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不同温度与应力比下7B05铝合金疲劳裂纹扩展速率预测

Prediction of fatigue crack growth rate of 7B05 aluminum alloy under different temperatures and stress ratios

  • 摘要: 铝合金具有轻量化、高比强度、耐腐蚀和疲劳性能优异等优点,在海洋装备中具有广泛应用前景,准确预测不同裂纹扩展阶段的疲劳裂纹扩展速率(FCGR)对于评估海洋装备关键承载部件的使用寿命和结构完整性至关重要。传统基于物理机制的理论模型或者经验公式通常难以准确捕捉疲劳裂纹扩展速率(da/dN)与应力强度因子范围(ΔK)之间复杂的非线性关系。此外,应力比(R)和温度(t)对铝合金材料的疲劳裂纹扩展速率的影响规律还受到材料成分/制备工艺的显著影响,这对现有裂纹扩展速率和寿命预测模型的通用性构成挑战。本研究首先开展7B05铝合金材料的疲劳裂纹扩展速率试验,获得在不同t和R条件下3个阶段裂纹扩展速率曲线,并研究了温度、应力比对裂纹扩展速率的影响规律;进一步收集了文献中铝合金裂纹扩展速率数据,并与上述试验数据融合,构成铝合金疲劳裂纹扩展速率数据集;分别比较了极端梯度提升(XGBoost)、随机森林(RF)模型在预测所有3个阶段的铝合金疲劳裂纹扩展速率的有效性。研究结果表明,仅基于文献数据训练时,2种机器学习模型的预测结果均不够理想。然而,使用该材料的试验数据显著提高了预测准确性,凸显了此类数据对于海洋工程用铝合金的重要性。鉴于极端梯度提升算法提供了最佳的预测,在其中纳入更广泛的自变量集并优化超参数,在预测不同t和R下的疲劳裂纹扩展速率方面表现出高准确性,从而减少对广泛且昂贵的试验程序的依赖。研究结果不仅推进了对这种特定铝合金疲劳裂纹扩展的理解,而且为预测具有极端环境温度和复杂应力比行为的其他材料的裂纹扩展提供了一种更具普适性的方法。

     

    Abstract: Aluminum alloys feature light weight, high specific strength, favorable corrosion resistance and outstanding fatigue properties, and possess wide application prospects in marine equipment. Accurate prediction of fatigue crack growth rate (FCGR) at various crack propagation stages is crucial to evaluate the service life and structural integrity of key load-bearing components of marine equipment. Conventional physics-based theoretical models and empirical equations generally fail to accurately capture the complicated nonlinear relationship between fatigue crack growth rate (da/dN) and stress intensity factor range (ΔK). Furthermore, the influences of stress ratio (R) and temperature (t) on the FCGR of aluminum alloys are remarkably affected by material composition and manufacturing processes, which imposes challenges to the generality of existing crack growth rate and life prediction models. In this work, fatigue crack growth rate tests were firstly performed on 7B05 aluminum alloy. Three-stage FCGR curves under different t and R were acquired, and the effects of temperature and stress ratio on crack growth rate were investigated. Published aluminum alloy FCGR data from literatures were further collected and fused with the above experimental data to establish a dataset of aluminum alloy fatigue crack growth rate. The effectiveness of Extreme Gradient Boosting (XGBoost) and Random Forest (RF) models for predicting FCGR covering all three stages was compared respectively. The results show that prediction outputs of the two machine learning models are unsatisfactory when trained merely with literature data. Nevertheless, the introduction of experimental data of the target material greatly improves prediction accuracy, which highlights the significance of such data for aluminum alloys applied in marine engineering. As the XGBoost algorithm achieves optimal prediction performance, a wider range of independent variables were incorporated and hyperparameters were optimized. The optimized model realizes high accuracy in predicting FCGR under various t and R conditions, so as to reduce dependence on extensive and expensive experimental programs. These findings not only deepen the understanding of fatigue crack propagation of this specific aluminum alloy, but also offer a more universal method to predict crack growth of other materials subjected to extreme ambient temperatures and complex stress ratios.

     

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