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制备晶粒尺寸不同的In718合金试样,采用经验模态分解(EMD)研究超声背散射信号的时频域特征,分析晶粒尺寸对不同频段固有模态函数(IMF)的影响,并探求各IMF信号的功率与晶粒尺寸之间的相关性.结果表明,原始背散射信号和IMF1信号的频带宽受晶粒尺寸变化影响均不显著;IMF2信号频域分布较为集中,峰值频率的幅值随晶粒的增大而增大,其功率与晶粒尺寸相关系数达0.995,显著高于其它模态,EMD过程实质上滤除了与晶粒尺寸无关的成分.以充分反映晶粒散射强度的IMF2成分作为晶粒尺寸评价的特征信号,建立面向In718晶粒尺寸的超声背散射EMD评价模型.晶粒尺寸实测结果显示,本方法的灵敏度是传统背散射法的3.7倍;对2个验证试样的评价误差分别为-3.72%和2.87%,精度显著高于声速法;与衰减法相比,本方法无需厚度信息,评价结果不受测厚误差的影响;此外,相比于金相法具有效率高及无需破坏待测件的优势.
In718 alloy samples with different grain sizes were prepared. Empirical Mode Decomposition (EMD) was used to study the time-frequency characteristics of ultrasonic backscatter signals and analyze the effects of grain size on IMFs in different frequency bands. IMF signal power and grain size.The results show that both the original backscattering signal and IMF1 signal bandwidth are not significantly affected by the grain size changes; IMF2 signal frequency distribution is more concentrated, the peak frequency amplitude With the increase of the grain size, the correlation coefficient between the power and the grain size reaches 0.995, which is significantly higher than that of the other modes. The EMD process essentially filters out the grain size independent components. In order to fully reflect the intensity of the grain scattering The IMF2 component was used as the characteristic signal of the grain size evaluation to establish the EMD evaluation model for the backscattering of the grain size of In718.The experimental results show that the sensitivity of this method is 3.7 times that of the traditional backscattering method, The error of evaluation is -3.72% and 2.87% respectively, the precision is much higher than the speed of sound method. Compared with the attenuation method, the method does not need the thickness information and the evaluation result is not influenced by the thickness error. In addition, compared with the metallographic method, High rate and without undermining the test pieces of the advantages.