Prediction of mode II fatigue delamination propagation in fibre reinforced composites: From strain energy release rate-life (G-N) curve to Paris' law
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摘要: 疲劳分层是复合材料最常见、最危险的失效模式之一。本文建立了II型加载条件下复合材料疲劳分层扩展的模拟方法。基于对疲劳分层扩展提出的新的物理解释:疲劳分层扩展为一系列连续发生的疲劳分层起始扩展,将疲劳损伤累积描述为层间界面断裂韧性衰减,构建了新的疲劳内聚力单元模型。针对II型加载条件下的材料层间开裂变形场的特殊性,提出了用以描述II型加载条件的层间界面疲劳损伤累积的衰减法则,确立了依据应变能释放率-寿命(G-N)曲线的材料本构参数标定方法。引入疲劳内聚力单元模型,预测了复合材料II型疲劳分层扩展行为,与疲劳分层扩展实验所得Pairs' law能够很好地吻合。本文新提出的疲劳分层模拟方法相较于已有模型的优势在于:无需追踪裂纹扩展路径,降低了模型的应用难度,提高了计算效率;模型所需材料参数标定仅依赖于实验G-N曲线,无需实验Paris' law,参数标定所需的疲劳实验数量及时间大幅减少。
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关键词:
- 疲劳 /
- 分层 /
- 内聚力单元模型 /
- 纤维增强树脂基复合材料 /
- 有限元模拟
Abstract: Fatigue delamination is one of the most severe damage mode for laminated composites. A new cohesive zone model was adopted in this article for modeling fatigue delamination propagation in laminated composites, in which the strain energy release rate-lifetime (G-N) curve and Paris' law were linked. This model was developed based on a new interpretation of fatigue delamination propagation: Fatigue delamination propagation is a result of multiple onsets. A new fatigue cohesive constitutive law was constructed for describing fatigue damage accumulation in the inter-laminar interface of composites. All the parameters used in the constitutive law are with clear physical meaning and can be calibrated from the experimental G-N curve. Compared to the existing models for fatigue delamination in composites, the constitutive law developed in this model works independently in each element, without algorithms for getting the global crack information or tracking crack tip position. Considering the different deformation fields around the crack tip under mode II loading conditions, a new fatigue damage accumulation law was developed for mode II fatigue delamination propagation, and the predicted Paris' law for mode II was compared well with the experimental results. -
表 1 IM7/8552碳纤维/环氧树脂单向纤维复合材料层合板的相关材料参数[8]
Table 1. Material properties of IM7/8552 carbon fiber/epoxy unidirectional laminates[8]
Intra-ply properties E11/GPa E22=E33/GPa ν12=ν13 ν23 G12=G13/GPa G23/GPa $G_{\text{c}}^{{\text{static}}}$/
(N·mm−1)$\sigma _0^{{\text{static}}}$/MPa K0/
(N·mm−3)161 11.38 0.32 0.436 5.17 3.98 0.739 90 106 表 2 ENF实验测试IM7/8552碳纤维/环氧树脂复合材料起始扩展(FDO)寿命Ntest及柔度增加百分比[8]
Table 2. List of experimental fatigue delamination onset (FDO) life Ntest and percentage of compliance increase in ENF test of IM7/8552 carbon/epoxy composites[8]
$ {G_{\sup }}/G_{\text{c}}^{{\text{static}}} $ 50% 40% 30% 20% FDO life Ntest 156 257 1597 41642 133 449 987 11080 170 746 1275 34114 116 545 2246 41643 199 436 2420 38271 Average Ntest 155 487 1705 33350 Compliance increase/% 1.06 0.77 0.95 0.73 表 3 IM7/8552碳纤维/环氧树脂复合材料G-N曲线的拟合参数
Table 3. Fitting parameters of G-N curves for IM7/8552 carbon/epoxy composites
α 10 15 20 ξ1 0.739 0.739 0.739 λ1 −0.146 −0.148 −0.149 ξ2 1.048 1.042 1.040 λ2 −0.219 −0.221 −0.222 ξ3 0.371 0.361 0.355 λ3 −0.103 −0.101 −0.100 -
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