Mechanical Properties Of Foam Filled Re-entrant Honeycomb With Negative Poisson’s Ratio And Engineering Applications On Ship Side Anti-collision Structure

Novel materials & structures would be used in the ship side anti-collision structure for the purpose of improving crashworthiness of the ship side structure without affecting overall performance of the ship.A novel composite structures with unique mechanical properties composed of re-entrant honeycomb with negative Poisson’s ratio and porous foam have been conducted in the present research.Systematic investigations on the geometrical configurations,manufacturing method,mechanical behavior under planar compression and low velocity impact of the novel foam filled re-entrant honeycomb under various loads have been carried out.The present research provides theoretical basis for the engineering application of the novel composite structure in the anti-collision ship structure.The following research contents have been carried out:(1)Mechanical properties of foam filled re-entrant unit cell have been investigated.In-plane mechanical properties of re-entrant unit cells with various strengthening topology have been carried out by quasi-static test,FE simulation and analytical method,and strengthening effect have been proposed.Results show that the foam filled in the unit cell provide an excellent strengthening effect.The equivalent compressive modulus has been strengthened in small deformation.Due to the negative Poisson’s ratio effect,the foam filled in the void of the re-entrant cell suffer a biaxial compression under large deformation.Load carrying capability and energy absorption efficiency have been strengthened by the PUR foam.(2)Mechanical performances of the foam filled re-entrant honeycomb with negative Poisson’s ratio under planar compression has been investigated.Experimental test and FE results show that both void and foam-filled honeycombs represent a macro negative Poisson’s ratio.The negative Poisson’s effect of re-entrant honeycomb would move toward when subjected to compression along the orthogonal direction,which lead to biaxial compression for the foam.Due to the additional support,the foam prevent braces from bending and sliding.Under the combined effect of these factors,the stiffness and stress are increased finally.Based on the rigid-plastic assumption,an analytical method for predicting the nominal plateau stress and macro Poisson’s ratio has been established by virtual energy theory,Rapid prediction could be achieved by the analytical method with accuracy.(3)Dynamic responses of the re-entrant honeycomb under low velocity impact have been investigated.Both the numerical results and experimental results show that the re-entrant honeycomb undergo local deformation under low-velocity impact loading,compared to global deformation under planer compression.Foam has a significant strengthening effect on the reentrant negative Poisson’s ratio honeycomb,which makes the cell wall undergo lateral bending,inward contraction and shear under the impact,thus improving the impact stiffness and energy absorption efficiency.Once the condition of the ratio of diameter of the impactor to the width of the unit cell of the honeycomb is greater than 1,the re-entrant honeycomb would avoid premature failure.More unit cells would undergo plastic deformation,thus load carrying and energy absorption capability of the re-entrant honeycomb would be increased.(4)Mechanical responses of a ship side protective structure based on re-entrant honeycomb under collision of rigid bulbous bow have been investigated.Taking double-hulled carriers as application object,a novel ship side protective structure is obtained by filling the auxetic reentrant honeycomb into the space between the two shell plates of the ship side structure.For the novel ship side anti-collision structure,the re-entrant honeycomb filled in the space between the two shells would undergo plastic deformation after rupture of the outer shell,thus a sudden drop in the collision force and a decrease in energy absorption are avoided.Under collision of the bulbous bow,re-entrant honeycomb undergo auxetic deformation in the local collision area,thus the foam filled in the unit cells would be compressed both in the horizontal direction and the vertical direction,the energy absorption capability of the foam filled structure would be further improved.Compared to the conventional double hull structure,SEA of the novel side structure without foam filled would be increased by 49 %,while 63 % of the novel side structure with foam filled.The load carrying capacity and energy absorption of the honeycomb structure could be increased by increasing of the cell wall thickness,while do little effect on the specific energy absorption.Both the load carrying capacity and specific energy absorption could be increased by increasing the numbers of the array of the unit cells due to increasing of the plastic hinges existing in the honeycomb structure under collision of the bulbous bow.In the present research,a novel re-entrant honeycomb with negative Poisson’s ratio has been established based on sheet stacking and foam filling method.The deformation,damage and energy absorption characteristics of the honeycomb structure under various load including compression,low-velocity impact are investigated.Based on the rigid-plastic assumption,a simplified analytical method for the plateau stress and macroscopic Poisson’s ratio of the auxetic honeycomb structure under compression is established by using the energy method.Engineering applications of the auxetic honeycomb for ship side anti-collision structure have been proposed,mechanical responses including collision force,energy absorption efficiency have been identified.The present research provides through insight into the structural performance of the foam filled re-entrant honeycomb with negative Poisson’s ratio,provides technical support for the improvement of the safety of ship structure,and would be beneficial to the engineering application of the novel composite structure.