Designing for Rollover Impacts With Narrow Objects

While some debate has existed in the literature regarding the relationship between roof crush and occupant injury, the United States (U.S.) National Highway Traffic Safety Administration (NHTSA) has identified an increased safety benefit in improving roof strength and has mandated new higher roof crush resistance requirements. Frequently, roof impacts occur in rollover crashes when a vehicle travels off the lanes of the roadway and impacts various types of narrow objects along the roadway edge such as light poles, utility poles and/or trees. A previously reported tilt-test device and methodology is presented along with a new pendulum-test device and methodology, both of which allow for dynamic, repeatable impact evaluation of vehicle roof structures with narrow objects. The data collected includes not only residual crush, but also dynamic vehicle instrumentation and high speed video analysis. Two series of full vehicle tests are reported which represent each of the methodologies. The testing conditions for each series was determined based upon analysis of a real-world narrow object rollover impact. Each testing series allows for analysis of the damage resulting from the narrow object impact to the roof structure for a production vehicle as well as one that has been structurally reinforced. Results demonstrate that the reinforced roof structure significantly reduced the roof deformation compared to that of the production roof structure. The input energy of each test and resulting damage patterns can be used as both a reconstruction tool and structural assessment test.