Ecofriendly anti-fouling surfaces are usually produced by lithographic techniques which will fabricate micropillar-like surfaces made of low surface energy materials such as Polydimethylsiloxane (PDMS). The purposes of this research were to investigate the most suitable Polydimethylsiloxane (PDMS) material model available in ANSYS APDL program to simulate structural behaviors of micropillars subjected to shear loading and to develop micropillar with improved lateral strength. In this research, PDMS material models were derived from experimental data from uniaxial tensile test. The accuracies of the PDMS material models, which were the Neo-Hookean, Mooney-Rivlin 3 and 5 parameters, Ogden (1, 2, 3 terms), Yeoh (1 st , 2 nd , 3 rd order) and Arruda-Boyce material models, were evaluated and compared to experimental data from uniaxial tensile test and punch-shear test. Moreover, micropillars made of a pure PDMS and a Polyurethane Acrylate (PUA) core coated with PDMS were studied to compare their lateral strength under shear loading. We found that the most accurate material model to simulate both the uniaxial tension and shear loading was the Yeoh 3rd order material model; however, these accuracies would valid for small strain range. The lateral strength of a micropillar made of PUA core coated with PDMS was 8.67time of the one made of pure PDMS. The optimal coating thickness was 100 nm because of its lateral strength and manufacturing cost.

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Abstract. This paper presents the accuracy of finite element models of human tibia bones generated from CT-images used for analyzing stress distribution under loading. The effects of bone structures and material properties (isotropic and orthotropic materials) on stress distribution during stance phrase running were studied. Three-dimensional tibia models were constructed by using Mimics V.10.01, Geomagic V.10 and Catia V.5 software. Then these models were imported into the Hypermesh V.12 software to generate the FE models. Finally the FE models are imported to ANSYS (APDL) V.14.5 software to analysis the stress distribution in the tibia bones. By compared to the benchmark FE model of tibia bones (case studies 13 and 14) resembling to the real bone, we found that there were two sites of maximum von Mises stresses found on tibia bones which were on the middle of posterior tibia and the proximal tibia. However, FE models formed only by cortical bone could not capture the peak stresses on the proximal tibia due to the lack of relatively soft subsurface. The FE models with the medullary cavity formed by cortical bone over predicted the maximum von Mises stress on the middle of posterior tibia while ones with the medullary cavity formed by cancellous bone, bone marrow or bone marrow fat obtained quite similar results. The bone marrow fat in the medullary cavity could not assist to support load on the proximal tibia due to the relatively soft material. The maximum von Mises stresses obtained from FE models with cortical bone formed by orthotropic material were slightly different from ones formed by isotropic material. However, the difference of these FE results was directional cosines that indicated the direction of the crack initiation.

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Abstract. Water-filled containers have long known for its structural characteristic of impact load absorption. This paper presents design of structures resisting to impact load resulting from a high-velocity tennis ball. One cubic meter water containers consisting of rectangular, cylindrical, and spherical water containers and water levels were studied for their stress distribution and deformation during maximum deformation period using finite element analysis in the ANSYS 15.0 software. The containers were modeled by using shell elements and made of elasto-plastic material of HDPE plastic. The filled water was model by using fluid elements. We found that as ball velocity increased, maximum von Mises stress increased. However, for post-yielding behavior, maximum von Mises stress approached a constant near yield stress of HDPE material. As ball velocity increased, deformation increased. When water level increased, maximum deformation decreased. For the rectangular and cylindrical containers, when the water level increased, the maximum von Mises stress increased. However, in the spherical container, as water level increased, the maximum von Mises stress was not significant change. Among three water-filled containers, the rectangular container has the highest efficiency in impact absorption, followed by the cylindrical container and the spherical container respectively.