Key results:
1. Validate design before manufacturing
2. Numerical replicate of actual testing
3. Comparison of different fastener scenarios

School buses sold in the USA must meet minimum performance requirements defined by the Federal Motor Vehicle Safety Standard (FMVSS). Among these standards, FMVSS 220 establishes performance requirements for school bus rollover protection. The purpose of this standard is to reduce the number of deaths and the severity of injuries that result from the failure of the school bus body structure to withstand forces encountered in rollover crashes.

A force equal to 1.5 times the unloaded vehicle weight (UVW) is applied to the roof of the vehicle’s body structure through a flat, rigid, rectangular plate. FMVSS 220 requires the resulting downward displacement to remain below 5 1/8 inches (≈ 130 mm).

Our customer wanted to assess if its structure would meet FMVSS 220 requirements.

Main challenges
1. Highly non-linear behavior of the structure
2. Connector failure definition for rivets

The testing procedure was numerically duplicated with a finite element model (FEM). Due to the non-linear behavior (buckling…) of the structure submitted to that loading, Abaqus/Explicit solver was used.

Particular attention was given to respecting the quasi-static nature of the test by making sure that inertial effects remain negligible compared to internal energy.

Several design iterations were achieved. These simulations included different sorts of rivets whose integrity was validated during the FEA since rivet failure was initially defined providing a more realistic behavior of the structure.

Results from these analyses enabled our customer to move forward with a design meeting the standard requirements while providing the minimum specifications for rivets fastening the structure.