Ultimate Strength Of Composite Sandwich L-joint With Damage

Sandwich composites are increasingly used in ship structures because of their excellent mechanical properties and corrosion resistance.L-joint is a typical local structure in composite hull structure,which is mainly used for the connection between deck and side.In the construction and use of sandwich composites,the damage problem is almost inevitable,and the damage will affect the safety of the structure.Therefore,for the first time,L-joints of sandwich composite materials with damage are studied in this paper,which can provide reference for the application of L-joints in composite hull structures.Firstly,the finite element model of L-joints is established by ABAQUS software.Based on the composition of knitting fiber,the three-dimensional Hashin failure criterion of knitting fiber composites is defined.Combining the progressive failure analysis and cohesive zone model,the ultimate strength and failure mode of L-joints are predicted,and the results are compared with the experiments,which verifies the validity of the simulation method.The circular fiber fracture damage and debonding damage with a radius of 20 mm are introduced into the arc elbow area of L-joints.The ultimate strength of L-joints with damage is studied.The results show that the ultimate strength of L-joints with fiber damage is 14% lower than that of non-damaged joints,while that of L-joints with debonding damage is only 3% lower than that of non-damaged joints.Then,the influence of damage shape on the ultimate strength of L-joints is studied by numerical simulation.The results show that the ultimate strength of L-joints with penetrating damage is significantly lower than that of L-joints with circular and elliptical damage.The ultimate strength of L-joints decreases by 43% due to penetrating fiber fracture damage,and the ultimate strength of L-joints decreases by 8% due to penetrating debonding damage.Subsequently,the size effects of circular and penetrating damage are studied.For debonding damage,the ultimate strength of L-joints decreases with the increase of circular and penetrating damage size;for fiber fracture damage,the ultimate strength of L-joints decreases only with the increase of circular damage size,but has little relationship with penetrating damage size.The research on damage location shows that the ultimate strength of L-joints with fiber fracture damage on the front of arc elbow plate is lower than that of L-joints with fiber fracture damage on the side of arc elbow plate,while the debonding damage on the front of arc elbow plate has little effect on the bearing capacity of L-joints.Finally,from the perspective of structural design,the effects of sandwich material properties,skin thickness of stiffener,size of stiffener and radius of arc elbow on the ultimate strength of L-joints with fiber fracture damage and debonding damage are discussed.The results show that the change of sandwich properties is only effective for L-joints with debonding damage,but has little effect on L-joints with fiber fracture damage.Increasing the thickness of skin,the size of stiffener and the radius of arc elbow can increase the ultimate strength of L-joints.Increasing the thickness of skin on the front of stiffener and the height of stiffener can enhance the ultimate strength of L-joints more obviously.