tailieunhanh - 3D Fibre Reinforced Polymer Composites Part 9

Tham khảo tài liệu '3d fibre reinforced polymer composites part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 146 3D Fibre Reinforced Polymer Composites composite are then obtained by averaging the properties of the RVE for the different yarn orientations present in the global coordinate system. More recently Chen et al. 1999 described the use of a Finite Multiphase Element method to predict the elastic properties of 3D braids. This process uses a two step numerical approach of generating a fine local mesh at the unit cell level to analyse the stress strain response of the unit cell then a coarse global mesh to obtain the overall response of the composite at the macroscopic level. To date these models have only been used for the prediction of elastic constants and there does not appear to be any attempt made to predict the strength of 3D braided polymer matrix composites. The comparison of predicted and experimental elastic constants is reasonable good mostly within 10 Chen et al. 1999 but in general the predicted properties are less than that measured via experiment. SUMMARY 3D braided preforms are very versatile forms of textile reinforcement for composite structures. As discussed in Chapter 2 3D braids can be produced in a wide range of cross-sectional shapes and these shapes can be varied along their length to form structural details such as tapers bifurcations holes etc. However there has only been relatively limited data published on the mechanical properties of 3D braided polymer matrix composites much of the development in the area of 3D braids appears to be focussed on ceramic and metal matrix composites. In particular there has been little comparison made between the performance of 3D braided composites made by different braiding processes and between 3D braids and 2D laminates. From the data that has been published it is evident that the presence or absence of axial fibres and the angle of the braiding yarns both play an important role in controlling the mechanical properties. Improved longitudinal performance results from increased axial fibre content and .