基于DIGIMAT的碳纤维增强环氧树脂编织复合材料的力学性能

Mechanical properties of carbon fiber reinforced epoxy resin woven composites based on DIGIMAT

为准确预测不同编织工艺参数下编织复合材料的等效弹性性能,拓宽碳纤维增强环氧树脂编织复合材料的应用领域。建立了考虑随纤维路经产生扭结缺陷的二维三轴编织复合材料的代表性体积单元(RVE),并基于平均场均匀化方法,利用DIGIMAT预测复合材料的等效弹性模量,分析不同编织角对编织复合材料等效工程常数的影响规律;其次基于强度失效准则,预测编织复合材料在单轴拉伸加载情况下的力学性能;最后通过数值模拟获得编织复合材料RVE的应力与应变。结果表明:预测的编织参数对等效工程常数的影响规律与试验测量一致,获得的应力、应变可为进一步研究其损伤破坏行为提供参考。

Objective Braided composites have many advantages such as high specific strength,high specific stiffness,high impact damage tolerance and designable mechanical properties,and have been widely used in aerospace,machinery and other fields,and it is particularly important to optimize or design their mechanical properties.In this paper,based on a new composite simulation software DIGIMAT,a representative volume element(RVE)considering the kink defects of fiber bundles with fiber path is established to accurately and quickly predict the equivalent elastic properties of the material at different braiding angles and to explore the influence of the weaving angle on them;and then the stress distribution of two-dimensional triaxially braided composite RVE is obtained to provide a basis for further study of its damage and failure.Method Although the internal structure of two-dimensional triaxially braided composites is relatively complex,it has a certain periodic distribution on the mesoscale.Therefore,an RVE considering the kink defects caused by fiber bundles along the fiber path was established by using the nonlinear composite modeling platform DIGIMAT,and the equivalent elastic properties of materials were predicted based on the DIGIMAT-MF module mean field homogenization method.Based on the strength failure criterion,the DIGIMAT-FE module was adopted to predict the mechanical properties of braided composites with different braiding angles under uniaxial tensile loading(peak strain of 0.5%).Results The equivalent engineering constants of two-dimensional triaxial braided composite RVE were predicted with the longitudinal tensile modulus E1 of 48.33 GPa,the transverse tensile modulus E_(2) of 6.70 GPa,and the longitudinal Poisson′s ratioμ_(12) of 0.71,the transverse Poisson′s ratioμ23 of 0.45,and the shear modulus G_(12) of 6.77 GPa.In addition,nine braiding angles of 15°,19°,23°,27°,30°,35°,37°,41°and 45°were selected to analyze their influence on the equivalent engineering constant.The longitudinal tensile modulus E1 was inversely proportional to the braiding angle.With the increase of braiding angle,E1 demonstrated a gradual decrease,whereas the transverse tensile modulus E_(2) showed an opposite trend.With the increase of braiding angle,the longitudinal shear modulus G_(12) firstly increased and then decreased,while the transverse shear modulus G23 remained virtually unchanged(Fig.3).With the gradual increase of braiding angle,the longitudinal Poisson′s ratioμ_(12) first increased and then decreased,while the transverse Poisson′s ratioμ23 shows a decreasing trend(Fig.4).The longitudinal uniaxial tensile simulation of two-dimensional triaxially braided composite RVE with different braiding angles showed that the elastic modulus of the material decreases with the increase of braiding angle,while the fracture strain is the opposite(Fig.5).From the contour,it can be observed that the overall stress distribution is not uniform,and the stress peak tends to appear at the yarn,while the stress valley appears at the matrix,and a large stress gradient exists in the contact area between the two(Fig.6 and Fig.7).This is mainly because under the longitudinal tensile load,the axial fiber bundle bears most of the load,and the warp and weft yarns also bear part of the load,while the matrix basically does not bear the load effect,the warp and weft yarns improve the longitudinal bearing capacity of the material,so that the structure bears the load more uniformly.There are obvious stress concentrations in the mutual twist zone and the contact zone between the yarns and the matrix,which may lead to local deformation and crack expansion,and then cause material failure.Conclusion The effect law of braiding angle on the equivalent engineering constant derived in this study is consistent with the law derived by experimental methods in the documents,the accuracy of the finite element model developed in this paper is verified.Based on this finite element model,the stress distribution of the two-dimensional triaxially braided composite RVE was predicted.The overall stress distribution is not uniform,and the stress of the yarn is significantly higher than the stress of the matrix.There are obvious stress concentrations in the yarn mutual kink area and the contact area between the yarn and the matrix,which may lead to the occurrence of local deformation and crack expansion,and then cause the material failure.