复合材料层板冲击损伤空气耦合兰姆波成像检测方法研究

发布时间：2018-01-30 02:03

本文关键词： 复合材料层板兰姆波冲击损伤空气耦合超声成像检测　出处：《南昌航空大学》2017年硕士论文　论文类型：学位论文

【摘要】：复合材料层板由于具有密度小、强度好、力学性能强等优点,而被广泛应用于航天航空等重要领域。然而,由于复合材料层板的垂直方向抗冲击性能较差,在役期间可能遭受来自冰雹、碎石、工具坠落等各种情况的冲击。复合材料的冲击损伤缺陷在表面目视检查时并不明显,但内部损伤可能对材料强度和力学性能产生了较大的破坏,对飞行器整体结构的安全性形成了严重的威胁。对大面积复合材料层板的在役检测而言,空气耦合超声兰姆波检测方法以非接触快速检测、可单侧面布置传感器的特点,在自动成像检测上有着突出的优势。本文首先基于薄板兰姆波的基本理论,介绍了多层结构各向异性材料频散曲线计算推导过程。以飞机蒙皮结构常采用的碳纤维复合材料层板作为研究对象,研究了相应兰姆波传播的频散关系曲线和板厚方向质点振动位移分布,并分析了检测频率与入射角的之间的影响规律。结果表明,利用空气耦合兰姆波检测该材料时,宜选用A0模态兰姆波,0.4MHz的检测频率下,激发A0模态兰姆波的理论入射角为11.5°。其次,基于时域有限差分数值计算方法,建立了碳纤维复合层板的漏兰姆波检测模型。通过对模拟和实验对比和分析了传感器入射角、缺陷和材料各向异性对漏兰姆波信号的影响。结果显示,入射角处于11.0o至14.0o范围内,漏兰姆波接收效率最佳,缺陷处的兰姆波信号有着明显的衰减,扫描检测方法可判断缺陷严重程度,沿试件水平方向传播的兰姆波的传播速度和衰减规律基本呈各向同性。再其次,采用焊缝TOFD相类似的扫描成像方法,对含冲击损伤的实验试件进行了兰姆波D扫(非平行扫查)成像检测研究,引入了四种损伤指数DI(Damage Index)来表征复合材料层板的冲击损伤,根据其分析方法特点分类为:时域损伤指数、频域损伤指数、时频域损伤指数、时间反转损伤指数。以D扫检测信号的时频分析、时反处理等信息变换结果为基础,计算得到了表征损伤的特征值DI。对比可知,四种损伤指数算法的数值范围以及适用条件不同,但都能明显得表征缺陷严重程度,其中时频域损伤指数表征缺陷区域的效果最佳。最后,基于概率算法的椭圆成像理论,根据空气耦合兰姆波扫描检测的实际情况,改进了概率损伤扫描成像算法。在概率损伤成像算法中以四种损伤指数作为板结构缺陷重构成像的特征值,将不同扫描路径上的特征值数据进行融合,得到了复合材料层板冲击缺陷的二维图像,实现了冲击损伤缺陷的位置和形状等定量特征的描述。对比四种损伤指数下的融合图像可知,时域损伤指数成像图中干扰信号较多,频域损伤算法与时频域成像成像相对较为清晰,时间反转损伤指数成像对比度较小。
[Abstract]:Composite laminates are widely used in aerospace and other important fields because of their low density, good strength and strong mechanical properties. However, the vertical impact resistance of composite laminates is poor. During service may suffer from hail, gravel, tool fall and other circumstances of impact damage defects in the composite surface visual inspection is not obvious. However, the internal damage may cause great damage to the strength and mechanical properties of the material, and pose a serious threat to the safety of the whole aircraft structure, and also to the in-service detection of large area composite laminates. The air-coupled ultrasonic Lamb wave detection method has the advantages of non-contact fast detection and single-side arrangement of sensors, so it has outstanding advantages in automatic imaging detection. Firstly, this paper is based on the basic theory of thin plate Lamb wave. This paper introduces the calculation and derivation of dispersion curve of multilayer anisotropic materials. The carbon fiber composite laminates, which are often used in aircraft skin structures, are taken as the research object. The dispersion curve of the corresponding Lamb wave propagation and the vibration displacement distribution of the particle in the plate thickness direction are studied, and the influence of the detection frequency on the incident angle is analyzed. When using air coupled Lamb wave to detect the material, the theoretical incident angle of excited A0 mode Lamb wave is 11.5 掳at the detection frequency of 0.4 MHz of A0 mode Lamb wave. Based on the finite difference time domain (FDTD) numerical calculation method, the leakage Lamb wave detection model of carbon fiber composite laminates is established. The incident angle of the sensor is compared and analyzed by simulation and experiment. The effect of defects and material anisotropy on the leaky Lamb wave signal. The results show that the incident angle is between 11.0o and 14.0o, and the receiving efficiency of leaky Lamb wave is the best. The Lamb wave signal at the defect has obvious attenuation, scanning detection method can judge the severity of the defect, the propagation velocity and attenuation law of the Lamb wave propagating along the horizontal direction of the specimen is isotropic basically. The Lamb wave D-scan (non-parallel scanning) imaging detection was carried out on the experimental specimens with impact damage by using a similar scanning imaging method of weld TOFD. Four kinds of damage indices (DI(Damage Index) are introduced to characterize the impact damage of composite laminates. According to the characteristics of the analysis methods, the damage index in time domain and frequency domain are classified as: time domain damage index and frequency domain damage index. Time-frequency domain damage index, time reversal damage index. Based on the results of time-frequency analysis, time-inverse processing and other information transformation results of D-scan detection signal, the characteristic value Di is calculated to characterize the damage. The numerical range and applicable conditions of the four damage index algorithms are different, but all of them can clearly characterize the severity of defects, and the damage index in time-frequency domain is the best. The elliptical imaging theory based on probabilistic algorithm, according to the actual situation of air coupled Lamb wave scanning detection. In the probabilistic damage imaging algorithm, four damage indices are used as the eigenvalues of the reconstruction imaging of plate structure defects, and the data of the eigenvalues on different scanning paths are fused. The two-dimensional images of impact defects of composite laminates are obtained, and the quantitative characteristics of impact damage defects such as location and shape are described. The fusion images under four damage indices are compared. There are many interference signals in time-domain damage exponent imaging, the frequency-domain damage algorithm and time-frequency imaging are relatively clear, and the contrast of time-reversal damage index imaging is relatively small.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB33;TB302.5

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