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## Impact

Parameters on this tab control when the object to which this data is applied can fracture.

Impact Group

An impact with objects in the specified group can potentially cause this object to fracture.

Min/Max Impact

The minimum impact impulse that can cause this object to fracture.
Any impact over the minimum can cause a fracture; the range is
used in conjunction with the **Radius Scale** parameter, allowing
heavier impacts to map to a larger impact radius.

The minimum impact gets mapped to the minimum impact radius scale, and the maximum impact force gets mapped to the maximum impact scale. Having a maximum ensures that values are clipped so that really strong impacts from creating huge impact zone.

Minimum Volume

The minimum volume an object must have to be eligible for fracturing. The object’s volume is calculated by dividing its mass by its density.

Note

This volume only work this way if you turn on **Compute Mass** on your RBD Objects. If you don’t, the volume will not be what you expect and you may have to just set it to 0.

Re-fracture Delay

The interval (in seconds of simulation time) after an object fractures before it can be eligible for fracturing again.

Fracture From Magnet Force Metaballs

Use the metaball geometry associated with any Magnet Forces applied to the object as a source for potential fracturing. This can be used to cause explosion-type effects, where the magnet force itself causes the fracture.

Minimum Magnet Volume

The minimum ratio of the object’s collision volume that must be overlapped by the magnet metaball before fracturing can occur. It can be useful to delay the fracturing until the metaball overlaps much of the object’s volume when using animated metaball geometry.

Maximum Fractures

Controls how many times the object can break. A maximum fracture of 1 will break on the first impact, but the resulting pieces won’t break again. A maximum fracture of 2 will allow all the pieces from the first fracture to break.

Note

When some pieces break off the main chunk, the main chunk is still considered a "piece", which means it will lose one of its max fractures.

Impact Radius

The radius of the metaball to be copied to each impact point.

Min/Max Scale

Scale the impact radius by this amount, based upon the ranges
specified in the **Minimum Impact** parameter. **Radius scale** multiplies the **Impact Radius** gives you the size of metaball around each impact point. So given a single point of impact, it is roughly your crater radius. There are two values for the min/max.

## Points

Parameters on this tab control the generation of fracture points from the eligible impacts. See the Voronoi Fracture Points SOP help for more information.

Compute Number of Fracture Points

Calculates the number of points to scatter in each fracture region based on its surface area.

Points Per Area

The number of points per unit of surface area. This can be scaled
by the **Point Density** parameter for each region.

Number of Points

The number of points to generate.

Per Impact

Whether the **Number of Points** parameter specifies the total
number of generated points or the number of generated points for
each impact point.

Show Fracture Points

Displays the generated points. Yellow is for the surface region, red for the interior, and blue for the exterior.

### Surface

Point Density

The density of point generation for this region. If **Compute
Number Of Points** is enabled, this parameter is a multiplier of
the **Points Per Area** value. If an explicit **Number of Points**
value is being used, this parameter determines the proportion of
those points allocated to this region.

Surface Offset

The amount to offset the generated points from the object surface. Offsetting by a small amount can cause smaller, more debris-like fractured pieces from the Surface region.

Radius Scale

The amount to scale the impact radius before calculating the Surface region.

Clustering

Use Fracture Settings

Use the parameters on the Cluster tab to control the size of the clustered pieces.

Disabled

Disable clustering for every fractured piece from this region.

Single Piece

Cluster all pieces in this region together as a single piece.

### Interior

Point Density

The density of point generation for this region. If **Compute
Number Of Points** is enabled, this parameter is a multiplier of
the **Points Per Area** value. If an explicit **Number of Points**
value is being used, this parameter determines the proportion of
those points allocated to this region.

Clustering

Use Fracture Settings

Use the parameters on the Cluster tab to control the size of the clustered pieces.

Disabled

Disable clustering for every fractured piece from this region.

Single Piece

Cluster all pieces in this region together as a single piece.

### Exterior

Point Density

The density of point generation for this region. If **Compute
Number Of Points** is enabled, this parameter is a multiplier of
the **Points Per Area** value. If an explicit **Number of Points**
value is being used, this parameter determines the proportion of
those points allocated to this region.

Scatter Location

At Impact

Scatter points at the boundary of the Interior and Exterior regions.

Exterior Volume

Scatter points throughout the exterior volume.

Both

Scatter points at both of the above locations.

Impact Offset

The offset of the Interior / Exterior boundary when scattering
using the **At Impact** or **Both** setting above.

Clustering

Use Fracture Settings

Use the parameters on the Cluster tab to control the size of the clustered pieces.

Disabled

Disable clustering for every fractured piece from this region.

Single Piece

Cluster all pieces in this region together as a single piece.

## Fracture

Parameters on this tab control the fracturing of the geometry from the generated fracture points. See the Voronoi Fracture SOP help for more information.

Cusp Interior Normals

Computes vertex normals on the edges of the interior geometry, so that they will have a cusped appearance.

Cusp Interior Normals Angle

Computes vertex normals on the edges of the interior geometry with angles greater than this angle, so that they will have a cusped appearance.

Cusp Exterior Normals

Computes vertex normals on the edges of the input geometry, so that they will have a cusped appearance. If the input geometry already has normals, you may want to disable this.

Cusp Exterior Normals Angle

Computes vertex normals on the edges of the input geometry with angles greater than this angle, so that they will have a cusped appearance. If the input geometry already has normals, you may want to disable this.

### Cut

Cut Plane Offset

Offsets the cut plane between adjacent cell points before cutting. Increasing this has the effect of putting space between each fractured piece.

Note

Setting this parameter to a non-zero value disables **Clustering**.

### Cluster

Cluster Pieces

Fuse the individual pieces into larger clusters based on their input points sharing a common, non-zero cluster attribute value. Values for this attribute can come from the generated fracture points, or from noise as specified below.

Size

The size of the cells for the noise added to the input points. This roughly corresponds to the size of the clusters.

Offset

The offset of the cellular noise added to the interior points.

Jitter

The jitter of the cellular noise added to the interior points.

Random Detachment

Randomly detach pieces from clusters.

Detach Seed

The random seed used for detachment.

Detach Ratio

The probability that a particular piece will be detached.

### Interior Detail

Add Interior Detail

Adds additional polygons to the interior surfaces of pieces.

Detail Size

The size of the polygons added to the interior surfaces.

Noise Type

The type of noise added to the interior points.

Frequency

The frequency of the noise added to the interior points.

Offset

The offset of the noise added to the interior points.

Turbulence

The turbulence of the noise added to the interior points.

Depth / Noise Scale Bias

The value for the bias curve that maps depth within the surface to the amplitude of the noise applied.

## Velocity Transfer

Parameters on this tab control how velocity is transferred from the intact object to the fractured pieces at the time of impact. Fractured pieces can inherit velocity from the intact object’s pre- and post-impact velocity. At the time of fracture, a velocity impulse is also calculated for each fracturing impact, and is added to the pieces' point velocities with a user-specified strength and falloff. This impulse can add velocity to the pieces even when the intact object has no velocity before or after impact.

Pre/Post Velocity Bias

The amount of pre- or post-impact velocity that the fractured pieces should inherit.

Setting this to a low value (biased towards pre-impact velocity) makes the pieces inherit little of the object’s collision response, and the object will appear brittle, with little internal strength.

Setting this to a high value (biased towards post-impact velocity) causes the pieces to inherit much of the object’s collision response, and the object will appear harder, with more internal strength.

Impulse Distance

The distance over which the velocity impulse falls off from each impact. The impulse will have no effect past this distance.

Radial Impulse Scale

A scale for the radial component of the velocity impulse. Increasing this value will give velocity in an outwards direction from the fracturing impacts to the pieces within the Impulse Distance.

Normal Impulse Scale

A scale for the normal component of the velocity impulse.
Increasing this value will give velocity (in the direction of the
collision response) to the pieces within the **Impulse Distance**, even
if the velocity bias for the entire object is towards pre-impact
velocities.