The Compression Properties Research Of 2D Two Axis Over-braiding Composites Materials

Over-braiding composites materials have been applied widely into different field such as areospace field,military and civil fields and so on,the research of its mechanical properties is one of the major problems faced by scholars both at home and abroad currently.And compression is not only one of the difficulties which is not easy to measure but also the important research direction.This paper is mainly discussing the compression properties of over-braiding structure composites materials in order to deduce a method that can represent or quantitatively describe the compression elastic properties.Then,briefly analysis compression failure mode.Firstly,through 2D vertical braiding machine,design the size of braiding mandrel,then braid different layers of Over-braiding composites material,do compression experiment on MTS 647 Hydraulic Wedge Grip machine,discussing different layers compression material of carbon fiber/epoxy resin over-braiding composites.Then we obtain a great deal testing data.Secondly,by the Nikon SM27457 Stereo Microscope,the braiding yarn undulation section of over-braiding composites was observed.Considering the yarn buckling when braiding,fiber axial modulus will loss in some extent,we provide ? as loss coefficient.By measuring the basic parameters of the braided composite material,combined with composite materials microscopic structure,theory of Elastic Mechanics,Laminated theory and multi-layers equivalent elastic mechanics model to deduct a set of simple and practical method which is calculating average compression modulus of 2D 2×2 braided composites.Last,analysis different layer,different braiding angle of over-braiding's average compression modulus variation and failure mode of over-braiding composites.The results show that:1.A set of simple and practical method which is calculating average compression modulus of 2D 2×2 braided composites,the theoretical value is quite coincident withactually measured value which providing sample and practical calculating method for industrial application of braided composites.2.After the compression test,we know that:(1)When fiber volume fraction show much consistence,in the same over-braiding composites,there are differences in different braiding angle and it will have a big influence on over-braiding composites compression performance.Braiding angle is large while average compression modules is small.With layers increasing,the thickness will increase while average compression modulus of over-braiding composites is on the decline.(2)Before composites broken,the stress-strain curve is linear,present elastic deformation in the initial stage.With strain increasing,stress rapidly rise to the pear,then decline slowly.(3)The main damage form and compression failure of over-braiding strcture is statified phenomenon.The damage degree of stratification is between UD composites and 3D composites.At the same experimental conditions,layer which is more will damage much more serious than less number layer composites.In the same layer,the inner side that braiding angle is small damage more serious than the outer edge which braiding angle is large.Moreover,crack and load direction has some extent angle,crack propagation does not exceed valid compression length.