>>14331582It's a unit stress element.
There's psi, like pressure. The surface of your butt in a chair is low pressure. The point of a fork is high pressure.
There's psi, like stress, which is completely different. It's the cross sectional area of a material supporting a load, like weight or wind or inertia. A 0.5mm lead refill for your mechanical pencil is low cross section area and will break easy. A 30" pipe or a 28" I-beam is high cross section area and you'll need a cannon to break it.
There's normal loading, like pulling or pushing straight onto the cross section. There's shear, which is using a length of the material to transmit the force. Shear's parallel to the cross section. Shear's also always in two planes. It's possible to maintain one plane reaction forces in shear by rotating that cube. That cube is not rotating, so shear is always two planes.
Some people think of a vector like letters in a line, arrays like letters in a page, and tensors as letters in a book of pages. That's not this tensor. This tensor is more like letters on a page with an arrow over each. It's a tensor as in an array of vectors, and each vector direction is set, normal to each other.
Tensor math makes equations really easy. You plugin in the numbers and get your principle stresses and can figure out if something is going to break, or stay within safety and service factors. You can have odd shapes and loads and break them up into related finite elements, and calculate per von Mises stress or maximum distortion energy.
You can also rotate the stress element between multiple loads at 90 degrees from each other, so the stress element is like a diamond grid instead of a square grid.
