Collision Repair Terminology and Vehicle Construction
Construction types
- Body-over-frame: a ladder frame carries the loads and the body is isolated on mounts. Straightening loads usually go to the frame, so cab damage is often more limited than it looks.
- Unibody: rails, aprons, rockers, and body sides form the structure. The repair must restore both shape and load path, because the panels are the frame.
- Space frame and aluminum-intensive or mixed-material bodies: adhesives and mechanical fasteners replace many spot welds, so construction vocabulary predicts the joining method.
Materials vocabulary
Mild steel, HSLA (high-strength low-alloy), AHSS families (dual phase, TRIP, complex phase, martensitic), press-hardened or boron steel at roughly 1500 MPa, tailor-rolled blanks (thickness changes within one part), hydroformed rails, and one-piece body sides. Strength and ductility trade off: as strength rises, the amount of straightening the part will tolerate falls.
Repair terminology
Sectioning means replacing part of a component at an OEM-defined location. Partial part replacement and full part replacement are different procedures with different rules. Repair-versus-replace decisions come from the OEM procedure, never from convenience. Programmed deformation zones must be restored exactly, because the occupant safety cage depends on those sections collapsing as designed.
Worked example
A B-pillar has a kink. Knowing the part is press-hardened explains the OEM statement “replace only, do not heat, do not straighten.” The reasoning is metallurgical: the martensitic structure that provides the strength is destroyed by the heat that straightening would require, so replacement restores the design intent and straightening does not.
Traps that cost marks
Assuming a high-strength label means repairable; applying mild-steel procedures to AHSS; forgetting that frame versus unibody changes anchoring and pulling; confusing marketing names with metallurgy.