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In the era of electric vehicles(EVs), the need for weight reduction of the vehicle body is increasing in order to maximize the driving distance of the EV. Accordingly, there is an increasing need for research to efficiently apply lightweight materials, such as aluminum and CFRP, to the EV body parts. In this study, design methodologies and optimization measures to increase lightweight efficiency when applying lightweight materials to EVs will be discussed. Based on theoretical basis and basic performance of each part of the EV, the “Material Substitution Method” of replacing existing parts of a steel body with aluminum materials will be defined, and the optimal design process on how to overcome performance trade-off caused by material characteristics will be addressed. In applying the “Material Substitution Method” to the actual EV body design process, it was possible to convert 93% of the components from steel to aluminum and reduce the overall weight of the body by 23%. Based on these results, the “Material Substitution Method” helps secure basic performance for each part with relative ease when changing the material of the body part from steel material to lightweight material (AL, CFRP, etc.). In addition, it is verified that the optimal design process defined in this paper is effective in maximizing the weight reduction efficiency of the lightweight body.

A composite B-pillar was designed and manufactured by design optimization combined with an impact analysis. A carbon-fiber-reinforced plastic (CFRP) was used for the reinforcement part of the B-pillar assembly to substitute the conventional steel materials for reducing the weight of vehicle. To maximize the impact performance by finite element method, the equivalent static loads method was used. The shape, stacking sequence, and thickness of the CFRP reinforcement were optimized to minimize the deflection profile for improving the crashworthiness while reducing the weight. The designed CFRP B-pillar was manufactured and its performance was evaluated by a drop weight test. As a result, the CFRP B-pillar exhibited an improved impact performance and reduced weight compared to those of the conventional steel B-pillar.

In this study, a combined forming-structural analysis of composite structures was performed. Fiber orientation and shear angle changes of the composite materials during its thermo-compression molding processes were predicted with commercial software PAM-FORM. In addition, the material properties, such as elastic modulus and strength, from the shearing of woven fabrics, were measured. The predicted shear angle changes were transformed and reflected to the structural analysis by a self-developed vector-mapping program. The load-displacement curves of the composite structures from the combined forming and structural simulation were compared with the experimental compression and bending test results of hemispherical and U-shaped components, respectively. Finally, it was found that the mechanical behaviors of composite structures can be accurately predicted by the developed combined thermo-forming structural analysis method.

In this study, design optimization of a composite hood for automobiles was carried out to mitigate the impact of pedestrian head injuries based on finite element analysis. Reduced vehicle, headform impactor and single hood models were established to obtain optimal composite hood designs. The carbon fiber reinforced composite (CFRP) and the hybrid Glass fiber reinforced composite (CFRP/GFRP) laminates were selected as composite material candidates. Both stacking angle sequence and topometry of the composite hood were optimized based on the equivalent static load method. After the optimization, the head injury criterion (HIC), deflection and weight were measured to evaluate the performance of the composite hood. The developed CFRP and hybrid CFRP/GFRP type hoods with optimized final design exhibited the improved impact performance and significant weight reduction while satisfying bending and torsion deflection requirements compared to those of conventional steel and aluminum hoods.

In this paper, the non-linear mechanical behavior of shear deformed woven composite was predicted using a representative volume element (RVE) model based on multi-scale progressive failure analysis. The micro-scale RVE model, consisting of single fiber and a matrix, was employed to determine the stress amplification factor and distinguish the failure of each fiber and the matrix constituent. Then, a meso-scale RVE model of shear deformed twill woven composite was developed to predict non-linear behavior using micro-stress transferring with finite element simulation. Fiber yarn shapes were observed with respect to the shear angle of the twill fabric. Based on the observed yarn geometry, shear deformed twill composite was modeled by using the open source software TexGen. To prove validity of the proposed model, shear deformed twill woven composite was fabricated using a picture frame, followed by a vacuum assisted resin transfer molding process. Mechanical tests were conducted and the failure progress during the tests was observed to determine their failure analysis. As a result, a good correlation between the multi-scale progressive damage model and experimental results such as mechanical properties, the non-linear stress-strain curve, and failure modes were achieved.