Hydroform Components 
Euro NCAP Offset Barrier 
Euro NCAP Intrusion 
Performance
Hydroform Components 
FMVSS 216A Roof Crush 
216A Stamped vs Hydroform 
IIHS Side Impact Crash 
IIHS Side Impact 
Performance
Material 
Hydroform Components 
FMVSS 301 rear Impact Stamped Crash 
FMVSS 301 Rear Impact Hydroformed Crash 
FMVSS 301 Stamped vs. Hydroform 
Performance
Tube Thicknesst = 1.1 mm
t = 1.3 mm
- Baseline gage of the tubes were 1.3 mm (HIBS I)
- Straighten areas reduced to 1.1mm
- Bends maintained at 1.3mm
Targeted for opportunity to take out weight and cost.
In order to maintain continuity from the front structure to the dash/underbody, the rails of the front structure were lengthened and assumed to be laser welded into the floor structure. In addition, smaller stampings were added to provide an attachment for the front cradle.
G-Loading Data 
G-Loading Example
Incremental Changes| Structure | Weight (kg) | Cost ($) |
| Stamped | 50.0 | 185.00 |
| HIBS I | 44.6 | 163.27 |
| HIBS II | ||
| Manufacturing | 43.7 (-.9 kg) | 155.92 (-$7.35) |
| Material Change | na | na |
| Variable Gage | 43.0 (-1.6 kg) | 178.51 (+$15.24) |
Eliminate Brackets 
Gage Optimization 
Tube Material
Pillar Structures
By calculating the critical buckling stress for the section, we can better refine our choice of material parameters. Shown below is the equation to determine the critical buckling stress of a simple section. Please note that in this equation, geometry is the main factor with no influence of material strength. 
First, the edge boundary conditions and the aspect ratio (a/b) of the compression surface(s) are needed to determine the buckling coefficient kc.
Buckling Coefficient
Using the buckling coefficient chart 
we observe that as the aspect ratio (a/b) approaches 2, the buckling coefficient (kc) can be considered constant for a defined edge boundary condition.
Depending on the section, the edge boundary conditions can fall between fully constrained (Curve A) and simply supported (Curve C). For this example we will assume a balance between simple supported (kc = 4) and fixed (kc = 7), so kc will be 5.5
Poisson’s Ratio
Assuming Poisson’s Ratio for steel is 0.3 and Young’s modulus of elasticity is 29.6×106 psi, the critical buckling stress is: 
By plotting the critical stress against the t/b ratio we can then narrow down our material parameters. For a given t/b ratio, there is a critical stress above which
the material is no longer effective in resisting local buckling. Increasing the material grade will get you very little performance as the structure is “geometry-limited”.
Any improvements will need to be focused on section shape before reconsidering material grade.
Another way to interpret is to consider the typical yield strengths of common steel grades. For a t/b ratio that falls to the right of the critical stress curve, a material upgrade could improve performance. However, for those ratios that fall to the left of the curve, the shape of the section (compression side) will drive performance.
Example:
A t/b ratio of 0.02 is a likely ratio in automotive structures (such as a 1.2mm thick surface (t) with a width of 60mm (b)). Using Figure 6, for 0.02, the critical buckling stress is approximately 420MPa. A BIW engineer could specify up to a DP780 material and be confident the material is working efficiently. Anything more than that will fall to the left of the critical stress curve and provide little strength benefit.
Results (designs with similar performance):
and read off a certain t/b ratio to determine if a structure is geometry-limited. Real-world examples cannot be categorized this easily. As can be seen from the surfaces there are holes, formations etc. which complicate the choice of a simple t/b ratio. Vari-Form has done extensive CAE analysis on both production intent sheet metal and hydroform structures. 
Shown here are the results of a roof crush was performed on a structure and iterated for three material grades. Once the material strength approaches 1000 MPa (tensile strength) on the roof rail reinforcement, there is little performance difference in roof crush if the material properties are upgraded to UHSS grades. Yet, if you reduce the material strength, you see a proportional drop in load carrying capability that is directly proportional to the drop in yield strength.
So if you go back to the Critical Buckling stress curve, we believe that most of the structure is going to act in the t/b range of ≤.025. At this point, material > DP 980 strength is not fully utilized because the structure buckles before the full yield strength is reached.
Our experience over many similar roof studies show that materials beyond 1000MPa provide little roof crush improvements unless the geometry supports it.
While boron has good formability on its side, much of the potential strength of the material is never utilized. BIW engineers are well advised to explore technologies that allow geometric optimization and more material flexibility. That is why hydroformed tube structures are an excellent choice to maintain performance and be competitive in weight.
Mazda demonstrates that, as thickness decreases in a structure, the actual percentage of “useable” yield strength decreases. Another way to look at it is if you increase the yield strength of the material by 2x, don’t expect to get a 2x gain in load carrying capability.
If you go back to our roof crush analysis (Figure 7), this is exactly what you see. Ford released similar findings at the 2011 Great Designs in Steel Conference in Michigan.