Structures And Properties Of Three-dimension Woven Integrated Sandwich Composites

The 3D woven integrated sandwich composites are new types of sandwich structure materials, which are also called sandwich structures in overseas. The 3D composites are mainly made of 100 percent of E-Glass fibers, and the sandwich structures are formed by the Z-direction fibers connecting the down and upper face-sheet of the fabrics. The typical spatial characteristics of the composites are that the piles show "8"-shape in warp direction, and " I "-shape in weft direction. The 3D composites have excellent integrated performance, which overcomes the weakness of easy delamination and poor impact resistance of the traditional sandwich structures, such as honeycomb and foam ones. Nowadays the 3D composites have been widely used in large areas of boats, aircraft wings, sandwich of oil tanks, various floors, and partition walls.So far the studies on the 3D composites have mainly focused on the experimental tests, such as the basic mechanical performance, low-velocity impact and other properties. However, the other studies on the 3D composites, such as the preparation of the 3D integrated sandwich fabrics, the effect of the structure parameters on the mechanical performance and low-velocity impact, the residual strength of the composites after low-velocity impact, and the structural theory of the composites, have not been properly studied.In the paper, the studies of the 3D composites on the mechanical performance, low-velocity impact, and structural theory were carried out in detail. The main work includes as follows.(1) The preparation of the 3D woven integrated sandwich composites. First step, the design of different types of 3D integrated sandwich fabrics, included "8"-shape, "88"-shaped, and 2.5D integrated sandwich fabrics. Second step, the weaving of the 3D sandwich fabrics, included processing adjustment, weaving production, and so on. Third step, the preparation of the resin matrix, which was made from the resin (epoxy resin 618), curing agent (PA 651), diluents (propylene oxide-butyl ether 660), and the ratio of the resin matrix is 100:50:30. Fourth step, the molding of the 3D integrated sandwich fabrics. In the paper, the method of hand lay-up molding and vaccum assisted resin infusion molding (VARIM) were used to prepare the 3D composites.(2) The studies of the mechanical properties on the 3D woven integrated sandwich composites.In the paper, the mechanical characteristics of the 3D integrated sandwich composite under flat compressive, side tensile, side compressive, shear and flexural loads were studied, and the effects of pile height and pile density on the mechanical properties were investigated too. The results indicated that the side tensile strength, side compressive strength and flexural strength increased, while the flat compressive strength and shear strength decreased with the increase of the pile height. The flat compressive strength, side tensile strength, side compressive strength, shear strength, and flexural strength all increased with the increase of the pile density. The results contribute to the optimal design of the 3D sandwich composites.(3) The studies of low-velocity impact behavior on the 3D woven integrated sandwich composites. First step, the low velocity impact characteristics of the 3D composites were investigated as a function of the pile height with 5mm under different impact energy from 1 to 10J respectively. Second step, the effects of pile height on low-velocity impact behavior were investigated as a function of the pile height with 5mm,6mm and 7mm under impact energy of 8J. Third step, the effects of covered skins on the low-velocity impact behavior were investigated by the comparison of behavior of the 3D composites that covered and uncovered with aluminum skins for 7mm.(4) The studies of residual strength on the 3D woven integrated sandwich composites after low-velocity impact. First step, the residual strength characteristics were investigated as a function of pile height with 5mm,6mm and 7mm under impact energy of 8 J. Second step, the effect of impact energy on the residual strength was investigated as a function of pile height with 7mm under impact energy of 6J,8J and 10J. Third step, the effects of covered skins on the residual strength were investigated by the comparison of behavior of the 3D composites that covered and uncovered with aluminum skins for 7mm.(5) The studies of structure theory on the 3D woven integrated sandwich composites. On the basis of previous studies, a new structural model was developed for the compressive analysis of 3D integrated sandwich composites by using the finite element software ANSYS. The effects of pile height, pile density, material elastic modulus and poisson ratio of the 3D composites on the compressive properties were studied in detail. The results show that the maximum value of the stress appears in the interface between pile and face-sheet when the 3D composites are subject under compressive loads, in which the composites damage easily. The compressive properties of the 3-D composites increase with the increase of the pile density, poisson ratio, and decrease with that of the pile height. The elastic modulus has little effect on the compressive properties of the composites. The results provide reference for the structure optimum of the 3D composites.