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Fracture Tips 773
it breaks off from the fracture object. The
size or mass of the object is not be t a ken into
account.
Energy Loss—The amount of extra kinetic energy
is lost in the collision due to the breaking of the
fracture b onds. This has the effect of dampening
the collision somewhat and also transferr ing
energy to the remaining, unbroken pieces of the
fracture object. To simulate a brittle object, with
maximum shatter effect, keep this value low. To
sim ulate breakage of a material more lik e wood or
concrete, use a high Energy Loss value.
Tip: Increasing this value can improve the
performance and stability of the simulation.
Display : Show B ounding B ox —When on, the
viewports display a b ox that contains all the pieces
ofthefractureobject.
Disabled —When on, the Fracture helper has no
influence on the rigid bodies that are part of it.
Reset Default Values—Returns the settings to their
default values.
World rollout > Fracture Penetrations group
Severaladditionalvaluesgovernfracturebehavior.
These are global in that they apply to every rigid
bo dy added to a Fracture object, and are found in
the Utility p a nel > reactor > World rollout.
These values control the behavior of penetration
depth collision detection and response, and apply
only to objects that are included in a Fracture
helper.
Separation Time—Forces are applied to penetrating
bodies that are strong enough s o t he bodies
become sepa rated within the time specified. To
simulate an explosion e ffect, ma ke this value very
small and reduce the Velocity Cap value.
Velocity Cap—reactor won’t apply penetration
recovery forces if they cause the relative velocity
between two penetrating bodies to exceed the
specified value.
Scale Tolerance—Thecollisiontolerancefor
bodies that use the penetration depth algorithm is
determined by multiplying the Collision Tolerance
value by the value specified. If this value is
negative, the collision tolerance will extend inside
the bodies, effectively shrinki ng the collision
geometry.
For more information about using these values,
see the Fracture Tips (page 2–773) topic.
Fr act u re Tip s
After you procedurally slice up an object for
fracture, the new pieces fit snugly among each
other. When one piece breaks loose after a frac ture
event, it mi ght be in contact with other pieces that
are still part of the non-fractured body. This can
throw the brok en piece into unstable oscillations
against two or more opposing pieces. The result
isachain-reactionthroughoutthefracturebody,
with all t he pieces flying off into space. It might
appear as though some of the pieces simply wink
out of existence. U nlike normal rigid bodies in
reactor, Fracture pieces are allowed to exist in a
state of interpenetration, where restoring forces
are applied to separate them. Many objects sitting
in penetrating states next to each other can result
in an unstable system.
To make the sy stem more stable a nd less prone to
ex plo di ng:
Try one or more of the following:
•ReducetheScale Tolerance value in the Fracture
Penetrations group of the reactor utility World