An automobile body consists of many different component parts, each of which is stamped from a thin steel. Most parts are united into a complete unitized body using electric resistance spot welding. In this fashion, a unitized body, or “unibody”, structure has no independent frame. Stamped parts are assembled as part of the body. Components such as an engine, suspension, and steering system are directly installed to the body structure. Unibody construction is the most common vehicle construction method in the automotive industry.
A unibody is structured by a wide variety of stamped steel parts in different shapes and dimensions, joined by welding into one complete body. In order to meet all of the requirements of the body as a whole, each of those parts share the responsibility of meeting the necessary criteria on strength and rigidity as well as weight reduction, accuracy, durability performance etc.
In addition, to protect the passengers in case of collision, the body structure must allow a certain amount of deformation if a front or rear crash impact occurs. By effectively absorbing the impact energy through “crush zones” in the body structure, a “survival space” is maintained in the passenger compartment. Effects of the impact on the vehicle’s passengers are also mitigated.
The image below shows typical body crush zones. The passenger compartment is reinforced by structural members to dissipate front and rear impacts. The side frame is similar in strength to the front and rear body, receives impact forces. This will cause ripple effects and secondary damage, but the side frame is designed to minimize deformation in the passenger compartment area.