On the Crush Worthiness of a Laterally Confined Bar Under Axial Compression

A combined experimental∕analytical work is carried out to elucidate the energy absorption potential of laterally confined bars under monotonically increasing edge displacement. The thickness $t$ and length $L$ of the bar, as well as the wall-to-wall separation distance, $h$⁠, are systematically varied. Real-time observations show that the deformation of the bar is characterized by progressive buckling and folding, with the fully compacted material exhibiting repetitious cell unit whose wavelength approximately equals four times the bar thickness. The specific crush energy is little sensitive to the thickness of the bar but strongly varies with $t∕h$⁠, the “volume fraction” of the structure, attaining a maximum when $t∕h≈0.5$⁠. The main sources for energy dissipation are simple compression, plate folding and friction between the bar and the constraining walls, the latter of which dominates for $L∕t>10$⁠. The experimental data are found to be well predicted by simple analytic expressions derived from limit plasticity analysis and incompressible material behavior. The simple configuration studied may shed light on the behavior of more complex structures such as honeycombs, foams, and thin-walled tubes, and may serve as a basis for multi-layer design possessing improved crush energy.