12 February 2012

Fractures on a seismic sign

Posted by Callan Bentley

On the campus of the University of Texas at El Paso, there is a sign for the Kidd Seismic Observatory. The sign has seen some brittle deformation of its reflective letters. I infer this due be due to differential shrinkage of the letters (relative to the sign they are attached to) in the intense Texas heat.

I like seeing deformation in materials other than rocks. This is a neat example of evident tensional stresses on the golden reflective letters that I’m sure experienced some scorching temperatures over many days in many summers over many years. As that dark sign heated up, the material (sticker?) of the golden letters contracted, and contracted by more than it was capable of standing up to. The letters broke into pieces. Thankfully, these stayed stuck to the vertical face of the sign. The orientation of the initial fractures is interesting to me: notice that it is everywhere perpendicular to the edge of the letter. Inside the letter, smaller “connecting” joints initiate perpendicular to the original joints and divide the gold sticker into a grid, or warped grid.There is also some blistering of the golden material (or at least its outermost transparent layer) outward, away from the face of the sign.

Pretty cool, methinks.