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A Study of the Ditch Fall-over Test Method Using Numerical Simulation
Abstract:
Rollover tests are performed to design the algorithms for deployment of countermeasures to mitigate occupant ejection in rollover situations. The ditch fall-over test is one of the rollover test methods in which a vehicle on a steep slope, representing a ditch embankment, is subjected to a forced steering operation that results in a turnover. An accurate prediction method is needed to determine the specifications of the ditch fall-over test equipment and test conditions because a test-based trial-and-error process involves high cost of performing repeated experiments and preperation for various types of related test equipment.
This paper presents a newly developed numerical simulation method for simulating vehicle behavior in ditch fall-over tests. The vehicle model used in the simulation incorporates a finite element tire model for calculating the contact forces to a steep slope in a rollover situation characterized by large contact patch deformation with very large camber angles relative to the slope, an operating condition that ordinary vehicles cannot handle. The vehicle model also includes the suspension systems, steering system and inertial properties of the vehicle. Under various test conditions, the simulation results agreed well with those of actual ditch fall-over test data to judge whether turnover occurred or not and also the dynamic response such as vehicle roll rate. Simulations were conducted to investigate the test equipment specifications and test conditions for a vehicle. It was found that the slope angle, the friction coefficient of the slope, initial vehicle velocity and the sectional shape of the slope at the top influence vehicle turnover behavior.
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