Structural interaction has been one of the critical issues for improved frontal impact protection. An evaluation procedure for structural interaction has been difficult to develop using objective test data procedures. While previous research with the PDB barrier has been promising based on subjective evaluations, an objective assessment criteria has been elusive. Part of the EU project FIMCAR focused on the development of an assessment procedure to assess important frontal impact characteristics like load spreading.

Test and simulation data from vehicle impacts with the PDB or MPDB were collected for different vehicle models, spanning a range of vehicle masses and vehicle classes. Available car-to-car crash tests were also collected for reference. The main information analyzed w.r.t. the assessment of load spreading was the deformation pattern of the PDB barrier after a test. These deformation plots were reviewed and subjectively assessed by experts. The subjective assessments were used to develop key characteristics that should be detected by a numerical assessment of the 3D data. These subjective assessments were then compared to different objective (numerical) assessments for the barriers to ensure correlation of the results and then validated with available car-car data. Assessment of the influence of assessment area and scanning resolution were also performed.

The deformation profiles could be grouped into three main groups where the horizontal and vertical load spreading distinguished vehicles with good or poor performance. The main focus was the development of an assessment of the horizontal load spreading between the longitudinals. A metric based on the slope or gradient, of barrier deformations in the lateral or vehicle Y axis proved to be the best candidate. A horizontal assessment area based on 60% of the overall vehicle width and a vertical area between 330 and 580mm from ground was used. The 99%ile value for the Digital Derivative in Y (DDY) with a threshold value of 3.5 could discriminate between vehicle with an even (homogeneous) deformation pattern or a vehicle with localized structures.

The candidate for an (M)PDB metric that assesses horizontal load spreading provides an objective method to assess structural interaction. The assessment has been validated for the vehicles that can be clearly grouped into a good or poor performance category. There are a number of vehicles that are in a borderline area that require further evaluation. The cases where vehicle-tovehicle crash data is available have validated the performance of those vehicles. Further validation using field data and car-to-car test or simulation results can finalize the metric development.

The paper addresses a central issue for frontal impact performance. While structural alignment and occupant compartment stability issues can be addressed by adding the FWDB test procedure as proposed by the FIMCAR project to the current ODB procedure, there is no test procedure available that reliably assesses horizontal load spreading. The proposed DDY metric for the PDB test procedure allows the front structure for vehicles to be assessed and be updated to also assess vertical load spreading.