There are various methods to fracture solid objects in Houdini 19.5 but most fracturing tools in Houdini support a pre-fracturing workflow, where you break the geometry into pieces in SOPs, with the pieces held together by glue constraints.
Pre-fracturing gives you full artistic control over the look of the destruction (for example, carving big blocky pieces or small jagged pieces). The object will crumble when a force overcomes the glue strength, or you can manually animate the glue off when you want the object to break down [3].
The high-level tool for pre-fracturing geometry is the RBD Material Fracture SOP, with plenty of controls over different types of fracturing. There are many lower-level SOPs if you need even more control over fracturing.

To fracture an object using RBD Material Fracture SOP, follow these steps:
1. Use the RBD Material Fracture node to pre-fracture your model in SOPs [3].
2. RBD Material Fracture automatically creates glue constraints between the fractured pieces. On the Constraints tab, you can set the Primary strength to the initial glue strength you want [3].
3. Go up to the object level and select the fractured object. On the Rigid Bodies shelf tool, click the RBD Objects tool to import the object into DOPs as rigid body pieces [3].

Apart from using RBD Material Fracture SOP, you can also use the "Voronoi Fracture" node to pre-fracture the geometry manually in SOPs or use "Solid Objects":
* Voronoi fracturing pre-fractures a model into pieces and then creates a glue constraint network between the pieces. When the pieces collide with enough force, they will separate.
Use the `Make Breakable` shelf tool on an RBD object. Houdini adds a node rig that automatically fractures and glues the object if and when it collides with another object [2].
* Solid objects (also known as Finite Element Method or FEM) converts the model into a solid made up of 3D tetrahedrons. The solid FEM Solver simulates the object as solid matter: it can bend, have elasticity, shift internal mass, chip, crumble, or shatter depending on its physical parameters [2].
On the Solid Object node, turn on Fracturing. Use the Fracture threshold to control how much force is necessary to fracture the object [2].