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Mass Reduction and Energy Absorption maximization of automotive bumper systems

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Figure 1 - Bumper Parameterization

On 20th & 21st of May, EnginSoft Germany presented at the NAFEMS German Conference in Bamberg. The conference was focused on applications, developments and trends in Computer Aided Engineering. The list of participants included worldwide accredited and leading companies like Audi, Bosch, Airbus, Siemens, Continental among many others. To this audience we presented the optimization of an automotive front bumper, performed with modeFRONTIER, automating CATIA V5, HYPERMESH & LS-DYNA to find the optimal design that best meets the bumper mass and crash energy objectives. This article briefly summarizes the content of this project.

Case description:
Bumpers are one of the most underestimated parts of a car, even though they can save lives in the event of a collision.
The main function of the bumper is to absorb kinetic energy during plastic structural deformation. Absorbing energy in this way is important when trying to prevent occupant injury, because it limits the amount of energy being passed directly to the occupants. The amount of energy allowed to act upon an occupant is restricted by law and must be kept below certain limits in order for the vehicle to be approved for release. This is achieved in legislation by limiting the amount of deceleration an occupant experiences. Because of this, bumpers must absorb as much energy as they can. Typically, the more mass a bumper has, the more energy it can absorb, since more energy is needed to move/deform the bumper; but this is only partially true. In addition to this, more mass means more material, higher production costs and worse fuel consumption. Fortunately, there are other parameters that can be modified besides mass, such as bumper profile/shape or material which contributes to the bumper’s energy absorption.
In order to achieve the best energy absorption while obtaining the lowest mass, several bumper parameters have been selected for optimization (Figure 1).



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Figure 2 - Design Simulation Process

In order to achieve the best energy absorption while obtaining the lowest mass, several bumper parameters have been selected for optimization (Figure 1).

The input parameters Profile Depth, Crimping Depth and Radius were defined inside the CAD-Model. Bumper Steel Properties were defined by the means of 10 different material set cards, used as meshing inputs. Bumper Sheet Thickness and Closing Sheet Thickness were defined inside the crash simulation model. The CAD-Tool CATIA V5 was used to modify the 3D geometry, HYPERMESH to convert the CAD to an LS-DYNA mesh and LS-DYNA to run the crash simulation and asses the bumper design (Figure 2).

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Figure 3 - modeFRONTIER bumper Simulation Workflow,
integrating CATIA, HYPERMESH and LS-Dyna to minimize
bumper mass and crashbox forces

The design simulation process was successfully automated using the design optimization tool modeFRONTIER (Figure 3).
CATIA was integrated using modeFRONTIER’s CATIA Direct Integration node without the need for any complicated scripting. HYPERMESH and LS-DYNA were coupled through macro scripts, automatically recorded while setting up the meshing and simulation model. The bumper design parameters were set up in modeRONTIER according to Table 1.

The design objective was to minimize mass and the force acting on the crush cans behind the bumper. The optimization started from an initial Design of Experiment (DOE) using a Uniform Latin Hypercube technique. Firstly, this technique ensures the DOE is statistically appropriate for performing a correlation analysis (understanding the relationships between inputs and outputs). Secondly, it uniformly fills the design space and gives a good starting population for the optimization while not requiring too many designs.

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Figure 4 - Bumper Correlation Analysis in modeFRONTIER

The Correlation Analysis (Figure 4) helped show the Radius has little influence on the mass and only a small positive effect on the crush can forces (the bigger the radius, the bigger the forces on the crash boxes). For this reason the Radius was held constant; the number of optimization variables was therefore reduced from 6 to 5. Additionally, due to the Correlation Analysis, we were able to prove the conflicting relations between the other input and the output variables and prove the need for the multi-objective optimization.
A multi-objective optimization was then conducted using a MOGAII algorithm. The results are shown in Figure 5.
A design was chosen from the Pareto Frontier which improved the force by ~6.25% while reducing the bumpers mass by ~8.25%.

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Figure 5 - modeFRONTIER bumper simulation workflow, integrating CATIA, HYPERMESH and LS-DYNA


Conclusion
This project has proven the effectiveness and reliability of the design optimization methodology and has been reproduced at many of our customer sites. Bumper designers can now concentrate on new bumper concepts while automatically performing the bumper concept optimization with the help of modeFRONTIER.

 

 

 

 

 

 

 

 

 

 

 


Articolo pubblicato sulla Newsletter EnginSoft Anno 11 n°3

Giorgio Buccilli, René Wohlgethan
Aviospace, an Airbus Defence & Space company

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