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Abstract

Crash boxes play a vital role in vehicle crashworthiness by dissipating kinetic energy during frontal impacts. Positioned between the bumper and side rails, they limit vehicle damage, reduce repair costs, and improve passenger safety. Enhancing their energy absorption capacity is therefore critical. Graded fillers have emerged as an effective approach, providing controlled crushing behavior, reduced initial peak forces, and improved performance. While most prior studies have focused on rectangular and cylindrical crash boxes, limited work has explored conical designs, particularly with graded honeycomb reinforcement. This study examines the crashworthiness of conical steel crash boxes using finite element analysis in ABAQUS under axial impact with a 600 kg impactor at 17 m/s. Three configurations were analyzed: S1 (empty), S2 (filled with uniform-cell honeycomb), and S3 (filled with graded-cell honeycomb). The novelty lies in introducing a conical crash box with graded reinforcement, which enables controlled progressive folding, reduces peak forces, and enhances energy absorption compared to conventional designs. The measured energy absorption (EA) for S1, S2, and S3 was 3.54, 8.04, and 11.67 kJ, respectively. Specific energy absorption (SEA) reached 9.18, 8.67, and 12.21 kJ/kg, while crush force efficiency (CFE) was 22.25, 30.77, and 29.99%. Stroke efficiency values were 78.33, 48.32, and 56.19%, respectively. Compared with S2, the graded design (S3) achieved 45.14% higher EA and 40.83% higher SEA, with only 2.53% lower CFE, while outperforming S1 by 229.66, 33, and 34.78%. These results demonstrate the superior crashworthiness of graded honeycomb–filled conical crash boxes, highlighting their potential for lightweight and cost-effective automotive structures.

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