FRACTAL MORPHOLOGY IN DLA UNDER MULTIPARAMETER

Various fractal morphologies are obtained by introducing noise reduc-tion, tansential and radial probabilities into DLA (diffusion-limited aggregation)medel. As the noise is reduced, perimeter sites with extremely small values of lo-cal field gradient ar

Hierarchical structure observation and nanoindentation size effect characterization for a limnetic shell

In the present research, hierarchical structure observation and mechanical property characterization for a type of biomaterial are carried out. The investigated bioma- terial is Hyriopsis cumingii, a typical limnetic shell, which consists of two different structural layers, a prismatic ＂pillar＂ structure and a nacreous ＂brick and mortar＂ structure. The prismatic layer looks like a ＂pillar forest＂ with variationsection pillars sized on the order of several tens of microns. The nacreous material looks like a ＂brick wall＂ with bricks sized on the order of several microns. Both pillars and bricks are composed of nanoparticles. The mechanical properties of the hierarchical biomaterial are measured by using the nanoindentation test. Hardness and modulus are measured for both the nacre layer and the prismatic layer, respectively. The nanoindentation size effects for the hierarchical structural materials are investigated experimentally. The results show that the prismatic nanostructured material has a higher stiffness and hardness than the nacre nanostructured material. In addition, the nanoindentation size effects for the hierarchical structural materials are described theoretically, by using the trans-scale mechanics theory considering both strain gradient effect and the surface/interface effect. The modeling results are consistent with experimental ones.

Microstructure and Property of High Carbonic-Chromium Cast Steel with Different Hot Deformation Ratio

The microstructure and properties of high carbonic-chromium cast steel subjected to different hot deformation ratios were studied.The experimental results show that the microstructure and properties of high carbonic-chromium cast steel are obviously improved after hot deformation,and the best mechanical properties of the cast steel can be obtained under hot deformation ratio of 40 %-50 %,which leads to the morphology change of eutectic carbide and the precipitation of granular carbides.

Mechanical properties and microstructure analysis of refilling friction stir welding on 2219 aluminum alloy

The 2219 aluminum alloy under refilling friction stir welding （RF-FSW） was investi- gated. The micrographs showed that the bead could be divided into six zones, and the grain size and shape were greatly different in these zones. According to the mi- crostructure analysis, the weld nugget zone and the shoulder stirring zone consisted of equiaxed grains, while the grains in the heat affected zone were seriously coars- ened. It was obvious that bending deformation occurred in the thermo-mechanically affected zone. According to the microhardness analysis, the lowest hardness of the weld was at the thermo-mechanically affected zone, and the microhardness increased with the retraction of the stir-pin. The tensile strength and elongation of the bead were 70% and 80% of the base metal, respectively. The tensile strength was slightly different for the stable stage and the retraction stage, while the elongation decreased in the retraction stage. The mechanical different retraction speed were analyzed, with increasing retraction speed. properties and microstrueture responded to and it showed that the elongation decreased