【摘要】：碳纖維復(fù)合材料廣泛應(yīng)用于各個(gè)領(lǐng)域,隨著材料結(jié)構(gòu)和工藝的不斷發(fā)展,傳統(tǒng)的超聲檢測(cè)技術(shù)在復(fù)合材料無(wú)損檢測(cè)中遇到了很多問(wèn)題。本文針對(duì)碳纖維復(fù)合材料在使用超聲波脈沖反射法檢測(cè)時(shí),傳統(tǒng)的底波衰減法難以對(duì)材料缺陷進(jìn)行定位以及由于材料形狀復(fù)雜及超聲波衰減嚴(yán)重導(dǎo)致沒(méi)有底波的情況,結(jié)合復(fù)合材料微缺陷超聲背散射檢測(cè)相關(guān)自然科學(xué)基金項(xiàng)目,通過(guò)理論分析背散射信號(hào)的機(jī)理和特點(diǎn)并結(jié)合具體實(shí)驗(yàn)研究,為復(fù)合材料的超聲波檢測(cè)技術(shù)提供了新的思路。第一章闡述了論文的研究背景和意義,介紹了碳纖維復(fù)合材料主要的微缺陷類(lèi)型,對(duì)微缺陷的無(wú)損檢測(cè)技術(shù)以及與復(fù)合材料超聲檢測(cè)相關(guān)的信號(hào)處理技術(shù)進(jìn)行分析,并給出論文研究的主要內(nèi)容和章節(jié)安排。第二章研究了超聲波在層狀復(fù)合材料中的傳播特性,分析了層狀復(fù)合材料結(jié)構(gòu)噪聲的原理,給出了結(jié)構(gòu)噪聲一階諧振頻率的計(jì)算公式。研究了缺陷的低通濾波特性,分析了背散射信號(hào)的組成成分及其特點(diǎn)。第三章介紹了常用的超聲檢測(cè)信號(hào)頻譜分析方法及其不足之處,分析了選取小波時(shí)頻分析方法處理背散射信號(hào)的優(yōu)點(diǎn),深入分析了CMOR基小波的特性,選擇了較佳的CMOR小波參數(shù),介紹了背散射信號(hào)時(shí)頻圖像的意義。第四章介紹了本論文實(shí)驗(yàn)所采用的五自由度水浸式超聲檢測(cè)系統(tǒng),提出了用區(qū)域劃分的方法對(duì)碳纖維復(fù)合材料超聲檢測(cè)背散射信號(hào)進(jìn)行時(shí)頻分析,采用三維時(shí)頻圖像和紋理子圖對(duì)背散射信號(hào)頻率輪廓與系統(tǒng)噪聲頻率的變化趨勢(shì)進(jìn)行了分析。第五章選擇了小波閾值去噪方法對(duì)遠(yuǎn)表面背散射信號(hào)去噪處理,針對(duì)背散射信號(hào)不同區(qū)域內(nèi)缺陷的特征建立了不同的缺陷識(shí)別定位算法,通過(guò)實(shí)驗(yàn)驗(yàn)證了采用時(shí)頻分析和缺陷定位方法對(duì)碳纖維復(fù)合材料微缺陷評(píng)估的可行性。第六章總結(jié)了全文的主要內(nèi)容和研究成果,并對(duì)接下來(lái)的研究?jī)?nèi)容作了展望。
[Abstract]:Carbon fiber composites are widely used in various fields. With the continuous development of material structure and technology, the traditional ultrasonic testing technology has encountered many problems in the nondestructive testing of composite materials. In this paper, when carbon fiber composites are detected by ultrasonic pulse reflection method, the traditional bottom wave attenuation method is difficult to locate the material defects and there is no bottom wave due to the complex shape of the material and the serious ultrasonic attenuation. Combined with the related natural science fund projects of ultrasonic backscattering detection of composite microdefects, the mechanism and characteristics of backscattering signal are analyzed theoretically and combined with specific experimental research, which provides a new idea for ultrasonic testing technology of composite materials. In the first chapter, the research background and significance of the paper are described, the main types of micro-defects of carbon fiber composites are introduced, and the nondestructive testing technology of micro-defects and the signal processing technology related to ultrasonic testing of composite materials are analyzed. The main contents and chapter arrangements of the paper are given. In chapter 2, the propagation characteristics of ultrasonic wave in layered composites are studied, the principle of structural noise of layered composites is analyzed, and the formula for calculating the first order resonance frequency of structural noise is given. The low pass filtering characteristics of defects are studied, and the composition and characteristics of backscattering signals are analyzed. In the third chapter, the common spectrum analysis methods of ultrasonic detection signals and their shortcomings are introduced, the advantages of selecting wavelet time-frequency analysis method to deal with backscattering signals are analyzed, the characteristics of CMOR based wavelet are deeply analyzed, and the better CMOR wavelet parameters are selected. The significance of time-frequency image of backscattering signal is introduced. In the fourth chapter, the five-degree-of-freedom water immersion ultrasonic testing system used in this paper is introduced, and the time-frequency analysis of the backscattering signal of carbon fiber composite ultrasonic testing is carried out by using the method of region division. The frequency profile of backscattering signal and the changing trend of system noise frequency are analyzed by using three-dimensional time-frequency image and texture subgraph. In chapter 5, wavelet threshold denoising method is selected to Denoise the far surface backscattering signal, and different defect recognition and location algorithms are established according to the characteristics of defects in different regions of backscattering signal. The feasibility of using time-frequency analysis and defect location method to evaluate the micro-defects of carbon fiber composites is verified by experiments. The sixth chapter summarizes the main content and research results of the full text, and looks forward to the next research content.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類(lèi)號(hào)】：TB332

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本文編號(hào)：2480026