68 Section 1 Introduction to Collision Repair
Copyright Goodheart-Willcox Co., Inc.
area of direct contact. All the damage except for the
damage on the molding is indirect damage. Indirect
damage occurs away from the point of impact and is
a result of the direct damage. In the indirect damage,
arrowheads and low areas can be seen. The arrow-
heads are located at the furthest extent of the damage.
The arrowheads consist of two ridges, or high areas,
converging to a point. This damage wa s caused by the
lateral force of the bumper.
In a high-crown panel, lateral force causes a
compression of the grains until the panel can no longer
collapse. This compression of the grains is called
upset. The compression of the grains is most notice-
able at the point of the arrowhead and causes a reduc-
tion in surface area. The point of the arrowhead is
sharp and the paint at the point is often chipped. This
paint damage is also indirect damage. The paint chips
off at the upset area because the paint cannot shrink in
surface area the way metal can.
Each arrowhead consists of two types of buckles.
The upset area at the point of the arrowhead is a
collapsed rolled buckle. The two high ridges extending
away from this point are simple rolled buckles. The
metal between the ridges is low, but it is not buckled.
It is simply displaced. Remember that metal can be
held out of position but otherwise be undamaged. If the
ridges holding the displaced metal out of position are
released correctly, the displaced metal will move back
into position with minimal effort.
If enough force is applied to a high-crown panel,
the crown will collapse. The panel then reacts like a
low-crown panel. Force beyond the point of collapse
causes stretching and tearing.
The vehicle in Figure 4-20 was hit longitudinally on
the rear bumper. When the vehicle was rear ended, the
frame rail collapsed from the force on the rear bumper.
Some of the force was transferred to the quarter
panel. The force traveled through the panel, and the
panel moved forward somewhat. Also, the collision
force caused a rearrangement of the grain structure in
the panel. Remember that longitudinal force on a flat
panel causes folds at the pivot points. A pivot point is
a strong area in the panel. In this quarter panel, the
strong areas of the panel are the body line, the area
behind the wheel opening, and the internal brace.
These are areas where the folding occurred. These
folds are collapsed hinge buckles. Because the impact
was on the bumper and not on the quarter panel, all
the damage to the quarter panel is indirect damage. If
you were to feel the buckles, you would find that they
are smooth. The displaced metal in the damaged area
is held out of position by the buckles in the quarter
panel and the collapsed frame rail.
Figure 4-21 shows a simple dent in a combination-
crown panel. All the damage is direct damage. The
metal in the low-crown area is more elastic than that in
a high-crown area. If you were to feel this damage, you
would find only a low spot. The body line around the
wheel opening is flattened. If the dent is deep enough,
the metal in the dent will be stretched.
Bend-versus-Kink Rule
The bend-versus-kink rule states that damaged
high-strength steel parts can be repaired if they are
bent but must be replaced if they are kinked. When
high-strength steel is kinked, the grain structure will
Goodheart-Willcox Publisher
Figure 4-20. The damage on this quarter panel is
indirect. The vehicle was hit on the rear bumper.
Goodheart-Willcox Publisher
Figure 4-19. A bumper striking the molding caused
this damage. Notice the door gap is wider in the
center of the door than it is at the top and bottom
edges.