# Hinge component

Hi!
I’m using the hinge component of kangaroo for a paper crease. I’m trying to model the spring back effect in paper creases. It is the property of a paper to bounce back to normal state when a force is applied on a hinge. This gives it spring like nature where the rebound force is proportional to the amount of folding. I wanted to know how the strength parameter of the hinge component is related to this.

Hi,

The standard hinge goal models purely elastic bending - when the applied force that was causing it to bend is removed, it returns all the way to its original rest state. So it can be seen as 100% spring back.

Normally though when we talk about spring back, it is in combination with plasticity, meaning that beyond a certain amount of deformation the rest state of the material is changed, and when the deforming force is removed it only returns only to this new rest state, instead of all the way back to its original geometry. Greater plasticity is the same as less spring back.

In Kangaroo you can model this with the PlasticHinge goal.
If you want to make the paper fold and keep its fold just along a particular curve, like when it is scored, you can make only these hinges plastic, but keep the rest purely elastic.

I’ll make an example now to demonstrate

Hi Daniel, Thanks for the info! But I’m fine with the ideal case of 100% spring back. I just need to know how the value of strength ‘k’ and bending angle ‘rest angle - new angle’ is related to reboounce.
Is the re bounce force F = k*(rest angle- new angle)?

You can see the code that is inside the hinge goal here, and it includes links to the main references the approach is based on:

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That got complex real quick
But thank you so much for sharing the code! I’ll try to translate the C# code into understandable format.

I realise this isn’t exactly what you were asking about, but thought I’d share the example anyway as others might find it useful:

_

curvecrease_example.gh (19.2 KB)

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