Topology optimization is one complex method due to a final layout obtained by an initial shape is not a consideration. This paper purposes a proportional technique to determine an optimal layout by employing the topology optimization method. The objective function is to maximize an internal energy density by stress constraint based on the bi-linear elastoplasticity material properties. Fully stress design criterion is concerned to be a factor of the proportional technique for updating the design variable. Finally, the optimal layout acquires from the proportional technique and results are faster to converge with an over-relaxation factor which applied to the fully stress design.

An electric heavy quadricycle, categorized as an L7e vehicle, is an alternative solution for sustainable mobility with a lower carbon footprint and high energy consumption efficiency. However, accidental crashes of quadricycles with larger vehicle opponents can cause extensive damage to their structures and fatal injury to the occupants due to their geometry drawback in limited space in the front crumple zone. This work investigates the crashworthiness performance and safety assessment of the L7e vehicle under rigid wall crash tests and crash compatibility in car-to-car collisions with a sedan and an SUV. Crash scenarios are simulated using a nonlinear finite element analysis via LS-DYNA to evaluate structural crashworthiness and occupant injuries of a hybrid III 50th percentile male dummy. The compatible vertical alignment of the primary energy-absorbing structure substantially affects the safety of the quadricycle under a frontal crash. A secondary energy-absorbing component should be adapted to the L7e vehicle to achieve vertical alignment with different vehicle sizes. In addition, the typical rigid-wall frontal crash test at 50 kph considerably underestimates the structural damage and occupant injury of the L7e vehicle compared to car-to-car collisions. Thus, additional crash tests representing car-to-car collisions that account for the car’s smaller size and lighter mass should be included in the safety regulation for the L7e vehicle.

An electric small four-wheeler, categorized by the European Union as L7e so-called heavy quadricycle or microcar, is one of the solutions to eco-friendly and sustainable mobility for personal transport. Nonetheless, quadricycles typically do not offer the equivalent passive safety as larger passenger car models, in case of accidents, owing to the lack of energy absorption in the vehicle’s structure. This paper presents a proposed heavy quadricycle structure using plain weave carbon fibre-reinforced polymer in the passenger cell and aluminium alloy 6061-T6 in the crumple zone. The behaviors of electric heavy quadricycles under impact are simulated in accordance with the test guidelines of European New Car Assessment Programme using a non-linear finite element analysis via LS-DYNA to examine structural crashworthiness and characteristics. A full-frontal crash with a rigid wall at 30 km/h to 50 km/h shows that the front crush box, longerons and subframes in the crumple zone can efficiently absorb energy from a frontal crash up to 54.8%. The maximum damage in the structure occurs at the joints of the A-pillars and side beams to the front panel. Whilst the occupant safety space is safe under side collision by a 1350-kg moving deformable barrier at 50 km/h speed. However, the quadricycle tends to experience overturns from a side crash due to the vehicle’s lightweight and high center of gravity. Finally, suggestions for crashworthiness improvements to the composite passenger cell are provided based on the attained damage mechanism under a crash.

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