内聚力模型在飞机金属薄壁结构断裂模拟中的积木式验证
BUILDING-BLOCK VALIDATION OF COHESIVE ZONE MODELS IN FRACTURE SIMULATION OF AIRCRAFT THIN-WALLED METALLIC STRUCTURES
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摘要: 内聚力模型(Cohesive Zone Model, CZM)凭借参数少、标定简便及鲁棒性强等优势, 在飞机金属薄壁结构断裂评估中极具应用潜力. 然而, 实际飞机结构形式复杂, 且裂纹扩展常伴随面外屈曲现象, 由防屈曲小试样标定的内聚参数能否跨尺度、跨构型地应用于这类结构, 尚待系统研究. 针对此问题, 本文聚焦于飞机金属薄壁结构的准静态I型裂纹扩展过程, 严格遵循NASA积木式验证体系, 系统验证了基于防屈曲小试样标定的内聚参数在预测大尺寸平板、共线多裂纹板及平直加筋壁板断裂行为中的适用性. 结果表明: 在给定材料与厚度条件下, 当裂纹长度与韧带宽度均不小于四倍厚度时, 标定后的内聚参数与面内几何尺寸及加载方式无关. 基于防屈曲小试样标定的内聚参数, 不仅能够准确预测大尺寸防屈曲结构的裂纹扩展过程, 获取结构的剩余强度、多裂纹连通载荷及筋条应变分布等特征参量, 还能够有效模拟大尺寸平板与平直加筋壁板的面外屈曲位移分布并准确预测其剩余强度. 本研究有效验证了CZM作为弹塑性断裂分析模型, 其经防屈曲小试样标定的内聚参数具备跨尺度可迁移性, 对飞机金属薄壁结构的剩余强度评估、损伤容限设计及服役寿命预测具有重要工程价值.Abstract: The Cohesive Zone Model (CZM) exhibits tremendous application potential in the fracture assessment of aircraft metallic thin-walled structures due to its advantages of requiring few parameters, easy calibration, and strong robustness. However, actual aircraft structures feature complex configurations, and crack propagation is often accompanied by out-of-plane buckling. Whether the cohesive parameters calibrated from anti-buckling small specimens can be applied to such structures across different scales and configurations remains to be systematically investigated. To address this issue, this paper focuses on the quasi-static Mode I crack propagation in aircraft metallic thin-walled structures. Strictly following the NASA building block validation approach, the applicability of cohesive parameters calibrated from anti-buckling small specimens is systematically verified in predicting the fracture behavior of large flat panels, collinear multi-crack panels, and flat stiffened panels. Results indicate that, under a given material and thickness, the calibrated cohesive parameters are independent of in-plane geometric dimensions and the loading type when both the crack length and the uncracked ligament size are no smaller than four times the thickness. The cohesive parameters calibrated from anti-buckling small specimens can not only accurately predict the crack propagation process of large anti-buckling structures—obtaining characteristic parameters such as residual strength, multi-crack link-up load, and stiffener strain distribution—but also enable effective simulation of the out-of-plane buckling displacement distribution and accurate prediction of the residual strength for both large flat panels and flat stiffened panels. This study effectively verifies that as an elastoplastic fracture analysis model, the cohesive parameters of CZM calibrated via buckling-resistant small specimens possess cross-scale transferability, which is of significant engineering value for residual strength assessment, damage tolerance design and service life prediction of aircraft metal thin-walled structures.
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