Reinforcements

The number of reinforcements used on some later model vehicles has increased over the years and may be difficult to identify simply by visual inspection. Vehicle makers were challenged with greatly improving side-impact crash performance and roof crush. To meet that goal some vehicle makers increased the number of reinforcements that were used to strengthen the side of the vehicles. (see Figure 1).

Additionally, reinforcements were also being used in other areas, such as lower front rails. Similar to the side of the vehicle, reinforcements can be used for collision energy management. In a lower front rail, a reinforcement may be used to transfer energy around a particular area. Does this mean now that AHSS is available as a construction material fewer reinforcements are being used? Not exactly. Some of the AHSS used on today’s vehicles is being used as a reinforcement, or as a collapse zone.

Collapse or Crush Zones

Figure 2. Rails are often “tailor made” today with different strengths or thicknesses of steel in the same part.

In the past, collapse zones were fairly easy to identify and to avoid following general sectioning guidelines. Often the collapse zones appeared accordion-like and were located near the end of a rail. While there are a number of vehicles with collapse zones that can still be easily identified, new design technologies have made identification more difficult. Tailored blanks are used by a number of vehicle makers to build collision energy management into front lower rail designs (see Figure 2) .

Tailored blanks include multiple strengths and thicknesses of steel in a single part that is “tailored” for the design engineer’s intent. The tailored blank may be used to absorb energy (a collapse zone), or to transfer energy (a type of reinforcement). Some tailored blanks are easier to identify than others. Tailor-welded blanks may have a visible laser weld seam identifying it as a tailored blank.


However, tailor-rolled blanks make identification more difficult. Tailor-rolled blanks may vary a fraction of a millimeter in a given area. The Dodge Caliber, for example, has areas on the B-pillar that are 1.00, 1.05, 1.65, 1.75, 1.85, and 1.9 mm thick on the same part. (see Figure 3).

So, how do you identify if a tailored blank is used and if it is designed to collapse or transfer collision energy? The only way to begin speculating would be to know the strength and thickness of the steel used in a given area. However, that also presents some obstacles. How would you determine the thicknesses and steel strengths of a tailored blank? If you knew the thickness and strength of different areas on a tailored blank, could you effectively conclude the design intent of that area? If you answered “yes,” ponder this for a moment. Which is stronger; a 1.65 mm area of Bake Hardenable 210, or a 1.5 mm area of HSLA340?