This week you will be given strips of transparency film. Each strip has four printed squares, with each rotated a different amount, representing four coordinate systems. You will measure the size and orientation of each square, stretch the strip in one direction, and then remeasure. Between your calipers, a protractor, and some averaging you should be able to calculate the normal and shear strains for each square. You will then check whether the squares provide the same principals, max shear, and θp....which they should.
This will hopefully demystify the topic of strain transformation, because we can visually see the deformation (unlike with a strain gage) and measure it by hand. The logic is simple enough for everyone to get an intuitive feel for the different strain concepts.
We will also look at photoelasticity, which will hopefully help us visualize how force flows through a few basic shapes.
Video Lecture (17 minutes)