基于Lamb波薄板损伤识别的若干问题研究

发布时间：2018-04-04 12:41

本文选题：Lamb波频散方程　切入点：波结构　出处：《哈尔滨工程大学》2014年硕士论文

【摘要】：薄板状结构在工程中应用广泛,由于外界作用,薄板在服役期间会逐渐出现损伤。若不及时发现,有可能会影响结构的正常使用,甚至危机生命和财产安全。因此,应该及早发现损伤,并对其进行识别和定位,以避免出现结构失效情况。基于Lamb波的薄板监测是结构健康监测领域有发展前景的方法之一,本文通过理论与实验结合的方式,对损伤检测、定位和优化做了若干研究。依据弹性动力学的理论,由位移势函数法推导出了 Lamb波的频散方程。利用Matlab语言进行编程计算数值解,以Q235钢板为例绘制出了频散曲线,并对Lamb波的多模态和频散特性做了讨论。对Lamb波波结构的位移分量和应力分量做了理论上的求解,讨论了不同频厚积下SO和A0模态对不同缺陷的敏感度。通过实验说明了低频厚积情况下对缺陷检测的可行性,并利用峰值损伤因子的变化大小证明了低频厚积下的A0模态比较适合检测表面缺陷。详细阐述了能量衰减法的原理,并介绍了计算波包能量的方法,指出利用该方法用来进行损伤定位的可行性。通过对薄板中孔状损伤的实验分析,得出了波形能量随着损伤深度的增加而变化的规律,利用波形的能量变化计算不同路径的损伤率,并采用该方法实现了损伤位置的初步定位。与实际损伤位置和利用椭圆定位法计算的位置做对比,证明了该方法的可行性,为大面积的薄板监测提供了参考。介绍了对构件进行测点优化的必要性,对传感器的位置和数目优化做了简介。以4点固支的薄板为例,利用遗传算法,计算了优化前后的可识别单元数目。通过数据对比可以发现,进行传感器的位置和数目优化对提高可识别单元的数目有着很大的作用。
[Abstract]:Thin-plate structure is widely used in engineering, because of external action, thin plate will gradually appear damage during service.If not detected in time, it may affect the normal use of the structure and even endanger the safety of life and property.Therefore, damage should be detected early, identified and located to avoid structural failure.Thin plate monitoring based on Lamb wave is one of the promising methods in the field of structural health monitoring. In this paper, damage detection, location and optimization are studied by combining theory with experiment.Based on the theory of elastic dynamics, the dispersion equation of Lamb wave is derived from the displacement potential function method.The numerical solution is calculated by programming with Matlab language. The dispersion curve of Q235 steel plate is plotted, and the multimodal and dispersion characteristics of Lamb wave are discussed.The displacement and stress components of Lamb wave structures are solved theoretically, and the sensitivity of so and A 0 modes to different defects under different frequency and thickness products is discussed.The feasibility of defect detection under the condition of low frequency thick product is demonstrated by experiments, and the change of peak damage factor is used to prove that the A0 mode under low frequency thick product is more suitable for surface defect detection.The principle of energy attenuation method is described in detail, the method of calculating wave packet energy is introduced, and the feasibility of using this method to locate damage is pointed out.Through the experimental analysis of the hole damage in thin plate, the law of wave energy changing with the increase of damage depth is obtained, and the damage rate of different paths is calculated by using the variation of wave energy.This method is used to realize the initial location of the damage.Compared with the actual damage location and the position calculated by the elliptical positioning method, the feasibility of the method is proved, which provides a reference for the monitoring of a large area of thin plates.This paper introduces the necessity of optimizing the measuring points of the components, and introduces the optimization of the position and number of sensors.Taking the 4-point clamped thin plate as an example, the number of identifiable units before and after optimization is calculated by using genetic algorithm.It is found that optimizing the position and number of sensors plays an important role in increasing the number of identifiable units.
【学位授予单位】：哈尔滨工程大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU317

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