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Abstract Dynamic loading of materials is fundamental in understanding the mechanical response of cellular solids and elucidates time dependent properties that pertain to energy absorption under extreme conditions. Of particular interest is how the discrete behavior of the individual cell in a stochastic foam affects the dynamic shockwave behavior. The deformation mechanism in a stochastic open-cell foam is bending-dominated versus stretch-dominated in periodic lattice structures, resulting in a decrease in the plastic yield stress. Here, we investigate shockwave dynamics in stochastic open-cell foams through phase contrast imaging and finite element modeling. We observe that the distribution of pore sizes and the proximity of each produces a random topology with varying cell wall thicknesses that cause points of high strain creating irregularity in the shock wave at higher impact speeds. The shockwave dynamics of the stochastic foam are compared to periodic additive manufactured (AM) foams with similar density and it can be observed that modulation via microstructural control in elastomer foams has a dramatic effect on shockwave dynamics. Graphical abstract Image Highlights • X-ray phase contrast imaging was employed to investigate deformation mechanisms of stochastic and additively manufactured polymer foams under shock loading. • Compaction and localization phenomena were found to vary under shockwave compression due to local microstructures well above the elastic yield condition. • Finite element modeling illustrates that stress behind the wavefront varies with compaction and densification of the non-uniform material density distribution. [ABSTRACT FROM AUTHOR]

The existence issue of shock waves during dynamic deformation of plastic porous materials is analyzed. The analysis is based on the mechanics of plasticity for porous continuum. The deformation routes typical for both the use of shock resistant materials and dynamic compaction of powders and porous bodies are considered. It is established, that unlike compacts, the deformation of porous bodies can be accompanied by shock waves. For the routes where the changes in volume dominate over the changes in shape, the deformation is always accompanied by the formation of shock waves. Meanwhile, in case of free deposition (and similar routes), shock waves appear only if the starting porosity is high. [ABSTRACT FROM AUTHOR]

Spall strength data of sintered and hot-pressed silicon carbide show an initial increase with an increase in the shock-induced stress to around 4 GPa. At impact stress around 6 GPa and above, spall strength data of these materials show a continuous decrease in the magnitude of spall strength. This unusual trend in the spall strength of silicon carbides may be due to the competing roles of (i) localized plasticity, (ii) generation and propagation of cracks taking into consideration their relative dominance below and above a given magnitude of stress. This work presents the results of spall experiments conducted to test the relative dominance hypothesis by determining whether the observed initial increase in spall strength of silicon carbide is due to dominance of localized plastic deformation over crack-dominated brittle deformation, while the observed decline in the spall strength with an increase in the shock-induced stress reflects a dominance of crack-induced brittle deformation over plastic deformation. [ABSTRACT FROM AUTHOR]