One of my Facebook friends recently saw my NADDRG 2016 Fall Symposium talk titled, "X-ray Stress Measurements during Multi-axial Deformation."
He commented, "ELI5" (see title)
It's taken me over two weeks to get back to him, but this was my response:
Grab something by one end in one hand and the other in other hand. Maybe it's a piece of tape or strip of paper. Pull the ends apart from one another slowly and you're performing a uniaxial (single axis) tension experiment. As you deform the material, that change in length compared to its starting length is how much you strain the material by, and how much force you need to keep that strain is the stress.
Now let's take a sheet of paper. You're going to grab two sides of the sheet and someone else will take the other two. You guys will both slowly pull, so now you're stretching the sheet. This is multi-axial deformation now (in this case with two perpendicular axis). For uniaxial deformation, we have a pretty good idea of the math to relate the strain and stress, but this is not the case in multi-axial deformation.
To find the relationships between strain and stress in multi-axial deformation, we have ways to find the strain, but not so much the stress. To solve this, we use x-rays to look at what's happening at the atomic level. Materials are made out of atoms and those atoms are ordered. When we pull on a material, those atoms also move apart from one another. We can relate that separation of atomic distances to a stress, but we can't see those distances with our eyes.
X-rays are amazing. How we use x-rays here is not like medical imaging when a doctor wants to see your bones. We use x-ray diffraction to find the separation of those atomic distances. Think about when you shine light onto you hand in a room and look at the shadow behind it. The shadow has the same shape as your hand but is much larger than your actual hand. This is a simplified idea, but we use x-rays in the same way to magnify and observe those separations in atomic distances in the material during multi-axial deformation to get desired information about the stress.
How'd I do?
*Corrected for typos at 11:27 pm courtesy of my editor
