Structural Improvement Of The S Beam Based On Vehicle Safety

Since entering the 21th century, the vehicle safety has attracted more and more attention and has become one of the major considerations when people make up their minds to purchase a car. Sport utility vehicle (SUV) has become one of the most popular urban vehicles for its large interior space and good trafficability characteristic. Although the SUV has huge and stiff body, some still can not achieve good crashworthiness, especially for the body-on-frame SUV studied in the paper. For that vehicle, the energy absorption length of the longitudinal beam is short, and energy absorption capability is limited in frontal crash. Besides, the areas of prototype vehicle connecting the longitudinal beams to the front suspension and the bracket of steering system are greatly reinforced, so little deformation appeares in these areas. Additionally, the length of energy absorption segment of the longitudinal beam is significantly shortened. Due to the longitudinal beam is slender rod structure, so significant instability deformations of the S beam occurs in a frontal crash, and large intrusion in the passenger compartment.The longitudinal beams play a primary energy absorption role in frontal crash process. Using new high-strength materials or increasing the wall thickness can improve energy absorption capability of longitudinal beams. However, with these improvements, higher crash acceleration may be generated in the crash test and the structure instability is still inevitable, which is not conducive to occupant protection.Taking the S beam of one production SUV as an example, three improvement programs were proposed to increase stiffness of S beam. In program 1, internal reinforcements were welded with the inner face of the S beam to strengthen its rigidity. In program 2, upper reinforcements were welded with the upper S beam to control deformation in Z direction. Meanwhile, a U crosssection rail was added between two longitudinal beams to reduce deformation in horizontal direction. In program 3, upper reinforcements and lateral reinforcement were used to control the deformation of S beam.In this paper, a frontal crash finite element model of SUV was developed using HYPERMESH and LS-DYNA, and a multi-rigid body simulation model of frontal crash was developed using MADYMO, which were validated by front crash test. The simulations of 100% frontal crash and 40% offset deformable barrier crash were studied. The deformation pattern and the maximum deformation in horizontal and vertical directions of S beam were analyzed. Meanwhile, deformations of passenger compartment and varations of B pillar acceleration curves were analyzed. Besides, B pillar acceleration curves were brought into multi-rigid body to study human injuries risk. Three better improvement structures were brought into the chassis to anlalyze the deformation of S beam in frame-only crash tests. Finally, the better structure was then adopted and assembled on two SUV’s for 100% overlap frontal and 40% overlap offset frontal crashes.The simulations and tests showed that the deformation pattern of S beam could be controlled effectively by the improvement programes, and the structural instability could be avoided. Visible deformations of S beam appeared in program 1 and 3. In program 2, the upper reinforcements with a U cross rail between two beams could strengthen the S beam properly. It could reduce the deformation of S beam effectively, and provide sufficient stiffness to sustain the crush, which could reduce the passenger injury risk. Programe 2 has better improvement effect.