Stress concentration factors like this are the bane of all structural engineering. Anything with too sharp an internal corner will concentrate stress and lead t

Stress concentration factors like this are the bane of all structural engineering. Anything with too sharp an internal corner will concentrate stress and lead to material fatigue failure if there's any stress there. Given I've spent all morning staring at it in some finite element analysis work, I'm going to ramble about it to give myself a break. Sometimes dealing with it can be a pain, for example if you need two rectangular things to sit together along two faces, since you have to radius both corners with a larger radius on the smaller object. One way to combat this is to drill a hole in the corner, removing additional material but creating a little 270ish-degree-C-shaped radius in place of the sharp corner. Take what would've originally been a sharp corner, but then drill it out (example: [1]). What you lose on less material, you more than gain back with eliminating the stress concentration. This has the advantage that then a rectangular object can fit snug into the corner, because the smaller's sharp corner just sits inside the larger's C-shape cutout. The best visualisation tool of this phenomenon that I learned is force lines [2]. Where they bunch up closely together is where high stress occurs. It follows naturally that a sudden sharp corner will concentrate all those lines close to it, whereas a gentler radius encourages a more gradual transition. Think of the lines as similar to Isobars (probably the most well-known contour line) [3], in that the lines represent points of constant pressure/force, and so will sort-of repel adjacent lines (since there needs to be a smooth gradient between those lines). The more gradually they're forced to change, the more gradual that gradient between lines will be (represented by them being farther apart). Anyhow, all of this is also why you see countless concrete footpaths, driveways, etc. with cracks growing out from sharp corners in the concrete. Look at any internal corners where the concrete runs in an L shape. You'll not uncommonly find a crack growing from it. However, no one really cares (except for aesthetic properties) because it doesn't cause a functional problem, and forming concrete into straight sides is orders of magnitude easier than forming smooth curves. Bonus points if you notice that it's generally not parallel to one of the edges that form the corner, and can figure out why :) (I'd be guessing if I gave my answer, but I'm somewhat confident it'd be right: thermal expansion/contraction affects both sides simultaneously, meaning that the shear stress runs generally at 45 degrees to the corner rather than perpendicular to one, which would be the case if only one side expanded/contracted.) [1]: https://img3.gmdu.net/35780.0.jpg https://img3.gmdu.net/35780.0.jpg [2]: https://en.wikipedia.org/wiki/Force_lines https://en.wikipedia.org/wiki/Force_lines [3]: https://en.wikipedia.org/wiki/Contour_line#Barometric_pressure https://en.wikipedia.org/wiki/Contour_line#Barometric_pressu...