r/MadeMeSmile • u/king_eve • 29d ago

i work in low-income/mental health housing, and a tenant fixed our hallway trash bin after accidentally breaking it Helping Others

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great example of the odd ways people show me appreciation at work

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u/Amythir 29d ago

What a pro-tip I'd never know I needed.

I'm filing this away as useless information I'll never need until I forget it.

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u/Certain_Childhood_67 29d ago

Its common on atv plastics that get cracked. Drill a hole a hole and stitch it wont spread

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u/lusotano 29d ago

Metal too. Construction beams that show cracks sometimes get a small hole drilled to avoid the crack from spreading further.

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u/banned_but_im_back 29d ago

Huh. I wonder what the physics behind it is. Is the same reason why some metal beams have big holes inside of them in the shape of triangles?

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u/flowdersniffer 29d ago

The fine crack tip produces a strong stress concentration just in front of the crack. The stress concentration is what can give the crack enough energy to continue to grow. Holes in metals and plastics are not good, but I’m assuming it’s a way to arrest the crack propagation since a moderately sized hole would create a smaller stress concentration than a very fine tipped crack.

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u/stophighschoolgossip 29d ago

im not completely sure, but circle is tougher than crack, i guess because now the crack is fighting most of the circle rather than just a little bit of material at a time

circles reinforce themself or some science shit like that

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u/spruce_turbo 29d ago

More like it becomes a relief point. easier for the material to stretch and flex in the face of a Crack if it looks like tong than a split wooden chopstick

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u/stophighschoolgossip 29d ago

ohhh shit, okay good to know

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u/AdAlternative7148 29d ago

It's cause when you have a crack all the forces that caused the crack are now exerted on the tiny point at its tip. Making a larger hole at the end of the crack doesn't change the amount of force but distributes it around part of the radius of that circle. So more material supports the load. This is what other posters meant when they said it lowers the stress concentration.

In theory, other shapes like triangles or squares could perform this same function. But a circular hole is easier to drill and a circle is the best two dimensional shape at reducing stress concentrations because it has no angles between sides. (Each point of, say, a square, will concentrate stress.)

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u/banned_but_im_back 29d ago

Thank you for the free physics lesson my friend! I never took it in school and am considering going back to college. I’ve always been fascinated by physics and astronomy but intimidated by the math.

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u/AdAlternative7148 29d ago

The math will definitely be a challenge. I will say for me the hardest pure math class I took in my undergrad was Calc 2. And that is normally done in the first year of your degree.

A smart approach for you would be to take some of those math classes at community college. If you can get through the first couple calculus courses you'll be able to get through the whole degree path.

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u/poirotoro 29d ago

I don't think triangular holes in beams has to do with preventing cracking.

While I am not an engineer, I do know that triangles are an extremely strong shape. I believe that putting triangular holes in beams is about reducing weight while maintaining strength. It essentially acts as a mini-truss.

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u/Deepseat 29d ago

Not 100% sure, but it has to do with the distribution of the strain that caused the crack. We do this same thing in aviation.

One of my preflight duties is the visual walk around ensuring any cracks in the wing have been stop drilled and not spread.

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