The Residual Strength Analysis Of Plain-woven Composite Laminates After Low-velocity Impact

Plain-woven composite materials have been widely used in Aerospace structure due to its high strength to weight ratio,light,good stability and so on.But the properties of plain-woven composite materials become weak when they subject to low-velocity impacts,The composite structures will fail because of-fibe breakage,matrix cracking and delamination when they subject to low-velocity impacts.The bearing capacity of the structure will decrease,leading to accident.It is important to study the compressive properties of the composites after impact in order to evaluate the damage tolerance of the structure.This paper investigated the impact characteristics of three laminates through the low-velocity impact tests according to ASTM D7136.The damage rules was studied by using Abaqus finite element software to simulate low-velocity impact process.The compression tests after impact was conducted to find the relationship between impact energy and residual strength.Then the whole process containing low-velocity impact damage and compressive analysis was performed by setting the state after impact as initial state of compression simulation.Finally,effects of temperature and humidity on impact and strength were considered.(1)The low velocity impact tests were carried out with different impact energy on the laminates of three layers It was found that the depth of the pit-the impact energy curves of the three layers of laminates will appear turning point.Delamination occurs in the laminate before the turning point,through the ultrasonic C scan fiber breakage occur within the structure.The matrix cracks on the back of the impact point after turning point.The impact model of laminates use Hashin failure criteria to simulate the material failure with in plane,adding cohesive element between laminate units with Quads criterion to determine the damage initiation.The results show that the delamination damage area is similar to that of peanut shape and ellipse,close to the experimental value.The delamination damage of the three laminates are extended from the impact back to the front,and a small amount of fiber breakage and matrix cracking damage can be found by the simulation results.(2)it shows local buckling,dalamination initiate and propagation and eventually occurs shear delamination failure on compression test of impact damaged laminates.and the residual strength is affected by the impact energy,when impact energy become higher,residual strength declines more;Compared with the no damage laminates,the residual strength decreased by 30% to62.5% in different degrees.After the numerical simulation of the damaged laminate: compression damage will gradually expand to the surrounding area in the impact damage area,that the 90 degree of the direction is expand the fastest,the degree of 45 and-45 in the middle,the slowest in the direction of 0 degrees.The simulated compression failure load is in great agreement with the experimental.(3)The moistured laminates decreased by more than 10% compared with the impact damage laminates at room temperature.The results show that the temperature and humidity effect can reduce the compression performance of the laminates.