An anti-intrusion bar or beam is a passive safety device, installed in most cars and other ground vehicles, which must protect passengers from side impacts.[1] Side impacts are particularly dangerous for two reasons: a) the location of impact is very close to the passenger, who can be immediately reached by the impacting vehicle; b) in many side-impact accidents, the impacting vehicle may be larger, taller, heavier, or structurally stiffer than the struck vehicle. The role of an anti-intrusion bar is to absorb the kinetic energy of the colliding vehicles that is partially converted into internal work of the members involved in the crash.


The performance of a side beam is measured by several indicators. The most important are:


Typical design

The anti-intrusion beams commonly span the length of the door at about a vertical midsection of the door. As the figure shows, the typical profiles can be open or closed (tubular, usually with a round cross section).

Some examples of anti-intrusion bars for cars
Some examples of anti-intrusion bars for cars

They are conventionally made by stamping or hydroforming processes. When the cross section is closed, the tubes can be used as-received. In the scientific and technical literature, some unconventional designs have been proposed.[2]

Typical materials

The anti-intrusion bars are generally made of high strength steels.[3] However, some studies indicate that stainless steel 304 might be a better choice, because of its larger plastic field and a larger amount of potentially absorbed energy before fracture.[4] In the scientific and technical literature, some unconventional material combinations have been proposed, too, e.g. based on metal foam filled tubes[5] or composite materials.[6]


  1. ^[bare URL PDF]
  2. ^ "Vehicle anti intrusion bar by Bond, Sam – AU 1999065514".
  3. ^ High Strength Steel for Automotive Safety Components Archived December 20, 2011, at the Wayback Machine
  4. ^[bare URL PDF]
  5. ^ Strano, M.; Mussi, V.; Monno, M. (2010). "Non-conventional technologies for the manufacturing of anti-intrusion bars". International Journal of Material Forming. 3: 1111–1114. doi:10.1007/s12289-010-0966-y. S2CID 136670060.
  6. ^ "Archived copy". Archived from the original on 21 April 2013. Retrieved 6 June 2022.((cite web)): CS1 maint: archived copy as title (link)