Study on Curved Surface Formability of 3D Woven Preform for Ballistic Helmet
Three-dimensional woven preform(3DWP),because of its better formability and significant interlaminar bearing capacity,is expected to achieve the integrated molding of helmet curved surfaced,and reduce the waste of cut and raw materials.Because of the structure characteristics of ballistic helmet with multiple curved surfaces and high curvature,it is important to study the deformation mechanism of 3DWP during curved surface forming for the integrated forming of helmet.The curved surface formability of a layer-to-layer interlock 3DWP with stuffer yarns under high curvature and large deformation is studied systematically.The deformation mechanism and wrinkle defects formation mechanism of 3DWP are described comprehensively from in-plane/inter-layer dimensions and macro/mesoscale.The results indicate that significant in-plane shear deformation of 3DWP can be observed along the 45°direction at the same latitude.The maximum in-plane shear angle of the concave surface is 38°,which is greater than that of the convex surface.The maximum inter-layer shear angles of 3DWP warp and weft rows are 34.83°and 27.76°,respectively.After forming,3DWP has reached 62° intra-ply shear locking angle,which induces the buckling of yarns microscopically and forms the ridged wrinkles macroscopically.In the wrinkle area,the maximum in-plane shear angle is only 4.8°,and the maximum inter-layer shear angle is 18°.This conclusion has guiding significance for structure selection and forming process of reinforced fabric for ballistic helmet in practical application.
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