Structure Crack Extension Acoustic Emission Modeling And Characteristic Research Under Welding Heat

During the acoustic emission monitoring of structure crack in welding process,the acoustic emission signal produced by crack propagates from the structure with non-uniform temperature field to acoustic emission sensors, its propagation characteristics(attenuation, transmission speed, the time domain, frequency domain in time frequency domain features) depend not only on material, size, shape, structure,but also the influence of the heating effect, especially in the instantaneous thermal shock field, thermal wave and the cracks acoustic emission signal mutual coupling and transmission in the structure, seriously affected the detection of crack extension acoustic emission signals and recognition of acoustic emission sources. At present,theory and solving methods in homogeneous medium, heterogeneous medium of wave propagation, it is difficult to describe and obtain the characteristics of acoustic emission elastic wave under the affection of non-uniform temperature field caused by welding heat source in the structure.Therefore paper proposed crack extension acoustic emission modeling and characteristic research under welding heat.On the basis of intensive study of acoustic emission elasticity undulation model and solution in the structure with non-uniform temperature field. The paper built acoustic emission elastic wave model of crack formation and extension under the action of welding moving heat source as well as the finite element solving method.Characteristics and laws of acoustic emission transmission in welding structure under the action of moving heat were discussed.The paper provides the theory basis for realizing welding manufacturing quality detection by acoustic emission. The main contents are as follows:1. Based on the finite element theory of thermal elastic mechanics and extended finite element method of crack(XFEM), welding process under the action of thermal crack propagation dynamics model was set up,and the thermal characteristics of structure crack in welding process were calculated and analyzed. First of all, the welding plate 3 d finite element model was established, welding temperature field by selecting gauss moving heat source model as boundary conditions was calculated;Secondly, structure crack extension dynamics model in welding process based on XFEM was built, stress and energy parameters of crack unit were calculated by using indirect coupling method, and the welding thermal crack extension acoustic emission source mechanical model was set up by analyzing stress and energy change law of crack unit.2. Acoustic emission wave simulation model under the influence of welding thermal was built,and acoustic emission wave was calculated by choosing welding temperature field acoustic emission source as boundary conditions.The effect of welding moving point heat source on the influence of the law of acoustic emission wave propagation characteristics was summarized by analysis acoustic emission wave diagram and acoustic emission displacement waveform diagram obtained by calculation.The accuracy of wave simulation model and solution method were verified by comparing simulation signal with experimental signal.3. The plate structure crack extension acoustic emission wave simulation model under the influence of welding thermal was built. The amplitude of acoustic emission signal along different angles as well as acoustic emission signal waveform and time-frequency diagram of plate structure crack extension with different length or depth during the welding process of heating and cooling process were calculated and analyzed.The influence of welding thermal effects on amplitude of acoustic emission and spreading angle as well as relationship between acoustic emission signal time-frequency energy and plate structure crack with different length and depth during welding process of heating and cooling were analyzed and summarized.