60 Section 1 Introduction to Collision Repair
Copyright Goodheart-Willcox Co., Inc.
Introduction
This chapter will introduce you to the fundamentals
of collision damage. It will discuss the properties of
the various types of metal used in vehicle construction
and detail the way that the shape of body panels and
structural components impact the way they react when
damaged. It also explains the factors that determine
the amount of damage that occurs when a vehicle is
involved in a collision. Finally, the types of damage
that occur in full-frame and unibody vehicles will be
discussed.
Vehicle Design Factors
Vehicle design factors influence the way a vehicle
will react in a collision. These factors include the prop-
erties of the metals used in vehicle construction and
the way these metals are shaped.
Metal Properties
The properties of the metals used in a vehicle will
affect the amount of damage that occurs when the
vehicle is involved in a collision. A basic understanding
of these properties will help you assess and repair
collision damage.
If a piece of metal is examined under a micro-
scope, units called grains will be visible. Grains are
formed by the crystalline pattern of the metal and alloy
molecules. Different types of metals have different
grain patterns. For example, mild steel has a large,
loose grain pattern, Figure 4-1. High-strength steel,
on the other hand, has a small, tight grain pattern.
See Figure 4-2. The types and amounts of alloying
elements added to metal and the annealing process
determine the grain pattern. During the steelmaking
process, a uniform grain pattern will be set in the
metal. When the metal is formed into a part, the grain
pattern is changed in areas that have a bend or a
stretch. Differences in grain pattern in a bend or stretch
translate into differences in the metal’s properties in
these areas.
Elasticity
Elasticity is the ability of a metal to bend without y
permanent deformation. If force is applied to one end of
the metal and does not move the metal beyond its yield
point, the grain arrangement will not change, and there
will be no permanent deformation. See Figure 4-3. The
strip will spring back to its original shape because move-
ment in the grains is not great enough to arrange them
into a new set.
Different types of sheet metal have varying
degrees of elasticity. Some variables in the elasticity of
sheet metal include the types of alloying elements and
annealing procedure. The shape of the metal will also
have an impact on elasticity.
Some damage in a panel may be elastic deforma-
tion. Metal with elastic deformation will return to its
original position if the force holding the metal out of
position is removed.
Plasticity
Plasticity is the ability of a metal to be shaped. As y
stated previously, panels are shaped by bending and
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Figure 4-1. When viewed under a microscope, mild
steel has a large, loose grain pattern.
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Figure 4-2. High-strength steel has a small, tight grain
pattern when viewed under a microscope.
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Figure 4-3. In elastic deformation, the panel springs
back to original shape once the pressure is released.