For design of multi-layered environmental barrier coatings (EBCs), it is essential to assure mechanical reliability against interface crack initiation and propagation induced by thermal stress owing to a misfit of the coefficients of thermal expansion between the coating layers and SiC/SiC substrate. We conducted finite element method (FEM) analyses to evaluate energy release rate (ERR) for interface cracks and performed experiment to obtain interface fracture toughness to assess mechanical reliability of an EBC with a function of thermal barrier (T/EBC; SiC/SiAlON/mullite/Yb-silicate gradient composition layer/Yb 2 SiO 5 with porous segment structure) on an SiC/SiC substrate under thermal stress due to cooling in fabrication process. Our FEM analysis revealed that a thinner SiAlON layer and a thicker mullite layer are most suitable to reduce ERRs for crack initiation at the SiC/SiAlON, SiAlON/mullite and mullite/Yb 2 Si 2 O 7 interfaces. Interface fracture tests of the T/EBC with layer thicknesses within the proposed range exhibited fracture at the SiC/SiAlON and SiAlON/mullite interfaces. We also estimated the approximate fracture toughness for the SiC/SiAlON and SiAlON/mullite interfaces and lower limit of fracture toughness for the mullite/Yb 2 Si 2 O 7 interface. Comparison between ERR and fracture toughness indicates that the fabricated T/EBC possesses sufficient mechanical reliability against interface crack initiation and propagation.Coatings 2019, 9, 697 2 of 27 with the following properties as the water vapor shielding layer; significant wall-thinning resistance in the combustion gas environment, and coefficients of thermal expansion (CTEs) being close to that of the SiC/SiC. Klemm conducted burner-rig tests for various heat-resistant materials under the condition simulating the actual combustion gas environment to quantitatively evaluate relationship between CTEs and wall-thinning rate [8]. The result indicated that ytterbium silicate (Yb 2 SiO 5 ; YbMS and Yb 2 Si 2 O 7 ; YbDS) has prominent wall-thinning resistance. He reported that the resistance of YbMS is particularly outstanding and that the CTE of YbMS is slightly larger than that of the SiC/SiC substrate, which is almost equal to that of YbDS. Yb-silicate is unlikely to fracture by phase transition during thermal cycle because phase transition causing the large volume change does not appear in the material throughout a wide temperature range from room temperature to high temperature. On the basis of these features, Yb-silicate is considered to be an attractive material as the water vapor shielding layer. By the way, YbMS is expected to be applied as the thermal barrier coating (TBC) for SiC/SiC substrate because the thermal conductivity of YbMS [9] is smaller than that of Y 2 O 3 -ZrO 2 (YSZ), which is used as TBC for Nickel-based super alloys.Under the combustion gas environment, EBCs are exposed to a steep gradient of oxygen chemical potential (dµ O ). It is known that, in an oxide layer under the environment of high temperature and dµ O , th...
A model of a walking pattern imitating human motion is presented. An accurate imitation of human motion and a robust bipedal walking motion are, however, hardly realized together. We therefore focus on only three characteristics of human walking motion: single toe support, knee stretching, and swing leg motion. Based on a conventional pattern generator, single toe support is added, waist height is changed in order to stretch the knees as much as possible, and swing leg motion is generated approximating the human's motion. The generated motion is then filtered to provide a feasible pattern. In addition, the stabilizer is improved in order to keep the Zero Moment Point (ZMP) within the tiny support polygon during the single support phase with toe link. Finally, we successfully demonstrate the generated walking pattern with the robot HRP-4C.
Robot audition, which aims at multiple simultaneous human-robot communications in noisy environments, has undergone rapid development since last decade. For a common scenario, robot audition systems usually generate a huge amount of chronological data. These data fall into several categories: sound source locations and orientations, separated sound sources and recognized speeches. In order to efficiently assist people in understanding and analyzing the scenario, it is necessary to organize the data in a delicate way. To achieve this goal, we suggest Speech Arrow which conveys recognized speeches in animated arrow shaped frames. Speech Arrow is highly integrated, intuitive and vivid. In this paper, a single pane auditory scene visualizer is implemented to support Speech Arrow. The visualizer is 3D real-time virtual reality system based on the open source robot audition system HARK. It includes two versions, one of which restores original auditory scenes with offline raw data. The other analyzes and displays online instant data without any delay to help hearing impaired people. We demonstrate that our visualizer improves auditory awareness considerably with experiments.
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