We investigate dynamic fracture of C/SiC composites under high strain-rate compression or tension with split Hopkinson pressure bar (SHPB) and gas gun loading. Components of the as-fabricated composites are mapped and quantified with X-ray computed tomography, including C fibers and fiber bundles, SiC matrix, and inter-and intrabundle voids. Compression loading is applied along the out-of-and in-plane directions by SPHB at strain rates of 10 2 − 10 3 s −1 along with in situ X-ray phase contrast imaging. Out-of-plane direction compression and tension are examined with gas gun impact at strain rates 10 4 − 10 5 s −1. For the out-of-plane loading, compression induces fracture via void collapse and shear damage banding, while delamination dominates fracture for the in-plane direction compression. With increasing strain rates, the compression failure modes transit from interbundle to intrabundle fracture of SiC, and then to fiber and bundle breaking. Tensile failure involves delamina
In this article, osteoblast activity on two functionalised hydroxyapatite (HA) and hydroxyapatite/ collagen (HAzCOL) surface layers is studied, and the effects of the concentrations of collagen and the collagen adding method on osteoblast activity are investigated. The morphology and elements of the HA and HAzCOL on porous titanium are observed using a scanning electron microscope and an energy dispersive spectrometer. The number of living osteoblasts is found by comparing the optical density value against a control group. The experimental results showed that osteoblasts have different responses at HA and HAzCOL surfaces that have different chemical compositions. The different concentrations and the means of collagen addition can all significantly improve the survival rate of the osteoblasts, but a 7 mg mL 21 concentration of the added amount of collagen in cell activity gives the best result. It can be concluded that collagen molecules deposit on the HAcoating uniformly and provide a favourable position for the osteoblasts.
Predicting mental workload of pilots can provide cockpit designers with useful information to reduce the possibility of pilot error and cost of training, improve the safety and performance of systems, and increase operator satisfaction. We present a theoretical model of mental workload, using information theory, based on review investigations of how effectively task complexity, visual performance, and pilot experience predict mental workload. The validity of the model was confirmed based on data collected from pilot taxiing experiments. Experiments were performed on taxiing tasks in four different scenarios. Results showed that predicted values from the proposed mental workload model were highly correlated to actual mental workload ratings from the experiments. The findings indicate that the proposed mental workload model appears to be effective in the prediction of pilots’ mental workload over time.
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