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I want to bend a square bar with a hollow inside. What should I do to bend it into the shape as shown in the reference pictures?

If possible, I would like to know how the square bar bends in Blender using physics.

I'd like to make a video where the square bars are bent and crushed.

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  • $\begingroup$ There are so many ways and approach to this : you can model it by hand, sclupt or even use physics or what not. What have you tried already? $\endgroup$ Aug 1, 2023 at 4:33
  • $\begingroup$ I've just started blender, and I'm still researching how to do it on the web. $\endgroup$ Aug 1, 2023 at 4:42
  • $\begingroup$ If possible, I would like to know how the square bar bends on the blender using physics. $\endgroup$ Aug 1, 2023 at 4:45
  • $\begingroup$ I'd like to make a video where the square bars are bent and crushed $\endgroup$ Aug 1, 2023 at 4:47
  • $\begingroup$ Maybe this tutorial could lead you to the right direction youtube.com/… ? $\endgroup$ Aug 1, 2023 at 5:13

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Playing around with a cloth simulation, I managed to get that far:

Adding subdivisions before the cloth simulation will increase the foldiness, though that also depends on cloth resistances:

I started with the default cube, resized it on $z$ axis, ✲ CtrlR added loopcuts to make it roughly square-quads based again, but then decided to add much more loopcuts in the bending area:

Probably many of those sparse loopcuts away from bending can be removed, and the dense loopcuts shifted up, as I wrongly predicted where I'll bend…

The bending animation is done using this modifier stack:

  • bevel to add holding loops for Subdivision Surface
  • Subdivision Surface to give it the final base profile and geometry density
  • Simple Deform to bend by 90°
  • The magic of cloth sim
  • Smooth the bends so faces don't overlap on themselves
  • Another Subdivision Surface to further smooth the output by adding vertices

Proper Weight Painting is crucial, and so by improving it you will get better results than me:

Cloth settings are extremely important as well, but I left most settings to defaults and just pinned the weights from above and added just a touch of pressure from inside to direct the bends outside:

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  • $\begingroup$ What a beauty! I wonder whether a blurred GN-generated tension-map would stand any chance of doing your weight-painting for you. $\endgroup$
    – Robin Betts
    Aug 1, 2023 at 9:45
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    $\begingroup$ @RobinBetts nice idea, I was thinking of something similar: after first pass, convert it to shape keys, then weight-paint the areas based on how much you want them to change. Could even weight-paint individual frames differently using this, then replay simulation, rinse, repeat until happy with the result… $\endgroup$ Aug 1, 2023 at 10:28

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