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OCR for page 47
47 Figure 55. Passing and failing crash tests OCD versus internal energies of floorboard. noted that the interaction of the vehicle with this rail is con- GENERALIZED SURFACE sidered to be substantially different than what typically ASPERITY DEFINITION occurs in an impact with a "solid" barrier. In the test of the Oregon barrier, the frame rail of the pickup truck protruded In order to model asperities on the barrier surface for inside one of the "windows" and snagged severely on the evaluation in the parametric simulation effort, it was nec- inside of one of the concrete balusters. As a result, instead essary to adequately define their geometry. Almost all sur- of the load going to the floorboard as it does in most OCD face asperities can be placed within one of three categories: failures, the load was directed to the frame. Therefore, the perpendicular, rounded, or angled surface interruptions. Oregon bridge rail crash test was not taken into considera- These generalized types of surface asperities are shown in tion when selecting the failure limit. Figure 56. The outcome of impacts with solid barriers in which the The angled or inclined asperity can be defined in terms internal energy of the floorboard is between 2,200 N-m and of a depth d and angle , either of which can be varied to 10,700 N-m is largely unknown due to lack of crash test data achieve a different profile. The perpendicular asperity is with a sufficient range of OCD values. As is described in a subset of the angled asperity with = 90 degrees. The Chapters 6 and 7, the full-scale crash tests were designed to rounded asperity can be approximated as an angled surface adjust these energy thresholds and reduce the size of the region asperity by selecting an effective angle . The illustration with unknown performance. shown in Figure 56 uses a tangent to the rounded surface Figure 56. Generalized types of surface asperities.