Propagation Characteristics Of Acoustic Emission Signals In Interface Structures And Its Application

Acoustic emission(AE) is a dynamic non-destructive testing techniques, It is widely used in the field of mechanical fault detection. There are a large number of interface structures on critical infrastructure components which can make the mapping relationship between the fault and the characteristic signal becomes complicated and the fault detection results become unreliable. To solve these problems, the AE signal propagation characteristics in interface structure are simulated. Simultaneously, the influence of acoustic emission signal propagation characteristics is caused by signal propagation direction contact area and specimen thickness in interface structures are studied by experiment. The work done as follows.(1) AE signal reflection and transmission characteristics and the effect of AE signal propagation characteristics caused by connection length and specimen thickness in the interface structure are simulated by finite difference method. The simulation results are analyzed by relative decay rate of AE signal amplitude and energy.(2)The effect of AE signal propagation characteristics caused by AE signal different propagation direction, contact area and specimen thickness in the interface structure are studied by experiment. Experimental results show that AE signal propagation direction is an important factor affecting the propagation characteristics. The attenuation is smaller when AE signal propagation from large specimen to the small specimen. AE signal amplitude and energy relative attenuation becomes larger with increasing contact area, but the attenuation trend changed dramatically when contact area ratio is 9. Compared with the simulation results of different contact length, the attenuation trend of energy is analogous,but the attenuation of amplitude is greater in experiment. The relative attenuation of amplitude and energy are gradually increased with the increasing thickness of the specimen. At the same time, the attenuation of energy was more. Compared with the simulation results of different specimen thickness,the attenuation trend of AE signal energy and amplitude are very analogous, but energy and amplitude of simulation are greater.(3) The microcrystalline graphite / polyvinyl alcohol(PVA) composite material is treated as an object, a new material component detecting methods based on the AE signalpropagation characteristics are proposed. Different microcrystalline graphite mass cause the quantity of interfaces between the PVA and microcrystalline graphite is different. So the relationships between propagation characteristics of the original signal and the wavelet packet and material composition fractions are studied. Finally, the relation is verified. For the microcrystalline graphite/PVA composite, the error of the microcrystalline graphite component fraction calculated by the feature packet energy is 2.2%, which is lower than that of the original signal 1.6%. For the purified microcrystalline graphite / PVA composite,the error calculated by the feature packet energy is 2.4%, which is lower than that of the original signal 2.0%. The measured results have the higher degree of agreement with the actual composition fractions. Therefore, the method provides a new research tool for the non-destructive testing of material component fractions.