The Study On Acoustic Emission Characteristics Of Metal Material Fatigue Damage

As a new type of dynamic testing technology, acoustic emission has been widely applied to NDT and real-time monitoring of equipments. Using acoustic emission technique to analyze the characteristic parameters of metal fatigue damage signal has a significant meaning for safe operation and production of metal structure or equipment. This paper based on acoustic emission technique, monitored the whole process of fatigue test of metal, and analyzed the acoustic emission signal characteristics of the fatigue crack initiate, expand, and eventual failure during whole test process. Here are the primary works:(1) The acoustic emission characteristics of metal crack and acoustic emission sources of the damage of metal materials are analyzed, and current acoustic emission research of the damage of metal materials is summarized.(2) By the fatigue tests of metal materials, analysis of acoustic emission characteristics of metal fatigue crack propagation at different stress ratios has been made. When the stress ratio is over zero, it has been discussed that the metal specimen fatigue life came up with the increase of the stress ratio, and the growth rate of its cumulative ring count came down with increase of stress ratio, but the volume increased with that. Cumulative energy increases with the increase of the stress ratio, which only reflects the relative energy or strength of events, including an energy release mechanism.(3) Crack signal which reconstructed by wavelet noise cancellation technique has been made in the spectrum analysis, and the spectrum characteristics of the signals of crack has been obtained(4) By analyzing ringing count process diagram and its cumulative process diagram, and it turned out that the transition points form the first stage to the second stage can serve as a symbol of macroscopic crack formation. It shows that we can quantitatively determine the damage rate of the sample form the slope of the fitted curve change degree and size which established by the cumulative ring count and time. Fatigue cumulative damage model has been established by the cumulative ringing count and cumulative fatigue crack length, which can forecast the damage degree of structure or component more intuitive.(5) Static tensile test have been taken on both the metal specimen with prefabricated fatigue crack and the other without. The propagation rule of both crack has been analyzed and compared with each other, and the result was that the test specimen with prefabricated fatigue crack has longer hardening stage in test, and the acoustic emission peak appears in different stages, that is, the former in the necking phase, while the latter in the strengthening phase. We can classify experiments at a stage so as to achieve the purpose of estimated residual life of the specimen by the mutations features of accumulate energy.(6) AE characteristics during the test of fracture toughness have been analyzed, the results show that AE parameters can reflect changes in the case of crack propagation and fracture toughness properties of the critical point.