No abstract

Sandwich composite is ideal for lightweight monocoque structure owing to not only its superiority in strength-to-weight ratio and specific flexural properties but also its manufacturability to any desired complex shape. In this work, an optimum lightweight design of monocoque composite sandwich-structure microbus subjected to bending and torsion stiffness criteria and natural frequency constraints is further investigated under crash conditions through finite element analysis. A composite sandwich panel made of 5.4-mm woven glass fabric-epoxy face sheets and 50-mm rigid polyurethane foam core is tested under low-velocity impact with a hemisphere headed impactor following ASTM D7136 to characterize the failure characteristics. An enhanced composite damage material model so-called MAT54 in LS-DYNA with damage progression in each lamina utilizing strength-based Chang-Chang criteria is implemented with various formulations to validate and compare for their efficiency and accuracy under impact test. The reduced-integration Balytschko-Tsay shell element with 5 through-thickness integration points is applied to the monocoque composite microbus model. The structural crashworthiness under the frontal crash of the bus at 20, 40 and 50 km/h to a rigid wall barrier is examined. The front structure absorbs the most frontal impact energy up to 60% and shows severe damage when the crash velocity is 40 km/h or higher. For the bus impact velocity of 50 km/h, the maximum deformation of the bus front is 809 mm resulting in the intrusion of the structure into the specified driver survival space. Design improvement of the sandwich structure should be further explored to enhance its energy absorption and safety of the bus under crash events.