本文選題：鑄造奧氏體不銹鋼　切入點(diǎn)：仿真　出處：《大連理工大學(xué)》2016年博士論文

【摘要】：鑄造奧氏體不銹鋼(Cast Austenitic Stainless Steel,CASS)以其良好的斷裂韌性、耐腐蝕性和焊接性,被用作壓水堆核電站一回路壁厚66～96mm主管道建造材料。核動(dòng)力裝置的檢驗(yàn)規(guī)范中,對(duì)CASS管道加工質(zhì)量及服役期間狀況提出無損檢測(cè)的強(qiáng)制性要求。目前,現(xiàn)有檢測(cè)標(biāo)準(zhǔn)要求對(duì)厚壁CASS管道進(jìn)行射線檢測(cè)和滲透檢測(cè)。然而,射線檢測(cè)具有對(duì)危害性大的面積型缺陷不敏感、無法進(jìn)行缺陷定位、具有放射性等缺點(diǎn)。滲透檢測(cè)無法對(duì)亞表面及內(nèi)部深層缺陷進(jìn)行檢測(cè)。相比于射線和滲透檢測(cè),超聲檢測(cè)(Ultrasonic Testing,UT)具有對(duì)面積型缺陷敏感、能夠?qū)ι顚尤毕荻ㄎ欢康葍?yōu)點(diǎn)。但是,CASS具有粗大的彈性各向異性等軸、柱狀和等軸-柱狀混合結(jié)構(gòu)。超聲檢測(cè)過程中會(huì)引起嚴(yán)重的散射衰減和結(jié)構(gòu)噪聲。當(dāng)CASS管道中缺陷深度達(dá)到50 mm或更深時(shí),缺陷回波聲能很弱,檢測(cè)信噪比甚至小于10 dB,缺陷誤檢和漏檢概率顯著增加。正因如此,厚壁CASS主管道的超聲檢測(cè)是無損檢測(cè)領(lǐng)域內(nèi)公認(rèn)的挑戰(zhàn)性課題。對(duì)此,在開發(fā)專用相控陣超聲檢測(cè)設(shè)備和探頭的同時(shí),研究者們提出利用超聲檢測(cè)仿真建模和信號(hào)／圖像后處理算法解決低信噪比問題。利用仿真建模描述CASS的超聲檢測(cè)過程,有助于弄清超聲波在粗晶結(jié)構(gòu)中的傳播機(jī)理,為缺陷的有效判別、檢測(cè)參數(shù)優(yōu)化和檢測(cè)設(shè)備開發(fā)提供理論指導(dǎo)。然而,建模過程中晶粒結(jié)構(gòu)、晶體取向和材料彈性參數(shù)的量化描述十分困難,使得模擬結(jié)果與實(shí)際情況存在較大出入,無法有效指導(dǎo)實(shí)踐。發(fā)展用于提高信噪比的后處理算法是解決CASS超聲檢測(cè)問題的另一有效途徑�，F(xiàn)有超聲信號(hào)／圖像后處理算法主要利用信號(hào)濾波和延時(shí)疊加(Delay and Sum,DAS)圖像重建提高信噪比。其中,DAS后處理算法可通過延時(shí)疊加提高成像區(qū)域內(nèi)的信噪比。然而,多數(shù)DAS成像的信號(hào)采集過程是通過單探頭B掃查完成的。此方法會(huì)導(dǎo)致厚壁CASS管道深處聲能較弱,深層缺陷信噪比增強(qiáng)能力有限。本文以CASS超聲檢測(cè)建模和超聲圖像后處理算法為研究?jī)?nèi)容,探索提高厚壁CASS超聲仿真模擬的有效性和改善信噪比的方法,主要研究?jī)?nèi)容和結(jié)論如下：利用電子背散射衍射(Electron Back-Scattered Diffraction,EBSD)技術(shù)對(duì)CASS的晶粒結(jié)構(gòu)和晶體取向進(jìn)行分析,得到了尺寸為96mm×12mm的軸-徑向截面EBSD圖譜。通過取向相(差)角選擇和晶體取向歸一化處理,建立了基于EBSD圖譜的CASS超聲仿真模型。該模型不僅能夠通過掃描微區(qū)之間的取向差異描述晶粒結(jié)構(gòu),而且能夠通過取向微區(qū)對(duì)應(yīng)的歐拉角描述晶體取向,克服以往模型難以量化描述晶粒結(jié)構(gòu)和晶體取向的問題。利用Bond變換法賦以晶粒在對(duì)應(yīng)晶體取向下的剛度矩陣,確定晶體取向與彈性常數(shù)之間的對(duì)應(yīng)關(guān)系,實(shí)現(xiàn)模型中晶粒彈性特征的量化表征。采用時(shí)域有限差分法對(duì)模型進(jìn)行數(shù)值計(jì)算,結(jié)果表明,模擬得到的A掃描信號(hào)中重現(xiàn)了粗晶結(jié)構(gòu)引起的散射衰減、主頻降低和結(jié)構(gòu)噪聲等現(xiàn)象,模擬結(jié)果與實(shí)際檢測(cè)結(jié)果基本一致。模擬相控陣扇掃描圖像的噪聲幅值和信噪比與實(shí)際檢測(cè)結(jié)果基本吻合。利用數(shù)值模擬分析晶粒形態(tài)(長(zhǎng)徑比l/d和晶粒生長(zhǎng)方向θ)對(duì)超聲散射程度的影響,結(jié)論如下：當(dāng)l/d=1時(shí),晶粒為等軸晶結(jié)構(gòu),晶界對(duì)聲波的散射程度不隨θ(0°≤θ90°)的改變發(fā)生變化。當(dāng)長(zhǎng)徑比l/d1時(shí),晶粒為柱狀晶結(jié)構(gòu),晶界對(duì)聲波的散射程度隨啪增加而增加。超聲散射程度隨θ的變化幅度隨長(zhǎng)徑比l/d的增加而增加。柱-等混合結(jié)構(gòu)中等軸晶結(jié)構(gòu)的存在會(huì)削弱l/d和θ的超聲散射程度的影響。上述工作為揭示超聲波在彈性各向異性粗晶結(jié)構(gòu)中的散射機(jī)理提供了解決思路。為進(jìn)一步提高厚壁CASS深層缺陷超聲檢測(cè)信噪比,利用一發(fā)一收探頭所形成的“偽聚焦”聲場(chǎng)提高深層缺陷的回波聲能。聲場(chǎng)對(duì)比結(jié)果表明,50～70 mm深度上,探頭中心距為100 mm的一發(fā)一收探頭聲能在40～75%,寬度為1.5 mm的單探頭聲能在25～40%。在此基礎(chǔ)上,利用相位相干成像(Phase Coherence Imaging,PCI)算法構(gòu)建表示DAS圖像中各像素點(diǎn)相位分布特征的循環(huán)相干因子(Circular Coherence Factor,CCF)和符號(hào)相干因子(Sign Coherence Factor,SCF),通過動(dòng)態(tài)加權(quán)處理有效降低相位分布散亂的結(jié)構(gòu)噪聲幅值。將這種聲束傳播路徑優(yōu)化設(shè)計(jì)和圖像后處理算法相結(jié)合的方法用于壁厚78 mm的CASS焊縫后,深度60 mm的Φ3邊鉆孔信噪比由20 dB以下提高到30 dB以上。根據(jù)相干因子的特點(diǎn),SCF能夠獲得較高的信噪比,但SCF圖像中的缺陷影像不連續(xù)。CCF能夠獲得缺陷影像連續(xù)的圖像,但僅在“偽聚焦”聲場(chǎng)內(nèi)具有較高的信噪比。因此,SCF適用于對(duì)檢測(cè)對(duì)象進(jìn)行初步掃查,CCF適用于對(duì)“偽聚焦”聲場(chǎng)內(nèi)的缺陷進(jìn)行精確定量和定位。
[Abstract]:Cast austenitic stainless steel (Cast Austenitic Stainless Steel, CASS) with good toughness, corrosion resistance and weldability, is used as a loop with thickness of 66 ~ 96mm main pipeline construction materials of PWR nuclear power plant. Test specification of nuclear power plant, the processing quality of CASS pipeline and service condition proposed mandatory lossless detection requirements. At present, the existing detection standards for X-ray detection and penetrant testing of thick wall CASS pipe. However, X-ray detection is not sensitive to the type of damage area of large defects, unable to locate the defect, radioactive and other shortcomings. To detect the penetration of sub surface and internal deep defects were detected. Compared to ray and penetration testing, ultrasonic testing (Ultrasonic Testing UT) is sensitive to the defect area, can the advantages of deep defect localization and quantification. However, CASS has a coarse elastic anisotropy Anisotropy axis, columnar and equiaxed columnar structure. Mixing will lead to serious scattering attenuation and noise in ultrasonic detection process. When the defect of CASS pipeline reached a depth of 50 mm or more, the defect echo sound is very weak, the signal-to-noise ratio is even less than 10 dB, defects and false detection probability of missed detection significantly increase. Because of this, ultrasonic testing of thick wall CASS main pipe is a challenging subject in the field of NDT accepted. In this regard, the development of special equipment and phased array ultrasonic detection probe at the same time, researchers have proposed the use of ultrasonic detection of simulation modeling and signal / image postprocessing algorithm to solve the problem of low signal-to-noise ratio by using the simulation. Describe the modeling process of CASS ultrasonic testing, to help clarify the mechanism of ultrasonic propagation in the coarse grain structure, effectively distinguishing defects, provide theoretical guidance for testing parameters optimization and testing equipment development. However, in the process of modeling The crystal structure, crystal orientation and quantitative description of material parameters is very difficult, so the simulation results with the actual situation, can not effectively guide the practice of development. To improve the signal-to-noise ratio of the postprocessing algorithm is another effective way to solve the CASS problem. The existing ultrasonic ultrasonic signal / image postprocessing algorithm mainly uses signal filtering and the time delay (Delay and Sum, DAS superposition) image reconstruction SNR. The DAS postprocessing algorithm can improve the imaging area through the superimposed signal to noise ratio. However, most of the DAS imaging signal acquisition process is through a single probe B scan completed. This method will lead to the depths of thick walled pipes CASS energy is weak, deep defects of SNR enhancement ability is limited. This paper takes CASS ultrasonic modeling and ultrasonic image postprocessing algorithm as the research content, exploring and improving the simulation of thick wall CASS ultrasound simulation The validity of the method and improve the signal-to-noise ratio, the main research contents and conclusions are as follows: using electron backscatter diffraction (Electron Back-Scattered, Diffraction, EBSD) of CASS crystal structure and crystal orientation are analyzed, the size of 96mm * 12mm - axis radial section of the EBSD map. The phase angle orientation (difference) and the crystal orientation normalization, established the CASS simulation model of EBSD based on ultrasonic map. This model can not only describe the difference between the orientation of grain structure by scanning micro area, but also the orientation of micro area corresponding to the Euler angles to describe the crystal orientation, overcomes the model to quantitative description of grain structure and crystal orientation. By using Bond transform method to Fu grain in the crystal orientation of the corresponding stiffness matrix, to determine the relationship between crystal orientation and elastic constants, elastic model in grain Quantitative characterization. Using FDTD method to model numerical calculation, the results show that the simulated A scan signal obtained to reproduce the scattering caused by coarse grain structure and reduce the structure noise attenuation, frequency and other phenomena, simulation results and actual test results are basically the same. The basic agreement with the measured analog phased array fan scanning image noise amplitude and signal-to-noise. By numerical simulation analysis of grain shape (length / diameter ratio l/d and grain growth direction) conclusion effect of ultrasonic scattering degree is as follows: when l/d=1, the grain equiaxed grain structure, the degree of scattering of acoustic boundary with angle (0 DEG to 90 DEG theta) change. When the ratio of length to diameter l/d1, the grains are columnar crystal structure, degree of acoustic scattering increases with the increase of grain boundary. With ultrasonic scattering degree of variation of theta with slenderness ratio l/d increases. The column - mixed structure The equiaxed grain structure can weaken the effect of ultrasonic scattering degree of l/d and theta. The above work to reveal the mechanism of ultrasonic scattering in the coarse grain structure of elastic anisotropy in providing a solution. In order to further improve the thick wall CASS deep defect ultrasonic signal to noise ratio, using a charge probe formed by the pseudo focus on the defect echo sound field to improve the deep sound field. The comparison results show that the depth of 50~70 mm, the probe center distance of 100 mm sending and receiving probe energy in the 40 ~ 75%, the width of 1.5 mm single probe energy in the 25 ~ 40%. based on coherent imaging using phase (Phase Coherence Imaging, PCI) algorithm for constructing DAS pixels in each phase distribution of the cyclic coherence factor (Circular Coherence Factor CCF (Sign) and Coherence symbol coherence factor Factor, SCF), through dynamic weighted effective reduction The structure of low phase noise amplitude distribution. The scattered beam propagation path optimization design method and image postprocessing algorithm combining CASS mm 78 for weld wall thickness, depth of 60 mm with 3 side drilling signal-to-noise ratio by 20 dB increased to more than 30 dB. According to the characteristics of the coherence factor. SCF can obtain higher signal-to-noise ratio, but the defect image SCF image discontinuities in the.CCF can obtain image defects of continuous image, but only in the "pseudo high focus acoustic signal-to-noise ratio. Therefore, SCF is suitable for detection of initial object scanning, CCF for accurate quantitative and positioning in the the defect of" pseudo focus "in a sound field.

【學(xué)位授予單位】：大連理工大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TG115.285

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7 王一然;基于I-ASM1的CASS工藝活性污泥法數(shù)學(xué)建模研究[D];哈爾濱工業(yè)大學(xué);2016年

8 周竹楓;磷霉素鈉和苯乙胺高效降解菌的篩選及其在CASS中的實(shí)際應(yīng)用[D];遼寧大學(xué);2016年

9 肖劍波;CASS工藝脫氮調(diào)控的實(shí)驗(yàn)與模擬研究[D];重慶大學(xué);2016年

10 施君君;牡丹籽粕多糖理化特性及抗氧化、抗腫瘤功能研究[D];合肥工業(yè)大學(xué);2017年

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