## 4 Results and Discussion
### The Interaction Occurred in the Nested Sample  
The deformation of tubes arranged in nested configurations leads to interactive phenomena that substantially affect the energy absorption properties of these structures. In this context, the force-displacement characteristics of the NT3-T\({}_{\text{S}}\)+T\({}_{\text{M}}\) specimen, along with the force curves corresponding to the individual tubes that constitute this specimen, are collectively illustrated in Figure 5. The force curve associated with the NT3-T\({}_{\text{S}}\)+T\({}_{\text{M}}\) sample is clearly represented in a maroon color within the figure, contrasting with the force curves of the individual tubes, which are depicted in different shades of blue (specifically blue, dodger blue, and cyan) to enhance differentiation. The segmentation of the force curve into three distinct parts clarifies the sequential deformation processes encountered by tubes of different dimensions. The initial segment specifically illustrates the deformation occurring in the largest tube alone, while the following segments indicate the gradual involvement of the medium and smallest tubes in the deformation process, respectively. The force curve for each individual tube was derived by algebraically summing the initial force values associated with each tube, starting from the force value recorded in the previous section. The NT3-T\({}_{\text{S}}\)+T\({}_{\text{M}}\) specimen demonstrated a significant increase in energy absorption, amounting to 19.9 J, when compared to the total energy absorbed by the individual tubes at the same displacement threshold. Additionally, the assessment of the maximum crush displacement metric was based on the highest crush displacement recorded in the tri-tubular specimen configuration. \begin{table}
\begin{tabular}{c c} \hline
**NT2-T\({}_{\text{S}}\)** & \\ \hline NT2-T\({}_{\text{M}}\) & \\ \hline NT3-T\({}_{\text{S}}\)+T\({}_{\text{S}}\) & \\ \hline NT3-T\({}_{\text{M}}\)+T\({}_{\text{S}}\) & \\ \hline \end{tabular}
\end{table} 
Table 1: Cont. In the context of three-tube nested specimens, the investigation extends to configurations wherein tubes are fabricated from dissimilar materials, scrutinizing the resultant interactions as previously delineated. The subsequent figures (referenced as Figure 6) delineate the force-displacement trajectories for specimens characterized by the employment of TB and TS tubes composed of heterogeneous materials. Specifically, Figure 6a illustrates a composite of aluminum T\({}_{\text{B}}\) and CFRP TS tubes, whereas Figure 6b depicts the inverse material configuration. Notably, Figure 6a reveals a precipitous decline in the force curve at approximately 25 mm of displacement when CFRP tubes are utilized internally--a phenomenon absent in specimens comprising aluminum analogs. This decline is attributable to fractures manifesting on the lateral aspects of the CFRP TS tubes, engendering a 4% reduction in energy absorption capacity of the specimen. Furthermore, the incorporation of CFRP TS tubes results in a substantial mass reduction exceeding 27%, enhancing the specimen's overall efficiency. Conversely, the specimen illustrated in Figure 6b, despite the decrement in absorbed energy due to the substitution of aluminum T\({}_{\text{S}}\) tubes with CFRP, experiences a compensatory reduction in mass that ostensibly mitigates the impact of reduced energy absorption. The juxtaposition of different material tubes not only influences the absolute energy absorption but also significantly affects the energy absorption efficiency. Intriguingly, specimens evidencing a decline in absorbed energy exhibit enhanced specific energy absorption capabilities relative to their original configuration. Conversely, an augmentation in absorbed energy correlates with a diminution in specific energy values. Consequently, this suggests that the pivotal metric in evaluating energy absorbing structures is not merely the quantum of energy absorbed but rather the efficiency with which this energy is assimilated.