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328 Biomimetics: Biologically Inspired Technologies

100.0
Temperature rise ( C) 60.0
80.0

40.0
20.0
0.0
0.000 0.020 0.040 0.060 0.080 0.100 0.120 0.140
2
Power density (W/cm )
insulated panel

80.0
Temperature rise ( C) 60.0

40.0
20.0

0.0
0.000 0.050 0.100 0.150 0.200 0.250 0.300
2
Power density (W/cm )
exposed panel
Figure 12.24 Experimental temperature rise vs. power density for insulated (top) and exposed (bottom) panels.

predicts a local temperature difference of 158C between different areas in the composite, while this
temperature difference is only about 58C in the actual test.
The tests were carried out for different levels of electrical power, and a linear correlation was
found between the final temperature and the power input (Figure 12.24). Power density over
the face of the panel is used in place of total electrical power so that the value is normalized for
any size of composite panel. Temperature rise is used in place of the actual final temperature so that
temperature results are normalized for any initial temperature. According to the graphs, an insulated
panel requires about 60% less power than the exposed panel to reach the same temperature. If an
ambient temperature of 208C is assumed, and our target temperature is 808C, then a temperature
2
increase of 608C is desired, which corresponds to 0.073 W/cm power input for the insulated panel,
2
compared to the exposed panel’s 0.20 W/cm .
Thermal management within the composite may be leveraged for a number of applications. In
our multifunctional composite, we may utilize this heating function to induce a thermally activated
healing process as detailed in the next section.

12.2.3 Healing Functionality

A material that can heal itself is of great utility where access for manual repair is limited or
impossible, as in a biological implant or a material that is launched into orbit in the solar system.
Structures made of such a material may have significantly prolonged service life in addition to
improved safety if failure mechanisms such as cracking can be repaired in situ. Nature has long
demonstrated this property in various biological materials, whereas, until recently, man-made
healing materials have essentially not been demonstrated. However, interest in synthetic healing
materials has recently gained significant attention with the creation of a truly autonomic healing
polymer by White and other researchers at the University of Illinois (White et al., 2001). Since then
other healing materials have been proposed (Bleay et al., 2001; Chen et al., 2002), one of which is a
novel polymer that will be the focus of further research at UCSD. Wudl and his research group at