## 4 Results and Discussion
### Crashworthiness  
The findings of the experimental study, inclusive of all utilized specimens and specific crashworthiness parameters, are comprehensively delineated in Table 3. This table elucidates a discernible variance in the force exerted by specimens contingent upon the material composition. It is observed that both the mean and peak force metrics for the single and nested CFRP composite tubes are markedly inferior to those of their aluminum counterparts across all specimen configurations. This discrepancy is attributed to the brittle nature of carbon fiber composites, which detrimentally impacts the specimens' capacity to bear loads. Furthermore, the crushability indices of the samples exhibited variability correlating to the quantity of tubes employed. For singular tubes, the crushability index was ascertained through the calculation of the ratio of 85% of the tube's inner diameter to its outer diameter. The method for determining the crushability of nested samples adhered to a similar paradigm. Nonetheless, a distinct approach was employed for nested samples wherein 85% of the value derived from subtracting the cumulative wall thickness of the interior tubes from the inner diameter of the TB tube was established as the sample's crushability ratio. Consequently, an inverse relationship between the crushability ratio and the number of tubes in the nested samples is anticipated. Independent of material composition, it was noted that tubes of smaller diameter exhibited superior maximum force values relative to their larger counterparts. This phenomenon aligns with the premise that the force requisite to deform a specimen should escalate inversely with its diameter. Evidently, the maximum force values recorded for the nested specimens utilizing the T\({}_{\text{S}}\) tube significantly surpassed those of specimens employing the T\({}_{\text{M}}\) tube, a trend that was consistent among specimens integrated with EPP foam.  
The outcomes derived from the utilization of various specimens within the experimental framework, alongside associated crashworthiness metrics, are systematically documented in Table 1. This tabulation elucidates a pronounced disparity in the force exerted by specimens based on their material composition. Specifically, both average and maximum force exertions by single and nested carbon fiber-reinforced polymer (CFRP) composite tubes were observed to be inferior to those of their aluminum analogs across all specimen configurations. This phenomenon can be attributed to the brittle character of the carbon fiber composite, which negatively impacts the load-bearing efficacy of the specimen. Additionally, the crushability indices of the samples manifested variations contingent upon the number of tubes employed. For individual tubes, the crushability index was derived by calculating the ratio of 85% of the inner diameter to the outer diameter of the tube. The computation of crushability for nested configurations adhered to a similar methodology. However, for nested samples, 85% of the resultant value obtained by subtracting the aggregate wall thickness of the internal tubes from the inner diameter of the T\({}_{\text{B}}\) tube was designated as the crushability ratio for the sample. Consequently, an augmentation in the number of tubes within nested configurations is anticipated to affect the crushability ratio inversely. Irrespective of the material composition, the maximum force value associated with tubes of smaller diameters surpassed those of larger diameters. This observation corroborates the hypothesis that a decrease in diameter necessitates an increase in the force required to deform the specimen. Indeed, the maximum force values for nested specimens  
\begin{table}
\begin{tabular}{c c} \hline \hline
**FF\_NT3-T\({}_{\text{S}}\)+T\({}_{\text{M}}\)** \\ \hline \hline \end{tabular}
\end{table}
Table 2: Cont.  
utilizing the T\({}_{\text{S}}\) tube significantly exceeded those involving the T\({}_{\text{M}}\) tube, a pattern that remained consistent for specimens incorporating EPP foam.