Plasticity is normally a feature of soft bodies, but it is also available with joints. “Plasticity” means that deformations are irreversible and the vertices’ displacement is final. Reversible deformations can be observed with rubber balls, foamed materials or jelly-like substances, to name but a few. Irreversible transformations can be observed with metals, styrofoam or clay, for example. Here, plasticity means that the separation of points, linked by joints, becomes permanent under certain conditions. Since a certain amount of separation is essential for plasticity effects, this mode is only available if “Force max mode” is not set to “Unlimited”. The result is a very realistic behaviour in situations where you want to create cracking effects, for example a breaking dam.
It is not possible to use plasticity effects with “Limit processed joints”.
Plasticity
To enable permanent dislocation of points, switch to “Yes”. The effect of “Plasticity” is exactly the same as described in the previous introduction. The image below shows a simulation of a breaking wall made of two layers and two "MultiJoint" nodes. The white layer has been simulated without activated "Plasticity" and the fragments collapsed without deformation. The orange layer uses "Plasticity" and shows a strong non-reversible deformation. Some fragments stick together as if they were connected with a kind of underlying "tissue" or "grid", but other parts can still leave the assembly. Here some joints are broken.
@ Plasticity distance
When the entered distance is reached, the connection between joints becomes irreversible, behaving like an overstretched rubber band.
@ Plasticity distance random
To give your simulation a more realistic appearance, we recommend that you add a certain amount of randomness. The value that is added to “@ Plasticity distance” ranges between 0 and the number entered here.
@ Plasticity acquired
This parameter has the same meaning as "@ acquired" with soft bodies. It is the percentage of deformation kept as permanent by the joint. This means that the joint will not try to recover its initial situation any more. So, with a value of 0.2, 20% of the currently observed joint's deformation will be permanent. Thus, the value can range between 0 and 1.
In both cases (soft bodies and “MultiJoints”) "acquisition" means a percentage of the deformation suffered at each time step (changing the physical situation at each time step). This can lead to high acquisition of deformation with relatively low values. You have to play a little with the "@ threshold" (soft bodies), "@ Plasticity distance" (“MultiJoints”) and the acquired percentage to obtain the desired results.