Simulating Breaks

Breaks are generally characterized by little losses of material over a part surface, normally hard to be detected with the naked eye. Although this kind of defect clearly affects the object geometry in a visible way, only the surface seems to be affected.

We will simulate each break depending on its size. First we will simulate bigger breaks like the one on this part:

Part 4704 broken

For bigger breaks we extract the lost material using CSG or boolean operations. This consists of placing a second object on the part surface and extracting the difference between them. The second object acts as the extraction tool and the result of this operation depends on its shape and position. Next image shows the result of the extraction operation between the part and a spherical tool:

Tool placed on part's surface
After boolean operation

Once the break is placed we need to define the texture or detail of the break. This will be defined using an image or 2D texture like the next ones, which are fractal textures:

Bump texture
Displacement texture

Those textures will be applied then to the broken zone using bump mapping [Blinn 78] or displacement mapping [Cook 84], depending on the detail size and the distance to the camera. For big details and close views of the broken zone it is better to use displacement mapping, because the results are more realistic although less faster. For the rest of cases the use of bump mapping can approximate well the detail.

Next images show the results of simulating the break of the previous metallic part: after the boolean operation (left), after applying displacement mapping (center) and after applying bump mapping (right) using previously seen textures:

Broken zone Higher detail is applied with displacement mapping Lower detail is applied with bump mapping

The final simulation of the broken part is shown in the next image:

Final simulation

In metallic parts we can find also very little losses of material like the one on this part:

Part 5036 broken

Those kinds of little breaks can be very difficult to model using extraction tools and CSG operations, especially if its shape doesn't look like any shape of tool. In these cases the extraction of material is provably best performed using a sculpting tool, like the one in Maya. This tool consists of pushing and pulling polygons on the object surface until the desired shape is achieved, in this case the shape of the brake. In the next images we can see the result of the sculpting operation made into the part to simulate the previous brake, before its rendering (left) and after (right):

Sculpted brake Brake without detail or material properties

Once we have modeled its shape we must define the detail pattern of the zone. We have used the next texture, a fractal one too.

Texture for bumping

Next images show the results of applying this texture to the broken zone using bump mapping, before (left) and after (right) applying the material and color properties.

Brake detail applied with bumping Final simulation with material properties

Finally, the resulting simulation of the brake seen from afar is shown in the next image:

Final simulation