Mechanical Properties Of The 3D Woven Glass/Epoxy Composites With Drilled Holes

The composites have the advantages: low density and high strength. Today, the composites are used in many fields: automotive industry, aerospace industry, new energy, construction and so on. Especially, some components, like the car body and blade of aero-engine, want to be lighter while still have good mechanical properties. It already becomes the trend to use continuous fiber reinforcement composites. Some international companies make use of these composites in their production components instead of using metal. When we assembly these components, it is inevitable to have drilled holes. For example, use the screw bolt to connect pieces. In order to meet the requirements of strength and safety, make the research for mechanical properties of notched composites is necessary.This paper use the glass fiber woven as the reinforcement, and use epoxy as the matrix. The glass fiber and epoxy are widely used in the industry. 3D woven fabric and 2D plain fabric were formed with 3D weaving process, cured with VARTM, and composites were prepared with drilled and moulded-in holes. Then run the test for tensile and flexural properties.The mechanical properties of 2D woven composites(2DWCs) with drilled holes and 3D woven composite(3DWCs) with drilled holes are different. Tensile strength and bending strength of 3DWCs with drilled holes are 294.24 MPa and 367.38 MPa separately, which are much higher than these of 2DWCs with drilled holes(192.56 MPa and 253.55MPa). Strain at break of tensile and bending of 3DWCs with drilled holes are 5.68% and 5.80%, which are also higher than these of 2DWCs with drilled holes(4.10% and 2.58%). Because the fiber in 3DWCs is without crimp and the 3DWCs have damage tolerance to the thrust force during the drilling process. The mechanical properties of 3D woven composites(3DWCs) with moulded-in holes and 3D woven composite(3DWCs) with drilled holes are different. Tensile strength and bending strength of 3DWCs with moulded-in holes are 308.34 MPa and 491.64 MPa separately, which are higher than these of 3DWCs with drilled holes(284.99 MPa and 329.58MPa). Strain at break of tensile and bending of 3DWCs with moulded-in holes are 6.29% and 5.33%, which are also higher than these of 3DWCs with drilled holes(4.92% and 4.72%). Because the fibers are pushed to the around of the holes, still keep continuous and become denser. The drilling process would have less influence on the surrounding area of the hole because of less resistance for the drill. As the drilled holes diameter increased, the tensile strength of composites with drilled holes decrease from 294.24 MPa to 268.06 MPa, and the bending strength decrease from 367.38 MPa to 324.20 MPa which are caused by the stress concentration. But for the composites with moulded-in holes, the trend is not clear. When the diameter of the holes increase, the composites with moulded-in holes have a higher fiber volume fraction, which is benefit for improving the properties. However, the properties of composites also are affected by stress concentration. So there are different trends for the response.When observe the section of the holes area, it is easy to see the phenomenon such as fiber facture, matrix cracking, and tow debonding. The 2DWCs is more likely to have delamination cracks. The break of fibers in 3DWCs is more uniform, while the fiber in 2DWCs is pulled out different distance from the resin. It means, when the fiber is straight, the resin is easier to soak into fibers.