye Crystal Violet (CV) and anionic dye Methyl Orange (MO) for example, the adsorption properties of MAP nanocomposite hydrogel were analyzed with UV-visible spectrophotometer method. The results show that MAP nanocomposite hydrogel had strong superparamagnetic properties. The introduced Fe₃O₄ magnetic particles illustrated spinel structure, and nanoparticle size of 8.52 nm. The swelling rate of MAP sample was up to 30.542, showing excellent swelling ability. Compared with AP nanocomposite hydrogel, MAP nanocomposite hydrogel had stronger mechanical strength with the tensile stress of 0.39MPa. Adsorption experiments indicated that MAP nanocomposite hydrogel had favorable adsorption properties on CV with removal rate of 97.6%, 1.27 times that of AP nanocomposite hydrogel. The conclusions confirm the application prospect of MAP nanocomposite hydrogel as dye adsorbent in textile printing and dyeing wastewater treatment.