Key Engineering Materials Vol. 810

Abstract: The availability of TiC healing agent has been evaluated in low temperature self-healing behavior of Al₂O₃ based self-healing ceramics. For this purpose, some technical issues to actualize the advanced fiber-reinforced self-healing ceramics containing TiC based interlayer as healing agent were discussed. Especially, the mechanical matching between the matrix and the interlayer was focused. Moreover, the self-healing behavior of the advanced shFRC containing the optimized TiC based healing agent was investigated. As a result, 30 vol% TiC-70 vol% Al₂O₃ interlayer was confirmed to be the optimized healing agent in the self-healing ceramics, and the self-healing ceramics was found to enable to attain the perfect healing at 600°C within 10 min. And we succeeded in prototype production of fiber-reinforced self-healing ceramics for low pressure turbine blade.

Abstract: Shape recovery fiber reinforced self-healing plastic which achieves full strength recovery is developed. In this system, microcapsules containing dicyclopentadiene (DCPD) as healing agent are dispersed in epoxy resin matrix. Moreover, thermal shrinkage fibers coated by weak interlayer with Grubbs catalysts are uniaxially oriented. When a crack is introduced to the material, it propagates through the matrix and branches along the interlayer while breaking the microcapsules. Then DCPD flows from microcapsules into the cracks and polymerizes. At the same time, the fibers thermally shrink due to the polymerization heat, and the cracks are completely healed and closed. Furthermore, shape recovery ratio is defined as ratio of "closed crack width" with respect to "initial crack width", and can be rewrote as ratio of loads. Tensile tests were carried out using flat plates with a notch, and they were pulled in the fiber direction. After the crack introduction, the displacement was kept constant. The specimen was heated to about 70°C, and temperature and load change were measured until the stress reduction was done. As a result, the shape recovery ratio was calculated to be 7.89% due to the temperature rose caused by polymerization. Therefore, the full strength recovery can be expected by demonstrating the shape recovery effect of this material.

Abstract: Fast development of nanotechnology leads to the top-down preparation of nanoparticles by various disintegration techniques taking a major part in the industrial sector. A very promising way seems to be the use of cavitation implosions. In our approach, the main mechanism of this type of disintegration is based on mutual collisions of solid microparticles in dense dispersions, powered by implosions of vapour cavitation bubbles generated between the particles.This paper presents experimental results of the disintegration of silicon microparticles to the sub-micron scale. In our experiments, the primary silicon particles of mean size of 5927 nm were reduced to 160 nm and 736 nm by the ultrasonic disintegration process after 240 minutes and at the ultrasonic frequency of 32 kHz. We also present a phenomenological model of particles erosive disintegration where particle fragments are approximated by spheres of equivalent volume. This model allows us to calculate the energy needed for successful disintegration of primary microparticles by measuring the particle size distribution. Thus, we can estimate the minimal energy conserved in the cavitation bubble alongside with its radius at a normal pressure of the surrounding liquid.

Abstract: The paper is focused on computation of a compressive strength of composite materials by limit analysis. This method enables to determine the strength or other types of limit loads by solution of a specific optimization problem. It is also capable to predict failure zones. Abilities of the method are investigated on a particular composite -- a laboratory prepared sample consisting of a hard coal matrix and a polyurethane binder. This sample is chosen due to available CT images of the inner structure and laboratory experiments. Appropriate yield criteria are proposed for the coal and the binder in order to define the limit analysis problem. This problem is penalized and then discretized by higher order finite elements. For numerical solution, the semismooth Newton method and adaptive mesh refinements are also used. Numerical experiments in 2D for various CT scans and material parameters are performed.

Abstract: In this study, mechanical activation is used to generate ultra-fine fly ash (UFA) for high volume fly ash（FA）cement composites. The effects of different content and medium particle size of FA on mortar`s electrical resistivity, chloride penetration and mechanical properties are investigated. The results show that the compressive strength and resistance to chloride permeability of specimens with UFA have been enhanced, owing to higher pozzolanic reaction and higher dissolution rate of Si and Al units of UFA to accelerate the generate of reaction products. However, At the early ages, electrical resistivity of specimens increases with the increase of UFA; at later ages, specimens have a higher electrical resistivity with the increase of UFA.