MANHASSET, NY -- Civil engineers at the Massachusetts Institute of Technology working with physicists at the University of Potsdam in Germany recently proposed a new method for the electronic, continual monitoring of structures.
The research group says a flexible skin-like fabric with electrical properties could be adhered to areas of structures where cracks are likely to appear, such as the underside of a bridge, and detect cracks when they occur.
The prototype of the sensing skin is made of soft stretchy thermoplastic
elastomer mixed with titanium dioxide that is highly sensitive to
cracks, with painted patches of black carbon that measure the change in
the electrical charge of the skin. A patent for the sensing method was
filed in March 2010.
Different types of rectangular patches of this "sensing skin" could be glued to the surface of a structure for detecting the type of crack likely to form in a particular part of a structure.
A sensing skin formed of a 3.25 x 3.25-in. diagonal sq. patches, for instance, could detect cracks caused by shear, the movement in different directions of stacked layers. Horizontal patches could detect the cracks caused when a horizontal beam sags.
The electronics behind the patch consists of a computer system attached to the sensing skin that would send a current once a day to measure the capacitance of each patch and detect any difference among neighboring patches. The formation of a crack would cause a tiny movement in the concrete under the patch, which would cause a change in the capacitance--the energy it is storing--of the sensing skin.
The computer would detect the flaw within 24 hours and know its exact location, a task that has proved difficult for other types of sensors proposed or already in use, which tend to rely on detecting global changes in the entire structure using a few strategically placed sensors, according to the researchers.
The researchers reported the largest protoype patch tested being 8 inches by 4 inches.
"The sensing skin has the remarkable advantage of being able to both sense a change in the general performance of the structure and also know the damage location at a pre-defined level of precision,"said Simon Laflamme Ph.D. '11, in a statement.
Laflamme did this research as a graduate student in the MIT Department of Civil and Environmental Engineering (CEE). He worked with professor Jerome Connor of MIT CEE, and with University of Potsdam researcher Guggi Kofod and graduate student Matthias Kollosche, whose work was funded by the German Ministry of Education and Research.