NHTSA’s Proposed Frontal Oblique Impact Test Protocol: Analyses and Evaluation 2017-01-1475
On December 2015, The National Highway Traffic Safety Administration (NHTSA) published its proposal to implement U.S New Car Assessment Program (NCAP) changes covering three categories of crashworthiness, crash avoidance and pedestrian protection, beginning with the 2019 model year. The crashworthiness category included a new frontal oblique impact (OI) test protocol. The test compromises of a new Oblique Moving Deformable Barrier (OMDB), new THOR 50th percentile male (THOR-50M) anthropomorphic test device (ATD), and a new test configuration. An OMDB of 2,486 kg (5,480 lb) impacts a stationary target vehicle at a speed of 90 kph (56 mph) at an angle of 15 degrees with a 35% barrier overlap with the front end of the target vehicle. In vehicle-to-vehicle collisions, the lighter weight vehicle experience higher velocity change and higher acceleration levels, thereby, occupants in the lighter vehicle experience higher injury risk. This paper describes the analyses of a series of 31 OI tests conducted by NHTSA, in which the target vehicles used were of different sizes and weight distribution ranging between 1034 Kg (SMART)-2624 Kg (Silverado).
Deformation Energy in the OMDB was calculated from the honeycomb deformation and its associated stiffness. Target vehicle Deformation Energy (DE) in each of the 31 OI tests was determined and compared to its 56 kph (35 mph) NCAP DE. This was shown in a diagram of DE versus mass ratio of the target vehicle to the OMDB. THOR M50 dummy responses for each test were plotted against target vehicle Velocity Change (Δv2),calculated from momentum equation and from test’s velocity time histories. Results indicated that target vehicles absorb more DE in the proposed OI compared to a 56 kph (35 mph) full frontal barrier impact. Lighter weight vehicles, in particular, have to manage approximately 50-60% more DE in the proposed OI. Larger vehicles that have similar weight to that of the OMDB manage approximately same DE as in the NCAP full frontal barrier impact. Therefore lighter vehicles will require significant structural reinforcing and stiffening to manage the crash energy in the OI. This may have a negative impact on attributes such as occupant safety, vehicle compatibility, and fuel economy. For example, it could result in a stiffer crash pulse in light vehicles which may lead to issues associated with occupant safety in all seating position, elderly occupants in particular. Injury risk associated with THOR-M50 dummy responses in NHTSA’s OI tests showed weak or no correlations with (Δv2).The proposed OI mode did not demonstrate the expected injury trend with velocity change which may be attributed to potential issues with the barrier mass, barrier stiffness, THOR dummy, and the test configuration. It is concluded that further research is needed to develop appropriate OI test parameters, OMDB, and dummy type and / or injury criteria.