应力水平和纤维角度对CGF/PP复合材料蠕变行为的影响及其Burgers模型参数的数值预测

Effects of stress levels and fiber orientations on creep behavior of CGF/PP composite and numerical prediction of Burgers model parameters

采用DMA的Creep模式分别测试了短时间内(15min)聚丙烯(PP)在不同应力水平和温度下的单向拉伸蠕变行为,长时间内(10h)连续玻璃纤维增强聚丙烯(CGF/PP)复合材料单层板在不同应力水平和不同纤维角度上的拉伸蠕变行为。利用Burgers黏弹性模型拟合了蠕变测试数据,构建了相关参数与应力水平和纤维角度的依赖性。结果表明:PP和CGF/PP单层板的蠕变柔量均随应力增大而显著增加,稳态蠕变速率也随之增加,蠕变模量保留率明显下降,PP基体的黏弹性主要决定了CGF/PP单层板在低应力水平下的蠕变行为;30%应力水平下,偏轴拉伸的纤维角度在0°～90°范围内存在拉-剪耦合效应,在45°时最为显著,此时稳态蠕变速率和蠕变变形量最大;利用四元件Burgers黏弹性模型拟合各条件下蠕变曲线得到的数值模型与实验数据具有较好的相关性,相关系数达到0.99,从得到的数值模型可知相关模型参数存在明显的应力和角度依赖关系;利用模型参数的数值拟合公式分别预测10MPa应力下0°纤维方向的蠕变曲线及45°纤维方向上30%应力水平的偏轴蠕变曲线均与实验曲线一致,表明本文得到的数值模型的可靠性。

In this study, the short-term (15 min) tensile creep behaviors of polypropylene (PP) at different temperature and stress levels were examined by DMA creep model test, followed by the characterization on the longterm tensile creep behavior (10 h) continuous glass fiber reinforced polypropylene composites (CGF/PP) at the different stress levels and fiber orientations. The Burgers viscoelastic model was adopted to simulate the materials creep curves and pertinent model parameters associated with the stress levels and fiber orientations were derived. The results show that, with the rise of loaded stress, the creep compliance and steady-state creep rate of PP and unidirectional CGF/PP laminate both increase significantly and the creep modulus retention rate decrease obviously? demonstrati ng that the creep behaviors of CGF/PP under low stress levels is dependent on the viscoelastic properties of PP matrix. The tensile-shear coupling effects occur in the loaded angle from 0° to 90° for the off-axis tension with a stress level of 30%, specifically in the 45° where steady-state creep rate and the creep deformation of composites exhibit maximum values. The derived numerical model by means of four element Burgers viscoelastic model to fit the creep curves in different conditions matches well with the experimental data, with a correlation coefficients of 0. 99 between them. The numerical clearly illustrated the stress and fiber orientation dependence for the pertinent model parameters. The numerical formula of model parameters was established. The estimated tensile creep curve in the 0° fiber direction at 10 MPa and the estimated off-axis tensile creep curve in the 45° off-axis fiber direction at 30 % of stress level are nearly identical with the experimental curve, showing the reliability of the derived numerical model in this paper.