| Fiber reinforced composites are widely used in aerospace,national defense and military industry,transportation and other fields due to their light weight and high strength.The traditional laminated structure composites only rely on matrix adhesion between layers,which is easy to cause delamination damage when subjected to external loads during use.Threedimensional textile structural composites represented by three-dimensional weaving have overcome the shortcomings of traditional laminated structures such as easy delamination and low damage tolerance,which have attracted more and more attention.In this paper,the three-dimensional woven fabric is used as the basic structure to design and weave the integrated structure reinforced preform.The vacuum assisted resin transfer molding process(VARTM)is used to prepare the composite material,and the damage mechanism of the composite material under low-velocity impact is explored.Firstly,the fabric structure of stiffened plate was designed and optimized,and the stiffened plates with different structural parameters were successfully completed on the sample loom.Then,the static threepoint bending test and dynamic low-speed impact test were carried out to analyze the damage mechanism of stiffened plate composites under low-speed impact.Finally,finite element software is used to simulate and verify the dynamic impact process.The results show that:(1)Through the reasonable design of the fabric structure,the weaving work of the integrated stiffened plate preform with different structural parameters can be completed on the sample loom.(2)The maximum load of the static bending load of the reinforced sample is significantly enhanced.When the number of weft layers of the reinforcing rib is 9,the peak load is 51.2 %higher than that of the flat specimen.When the width of the reinforcing rib is 40 mm,the peak load is 84.1 % higher than that of the flat specimen.The trend of dynamic low-speed impact results is similar to that of static state.The higher the stiffener,the larger the peak load,and the smaller the stiffener spacing,the larger the peak load.(3)The fracture positions of static three-point bending and dynamic low-velocity impact specimens are the same.The plate and double-reinforced specimens break at the test loading point,that is,the center of the specimen.The single-reinforced specimen breaks at the junction of the reinforcing bar and the bottom plate,and the fracture mouth presents a shape.The damage of the specimen is mainly matrix cracking,fiber-matrix debonding,fiber bundle extraction,and fiber breakage.There is no obvious delamination damage between layers.Only a small part of the single weft yarn is layered after the binding yarn is broken.The difference between static and dynamic fracture is that the damage area of the static three-point bending specimen is small.The fracture of the bending specimen is mostly the crack of the lower surface extending upward and then extending to both sides,and a small amount of internal shear failure.The specimen is not completely broken,and the upper surface matrix and fiber have no obvious damage.However,the damage of the dynamic specimen is serious.There are a large number of crushed and broken matrix debris on the upper surface of the specimen,and some specimens are completely penetrated to produce penetrating damage.(4)The unit cell method can effectively simulate the damage process of materials under low-velocity impact.In the finite element simulation,the plate specimen and the doublestiffener specimen are fractured in the center,and the single-stiffener specimen is fractured at the junction of the stiffener and the bottom plate.The fracture morphology is similar.The average error between the simulated load peak and the actual test is 8.29 %.The finite element and the actual test have achieved good consistency,which verifies the accuracy of the finite element simulation. |
PDF Full Text Request