The formation of black ceramic layer produced by plasma electrolytic oxidation (PEO) coating has been investigated as a function of coating time. A series of PEO coatings was carried out on aluminum alloy sample in a phosphate electrolyte containing sodium tungstate (Na 2 WO 4 ) with four different coating times, i.e., 20, 100, 200 and 300 s. As the coating time increased, the amount of tungsten element in the ceramic layer increased, resulting in the black ceramic layer. This phenomenon was discussed based on the electrochemical reaction assisted by micro sparks to form WO 3 compounds in the ceramic oxide layer.

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The mechanical behavior of 3D multi-layered braided composite tubes was analyzed using a multi-scale modelling approach. Considering the braiding parameters and the fiber volume fraction of the composite tubes, firstly a unit-cell of the composites was determined based on the motion of yarn carriers and modeled using TEXGEN software. The unit-cell was imported into finite element software to calculate its meso-scale material properties. In this calculation the yarns in the unit-cell were assumed to be solid constituents without considering each filament in them, i.e., a meso-scale approach was adopted for the yarn modelling. Then, the calculated material properties were used to analyze macroscopic deformation behavior of the composite tubes using finite element analysis. The validity of the current meso-and macro-scale analysis will be discussed for designing composite tubes such as mountain bike (MTB) frames, e.g., in finding optimums of the fiber volume fraction, the braiding angle, and the number of layers.