本文選題：焊接熱作用 + 裂紋擴展　； 參考：《湖南科技大學》2016年碩士論文

【摘要】：焊接過程結(jié)構(gòu)裂紋聲發(fā)射檢測中,裂紋產(chǎn)生的聲發(fā)射信號經(jīng)由非均勻溫度場分布的結(jié)構(gòu)傳播至聲發(fā)射傳感器,其傳播特性(衰減、傳播速度、時域、頻域及時頻域特性)不僅取決于結(jié)構(gòu)材質(zhì)、尺寸、形狀,還受熱作用的影響,尤其在瞬時熱沖擊場中,熱波在結(jié)構(gòu)中與裂紋產(chǎn)生的聲發(fā)射信號相互耦合與傳播,影響聲發(fā)射信號的檢測及聲發(fā)射源的識別。目前,均勻介質(zhì)、非均勻介質(zhì)波動傳播理論所包含的波動方程及求解方法,難以描述和獲取焊接熱源作用下非均勻溫度場分布結(jié)構(gòu)的聲發(fā)射彈性波動特性。因此論文提出焊接熱作用下結(jié)構(gòu)裂紋聲發(fā)射建模及特性研究,通過對非均勻溫度場分布結(jié)構(gòu)聲發(fā)射彈性波波動模型及求解進行深入研究,建立焊接移動點熱源作用下裂紋形成和擴展的結(jié)構(gòu)聲發(fā)射波動模型及有限元求解方法,探討移動點熱源作用下焊接結(jié)構(gòu)聲發(fā)射特性及規(guī)律,為實現(xiàn)焊接過程裂紋的聲發(fā)射在線檢測提供理論依據(jù)。主要內(nèi)容如下:1.基于熱彈性力學和裂紋擴展有限元理論(XFEM),建立焊接過程熱作用下裂紋擴展動力學模型,計算分析了焊接過程結(jié)構(gòu)裂紋熱力特性。首先,建立了焊接平板三維有限元模型,選取移動高斯熱源模型作為邊界條件,進行焊接溫度場求解;其次,建立了基于XFEM的焊接過程結(jié)構(gòu)裂紋擴展動力學模型,采用間接耦合方法,求解焊接熱作用下裂紋單元近場的應力和能量參數(shù),并通過分析裂紋單元的應力和能量變化規(guī)律,建立了焊接熱作用下裂紋擴展聲發(fā)射源力學模型。2.建立了焊接熱作用下聲發(fā)射波動仿真模型,以焊接溫度場和聲發(fā)射源作為邊界條件,進行聲發(fā)射波動求解,通過分析計算得到的焊接移動點熱源作用下的聲發(fā)射波動云圖及聲發(fā)射位移波形圖,總結(jié)了焊接移動點熱源作用對聲發(fā)射波動傳播特性的影響規(guī)律。并將仿真信號與實測信號進行對比分析,驗證了波動仿真模型及求解方法的準確性。3.建立了焊接熱作用下平板結(jié)構(gòu)裂紋擴展聲發(fā)射波動仿真模型,計算分析了沿不同角度傳播的聲發(fā)射信號幅值及焊接加熱和冷卻過程平板結(jié)構(gòu)不同長度和深度裂紋擴展的聲發(fā)射波形信號及時頻圖,分析總結(jié)了焊接熱作用對聲發(fā)射幅值和傳播角度的影響及焊接加熱與冷卻過程平板結(jié)構(gòu)不同長度和深度裂紋與聲發(fā)射信號的時頻能量關系。
[Abstract]:In the detection of structural cracks in welding process, the acoustic emission signals generated by the cracks propagate to the acoustic emission sensors through the structure with non-uniform temperature field distribution. The propagation characteristics (attenuation, propagation velocity, time domain), The characteristics of frequency domain in time frequency domain) not only depend on the material, size, shape, but also the effect of heat, especially in the instantaneous thermal shock field, the acoustic emission signal produced by the crack and the thermal wave in the structure are coupled and propagated. It affects the detection of acoustic emission signal and the identification of acoustic emission source. At present, the wave equation and solution method contained in the wave propagation theory of homogeneous medium and non-uniform medium are difficult to describe and obtain the acoustic emission elastic wave characteristics of the non-uniform temperature field distribution structure under the action of welding heat source. In this paper, the acoustic emission model and characteristics of structural cracks under welding heat are proposed, and the wave model and solution of elastic wave of acoustic emission of non-uniform temperature field are studied deeply. The structure acoustic emission wave model and finite element solution method for crack formation and propagation under the action of moving point heat source are established, and the characteristics and regularity of acoustic emission of welded structure under moving point heat source are discussed. It provides a theoretical basis for on-line detection of cracks in welding process. The main content is as follows: 1. Based on the finite element theory of thermoelastic mechanics and crack propagation, the crack growth dynamics model of welding process is established, and the thermal characteristics of structural crack in welding process are calculated and analyzed. Firstly, the 3D finite element model of welding plate is established, and the moving Gao Si heat source model is selected as the boundary condition to solve the welding temperature field. Secondly, the dynamic model of structural crack growth based on XFEM is established. By using indirect coupling method, the stress and energy parameters of crack element under welding heat are solved. By analyzing the variation of stress and energy of crack element, the mechanical model of acoustic emission source of crack propagation under welding heat is established. The simulation model of acoustic emission fluctuation under welding heat is established. The wave of acoustic emission is solved by using welding temperature field and acoustic emission source as boundary conditions. By analyzing and calculating the acoustic emission wave cloud and acoustic emission displacement waveform of welding moving point heat source, the influence law of welding moving point heat source action on acoustic emission wave propagation characteristic is summarized. The simulation signal and the measured signal are compared and analyzed to verify the accuracy of the wave simulation model and the solution method. An acoustic emission wave simulation model for crack propagation of plate structure under welding heat is established. The amplitude of acoustic emission signal propagating along different angles and the time-frequency diagram of acoustic emission waveform signal with different length and depth of crack propagation in plate structure during welding heating and cooling are calculated and analyzed. The influence of welding heat on the amplitude and propagation angle of acoustic emission and the time-frequency energy relationship between cracks of different length and depth of plate structure and acoustic emission signal during welding heating and cooling are analyzed and summarized.
【學位授予單位】：湖南科技大學
【學位級別】：碩士
【學位授予年份】：2016
【分類號】：TG441.7

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