## 3 Results and Discussions
### Deformation Mechanism and Failure Mechanism  
As shown in Figure 13, the mechanical properties of foam aluminum are significantly affected by different strain rates under static and dynamic conditions. With the increase of  
Figure 12: Comparison results of each characteristic parameter at different strain rates: (a) 0.001 s\({}^{-1}\); (b) 0.01 s\({}^{-1}\); (c) 0.1 s\({}^{-1}\). strain rate, the yield stress and plateau stress gradually increase, while the elastic strain gradually decreases. The yield point stress increases by nearly 40%. The stress-strain curve trend under low strain rate is basically consistent with that under high strain rate. As shown in Figure 14, during the elastic stage, the deformation of foam aluminum occurs within a very small region. The stress-strain curve in this stage can be approximated as a straight line, indicating that the pore shapes of foam aluminum have not yet changed significantly and the pore walls have not yet buckled. The end of the elastic segment is its yield point. When the strain of foam aluminum enters the plateau segment, the strain gradually increases while the stress does not rise significantly, because during this period, the pore walls of foam aluminum begin to buckle and collapse gradually. As the pores in foam aluminum are completely compacted and enter the compaction segment, the material itself begins to undergo compressive deformation, and the stress rises sharply. The static compression and dynamic deformation processes of closed-cell aluminum foam stress-strain curves are shown in Figure 15. During the compression process, the cell structure first deforms, causing stress concentration. As the load increases, the cell walls bend and fracture, and the pores collapse. Subsequently, the collapse expands layer by layer, resulting in a step-by-step collapse deformation, and eventually the entire specimen is compacted. The deformation and failure process is divided into three stages: (1) elastic deformation stage; (2) plateau collapse deformation stage; (3) densification stage. The  
Figure 14: Characteristics of the stages of the compressive stress-strain curve of aluminum foam. Figure 13: Compressive stress-strain curves of aluminum foam at different strain rates. linear elastic deformation stage of closed-cell foam aluminum is mainly characterized by the elastic bending and extension of the cell walls, and the work done by the external force is converted into the elastic deformation energy of the foam aluminum. This stage mainly reflects the strength characteristics of the pore structure. When the compressive stress reaches the yield strength that foam aluminum can withstand, the recoverable elastic deformation of the cell walls evolves into irreversible plastic yielding. Due to the inhomogeneity of the foam aluminum material structure, plastic deformation cannot occur simultaneously when subjected to external forces. The failure first occurs at the weak points of the cell walls, where the local cell walls first transition from elastic bending to plastic bending, leading to stress concentration in the plane perpendicular to the external force and containing this pore, causing the cell walls to be crushed. The crushed cell walls connect to form the first deformation band, with most of the cell walls outside the deformation band still in the elastic deformation stage. As the load increases, new weak deformation bands gradually form and develop, and the continuous formation of weak deformation bands indicates that foam aluminum exhibits significant localization during the compression process. When collapse occurs again, the failure occurs within a new layer and repeats the above process, compacting the material layer by layer, with little change in stress throughout the process. This stage mainly reflects the yielding and crushing process of the pore structure.