Criteria Existing for Partner-Protection in Offset Tests

As explained in Section 4.1.3, the ODB will bottom out in almost all tests with new generation vehicles. Therefore, the deformation of the barrier face does not include any valuable information for evaluating partner-protection.

EEVC W15 [97, p. 18] developed a criterion for controlling the force levels using LCW data. In this criterion, the peak of the forces is measured in a 10 ms time window (Fig. 5.3). Limiting the measurements to 10 ms intends to filter out the unrealistic additional short duration peak loads on the LCW, e.g., due to the engine impact on the rigid wall.

The objective of this criterion was to limit the force levels, similar to KW 400, to avoid over-crushing of lighter vehicles in car-to-car collisions with heavier vehicles. The main

Figure 5.3: LCW data in the ODB test showing the additional load caused by the engine

issue of KW 400 exists also here; thus, applying a limit for force levels in the ODB test reduces the self-protection of heavy vehicles or results in many infeasible side effects for the vehicle design. EEVC WG15 stated that the ODB may deform in different manners in repeated tests with the same vehicle model, resulting in different energy absorption levels in the deformable block [97, p. 35]. Thus, any criterion based on the behavior of the ODB would confront with reproducibility issues.

The LCW data cannot be used in the PDB tests since the high depth deformable block filters the load spreading. However, as described in Section 4.1.4 and Section 4.1.5, the PDB shows stable behavior and the deformations on the barrier face can therefore be used to develop a criterion for partner-protection.

FIMCAR developed a criterion for the PDB to evaluate the load spreading and structural interaction of the test vehicle by assessing deformations on the barrier face. The barrier is divided into three areas (Fig. 5.4) for evaluating the deformations. Significant deformations in the upper areas mean a high risk of override/underride, homogenous deformations in the middle area improve partner-protection, and deformations in the lower area show the existence of SEAS, which improves partner-protection [142, p. 4].

Del Pozo et al. [142, pp. 5-7] proposed a two-stage criterion for evaluating partner-protection in the PDB tests, which uses a pass/fail concept (Fig. 5.5). The objective is to assure that a load path is present in the common interaction zone and the load spreading is homogenous.

Figure 5.4: Assessment areas of the PDB According to [142, p. 4]

Figure 5.5: Concept of the proposed criterion for the PDB tests; CIZ = Common Interaction Zone

In the first stage, the longitudinal deformation is assessed using the criterion (d) (Fig. 5.6), which gives some scores with respect to the deformation depth in different areas. If the deformation depth is in the predefined zones, the load path is detected and this stage is passed. Presence of crashworthy structures in the middle area (i.e. common interaction zone) is considered as more important for crash compatibility and therefore, scores of this area are higher.

In the second stage, when the load path is detected in the lower or middle area, the criterion Digital Derivative in Y Direction (DDY) determines the homogeneity of the load spreading. First, the area is divided in 𝑁 equal subzones, for which the differences in longitudinal deformations are analyzed through the following parameters:

• 𝐷_𝑖 is the average longitudinal deformation in subzone 𝑖.

• 𝑄%𝑖𝑙𝑒 is the quantile of the longitudinal deformation in a subzone, e.g., 99%ile means 99% quantile of the longitudinal deformations in a subzone.

The DDY is defined using Eq. (5.9).

𝐷𝐷𝑌 = | 𝑋_(𝑦,𝑧)− 𝑋_{(𝑦−1,𝑧)}

𝑠𝑖𝑧𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑠𝑢𝑏𝑧𝑜𝑛𝑒|, (5.9)

where 𝑋_(𝑦,𝑧) is the 99%ile longitudinal deformation of the subzone (𝑦, 𝑧). Lower values of the DDY correspond to more homogenous load spreading.

Del Pozo et al. [142, pp. 7-9] conducted three car-to-car crash tests and analyzed the results to make a statement about crash compatibility of the test vehicles. The expect-ations are compared with the PDB test results to validate the proposed criterion. The car-to-car test results showed the following:

• Supermini 1 should acquire a clear pass.

• Supermini 2 should acquire a pass.

• SUV 1 should acquire a clear pass.

• SUV 2 and Small Family Car 1 showed a fork effect and need to be evaluated further.

Figure 5.6: Criterion (d) is the sum of scores for evaluating the longitudinal deformations in the first stage of the PDB criterion

According to [142, p. 6]

The DDY values of Supermini 2 and SUV 1 are both below two [142, p. 7], which is a clear pass for the proposed threshold of 3.5 for DDY. However, the DDY value of Supermini 1 is more than nine [142, p. 7], which is a clear fail instead of the expected clear pass. Furthermore, the DDY values of a repeated test for Small Family Car 3 (2.27 for test 35, and 1.27 for test 18 [142, p. 7]) showed repeatability issues with the developed criterion for assessing partner-protection in the PDB tests. The FIMCAR consortium [98, p. 113] stated another issue for the PDB criterion; the rating results show step effects, which are inconsistent when applied to different vehicle models.

The same criterion can be used for the MPDB test results. However, the same issues arise. ADAC modified the MPDB test procedure to reach increased representability of car-to-car collisions [14, pp. 9−13]. ADAC uses a three-stage concept for evaluating the test results:

1. The rating area is 45 % of the vehicle width, 200 mm from the barrier side, and between the height of 250 mm to 650 mm from the ground (Fig. 5.7).

2. The average intrusion depth and standard deviation are evaluated, while the average deformation depth should be between 320 mm and 480 mm [154, p. 20], and the standard deviation should be low.

3. Change in the trolley speed should be equal to or less than 50 km/h, and the test vehicle should absorb kinetic energy in its crumple zone.

Some crash tests from ADAC [154, pp. 18-20] showed that the ADAC criterion can recognize the general compatibility problems. However, limits and weightings of the criteria are not yet finalized (e.g., mechanism of penalizing due to the high deformation depth or the limit for minimum absorbed energy in the crumple zone of the vehicle).

Therefore, a comparison of the criterion results with car-to-car test results is not possible, and more investigations are required to confirm the reproducibility and repeatability of the assessment results. Furthermore, since the conducted tests contain vehicles with extreme compatibility issues, more studies are required to ensure the ability of the ADAC criterion for grading the compatible vehicles.

Another issue of the ADAC criterion is limiting the deformation depth. Similar to KW 400, it might be infeasible to apply this limited deformation depth to the whole range of passenger vehicles (up to 3.5 ton) due to the side effects on the vehicle size (longer front-end) and lower self-protection (lower strength).

Figure 5.7: Rating area of the ADAC criterion for the modified MPDB [14, p. 12]

650 mm

250 mm

200 mm 45 % of the vehicle width