Research On Monitoring And Evaluation Methods Of Steel Damage Process Based On Acoustic Emission

With the rapid development of industrial production, steel has been widely applied in all walks of life and has been become the basic material required for social production. At the same time, there are many issues with steel damage failure. It is difficult to realize the real-time monitoring for the steel damage by the common non-destructive testing methods, which are usually used for static defect detection of steel products. However, acoustic emission monitoring technology can realize real-time monitoring for the steel damage, which can find the location of the damage and evaluate the harm extent of damage timely and accurately, so that all kinds of accidents and losses which are produced in the process of using steel products in industry can be reduced largely. In this paper,the different damage mechanisms of the acoustic emission signal source produced in the steel damage process and the effects of different damage factors under each damage mechanism are mainly studied. Through analysis, two kinds of the most typical damage mechanisms of the acoustic emission signal source produced in the steel damage process were obtained, that is plastic deformation and crack propagation. In terms of two damage mechanisms, firstly the acoustic emission monitoring experimentation and evaluation for the tensile specimens in the tensile damage plastic deformation process under the different damage factors were studied, secondly, the acoustic emission monitoring experimentation and evaluation for standard single edge notched three-point bending fatigue specimens in the fatigue crack propagation process under the different damage factors were studied.For the acoustic emission monitoring experimentation studies and evaluation studies of steel tensile damage process under different damage factors, at first, Q235 steel and cast iron were processed into symmetric semicircle gap, linear gap and no gaps standard tensile samples, which were monitored by acoustic emission technology in the tensile test under different tensile rates. Then Combined with plastic properties and brittleness properties of different materials, different notch effects, different tensile rates respectively, mechanical effects of tensile damage were analyzed. And the general rules and characteristics of acoustic emission signal that from each mechanical behavior stage were studied by different characteristic parameters of acoustic emission analysis method. At last the quantitative evaluation on tensile damage was carried on based on different feature parameter accumulation curve and its normalized curve, and the correlation between cumulative curve of different feature parameter was analyzed. Moreover, the effect regularity of three different damage factors on the characterization of acoustic emission monitoring signal in the process of tensile damage was discussed and summed.The signal processing methods of acoustic emission monitoring signal were studied based on the acoustic emission monitoring tests of tensile damage. By contrasting with short-time Fourier transform and continuous wavelet transform, standard S transformation, it find that the time-frequency analysis method in Generalized S transform is the best method for non-stationary signal processing, which can obtain the best time-frequency resolution. Through using spectrum analysis method and time-frequency analysis method both in Fourier transform and adaptive generalized S transform on the signal that at various stages in the steel tensile damage process and the environmental noise signal respectively, spectrum characteristics and time-frequency characteristics of acoustic emission signals at the yield stage, strengthening stage, and Fracture stage and environmental noise signal were analyzed and summed.For the acoustic emission monitoring experimentation studies and evaluation studies of the steel fatigue crack propagation damage process under different damage factors, at first, Q345 steel and 45 steel were processed into standard single edge notched three-point bending fatigue specimens, which were monitored by acoustic emission technology in the fatigue crack propagation damage process under different stress ratio and fatigue frequency. Then the mechanical laws impacts of different plastic, different loading frequency and different loading stress on the fatigue crack of the steel were studied, then the general rules and characteristics of the acoustic emission signals when fatigue crack at the beginning stage, stable growth stage and unstable stage under various fatigue loading were analyzed by the characteristic parameter of acoustic emission based on the mechanical laws mentioned above. Moreover, the effect regularity of three different damage factors on the characterization of acoustic emission monitoring signal in the process of steel fatigue crack propagation was discussed and summed.Based on acoustic emission monitoring of steel fatigue crack propagation test, the relationship between acoustic emission monitoring signal parameters and steel fatigue crack growth mechanical parameters were analyzed. Combined with Paris experience formula, the relationship between characteristic parameters of acoustic emission and steel fatigue crack propagation parameters was established so that it can achieve the evaluation on fatigue crack propagation by acoustic emission parameters.