Fig. 6. The simulation for the 10-µm crack oriented against grav- ity showed the agent would almost fill the entire crack (a) or solidify and seal it (b).
(1 mm, 0.25 mm and 10µm) were placed on the center of the matrix at different angles (30 degrees and 60 degrees). The ef- fect of gravity in the liquid healing agent also was investigated by orienting the crack in the direction of gravity and against it. CFD was used to simulate the distribu- tion of liquid flow into and out of the reinforcements and the crack. The simulation showed that a
1-mm crack oriented towards grav- ity could be completely filled using this mechanism (Fig. 4). The healing liquid was not able to fill the crack when the gravity was oriented in the opposite direction. The contact angle between the healing agent and matrix was higher than 90 degrees, and the effect of capillarity was not enough to pull the liquid from the container. For a 0.25-mm crack placed
against gravity, the liquid flowed from the tube to the crack by capil- lary effect to a certain height (Fig. 5). When oriented against gravity at angles of 30 and 60 degrees, com- plete filling of the crack could not be achieved, but changing the crack orientation affected the ability of the liquid to flow under capillary action. The results of the simulation for
the 10-µm crack oriented against gravity are shown in Fig. 6. When any of the three cracks were
oriented with gravity at angles of 30 degrees, they were completely filled by the healing agent (Fig. 7). Self-healing has been incorporated
in polymers using hollow micro-bal- loons and tubes where certain healing agents polymerize upon contact with
July/August 2011 MetAl CAsting Design AnD PurChAsing 29
Fig.
7.The simulation for the 10-µm (a), 0.25-mm (b)and 1-mm (c) cracks at 30 degrees toward gravity are shown.
the catalyst flowing into the crack and sealing it. In ceramics, hollow reinforcements rupture to release healing agents that expand upon oxidation, filling small cracks. The same concept can be extended to cast metals.
METAL
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