Interior

In between each neighboring vertex of a mesh, you typically create edges to connect them. Imagine each edge as a spring. Any mechanical spring is able to stretch under tension, and to squeeze under pressure. All springs have an ideal length, and a stiffness that limits how far you can stretch or squeeze the spring.

In Blender’s case, the ideal length is the original edge length which you designed as a part of your mesh, even before you enable the Soft Body system. Until you add the Soft Body physics, all springs are assumed to be perfectly stiff: no stretch and no squeeze.

You can adjust the stiffness of all those edge springs, allowing your mesh to sag, to bend, to flutter in the breeze, or to puddle up on the ground.

---

To create a connection between the vertices of a soft body object there have to be forces that hold the vertices together. These forces are effective along the edges in a mesh, the connections between the vertices. The forces act like a spring. Fig. Les sommets et les forces sur leurs arêtes de connexion. illustrates how a 3×3 grid of vertices (a mesh plane in Blender) are connected in a soft body simulation.

Les sommets et les forces sur leurs arêtes de connexion.

Les forces supplémentaires avec Stiff Quads activé.

But two vertices could freely rotate if you do not create additional edges between them. The logical method to keep a body from collapsing would be to create additional edges between the vertices. This works pretty well, but would change your mesh topology drastically.

Luckily, Blender allows to define additional virtual connections. On one hand you can define virtual connections between the diagonal edges of a quad face (Stiff Quads Fig. Les forces supplémentaires avec Stiff Quads activé.), on the other hand you can define virtual connections between a vertex and any vertices connected to its neighbors” Bending Stiffness. In other words, the amount of bend that is allowed between a vertex and any other vertex that is separated by two edge connections.

Settings

The characteristics of edges are set with the Springs and Stiff Quads properties in the Soft Body Edges panel. See the Soft Body Edges settings for details.

Tips: Preventing Collapse

Stiff Quads

To show the effect of the different edge settings we will use two cubes (blue: only quads, red: only tris) and let them fall without any goal onto a plane (how to set up collision is shown on the page Collisions). See the example blend-file.

Without Stiff Quads.

Trame 1.

Trame 36.

Trame 401.

Dans Fig. Without Stiff Quads., les réglages par défaut sont utilisés (sans Stiff Quads). Le cube « quad only » va complètement, le cube composé de tris garde sa forme, bien qu’il se déformerait temporairement à cause des forces créées pendant la collision.

With Stiff Quads.

Trame 1.

Trame 36.

Trame 401.

Dans Fig. With Stiff Quads., Stiff Quads est activé (pour les deux cubes). Les deux cubes gardent leur forme, il n’y a pas de différence pour le cube rouge, parce qu’il n’a aucun quad de toute façon.

Bending Stiffness

La seconde méthode pour empêcher un objet de s’effondrer est de changer sa raideur Bending. Ceci comprend les arêtes diagonales (l’amortissement s’applique aussi à ces connexions).

Bending Stiffness.

Trame 1.

Trame 36.

Trame 401.

Dans Fig. Bending Stiffness., Bending est activé avec un réglage de force à 1. Maintenant les deux cubes sont plus rigides.

Deux plan venant à collisionner.

No bending stiffness.

High bending stiffness (10).

Bending stiffness peut aussi être utilisé si vous voulez faire un plan subdivisé . Sans Bending les faces peuvent tourner librement l’un contre l’autre comme des charnières Fig. No bending stiffness.. Il y aurait aucun changement dans la simulation si vous avez activé Stiff Quads, car les faces ne sont pas déformées du tout dans cet exemple.

Bending stiffness is the strength needed for the plane to be deformed.