The client and challenge
The client, an automotive OEM, needed help establishing a computer-aided engineering methodology to evaluate door trim armrest performance. Because the complete evaluation of side impact crash is performed during full vehicle test, engineers are not able to test the door performance during the development cycle. This creates a need for door trim assembly component-level testing to meet the performance requirements for protection of occupants in side impact crashes mandated by Federal Motor Vehicle Safety Standard No. 214.
A side impact crash test is considered to be a severe crash mode due to the limited crush space. This requires increased countermeasures in the door trim assembly per FMVSS 214. In the vehicle development cycle, it is essential to evaluate the subsystem at various design stages before building the prototypes. However, testing multiple prototypes is expensive and time-consuming.
CAE methodology can be used to evaluate door trim side impact performance in the design stage before building the prototypes, reducing cost and time required to evaluate the designs through simulations.
The client requested that EASi e
stablish a CAE methodology to evaluate door trim armrest performance in a Lateral Impact New Car Assessment Programme (LINCAP) impact and Oblique Pole side impact component level testing. The methodology needed to simplify door side impact test and have good correlation to test data.
The EASi solution
EASi assessed the capabilities of a CAE methodology as a base engineering approach without the need for testing of multiple traditional physical prototypes of the door trim. For interior door trim evaluation, door assembly stiffness is the main driving factor with respect to occupant safety. Side impact positions are based on the occupant position as per FMVSS 214-Side Impact protection. Additionally, the impactor locations are determined based on the country of vehicle release and door (front or rear); for example LINCAP, CNCAP (China), ENCAP (Europe) or Insurance Institute of Highway Safety.
EASi developed a CAE methodology for the armrest side impact study. The impact simulation nonlinear problem is performed using the LS-Dyna explicit solver method. EASi developed a CAE simulation by:
Building an FE model of the door trim.
CAE was modeled per CAD data being tested and checked for quality. In plastic parts, thickness variation is common, so care was taken to capture these thickness variations in the CAE model. Foam and skin of the armrest were also considered in the CAE model. The foam was modeled using Hexa elements. Correct representation of the door trim attachments was also considered as it is very important for the analysis.
Modeling the test fixture to represent actual test environment.
The fixture was modeled to represent the test environment, which is required to have good correlation to test data.
Positioning the impactor accurately and with same initial velocity as per test set-up.
The impact location was observed to vary the results significantly, so a measurement of impactor distance from a reference point was used. In CAE, the impactor was considered as rigid and made to impact the door trim with an initial velocity of 2.5m/s.
Representing the materials’ elastic-plastic nonlinear behavior accurately.
Door trim components are mainly of thermoplastic polymers materials like Acrylonitrile-Butadiene-Styrene (ABS), TPO or Poly Propylene (PP). Material stress-strain curves with higher strain rates were used to represent these materials’ nonlinear behavior more accurately.
Performing analysis for multiple test locations.
The armrest side impact was performed for two impactor locations on one door trim. The cross-plot of the reaction force and displacement were monitored during the impact.
The results of EASi’s CAE methodology showed good results at about 90 percent correlation to the test data. The maximum variation was found at the later stage when parts are crushed and begin to disintegrate. With the contributing factors and gaps between CAE and physical testing for door trim safety analysis identified, this CAE methodology is now able to drive design changes. This is done by performing simulations in the initial design phases without waiting for the prototype designs to be built and tested.
EASi’s methodology helps the customer expedite its design development cycle from the beginning of the design phase to the production phase by providing feasible recommendations. Our CAE methodology has been implemented in multiple vehicle programs for this customer.
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