Papers by Keyword: Graded Structure

Abstract: The behaviour of aluminium matrix syntactic foams (AMSFs) with homogeneous and graded structures have been studied under quasi-static compression and impact. Particle size of ceramic microspheres and impact velocity had significant effects on the static and impact responses. Smaller microspheres led to higher strength but lower toughness. The compressive yield stress, plateau stress and specific energy absorption of the graded AMSF specimens were approximately the averages of the constituent layers, following the rule of mixture, although the order of the layers had some influence on the compressive behaviour. The syntactic foams were brittle under impact, no matter whether they were brittle or ductile in quasi-static compression. They had higher peak stresses and absorbed more energy in impact than in quasi-static compression. The location of the most brittle layer of the small ceramic microspheres had a significant effect on the impact failure pattern and sequence of the three-layer graded AMSFs.

Abstract: To evaluate bond strength of veneering ceramics to a graded zirconia core. Two zirconia core ceramics (Y-TZP and graded zirconia) were fabricated and veneered with IPS e.max Ceram. A metal ceramic system (IPS d.SIGN, Ivoclar Vivadent, Liechtenstein) was used as a control group for the two all-ceramic test groups (n=20). Shear bond strength test and microtensile bond strength test were conducted by a universal testing machine. Fracture surfaces were also evaluated to determine the failure modes. Additionally, one-way ANOVA and Tukey's HSD tests were used to analyze the data. The shear bond strength test and microtensile bond strength test showed the familiar results. Graded zirconia exhibited the highest bond strength value (SBS: 31.01±2.01 MPa, MTBS: 40.95±1.95 MPa), significantly higher than that of Y-TZP (SBS: 28.14±2.28 MPa, 37.99±2.83 MPa). No significant differences were found between the metal core group and the two zirconia core groups. All test groups demonstrated cohesive failure within the veneer, as well as adhesive failure between the core and the veneer. Glass infiltration to zirconia may affect bond strength between zirconia core and veneering ceramics. A graded zirconia glass structure exhibits a benign bond to a veneering ceramics which could be similar to that of a metal ceramic system.

Abstract: Secure and cost effective joining methods are key points for practical applications of plastic pipelines. The morphology and material structure of welded joints are complicated in comparison with the base pipe material. The formation of the weld is highly dependent on both thermal history and stress state. Consequently, the material parameters characterizing the weld joint and corresponding heated zone influence the reliability and safety of the welded pipe system as a whole. In the contribution a welded polymer-polymer butt joint is considered and its possible damage caused by slow crack growing in the weld zone is numerically analyzed. The numerical model takes into account the geometry of the bead and changes in material properties inside the weld zone. The results obtained from welded specimens are compared with those for a smooth specimen from the base material. The conclusions described in the paper can be used for a better transfer of fracture mechanics characteristics between laboratory specimens and real pipes.

Abstract: The atomic-scale graded structure of In-Pb alloy was formed by an ultracentrifuge under a gravitational field of 0.81 x 106 g for 100 hours at 150 °C in solid state. The isotope ratio measurements were performed on the centrifuged sample with secondary ion mass spectrometer (SIMS, CAMECA IMS-6f). 206Pb/208Pb and 207Pb/208Pb isotope ratio changed with negative gradient in the direction of centrifugal force approximately 1.5% and 0.8%, respectively. There was a tendency that the heavy 208Pb isotope abundance increased and the light 206Pb isotope abundance decreased in the direction of centrifugal force. Three-isotope diagram of 206Pb/208Pb versus 207Pb/208Pb proved that the isotope fractionation depends on the isotopic mass difference. These results showed that a strong gravitational field not only affected the inter-diffusion but also the self-diffusion in this alloy by causing isotope fractionation effect, which was dependent on the mass-difference.

Abstract: Three-dimensional electromagnetic or photonic crystals with periodic variations of the dielectric constants were fabricated by using a rapid prototyping method called stereolithography. Millimeter-order epoxy lattices with a diamond structure were designed to reflect electromagnetic waves by forming an electromagnetic band gap in GHz range. Titania based ceramic particles were dispersed into the lattice to control the dielectric constant. The diamond lattice structures formed the perfect band gap reflecting electromagnetic waves for all directions. The location of the band gap agreed with the band calculation using the plane wave propagation method. The diamond structures with graded lattice spacing were successfully fabricated as well, resulting in the directional transmission of microwaves. The stretching ratio of the lattice spacing in the crystal structure was changed according to the electromagnetic band calculation. A microwave antenna head composed of the diamond structure with graded lattice spacing was fabricated which achieved the unidirectional transmission.

Abstract: The microstructure evolution during high-temperature deformation at (a) high strain rates and low strains (dynamic densification, shock compression) and (b) low strain rates and high strains (quasi-static densification, superplastic regime) was studied. Off-stoichiometric titanium carbide was selected as a testing system. The results demonstrate that high-temperature deformation in a broad range of strain rates provides means for controlling the microstructure of titanium carbide. By varying deformation conditions, one can obtain materials differing in microstructure and chemical composition, in particular, with equilibrium and nonequilibrium microstructures. Accordingly, the physicochemical properties of such materials are also different.

Abstract: Structure-property relationships in bovine cortical bone have been characterised using grazing-incidence synchrotron radiation diffraction, Vickers indentation and mechanical testing. Depth profiling results indicated the existence of distinct gradual changes in crystal disorder, phase abundance, and texture of hydroxyapatite whilst the crystallite size was depth-independent.

Abstract: Structure-property relationships in baby and adult teeth have been characterised using grazing-incidence synchrotron radiation diffraction and Vickers indentation. Similarities and differences between both types of teeth have been highlighted and discussed. Depth profiling results indicated the existence of contrasting but distinct gradual changes in crystal disorder, phase abundance, crystallite size and hardness within the baby and adult canine enamel, thus confirming the graded nature of human teeth. When compared to the adult tooth, the baby enamel is softer, more prone to fracture, but has larger hydroxyapatite grains.

Abstract: Aiming at ceramic-lined layered pipes employed under special conditions, layered structure of ceramic-lined pipes is redesigned by adding (TiO2+Al+C+Ni) subsystem with different contents in (CrO3+Al) main system，and the composite pipe with three-layer structure of steel substrate, the intermediate and ceramics is obtained. SEM images and EPMA analyses indicate that the intermediate is made of Cr-Ni-Fe-Al-Ti, in which Ti carbide particles or fine dendrites of Ti enrichment are embedded with graded distribution. Mechanical tests and SEM images show that as (TiO2+Al+C) subsystem and Ni metallic additive is up to 10% and 15% of whole combustion system respectively, compressive strength and compressive shear strength of the pipe simultaneously reach the maximum values.