焊接热作用下结构裂纹声发射建模及特性研究

发布时间：2018-06-05 17:46

本文选题：焊接热作用 + 裂纹扩展　；参考：《湖南科技大学》2016年硕士论文

【摘要】：焊接过程结构裂纹声发射检测中,裂纹产生的声发射信号经由非均匀温度场分布的结构传播至声发射传感器,其传播特性(衰减、传播速度、时域、频域及时频域特性)不仅取决于结构材质、尺寸、形状,还受热作用的影响,尤其在瞬时热冲击场中,热波在结构中与裂纹产生的声发射信号相互耦合与传播,影响声发射信号的检测及声发射源的识别。目前,均匀介质、非均匀介质波动传播理论所包含的波动方程及求解方法,难以描述和获取焊接热源作用下非均匀温度场分布结构的声发射弹性波动特性。因此论文提出焊接热作用下结构裂纹声发射建模及特性研究,通过对非均匀温度场分布结构声发射弹性波波动模型及求解进行深入研究,建立焊接移动点热源作用下裂纹形成和扩展的结构声发射波动模型及有限元求解方法,探讨移动点热源作用下焊接结构声发射特性及规律,为实现焊接过程裂纹的声发射在线检测提供理论依据。主要内容如下:1.基于热弹性力学和裂纹扩展有限元理论(XFEM),建立焊接过程热作用下裂纹扩展动力学模型,计算分析了焊接过程结构裂纹热力特性。首先,建立了焊接平板三维有限元模型,选取移动高斯热源模型作为边界条件,进行焊接温度场求解;其次,建立了基于XFEM的焊接过程结构裂纹扩展动力学模型,采用间接耦合方法,求解焊接热作用下裂纹单元近场的应力和能量参数,并通过分析裂纹单元的应力和能量变化规律,建立了焊接热作用下裂纹扩展声发射源力学模型。2.建立了焊接热作用下声发射波动仿真模型,以焊接温度场和声发射源作为边界条件,进行声发射波动求解,通过分析计算得到的焊接移动点热源作用下的声发射波动云图及声发射位移波形图,总结了焊接移动点热源作用对声发射波动传播特性的影响规律。并将仿真信号与实测信号进行对比分析,验证了波动仿真模型及求解方法的准确性。3.建立了焊接热作用下平板结构裂纹扩展声发射波动仿真模型,计算分析了沿不同角度传播的声发射信号幅值及焊接加热和冷却过程平板结构不同长度和深度裂纹扩展的声发射波形信号及时频图,分析总结了焊接热作用对声发射幅值和传播角度的影响及焊接加热与冷却过程平板结构不同长度和深度裂纹与声发射信号的时频能量关系。
[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.
【学位授予单位】：湖南科技大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG441.7

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