Prediction of mode II fatigue delamination propagation in fibre reinforced composites: From G-N curve to Paris’ law
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摘要:
复合材料由于其高比刚度、比强度和可设计性等优点,在航空航天、汽车制造和风力发电等领域得到了越来越多的应用。复合材料层合板由于层间缺少增强相,层间力学性能相比于其层内性能较弱,因此疲劳分层损伤是复合材料层合板在长期服役过程中最常发生的、最危险的失效模式之一。本文针对复合材料层合板加载过程中最常出现的层间界面剪切失效,建立了适用于预测II型加载条件下复合材料层间疲劳分层扩展行为的模拟方法。基于分层增量起始扩展假设,对疲劳分层扩展提出了新的物理解释,解释了疲劳分层起始扩展的G-N曲线与疲劳分层扩展Paris’ law之间的物理关系,并建立了内聚力单元模型。相较于I型加载,II型加载条件下复合材料层间界面变形区域显著增大,由此产生了更大的损伤区域、更早的疲劳损伤累积。基于此,本文提出了用以描述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II型疲劳分层起始扩展实验G-N曲线的层间界面本构参数的标定方法,引入内聚力单元模型,成功地预测了纤维增强树脂基复合材料层间界面的II型疲劳扩展行为Paris’ law。相较于已有疲劳分层模拟方法,本文提出的新方法无需追踪裂纹扩展路径,极大地降低了模型的应用难度;内聚力本构关系中的材料参数标定仅需要实验G-N曲线,参数标定所需的疲劳实验数量及时间均大幅减少;为工程中复合材料结构疲劳行为及寿命的预测提供了有效工具。 内聚力单元模型(a)利用疲劳分层起始扩展G-N曲线标定材料参数,(b)预测疲劳分层扩展Paris’ law。 -
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 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 FDP, and the predicted Paris’ law for mode II was compared well with the experimental results.-
Key words:
- fatigue /
- delamination /
- cohesive zone model /
- fibre reinforced polymer composites /
- FEM
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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 UD 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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