Mechanical Properties Researches Of Novel Negative Poisson's Ratio Foams Structure

Negative Poisson's Ratio foams,a kind of mechanical meta materials having abilities of modifying strength and toughness,not only play an important role in aerospace and architecture grounds,but also can be used as biological scaffolds in medical fields.As is well known,Negative Poisson's Ratio has a great influence in mechanical properties.However,due to limited researches of NPR struts foams which having a concave-convex character,it is imperative to develop and study novel foams actively.In my work,a novel NPR foams was designed by using concave-convex characteristic.By comparison with conventional open foam,three concave-convex foams(CCF1,CCF2 and CCF3)are obtained through using different bending parameter h.Four foams are manufactured by 3D printed technology.Two polymers,Vero White Plus and Nylon 12 of thermo plasticity,are used in printing processing.Soon afterwards,static compressive test and low cycle fatigue test are executed for them,respectively.Strength of four foams is calculated by using ABAQUS software.The result shows that conventional foam CCF1 has a greater stiffness than that of CC1,CCF2 and CCF3.Moreover,Poisson's ratio of COF0 is closed to zero,while CCF1,CCF2 and CCF3 have Poisson's ratio of-0.12,-0.30 and-0.35,respectively.Through the static compressive test of Vero White Plus foams,conventional foams COF0 has a more brittle broken tendency and the buckling is easy to happen.On the contrary,concave-convex foams CCF1,CCF2 and CCF3 has an increasing energy absorption ability.Bending is the main deformation behavior of concave-convex foams.Plastic damaged model can be well described constitutive model of Vero White Plus material.Damage results of four foams shows that conventional foams COF0 has a lowest damage resistance,and concave-convex foams' damage resistance increase with adding of Negative Poisson's Ratio.Compared with struts cross damage and fracture surface,cracks initiate in tension damage.Meanwhile,the smaller initial damage is,the higher foams' toughness is.Through the low cycle fatigue test of Nylon 12,Coffin-Manson law can well predict the relation between strain amplitude and fatigue life.By the fitting of fatigue test result,the strength of foams decline with higher Negative Poisson's Ratio,but the fatigue ductile coefficient increase.In addition,during the cycle test,Negative Poisson's Ratio foams have a higher stability of elastic modulus,but plastic deformations add.