【作者】 郭建；

【导师】 李成；

【作者基本信息】 郑州大学 ， 机械设计及理论， 2021， 硕士

【摘要】 由于较高的强度重量比与良好的抗疲劳性等特点,碳纤维增强复合材料(CFRP)板在航空、建筑和工程等关键领域中被广泛使用。但是服役期间碎屑的撞击、工具掉落等,会使其结构内产生多种形式的冲击损伤,这些损伤会对结构的安全性产生巨大的威胁。非线性超声检测凭借着对微损伤的敏感性在早期损伤检测领域得到广泛应用。本文利用试验与仿真分析对CFRP板不同冲击参数和检测距离的超声非线性响应进行研究,同时针对检测过程中二次谐波生成效率较低的问题,提出基于脉冲反相技术的检测方法。首先,基于单层各向异性介质的应力-应变扩展矩阵对多层复合材料内Lamb波的波动方程进行推导,接着对Lamb波的传播特点和非线性超声检测的优点进行介绍,通过DC软件绘制的频散曲线对Lamb波的频散和多模态特性进行介绍。同时,对脉冲反相法的原理进行解释,并推导和定义了改进非线性系数IRANP。接着,对CFRP板不同冲击能量损伤的非线性Lamb波响应进行试验研究。对脉冲反相非线性超声检测平台进行搭建,并对激励信号和耦合剂进行挑选、对检测系统的稳定性和脉冲反相法的正确性进行验证。随后对含损伤的CFRP试件进行制备,通过超景深设备对不同冲击能量所产生的损伤进行对比,并在此基础上研究不同冲击能量的冲击损伤对改进非线性系数的影响。结果表明:脉冲反相法可以有效提高二次谐波的检出幅值,而冲击能量的增加并不会对基波的幅值产生明显的影响,但是会导致第二波包幅值、二次谐波幅值以及IRANP的增大。最后,考虑到试验条件的限制,本文建立了CFRP板冲击-振动消除-非线性超声检测的有限元模型,用以研究不同参数下的非线性超声响应。在对一体化模型的创建过程进行介绍后,验证了模型的正确性和脉冲反相法的有效性。接着,结合基体拉伸损伤和能量吸收,利用此模型进一步研究冲击能量、冲击角度所产生损伤以及上述冲击参数与检测距离对非线性超声响应的影响。结果表明:冲击能量与冲击损伤正相关、冲击角度与冲击损伤负相关;在进行损伤检测时,IRANP与冲击损伤正相关,因此可以通过对比IRANP对不同冲击参数所产生损伤的大小进行评估;同时,检测距离也对IRANP有重要影响。更多还原

【Abstract】 Carbon fiber reinforced polymer(CFRP)panels are widely used in critical areas such as aerospace,construction and engineering due to characteristics such as high strength-to-weight ratio and good fatigue resistance.However,impacts from debris and dropped tools during service can cause many forms of impact damage within their structure,which can pose a significant threat to the safety of the structure.Nonlinear ultrasonic detection is widely used in the field of early damage detection by virtue of its sensitivity to micro-damage.In this paper,the ultrasonic nonlinear response of CFRP panels with different impact parameters and detection distances is investigated using experimental and simulation analyses,and a detection method based on the pulse inversion technique is proposed to address the problem of low efficiency of second harmonic generation during the detection process.Firstly,the fluctuation equations of Lamb wave in multilayer composites are derived based on the stress-strain expansion matrix of single-layer anisotropic media,then the propagation characteristics of Lamb waves and the advantages of nonlinear ultrasonic detection are introduced,and the dispersion and multimodal characteristics of Lamb wave are introduced through the dispersion curves of Lamb wave drawn by DC software.At the same time,the principle of the pulse inversion technique is explained and the improved nonlinear parameter is derived and defined.Then,the nonlinear Lamb wave response of CFRP panels with different impact damage is investigated experimentally.Nonlinear ultrasonic detection platform based on pulse inversion technique is constructed and the excitation signal and coupling agent are selected,the stability of the inspection system and the correctness of the pulse inversion technique are verified.Then CFRP specimens containing damage are prepared,and the damage produced by different impact energies is compared by means of the ultra-depth-of-field microscopy system.The results show that the pulse inversion technique can effectively improve the detection amplitude of the second harmonics,while the increase of the impact energy does not significantly affect the amplitude of the fundamental wave,but leads to the increase of the second wave packet amplitude,the second harmonic amplitude as well as the IRANP.Finally,considering the limitations of the test conditions,a finite element model for impact-vibration cancellation-nonlinear detection of CFRP panels is developed in this paper to study the nonlinear ultrasonic response under different parameters.After the introduction to the creation process of the integrated model,the accuracy of the model and the validity of the pulse inversion technique are verified.This model is then used to further investigate the damage caused by impact energy,impact angle in combination with substrate tensile damage and energy absorption and the effect of these impact parameters and detection distance on the nonlinear ultrasonic response.The results show that impact energy is positively correlated with impact damage and impact angle is negatively correlated with impact damage.IRANP is positively correlated with impact damage when performing damage detection,so the magnitude of damage from different impact parameters can be assessed by comparing IRANP.Also,the detection distance has an important influence on IRANP.更多还原