Advanced Materials Research Vols. 152-153

Abstract: A newly developed pure rolling fatigue test rig with three contact points for bearing balls was used to perform rolling contact fatigue (RCF) tests and the fatigue properties of two kinds of zirconia ceramic balls produced with different materials composition and identical technologies were compared. Ball surfaces were examined after failure with optical microscopy and scanning electron microscopy. It was identified by tests that the failure mode of zirconia ceramic balls was surface spall. Life tests data, summarized in accordance with the Weibull theory, showed that the life of two kinds of zirconia balls was close, and no remarkable difference in the divergence between the tested two kinds of balls was found

Abstract: The Effect of tempering on microstructure and mechanical properties of ultra low carbon heavy steel plate with intercritical quenching were studied by utilizing SEM, TEM, tensile and impact tests. Mobile dislocations decreased, plenty of carbides and secondary phase particles precipitated dispersedly in the matrix, and then some dislocations were pinned by these precipitations, which made the YS increase when tempered from 180 to 450 oC. However, the bainite islands, formed after intercritically quenched, were still existed, the boundaries of which were clear but just laths broadening in the interior, so the UTS had a slight variation. With increasing tempering temperature from 450 to 630 oC, carbides became coarse, the bainite islands were gradually polygonized, even the boundary of which became fuzzy, dislocations transferred and formed the cellular sub-grain, which caused synthetically both YS and UTS decreasing evidently, the low temperature toughness gradually increasing, and the mixed fracture of impact specimens converting into ductile fracture.

Abstract: The tensile tests of 3-dimension and 5-direction braided/epoxy resin composites were carried out at 150°C and 180°C with 15 minutes, 10 hours and 30 hours heating period of time, respectively. The reasons for the variations of tensile property of these composites with different heating period of time at 150°C and 180°C were analyzed. At 150°C and 180 °C，with heating period of time increasing the tensile strength of samples keeps the same level. the average tensile strength of samples at 180 °C is decreased only 5.0% compared with that at 150°C. The variation coefficient (CV) of tensile strengths at 180°C is also close to that at 150°C. These show that the tensile strength of 3-dimension and 5-direction braided/resin composites has no great change under 180 °C. However the resin in samples tested at 180°C is damaged more seriously than that at 150°C. The reason of damaged resin no great effect on tensile strength is that at high temperature, 3-dimension and 5-direction braided reinforcement still keeps an integrated structure, which can recuperate the loss of tensile strength made by resin damage. So the structure of reinforcement plays an important role at the tensile property of 3-dimension and 5-direction braided/resin composites at high temperature. The results derived from this paper will provide a useful reference for the application of 3-dimension and 5-direction braided/epoxy resin composites at high temperature and over a relatively long period of time.

Abstract: Through analysis of densification curve characteristic of gyratory compaction, influence rules of the content of mineral aggregates of all sizes and asphalt on compaction characteristic of mixtures were studied. Test studies show that the mixture having more of asphalt has a faster density-increasing speed, that there is an optimal amount of fine aggregates for optimal compaction, and that an appropriate amount of mineral powder will improve workability of mixtures but overmuch mineral powder will make mixtures dry and hard. Conclusions from this research can provide basis for how to adjust material composition for improving compaction performance of mixtures.

Abstract: Employing the dies for aluminum alloy parts, the hot die-forging forming and numerical simulation of semi-continuous casting Mg-7.0Al-0.4Zn (AZ70) were carried out. It was indicated that AZ70 has a worse fluidity during forging and is consequently difficult to fill fully compared to aluminum alloys. The microstructure of the AZ70 forgings is in good agreement with the strain distribution generated by simulation, and strain distribution can predict the microstructure evolution. The comparison results can give a guideline on developing forging process and controlling forgings quality of the AZ70 alloy.

Abstract: The Shoushan Stone is one of the famous craft carving stones in China and the transparency is one of the decisive factors to appraise its value. The better the transparency is, the higher the value is. In this paper, the mineral compositions and morphology of some Shoushan Stone samples were investigated by XRD and SEM methods. Combining with the characterization of Shoushan Stone, the relationships between the morphology and the transparency of Shoushan Stone were studied. The results show that the transparency of Shoushan Stone samples was determined by their microstructures, such as the mineral particle sizes and its arrangement, the gaps and porosity. The Shoushan Stone samples with high transparency are those with good arrangement, bigger crystal particle and less porosity and gaps.

Abstract: Using 1,3,5-benzenetrioxyundecanol (mTU) as the core, and more cheaper D,L-lactic acid (D,L-LA) as starting material, a novel star-shaped poly(D,L-lactic acid) (SPDLLA) was synthesized via direct melt polycondensation with simple process and low-cost. The obtained biodegradable polymer SPDLLA was systematically characterized with the intrinsic viscosity [η], FTIR, 1H-NMR, GPC and XRD. The Tg and crystallinity of all SPDLLA were much lower than that of the linear poly(D,L-lactic acid). When n(D,L-LA) : n(mTU) was 120 : 1, the biggest Mw was 10800, which was bigger than that obtained from L-lactic acid (L-LA). All Mw meet the requirement for drug delivery application.

Abstract: Fluor-hydroxyapatite (FHA) powder was synthesized using polyacrylamide gel method with Ca(NO3)2•4H2O as raw material of calcium, (NH4)2HPO4 as raw material of phosphor, and different amounts of ammonium fluoride (NH4F) acting as fluorine source. XRD and FT-IR results showed that, the F- enter the crystal lattice of hydroxyapatite and substitute for some of the OH-, and result in the change of the symmetry of crystal structure. As the fluorine addition was increased, the a-axis of the apatite decreased gradually while the c-axis does not obviously changed, and the content of the β-TCP decreased gradually. So addition of fluorine ions effectively suppresses the decomposition and enhances the thermal stability of pure HA. The lattice parameter has a good liner relationship with fluorine content: a = -1.29×10-3 x + 0.94063; c = 4.3×10-4 x + 0.68772(R2≥0.95). But addition of F- has no effects on microstructure of HA, and fluorine-substituted hydroxyapatite remains hexagonal morphology.

Abstract: Two-component Bose-Einstein condensates systems are investigated in the presented work, using the trigonometric function transform method, and several families of exact solutions are obtained for coupled two-component nonlinear Gross Pitaevskii equations. The solutions obtained in this paper include four kinds of soliton solutions and five kinds of trigonometric function solutions. Finally, the corresponding exact solutions of the uncoupled NLS equations are easy derived in fiber optics.

Abstract: In this paper, the compression test on the bulk nanocrystalline sliver ( n Ag) with average grain size of 50 nm was made. The stress-strain curves under different strain rates were obtained by test. The test results show that the mechanical behavior of n Ag is rate-dependent, and the dynamic compress yield stress are about 1.5 times of that n Ag in static test condition; The effect of strain harding on n Ag is smaller than that of coarse-grained silver (c Ag) in plastic deformation; The relationship between the yield strength and the logarithm of strain rate is approximately linear.