69 Chapter 4 Fundamentals of Collision Damage
Copyright Goodheart-Willcox Co., Inc.
be changed enough to be permanently weakened by
microscopic cracks. A kink has a buckle that is greater k
than 90° in a short area. The metal is folded so tightly
that the radius of the buckle is 1/8″ (3 mm) or less. The ″
metal may be cracked in the tightest part of the kink.
If repaired, the weakened high-strength steel will not
properly support the weight of the vehicle or protect
the passengers during a collision. Therefore, a kinked
high-strength steel panel must be replaced.
N N N N O O O O T T T T E E E E
The Th e term te rm bend be nd is i s often of te n used us ed in i n the th e d d
collision repair industry when referring
to a buckle. For example, the bend-
versus-kink rule actually y deals with
differences between buckles and kinks.
The grain structure in slightly damaged high-
strength steel does not change enough to produce the
microscopic cracks. Slightly damaged high-strength
steel is not weakened. Slightly damaged high-strength
steel has a buckle that is not tightly folded and is less
than 90°. A buckle is smooth, while a kink is severely
folded.
Many full-frame and unibody vehicles are made
from a combination of mild steel and high-strength
steel. A technician cannot tell mild steel from high-
strength steel. Because it is so important that high-
strength steel be replaced if it is kinked, and because
mild steel cannot be distinguished from high-strength
steel, I-CAR recommends that all the steel in a vehicle
be treated as high-strength steel. Based on this recom-
mendation, all-load bearing and structural parts of a
damaged vehicle should be replaced if kinked. Only
buckles should be straightened.
However, this rule does not necessarily apply to
aluminum structural parts. Check the manufacturer’s
recommendations to determine what type of damage can
be repaired and what type requires part replacement.
Full-Frame Damage
A full-frame vehicle, such as a pickup truck, has
a frame made of hot-rolled steel. The frame members
can be U-shaped or boxed. Four-wheel-drive vehicles
often have a frame made entirely of boxed members.
Two-wheel drive vehicles can have a frame made
entirely of C-shaped members or a frame consisting
primarily of C-shaped members with some boxed
members for extra reinforcement. The two sides of
the frame are called the frame rails. The frame rails
are connected by bolted, riveted, or welded cross
members. When viewed from the top, some frame rails
are stepped in near the front suspension mountings as
shown in Figure 4-22. When viewed from the side, all
frame rails have some type of arch. See Figure 4-23.
Toyota
Figure 4-22. The step-in area is near the suspension mounting area. The frame is slightly narrower in the front.
Goodheart-Willcox Publisher
Figure 4-21. The scratches in the paint show the
direct damage.