Time-frequency Modeling and Localized Pores Detection Method of Low-porosity Composites
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摘要: 本文研究了孔隙率不高于1%的低孔隙率碳纤维复合材料(CFRP)的时频模型和局部孔隙检测方法。将现有的超声波在CFRP内传播的频域模型扩展到时频模型,通过仿真验证了共振结构噪声的存在,研究了共振结构噪声和局部孔隙形成的缺陷回波的频率差异。在此基础上,提出应用变分模态分解分离高频随机噪声和共振结构噪声,提取包含缺陷回波的低频成分进行局部孔隙检测。提出能量函数和瞬时增益的概念,以克服由于声波能量随传播距离降低而造成的近表面信号对远表面信号的遮蔽效果。对低孔隙率CFRP试块的实验表明,基于变分模态分解和瞬时增益的方法能够有效抑制噪声干扰、克服遮蔽效应,实现局部孔隙的准确检测。Abstract: The development of aviation and aerospace technologies increases the demand of low-porosity composites. Localized pores in composites will lead to performance degradation. Method for detecting localized pores in those composites is proposed in this paper. Firstly, the propagation of ultrasonic wave in composite is investigated. The available model given in frequency domain is extended to the time-frequency domain. The existence of resonant structural noise is validated; the frequency diversity between resonant structural noise and flaw echoes are investigated. Secondly, the variation mode decomposition (VMD) is used to separate random noise and resonant structural noise from low-frequency component. The low-frequency component, which contains the flaw echoes, is used for localized pores detection. Thirdly, the concepts of energy function and instant gain are put forward to solve the shadowing problem. The experimental results have shown that the established method based on VMD and instant gain is able to suppress noise interference and alleviate the shadowing effect, and validated the effectiveness in localized pores detection.
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表 1 中心频率分布
α ω/(2π)/MHz ω1/(2π) ω2/(2π) ω3/(2π) 1 500 31.11 10.98 7.04 1 750 31.28 11.00 7.08 2 000 31.39 11.02 7.12 2 250 31.47 11.03 7.15 2 500 31.53 11.04 7.18 -
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