Study On Failure Behavior Of Three-dimensional Inline Fabric Laminate Composite

Three-dimensional layer-to-layer interlock woven composites（2.5DWC）are used in aerospace and other fields due to their good impact resistance tolerance and fatigue resistance.However,due to the limitation of the number of warp and weft layers on the three-dimensional loom,the thickness of the fabric product is limited.As a result,the thickness of a single-layer 2.5D woven fabric cannot meet the design requirements of some composite products.At the same time,weaving a thicker fabric will increase fiber damage.Compared with two-dimensional fabrics,2.5D woven fabric as a layering unit can significantly reduce the number of design layers while meeting the design thickness of the product,which is beneficial to improve efficiency and reduce production costs;On the other hand,fewer layers lead to less risk of delamination failure of composite materials.Therefore,this paper studies the failure behavior of three-dimensional layer-to-layer interlock laminate composites（2.5DWLC）,which provides a theoretical basis and reference for its application in engineering.Firstly,2.5D woven fabrics with thicknesses of 0.8 mm,1.33 mm,and 2 mm were woven.For each thickness of fabric,5 layers,3 layers,and 2 layers were laid along the warp direction to prepare 3 kinds of composite materials 2.5DWL_iC（i=0.8,1.33,2）and 2.5DWC with a thickness of 4 mm was fabricated as a reference.The influence of the thickness of a single layer on the failure behavior of composite materials in tension,bending and compression is explored.Tensile experiments show that as the thickness of the single layer increases,the tensile performance increases,and the difference in the failure strain between the individual layers is deepened,resulting in asynchronous fracture of each layer of 2.5DWLC during the stretching process.The failure mechanism mainly includes fiber fracture,fiber pull out,interface debonding,matrix cracking and delamination.Compression experiments show that with the increase of single layer thickness,the 2.5DWLC compressive modulus increases.When the number of layers is greater than two,the edge layer produces significant bending yield stress and affect the improvement of compressive strength.The failure mechanism mainly includes kink band failure,matrix cracking and delamination.The bending test shows that the bending performance does not increase with the increase of the thickness of the single layer,which is beneficial to the enhancement of bending performance when the number of plies is even.The failure mechanism mainly includes the formation and failure of kink bands,fiber fracture,and matrix cracking and delamination.Secondly,2.5DWL_1.33C was selected for open-hole tension（OHT）and open-hole compression（OHC）experiments,and the effects of opening diameters of 6mm,10mm,and 14mm on the tensile and compression failure behavior of 2.5DWLC were explored.The OHT experiment shows that compared with 2.5DWC,the total amount of strain accumulation and OHT strength decrease,and with the increase of the opening diameter,the gradient of this change gradually slows down.The change of the opening diameter has little effect on the OHT modulus,and the loss rate is about keep within 6%.Analyzing the failure samples,it was found that the matrix on the left and right sides of the hole was cracked,the weft yarn was pulled out seriously,the yarn pulling phenomenon was more near the two sides of the hole,and the brittle fracture of the yarn was farther away from the hole.And the yarns near the left and right sides of the hole are damaged preferentially,while the upper and lower ends of the hole are hardly suffer from damage.The failure mechanism mainly includes yarn pulling,yarn breakage,matrix cracking and delamination.The OHC experiment shows that the damage of the interlayer matrix is the most serious when the samples with the three pore diameters reach 97 percent of the maximum stress.At the same time,the fibers and the single layer are buckled and damaged by extrusion,and the stress-displacement curve fluctuates.As the diameter increases,the OHC strength decreases,and the failure mechanism mainly includes the formation and failure of fiber kinks.Finally,2.5DWL_1.33C with a hole diameter of 10mm was selected for the reinforcement experiment of the hole sample to explored the influence of different stitching processes on the OHT failure behavior.The results show that the stitching process reduces the OHT strength,but has little effect on the OHT modulus.When the needle pitch away from the edge of the hole decreases,the stress concentration deepens,so that the stress concentration on the edge of the hole is dispersed,which is conducive to the improvement of the OHT strength.At the same time,the yarn drawing phenomenon far away from the two sides of the hole is increased,and no delamination occurs in the failure sample,which improves the interlayer performance.The failure mechanism mainly includes yarn pulling,yarn breakage,and matrix cracking.