Study Of Low Velocity Impact Properties Of SMA Reinforced Resin Matrix Composites

Fiber reinforced resin matrix composites that with the advantages such as high strength,strong designability,simple preparation process,easy industrial production,etc.,which have been widely used in aerospace,marine,automotive,construction and daily necessities and so on.However,the fiber-laminated composite structure is susceptible to impact from external objects,such as the fall of tools during maintenance.In addition,due to the poor toughness of fiber-laminated composites,composite materials tend to produce impact damage that is difficult to observe by visual methods when subjected to external loads,and these invisible internal damages can cause the strength,stability and service life of the composite greatly reduce.In 1963,the US Naval Weapons Laboratory first discovered nickel-titanium(Ni-Ti)alloy,which is a shape memory alloys(SMA)with memory effect and superelastic effect.With the deepening of the study,researchers consider embedding the nickel-titanium SMA into the laminate,and improving the overall load-bearing capacity and energy absorption characteristics of the composite laminate,thereby reducing the impact damage of the composite laminate.In this paper,the low velocity impact behavior of SMA reinforced resin matrix polymer,and SMA and fiber hybrid reinforced composite laminates are studied.The main contents include the following aspects:(1)The impact test pieces of resin matrix polymer and SMA reinforced resin matrix polymer are prepared,and the impact properties of all polymer test pieces are characterized by the drop weight low velocity impact test.The effect of the laying spacing and diameter of SMA on the impact behavior of polymer specimens.The test results show that the spacing and diameter of the SMA have a certain influence on the overall damage state,load bearing capacity and energy absorption characteristics of the polymer test piece.For the same SMA diameter of 0.5 mm,the impact resistance of the polymer specimens with the SMA laying spacings of 3 mm is best.For the same SMA laying spacing of 3 mm,the impact resistance of the polymer specimens with the SMA diameter of 0.5 mm is best.(2)The impact test pieces of unidirectional glass fiber reinforced composite laminates,and SMA and unidirectional glass fiber hybrid reinforced composite laminates are prepared by vacuum assisted resin injection molding process.The low velocity impact behavior of all composite laminates specimens is characterized by drop weight low velocity impact test,the microscopic damage morphology of the composite laminate is observed by electron microscopy,and the position of the SMA embedded into the laminate is further optimized.The test results show that embedding the SMA wire into the composite laminate can effectively improve the bearing capacity and energy absorption characteristics of the laminate and reduce the damage of the composite laminate.In the cases of 32 J impact energy,the laminates with laying sequences(from bottom to top)of[0/SMA/90/(0/90)7],[0/90/SMA/(0/90)6/SMA/0/90],and[0/SMA/90/(0/90)3/SMA/(0/90)4]have the largest peak contact force,the least plastic deformation,and the highest recoverable absorbed energy,respectively.In the cases of 64 J impact energy,the laminates with laying sequences(from bottom to top)of[(0/90)4/SMA/(0/90)4],[0/SMA/90/(0/90)7],and[0/SMA/90/(0/90)3/SMA/(0/90)4]have the largest peak contact force,the least plastic deformation,and the highest recoverable absorbed energy,respectively.(3)Based on the SMA constitutive relation,3D Hashin failure criterion and interlayer failure criterion,the numerical model of the low velocity center impact of unidirectional glass fiber reinforced composite laminates,and SMA and unidirectional glass fiber hybrid reinforced composite laminates are established,and the validity of the model is verified by comparing with the impact test results.In addition,the impact damage behavior of composite laminates under different impact energies(16 J,32 J,48 J and 64 J)is further analyzed and the effects of vibration boundary conditions on the impact damage behavior of composite laminates are studied based on this model.The results show that the greater the impact energy,the greater the contact force between the impactor and the laminate,and the more the dissipation energy of the laminate.The greater the impact energy,the larger the damage area of the composite laminate,and the more of failure modes.Under the same impact energy,the composite laminates embedded with SMA have a higher peak contact force.At the same frequency,the greater the amplitude applied to the laminate,the larger the damage area produced by the laminate.In the case of the same amplitude,the greater the frequency applied to the laminate,the larger the damage area of the laminate.(4)Based on the theory of SMA constitutive relation,3D Hashin failure criterion and interlayer failure criterion,the numerical model of low velocity eccentric impact of SMA and woven glass fiber hybrid reinforced composite laminates is established,and the validity of the model is verified by comparing with the literature[170].In addition,the stress and energy absorption of the points on the square laminate and the rectangular laminate under eccentric impact are analyzed.The results show that the composite laminate under eccentric impact has a shorter impact contact time,a larger peak contact force,and a smaller maximum displacement compared to the center impact.The closer the impact point is to the boundary,the smaller the effect of the superelasticity of the SMA,and the weaker the effect of the SMA on reducing the deformation of the laminate.