Dynamic crushing behavior and energy absorption of hybrid auxetic metamaterial inspired by Islamic motif art

Auxetic honeycomb structures are promising metamaterials with outstanding mechanical properties,and can be potentially used in energy absorption applications.In this study,a novel modified re-entrant hybrid auxetic metamaterial inspired by Islamic motif art is designed by integrating four-pointed double re-entrant motifs with symmetric semi-hexagonal unit cells to achieve a high energy absorption capacity(EAC).Theoretical analyses and numerical simulations are performed to examine the dynamic crushing behavior of the four-pointed double re-entrant combined structure(FDRCS).The developed finite element models(FEMs)are validated by the experiments under quasi-static compression.The deformation mode and stress-strain curves are further studied under low,medium,and high crushing velocities.The theoretically predicted plateau stress of the FDRCS under different crushing velocities is consistent with the numerical simulation results.The crushing stress and the EAC of the FDRCS are influenced by the geometric parameters and crushing velocities.The FDRCS exhibits a negative Poisson's ratio(NPR),owing to the four-point re-entrant structure(RES).Moreover,the specific energy absorption(SEA)of these structures is higher than that of nonauxetic hexagonal and auxetic re-entrant structures,owing to the generation of more plastic hinges that dissipate more energy during dynamic crushing.

Effects of Cell Microtopology on the In-plane Dynamic Crushing Analysis of Re-entrant Square Cellular Material

With the development of three-dimensional printing technologies, so-called cellular materials have achieved increasingattention due to outstanding properties. Unlike pure solid structures, properties of cellular materials are influenced by bothutilized material and cell microtopology. The present paper proposes a novel type of re-entrant square cellular material.To explore the relationship between microtopology and macrodynamic responses systematically, an explicit dynamic finiteelement simulation method is used. This work starts by constructing theoretical models of relative density employing atwo-dimensional unit cell. Then, the effects of geometric features and configurations on dynamic properties are explored,and simulations indicate that variations of geometric parameters strongly affect properties and that the staggered re-entrantsquares are more stable than the regular re-entrant squares. Subsequently, the effects of the impact velocity on dynamiccrushing behaviors are elaborated. On this basis, the relationship of unit mass energy absorption and geometric features isobtained by employing the response surface method. Furthermore, with targets of maximum unit mass energy absorption andminimum relative density, the optimal structural parameters are achieved by using non-dominated sorting genetic algorithm.The study provides a detailed introduction to dynamic behaviors of cellular materials and guidance to design new structureswith superior characteristics of energy absorption.

Hemodynamic change in wall shear stress in patients with coronary bifurcation lesions treated by double kissing crush or single-stent technique

Background Fluid dynamic mechanisms attributed to coronary bifurcation lesions remain a subject of study. The present study aimed at investigating the hemodynamic change of wall shear stress （WSS） in patients with coronary bifurcation lesions treated by double kissing （DK） crush or one-stent with final kissing balloon inflation （FKBI）. Methods Eighty-one patients with bifurcation lesions treated by stenting who had 3-D model reconstruction were studied. The bifurcation vessels were divided into main vessel （MV）, main branch （MB）, side branch （SB）, and polygon of confluence （POC）. MB and SB were classified by internal- and lateral-subsegments, respectively. Results The baseline magnitude of WSS in proximal MV, POC-MV, POC-MB, POC-SB and MB-internal segments increased significantly, compared to MB-lateral, SB-internal and SB-lateral. DK crush had the potential of uniformly reducing WSS, turbulent index and the WSS gradient. The WSS value at the POC-SB and SB in the one-stent group remained higher. The turbulent index and WSS gradient between the POC-SB minus the SB-lateral had equal predictive values for in-stent restenosis （ISR）. Conclusion Fluid dynamic results favor the use of DK crush over the one-stent technique.