The body is designed to maintain rigidity and durability during normal driving conditions. Front and rear portions of the body should absorb the maximum amount of energy in a severe collision for minimizing the influence to occupants, and the passenger compartment should not deform easily to provide safety for the occupants.
Methods to propagate the force of a collision throughout each part of the body are shown below.
FIVE ELEMENTS OF FORCE
In general, direction, magnitude, and point of impact are the major elements of force. In body repair work, the following five elements should be considered.
Direction of force
Magnitude of force
Point of impact
Number of forces applied
Sequence of impact
DIRECTION OF IMPACT FORCE
The impact force (input) of a collision is composed of three-dimensional components. Force propagation can be analyzed through careful examination of these components.
The figure shows an impact force applied to the body from the front at an angle of "a" in the direction of A-G.
This force can be divided into three-dimensional directions as shown in the figure to the right. The impact force can be divided into AB, AD, and AE.
Each of these forces damages the corresponding panel.
If the impact force is applied away from the center of gravity, a moment of rotation is caused which absorbs the impact force. If the force aims at the center of gravity, no such moment is caused and the resultant damage will be greater.
IMPACT FORCE AND COLLISION AREA
Consider the impact force (f) per unit area in a frontal collision.
f = F/A
F: Impact force (input)
A: Collision area
The smaller the collision area, the greater the impact force (f) per unit area. The deformation will also be larger and deeper.
CONCENTRATION OF STRESS
If a panel has cuts or holes, stress distribution will be uneven. As shown in the figure to the right, stress concentrates where the sectional shape changes, thus producing deformation.
This principle is utilized in panel design. Impact force is absorbed, and further propagation of deformation is prevented.
PROPAGATION OF IMPACT FORCE
The impact force, while absorbed somewhat at the impact absorbed area, propagates to various portions by passing through each rigid contact point.
DIRECT DAMAGE AND INDIRECT DAMAGE
The body panel may be damaged indirectly by inertia. Portion A in the figure is the direct damage, and portion B shows a type of indirect damage. Therefore, it is necessary to closely check for both types of damage.
FEATURES OF IMPACT APPLIED TO EACH PORTION OF BODY
FRONTAL COLLISION AND DAMAGE
Impact force is absorbed at the circled portions in the figure. If it is not absorbed completely impact damage can propagate to the dash panel.
SIDE COLLISION AND DAMAGE
If an impact is applied to the center of the passenger compartment, damage extends to the floor. The wheelbase also becomes misaligned.
Accordingly, wheelbase measurements, wheel alignment, and steering system checks are important.
REAR COLLISION AND DAMAGE
Impact force is absorbed at the circled portions in the figure. The panels may be damaged up to these portions according to the magnitude of impact.
IMPACT FROM TOP AND DAMAGE
Small impact is absorbed with the roof and roof bow. If the impact is great, it is also absorbed with the pillars. However, broken glass and a deformed rear fender may result.