基于激光超声技术的复合材料疲劳状态评定和寿命预测方法研究

纤维增强复合材料已广泛应用于航空航天飞行器、风电叶片等大型结构，而且应用领域日益广泛。通过无损检测实现复合材料结构的疲劳状态评定以及寿命预测，对保证复合材料结构的服役安全性具有重要的意义。本项目提出基于波速退化实现疲劳状态评定和寿命预测的方法，并对该方法的实现中存在的关键基础问题开展研究。在前期研究的基础上，通过疲劳控制实验的方法探索在单轴以及多轴周期载荷下层合板中不同模态的超声波波速的退化规律，以及载荷形式对波速退化的影响规律；分析板结构中疲劳损伤积累和波速退化现象之间的相互关系，从复合材料的损伤机理出发，建立超声波波速退化的理论模型；在波速退化模型的基础上，考虑随机因素的影响，建立基于波速的失效准则以及基于贝叶斯推断的剩余寿命预测模型；研究检测时的环境温度以及应力状态对波速的影响规律，提出相应的预测模型修正方法，进一步提高预测精度，为实现该寿命预测方法的工程应用奠定理论基础。

Fiber Reinforced Polymer/Plastic (FRP) composites have been widely used in large-scale structures, such as aircraft, spacecraft, wind turbine blades, etc. and their application fields keep increasing. The methods of fatigue evaluation and residual life prediction based on Non-destructive Testing (NDT) are very important for the safety of the composite structures in service. In this project, a new method of fatigue evaluation and residual life prediction based on velocity degradation of ultrasonic waves is proposed and the fundamental issues in realization and implementation of this method are to be studied. First, based on the former preliminary work by the applicant, the velocity degradation of different ultrasonic wave modes in FRP composite plate-like structures with different types of lamination under different types of cyclic loads will be investigated experimentally and the relationship between the pattern of wave velocity degradation and the type of cyclic loads will also be studied. Second, the mechanism and types of micro-scale damage in different types of composite materials under different types of load will be analyzed and a wave velocity degradation model are to be established based on the mechanism of damage and the theory of damage mechanics. Third, a method to estimate the failure criterion of wave velocity anda statistical model ofresidual life prediction are to be establishedbased on the wave velocity degradation model using the Bayesian theory, taking the uncertainties caused by the factors such as the measurement error, variation of material properties, etc. into consideration. The influence of temperature and the state of stress during measurement on the ultrasonic wave velocity will also be studied and a method of compensation for the residual life prediction model to achieve higher accuracy is to be proposed. This research will serve as the theoreticaland methodological foundation for the future application of laser ultrasonic technique-basedapproach for fatigue evaluation and residuallife predictionof FRP compositestructures.